Introduction The utilization of seawater and sea sand for concrete production can effectively relieve the environmental pressure caused by the consumption of freshwater and river sand resources. Previous studies demonstrate that the mechanical properties of seawater sea sand concrete are consistent with those of normal concrete, which can meet the construction needs. However, the multiple element ions in seawater alternate the components and microstructure of hydration products via participating in the hydration reaction, affecting its durability performance. Mineral admixtures can be used to mitigate the possible adverse effects of multiple element ions on cementitious materials. The existing research on the interaction between inorganic ions and the internal microenvironment of cementitious materials mainly focus on the effect of single ions, and the influence mechanism of multiple element ions lacks systematic investigations. Meanwhile, the influence mechanism of mineral admixtures on the performances of seawater sea sand concrete Is still unclear. In this paper, the pore solution composition and the mineral phases of the hydration products were characterized to reveal the evolution mechanism of the internal microenvironment under the coupling effect of multiple element ions in seawater and mineral admixtures. Methods A cementitious system was designed via the centroid simplex optimization of Portland cement, fly ash and silica fume. The artificial seawater was prepared according to the standard (ASTM D1141-98) at a pH value of 8.29. Sea sand from Jiaozhou Bay, China, was used as fine aggregates with a fineness modulus of 2.65. The polycarboxylic acid high-performance water reducer with a water reduction rate of 30% was used to adjust the flowability of fresh stage cement paste, (Shanxi Feike New Material Science and Technology Co. Ltd., China). The specimens with a water/binder ratio of 0.35 and a sand/binder ratio of 1.0 were then prepared for characterization, and the water-reducing agent dosage was adjusted to maintain the same fluidity among different sample groups.After curing for 3, 7 d and 28 d, the ion concentration in pore solution obtained from a pressure filtration method was characterized by inductively coupled plasma emission spectrometry, and its pH value was measured by a pH meter. The phase composition of powder samples after soaking in isopropanol and further drying was characterized by a model MiniFlex 600 X-ray diffractometer. In addition, the thermal behavior of the powdered samples aged at 28 d was determined by thermogravimetric analyzer/derivative thermogravimeter. The compressive strength of cubic mortar specimens with the sizes of 70.7 mm×70.7 mm× 70.7 mm aged for 3, 7 d and 28 d was measured.Results and discussion The compressive strength of seawater sea sand mortar specimens is higher than that of freshwater river sand mortar specimens aged at 28 d. This can be attributed to the pore filling effect by hydration products and the formation of more compact C-S-H gels in the presence of the multiple element ions. The multiple ions in seawater also increase the pH value of the pore solution. The pore solution alkalinity can be further regulated via mixing mineral admixtures. At the same dosage, silica fume significantly outperforms that of fly ash in reducing the alkalinity of the seawater cement paste pore solution. Silica fume can nearly consume the calcium hydroxide component at a dosage of 30%, and the pH value of the pore solution decreases to 11.69 at 28 d. Also, silica fume can generate more hydrated calcium silicate gels with a low Ca/Si ratio to enhance its binding ability with sodium and potassium ions, and the enhancement effect is better than that of fly ash. The active aluminum phase in fly ash can promote the generation of aluminum phase products (i.e., AFt and Friedel's salt), and enhance the effective solidification of sulfate and chloride ions. The chloride ion solidification effect of fly ash is better than that of silica fume, and the chloride ion concentration of pore solution can reduce to 0.27 mol/L at the dosage of fly ash of 30%.Conclusions The results showed that the multiple element ions in seawater promoted the hydration of tricalcium silicate and dicalcium silicate in cement, increased the alkalinity of seawater cement pate pore solution and accelerated the pozzolanic reaction between mineral admixtures and calcium hydroxide. Silica fume significantly outperformed fly ash in reducing the alkalinity of the pore solution. The effective solidification of sodium and potassium ions was achieved through the generation of more hydrated calcium silicate gel products with silica fume. Fly ash could promote the generation of aluminum phase products (i.e., AFt and Friedel’s salt) and enhanced the solidification effect of chloride ions, and its enhancement effect was better than that of silica fume. This study could serve as a solid base for the alkalinity regulation and performance design of seawater sea sand concrete.

Introduction Sulfate attack and chloride-induced corrosion are recognized as crucial factors leading to the deterioration and failure of concrete structures. Chloride ingress triggers steel corrosion, while sulfate attack alters the microstructure of concrete matrix. When the concrete is subjected to a poorly mineralized or acid solution, calcium leaching happens and has also a negative effect on concrete durability. In harsh natural environments, concrete is vulnerable to the combined sulfate-chloride attacks, often accompanied by calcium leaching. The mechanism of coupled ionic attack differs substantially from that of individual attacks. This paper was to propose a numerical model on the interaction between sulfate attack, chloride attack and calcium leaching. The ionic transport patterns and hydration product distributions under coupled degradation were quantitively analyzed by the proposed model, thereby providing new insights into the deterioration mechanisms in concrete under the simultaneous sulfate-chloride attack and calcium leaching.Methods A comprehensive transport model was established based on the accelerating effect of aggressive ions on the calcium solid-liquid equilibrium curve. The impact of calcium leaching on the ionic binding effect was also taken into accounts. The chemical reactions between multiple ionic species and cementitious matrix were incorporated based on the transport model. A reaction source term intuitively reflecting the desorption effect of sulfate ions on chloride ions was also introduced. A transport-chemo model was further developed. Based on the volumetric changes induced by expansive hydration products and calcium leaching coupled with the damage effect caused by expansive cracking in the matrix, a time-dependent diffusivity model was established. Finally, an integrated coupled degradation model was proposed, encompassing transport, chemical reactions, and time-dependent diffusivity. The proposed model was validated through third-party experiments according to sulfate concentration distribution and chloride ion concentration distribution. This model is capable to predict ionic transport and product distribution based on given initial material parameters and external ion concentrations. Some indexes such as ionic penetration depth, time-varying diffusion coefficient and product content could be applied to monitor the deterioration process of concrete.Results and discussion Under combined sulfate-chloride attack, there are two distinct regions in the concrete, i.e., a sulfate-rich zone and a chloride-rich zone. The diffusion of free sulfate ions is restricted, so that the increase in total sulfate content peak at a concrete depth of 3 mm is attributed to the precipitation of ettringite (AFt). As an intermediate product of AFt, the content of newly produced gypsum remains low. In contrast, chloride ions progressively penetrate deeper, resulting in the accumulation of chlorine hydrate products such as Friedel’s salt, in which a peak gradually moves inward. The production of Friedel’s salt falls between AFt and gypsum in terms of concentration.The concrete surface is primarily affected via calcium leaching, leading to a more than fourfold increase in the diffusion coefficient. As the influence of calcium leaching diminishes with increasing concrete depth, there is a rapid reduction in porosity. A distinct trough in the porosity curve emerges at approximately 3 mm, precisely aligning with the sulfate-rich zone. The mutual counteraction of internal pore filling effect and damage effect due to expansive cracks results in the time-dependent diffusion coefficient close to the initial value.Simultaneous exposure to sulfate and chloride attacks may provide a short-term mitigation of either sulfate or chloride attack individually. Chloride ions have a more significant inhibitory effect on sulfate attack under these combined conditions. For calcium leaching, sulfate attack can become more severe and concentration peaks of ettringite, and gypsum appear near the surface. Neglecting calcium leaching inhibits the precipitation of ettringite, thus causing the peak content of ettringite to decrease from 201?mol/m3 to 23 mol/m3, which is only 1/10 of that for calcium leaching.Increasing external chloride concentrations amplify a suppressive impact on sulfate attack. Apart from the environment factor, a higher initial calcium aluminate content in concrete corresponds to a more pronounced sulfate attack in concrete matrix. The concentration of hydrate products increases linearly with the extension of time.Conclusions The proposed model had the interactions among various factors and provided a rational prediction of the coupled degradation process. Concrete had distinct sulfate and chloride zones. The sulfate penetration depth remained with the deposition of AFt near the surface. In contrast, the chloride penetration depth gradually increased with a broader distribution of generated Friedel’s salt. The trough of porosity distribution corresponded to sulfate-rich zone at depth of 3 mm, in which the diffusion coefficient was approximate to the initial value. The pore filling effect was offset by the damage effect caused by expansive cracks. Combined attack could mitigate sulfate or chloride attack in the short term. Chloride ions had a more pronounced inhibitory effect on sulfate attack. Calcium leaching led to less ettringite generation but a wider distribution in concrete. Based on the proposed model, a parameter analysis of environmental or material parameters was performed, thus having insights to service life prediction of concrete under chloride-sulfate attack.

Introduction Compared with conventional construction methods in terms of the building structure, 3D-printing concrete (3DPC) technology has the advantages of formwork-free, low labor costs, and less construction waste. The integration of digital design and automatic construction improvs the construction efficiency. 3DPC technology based on extrusion manufacturing is applied in various scenarios such as bridges, landscape sketch, and buildings. However, the stacking-up method also causes some issues like layered appearance, mechanical anisotropy, and high requirements of constructability. At present, the mechanical properties of 3DPC are investigated experimentally, however, the researches on the mechanical properties of 3DPC mainly focus on the static properties of materials, and a few studies involve the dynamic mechanical properties of 3DPC. For concrete structures, they bear static loads, and inevitably face dynamic load (i.e., earthquakes). As a typical dynamic load, the strain rate of concrete under earthquakes ranges from 10-4 s-1 to 10-2 s-1, causing a catastrophic damage to engineering structures. It is essential to understand the dynamic mechanical properties of 3DPC for engineering application. In this paper, the dynamic mechanical properties of 3DPC in three orthogonal directions were investigated by uniaxial compression tests, and the influences of strain rate and different directions on the compressive strength, elastic modulus, peak strain, and anisotropy of 3DPC were analyzed.Methods A 42.5 fast hardening early strength sulfoaluminate cement and silica fume were used as cementitious materials. A local river sand was used as a fine aggregate. A polycarboxylate based water reducing agents with a water reducing rate of > 30% and a tartaric acid retarder were used as additives. A water/cement ratio of 3DPC was 0.29. A concrete printing system was applied to print blocks with dimensions of 220 mm×240 mm×400 mm at an extrusion speed of 1 L/min and a printing speed of 30 mm/s. The printed filament had a width of 30 mm and a height of 10 mm. The moving direction of printing nozzle on the horizontal plane is defined as x direction, where y direction is perpendicular to x direction, and z direction is the gravity direction and perpendicular to the x-y plane. After 28-d standard curing, cylinder specimens were obtained via taking cores from three directions of printed block, and then they were cut into 100 mm×200 mm specimens for compressive strength tests. An electro-hydraulic servo universal testing machine was used to applied dynamic loads. The applied strain rates were 10-5, 10-4, 10-3.5 s-1, and 10-3 s-1.Results and discussion When the weak interface is parallel to the loading direction, 3DPC is prone to failure along the interface due to the development of microcracks at the weak interface. At strain rates of 10-5 s-1 and 10-4 s-1, vertical cracks develop along the inter-layer and inter-strip interfaces in the y and z directions. When the strain rate increases to 10-3.5 s-1 and 10-3 s-1, a diagonal crack appear in the y direction, while cracks in the z direction still appear in the inter-strip interfaces. As the strain rate increases, the deformation rate cannot meet the demand for dissipated energy, leading to an increase of damage in the matrix. Therefore, cracks appear in all three directions in the matrix at higher strain rates.The dynamic peak stress in each direction has a certain degree of strain rate dependence.The dynamic compressive strength in all directions significantly increases as the strain rate increases. The compressive strength in the y direction is more affected by strain rate, compared to that in the x and z directions. At the same strain rate, the compressive strength in the x direction (Fx) is larger than that of cast concrete (FC) in the z (Fz) and y (Fy) directions, indicating that 3DPC has significant anisotropic dynamic compressive strengths. During the elastic stage, pores and defects in concrete are compacted. Their deformation and quantity have a significant impact on the elastic modulus of concrete. When the specimens in the z and y directions are compressed, there are more interfaces perpendicular to the compression direction, and the static elastic modulus in these two directions are smaller. As a result, the growth factors of elastic modulus in these two directions are more sensitive to the strain rate. However, as the strain rate increases, the peak strains in the x, y and z directions stabilize at 0.002.At the strain rates from 10-5 s-1 to 10-3.5 s-1, the anisotropy index of 3DPC decreases rapidly with the increase of strain rate. Because more defects are compacted at high strain rates, the differences in material properties in various directions decrease gradually, that is, the anisotropy of printed concrete decreases gradually. Conclusions The failure of 3DPC originated from defects at the layers or strips interface parallel to the loading direction, which was the weak part of the printed concrete. Under dynamic loading, the compressive strength of 3DPC exhibited a strain rate-dependence in all the directions with Fx>FC>Fz>Fy, and the strain rate effect in the y-direction was dominant. The dynamic increasing factors of compressive strength and elastic modulus increased linearly with the logarithm of strain rate ratio. When the loading strain rate increased from 10-5 s-1 to 10-3 s-1, the dynamic strengths of 3DPC in the x, y, and z directions were increased by 33.47%, 49.88% and 32.90%, respectively, compared to the strength at a strain rate of 10?5 S1. The elastic modulus of printed concrete in the x, y, and z directions was increased by 15.63%, 40.53% and 40.68%, respectively. However, the dynamic strength and elastic modulus of cast concrete were only increased by 31.56% and 13.60%. When the applied strain rate increased from 10-5 s-1 to 10-3 s-1, the anisotropy coefficient decreased from 5.69 to 2.96. The anisotropy of 3D printed concrete decreased with the increase of strain rate, but the change range was small at a high strain rate.

Introduction Alkali-activated slag (AAS) cementitious material has attracted much attention due to its high early strength, good corrosion resistance, and low carbon emission. The microstructure of AAS has a decisive influence on its properties, which depends on the quantity and spatial distribution of the reaction products. It is thus of great significance for understanding the formation process of its microstructure to explore the distribution of reaction products in AAS system. In previous studies, the type of activator and the dosage of sodium oxide both have an effect on the microstructure of AAS. However, the underlying mechanism of sodium oxide content affecting the microstructure of AAS system via the product distribution is still unclear. In this paper, the dissolution behavior and product distribution characteristics of slag in sodium hydroxide solution with different concentrations were in-situ observed by a polarizing microscope. The dissolved ions, phase composition, microscopic morphology, distribution characteristics of reaction products, and pore structure of hardened AAS were also analyzed to elucidate the difference of reaction process of slag at different concentrations of sodium hydroxide solution.Methods Sodium hydroxide solutions with molar concentrations of 0.5, 2.0 mol/L and 4.0 mol./L were prepared. Slag was uniformly mixed with sodium hydroxide solution at a solid/liquid ratio of 1/100. 1-2 drops of the mixture were added into a single concave slide by a dropper. The excessive solution was removed with absorbent paper and the edges of the cover slip were sealed with paraffin. The prepared slide sample was placed on the stage of the polarizing microscope and independent slag particles were selected for the coming characterization. The area change rate of slag particles or reaction products was analyzed by a software named Image J. The surface morphology of slag and the distribution of reaction products were characterized by scanning electron microscopy, and the elemental analysis of different morphological substances was determined by energy-dispersive X-ray spectroscopy.After the mixed samples were stayed for 1, 6 h and 48 h, pore solutions were obtained through centrifugation and filtration, and the reaction products in the precipitate were dissolved by a methanol-salicylic acid solution. The ion quantity was determined by inductively coupled plasma optical emission spectroscopy. After the mixture was stayed for 6 h and 48 h, residual solids were obtained after centrifugation. In the hydration of residual solids, the phase composition was analyzed by X-ray diffraction, and the reaction degree was determined by a selective dissolution method.The alkali-activated slag pastes with different sodium oxide contents (i.e., 4%-8%) and a water-solid ratio of 0.4 were prepared. After standard curing for 3 d, the samples were broken, and then the hydration was terminated and dried. The dried samples were placed into the dilatometer, and the pore size distribution was determined by a model Auto pore IV 9500 mercury injection instrument.Results and discussion At a low concentration of sodium hydroxide (sample N1), the ion dissolves slowly because of the slow depolymerization of slag. Since the saturation concentration is not reached, the dissolved ion continues to diffuse outwards, forming a new gel phase zone containing a great amount of water, which makes the initial dissolved precipitate products distributed in a wide range. After 48 h reaction, the area of this region is increased by 257.8%, compared to the initial area of slag. The main reaction products are C-(A)-S-H gel and hydrotalcite. At a high concentration of sodium hydroxide (samples N2 and N3), [SiO4]4- and Ca2+ are dissolved in large quantities due to the rapid depolymerization of slag. Calcium hydroxide crystallizes out because its saturation index is greater than 0. Also, ion concentration rapidly reaches the solubility product (Ksp) of calcium silicate hydrate, forming a layer of dissolve-precipitate reaction products on the surface of slag particle. Therefore, the product distribution range of AAS system with a high concentration of sodium hydroxide is narrow. The area growth rates after 48-h reaction for samples N2 and N3 are 15.6% and 4.0%, respectively. The reaction products mainly consist of C-(A)-S-H gel, hydrotalcite, katoite and portlandite.At the same curing age, AAS with a high sodium oxide content has a higher reaction degree and a lower porosity, compared to AAS with a low sodium oxide content. However, AAS with a high sodium oxide content has more macro-pores due to the difference in the distribution characteristics of reaction products.Conclusions The concentration of sodium hydroxide had an influence on the product distribution in AAS system. For the AAS system with a low concentration of sodium hydroxide, the ions dissolved slowly and spread outward continuously, forming a new gel phase around the slag, and then polycondensation and dehydration with the area increment rate of 257.8%. For the AAS system with a high concentration of sodium hydroxide, the slag quickly dissolved a large number of silicate and calcium ions, resulting in the saturation index of calcium hydroxide of greater than 0 and the formation of portlandite crystals. The distribution range of reaction products was relatively narrow with the area growth rate of less than 15.6% because the surface of the slag particles was quickly covered by reaction products. Although the hardened AAS paste with a high Na2O content had a higher reaction degree and a smaller porosity, compared to AAS with a low Na2O content, the size of pore was larger.

