IntroductionCsPbBr3 perovskite quantum dots are considered as excellent green light materials in the field of wide color gamut displays due to their excellent luminescence characteristics, such as high photoluminescence quantum yield (PLQY) and narrow full width at half maximum (FWHM). However, CsPbBr3 quantum dots irreversibly deteriorate when exposed to oxygen, water, light and heat due to their low formation energy and strong ionic properties, which restricts their application. The preparation of CsPbBr3 quantum dots via in-situ crystallization in glass is considered as one of the effective strategies to improve their stability. In this study, borosilicate glass was used as a matrix to investigate the effect of Sc2O3 introduction on the glass network structure and the regulatory effect on the crystallization behavior and luminescence performance of CsPbBr3. In addition, the photostability and thermostability of the samples were analyzed. CsPbBr3 quantum dot glass powder with the high quantum efficiency and narrow FWHM could be used to prepare white LED with a high luminous efficiency and a wide color gamut.MethodsA series of CsPbBr3 quantum dot glasses were prepared by a conventional melt quenching-heat treatment method. The specific molar composition ratio of the glass was 42B2O3-20SiO2-4Li2O-8ZnO-3MgO-3Cs2O-6PbBr2-6NaBr-xSc2O3 (mole fraction, x = 0, 0.1, 0.3, 0.5, and 0.7). According to the composition of each glass stoichiometric ratio, the raw materials were weighed, and fully ground in a mortar for 30 min. The mixed powder was then transferred to a corundum crucible and placed in a high-temperature muffle furnace at 1200 ℃ for 15 min. Subsequently, the melt was poured into a preheated graphite mold and annealed for 3 h to relieve thermal stress. After cooling to room temperature, a transparent precursor glass (referred to as PG) was obtained. CsPbBr3 quantum dot glass was obtained via heat treatment of precursor glass samples at different temperatures (i.e., 460, 470, 480, 490 ℃, and 500 ℃) for 10 h. Finally, the prepared CsPbBr3 quantum dot glass was cut, polished or ground into a powder for further characterization and use.Results and discussionThe results show that the average particle size of CsPbBr3 quantum dots gradually decreases from 13.22 nm to 3.42 nm as the amount of Sc2O3 introduced increases. This indicates that the introduction of Sc2O3 can alter the glass network structure under identical external conditions, which in turn affects the particle size of the quantum dots. Note that the peak intensity of the [PbBr6]4- firstly increases and then decreases with increasing the amount of Sc2O3 introduced. The peak intensity of [BO3]/[SiO4] gradually decreases. This is primarily attributed to the Sc2O3 additive, which reduces the [BO3] content within the network structure, strengthens the glass network, and affects the crystallization behavior of the quantum dots.The obtained samples exhibit a typical narrow-band luminescence. Under the same amount of Sc2O3 introduced, PL spectra of CsPbBr3 quantum dot glass samples heat-treated at different temperatures show that the luminescence intensity firstly increases and then decreases with the increase of the temperature, and a phenomenon is attributed to fluorescence quenching. The long lifetime is reduced by 20 ns, but the proportion of long-lived emission gradually is increased as the amount of Sc2O3 introduction is increased. This is due to the improvement of the surface quality of the quantum dot, indicating that carrier quenching can be effectively minimized. Also, the the internal and external photoluminescence quantum yields of the optimal CsPbBr3 quantum dot glass samples are 62.98% and 37.92% at 460 nm excitation. Moreover, they can maintain 64.51% of the original luminescence intensity after continuous illumination upon a 455 nm blue LED chip (20 V, 20 mA) for a week, laying a foundation for developing high-brightness LED devices. After three cycles of heating and cooling (at 298-473 K), the luminescence intensity of the optimal sample can gradually return to the initial value, and the peak emission wavelength and FWHM also show obvious temperature dependence and excellent recovery ability, indicating that the CsPbBr3 quantum dot glass has a good luminescence thermal stability.ConclusionsCsPbBr3 perovskite quantum dots with different amounts of Sc2O3 were precipitated in a borosilicate glass matrix by a conventional melt quenching-heat treatment method. Under the same heat treatment conditions, the structure of the glass network improved and became dense, as well as the average size of the quantum dots decreased from 13.22 nm to 3.42 nm with the increase of the amount of Sc2O3 introduced. After optimization, the internal and external photoluminescence quantum yields of the optimal CsPbBr3 quantum dot glass samples were 62.98% and 37.92% at 460 nm excitation. The denser network structure effectively isolated the quantum dots from air, water, and oxygen erosion, significantly reducing phase separation and degradation caused by external environmental factors, thus having a good thermal cycle recovery. For the white LED prepared with the superior luminescent properties of the CsPbBr3 quantum dot glass powder, the color coordinates were located at (0.3135, 0.3077), the correlated color temperature was 6647 K, and the color gamut reached 130.95% of the NTSC standard and 97.90% of the Rec. 2020 standard, indicating a potential application in the backlight display field.

IntroductionZeolitic imidazolate framework (ZIF) material is a subset of metal-organic framework (MOF) materials with a structure similar to zeolite. Its basic structural unit is the [MN4] tetrahedron formed by the coordination bond between transition metal center ions M (Co, Zn, etc.) and imidazole anions (Im, C3H3N2-) and their derivatives. Among them, ZIF-62 [Zn(C3H3N2)2-n(C7H5N2)n] and ZIF-4 [Zn(C3H3N2)2] crystals can melt and form glasses before decomposition, which are widely used as basic research objects for MOF vitrification. For ZIF-62 and ZIF-4 glasses, changes in metal nodes can cause changes in the local coordination structure, including bond length and tetrahedral symmetry. This could further result in non-linear variations in properties such as glass transition temperature (Tg), which is known as a mixed-metal node effect. The impact of the coexistence of mixed ligands and metal nodes in ZIF structure on thermal properties and their structural origins is not elucidated. Therefore, a further exploration of the node metal mixing effect in ZIF glasses and its dependence on the ligand composition and structure can provide some insights into the relationship between the structure and performances of multi-component ZIF glasses. It is also of great significance to clarify the mixed former effect in inorganic glass and develop novel functional MOF glasses. In this study, the effect of ligand changes on the central metal node content and Tg of ZIF-4 and ZIF-62 glasses were discussed. In addition, the structural origin about the difference in mixed-metal node effect strength [(Tg)max] between ZIF-4 glass and ZIF-62 glass was also analyzed.MethodsZIF-4/62 crystals and ZIF-4/62 melt-quenched glass (MQG) were prepared by solvothermal and melt-quenching methods, respectively. The Zn1-xCox-ZIF-4 high-density amorphous phase (HDA) was prepared by differential scanning calorimetry instruments. The cobalt contents of bimetallic ZIF-4 samples were characterized by inductively coupled plasma-optical emission spectroscopy. The cobalt contents in bimetallic ZIF-62 samples were determined by ultraviolet-visible spectroscopy. The atomic structures of Zn-ZIF-4 MQG and Zn-ZIF-62 MQG were characterized by high energy synchrotron X-ray diffraction measurements. The total scattering structure factor S(Q) and pair distribution function g(r) were calculated based on the diffraction data. The in-house written code developed was used to calculate the structural parameters of MQG, i.e., the partial pair distribution functions of atom pairs, simulated total structure factor, [ZnN4] tetrahedral order parameter (TOP), and Zn-N bond length distortion degree.Results and discussionAccording to the results of elemental analysis, the measured cobalt molar ratio (R) in the ZIF-4 and ZIF-62 crystals is lower than the initial one (x). Compared with the single-ligand ZIF-4 crystals, R in the mixed-ligand ZIF-62 crystals is closer to x. This is due to the different coordination reaction rates between different metal ions and ligands. Also, the Tg of the mixed-ligand ZIF-62 MQG is higher than that of the single-ligand ZIF-4 HDA. For instance, the Tg of Zn-ZIF-62 MQG is 31 ℃ higher than that of Zn-ZIF-4 HDA, and the Tg of Co-ZIF-62 MQG is 42 ℃ higher than that of Co-ZIF-4 HDA. These phenomena can be due to the presence of the bIm (C7H5N2-) ligand in ZIF-62 MQG. Based on the nonlinear variation of Tg with R, the mixed-metal node effect strength [(Tg)max] of ZIF-62 MQG is greater than that of ZIF-4 HDA. Specifically, the (Tg)max of ZIF-62 MQG is 7 ℃, which is greater than the (Tg)max of about 1 ℃ for ZIF-4 HDA. The comparison in total scattering structure factors S(Q) shows that the intensity of the first sharp diffraction peak in Zn-ZIF-4 MQG is slightly greater than that of Zn-ZIF-62 MQG. Moreover, from the comparison in pair distribution functions g(r), the full width at half maximum of the peaks for Zn-N1 and Zn-C atomic connections in the coordination tetrahedron of ZIF-62 MQG are broader, compared to ZIF-4 MQG. The simulations reveal that the TOP (tetrahedral order parameter) value of ZIF-62 MQG is slightly lower than that of ZIF-4 MQG. Also, the Zn—N bond length distortion degree for ZIF-62 MQG is higher than that for ZIF-4 MQG. Based on the results, the coordination tetrahedron units of Zn-ZIF-62 MQG may exhibit a higher disordered degree, compared to Zn-ZIF-4 MQG, implying greater structural flexibility and sensitivity of ZIF-62 glass when the central Zn ion is substituted by other metal ions in the structure. This indicates that the higher (Tg)max on the Tg of ZIF-62 glass is due to the presence of mixed ligand (Im and bIm).ConclusionsBased on the solvothermal reaction mechanism of ZIF crystals, a faster reaction rate of Zn2+ with ligands to form complexes and a higher stability of the Zn2+-ligand coordination tetrahedra result in Zn2+ participating more rapidly in the formation of the ZIF network, thus leading to a lower R. Additionally, the stronger electron-donating property of the bIm ligand increases the coordination reaction rate of Co2+, leading to a higher R value in mixed-ligand ZIF-62, compared to that of single-ligand ZIF-4 crystals. According to the temperature-dependent topological constraint theory, the bIm increases both the number and strength of topological constraints in the ZIF-62 glass structure. As a result, the Tg of ZIF-62 glass is higher than that of ZIF-4 glass. The atomic arrangement in the [ZnN4] tetrahedra of Zn-ZIF-62 MQG has a higher disordered degree, compared to that of Zn-ZIF-4 MQG. This can be attributed to the steric hindrance and stronger electron-donating ability of the bIm ligand in the Zn-ZIF-62 MQG. The higher disordered degree of tetrahedra indicates that the local coordination structure around the Zn metal nodes in Zn-ZIF-62 MQG is more susceptible to the influence of substituted Co nodes, thus enhancing the mixed-metal node effect on the Tg of Zn-ZIF-62 MQG.

IntroductionThe chemical stability of phosphate glass is vital for its applications in various fields, i.e., biomedicine, laser gain media, sealing, and high-level nuclear waste solidification. Alkali metals affect the chemical stability of phosphate glass. Some studies indicate that alkali metals with a higher ionic field strength can enhance the chemical stability of glass via reinforcing the ionic crosslinking between alkali ions and non-bridging oxygen atoms. However, a few studies indicate that certain phosphate glasses containing low-field strength alkali metals exhibit a better chemical stability, compared to the glasses containing high-field strength alkali metals. These results cannot be explained based on the simple field strength. It is thus necessary to further investigate the influence of alkali metals on the chemical stability of phosphate glass. In this study, we utilized various advanced solid-state nuclear magnetic resonance (SSNMR) techniques to analyze the network structure of the aluminum phosphate glasses containing different alkali metals in an atomic scale. The intrinsic correlation among alkali metals, glass structure, and chemical stability was discussed.MethodsThe glasses with molar compositions of [xNa2O-yK2O-(41.6-x-y)Cs2O] -16.7Al2O3-41.7P2O5 were synthesized by melt quenching methods. The values of (x, y) used were (41.6, 0), (0, 41.6), (20.8, 0), and (0, 20.8), respectively. The raw materials required for glass preparation were Al(OH)3 (purity>99%), Al(PO3)3 (purity>99%), NaPO3 (purity>95.0%), KPO3 (purity>99%,), Cs2CO3 (purity>99%), and NH4H2PO4 (purity>99%). Each batch, consisting of 20 g of mixed raw materials, was loaded into a platinum crucible and subjected to a high-temperature furnace at 1250-1300 ℃ for 30 min to melt raw materials. Thereafter, the melt was poured onto a steel plate and quickly pressed to obtain a bulk glass.The chemical stability of these glasses was assessed by the Product Consistency Test B (PCT-B) method. 1 g of dried glass powder with particle sizes of 75-150 m was mixed with 10 mL of neutral deionized water in a sealed polytetrafluoroethylene (PTFE) container. The container was then placed in a constant temperature environment at 90 ℃ for 7 d. After the corrosion experiments, the concentrations of leached elements in the leachates were measured by inductively coupled plasma-atomic emission spectroscopy (ICP-AES), thus calculating the normalized mass loss (NL) of each element within the different glasses.All the SSNMR measurements were performed on a model Bruker Avance III HD 500 MHz spectrometer in a magnetic field of 11.7 T at room temperature. The measurements included 27Al magic-angel spinning (MAS), 31P MAS, 27Al{31P} rotational echo double resonance (REDOR), 31P{27Al} rotational echo adiabatic passage double resonance (REAPDOR), and 31P 1D refocused INADEQUATE.The Raman spectra were determined by a model Renishaw inVia spectrometer, with a laser wavelength of 488 nm.Results and discussionThe NL of phosphorus (P) in the glasses containing alkali metals Na, K, and Na/Cs are 0.7, 15.2, and 21.1 g/m2, respectively. The glass containing K/Cs exhibits a complete corrosion without detectable leachate obtained. These findings indicate that the chemical stability of the aluminum phosphate glasses with varying alkali metal compositions follows a decreased order of Na, K, Na/Cs, K/Cs. The P units within the different glasses are predominantly Q1 units (Qn, “n” represents the number of P-O-P bonds per P unit), indicating a consistent proportion of P—O—P bonds in these glasses. The variation in alkali metals does not affect the P—O—P bonds within the glasses. However, the variation in alkali metals significantly affects the Al species within the glasses. Specifically, the glasses containing alkali metals with a high ionic field strength exhibit a higher proportion of high-coordinated Al. In these glasses, the Al species with different coordinations are exclusively surrounded by phosphorus oxygen tetrahedra (PO4), indicating that all Al species exist solely in the form of Al—O—P bonds. The compactness of the glass network increases with the proportion of Al—O—P bonds. The compact glass network can impede the dissolution and leaching of glass elements, as well as the diffusion of hydrogen species from solution into glass, thereby enhancing the chemical stability of the glass. The compactness of the glass network can be characterized by the reciprocal of the molar volume (1/Vmol). A higher value of 1/Vmol indicates a greater number of atoms per unit volume, corresponding to a higher compactness of the glass network. The values of 1/Vmol (×104 mol/L) in these glasses containing alkali metals Na, K, Na/Cs, and K/Cs are 2.6, 2.2, 2.1, and 2.0, respectively. Correspondingly, the proportions of Al—O—P bonds are 54.5%, 52.6%, 50.7%, and 50.5%, respectively. A decreasing order of Na, K, Na/Cs, K/Cs is consistent with a decreasing order