Introduction With the rapid development of assembled buildings, the low-carbon and high-efficient production of precast concrete components becomes a hotspot for the industry. Portland cement (PC), as one of the most important cementitious materials for the preparation of precast components, has the disadvantages of insufficient early strength development and late volumetric shrinkage. To realize the volume stability of non-steam-cured precast components, expansion agents are often introduced into Portland cement. Sulphoaluminate cement (CSA) with a large amount of Ye’elimite and gypsum is often used to improve the early strength and volumetric stability of PC. Different types of CSA have different expansion capacities due to the different contents of Ye’elimite and gypsum, affecting the composition of the hydration products with the saturation of ettringite. In this paper, the mechanical properties and volumetric stability of the specimens were investigated via varying the relative contents of C4A3S and CS in Portland cement (i.e., CS/C4A3S molar ratio and C4A3S-CS content). The hydration process, phases composition, and the microstructure of system were characterized to analyze the effect of C4A3S -CS on the hydration of Portland cement.Methods Portland cement clinker (Tangshan Jidong Cement Sanyou Co., Ltd., China), and anhydrite (Tangshan Polar Bear Building Materials Co., China) were used as raw materials. CaCO3, Al2O3, and CaSO4-2H2O mixed in a molar ratio of 3:3:1 were heat-treated in a high-temperature muffle furnace for 2 h to obtain the C4A3S mineral. Four different CS/C4A3S molar ratios of M, 2, 5, 8 and 11 were designed, while five C4A3S-CS content levels of 5%, 10%, 15%, 20% and 25% were set up in a total of 20 sets of crossover experiments. The 10%-M2 represents the content of this sample of C4A3S-CS in Portland cement clinker is 10% at the CS/C4A3S molar ratio M of 2.The water-cement ratio was 0.35, and the paste was molded as a net paste test block with the sizes of 20 mm×20 mm×20 mm. The compressive strength at the corresponding age was determined. The phase compositions of the hydration products were analyzed by a model D/Max-RB X-ray diffractometer and a model STA 449F3 thermal analyzer. The pore structure of the specimens was characterized by a model AutoPore IV 9500 V1.09 instrument.Results and discussion C4A3S-CS has an effect on the free expansion rate of Portland cement, and it can significantly increase the early compressive strength of Portland cement clinker. When the C4A3S-CS content of ≤15% in the sample, the free expansion rate is small, the volumetric stability is better. When hydration time is 14 d, the free expansion rate remains stabilized, and the expansion rate of the specimen does not change at 28 d. The free expansion rate of the sample is lower than that of the sample with C4A3S-CS. The effect of C4A3S-CS on the expansion properties of Portland cement belongs to the ettringite-type expansion. The key reason of the volume stability and early strength development of the C4A3S-CS-PC system is affected by the amount of ettringte. Ettringite growth in the molding paste is limited as the crystal grows, the pressure of ettringite on the surrounding paste environment gradually increases, reaching a certain threshold that makes the specimen gradually collapse. As a result, the amount of ettringite generation is strictly controlled. At ettringite content of less than 8.51%, the compressive strength increases with the increase of ettringite content. Ettringite plays a role of dense pore. However, at the ettringite content of more than 8.51%, the expansion increases with increasing ettringite content, and the mechanical properties of the cement begin to decrease.The most available pore sizes of the specimens 10%-M11 were smaller than those of the specimens 5%-M11, while the specimens 10%-M11 have a narrower distribution of pore sizes and smaller total porosity, which can account for the maximum mechanical properties. The location and the crystallization situation of hydration products both have an influence on the expansion properties of Portland cement. Ettringite fills the pores of the paste, and the C-S-H gel can adhere other hydration products such as ettringite to enhance the performance of the cement, and avoid the ettringite abnormal growth.Conclusions The 10% content of C4A3S-CS appropriately increased the expansion deformation of Portland cement, limited its late volumetric deformation and stablized the expansion rate. The content of C4A3S-CS also improved the early mechanical properties of Portland cement, having a positive effect on the development of mechanical properties. Under the condition of 10% C4A3S-CS and the molar ratio of CS/C4A3S of 11, the compressive strength of Portland cement at 12 h was increased by 102%, and the free expansion rate at 28 d was 0.279%. There were three main reasons of high early strength in the C4A3S-CS-PC system, i.e., hydration of C4A3S-CS, hydration of C3A with CS, and rapid hydration of C3S. The increased content of C4A3S-CS facilitated the formation of ettringite, and hydration consumed Ca(OH)2 in the hydration product to generate ettringite to cause the expansion, accelerating the hydration rate of the silicate phase and improving the cement hydration degree. The ettringite generated by the hydration of C4A3S-CS-PC could compensate for the self-shrinkage of Portland cement, and the short and fine needle-like ettringite grew on the surface of the hardened cement paste and in the pores, and the staggered lapping filled the pores, reducing the total porosity of the cement and the most available pores. An appropriate amount of C4A3S-CS could optimize the distribution of ettringite in the system, and avoid the expansion caused by the abnormal growth of ettringite crystal size.

Introduction Magnesium phosphate cement (MPC) is a novel construction material that forms a gel material consisting primarily of insoluble phosphate salts after reaction of alkaline components with magnesia and soluble acid phosphate salts. However, the ceramic properties of MPC are significantly deficient in terms of fatigue resistance and toughness, and can lead to failure under vehicle loads. Short-cut basalt fibers can inhibit the initiation and propagation of concrete microcracks, but tend to wrap around and agglomerate during mixing. In addition, China has abundant island reef resources, and large quantities of concrete materials are required in various infrastructure construction processes. Transporting sand and fresh water from inland increases project costs, and extreme climate conditions can cause transportation inconveniences. Therefore, the use of seawater and marine sand from island reefs for road repair without damaging the environment can achieve a goal of localizing raw materials and reducing transportation burden. In this paper, effect of resin-modified basalt fiber on the workability, mechanical properties, fatigue resistance, microstructure, and engineering properties of seawater-sea sand MPC mortar was investigated.Methods Dead-burned magnesia, ammonium dihydrogen phosphate, borax retarder, highly active silica fume, and ultrafine low-calcium fly ash were used to prepare two groups of mortars with seawater sea sand or freshwater river sand. The modified basalt fiber was prepared, in which the surface of the modified fiber after coating with resin has a twist and wrinkle, which strengthens the bite force between the fiber and the mortar matrix. Different meshing structures were formed between the mortar and the end head (lengths of 23-25 mm, tensile strength of 2 900 MPa, Young modulus of 90 GPa). The basalt fiber with different volume fractions (i.e., 0%, 0.25%, 0.50%, 0.75% and 1.00%) was added to investigate the effect of fiber content on the matrix properties.The workability (flowability, setting time), mechanical properties (compressive/flexural strength), and fatigue resistance (sinusoidal reciprocal loading: 0.6, 0.7 and 0.8) of the MPC mortar were investigated in accordance with the standard for test methods of basic properties of construction mortars (JGJ/T 70—2009). The heat release, mineral phase composition, microstructures, and pore structures of the MPC mortar were investigated by a hydration thermal analysis, X-ray diffraction, field emission scanning electron microscopy, and X-ray computed tomography. The field rapid repair tests were conducted to comprehensively evaluate the structural layer characteristics of the surface layer by three-dimensional ultrasonic scanning, falling hammer bending, rebound, and coring methods.Results and discussion The hydration time of sea water-sea sand MPC mortar is short at a setting time for 30 min. The mortar can be compacted without vibration due to its workability available. However, the high dosage of modified basalt fibers has a challenge to fully wet the particle surfaces, increasing friction between particles and adversely affecting the workability of MPC mortar.The strength development of sea sand MPC mortar progresses rapidly with a compressive strength of 22 MPa after 1 h. The addition of a small amount of modified basalt fiber can slightly enhance the compressive strength of the MPC matrix. The fibers act as bridges in the fracture zone, improving the flexural deformation capacity of the MPC mortar. At different stress levels, the samples with 0.75% fiber content exhibit a fatigue life approximately one order of magnitude higher than that of mortar without fiber addition.In the hydration process of seawater/sea sand MPC mortar, a highly exothermic reaction occurs with the heat release primarily concentrated within the first hour, exhibiting a single peak. The crystalline phase content increases during the condensation and hardening process of MPC with major hydration products including struvite stone, sillimanite, and monticellite. Also, the introduction of seawater/sea sand leads to the formation of sulfate-chloride products. The hydration products of phosphate crystals form a strong bonding interface between the binder and an appropriate amount of modified basalt fibers. However, the incorporation of 1% fibers results in larger defects at the fiber-matrix interface, an increased internal porosity, and greater non-uniformity in pore distribution.Based on on-site experiments, the reliability of seawater-sea sand MPC mortar in repair projects is confirmed. The mortar pouring is convenient, the process is simple, and the surface consolidates and hardens quickly. The results obtained after 1 h of pouring indicate that although the bond between the newly poured MPC mortar and the bottom crushed stone layer is relatively weak, the overall integrity within the new surface layer is good, and the density is high. The surface rebound values and maximum deflection values are distributed evenly, and the strength at the interface between the pouring surface and the old concrete pavement is relatively low.Conclusions The setting time of the early-strength MPC mortar could be controlled within 30 min. Fibers could improve the bending deformation capacity of MPC, and the fatigue life of the samples with 0.75% fiber content was increased by approximately an order of magnitude, compared to the samples without fibers. The hydration reaction of the mortar was a highly exothermic process, accompanied by an increase in crystalline phase content. The gel composed of struvite and modified basalt fiber had a strong bonding interface, while the porosity and pore variability increased with the increase in fiber content. Besides, the newly poured MPC surface layer had a high compactness in engineering application, and the distribution rebound values and deflection values was uniform, confirming the feasibility of fiber-reinforced sea sand/sea water mixed MPC system.

Introduction Using coral concrete made from coral aggregates instead of conventional coarse and fine aggregates and seawater instead of freshwater for island reef construction can reduce costs and shorten the construction period for the development of the marine economy. However, coral concrete has some challenges such as high brittleness, poor toughness, and limited durability, thus restricting its application in engineering. Previous studies confirm that incorporating fibers can effectively enhance the mechanical properties of concrete. Therefore, in coral concrete, some microfibers with high elastic modulus are considered to reduce the microcracks, and some macro-fibers with high fracture toughness and elongation are considered to bridge the macrocracks, enhancing its mechanical performance in multiple scales. Carbon fibers (CFs) have the maximum elasticity modulus among commonly used micro-fibers. However, replacing carbon fibers with more economical and relatively high-modulus basalt fibers (BFs) is an effective approach. In this paper, CFs and BFs were selected as microfibers. High-elongation plastic steel fibers (PSFs) were also selected as macro-fibers instead of the steel fibers most commonly used in concrete. The CFs, BFs, and PSFs were incorporated into coral concrete. The mechanical properties of the hybrid fibers-reinforced coral concrete (HFRCC) under axial compression were investigated, and the corresponding constitutive model was proposed. Methods Cement used was ordinary Portland cement P·O 42.5, adhering to the code GB175. A coarse aggregate used was a crushed coral with a continuous gradation of 5 mm to 20 mm and a tube compressive strength of 3.1 MPa. A fine aggregate used was a coral sand with a fineness modulus of 3.0. Seawater was taken from Beibu Gulf，Guangxi, China. The admixtures include a polycarboxylate superplasticizer, a hydroxypropyl methyl cellulose (HPMC), and an antifoaming agent. The study involved sixteen mix proportions for HFRCCs with different dosages of CFs, BFs and PSFs.A uniaxial compression test was conducted on prismatic specimens with the dimensions of 100 mm×100 mm×300 mm by a model RMT-201 electro-hydraulic servo testing machine (1 500 kN). To measure the axial deformation of specimens, two LVDTs were placed in the middle of the specimen. Simultaneously, during the loading, a digital image correlation (DIC) system was arranged at the front and rear positions of the specimen to record complete deformations throughout the specimen failure. The failure process, failure modes, and stress-strain curves of the specimens were determined via uniaxial compression tests. Key parameters such as peak stress, peak strain, residual stress, and ultimate strain were extracted from the stress-strain curves. The strain field and failure process were analyzed by digital image correlation (DIC) system. In addition, a modified constitutive model suitable for HFRCC was also established based on the experimental data.Results and discussion The uniaxial compression process of HFRCC can be divided into four stages, i.e., linear elasticity, stable crack development, unstable crack propagation, and post-peak failure. Microfibers predominantly affect the crack development before the peak stage, while macro-fibers play a crucial role in the post-peak stage. In the post-peak failure stage, a combination of DIC system obtained horizontal strain distribution cloud maps reveals that HFRCC with micro-fibers exhibits a more uniform strain distribution, compared to HFRCC without fibers or with only macro-fibers. However, in HFRCC with macro-fibers, the main through crack has a width of approximately 1 mm, which is smaller than that of HFRCC without fibers or with only micro-fibers (approximately 1.5 mm). The incorporation of high-modulus microfibers and high-fracture toughness macro-fibers into coral concrete enhances its mechanical properties in multiple scales. This is attributed to a ability of micro-fibers at low dosages to form a randomly oriented fiber network in the concrete matrix. This network bridges the micro-cracks, suppresses the extension of initial cracks, and transfers stress across micro-cracks to reduce stress concentration as well as enhances the performance of the interface transition zone. However, most of them break or pull out after macro-crack formation due to the high modulus and low fracture toughness of micro-fibers. Also, macro-fibers with a higher fracture toughness can continue to bridge macro-cracks and transfer stress between them even after the formation of macro-cracks. For the both strength and toughness, HFRCC exhibits a superior performance when the volume fractions of CFs and BFs are 0.15% each, and PSFs dosage is 7 kg/m3. Compared to the coral concrete without fibers, the peak stress, peak strain, and post-peak compressive toughness of HFRCC are increased by 6.22%, 38.54% and 116.44%, respectively.A modified constitutive model suitable for HFRCC is proposed based on the CEB-FIP model and the Guo Zhenhai model, and the calculated data of the model fit well with the measured results. The damage evolution process of HFRCC investigated by the modified constitutive model reveals that the incorporation of CFs, BFs, and PSFs can synergistically delay the damage progression of coral concrete.Conclusions The uniaxial compression process of HFRCCs could be divided into four stages, i.e., linear elasticity, stable crack development, unstable crack propagation, and post-peak failure. Microfibers played a crucial role in expanding microcracks during the first three stages, showing beneficial effects on the peak stress, peak strain, and pre-peak compressive toughness. Macro-fibers acted as bridging elements for macro-cracks in the peak failure stage, demonstrating a more significant impact on the residual stress, ultimate strain, and post-peak compressive toughness. Each type of fiber had an optimal dosage level, and the reasonable dosage of fibers could generate positive synergistic effects. When only micro-fibers were added, BFs contributed more to the increase in peak stress rather than CFs, but their improvement in peak strain and compressive toughness was slightly lower than that of CFs. This indicated that for engineering applications with lower toughness requirements, it could be feasible to replace CFs entirely with more cost-effective BFs. The calculated data of the modified constitutive model aligned well with the experimental results. This work investigated the damage evolution process of HFRCC, revealing that the incorporation of CFs, BFs, and PSFs could collaboratively delay the damage progression of coral concrete.