of the chemical stability. These results provide an evidence that the proportion of Al—O—P bonds increases as the ionic field strength of alkali metal increased, resulting in an enhanced compactness of the glass network and improved chemical stability. Furthermore, it is noteworthy that the proportion of Al-O-P bonds in the glass containing Na/Cs is comparable to that in the glass containing K/Cs. The former demonstrates a denser glass network. This can be attributed to the smaller ionic radius and higher ionic field strength of Na, compared to K. The smaller ionic radius results in narrower structural gaps within the glass network, while the higher ionic field strength enhances its electric field attraction to non-bridging oxygen.ConclusionsThe chemical stability of the aluminum phosphate glasses containing different alkali metals decreased in an order of Na, K, Na/Cs, K/Cs. The chemical stability increased as the ionic field strength of alkali metals increased. The change in alkali metals affected the compactness of the glass network via modulating the electric field attraction to non-bridging oxygen, and substantially modified the network structure of the glass. In these glasses, the Al species with varying coordination numbers were exclusively surrounded by phosphorus oxygen tetrahedra (PO4). The proportion of high-coordinated Al increased with increasing the ionic field strength of alkali metals, resulting in an augmentation of the chemical bond connections between Al and PO4. This structural adjustment further enhanced the compactness of the glass network, ultimately improving its chemical stability.

IntroductionSilica aerogels are highly porous materials with interconnected three-dimensional networks of silica particles, which are typically obtained via removing the liquid in gels under supercritical conditions. Silica aerogels are widely applied in the fields of thermal insulation, adsorption, catalysis, and energy storage due to their ultralow density, large surface area, and unique nanoporous structure. However, silica aerogels are fragile at relatively low stresses due to the existence of rigid skeleton consisting of weak linking of silica particles. The inherent brittleness and poor reliability restrict the application of aerogel materials to a certain extent. In this paper, the preparation and properties of SiO2 nanotube aerogels (SiO2-NTA) with a three-dimensional nanotubular network structure were investigated.MethodsFor the prepatation of carbon aerogels (CA) as sacrificial templates, 3.24 g of resorcinol and 4.4 mL of formaldehyde solution were dissolved in 95.5 mL of deionized water. The solution was stirred for 1 h, and 3.9 mg of sodium carbonate was added. After further stirring for 30 min, the precursor solution was poured into a container, sealed and cured in an oven at 85 ℃ for 72 h to obtain a resorcinol-formaldehyde wet gel. The gel was washed with ethanol for several times to completely remove the residual solvents. The wet gel was dried using supercritical carbon dioxide to obtain the resorcinol-formaldehyde aerogel, which was subsequently placed in a tubular furnace and carbonized in a nitrogen atmosphere to obtain the CA templates.SiO2-NTA were prepared via chemical vapor deposition (CVD) with argon as carrier gas, tetraethoxysilane and aqueous ammonia solution as silicon and oxygen sources, respectively. Firstly, tetraethoxysilane source tank was heated to 60 ℃. Then, CA templates were placed in CVD chamber, and was heated to different deposition temperatures (i.e., 100, 150, 200, 250 ℃ and 300 ℃), respectively. C/SiO2 composite aerogels (CA@SiO2) were prepared via introducing tetraethoxysilane (5 mL/min) and aqueous ammonia (15 mL/min) into the chamber, and depositing for 20 h at a target pressure. Finally, CA@SiO2 was calcined in air at 500 ℃, and SiO2-NTA was obtained after removing the templates.The microstructural features and pore morphology of aerogels were determined by a model SEM4000Pro scanning electron microscope (SEM) and a model TH-F120 transmission electron microscope (TEM). The specific surface area and total pore volume were measured based on Nitrogen adsorption-desorption isotherms in a model V-Sorb X800 N2 adsorption analyzer. The compressive strength and Young's modulus of SiO2-NTA specimens were measured by a model UTM-4103 electronic universal testing machine at a crosshead speed of 0.5 mm/min.Results and discussionSiO2-NTA prepared by CVD method has a three-dimensional nanotubular network structure. The inner part of the skeleton is hollow, and the average thickness of tube wall ranges from 3 nm to 7 nm. The deposition temperature and pressure have a significant influence on the microstructure as well as density of SiO2-NTA. The deposition rate and weight gain of aerogels increase gradually, and accompany the skeleton coarsening process as the deposition temperature increases from 100 ℃ to 250 ℃, which inhibits the shrinkage of the SiO2-NTA after calcination. Silica preferentially deposits on the outside of the template as the deposition temperature further increases to 300 ℃, resulting in the blocking of SiO2-NTA surface. The density of SiO2-NTA firstly decreases and then increases as the temperature increases, which is strongly dependent on both weight gain and linear shrinkage. Similarly, SiO2-NTA density ranges from 65 mg/cm3 to 51 mg/cm3 with the increase of pressure. The preparation of SiO2-NTA based on CVD method is essentially a reaction transport process of multi-component fluids in a porous template. It is thus necessary to balance the mass transfer rate and reaction rate to obtain SiO2-NTA with a homogeneous microstructure.Compared with CA, the specific surface area and total pore volume of CA@SiO2 decrease significantly because of the preferential deposition of silica at defects and junctions of framework. After calcination in air, the feature mesopore is formed via removal of the carbon skeleton, and the specific surface area and total pore volume of SiO2-NTA can reach 592.717 m2/g and 1.047 cm3/g, respectively. The high pore volume and nanotubular skeletons lead to the low density of SiO2-NTA. SiO2-NTA shows relatively excellent mechanical properties. The elastic modulus and the stress at 60% strain of nanotube aerogels are 0.70 MPa and 0.83 MPa, respectively, and the specimens have no obvious fatigue damage after 100 cycles of compression, further indicating that SiO2-NTA has an outstanding structural reliability in a certain range of strain. In addition, SiO2-NTA also exhibits an excellent machinability while keeping a low density, compared with conventional silica aerogels, and a thin-walled aerogel specimen with a wall thickness of 200 m can be obtained via processing.ConclusionsSiO2-NTA with a three-dimensional nanotubular network structure could be prepared via CVD of silica coating on the skeleton of CA sacrificial templates. The deposition temperature and pressure had a significant influence on the microstructure as well as density of SiO2-NTA. Within a certain range, the density of SiO2-NTA reduced as the deposition temperatures and pressure increased because of the decrease of linear shrinkage after calcination. However, as the temperature further increased, silica preferentially deposited on the outside of the template, resulting in the blocking of SiO2-NTA surface. The preparation of SiO2-NTA based on CVD method was essentially a reaction transport process of multi-component fluids in porous template. It is necessary to balance the mass transfer rate and reaction rate to obtain SiO2-NTA with a homogeneous microstructure. The specific surface area and total pore volume of SiO2-NTA could reach 592.717 m2/g and 1.047 cm3/g, respectively. The high pore volume and nanotubular skeletons led to the low density of SiO2-NTA. SiO2-NTA had relatively excellent mechanical properties. The elastic modulus and the stress at 60% strain of nanotube aerogels were 0.70 MPa and 0.83 MPa, respectively, and the specimen could be significantly compressed without obvious brittle fracture. Moreover, SiO2-NTA had a superior machinability due to its outstanding structural reliability, which could be processed by turning, milling and laser.