Introduction Chloride-induced corrosion is a primary factor contributing to the degradation of coastal concrete infrastructure. To counteract the corrosion of steel reinforcement, epoxy resin coatings are commonly used. However, ensuring their durability in alkaline environments is a challenge, and these epoxy coatings also alter the mechanical bond between steel and concrete. It is thus crucial to develop thin inorganic conversion coatings. Layered double hydroxides (LDH) have a potential application in corrosion protection. However, steel tends to passivate in alkaline environments, limiting the growth of LDH on its surface. Hong et al achieved the in-situ growth of LDH on steel and elucidated its growth mechanism. Despite its potential in corrosion prevention, the growth of LDH presents a lamellar structure, creating micropores that serve as channels for the invasion of corrosive ions. Hence, developing a dense composite film for effective steel protection remains a challenge. This paper was to investigate two methods for LDH densification and characterize their composition, density, and corrosion resistance.Methods Steel sheets and rebars were sequentially polished with #240, #500, #1 000 and #2 000 SiC sandpaper to remove surface oxides. After polishing, they were placed in anhydrous ethanol for 5 min under ultrasonic cleaning to eliminate surface impurities, resulting in a smooth and uniform bare steel named as B. Subsequently, steel samples were immersed in solutions containing 0.057?5?mol/L Mg(NO3)2·6H2O, 0.025 mol/L Al(NO3)3·9H2O, and 0.375 mol/L urea dissolved in deionized water (DI). The surface of steel materials was washed with 5% dilute nitric acid and then vertically placed in a reaction vessel. The heating procedure was to increase from room temperature to 120 ℃ for 2 h, and maintain at 120 ℃ for 24 h. The pressure was self-supplied by the reaction vessel during the heating process. After the hydrothermal reaction, the samples were removed, rinsed with deionized water and dried for 3 d, resulting in the samples with only Mg/Al-CO32--LDH membrane growth, named as L1.Furthermore, LDH samples were placed in a 100% CO2 for half a day, then immersed in saturated calcium hydroxide for 2 h. Afterwards, they were taken out, placed in an oven at 50 ℃, and dried for 3 d. The sample represented the first method of calcium carbonate densification after LDH growth, named as L2. For the second method, LDH samples were immersed in saturated calcium hydroxide for 6 h, followed by exposure to CO2 for 10 s, and then dried in an oven for 3 d, resulting in the sample denoted as L3. This aimed to investigate the optimal method for calcium carbonate densification between LDH pores. All the samples obtained the two methods were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and specific surface area analysis (BET). The corrosion resistance of the composite films under different conditions was also determined by electrochemical impedance spectroscopy and potentiodynamic polarization analysis.Results and discussion Based on the XRD patterns and FTIR spectra, a layered double hydroxide (LDH) film and calcium carbonate composite occur on the steel surface. The results show that the peak intensity of calcium carbonate of the sample L3 is higher than that of the sample L2, indicating a higher content of calcium carbonate in the sample L3. Based on the SEM images, the surface pores and the compactness of calcium carbonate occur, and the thickness and cross-sectional compactness appear. The analysis of internal compactness reveals that the compacted samples maintain their thickness and achieve a compaction in internal pores. From the analysis of pore size and pore volume, the pore size and volume decrease for the samples L1, L2, and L3.The results by electrochemical impedance spectroscopy and potentiodynamic polarization curves indicate that the sample L3 has an optimum corrosion resistance. Also, the sample L3 has a superior corrosion resistance rather than the sample L2. This can be since the sample L2 is initially placed in CO2, resulting in some carbon dioxide remaining in the pores. However, the sample L3 is firstly immersed in Ca(OH)2 solution. In the soaking process, Ca(OH)2 solution effectively penetrates the pores in the film layer. This sample is able to form a large amount of calcium carbonate to compact the LDH film through carbonization, having a protective performance. This method of filling is simpler, more economical, and faster, making it more conducive to industrial applications.Conclusions The in-situ growth of MgAl-CO32--LDH films on steel substrates was achieved through two methods, allowing for the compact composite of calcium carbonate within the pores of the LDH film.The thickness of the LDH film hardly changed after the incorporation of calcium carbonate, remaining at approximately 17 μm. The compaction of calcium carbonate was on the surface of the LDH and permeated into the inner pores of the LDH film.All the LDH film layers exhibited a superior corrosion resistance in chloride ion intrusion. The sample subjected to Ca(OH)2 immersion followed by carbonization had a superior corrosion inhibition performance and an impressive corrosion inhibition efficiency of 95.22%.

Introduction Additive manufacturing has attracted recent attention for glass fabrication due to its advantages to manufacture parts with complex geometries. In 3D printing, various techniques such as fused deposition modeling, selective laser melting, direct ink writing, and stereolithography are developed for glass fabrication. For its high printing accuracy, fast speed, and excellent surface quality, stereolithography shows a great potential in fabricating fused quartz glass with intricate structures and optical lenses. This paper was to enhance the optical performance of fused quartz glass including optical absorption, photoluminescence and light scattering properties via infusing metal ions into the glass. We investigated the metal salt solution immersion, debinding and sintering processes based on liquid crystal display 3D printing technology. We fabricated a fused silica glass doped with Cr3+ and Co2+ metal ions. Methods A homogeneous solution of photopolymer was prepared via mixing 60% 2-hydroxyethyl methacrylate, 10% triethylene glycol diacrylate, and 30% phenoxyethanol. 2,4,6-trimethylbenzoyldiphenyl phosphine oxide, Sudan orange G, and diethyl phthalate were added to the solution and dispersed for 5 min. Silica nanoparticles of 53% (in mass fraction) were then added and dispersed by a dissolver for 10 min. The photosensitive paste was cured using an LCD 3D printer. Subsequently, the printed parts were heated at 600 ℃ for 2 h, and then soaked in a metal ions solution for 1 h. After being air-dried at 50 ℃ for 1 h, the doped debinding part was sintered at 1 280 ℃ for 2 h. Metal ion-doped glass in the furnace can be obtained after cooling to room temperature.Results and discussion After debinding and sintering, the printed fused quartz glass parts are densified. The removal of organic binder from the debinding parts causes a contraction of the parts. The micropores disappear after the sintering process, resulting in dense parts that are colorless and transparent. Furthermore, a high concentration of the doped mental ions leads to an extensive crystallization and reduces the transparency of the samples. Based on the Raman spectra of parts doped with Cr3+ and Co2+ and commercial glass KN7980, four characteristic peaks of fused silica glass appear, confirming that the finished parts are fused silica glass. In the Raman spectra of the fused silica, the characteristic peaks at 896 cm-1 and 985 cm-1 doped with Cr3+ correspond to the polymerized chromate species and the Cr—O stretching vibration of discrete chromate species (CrO42-), respectively. This indicates that chromium oxide crystallization occurs in fused silica glass doped with a certain concentration of Cr3+. The XRD patterns show that Cr3+ induces a crystal precipitation in the fused silica glass, for characteristic peaks of quartz at 2θ of 26.43° and cristobalite at 2θ of 63.56° and 67.91° in the glass doped with Cr3+. The characteristic diffraction peaks in the glass doped with Co2+ appearing at 2θ of 32.2°, 47.7° and 57.4° are consistent with those of CoO.The absorption spectra of the glass doped with 2.042?μmol/cm3 concentration of Cr3+ reveal that the bands at 471 nm and 660 nm are due to the spin-allowed transition A2g(F)→4T1g(F) and 4A2g(F)→4T2g(F), respectively. Consequently, Cr3+-doped fused silica glass can absorb blue light at 471 nm and red light at 660 nm. The absorption spectra of the parts doped with 12.249?μmol/cm3 concentration of Co2+ indicate that the bands at 597 nm and 662 nm result from the spin-allowed transition 4T1g(F)→4T1g(P) and 4T1g(F)→4A2g(F), respectively. Co2+-doped fused silica glass shows absorption of blue light at 597 nm and red light at 662 nm. Doping the glass with metal ions imparts unique optical and structural properties to the glass, so that chromium- and cobalt-containing glasses have applications in industries, such as Integrated optics, filters, fiber lasers and near-infrared laser materials.Conclusions LCD 3D printing technology was used to produce optical components of fused silica glass doped with Cr3+ and Co2+ metal ions, having the superior properties, compared with commercial glass KN7980. The Cr3+-doped green fused silica glass had a great filtering ability for blue light (471 nm) and red light (660 nm). The Co2+-doped blue fused silica glass had a great filtering ability for yellow light (597 nm) and red light (662 nm). The filtering performance of multilayered silica glass could be deliberately tailored to enhance its performance since the filtering ability of silica glass was correlated to the metal ion doping concentration.

Introduction Titanium (Ti)-based implants are one of the most commonly used materials in orthopedic surgery. Although Ti-based implants have good biomechanical properties and biocompatibility, their non-antibacterial shortcomings lead to orthopedic implant-related infections that seriously affect the effect of surgery and postoperative recovery. and serious cases need a second operation and increase the pain and cost of patients. Some studies reported metal or antibiotic antibacterial coatings on Ti-based implants, but they have some disadvantages (i.e., heavy metal coatings can cause damage to the human body, and excessive use of antibiotic coatings can lead to drug resistance). It is thus necessary to investigate the preparation of coatings with good antibacterial properties and biological activities on the surface of Ti-based implants, so as to provide an effective solution to the problem of bone implant-related infection in clinic. Magnesium (Mg) is a major element in human body. Some studies reported that Mg and its compounds have good antibacterial and biocompatibility. Methods Ti sheets were cleaned and immersed in an electrolyte containing sodium chloride and magnesium chloride (pH=9.5) and applied a DC voltage of 3.0 V for 0-12 h to obtain magnesium hydroxide [Mg(OH)2] coatings. After deposition, Mg(OH)2 coatings were calcined in a muffle furnace at a heating rate of 2 ℃/min at 650 ℃ for 6 h to obtain magnesium oxide (MgO) coatings. The phases of each group of samples were analyzed by X-ray diffraction (XRD), the surface morphology was analyzed by scanning electron microscopy (SEM) and the composition of surface elements was analyzed by energy dispersive spectroscopy (EDS). The in-vitro antibacterial properties of the samples were evaluated according to the standard ISO22196—2011. The bacterial liquid was resuscitated, diluting it to 1 × 105 cfu/mL (cfu is colony-forming units). The samples were firstly sterilized by drying, then 300 μL bacterial solution (i.e., Staphylococcus aureus and Escherichia coli) was then dropped onto each sample and incubated in a constant temperature incubator (at 37 ℃) for 24 h. After diluting the coating plate, the colony number was analyzed and converted to antibacterial rate. The in-vitro cytotoxicity of each sample was evaluated according to the standard ISO10993.5. After dry heat sterilization, the samples were placed in a 24-well plate (no sample cell suspension in the control group and complete culture medium in the blank group). 1mL mouse osteoblast suspensions (OB-6; 5 000 cell/mL) were dropped onto each sample and then incubated in a cell culture box (5% CO2 at 37 ℃) for 1 d, 3 d or 5 d. After the completion of culture, the absorbance value was detected by a method named CCK-8 and converted to a cell survival rate.Results and discussion Mg(OH)2 coating was prepared on titanium surface by an electrochemical deposition method, and MgO coating was obtained after calcination. Granular matter [Mg(OH)2 and MgO] are uniformly distributed on the surface of each group, and the particle density and coverage rate increase with deposition time. Mg(OH)2 and MgO coatings all have a good antibacterial activity against Staphylococcus aureus and Escherichia coli. The antibacterial rates increase with deposition time. When deposited for ≤3 h, the antibacterial rate of MgO is higher than that of Mg(OH)2. After deposited for ≥6 h, the bacteriostatic rate of both is close to 100%. The cytotoxicity of Mg(OH)2 and MgO coatings increases with the deposition time, and the toxicity of the two groups (i.e., deposited for 0.5 h and 1.0 h) decreases with the culture time, and the toxicity of the other three groups (i.e., deposited for 3 h, 6 h and 12 h) increases with the culture time. At 5 d, the survival rates of Mg(OH)2 and MgO samples deposited for 0.5 h are 152% and 90%, and the survival rates of the two groups of samples deposited for 12 h are 2% and 6%, respectively. Conclusions The surface morphology and thickness of Mg(OH)2 and MgO coatings changed with the deposition time. The cytotoxicity and antibacterial rate of the coatings were enhanced with the deposition time. It was speculated that there was a dose-effect relationship between them and the coating. The results showed that Mg(OH)2 coating could be prepared by electrochemical deposition, and the MgO coating could be obtained after calcination. Mg(OH)2 and MgO coatings deposited for 1 h had good comprehensive properties.

Introduction Water shortage and pollution become serious due to the improvement of economic and the acceleration of industrialization. Water bodies contain a large number of pollutants, affecting the environment and human-being health. Heterogeneous catalyst activation of peroxymonosulfate (PMS) is an effective degradation technology for organic pollutants, but SO4-· is difficult to effectively activate due to the high redox potential. It is thus necessary to develop catalytic materials that can activate PMS efficiently. The metal organic frame materials based on Prussian blue have the typical physical and chemical characteristics of metal-organic framework (MOFs) materials, adjustable and controllable chemical composition, high specific surface area and porosity, and diversified structure and function, etc., which become the hot materials in various fields. The conversion of Prussian blue analogue (PBA) into nitrogen-doped carbon materials with a high specific surface area, a high porosity and a high nitrogen content through high-temperature calcination or inert gas carbonization is of great significance for improving the catalytic performance of the catalyst. In this paper, a nitrogen-doped carbon nanosheet supported FeMnO catalyst was prepared by a high-temperature carbonization method. Its catalytic degradation performance was analyzed. The effects of different systems, pH value of solution, Rhodamine B (RhB) initial mass concentration, PMS mass concentration and catalyst mass concentration on the RhB degradation were investigated. In addition, the possible mechanism of RhB degradation was also proposed.Methods Fe-Mn PBA and colloides were prepared by a co-precipitation method. After grinding, the catalyst was heated in nitrogen atmosphere at 750 ℃ at 2 ℃/min for 2 h to synthesize transition bimetal oxide (i.e., Fe0.099Mn0.9010/FeMn2O4) N-doped carbon nanosheets. Compared with FeMnO and graphite C, the degradation properties of FeMnO@C in different systems and under different factors were characterized by ultraviolet-visible spectroscopy (UV-Vis). The structure and morphology were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FT-IR). Results and discussion Heterogeneous catalyst activation of PMS can inhibit the dissolution of metal ions and it is not easy to cause secondary pollution. An efficient nitrogen-doped carbon catalyst FeMnO@C was obtained based on Fe-Mn PBA, which has a high specific surface area and provides a high density of active sites for catalytic reactions, and can effectively activate PMS to rapidly degrade organic pollutants. FeMnO@C has good magnetic properties, which can be conducive to recycling. The interaction between different metals in the double transition metal materials makes the metals difficult to be dissolved, greatly reducing the concentration of toxic metal ions in the system. The redox cycle between Mn and Fe ions on the surface of FeMnO@C catalyst and a series of free radicals generated after the self-decomposition of PMS make FeMnO@C have a superior catalytic degradation performance. The effects of PMS amount, initial concentration of RhB, catalyst amount and initial pH value of RhB solution on the catalytic performance were analyzed. The optimal reaction conditions were PMS concentration of 0.15 g/L, concentration of RhB solution of 20 mg/L, catalyst concentration of 0.1 g/L and pH value of 7. The possible degradation mechanism was proposed based on capture experiments and EPR spectra. Conclusions A transition bimetallic oxide catalyst supported by nitrogen-doped carbon nanosheets was synthesized by a high-temperature carbonization method, which could be used as an efficient PMS activated heterogeneous catalyst to degrade the target pollutant RhB. In the PMS activation system, the FeMnO@C catalyst could degrade 95.5% of RhB within 10 min. The redox cycling between Mn and Fe ions on the surface of the FeMnO@C catalyst and a series of free radicals generated after the self-decomposition of PMS could make the FeMnO@C have a superior catalytic degradation performance. The capture experiments showed that 1O2 was the main contributing radical. In addition, FeMnO@C catalyst also had a magnetic property and a good cyclic stability. 84.7% RhB removal rate could be obtained after five consecutive cycles. The results indicated that FeMnO@C had a good magnetic property, which could be easy to be recycled, having a promising potential in treating organic wastewater.