IntroductionIn alpine saline soil environments, concrete has a multi-factor coupling degradation due to the freeze-thaw cycles, as well as sulfate and chloride corrosion. This degradation results in a significant decline in structural lifespan primarily due to reduced material durability. The maintenance process is complex and incurs substantial economic losses, attracting considerable attentions. Under the influence of these coupled factors, the presence of salt facilitates the migration of water toward the salt. Upon reaching the critical freezing point, ice jams occur, leading to concrete damage from ice pressure. Also, the formation of numerous expansion products generates an expansion pressure during dry-wet cycles, further contributing to concrete deterioration. Although the use of fiber-reinforced concrete has a potential to mitigate these issues, tight construction timelines can result in an initial damage, such as cracks during winter construction, which are often unavoidable. The existing research on the durability and mechanisms of fiber-reinforced concrete in real crack states within this environment remains insufficient, indicating a need for a further research.MethodsThis study examined the fiber-reinforced concrete used in a project located in the alpine saline soil region of Tibet, China. Three distinct types of fiber concrete specimens were designed and manufactured with polypropylene fiber (PPF), polyacrylonitrile fiber (PANF), and modified polyester fiber (PEF). After 150 d outdoor curing, the actual cracks were analyzed by a microscope. Two accelerated degradation tests were conducted, i.e., composite salt-freeze-thaw and composite salt-dry-wet cycles. The durability damage mechanisms and patterns were investigated in detail through measurements of ultrasonic wave velocity and splitting tensile strength, as well as by scanning electron microscopy.Results and discussionAccording to the crack information statistics of the specimens after outdoor exposure and curing, the cracks in plain concrete are straight and singular, whereas the cracks in fiber-reinforced concrete are interconnected, forming a ring network structure. The presence of these cracks accelerates the connection rate between surface and internal cracks during composite salt-freeze-thaw and dry-wet cycles, leading to a reduction in wave velocity and splitting tensile strength. The mechanistic analysis indicates that under the influence of salt-freeze-thaw, the saturation of the concrete pore solution increases, and the combined effects of crystallization pressure, stress, and chemical expansion products contribute to the initiation and propagation of internal cracks within the concrete. Damage can be categorized into surface damage and internal damage. During the composite salt-dry-wet cycle, the water pressure in the wet state gradually diffuses the salt solution from the concrete surface to its interior, resulting in the formation of expansive products. In the dry state, the solution is heated and evaporated, causing soluble salts to crystallize due to temperature effects. The alternating dry-wet conditions produce a compounded damage. The fibers exhibit a bridging-cracking-toughening effect, which enhances crack propagation resistance. Furthermore, an analysis model correlating the relative values of ultrasonic wave velocity damage with splitting tensile strength, which is proposed based on material decay theory, demonstrates a correlation coefficient of exceeding 0.95. This model effectively reflects the attenuation behavior of the splitting tensile strength of fiber concrete under conditions of composite salt-freeze-thaw and dry-wet cycles, highlighting its significance in predicting the tensile properties of concrete structures.ConclusionsThe initial crack width of plain concrete ranged from 6 m to 15 m with a maximum length of 20 mm. In comparison, the early crack resistance of polyester fiber reinforced concrete was superior, exhibiting a width of less than 10 m and a maximum length of approximately 10 mm, alongside the maximum anti-deterioration capability. Upon reaching the designated number of cycles in the durability test, the wave velocity was decreasesd by 29.36% and 16.05%, respectively, while the splitting tensile strength was diminished by 43.80% and 37.19%, respectively. This deterioration in durability resulted in the expansion of cracks within the interfacial transition zone of the concrete. However, the fibers could form a network that bridged these cracks, thereby reducing tensile stress, enhancing crack propagation resistance in the interfacial transition zone, ultimately delaying the overall damage.

IntroductionLead halide perovskites have attracted much attention in optoelectronic research due to their exceptional properties, such as long carrier diffusion lengths, low exciton binding energies, and cost-effective production. However, their inherent lead toxicity and poor environmental stability have challenges, restricting their wider adoption. It is thus important to search for safer, lead-free alternatives. Cesium copper halides emerge as promising candidates, offering the similar photoluminescent properties and potential for full-spectrum emission. Nevertheless, these materials still suffer from degradation under harsh conditions, which limits their practical use. Embedding cesium copper halides in glass matrices can enhance the stability via protecting the quantum dots from environmental factors like moisture and oxygen. However, challenges such as low transparency and limited tunability remain. To overcome these issues, the introduction of rare-earth ions like europium (Eu2+/Eu3+) into the glass matrix is proposed. In this work, transparent Eu2+/Eu3+ doped Cs3Cu2I5/CsCu2I3 dual-phase quantum dot glass was synthesized by an one-step melt-quenching method. The resulting glass exhibits a full-spectrum cold white light emission with a correlated color temperature (C) of 7 421 K, a general color rendering index (R) of 82, and a photoluminescence quantum yield of 75.1%.MethodsIn this study, a transparent Eu2+/Eu3+ doped Cs3Cu2I5/CsCu2I3 biphasic quantum dot glass was synthesized by an one-step melt-quenching method. The glass composition designed was 20% SiO2, 50% B2O3, 5% ZnO, 3% Al2O3, 10% Cs2CO3, and 12% NaI, all in molar percentages. To induce the precipitation of biphasic quantum dots within the glass matrix, additional components were introduced, i.e., 1% CuI to promote the formation of cesium copper iodide, 0.04% SnO to prevent the oxidation of Cu+, 1% CaO to facilitate the precipitation process, and 1% MnO to reduce the viscosity of the glass. Various concentrations of Eu2O3 (i.e., 0%, 0.02%, 0.05%, and 0.10%) were added to enhance the glass emission properties.The crystalline phases in the glass were determined by X-ray diffraction (XRD). The glass transition temperature and crystallization temperature were determined by differential scanning calorimetry (DSC) as indicatives of the thermal stability of the glass. The photoluminescence (PL) spectra were employed to evaluate the optical properties of the glass (i.e., the