Introduction Li6Gd(BO3)3 (LGBO) crystal is an effective scintillator for neutron detection as well as a laser host and phosphor material. However, it is difficulty to grow large-size and high-quality crystals because of high viscosity of the melt and crystal cracking. Although LGBO crystals are grown by the Czochralski and other methods, the crystal size is small and the quality is poor for its practical application. The vertical Bridgman method is suitable for growing borate crystals due to its slow growth rate and small temperature gradient. This paper was to investigate the crystallization behavior of deep supercooling melt and grow LGBO crystals prepared by a modified vertical Bridgman method. In addition, the thermal properties of crystals were also analyzed to provide a reference for practical application.Methods LGBO polycrystalline materials were synthesized with high-purity chemicals (i.e., Li2CO3, 99.99%；H3BO3, 99.99% and Gd2O3, 99.99%) by a high-temperature solid-state method. LGBO crystal was grown by a modified vertical Bridgman method. The crystals were characterized by X-ray diffraction, ultraviolet excitation and emission spectroscopy, and differential scanning calorimetry. The thermal expansion coefficient of the crystals was measured by a model TMA 402 F1 thermomechanical analyzer. The thermal diffusivity coefficient of the crystals was measured by a model LFA 457 laser thermal conductivity meter, and the thermal conductivity of the crystals was calculated accordingly.Results and discussion LGBO crystal was grown in a Platinum crucible with a seed well. Seed crystal was obtained via spontaneous nucleation in advance. The DSC curves of LGBO show that the melting point is 845 ℃, and the crystallization temperature is 731 ℃. Thus, the seeding and slow growth rates are the key issues for the growth of LGBO crystal because of the deep supercooling melt. The growth parameters are optimized with a -oriented seed, a?slope of 30 degrees at shoulder, a small temperature gradient of 30 ℃/cm at solid-liquid interface and a very slow descent rate of 2.4 mm/d. The transparent LGBO crystal with the sizes of 20 mm in diameter and 30 mm in length is obtained and the transmittance is close to 85% in a range of 320-800 nm. The excitation-emission spectra of the crystals are tested and the mechanism of luminescence is discussed. The thermophysical properties of the crystal are investigated via measuring the specific heat capacity, thermal expansion, thermal conductivity and diffusion coefficient. Since the specific heat capacity of the crystal is large and changes significantly with temperature, the temperature change is relatively small when the crystal absorbs heat, and the ability to withstand thermal shock is high. The thermal expansion coefficient is an important parameter in the thermal properties of crystals, which has an important reference value for the selection of seed orientation and crystal processing in crystal growth. The gap between the thermal expansion coefficients of the two directions becomes larger with the increase of temperature. The thermal diffusivity and thermal conductivity are both physical quantities that characterize the heat transfer of materials. The thermal diffusivity of crystal phases (020) and (100) decreases with increasing temperature at 25-300 ℃. The thermal conductivity curve of LGBO crystal at 25-300 ℃ obtained by the thermal conductivity calculation formula indicates that the thermal conductivity of LGBO crystal is larger in the similar crystals.Conclusions Large-size LGBO crystals were grown by a modified vertical Bridgman method. The high viscosity of the melt and the extra-large supercooling determined the extremely slow growth rate of LGBO crystals. The specific heat capacity of the crystal at room temperature was 0.898 J/(g·K). The thermal expansion coefficients for the crystal phases (100) and (020) were 12.768×10-6 K-1 and 21.146×10-6 K-1, respectively. The thermal conductivities for crystal phases (100) and (020) at room temperature were 2.72 W/(m·K) and 2.60 W/(m·K), respectively. The thermal expansion had a great anisotropy as the temperature increased, and the thermal diffusivity decreased with the increase of temperature. The results indicated LGBO crystal under a high power could have a potential application due to its large specific heat.

Introduction Cadmium manganese telluride (Cd1-xMnxTe, CMT) is an ideal material for room-temperature radiation detectors, which can be widely used in the fields of medical tests, radiation detection, and astrophysics. The higher partial pressure of Cd during the growth of CMT single crystals by the Bridgman method leads to severe volatilization of Cd, which in turn produces a high density of intrinsic point defects, such as Cd vacancies. This reduces the resistivity of the crystal and alters the conductive type of the crystal, making it difficult for the crystal to meet the requirements for device preparation. In this paper, CMT crystals were grown by a vertical Bridgman method with Te solution. The compositions were co-doped with In/V at 1017 atom/cm3 to compensate for the Cd vacancies and increase the crystal resistivity.In addition, the electrical properties of Au, Ag, Al and In electrodes in contact with CMT semiconductors were also investigated.Methods Te (9N), Cd (9N), In (9N), Mn (5N), and V (5N) were used as raw materials in a pellet form (Sichuan Ehalf High Purity Materials Co., China). Cd0.9Mn0.1Te single crystals co-doped with In and V (doping concentrations of 2×1017 atom/cm3 and 3×1017 atom/cm3, respectively) were grown by a vertical Bridgman method with Te solution. The grown ingots were 95 mm in length and 30 mm in diameter, and a diamond wire cutting machine was used to cut wafers with a thickness of 2 mm at the head, middle and tail of Cd0.9Mn0.1Te:In/V ingots, and further cut single crystals of 10 mm×10 mm×2 mm. The head, middle and tail single crystals of Cd0.9Mn0.1Te:In/V ingots were tested for the crystal structure by a model D/M-2500 X-ray diffractometer, respectively. The optical properties of crystals were determined by Fourier transform infrared spectroscopy and UV-visible-near-infrared spectroscopy. Four single-crystal samples in the middle of Cd0.9Mn0.1Te:In/V ingot were selected as CMT detector materials. Au, Ag, Al and In metal electrodes were deposited on the surface of the crystals by a model KYKY-SBC-21 vacuum evaporation machine. The four metals were deposited by using 4N-grade high-purity evaporation wires with a diameter of 0.5 mm and a length of 80 mm. In order to ensure a low background noise in the detector, a low leakage current of the crystal was required and the electrodes were passivated with hydrogen peroxide after preparation. Au and In electrode CMT detectors were annealed in a model OTF-1200X tubular annealing furnace at different temperatures (i.e., 350, 370, 390, 410 K and 430 K) for 1 h, respectively. The electrical performance of CMT detectors with different electrodes was tested by a model agilent model 4155c semiconductor parameter analyzer.Results and discussion Cd0.9Mn0.1Te:In/V single crystal is a crystal structure of sphalerite, in which the diffraction peak (111) has the maximum intensity, indicating that the preferred crystal growth direction is the direction (111). The average IR transmittance of the single crystal in the middle of the ingot is 67.3%, which is the maximum value reported in the literature. The high IR transmittance of In and V co-doped Cd0.9Mn0.1Te crystals is attributed to the fact that the double dopant adequately compensates for the acceptor defect Cd vacancies and reduces the vacancy defect concentration.The average roughness of Ag, Ag, Al and In electrodes deposited on the surface of CMT crystals are all below 20 nm. Based on the results of electrical performance tests, the ohmic coefficient of Au electrode is close to 1, and the ohmic contact performance of Al and Ag electrodes is poorer. The adaptability of different materials to the annealing temperature is different, the leakage current of Au electrode decreases as the annealing temperature increases to 390 K. The leakage current of In electrode decreases only slightly after annealing at 350 K, and the leakage current of In electrode is greater than that of the unannealed one after annealing at >370 K, indicating that there is a limitation of annealing on the improvement of the electrical properties of the In electrode.Conclusions The forbidden band width of Cd0.9Mn0.1Te:In/V single crystal was 1.52 eV, and the IR transmittance of the middle crystal was 67.3%, indicating that the middle crystal had superior optical properties. Al, Ag, In and Au electrode materials all formed ohmic contacts with the CMT, with the optimum electrical performance of Au and In electrodes. The optimum annealing temperatures for Au and In electrodes were 390 K and 350 K. Au and In electrodes were annealed at 390 K and 350 K, respectively. Au could be the most suitable electrode material for Cd0.9Mn0.1Te:In/V single-crystal radiation detectors.

Introduction Ammonia selective catalytic reduction of NOx with NH3 (NH3-SCR) is an effective technology for NOx removal. As a catalyst, V2O5-WO3 (MoO3) /TiO2 has a high denitrification activity, but suffers from the problems of poor low-temperature activity, high V-toxicity, and susceptibility to heavy metal toxicity at 300-400 ℃. Heavy metals such as Cd, Pb, Zn, etc. widely present in the flue gas of solid waste incineration and coal-fired power plants. The toxic effects on catalysts are manifested via covering the active sites on the catalyst surface, reducing the redox properties, acidifying the surface and chemically adsorbing oxygen, leading to severe catalyst deactivation. CeO2 as an effective catalyst has a higher oxygen release/storage capacity, which is characterized by a higher oxygen release/storage capacity, compared to the conventional catalysts. CeO2 is used as a main active component in the preparation of rare-earth-based denitrification catalysts due to its high oxygen release/storage capacity. Manganese oxide (i.e., MnOx) exhibits a good low-temperature catalytic activity, which is often used as a modified component to improve the low-temperature denitrification activity of catalysts. TiO2 interacts with the active component and has a higher thermal stability and a sulphur resistance. However, Ce-Mn/Ti catalysts are susceptible to poisoning by toxic substances in the flue gas, and there are more studies on the poisoning of Ce-Mn/Ti catalysts by SO2, H2O, etc.. However, a few studies on the poisoning of Ce-Mn/Ti catalysts by heavy metals are reported. Catalysts with three-dimensional ordered macroporous structures have superior redox properties, sufficient chemisorbed oxygen and suitable acid sites to promote its NH3-SCR denitrification reaction. In this paper, Ce-Mn/Ti catalysts with three-dimensional ordered macro-porous structures were thus prepared to increase the redox properties and acidic sites and promote the denitrification activity.Methods 17 mL of tetrabutyl titanate was added drop by drop into 30 mL of anhydrous ethanol under vigorous stirring, which was recorded as liquid A. Concentrated nitric acid (65%, in mass fraction) was added dropwise into the mixed solution of deionized water (1.5 mL) and anhydrous ethanol (10 mL) at pH values of 2-3, which was recorded as liquid B. The solution was then mixed into a mixture of deionized water (1.5 mL) and anhydrous ethanol (10 mL). Liquid B was slowly mixed into liquid A under vigorous stirring to obtain a homogeneous and transparent TiO2 solution. A certain amount of PMMA template was added to the TiO2 precursor solution, sealed and stayed for 12 h. The remaining precursor solution was removed by vacuum filtration and baked at 50 ℃ for 24 h. Finally, the samples were baked at 300 ℃ for 2 h, and then heated at a heating rate of 1 ℃/min at 500 ℃ for 5 h. The ordinary structure TiO2 carriers were prepared in the same process as 3DOM TiO2 without PMMA template. After the preparation of TiO2 carriers, Ce(NO3)3-6H2O and Mn(NO3)2 mixtures were prepared at different molar ratios, and impregnated with 3DOM TiO2 and normal TiO2, respectively, and stirred at room temperature for 4 h. Afterwards, the catalysts were transferred to an oil bath and stirred at 80 ℃ for 6 h. They were baked at 80 ℃ for 24 h, and finally, the catalysts were heated at 1 ℃/min at 500 ℃ for 5 h. The obtained samples were recorded as fresh-CMT-3DOM (i.e., fresh-CMT). The catalyst with heavy metals (i.e., Cd, Pb, Zn) were prepared by an excess impregnation method. A certain amount of cadmium nitrate, lead nitrate, and zinc acetate solution was prepared at different mass ratios of metal ions to catalyst (10% Cd, 10% Pb and 5% Zn), and fresh-CMT-3DOM and fresh-CMT catalysts were added to the heavy metal salt solutions, respectively. The morphology structure was detected by a scanning electron microscope (SEM, TESCAN MIRALMS Co., Czech Republic). The specific surface area and pore size were determined by specific surface area intruement based on BET (Micromeritics Co., USA). The crystalline phase structure of the catalysts was analyzed by an X-ray diffracometer (XRD, Bruker Co., Germany). The elemental valence states of the catalysts were analyzed by an X-ray photoelectron spectroscope (XPS, Thermo Scientific Co., USA) using Al Kα as X-ray sources. The redox properties of the catalysts were characterized using a FINESORB-3010 adsorption apparatus (Finetec Instruments Co., China). The ammonia adsorption experiments of the catalysts were carried out by a Nicolet 6700 instrument (Thermo Fisher Scientific Co., USA) to determine the type of acid on the catalyst surface. The NH3-SCR denitrification activity was analyzed in a fixed bed quartz reactor at 1 000 mg/L NO, 1 000 mg/L NH3, 5% (v/v) O2 and N2 as ab equilibrium gas. The denitrification efficiency of the catalyst was calculated according to the results that were determined by a flue gas analyzer. Results and discussion The NO conversion for 10% Cd-CMT-3DOM, 10% Pb-CMT-3DOM, and 5% Zn-CMT-3DOM exceeds 85% at 175-300 ℃. However, the denitrification activity decreases at 100-150 ℃. Compared to the activity of CMT and the three metals after poisoning, the maximum NO conversion of 10% Cd-CMT decreases to less than 85% at 100-300 ℃. The maximum NO conversion of 10% Pb-CMT is less than 100%, and fresh CMT is weakly poisoned by Zn. The three-dimensional ordered macro-porous structure enhances the CMT-3DOM catalyst's tolerance to Cd, Pb, and Zn to some extent. The ratio of Ce3+ can be determined via calculating the peak area ratio of Ce3+/(Ce3+ + Ce4+). The proportion of Ce3+ in fresh-CMT-3DOM (19.0%) is greater than that in fresh-CMT (15.7%), accounting for the favorable denitrification activity of CMT-3DOM catalyst. After adding Cd, Pb and Zn, the content of Ce3+ in the fresh-CMT-3DOM catalyst shows a better resistance to heavy metals, compared to the fresh-CMT catalyst. This indicates that the fresh-CMT-3DOM catalyst is more resistant to heavy metals. Based on the calculation results of Mn4+ content, which decreases similarly to Ce3+ content, fresh-CMT-3DOM and fresh-CMT display the greatest reduction in Mn4+ content after Cd poisoning, followed by Pb poisoning. Zn poisoning has a smaller impact on the Mn4+ content reduction. The Mn4+ content on the surface of fresh-CMT-3DOM is relatively higher after three heavy metals poisoning rather than that on the corresponding fresh surface. Also, the relative contents are higher than those of the corresponding fresh-CMT catalysts. This indicates that the Mn4+ content of fresh-CMT-3DOM catalysts is less affected by heavy metal poisoning, which is beneficial to improving the anti-heavy metal performance of fresh-CMT-3DOM catalysts. The relative content of Oα in the catalysts is obtained via the calculation. The amount of chemisorbed oxygen in fresh-CMT-3DOM catalysts (i.e., 35.2%) is greater than that of fresh-CMT. The relative content of Oα, Ce3+ and Mn4+ depict a consistent pattern of variation in these catalysts, which coincide with the outcomes of the NH3-SCR activity. This further shows the safeguarding ability of the catalysts active species through the three-dimensionally ordered macropore structure. Based on the H2-TPR reduction peak results, the reduction peaks of fresh-CMT-3DOM move to lower temperatures, compared to those of fresh-CMT catalysts. The relative peak areas of fresh-CMT-3DOM are greater, indicating that the 3DOM structure is more favorable for the redox reaction of the catalysts. When Cd, Pb, and Zn are introduced, the reduction peaks of both catalysts shift towards at higher temperatures, indicating that the heavy metals form bonds with the active species of the catalysts. The reduction peaks of all catalysts are analyzed to determine the relative peak areas. The influence of Cd, Pb, and Zn on the catalytic redox activity aligns with SCR denitrification performance. This indicated that the catalysts ability to undergo redox reactions is a crucial factor affecting their heavy metal resistance and SCR denitrification activity. The NH3-DRIFTS characterization results indicate that the Lewis acid is a primary acid type in both fresh-CMT-3DOM and fresh-CMT catalysts. Moreover, fresh-CMT-3DOM catalysts have a higher concentration of the Lewis acid sites rather than fresh-CMT. Fresh-CMT-3DOM after the heavy metal poisoning has the more Br?nsted acid sites, compared to fresh-CMT catalysts, and the influence of heavy metals on its acid sites is reduced. Fresh-CMT-3DOM catalysts possess a larger number of acidic sites, resulting in a greater resistance to heavy metals.Conclusions TiO2 carrier with a three-dimensional ordered macro-porous structure was prepared using PMMA template, and fresh-CMT-3DOM catalysts were obtained after loading with Ce and Mn. The activity and heavy metal resistance performance were investigated. The experimental results showed that the fresh-CMT-3DOM catalyst had the excellent activity with the NO conversion rate of more than 85% at 100-300 ℃. The low-temperature activity was higher than that of fresh-CMT, which still remained at 85% at 100-150 ℃. When Cd, Pb and Zn were introduced, NO conversion rate of fresh-CMT-3DOM at 175-300 ℃, while the fresh-CMT activity after Cd, Pb and Zn poisoning decreased, in which the maximum NO conversions of the catalysts corresponding to Cd and Pb poisoning were less than 85% and 100%, respectively. The characterization results indicated that the NO conversions of the catalysts corresponding to Cd, Pb and Zn poisoning were higher than those of fresh-CMT-3DOM and fresh-CMT-3DOM. 3DOM and fresh-CMT catalysts had the similar crystalline phases, but the diffraction peaks of fresh-CMT-3DOM were weaker in intensity and its active components were more dispersive. Compared with fresh-CMT catalysts, fresh-CMT-3DOM catalysts had excellent Mn4+/Mn3+/Mn2+ and Ce4+/Ce3+ redox cycling, higher redox capacity and more acidic sites, thus improving the anti-heavy metal performance of fresh-CMT-3DOM.