emission spectrum, quantum yield, and R). The oxidation states of the elements within the glass were analyzed by X-ray photoelectron spectroscopy, providing an insight into the distribution of Eu2+/Eu3+. The absorption spectra of the glass were characterized by UV-visible spectrophotometry.Results and DiscussionThe results demonstrate that the Eu2+/Eu3+ doped Cs3Cu2I5/CsCu2I3 biphasic quantum dot glass exhibits enhanced photoluminescent properties, compared to the undoped samples. The introduction of Eu2O3 can increase the overall emission intensity and broaden the emission spectrum, resulting in a full-spectrum cold white light emission. Specifically, the glass doped with 0.05% Eu2O3 achieves a photoluminescence quantum yield of 75.1%, with a C of 7421 K and a general R of 82. These results indicate that the Eu2+/Eu3+ co-doping effectively improves the glass emission characteristics via providing additional emission centers in the blue and red regions of the spectrum, attributed to Eu2+ and Eu3+, respectively. The structural analysis shows the effective incorporation of Eu2+/Eu3+ ions into the Cs3Cu2I5/CsCu2I3 matrix without disrupting the existing crystal structures. The XRD patterns indicate that the doped glass maintains the characteristic diffraction peaks of Cs3Cu2I5 and CsCu2I3, indicating that the addition of Eu2O3 does not alter the fundamental crystal structure of the biphasic quantum dots. Moreover, the DSC analysis reveal a high glass transition temperature of 652 K and a crystallization temperature of 717 K, indicating that the doped glass has an excellent thermal stability. The glass samples are also subjected to long-term stability tests, showing a minimal degradation in their optical properties after three months of storage. The photoluminescence spectra of the stored samples exhibit only minor shifts in emission peak positions and intensity, indicating that the glass retains its luminescent properties. In addition, the Eu2+/Eu3+ doping also improves the glass transparency and color rendering capabilities. The doped glass samples have a higher degree of transparency, compared to the undoped samples, which is attributed to the clarifying effect of Eu2O3. The Eu2+/Eu3+ ions provide complementary blue and red emission, thus enhancing the overall color rendering and allowing for the production of cold white light with a high color quality. The improved transparency and color rendering make the doped glass suitable for use in lighting and display applications in which high brightness and accurate color representation are required.ConclusionsEu2+/Eu3+ doped Cs3Cu2I5/CsCu2I3 biphasic quantum dot glass was synthesized as a stable, lead-free photoluminescent material. The synthesized glass demonstrated an excellent full-spectrum cold white light emission, making it a promising candidate for various optoelectronic applications (i.e., lighting, displays, and sensors). The one-step melt-quenching method was effective in producing a material with a high thermal stability, a robust structural integrity and an enhanced optical performance. The introduction of Eu2O3 provided additional emission centers, improved transparency, and enhanced color rendering, addressing the limitations of previous cesium copper halide quantum dot glasses. This study could provide a viable strategy for the design and fabrication of advanced quantum dot glasses that meet the stringent demands of modern optoelectronic devices, offering a safer and more stable alternative to lead-based perovskites.

IntroductionNear-infrared (NIR) luminescence with emission wavelengths ranging from 700 nm to 1100 nm has attracted much attention in the fields of nondestructive testing, biometrics, and night vision. In this paper, high-temperature solid-phase method was used to synthesize Cr3+ single-doped and Ce3+, Cr3+ co-doped Y2CaAl4SiO12 luminescent materials. Under 438 nm light excitation, Cr3+ could produce a near-infrared broadband emission at 740 nm and R-line narrowband emission at 690 nm. The quantum efficiency of mono-doped Cr3+ was calculated to be 24%, and the crystal field intensity was calculated to be 2.429 by excitation spectral analysis. The thermal stability and the luminescence intensity of Y2CaAl4SiO12: Cr3+ were analyzed by variable-temperature spectroscopy. In addition, Y2CaAl4SiO12: Ce3+, Cr3+ luminescent materials were also prepared, and the luminescence intensity and the quantum luminescence efficiency of Y2CaAl4SiO12: 0.005Ce3+, 0.007Cr3+ were analyzed.MethodsIn accordance with the stoichiometric ratios, Y2-xCaAl4SiO12: xCe3+ (where x = 0.001-0.011 mol) and Y2CaAl4-ySiO12: 0.005 Ce3+, y Cr3+ (where y = 0.001-0.011 mol) were prepared via solid-state reactions with raw materials of CaCO3, Cr2O3, CeO2, Al2O3, SiO2, and Y2O3. The mixture with anhydrous ethanol was then ground in a mortar. Subsequently, the ground material was dried in an oven at 80 ℃ before being transferred to a square crucible for sintering in a reducing atmosphere at 1550 ℃ for 4 h. Afterwards, the sample was removed and allowed to cool to room temperature for the coming analysis.Results and discussionY2CaAl4SiO12: Cr3+ belongs to a cubic structure, the space group is Ia3-d, the number of molecules Z=8. The optimal doping concentration of Y2CaAl4-ySiO12: yCr3+(y = 0-0.01) is 0.007, and the quenching mechanism of concentration is dipole-dipole interaction. After co-doping of Cr3+ and Ce3+ (Cr3+ is 0.007), the luminescence intensity is about 3 times greater than that of single-doped Cr3+, and the quantum efficiency is 45%. This indicates that the co-blending improves the luminescence performance of the material. When co-doped with Y2CaAl4SiO12:Ce3+ and Cr3+, the luminescence properties of the sample can reach 77.6% of the room temperature at 423 K (150 ℃), and the thermal stability is good.ConclusionsNear-infrared luminescent materials of Y2-xCaAl4SiO12: Cr3+ and Y2CaAl4SiO12: Ce3+, Cr3+ were synthesized via soild-state reactions. The luminescence properties and thermal stability of the samples were thoroughly analyzed, and Ce3+ was incorporated as a sensitizer to investigate the energy transfer mechanism between Ce3+ and Cr3+ within the matrix. The results indicated that Y2CaAl4SiO12 exhibits a garnet structure, Cr3+ generated a broad near-infrared emission spectrum peaking at 740 nm alongside a sharp peak at 690 nm, achieving a quantum efficiency of 24% when doped alone. Y2CaAl4SiO12: Ce3+, Cr3+ prepared had an energy transfer from Ce3+ to Cr3+. The energy transfer mechanism of this system was elucidated through IS0 and c fitting analyses. The luminous intensity of Y1.995CaAl3.993SiO12: 0.005Ce3+ and 0.007Cr3+ was threefold greater than that of Y2CaAl3.993SiO12: 0.007Cr3+. At this juncture, the quantum efficiency for co-doping reached 45%. When y was 0.011, the energy transfer efficiency measured was 30.01%. The thermal stability of Y2CaAl4SiO12: 0.007Cr3+ revealed that its luminous intensity at 150 ℃ retained 77.6% of its value at room temperature, with a thermal activation energy calculated of 0.207 eV. This work could provide essential data for future applications of this material.

IntroductionWith the increasing environmental protection and sustainable development, conventional water pollution treatment methods have some challenges in practical applications. Photocatalytic technology has potential advantages such as energy conservation and environmental protection, providing an effective and sustainable method for wastewater treatment. The design and synthesis of photocatalysts are crucial in photocatalytic reactions. Silver molybdate material has some advantages of controllable morphology, unique physicochemical properties, having potential application prospects. However, the narrow photoresponse range and the high recombination efficiency of photo generated charge carriers restrict its application in the field of photocatalysis. In this study, a ZnO/Ag2MoO4 composite photocatalyst was prepared by a hydrothermal method with ZnO. The purpose was to improve the photocatalytic activity of silver molybdate via constructing heterojunctions. The photocatalytic performance of different proportions of composite materials for the degradation of organic pollutants was investigated. In addition, the optical stability of the catalyst and the active free radicals involved in the reaction were also analyzed.MethodsZnO/Ag2MoO4 composite catalysts with different mass fractions of 10%, 50%, and 90% ZnO were synthesized by a hydrothermal method with ZnO, AgNO3, and Na2MoO4·2H2O, respectively.The photocatalytic degradation of organic pollutants was carried out in a photocatalytic reactor. 50 mg of photocatalyst was dispersed in 50 mL of Rhodamine B (RhB) or meloxicam (MLX) solution in each experiment. Prior to photocatalytic reaction, the suspension was stirred in the darkness for 30 min to obtain the absorption-desorption equilibrium. Afterwards, the suspension was placed under a xenon lamp (300 W) for photocatalytic degradation. At each interval, RhB or MLX solution with catalyst was sampled and centrifuged to remove the solid catalyst. The concentration of RhB or MLX was determined by a UV-Vis spectrophotometer. The similar experimental steps were used for the cyclic experiments. After each cyclic experiment, the solid catalyst was separated and washed with water and ethanol to continue the next cyclic experiment.To determine the main active species involved in the degradation of RhB, free radical capture experiments were conducted. The free radical capture experiment followed the same steps as the normal degradation experiment. Benzoquinone, ethanol, silver nitrate, and tert-butanol were added as a scavenger for superoxide radicals, holes, electrons, and hydroxyl radicals during the reaction.Results and discussionZnO/Ag2MoO4 composite catalysts with different ratios were prepared by a hydrothermal method. The results indicate the effective preparation of ZnO/Ag2MoO4 without other impurity elements. Based on the XRD patterns, the sharp diffraction peaks of ZnO/Ag2MoO4 composites indicate a good crystallinity. The SEM images show that ZAM-7 is a block shaped structure with uneven size, and ZnO is deposited in a columnar form on the surface of ZnO/Ag2MoO4. The minimum size of ZAM-7 is approximately 100-200 nm. The specific surface areas of ZnO, ZnO/Ag2MoO4, and ZAM-7 are 4.5795 m2/g, 0.0921 m2/g, and 2.6339 m2/g, respectively. The specific surface area of ZAM-7 is 28 times greater than that of ZnO/Ag2MoO4, indicating that the composition of Ag2MoO4 and ZnO is beneficial for increasing the specific surface area of the catalyst, thus providing more active sites for photocatalytic reactions.The photocatalytic performance of ZnO/Ag2MoO4 composite materials is investigated using RhB and MLX as simulated organic pollutants. After 90-min illumination, the removal rates of RhB by ZnO, Ag2MoO4, and ZAM-7 are 40.1%, 13.8%, and 89.6%, respectively. The rate constants of ZnO, Ag2MoO4, and ZAM-7 are 1.19×10-2 min-1, 0.22×10-2 min-1, and 3.60×10-2 min-1, respectively. The degradation of meloxicam is also carried out with ZAM-7. When the catalyst dosage is 50 mg, the MLX concentration is 100 mg/L, the degradation rate of MLX by the catalyst can reach 80.6% after 270 min visible light irradiation.ConclusionsZnO/Ag2MoO4 composite photocatalysts were prepared by a hydrothermal method. The minimum size of ZnO/Ag2MoO4 composite catalysts was 100-200 nm. ZnO was deposited in a prismatic shape on the surface of Ag2MoO4. ZnO/Ag2MoO4 composite catalyst exhibited a superior photocatalytic degradation activity for both organic dyes and drugs. Under the optimal reaction conditions, the degradation rate of RhB by the composite catalyst could reach 95.0%, and the degradation rate of the drug MLX could reach 80.6%. The maximum reaction rate constants for the degradation of RhB by composite catalysts were 3 times and 16 times greater than those of ZnO and Ag2MoO4, respectively. The improvement of photocatalytic activity after the composition of Ag2MoO4 and ZnO was attributed to the improvement of photogenerated carrier separation efficiency, the increase of visible light absorption intensity, the reduction of band gap width, and the increase of active sites. The cyclic experiment of the catalyst showed that ZnO/Ag2MoO4 composite catalyst had a good optical stability. The results could provide a useful reference for the development and design of photocatalysts for water pollution treatment.

IntroductionKaolinite as one of the most widely distributed and commonly utilized minerals has an increasing demand in various fields, including coatings, adsorption, catalysis, rubber, and biomedicine. The utilization of kaolinite is affected by various factors like particle size, layer thickness, and specific surface area. Kaolinite nanosheets as a type of two-dimensional (2D) nanomaterial exhibit novel properties that encompass quantum size effects, surface effects, small size phenomena, as well as macroscopic quantum tunneling effects. The existing preparation process of kaolinite nanosheets has some notable challenges, including high thickness, small specific surface area, and severe damage to the crystal structure, all of which constrain their potential applications in industries. This study introduced a process for the preparation of kaolinite nanosheets, including dimethyl sulfoxideintercalation, ball milling exfoliation, ultrasonic dispersion, and microwave drying techniques. The structural and morphological changes of kaolinite during the DMSO intercalation and subsequent ball milling exfoliation processes were analyzed.MethodsInitially, kaolinite of 5 g was accurately weighed and thoroughly ground in an agate mortar. Afterwards, the ground powder was mixed with 30 ml of DMSO and distilled water in a 100 ml beaker. The mixed suspension in the beaker was stirred magnetically at 66 ℃ for 400 min. After the suspension was centrifugated, the subsequent precipitate was subjected in an oven at 90 ℃ to yield the DMSO-kaolinite intercalation complex (DK). Subsequently, the DK of 10 g was mixed with 20 ml of distilled water. The mixed suspension with sodium hexametaphosphate as a dispersant was ground in a planetary ball mill with zirconia balls of 1-3 mm at 300 r·min-1 for 3 h. The resulting ground suspension was centrifuged at 4 000 r·min-1 for 5 min, and the precipitate was rinsed with ethanol for three times. Finally, the sample was placed in a microwave dryer at 700 W for 10 min, yielding kaolinite nanosheets (BDK). The structural and morphological transformations of kaolinite throughout the intercalation and ball milling exfoliation processes were thoroughly characterized by X-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR), BET surface area measurement (BET), scanning electron microscopy (SEM), and atomic force microscopy (AFM).Results and discussionThe XRD patterns of kaolinite nanosheets prepared indicate that DMSO intercalates into the layers of kaolinite, resulting in an expansion of the interlayer spacing to 1.12 