Introduction Steel slag is a solid waste produced from steelmaking, which has a potential cementitious activity. However, its cementitious activity is much lower than that of Portland cement. Mechanical grinding, acid activation, alkali activation, high-temperature curing, modification/reconstruction and organic activation methods are commonly used to improve the hydraulic activity of steel slag. Triethanolamine is commonly used as an organic admixture to improve cementitious activity of steel slag. The existing research on the hydration of TEA on steel slag still focuses on a steel slag-cement composite system, in which the proportion of cement is higher and the hydration rate is faster, so the results obtained are related to cement hydration, and it is difficult to characterize the effect of TEA on steel slag. It is thus necessary to investigate the hydration of pure steel slag in the presence of triethanolamine. In this paper, the hydration characteristics of pure steel slag under the complexation of TEA were characterized by compressive strength, heat of hydration, thermogravimetry, phase analysis, complexation ability and dissolution characteristics as well.Methods The compressive strength of hardened steel slag paste was tested. In this work, the hydration characteristics of steel slag were investigated at different TEA concentrations, and the concentrations selected were 0, 500, 1 000 mg/L and 2 000 mg/L. A mass ratio of TEA solution to steel slag was kept at 0.35. The size of test block was 20 mm×20 mm×20 mm, and the curing age was 3, 7 d and 28 d. In the process of compressive strength testing, the test entrance force was set to be 200 N, and the pressure was applied by force control, and the pressure rate was 100 N/s. After the compressive strength was tested, the specimens were smashed (<5 mm) and the center portion of the specimens was immersed in an isopropanol solution to terminate hydration, and the terminated hydrated steel slag pieces were dried in a vacuum drying oven at 40 ℃. After drying, steel slag pieces were ground and sieved through a 200 mesh (74 μm) sieve. A portion of steel slag powder was taken for thermogravimetric analysis and X-ray diffraction (XRD).The hydration heat of steel slag paste was determined using calorimetry, and the exothermic process of hydration was recorded from the addition of water or TEA solution for 72 h. The TEA solution concentration and its ratio to steel slag both were consistent with the tests of compressive strength. The complexation ability of TEA with different metal ions was determined by a conductivity method. The complexation ability of TEA with metal ions was characterized via continuously adding TEA to a solution of metal ions at the same concentration and recording the conductivity data. The conductivity method was also used to characterize the dissolution process of steel slag in the presence or absence of TEA. The conductivity of solution without steel slag was the initial value, which was measured from the contact of steel slag with water and recorded continuously for 25 min.Results and discussion The compressive strength of hardened steel slag paste with TEA is higher than that of the blank group without TEA at each age. This indicates that TEA can simultaneously increase the early and late compressive strength of hardened steel slag paste, and this strengthening effect increases with the increase of TEA concentration. When TEA is in steel slag paste, the diffraction peaks of monocarboaluminate (Mc) appear, and the diffraction peaks of C2F gradually become weaker. This indicates that TEA can promote the formation of Mc, and the content of CaCO3 is fixed at different TEA concentrations, so it can be inferred that TEA promotes the formation of Mc via promoting the hydration of aluminum phases. Meanwhile, TEA promotes the hydration of C2F, and [Fe] in C2F can participate in the formation of Mc as a substitutional ion of [Al] to form . The heat of hydration and thermogravimetric tests further indicate that TEA can promote the hydration of aluminate and ferrate phases. The hydration degree is enhanced by the formation of a large amount of Mc. The increase in hydration degree ultimately leads to an increase in compressive strength.The promotion of Mc formation by TEA is related to its complexation. When the concentration of TEA is less than or equal to 0.05 mol/L, i.e., the molar ratio of TEA to metal ions is less than or equal to 1, the complexation ability of TEA on Fe3+ is stronger than that of Al3+ and Ca2+. When the concentration of TEA is greater than or equal to 0.05 mol/L, i.e., the molar ratio of TEA to metal ions is greater than or equal to 1, the complexation ability of TEA on Al3+ is stronger than that of Fe3+ and Ca2+. TEA promotes the dissolution of mineral phase in steel slag through complexation. The free-moving metal ions and the complexed metal ions in liquid phase of steel slag can simultaneously participate in the precipitation reaction of hydration product, producing a large amount of Mc, and thus improving the early and late hydration of steel slag paste, which in turn manifests itself as an increase in the compressive strength.Conclusions The complexation ability between TEA and metal ions and effect of TEA complexation on dissolution and hydration characteristics of pure steel slag were investigated. TEA significantly increased the early and late compressive strength of hardened steel slag paste. The main reason for the increase in compressive strength of hardened steel slag paste was that TEA improved the hydration degree of steel slag paste in early and late stages. TEA promoted the hydration of aluminate phases (C3A, C12A7) and ferrate phase (C2F), and through the interaction with carbonate, a large number of were formed, and the formation of such hydration products was the main reason for the improvement of the hydration degree and the compressive strength of steel slag paste. The large formation of Mc was related to the complexation and solubilization effect of TEA. TEA could complex with Ca2+, Al3+ and Fe3+, and the complexation of TEA promoted dissolution of steel slag and formation of metal ions that could participate in the precipitation reaction, thus promoting the hydration of steel slag paste.

Introduction The surface properties, pore size distribution and specific surface area of porous carbon are the main factors affecting its electrochemical performance. To further improve the electrochemical properties of porous carbon materials, two commonly used strategies are activation and doping with non-metallic heteroatoms. In this paper, a hierarchical porous carbon (HPC) was prepared by a one-step carbonation-activation method with poly(vinylpyrrolidone) as a carbon source, fibrous brucite as a template, and trispotassium phosphate as an activator to achieve the passive regulation of the pore structure and surface properties of porous carbon. The pore structure and specific surface area of hierarchical porous carbon were modulated, and the in-situ doping of nitrogen atoms were achieved. In addition, the influence of tripotassium phosphate addition on the pore size distribution, specific surface area, pore structure and electrochemical properties of the porous carbon was also investigated. Methods A certain amount of polyvinylpyrrolidone (PVP), tripotassium phosphate and fibrous brucite were mixed with deionised water under ultrasonication and stirring, obtaining a homogeneously dispersed mixture. The mixture as a precursor was sintered in a tube furnace via high-temperature carbonization to obtain a template/carbon composite. Afterwards, the composite was acid washed to remove the template and dried, obtaining a hierarchical porous carbon. The physical phase, pore structure, morphology and elemental composition of the hierarchical porous carbon were analysed by X-ray difffraction (XRD), scanning electron microscopy (SEM), specific surface area measurement (BET), X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDS). The electrochemical properties of hierarchical porous carbon were determined by galvanostatic charge-discharge (GCD), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in a three-electrode system using Hg/HgO, Pt sheet and the obtained hierarchical porous carbon as reference, counter and working electrodes, respectively. For the preparation process of the working electrode, the synthesised hierarchical porous carbon, conductive carbon black and PTFE emulsion were mixed in a mortar at a mass ratio of 8:1:1, and the mixture with an appropriate amount of ethanol solution was ground into a homogeneous slurr. The slurry was coated on the nickel foam collector, dried, and then pressed in a manual hydraulic press for 5 min to obtain the working electrode.Results and discussion The results of XRD and EDS show that the characteristic diffraction peaks of potassium fluorosilicate appear in the synthesised hierarchical porous carbon in addition to the amorphous carbon, but their contrast capacitance hardly contributes. The hierarchical porous carbon has a one-dimensional hollow carbon tube stacked reticular structure, which is conducive to the rapid transfer of electrons. Meanwhile, the hierarchical porous carbon obtained after the activation of tripotassium phosphate contains abundant pores, which can provide a large number of active sites for the electrolyte ions and a convenient channel for the rapid diffusion and transport of ions. In addition, the microporosity and specific surface area of the activated hierarchical porous carbon increase significantly, compared with those of the unactivated porous carbon. The specific surface area and pore volume are 707.9 m2/g and 1.65 cm3/g, respectively. The large specific surface area and pore volume can lead to more active sites and diffusion channels. The results of XPS demonstrate that element N also appears in the hierarchical porous carbon, indicating that nitrogen in-situ doping is realised during the carbonisation process. The introduction of nitrogen improves the electrical conductivity and wettability of the carbon material, and also has active sites and pseudocapacitance. Compared with the unactivated porous carbon, the activated hierarchical porous carbon exhibits superior electrochemical properties due to its rich pore structure, suitable heteroatom doping and hierarchical porous structure.Conclusions Nitrogen-doped hierarchical porous carbon was synthesized by a one-step carbonation-activation method with fibrous brucite as a template and tripotassium phosphate as an activator. Meanwhile, the different additions of tripotassium phosphate could achieve the regulation of the morphology, specific surface area, pore structure and electrochemical properties of the hierarchical porous carbon. The hierarchical porous carbon with an appropriate addition of tripotassium phosphate exhibited high specific surface area and superior electrochemical properties. The results showed that the specific capacitance of HPC/K3 activated by tripotassium phosphate could reach 281.94 F/g at a current density of 0.5 A/g, which was greater than that of non-activated HPC/K0 (i.e., 200.31 F/g). The capacity retention rate after 8 000 charge-discharge cycles reached 84.7%. This study demonstrated that tripotassium phosphate activation could improve the electrochemical performance of porous carbon. In addition, this study could also provide some insights for the high value-added application of natural mineral fibrous brucite

Introduction Biomass as a near-zero emission and novel energy source is regarded as an optimal alternative to fossil fuels. Biomass gasification technology is extensively used due to its superior efficiency in energy utilization, environmental congeniality, and sustainability. However, tar as a predominant by-product of this process presents some formidable challenges, i.e., combustion difficulties, potential clogging of boiler flue gas ducts, damage to gas-operating machinery, and health risks. These issues constitute a significant impediment to the industrial deployment of biomass gasification technology. Addressing the efficient processing of tar is pivotal for the extensive utilization of biomass gasification. The strategy of employing catalysts for the catalytic reforming of tar to produce hydrogen is emerging as an effective solution, characterized by lower requisite temperatures and enhanced conversion rates. Biomass-derived carbon with its cost-effectiveness, high specific surface area, and outstanding thermal stability is projected to have a significant potential in the transformation of biomass tar. Nevertheless, the suboptimal metal loading capability in the catalyst preparation from biomass carbon results in a reduced catalytic activity and an inferior hydrogen selectivity during the reforming process. Furthermore, there is a notable deficiency in research pertaining to the tar produced in actual production processes. Consequently, there is an urgent need for comprehensive investigations into the mechanism of hydrogen generation via catalytic reforming using biomass-based carbon catalysts.Methods An apricot shell powder with a granularity of 100-150 mesh was utilized as a feedstock for char production. A biomass char carrier was obtained via carbonizing this material at 350 ℃ for 30 min. Subsequently, the biomass char carrier was impregnated and stirred in a 1 mol/L KOH solution for 3 h, followed by a filtration process, with an impregnation ratio of 1 g of char carrier to 10 mL of KOH solution. The impregnated material was firstly calcined at 300 ℃ for 2 h, and then at 800 ℃ for 1 h 30 min. For post-activation, the biomass char underwent oxidative modification. It was washed to a pH value of 7, impregnated with a 15% hydrogen peroxide solution for 3 h, further washed until the pH value was 7, and then dried the post-filtration. Nickel and cobalt were chosen as metals for loading by impregnation. A 100 mL solution of 1 mol./L Ni(NO3)2 and Co(NO3)2 was prepared, and a mixture of cobalt nitrate and nickel nitrate was configured in a ratio of 1:4 to produce a 100 mL mixed solution. This solution was then impregnated with the prepared char carrier in a water bath at 90 ℃ for 4 h and filtered. After drying for 12 h, the material was calcined at 800 ℃ for 4 h. For the experiment, a cold trap method was employed to collect tar at the outlet of a straw gasifier under atmospheric pressure. The experiment primarily utilized a vertical tube furnace, enabling the catalytic reforming of tar inside a quartz tube. A catalyst bed was placed inside the tube furnace. A basket containing tar was set in the quartz tube in the heating furnace. In the tube furnace, the tar transformed into a gaseous phase and passed through the catalyst bed, undergoing a reforming reaction with the catalysts on the bed. The reaction products entered two conical flasks containing dichloromethane at the lower part of the tube furnace. These flasks were placed in an ice bath pot to collect the residual tar, and after drying, the gases were collected in gas bags for gas chromatographic analysis. The prepared catalyst was characterized by specific surface area analysis, scanning electron microscopy and X-ray diffraction.Results and discussion The XRD patterns indicate that during thermal treatment, nickel forms metal-carbon complex compounds with surface carbon, while cobalt results in cobalt oxide formation on the biomass char surface. The SEM images revealed a porous structure on the Ni/C surface, with metal-carbon complexes causing indentations on the char carrier, evidenced by visible surface metal particles. A distinctive feature of Co/C compared to nickel-based catalysts is the presence of etched grooves on the surface. The EDS analysis showed an even distribution of nickel on the Ni/C surface with a localized enrichment, alongside some surface collapse. The nickel loading on the catalyst surface is 12.01%. Cobalt displays a more uniform distribution on Co/C, indicating a fewer cobalt oxide enrichment sites.The experimental results with and without catalysts for tar catalytic reforming demonstrate that catalyst addition increases a tar reforming efficiency and H2 and CO contents in syngas. Tar reforming conversion rate increases from 36.12% to 76.67%, and H2 and CO contents in syngas increase from 22.76% and 28.80% to 25.62% and 32.78%, respectively, while CO2 content decreases from 27.11% to 17.45%. The results for the temperature impact on tar catalytic reforming reveal that an hydrogen yield initially increases and then decreases having the maximum value at 700 ℃. Tar conversion rate gradually increases from 76.67% to 94.95% with increasing the temperature, finally stabilizing after 800 ℃. An optimal steam/tar ratio (i.e., mSteam/mTar) is 3 based on hydrogen yield, production, and tar conversion rate. Similarly, an optimal tar/catalyst ratio (mTar/mCatalyst) is 2. Comparing single metal catalysts with Ni?Co/C catalyst for tar catalytic reforming, Ni?Co/C composite catalyst has a higher hydrogen yield in the gaseous products (i.e., 72.86%) with reduced production rates of C2H4, CO and CO2.Conclusions The preparation of carbon-based metal catalysts consists of two stages, i.e., the preparation of the char carrier and metal loading. The optimal temperature for preparing apricot shell char carrier was 350 ℃. Through KOH activation, its specific surface area increased from 5.502 m2/g to 1 124.16 m2/g, with the formation of abundant mesopores and micropores. Subsequently, H2O2 oxidation of the activated char carrier effectively enhanced the oxygen-containing acidic groups on its surface. The char carrier, prepared through carbonization, activation, and oxidative modification, exhibited a well-developed mesoporous and microporous structure suitable for efficient metal loading. On the surface of nickel-based catalysts, complex metal-nickel and carbon compounds formed, whereas cobalt- and iron-based catalysts formed metal oxides. The catalyst surfaces showed a good integration of metal with the carbon carrier, with uniform distribution. The carbon-based catalysts with a large specific surface area and a developed mesoporous structure were suitable for tar catalytic reforming. The results indicated that under nickel-based catalyst conditions, a hydrogen yield of 91.52 g H2 per 1 kg of tar could be obtained at the optimal parameters for hydrogen production from tar catalytic reforming (i.e., 800 ℃, mSteam/mTar of 3 and mTar/mCatalyst of 2). Cobalt-based catalysts exhibited a stronger catalytic activity and a higher hydrogen selectivity, compared to nickel-based catalysts. However, nickel- and cobalt-based catalysts both demonstrated a lower catalytic activity, compared to the Ni?Co/C composite catalyst.

Introduction Ferroelectric materials are widely used in detection, conversion, storage and information processing. The development of energy-saving, environmental protection, multi-functional, miniaturized lead-free multi-functional ceramics becomes inevitable. However, lead-free ferroelectric ceramics as dielectric ceramic capacitors with a low energy storage density and a poor energy storage efficiency seriously hinder their practical application. The development of ceramic capacitors with a high energy storage density and a high energy storage efficiency thus greatly expands the applications of ferroelectric ceramics in the field of energy storage. Doping rare-earth elements is a simple, direct and effective modification method. Rare-earth elements with special electronic structure and stable luminescence properties are expected to give new luminescent properties and improve the electrical properties of ferroelectric ceramics. Ba0.85Ca0.15Ti0.90Zr0.10O3 (BCTZ) lead-free piezoelectric ceramics have a small dielectric loss and superior electrical characteristics. Rare-earth element Er3+ is widely used in laser and lighting due to its excellent green luminous intensity. In this paper, the effect of Er3+ doping amount on the microstructure, ferroelectric, energy storage and photoluminescence properties of BCTZ ceramics and their internal relations was investigated to broaden the applications in photoelectric materials.Methods Er3+ doped Ba0.85Ca0.15Ti0.90Zr0.10O3 (BCTZ:x%Er3+, x=0.0, 0.2, 0.4, 0.6, 0.8 and 1.0, in mole fraction) ceramics were prepared by a high-temperature solid-state reaction method. CaCO3 (99.9%), ZrO2 (99.9%), TiO2 (99.9%), BaCO3 (99.9%), Er2O3 (99.9%) were used as raw materials. The raw materials were firstly mixed and ground in a ball mill for 12 h, and then pre-burned at 1 100 ℃ for 6 h after drying The pre-burned materials were naturally cooled to room temperature, granulated and pressed. The pressed samples were sintered at 1 300 ℃ for 6 h. The crystal structure of ceramic samples was analyzed by a model D8 ADVANCE X-ray diffractometer (XRD, Germany). The surface morphology of the samples was characterized by a model JEM-7800F scanning electron microscope (SEM, JEOL Co., Japan). The electrical properties of ceramics were tested by a model TF Analyzer 3000E (Germany), and the both sides of the ceramics were plated with silver electrodes before testing. The luminescent properties of ceramics were determined by a model FS5 fluorescent spectrometer (Edinburgh Co., UK).Results and discussion Rare-earth Er3+ doped BCTZ ceramics all have a well-crystallization with a single perovskite structure and little impurities. The results show that the mean grain size of the ceramics decreases monotonically with the increase of Er3+ doping concentration, from 7.59 μm to 3.82 μm, which is decreased by 49.67%.All the ceramics exhibit superior ferroelectric properties. The ferroelectric domains are overturned and the density are different because of the lattice distortion and grain size change caused by the addition of different contents of Er3+, resulting in unstable polarization states. Therefore, the Er3+-doped BCTZ ceramics have a larger ΔP(Pmax-Pr) rather than pure BCTZ ceramic. The released energy density (Wrec) and energy storage efficiency (η) of the ceramics are increased by 29.81% and 122.79%, respectively. The worse the lattice symmetry, the better the photoluminescent (PL) performance. At a great doping amount of Er3+, Er3+ replace the A-position Ba2+ and Ca2+ positions, gradually occupying the gap position or replacing the B-position ions, resulting in more lattice distortion, reducing the lattice symmetry, and significantly enhancing the photoluminescent intensity. When the doping amount is 0.8% (in mole), PL strength reaches the maximum value. As the doping amount is greater than 0.8%, a cross relaxation phenomenon occurs due to the increase of luminescent ions and the decrease of luminescent ion spacing, resulting in fluorescence quenching and a decreased luminous intensity. The relative change in PL strength of BCTZ:0.8%Er3+ ceramic is enhanced by 173%, compared with BCTZ:0.2%Er3+ ceramic.Conclusions The mean grain size of the lead-free multifunctional ferroelectric ceramics decreased monotonously, and the microstructure became more compact and uniform with the increase of Er3+ doping concentration. All the ceramics had the superior ferroelectric properties. Er3+ doping could destroy the long-range order in BCTZ structure and the interaction between electric domains, so that the released energy density (Wrec) and energy storage efficiency (η) of the ceramics were increased by 29.81% and 122.79%, respectively, as Er3+ doping concentration increased. In addition, BCTZ:x%Er3+ ceramics exhibited an intense green emission at 548 nm under excitation of 487 nm near-ultraviolet light, and the luminous intensity was relatively adjustable up to 173.09%. The rich physical and photoelectric properties of BCTZ:x%Er3+ ceramics could lay a foundation for the development of new multi-functional materials with energy saving, environmental protection and low energy consumption.