nm. The diffraction peak shape of the BDK sample exhibits no significant alterations, indicating the preservation of kaolinite crystallinity with a crystallinity index value of 1.06. The FTIR analysis reveals that DMSO molecules formed bonds with the hydroxyl groups present on the internal surface of kaolinite. The peak intensities and positions of the BDK sample remain unchanged, compared to the raw kaolinite material, signifying the preservation of kaolinite's fundamental crystal structure throughout the process. The SEM and AFM images reveal that the thickness of the BDK nanosheets is diminished to approximately 15 nm, accompanied by a decrease in particle size. The nanosheets exhibit an average length ranging from 500 to 900 nm, distributing uniformly. The BET analysis further demonstrates that the specific surface area increases from 9.28 m2·g-1 to 26.62 m2·g-1, having a nearly threefold enhancement. Compared to the grinding method, the DMSO intercalation-ball milling-ultrasonic-microwave drying method achieves a significant exfoliation effect in a shorter time. The kaolinite nanosheets obtained through this process retain the basic crystal structure of kaolinite with a nanoscale vertical dimension (i.e., 1-100 nm). The kaolinite nanosheets prepared through this process can be used as coating fillers.ConclusionsThe kaolinite nanosheets with intact crystal shape, thin layers, and large specific surface area were prepared by DMSO intercalation-ball milling-flaking-ultrasonic dispersion-microwave drying techniques. The optimized parameters for DMSO intercalation and ball milling flaking were intercalation temperature of 66 ℃, intercalation time of 400 min, volume ratio of DMSO to H2O of 30∶3, ball milling time of 3.1 h, ball milling rotational speed of 300 r·min-1, and sodium hexametaphosphate additive of 0.22 g. The average particle size of the kaolinite nanosheets prepared under the optimum condition was 0.77 m. The characterization analysis showed that DMSO molecules bonded with the hydroxyl groups on the inner surface of kaolinite, and the basic crystal structure of kaolinite was maintained after ball milling. The thickness of ultrafine kaolinite nanosheets reduced to approximately 15 nm, with a uniform distribution of the layers and a well-maintained crystalline morphology. The specific surface area expanded to 26.62 m2·g-1. The interlayer force of kaolinite was reduced by DMSO intercalation, while maintaining its basic crystal shape. Low-speed ball milling separated the kaolinite layer, while maintaining the intact layer structure.

IntroductionSolid oxide fuel cell (SOFC) is one of the strong competitors of energy technology. SOFC has the characteristics of wide fuel selection, less pollution emission, high safety, and low noise as an excellent energy conversion and utilization device. However, the existing commercial SOFC still has some problems like high working temperature and large attenuation rate due to the limitation of material performance, restricting the application. Among the components of SOFC, the performance of air pole material is a key factor affecting SOFC. LSC material is one of the main research directions of solid oxide fuel cells (SOFC) air polar materials with the superior electrochemical properties, but its major disadvantage is a great thermal expansion coefficient (TEC). The negative thermal expansion (NTE) material provides an effective way to reduce the TEC of the SOFC air pole material. NTE material is named because of the characteristics of thermal contraction in the specific temperature interval. Theoretically, it can reduce the TEC of composite material and facilitate the thermal match between SOFC air electrode material and electrolyte material. Some NTE materials are a perovskite structure with a higher conductivity than Gd0.2Ce0.8O2- (GDC) of fluorite structure. These advantages make the theoretical cell power density of NTE composite air electrode material above the GDC composite cathode In this paper, La0.6Sr0.4CoO3- (LSC) material was used as a matrix, Sm0.85Zn0.15MnO3 (SZM) material with the superior negative thermal expansion characteristics was selected as a composite phase, and a series of LS-xSZM (x = 0-40%) materials were designed to achieve the thermal matching of composite materials.MethodsLSC and SZM powders were synthesized by a solid-liquid composite method. First, the corresponding quality of acetate raw materials was accurately weighed according to the stoichiometric ratio, and then the appropriate citric acid (CA) was weighed as a complexing agent according to the total metal particle weight and citric acid (CA) amount of 5:1. All the raw materials were mixed with an appropriate amount of deionized water and ground in a ball mill at a speed of 300 r/ min for more than 12 h. The turbid liquid in the ball mill was taken out and placed in a beaker, and the precursor powder was obtained after drying in the oven at 250 ℃ for 6 h, and then the LSC powder was obtained via calcination in a muffle furnace at 950 ℃ for 2 h, and the SZM powder was obtained via calcination at 1 300 ℃ for 2 h. The two powders were mixed with ethanol and ground in the ball mill for 6 h. The cathode slurry was prepared by mixing powders, and then full cells and symmetrical cells were made by screen printing for subsequent tests.Results and discussionThe X-ray diffraction patterns show that the SZM is chemically compatible with LSC. The thermal expansion test indicates that SZM has an excellent thermal offset ability, and the average thermal expansion coefficient of the composite material from room temperature to 800 ℃ at x of 30% is 13×10-6 K-1, which is similar to that of the barrier material. The area specific resistance of the LSC-30% SZM composite material at 800-500 ℃ decreases from 0.012-1.240 ·cm2 in the case of LSC to 0.008-0.620 ·cm2, indicating a good interfacial contact. The power density of the button cell at 750 ℃ is 1 702 mW·cm-2, while the pure phase LSC at the same temperature is 1 209 mW·cm-2, which is increased by 41%. The polarization resistance Rp reduces from 0.65 ·cm2 to 0.50 ·cm2. The voltage drop of thermal cycling and constant current discharge is below 1%. In the 200 h constant current discharge test at 300 mA·cm-2, the voltage of the battery remains stable after the initial increase, and the whole process only reduces to 10 mV, which is decreased by 1.2%, showing a good long-term stability. No delamination occurs in the SEM images of the battery cross-section after the test. The comprehensive analysis of a better interfacial contact due to a good thermal matching of the composites ultimately achieves a simultaneous increase in the power density and stability of the cell.ConclusionsA perovskite structural oxide material of Sm0.85Zn0.15MnO3 (SZM) with negative thermal expansion characteristics was synthesized by a solid-liquid recombination method. The XRD analysis indicated that SZM was chemical compatible with LSC. The pure phase SZM had special thermal shrinkage characteristics, while the thermal expansion characteristics of the composite materials decreased. The TEC of the pure phase LSC was 20 ×10-6 K-1, while the TEC of the 30% SZM composite LSC was only 13 ×10-6 K-1. The ASR of the composite material at 750 ℃ decreased from 0.02 ·cm2 to 0.013 ·cm2, while that at 550 ℃ decreased from 1.2 ·cm2 to 0.6 ·cm2, having an excellent performance. The battery of LSC-30% SZM material was improved at 750 ℃ from 1 209 mW·cm-2 of pure phase LSC to 1 702 mW·cm-2 of LSC-30% SZM, which was increased by 41%. In the thermal cycle test, the variation of battery OCV was within 1%, and the voltage decay rate of long-term constant current discharge at 200 h was 1.2%. The microscopic section analysis indicated that there was little interface stratification phenomenon. LSC-30% SZM composite material had good long-term thermal stability and structural stability.