Introduction Lithium sulfur batteries have attracted recent attention as the secondary batteries with a high specific energy, a long lifespan, and a high safety. Inhibiting the shuttle effect of polysulfides and improving reaction kinetics become challenges. The chemical interactions between polar metal compounds and polysulfide ions (i.e., polarity polarity interactions, Lewis acid-base interactions, and sulfur bond chain reactions) have some advantages in inhibiting the shuttle effect of polysulfide ions. In addition, many metal compounds exhibit an electrocatalytic activity during the conversion of polysulfides, promoting the conversion rate of polysulfide ions during charging and discharging, suppressing the uneven deposition of insoluble sulfides Li2S2/Li2S on the electrode surface, and thus achieving a goal of improving the utilization rate of active substances, inhibiting shuttle, and reducing the loss of active substances. The inherent conductive properties of conductive polymers are conducive to electron conduction, and their soft and elastic properties can effectively buffer the volume expansion of active substances during charge and discharge processes. The functional groups rich in them have a strong affinity for LiPSs and can inhibit shuttle effects. In this paper, Fe2O3@PPy composite materials were prepared via in-situ growth of polypyrrole on Fe2O3 nanosheets by acid etching. Methods Fe2O3 nanosheets were modified by a simple one-step method with polypyrrole to prepare high-performance lithium sulfur battery composite cathode materials. Fe2O3 nanosheets were placed in a solution of p-toluenesulfonic acid, and the surface was exposed to Fe3+ by acid etching. Fe3+ acted as an oxidant to promote the oxidation polymerization reaction of pyrrole monomers on the surface of the nanosheets. Also, p-toluenesulfonic acid was doped into the molecular structure of polypyrrole to obtain Fe2O3@PPy composite nanosheets. A series of Fe2O3@PPy composite nanosheets were prepared via adjusting the etching environment and the feeding amount of Fe2O3 nanosheets to control the modification amount of polypyrrole.Results and discussion The in-situ growth method induced by acid etching was used to modify the surface of α-Fe2O3 nanosheets with polypyrrole, in which p-toluenesulfonic acid played an etching and doping role. Fe3+ ion etched on the surface of Fe2O3 nanosheets is used as an oxidant, allowing pyrrole to polymerize and grow on the surface of Fe2O3 nanosheets. P-toluenesulfonic acid is doped into the molecular structure of polypyrrole as a para anion, resulting in Fe2O3@PPy composite nanosheets. The obtained Fe2O3@PPy nanocomposites combine the catalytic active sites exposed by Fe2O3 nanosheets with a high conductivity and a high specific surface area of polypyrrole. This increases the chemical adsorption of polysulfides and inhibits their shuttle, and accelerates the conversion of soluble LiPSs to insoluble products, greatly improving the utilization rate of sulfur, helping to improve the ion/electron transfer rate of nanosheets, and enhancing the reaction kinetics of electrode materials. Fe2O3 nanosheets form reinforced chemical bonds with LiPSs and promote the conversion of polysulfides, which effectively alleviates the shuttle effect of polysulfides, and improves the Coulomb efficiency, cycle stability and capacity retention of batteries. Polypyrrole enhances the conductivity of Fe2O3 nanosheets, their surface ion and electron conductivity, and improves Li+ diffusion kinetics. At a molar ratio of p-toluenesulfonic acid to Fe2O3 of 12:1, Fe2O3@PPy composite nanosheets exhibit a superior electrochemical performance. The discharge specific capacities of the S@Fe2O3@PPy-3 cathode at 0.1, 0.2, 0.5 C and 1.0 C are 734.7, 576, 468.7 mA·h·g-1 and 405.2?mA·h·g-1, respectively. At a current density of 0.1C, S@Fe2O3@PPy-3 cathode can recover more reversible capacity with a discharge specific capacity of 519.5 mA·h·g-1, having a superior rate performance. S@Fe2O3@PPy-3 provides an excellent cycling performance, maintaining a capacity of 414.5 mA·h·g-1 even after 500 cycles at a high rate of 1 C with a capacity retention rate of 86.2%. This material can be used to the development of power batteries.Conclusions The synergistic effect of Fe2O3 and PPy on the electrochemical performance improvement of lithium sulfur batteries was effective. According to the change in the relative content of polypyrrole on the surface of Fe2O3 nanosheets, the conductivity of Fe2O3 nanosheets improved with the increase of polypyrrole content. However, the excess polypyrrole nanoparticles covered the surface of Fe2O3 nanosheets at the excessive polypyrrole, leading to a decrease in active sites and in battery performance. In summary, as a carrier for sublimation of sulfur, Fe2O3@PPy could promote the adsorption of polysulfides and alleviate their shuttle effect, improving the utilization rate of sulfur in lithium sulfur batteries.

Introduction The development of high-performance fuel electrode materials suitable for reversible operation is crucial for the application of reversible solid oxide cells (RSOCs). The fuel electrode should have excellent catalytic activity such as hydrogen oxidation reaction and hydrogen evolution reaction in the solid oxide fuel cells/solid oxide electrolysis cells (SOFC/SOEC) dual mode. Conventional Ni-YSZ fuel electrode materials are susceptible to sulfur poisoning when using fuel gas containing sulfur impurities and carbon buildup when using hydrocarbon fuel. LaxSr1-xTiO3 perovskite materials have a superior resistance to coking and sulfur poisoning, which is widely used in RSOCs fuel electrodes in recent years. However, the poor ionic conduction and the non-ideal catalytic ability of fuel gas affect the further application of LaxSr1-xTiO3 fuel electrodes. It is thus necessary for the improvement of the catalytic activity and the electrochemical performance of the fuel electrodes to optimize the microstructure and surface modification. In this paper, La0.2Sr0.8TiO3-?(LST)/YSZ-based fiber fuel electrode by Ce0.9M0.1O2- (M=Fe,Co,Ni) impregnation modification was prepared, and the effect of impregnation on the electrochemical properties of fiber fuel electrode in SOFC/SOEC dual mode was investigated.Methods La0.2Sr0.8TiO3-?(LST)/YSZ composite fibers were directly prepared by an electrospinning method. In the preparation, stoichiometric amounts of La(NO3)3·6H2O, Sr(NO3)2 and C16H36O4Ti were weighed and dissolved with N, n-dimethylformamide (DMF) as a solvent and polyvinylpyrrolidone (PVP) as binder and one-dimensional template. The YSZ suspension was added to the LST precursor solution to obtain the LST/YSZ electrospinning solution for electrospinning. The high catalytic activity of Ce0.9M0.1O2- (M=Fe, Co, Ni, CMO) was loaded on LST/YSZ composite fiber skeleton by an ion impregnation method to prepare the fiber fuel electrode. The electrolyte-supported single cells (CMO@LST/YSZYSZYSZGDCLSCF/GDC) were fabricated to evaluate the electrochemical performance of the fiber fuel electrode. The phase composition of the prepared composite fiber and the fuel electrode after immersion and calcination was determined by X-ray diffraction (XRD). The composite fiber morphology and the cross-section morphology of the tested fuel electrode were characterized by scanning electron microscopy (SEM). The two-phase distribution of the composite fiber was determined by high resolution transmission electron microscopy (HRTEM). The electrochemical performance of the fiber fuel electrodes in SOFC/SOEC dual-mode was tested via assembling a single cell. The impedance data were analyzed via the distribution of relaxation time (DRT) , and the relationship between the microstructure and the electrochemical process was analyzed. Results and discussion The electrospinning solutions with stable spinning are prepared via adjusting the LST:YSZ mass ratio. The LST:YSZ with a mass ratio of 6:4 shows a criss-cross fiber morphology and smooth surface with uniform diameters (i.e., 150-200 nm) through the electrospinning and calcination. The composite fibers consist of the LST skeleton with YSZ particles dispersed and embedded, which is prepared directly by electrospinning, thus forming a three-dimensional network of mixed conductor channels with electronic channels as the main path and ionic channels interspersed. The LST:YSZ composite fiber was used to prepare a fuel electrode skeleton, and CMO precursor solution is prepared to impregnate and modify the fuel electrode. Compared with the fiber morphology, the morphology of fiber fuel electrode is smaller in length and diameter, showing a short rod-like morphology. The surface of the fiber is evenly covered by the impregnated CMO nanoparticles (i.e., 50-80 nm), still retaining abundant and interconnected pores. The three-dimensional network fiber electrode is constructed. The impregnate uniformly wraps on the fiber surface to strengthen the interfacial bonding between the fuel electrode and the YSZ transitional layer. The different impregnation modification has an effect on the catalytic activity of the fuel electrode in SOFC/SOEC dual mode. The fuel electrode using Ce0.9Ni0.1O2- as an impregnate has more Ni nanoparticles exsolution after the testing, effectively increasing the length of the three-phase interface and the active sites for the catalytic reaction. Based on the comprehensive analysis of EIS and DRT, the modified fiber fuel electrode can significantly affect the interfacial charge transfer process corresponding to the middle- and low- frequency. Ni nanoparticles exsolution can adsorb/dissociate hydrogen, and have a tendency to form an activated complex with water molecules, so that the fiber fuel electrode has great hydrogen oxidation capacity and hydrogen reduction capacity.Conclusions LST/YSZ composite?fiber with rich connected pores was directly?prepared?by?an electrospinning?technique. This fiber had a three-dimensional network hybrid conductor pathway with LST skeleton as the main electronic channel and YSZ particles as ion channel interspersed. The interface bond between the fuel electrode and the electrolyte layer was further enhanced via modifying the fuel electrode skeleton with CMO nanoparticles impregnation. The results showed that the fuel electrode with Ce0.9Ni0.1O2- impregnation had a high hydrogen oxidation and reduction capacity. Under the combined action of the impregnation and the precipitation of Ni nanoparticles, the single cell had the maximum power density of 342?mW/cm2 at 850?℃, 3% (in volume fraction) H2O/H2, and the current density of 0.313 A/cm2 under 46.8% H2O/H2 for electrolysis at 1.3 V.

Introduction The importance of environmental protection leads to the development on new energy hydrogen production technology. High-temperature solid oxide hydrogen production technology is widely investigated because of its non-polluting production process and close to 100% hydrogen production efficiency. However, the solid oxide electrolytic cell (SOEC) cannot be commercialized because of its short effective service life, in which the electrode degradation effect caused by the uneven distribution of reactant water vapor is one of the important reasons for the short life span of the SOEC. The flow inhomogeneity of the conventional parallel flow channel significantly affects the reaction efficiency and service life of solid oxide electrolytic cells, and the flow uniformity is dependent on the geometry of the SOEC flow channel. For the flow characteristics of the conventional Z-type solid oxide electrolytic cell, the molar fraction of water vapor gradually decreases from the two ends to the middle region, which affects the performance of SOEC. To improve the uniformity of water vapor distribution from the structure, a new channel structure was designed to change the width of the channel in accordance with a certain cross-sectional area ratio. The cross-sectional area of the channel from the two ends to the middle could be gradually increased to enhance a supply of water vapor in the middle region, so as to make the overall distribution of water vapor in the SOEC more uniform, eliminate the electrode degradation effect and prolong the service life of the solid oxide electrolytic cell. Methods The total cross-sectional area of the entire flow channel remained unchanged. Based on the characteristic of the water vapor mole fraction of the conventional Z-type flow channel that decreases regularly from the two sides to the middle, a control variable method was adopted according to a certain ratio of the width of the flow channel to calculate the size of the cross-sectional area of each channel. Different water vapor mole fractions of the different flow channels were used. A three-dimensional model of a Z-type flat plate solid oxide electrolysis cell with uniform and non-uniform channel widths was proposed. The continuity equation, momentum equations, energy equation, species transport equation coupled with the Nernst equation and the BV equation were numerically solved by a software named COMSOL to simulate the water vapor molar fraction, local current density, pressure drop, temperature and heat production power in the flow channel. The flow field characteristics of the conventional Z-type flow channel and the improved channel structure were obtained via simulating the process of solid oxide electrolysis of water. Results and discussion The non-uniformity coefficient at electric current densities from 1 000 A/m2 to 8 000 A/m2 at different channel width ratios (i.e.,1.000 0, 0.957 0, 0.920 0, 0.887 6, and 0.858 6) are simulated. The lowest inhomogeneity coefficients of the solid oxide electrolytic cell are obtained at all current densities when the channel width ratio is 0.920 0. Also, the non-uniformity increases with the increase of current density. When the current density is 8 000 A/m2, the non-uniformity coefficient is 0.152 for the traditional channel, but the non-uniformity coefficient for the optimized channel is 0.030 4 at a channel width ratio of 0.920 0, indicating that the distribution of water vapor mole fraction in the solid oxide electrolysis cell is the most uniform, with the difference in water vapor molar fractions between the middle and two end channels is only 10.2%. The hydrogen production rate is increased by 7%, compared to the traditional channel. Meanwhile, as the water vapor distribution becomes more uniform, the temperature difference of the solid oxide electrolytic cell decreases from 105.9 K to 97.2 K. The temperature uniformity is also significantly improved, thus reducing the electrode degradation effect and the risk of thermal stress concentration due to the electrochemical heat.Conclusions Changing the width ratio of Z-type channel could affect the distribution of water vapor. In the absence of water vapor in the middle region of the Z-channel, the flow field uniformity of the Z-channel optimized at a width ratio of 0.920 0 could be greatly improved. The main reason was that the cross-sectional area of the flow channel in the middle region was proportionally expanded, so that more water vapor was provided to the part lacking water vapor in the middle, and the electrolytic capacity of the electrolytic cell could be developed. The effect of electrode degradation was eliminated. This study indicated that the flow field inhomogeneity of the parallel flow channel itself could be mitigated via changing the geometry of the solid oxide electrolytic cell, which was more advantageous in terms of reprocessing cost and effectiveness rather than adding a flow distributor or using metal foam filling to improve the flow field distribution uniformity.

As one of the frontier domains of modern materials research, extreme cryogenic environments often expose materials with intrinsic properties that are completely different from those at ambient temperature. The existing concrete engineering in extreme cryogenic environments is ubiquitous, such as railway in northern or plateau cold regions of China (-40 ℃), cryogenic refrigeration warehouses (-80 ℃), the construction of the North and South Poles (-94.5 ℃), liquefied natural gas storage tanks (-161.5 ℃), liquid nitrogen storage tank (-196 ℃), liquefied hydrogen storage tank (-253 ℃), liquid helium storage tank (-268.9 ℃), etc.. In addition, the construction of future lunar bases has attracted recent attention and been put on the agenda by major aerospace countries, and the lunar concrete used for its construction will be subjected to long-term cryogenic temperatures as low as -183 ℃. Concrete is widely applied in structural engineering at ambient temperature due to its superior performance. Therefore, conducting a research on the synergistic mechanism between the macroscopic mechanical behavior and microstructure evolution of concrete under extreme temperature environments has a practical engineering application value for developing new concrete materials that can meet the requirements of extreme temperature service.Extreme cryogenic environments have a negative impact on the service performance and structural safety of concrete, and their deterioration process involves many complex physical and chemical reactions. In this review, the cryogenic concrete application and various methods to improve their cryogenic temperature resistance were systematically introduced. The macroscopic mechanical properties of concrete in cryogenic environments, such as compressive strength, tensile strength, flexural strength, bonding strength, and elastic modulus evolution, were elaborated in detail. The evolution of microstructure characteristics of concrete under cryogenic freeze-thaw cycles was summarized, i.e., pore water phase transition, interface transition zone destruction, and C-S-H gel degradation. From the point of view of the strength increase of C-S-H gel at cryogenic temperature and the enhancement of pore water icing, the enhancing mechanism of concrete performance at cryogenic temperature was summarized. Based on the hydrostatic pressure theory, osmotic pressure theory, crystallization pressure theory, micro-ice lens theory, glue spall theory, and unsaturated poroelasticity theory, the mechanism of concrete performance degradation after cryogenic freeze-thaw cycles was discussed. Finally, some key issues on concrete performance in extreme cryogenic environments were analyzed, and the research prospects in the future were proposed.Summary and prospects As one of the most extreme environments, the cryogenic temperature can make materials expose extremely complex and unpredictable potential intrinsic properties. Conducting the relevant research is to reveal the unknown attributes of materials in extreme environments, and to explore their potential applications in the future. This becomes a frontier topic and breakthrough point of scientific barriers in materials science research. The main conclusions are as follows: 1) In cryogenic environments, the mechanical properties of ordinary concrete can deteriorate. Therefore, the cryogenic temperature resistance of concrete structures can be greatly improved via increasing the ratio of stirrups, using prestressed steel bars, adding fibers, and filling high-strength steel pipes with UHPC. 2) The concrete strength is mainly related to its strength grade, temperature, water content, and porosity. As the temperature decreases, the compressive strength, flexural strength, and tensile strength of concrete firstly increase and then decrease, while the bonding strength shows a linear increasing trend. The critical temperature corresponding to the mechanical failure limit of concrete is different. 3) After cryogenic freeze-thaw cycles, the freezing, freeze-thaw and migration of pore water in concrete can destroy the pore structure. The uncoordinated thermal deformation, loose aggregate structure and high water absorption induce cracking in concrete interface transition zone. The C-S-H gel can undergo depolymerization fracture or interlayer ion bonding recombination, leading to interlayer pore collapse and shrinkage cracking. 4) At cryogenic temperature, the strength increase of C-S-H gel and the phase transition of pore water are the internal factors that enhance the concrete performance. During the cold freeze-thaw cycle, based on the volume expansion caused by pore water freezing and its thermodynamic process, the theories of hydrostatic pressure, osmotic pressure, crystallization pressure, micro-ice lens, glue spall and unsaturated poroelasticity are proposed. Although the relevant theories can explain a freeze-thaw failure at low temperatures, they are not fully applicable to explain the failure mechanism of concrete in cryogenic environments.The existing research are conducted in the related fields, but the preliminary conclusions are only drawn on the macroscopic properties, microstructure, and failure mechanism of concrete. However, the research and application of concrete materials in extreme environments involve multiple levels of physical and chemical reactions, coupled with a superposition effect of multiple external factors, which presents complex and variable characteristics. This has certain technical limitations for human-being to utilize the existing cognition to adapt or modify nature. There are still some key issues that need to be solved in this field, i.e., 1) For ordinary concrete, its extreme temperature-variation resistance is inferior due to the limitation of material properties, and the optimization technology and improvement effect are not effective. Therefore, there is an urgent need to develop new concrete materials with an excellent resistance to cryogenic temperatures and long-term service, and deeply analyze their performance evolution and enhancement mechanism in extreme environments. 2) The existing research on cryogenic concrete mainly focuses on macroscopic mechanical and thermal properties, while there is little research on the in-situ evolution of concrete microstructure characteristics at cryogenic temperatures. Meanwhile, the relevant failure theory is only proposed for ordinary freeze-thaw cycles in a small temperature range, and is not applicable to the deterioration mechanism of concrete in complex and extreme cryogenic environments. 3) From the perspective of technical methods, the temperature-variation effect in cryogenic environments has great challenges to the performance testing of concrete and how to coordinate its thermal coupling effect. Simultaneously, it is particularly momentous to achieve in-situ monitoring of concrete performance in extreme environments. That is because many conventional testing equipment, techniques, and methods for macroscopic or microscopic properties of concrete will no longer be applicable. 4) In cryogenic environments, the macroscopic properties and microstructure of concrete exhibit enhancement and degradation effects, and these effects show different dominant trends in different temperature ranges. It is thus necessary for further research to make clear the dominant effects of the reinforcement or deterioration behavior of cryogenic concrete in different temperature ranges and the internal causes of temperature-performance transition.

Portland cement is one of the basic building materials for economic development, with high frequency of use, large quantity and wide application range. Calcium silicate hydrate (C-S-H) gel is a main hydration product that affects the macroscopic properties of Portland cement-based materials, and it is important to clarify the relationship between its structure and performance for the improvement of cement industry. However, the C-S-H gel produced by hydration of cement-based materials is difficult to extract, and its composition, morphology and structure are affected by different factors, which further affects its application performance. Therefore, this review analyzed the relationship between the microstructure and performance of C-S-H gel, discussed its mechanism of action on cement hydration, and provided a reference for its large-scale preparation and application.C-S-H gel is an amorphous substance, its structure and composition are generally complex and variable. The structure of C-S-H gel has a certain regularity. Some work proposed three related theoretical models. The first model is an atomic structure model, which can provide a theoretical basis for the differences in phase composition and tetrahedral structure, and lay a reference for the mechanism of adsorption performance. The second model is a nanostructure model, which can make a reasonable explanation for the morphological changes of C-S-H gel and provide a theoretical support for improving the seed effect. The third model is an intermediary structure model, which can provide a more profound and comprehensive understanding of its internal microstructure. These models are an important basis for understanding the characteristics of cement as well as a key to analyzing the microstructure of C-S-H gel and applying its characteristics.The proposal and verification of the three models above usually rely on the research of single-phase C-S-H gel, and the hydration products of cement affect each other, so it is difficult to extract C-S-H gel from the hardened matrix alone. Therefore, some researchers usually use artificial methods to prepare and control the composition and structure of C-S-H gels, especially hydrothermal synthesis. Firstly, keeping the reaction temperature and time (i.e., 70 ℃ and 7 h), choosing a low Ca/Si ratio and adding Al3+ or Na+ can reduce the generation of impurities. Secondly, increasing the reaction temperature and time improves the degree of polymerization of hydration products, and changing the Ca/Si ratio and ion species within a certain range also affects the chain length. In addition, the temperature increases, the reaction time prolongs, and the C-S-H surface gradually changes from the loose state to the dense state as the Ca/Si ratio decreases in the presence of Mg2+. Therefore, the precise control of C-S-H gel structure and characteristics can be achieved via a reasonable selection of technical parameters and applied to improve cement strength, thus avoiding ion penetration and other fields.More importantly, the effective regulation of C-S-H gel can further improve the performance in different fields. The fiber-like morphology can be synthesized by properly reducing the Ca/Si ratio, adding Mg2+, increasing the temperature and extending the time, and the seeding effect of C-S-H gel can be improved to the greatest extent. Meanwhile, increasing Ca/Si ratio, mixing K+ and Na+, reducing reaction temperature, and shortening reaction time can increase the adsorption on the surface and accelerate the curing effect of C-S-H gel.Summary and prospects As an important source of strength in cement-based materials, the structural characteristics of C-S-H gel in microscale can determine its macroscopic applications in different fields. This review represented the typical structures of C-S-H gel at different stages and introduced the inherent connection between structure and performance. The precise control of different C-S-H structure using hydrothermal synthesis was introduced, and the influence of synthesis factors on its composition, morphology, and structure was described. The basic research on the synthesis of C-S-H gel in relevant fields was summarized. This review summarized the relationship between the structure and performance of C-S-H gel as well as the exploration of the prospects for the engineering application of C-S-H gel. This review provided a theoretical reference for fully understanding the hydration mechanism of cement and developing high-performance, environmentally friendly building materials.At present, the research on the essence and mechanism of C-S-H gel is still relatively weak, and there are still many problems to be solved and further explored:1. This review mainly summarized the influence of synthetic C-S-H gel doped with cement-based materials on the overall performance, but could not realize an integrated study of "structure-performance-application" of C-S-H gel. It is necessary to deeply analyze the influence of the structure and performance of cement hydrated C-S-H gel on the matrix, and further improve the growth regulation and performance application of C-S-H gel in cement concrete.2. In the process of hydrothermal synthesis of C-S-H gel, the influence and law of key variables such as Ca/Si ratio, alkali ion, reaction time and temperature on the particle size are not determined yet. In the future, it is necessary to continuously debug the experimental environment and parameters to explore a relationship between the particle size and properties.

The solid oxide fuel cell (SOFC) is a crucial solution for addressing global energy and environmental challenges, due to its high energy conversion efficiency and environmental friendliness. The electrolyte is a key component of SOFC as it determines the operating temperature and output performance.This review introduced the mechanism and influencing factors governing the electrical conduction of zirconia-based electrolyte. The electrical conduction of zirconia-based electrolyte originates from the diffusion of oxygen ions and vacancies, thereby depending on their intrinsic properties, (i.e., crystal structure, dopant cation, film thickness and grain size), and on operating conditions, (i.e., temperature, oxygen partial pressure, and time).To promote the commercialization of SOFC, electrolytes should maintain a low ohmic resistance at a lower operating temperature. One effective approach is to reduce the thickness of the electrolyte while maintaining a dense microstructure. However, achieving simultaneous reduction in thickness and enhancement in density often has challenges. The fabrication methods of electrolytes mainly consist of three processes, i.e., precursor preparation, thin film formation and heat treatment. This review represented common fabrication methods employed for zirconia-based electrolyte thin films from the perspective of solid phase powder forming, liquid phase forming and vapor phase forming methods.For solid phase powder forming methods, the precursor can be either ceramic slurry or ceramic powder. These methods are often simple with short forming time. Tape casting, screen printing, and electrophoretic deposition are representative slurry-based techniques that are used in industrial production. Tape casting enables the production of dense films with a wide range of thicknesses, allowing the prepared films to serve as supported or non-supported layers. However, conventional tape casting technology utilizes organic solvents that have environmental concerns. Thus, an environmental-friendly aqueous-based tape casting technology is developed. Nevertheless, there is still room for improvement in terms of slurry stability and film mechanical properties. For screen printing, the microstructure of the film can be adjusted via regulating the slurry components, but it is difficult to eliminate defects like holes and cracks. Surface modification can be used as an effective way to reduce defects. For electrophoretic deposition, electrolyte films can be deposited on various conductive substrates with a few restrictions on their shapes. Removable conductive coatings can be employed to facilitate the film deposition on non-conductive substrates. In addition, slurry spin coating also enables to fabricate dense electrolytes with thickness as low as two micrometers. For slurry 3D printing technology, electrolytes with a sophisticated structures can be fabricated to increase the effective contact area between the electrolyte and the electrode. Besides, dry pressing method is commonly utilized for fabricating supported electrolyte layers., Dense films with a thickness down to ten micrometers can be realized via reducing the bulk density of powder.Liquid phase forming methods mainly contain sol-gel and spraying technologies. For sol-gel technology, even though dense thin films can be easily obtained, the long preparation time and high cost retard its commercialization. For spraying technology, it offers advantages like high deposition rate and a few restrictions on substrate shapes and sizes. However, the electrolyte films prepared by conventional spraying methods exhibit a high porosity, resulting in a poor electrochemical performance. To address this issue, novel techniques, such as vacuum plasma spraying and electrostatic spray deposition, and post-treatments, such as solution impregnation, are developed.Gas phase forming methods can be categorized into physical vapor deposition and chemical vapor deposition based on the deposition mechanism. The main feature of these methods lies in the capability to fabricate dense electrolyte thin films with submicron-sized thickness at low deposition temperatures. Magnetron sputtering is a typical physical vapor deposition method, characterized by producing dense films with a good uniformity. However, the fabricated thin films often exhibit columnar microstructures with pinholes. Such microstructures can be improved through substrate modification, bias voltage application, post-treatments, etc.. Pulsed laser deposition as a representative physical vapor deposition method allows the precise control of the stoichiometric ratio in films. High-quality multilayer electrolyte thin films and interfaces can be prepared by this technology, leading to superior output performance. For chemical vapor deposition, it can fabricate uniform dense thin films in a wide range of substrates. Conventional technology may generate corrosive products, hindering its further applications. To solve this problem, various technologies such as metal-organic chemical vapor deposition and atomic layer deposition are developed. These techniques also enable to prepare dense films with 100-nm thickness, effectively reducing the ohmic resistance and thus enhancing the performance of SOFC at lower temperatures.Summary and prospects In general, the electrolyte preparation methods discussed can be categorized into two aspects. The first aspect refers to methods for high performance. The as-fabricated films exhibit a high quality (i.e., thin, dense, and uniform), and their microstructures can be highly adjustable. Typical methods include magnetron sputtering, pulsed laser deposition, and chemical vapor deposition. However, these methods are often featured by high cost and difficulty in large area preparation. The second aspect refers to methods for large scale industrial production, which features simple process, high robustness, low cost, and suitability for large area preparation. Representative approaches are tape casting, screen printing, spraying, etc.. However, the electrochemical performance of the as-fabricated electrolyte still needs to be improved.It is important to further elucidate the structure-property relationships for SOFC electrolytes through fine processing and characterizing methods. The structure factors that should be considered include compositions, phase structures, microstructures, mesostructures, and interfaces. Also, it is essential to develop large-scale, low-cost, and robust preparation methods, and explore the influencing factors of performance in actual service conditions. Synergistic collaboration between these aspects is conducive to further enhancement of electrochemical performance while holding cost. In addition, the development of SOFC electrolyte preparing methods is a systematic engineering, necessitating consideration of adaptability to other components and practical application scenarios. The pursuit of these development directions will contribute to the commercialization of SOFC, thereby facilitating the realization of ‘carbon neutrality’ target.

Transition metal nickel ions (Ni2+) situated in a six-coordinate octahedral crystal field exhibit a ultra-broad near-infrared (NIR) luminescence, with a fluorescence half width at half maximum (HWHM) 6-8 times that of rare-earth (RE) element ions like Pr3+ and Er3+. Ni2+-activated NIR gain materials can be used in broadband optical amplifiers and tunable lasers, which have attracted attention. Despite their impressive luminescent efficiency, Ni2+-doped crystals have some limitations in optical fiber amplifier and laser applications due to their intricate fabrication processes, machining, and fiber formation. Glass offers some advantages in processing and fiber formation, but lacks a conducive crystal field (coordination field) environment for Ni2+ to achieve an efficient NIR luminescence. Various types of nanocrystals can be generated in-situ within the glass via subjecting glass to heat treatment, resulting in the formation of nanocrystalline composite glass-ceramics (GCs). Also, a precise control of grain size within the glass to dimensions smaller than the visible light wavelength (e.g., less than 30 nm) effectively mitigates the Rayleigh scattering, endowing GCs with reduced optical losses that meet the practical demands of photonic devices. Johnson, et al. investigated the optical properties of Ni2+. They prepared MgF2 crystals doped with Ni2+ and observed fluorescence emission characteristics and optical laser oscillation phenomena under pulse xenon lamp or tungsten lamp excitation at low temperatures (i.e., 20, 77 K, and 85 K). Ohishi et al. reported Ni2+ activated LiGa5O8 nanocrystalline GCs with a broadband fluorescence emission centered at 1.3 μm with a half-width greater than 300 nm under 976 nm excitation. The lifetimes at 5 k and 300 k were greater than 900 μs and 500 μs, respectively, with internal and external quantum efficiencies of 100% and 9%, respectively. This emission was attributed to the transition of Ni2+ from 3T2g(3F)→3A2g(3F) level in the LiGa5O8 crystal octahedral coordination. Zhou et al. reported the phenomenon of NIR light amplification in Ni2+ doped β-Ga2O3 nanocrystalline transparent GCs. Zhou et al. designed a special glass system with the composition of SiO2/Na2O/Ga2O3/LaF3 = 51%/15%/20%/14% (in mole). This glass system can orderly precipitate LaF3 and Ga2O3 nanocrystals. For co-doping with Er3+ and Ni2+, the two active ions can enter the two different nanocrystals, respectively, the physical distance between the two active ions and the local crystal field changes effectively inhibit the energy transfer between the two different active ions, achieving the near-infrared ultra-wideband luminescence of an integrated multi-color visible and Er3+/Ni2+ composite.Summary and prospects The existing fluorescence regulation of Ni2+-doped GCs is studied , having a great potential in broadband amplifiers, tunable lasers, non-invasive sensing, infrared night vision sources, and infrared medical diagnosis. Numerous studies indicate that 1) the NIR emission band and bandwidth of Ni2+ can be regulated via controlling the types (oxides, fluorides) and modes (single phase or dual phase) of crystals in GCs; 2) the luminescence intensity of Ni2+ can be further enhanced by energy transfer through sensitizers such as Nd3+, Yb3+, Cr3+, etc..; 3) the luminescence intensity of Ni2+ can be also enhanced by optical field regulation, such as using noble metal nanocrystals to improve the collection efficiency of pump light.However, Ni2+-activated transparent GCs still have some challenges. The doping concentration of Ni2+ in microcrystalline glass and microcrystalline glass fibers is relatively low, usually less than 0.2% (in mole fraction), resulting in low NIR absorption coefficients; The matrix glasses that can carry Ni2+ activation are still limited. Exploring multi-component glass matrices that can precipitate new types of crystal phases is one of the main tasks; Residual Ni2+ at the glass phase or glass-crystal phase interface still accounts for a large proportion. Some strategies are needed to ensure that most Ni2+ enters the target crystals, further improving its infrared optical performance; The gain coefficient of Ni2+-doped microcrystalline glass/fiber is relatively low (<0.3 cm-1) due to the limited volume ratio of nanocrystals in the glass (i.e., crystallization rate) and the influence of surface/interface defects of nanocrystals. Meanwhile, efficient positive feedback cannot be formed due to the lack of high-quality resonant cavities, resulting in only room-temperature luminescence of Ni2+, and no laser emission is achieved yet. The prerequisite for achieving laser emission is to obtain laser materials with sufficient gain.The Purcell effect can accelerate the radiation relaxation process of luminescent materials, resulting in an increased radiation probability and a correspondingly increased quantum efficiency of photoluminescence. Based on whispering gallery mode (WGM) glass microspheres, light can be confined in the micron-scale cavity for a long time based on the principle of total reflection. Therefore, it has an extremely high quality factor (i.e., ≥105) and minimal mode volume (i.e., ≤103 μm3), which can fully utilize the Purcell effect to enhance the interaction between light and matter. With the unique advantages of the WGM glass microsphere cavity, the preparation of a new Ni2+-doped microcrystalline glass microsphere laser provides an effective way to break through the physical bottleneck of room-temperature Ni2+ laser emission and develop low-threshold, ultra-broadband near-infrared multi-wavelength micro-lasers.

The possibility and potential impact of a nuclear accident are a subject of debate and a key factor in public concern for nuclear facilities virtually since the first reactor. Although nuclear power plants have several built-in physical barriers to maintain the safety of the system, they are designed to prevent radioactive isotopes from escaping into the environment. However, the experiences for past few decades indicate that nuclear accidents can happen. The radioactive waste produced by nuclear power plants also threatens the natural environment and human health. It can exist in the natural environment for up to 100 000 years. Deep geological disposal of spent fuel and radioactive waste is the most feasible and safe option. The permanent disposal of highly radioactive nuclear waste is to place it in a container that can be isolated from the natural environment until the radioactivity of the fission products reducing to a safe level. The short-term and long-term corrosion mechanism of glass is one of the key points. The current research is to use various methods to simulate the short-term and long-term behaviors of the glass body in different geological environments. However, there is a lack of effective connections between various experiments. In just a few decades after the vitrified body is buried, countless problems that are not considered in the disposal of waste glass are discovered. The current situation is that existing research results lag far behind actual needs. From this point of view, research related to the corrosion of solidified glass is not a precautionary measure, but an urgent one that cannot be delayed.Borosilicate glass is currently a material of choice internationally for immobilizing high-level nuclear waste, including excess plutonium from dismantled nuclear weapons and highly radioactive liquid/solid waste from spent fuel reprocessing. In geological repositories, nuclear waste containing borosilicate glass is embedded in a multi-barrier containment system that should prevent water from entering the glass and the release of radioactive materials. However, groundwater corrosion of glass over long-term storage beyond geological time scales cannot be ruled out, so experimental glass corrosion studies, especially those dealing with corrosion mechanisms, are crucial to assess the long-term performance of glass. After long-term observation and experiments, the corrosion of glass in an aqueous solution environment is often divided into five stages, i.e., interdiffusion between solid and liquid stage, rapid initial reaction with the contact solution stage, corrosion rate decreases stage, residual rate stage and alteration recovery stage. Although these behaviors are not experienced by all materials under all corrosion conditions, one or more of the above can perfectly describe the corrosion process of the material. Three reactions usually occur during the reaction process, i.e., (1) hydration reaction (diffusion), water enters the glass as a complete molecule, (2) hydrolysis reaction, water reacts with the metal-oxygen bond in the glass to generate hydroxyl groups, and (3) ion exchange reaction, the modified cations in the glass are replaced by protons or other cations in the water. There is still controversy for the mechanism that controls the decrease in corrosion rate, but it is basically divided into two situations. One is due to the increase in the concentration of silicon at the interface, which causes the leaching rate to decrease, and another is due to the formation of a corrosion layer at the interface. Large molecules cannot be transferred. There are currently three most competitive models that are widely accepted. The first model is a chemical affinity model, which is based on the concept of "deviation from equilibrium" and can solve the problem of dissolution of the glass network, changes in pH value, precipitation of stable or metastable reaction products, and secondary problems at the interface (reaction zone) between glass and solution. Issues such as silicon oxide saturation and residual affinity of long-term reactions under near-saturated conditions; the second model is an alkali-proton exchange model to form a corrosion layer based on ion exchange reactions. The corrosion layer is considered as the ion exchange of protons with network modifiers such as Na+. The reaction produces products with silanol (Si—OH) groups. The silanol group is repolymerized to form the residual hydrated glass layer. The third model is a gel layer model, which believes that the corrosion layer formed can effectively protect the remaining glass from being corroded. It proposes the release of substances in the glass into the solution, that is, the corrosion rate is determined by the transmission characteristics of the "gel layer".Summary and prospects The corrosion of nuclear waste glass over long-time is undoubtedly the most complex problem in glass science to date. Because its components include dozens of oxides, there are cracks formed during the cooling stage, the geometry of the glass block is complex, the thermal, chemical and water boundary conditions are time-varying, involving many coupling phenomena. In addition, the time scale of deep geological disposal security assessment goes beyond direct verification. There is therefore a need to develop one or more rigorous, multi-scale theories to integrate basic understandings into models, which can be verified through dedicated experiments and compared with corrosion in natural or archaeological glass. Future models predicting a long-term corrosion of silicate glasses in aqueous environments should consider the spatial and temporal coupling of glass dissolution and silica precipitation and growth, controlling the transport of chemicals through the growing corrosion zone. Some specific issues include the evolution of porosity and structure over time in SAL, and how to control the transfer of materials between the aqueous solution and the glass; in the actual process, the nuclear fission products and actinides in the nuclear waste glass are what is the reaction during the glass corrosion process. Radioactive elements generate a large amount of heat during the placement process, and the ion irradiation they generate cause damage to the glass structure and SAL. The nucleation and growth of silicon dioxide at the reaction interface affect the glass dissolution rates and the use of ceramics and glass-ceramics for deep geological disposal of radioactive nuclear waste.

Aluminum nitride (AlN) crystal is one of the key frontier materials in semiconductors due to its superior properties such as ultra-wide band gap, deep ultraviolet transparency, high thermal conductivity, high sound velocity, and high temperature stability. AlN is an ideal substrate for gallium nitride (GaN)-based power semiconductor devices and deep ultraviolet photoelectronic devices, and is also a key material in deep ultraviolet photoelectronic and surface acoustic wave devices. Different AlN crystal growth related technologies have been developed since 1960s. Among them, a PVT AlN crystal technology is relatively mature, and several manufacturers are able to provide 2 inch AlN wafers. However, a high growth temperature (i.e., 2 300 ℃) used in this PVT AIN technology makes the growth of larger PVT AlN wafer extremely hard, and induces some impurities doping and relevant absorption in the ultraviolet region. Moreover, PVT AlN is hard to fulfill controlled doping. These factors and extremely high cost restrict the application.Hydride vapor phase epitaxy (HVPE) is considered an alternative to PVT AlN due to its potential advantages in terms of large-area wafer preparation, controlled doping and cost. Recent studies dealt with the preparation HVPE AlN. This review briefly introduced the crystal structure and fundamental properties, application scenarios, and requirements of AlN crystals. The growth technologies of AlN crystals were concisely categorized, and the HVPE method was elaborated in terms of principle, structure of the growth zone, temperature, atmosphere, substrates, process, application technology, advantages, and disadvantages. In addition, the main challenges for HVPE AlN technology were also proposed.The structural factors of HVPE growth zone (i.e., the horizontal or vertical configuration, the location and direction of gas outlet, the position and direction of substrate, and the size of the growth chamber) are coupled with process factors (i.e., flow rate, pressure and temperature), resulting in complicated flow and temperature fields. A reasonable flow field can create a uniform laminar flow pattern on the substrate surface, which is crucial for epitaxy, crystal quality and uniformity. For instance, a horizontal HVPE system, in which the gas flow direction is horizontal and perpendicular to the substrate surface, can produce a mirror-like AlN epilayer on a c-plane sapphire substrate at 1 100 ℃ with a growth rate of 1.1 μm·h-1 and obtain FWHM of planes (0002) and as low as 40 arcsec and 45 arcsec, respectively. A higher growth temperature can accelerate chemical reaction on the substrate surface and epitaxy. Meanwhile, a high temperature can significantly increase the migration rate of active Al and N atoms in the growth plane, thus promoting two-dimensional growth and crystal quality. HVPE AlN epilayers grown at 1 550 ℃ with a growth rate of about 20 μmh-1 can obtain a FWHM of planes (0002) and of 102 arcsec and 219 arcsec, respectively.The V/III ratio affects the concentration of growth atoms, diffusion distance, reaction rate and growth mode, significantly affecting the crystal quality and surface morphology of HVPE AlN. In general, the V/III ratio of HVPE AlN growth process ranges from 10 to 300. AlN film grown under V/III ratio of 150 can obtain FWHM values of planes (0002) and of 64 arcsec and 648 arcsec, respectively. When the V/III ratio is 150 and 300, the threading dislocation (TD) density can reach 8.9×106 cm-2 and 5.9×107 cm-2, respectively.The materials, crystal orientation and polarity of substrate are a basis for the crystal quality, morphology and performance of HVPE AlN epilayer. Except for commonly used sapphire, Si and SiC substrate, GaN or AlN templates are used to further reduce TD density. Especially, an association of patterned substrates with a lateral epitaxial overgrowth technology is proven as an effective way in reducing TD density. The optimization of growth process, such as surface nitridation of the substrate, buffer layer growth, adjustment of growth procedures, etc., is also investigated to improve the crystal quality of HVPE AlN epilayers.As an alternative to PVT AlN wafers, HVPE AlN wafers can enter into application only if an effective lift-off technology is established. There are only three processes, namely, chemical etching, mechanical lift-off, and self-seperation methods.This review also introduces HTCVD AlN technique, which is developed and can be regarded as a prototype or a variant of HVPE AlN. It also has the same advantages as HVPE AlN. Moreover, HTCVD AlN can grow at 1 700 ℃ and avoid harmful Si and O doping of AlN crystal, which happens in HVPE AlN process, leading to a significant promotion of AlN crystal quality. In addition, the HTCVD also adopts a safe Ar carrier and a solid AlCl3 source instead of explosive H2 and corrosive HCl and Cl2. Summary and prospects There are still some problems in HVPE AlN that need to be solved in the future.The most promising application of HVPE AlN is a large-area free-standing substrate, but the prerequisite for its realization is the development of effective lift-off technology. It is a long-standing challenge and a technical barrier for HVPE AlN application. A fundamental technological tactics to solve the lift-off problem is an idea regarding substrate technology, such as using patterned substrates with a large depth ratio, using template or buffer layers made of two-dimensional materials, or using the both. Little work on HVPE AlN epilayers with a diameter of 2 inches, a thickness of 100 μm and a TD density of 106 cm-2 has been reported yet due to the limitations of heteroepitaxy and growth temperatures below 1 400 ℃. The coupled temperature and flow fields as well as the position of the gas-solid interface can affect the uniformity and crystal quality of the AlN epilayers. A problem is an intense stress field caused by heteroepitaxy, which varies with the size of the epilayer. HVPE AlN epilayers with a thickness of several microns can crack, and those with a thickness of several tens of microns can cause a substrate fracture. A solution to the stress problem also can be innovative substrate technologies such as patterned substrates and two-dimensional material buffer layers.In addition, achieving n-type and p-type doping in HVPE AlN with a high carrier concentration and a high mobility remains a challenge. Specific issues such as nonpolar surface epitaxy and parasitic reactions also need further studies.

As the world major national space projects advance from near-Earth orbit to the deep space, spacecraft have some challenges to operate reliably in extreme environments. It is thus necessary for the development of spacecraft to solve the problems (i.e., From the deterioration of the space irradiated environment to the constraints of energy problems far from the sun, from the difficulties of high heat flow and heat dissipation of highly integrated devices to the development trend of highly sensitive sensors for spacecraft health monitoring). Diamond has five characteristics like "hard, high, transparent, wide and fast" due to its unique crystal structure, determining its high temperature resistance, high frequency resistance, high pressure resistance and irradiation resistance in extreme environments. Deep space exploration plays a role in space environment sensing and pulsar-based navigation by detecting X-ray, ultraviolet and particles from solar radiation. Diamond detectors are fabricated based on photovoltaic effect and/or interaction between particle and diamond. Electrode structure, device structure, and diamond quality have an impact on the detector performance. The detector arrays with large area and excellent performance with the heteroepitaxial diamond size of 1.0-3.5 inches are developed. In addition, a portable power supply based on isotope batteries is also an effective option to solve the problem of insufficient solar radiation during deep space exploration. A radio-voltaic effect isotope battery mainly utilizes the photovoltaic effect generated by the high-energy particle radiation released during isotope decay inside the semiconductor energy transfer junction to generate output current. Compared with other wide-bandgap semiconductors including SiC, GaN, AlGaAs and diamond, diamond has a higher electron-hole pair generation efficiency of 44.2%. The existing transducer junction structure focuses on metal/diamond Schottky junction and diamond/other semiconductors P-N junction, on account of the lack of efficient N-doping. A open circuit voltage of 5 V and a rectification ratio of 107 are obtained for diamond/β-Ga2O3 hetero-junction battery while a theoretical value of energy conversion efficiency of 26.8% is predicted for diamond P-N junction. As the thermal environment inside and outside the spacecraft changes, thermal management and control are crucial for the spacecraft in-orbit work. Diamond as a semiconductor with a high thermal conductivity can enhance the heat conduction as a heat spread or heat radiation as a near-field thermal radiation device. Space active phased array antenna typically features a high performance and a high heat flux due to the high device integration of transmit/receive (T/R) module. The T/R module generates a significant amount of heat in a very small space, leading to a challenge for the thermal management and dissipation from the “hotspot” of devices. When diamond is applied in four launched satellites, the temperature gradients of the T/R modules less than 2.2?℃ is recorded from the flight data, further verifing the rationality and effectiveness of using high-thermal-conductivity diamonds in the thermal design and implementation of active phased array antenna. Near-field thermal radiation device can be used as the heat dissipation surface of a satellite or other spacecraft. As an intelligent thermal control method, the emissivity can be adjusted upon the application of the electric field in the P-N junction and MIS junction. This technology is in the theoretical research stage, but this device based on diamond heterojunction has prospects. In the bargain, in addition to solar irradiation and cosmic rays, spacecraft operating in the space environment also faces many threats such as space debris and high/low temperature alternating environment, leading to the failure of spacecraft structure and bring great hidden dangers to space flight. It is thus important to monitor spacecraft temperature, pressure/strain, acceleration and other parameters in real time. The basic principle of diamond quantum sensing is to use the NV-spin energy level to be sensitive to physical signals such as electromagnetic field, strain, temperature, etc., via measuring the change in the intensity of the output fluorescence signal caused by the NV- change in the external field. Comparing the sensitivity of diamond quantum sensors and other types of sensors in detecting magnetic fields indicates that the sensitivity of diamond quantum sensors is still relatively high. Space optical sensors are known as the "eyes" of spacecraft, providing the positioning information for space missions such as deep space exploration and remote sensing mapping. Diamond has a high transmittance in the deep ultraviolet band, which can well meet the application requirements of the sensor optical system window, and has intense anti-irradiation characteristics and good stability in extreme space environments. With the development of large-scale curved diamond preparation technology, diamond could be used as an excellent optical alternative material in the future.Summary and prospects In this review, the application of diamond materials in deep space exploration (detectors), portable power supplies (isotope batteries), spacecraft thermal control (heat conduction and near-field thermal radiation devices), spacecraft health monitoring (quantum sensors), and optical windows (optical sensor windows were proposed). To represent the application advantages of diamond in the extreme field of aerospace, it is necessary to continue efforts in at least the following aspects. First, 2-inch large-area array polycrystalline diamond arrays are reported to have a good ultraviolet detection performance, and it is possible to effectively synthesize large-area heteroepitaxial single crystal diamond for diamond detectors with better electrical properties. Second, diamond isotope cells and near-field thermal radiation devices both are based on the construction of diamond semiconductor heterojunctions, but the effective diamond N-type doping technology has not yet been broken through. It is thus necessary to further develop the effective diamond doping technology based on new principles. Finally, diamond quantum sensing technology has the advantages of multi-parameter sensing, but how to distinguish the output signal under different field signal excitations and reduce the interference in the face of multi-source targets needs to be further investigated.