IntroductionA high-nickel ternary cathode material of LiNi0.8Co0.1Mn0.1O2 (NCM811) has a high energy density. However, this material suffers from interfacial/structural instability, leading to a loss of more than 10% of its capacity during cycling. Cathode materials can be surface coated to improve their overall performance, in which nano-powder of zirconium dioxide can be used as a coating material to effectively improve the structural stability of high nickel ternary materials. However, the method for zirconia preparation has some disadvantages like complicated process flow, high production cost, and easy particle agglomeration. Flame spray pyrolysis (FSP) is simple in operation, fast in reaction speed, high in product quality, and easy to scale up production. In this paper, a variety of metal-based nanomaterials with small particle sizes and well-dispersity were prepared via FSP. The effect of process parameters (i.e., precursor solution concentration, feed rate and hydrogen flow rate) on the particle size, morphology and specific surface area of the powder was investigated. The synthesis process parameters of ZrO2 were optimized, and the effect of optimal parameters on the coating modification of high-nickel ternary cathode materials was analyzed.MethodsA certain amount of ZrCl4 was weighed and dissolved in ethanol, and stirred at 40 ℃ to dissolve it completely and formulate precursor solutions at different concentrations (i.e., 0.16, 0.50, and 1.00 mol/L). At different hydrogen flow rates (3.3, 6.6, and 9.9 L/min) and feed rates (3, 5, and 7 mL/min), the precursor solutions with different concentrations were injected into a flame spray pyrolysis unit by a syringe pump. Finally, ZrO2 powder was collected through a filter. The physical and chemical properties of the powders were determined by Brunauer-Emmett-Teller (BET) surface area analysis, transmission electron microscopy (TEM), X-ray diffraction (XRD), and laser particle size (DLS) analysis.Results and discussionThe specific surface area of ZrO2 is inversely proportional to the feed rate, and the particle size of ZrO2 is directly proportional to the feed rate. The specific surface area of ZrO2 powder decreases from 54.89 m2/g to 28.99 m2/g as the feed rate of precursor increases from 3 mL/min to 7 mL/min. Also, the distribution of particle size gradually becomes wider, and the average particle size obtained from the fitting increases from 7 nm to 18 nm. The specific surface area of ZrO2 is inversely proportional to the hydrogen flow rate, and the particle size of ZrO2 is directly proportional to the hydrogen flow rate. The uniformity of the particle size distribution of ZrO2 nanoparticles decreases, and the fitted average particle size gradually increases from 7 nm to 10 nm, while the specific surface area of the product decreases from 61.57 m2/g to 44.73 m2/g as the hydrogen flow rate increases from 3.3 L/min to 9.9 L/min.The specific surface area of ZrO2 is inversely proportional to the precursor concentration, and the particle size of ZrO2 is proportional to the precursor concentration. The specific surface area of ZrO2 gradually decreases from 71.58 m2/g to 45.29 m2/g, the particle size gradually increases from 6 nm to 11 nm, meanwhile, and the large-size particles increases significantly as the precursor concentration increases from 0.16 mol/L to 1.00 mol/L.ConclusionsZirconium dioxide nanoparticles with a high specific surface area, a small particle size and a good dispersibility could be prepared via flame spray pyrolysis with ZrCl4 as a precursor, ethanol as a solvent at a feed rate of 3 mL/min, a hydrogen flow rate of 3.3 L/min, and the concentration of precursor solution of 0.16 mol/L. The feed rate, hydrogen flow rate and precursor concentration all affected the particle size and specific surface area of the product, and the effect of the feed rate was dominant. A lower feed rate was favorable for the synthesis of ZrO2 particles with a smaller particle size and a larger specific surface area. A high hydrogen flow rate exacerbated the agglomeration of ZrO2 particles and reduced their specific surface area. A high concentration of precursor solution induced the generation of more large-sized particles, resulting in a decrease in the specific surface area. Zirconia obtained under the optimal process conditions of 0.2% (mass fraction) coating on the surface of NCM811 cathode material could increase the capacity retention of the battery by 14% at 1 C and 2.7-4.3 V. Nano-sized powder of zirconium dioxide was prepared via flame spray pyrolysis at suitable process parameters, providing a promising method for the preparation of zirconium dioxide powder with a small particle size and a high specific surface. In addition, the application in anode capping could also improve the comprehensive performance of the battery.

IntroductionAs a core element of the sensor, the piezoelectric constant and dielectric constant of piezoelectric materials determine the sensitivity of the sensor. Piezoelectric materials with a high performance and a high stability are urgently needed. The electrical properties of perovskite ferroelectrics are closely related to the crystal orientation. Growing single crystals is thus an effective way to improve the electrical properties of perovskite ferroelectrics. However, the practical application of single crystals is limited due to their relatively high cost, low trigonal-rhombohedral phase transition temperature, and insufficient composition uniformity in inconsistent melting. To solve the above-mentioned single crystal application problems, the template grain growth (TGG) method for preparing textured ceramics is considered as one of the most promising methods.In this paper, a PSN-PMN-PT ternary solid solution piezoelectric material was prepared, and the [001] oriented growth of ceramics by TGG method was analyzed. In addition, the influence of template content on the phase structure, micromorphology, electrical properties and temperature stability of textured ceramics was also discussed.MethodsOxide raw materials were mixed in stoichiometric ratios and pre-sintered at 750 ℃ for 2 h to form a pure perovskite structure. The [001] oriented BaTiO3(BT) microcrystals were added as templates into a uniform slurry with 0.29Pb(Sc1/2Nb1/2)O3-0.39Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 matrix powder, solvent, dispersant, plasticizer, and binder, and then ground in a ball mill. The BT templates with x of 0, 1%, 2%, 3%, and 4% were added into the slurry. Afterwards, the slurry was cast via controlling the height of the scraper and the speed of the substrate. The dried raw embryo tapes were cut, stacked, and kept at 550 ℃ for 2 h to remove organics. Finally, the samples were sintered at 1 270 ℃ for 9 h.The phase structure of the random and textured ceramics was determined by X-ray diffraction. The microstructure of the ceramics was characterized by scanning electron microscopy. To measure the electrical properties, the samples were coated with a silver paste and sintered at 550 ℃ for 40 min to form electrodes and then polarized in silicone oil at 25 kV/cm for 15 min. The piezoelectric coefficient d33 was measured using a model ZJ-6A quasi-static d33 tester. The temperature dependence of the dielectric constant r and dielectric loss tan was determined by a model E4980A LCR meter. The polarization electric field (P-E) curve and the strain electric field (S-E) curve were analyzed by a model TF Analyzer 2000E ferroelectric test system. For the determination of temperature stability, the samples were annealed at high temperatures for 30 min and then tested for d33 at room temperature.Results and discussionFrom the XRD analysis, BaTiO3 as a template can effectively improve the [001] orientation of PSN-PMN-PT ceramics and achieve a high degree of [001] preferred orientation growth. The F001 of all the textured ceramics is 97%-99%, among which the F001 of 3%(volume fraction) BT-PSN-PMN-PT textured ceramics is 98.6%. From the scanning of the textured ceramics, the template exists stably and is well arranged in the matrix ceramics, which is a fundamental reason why the textured ceramics have a high texture degree. The piezoelectric constant of 3% BT textured PSN-PMN-PT ceramics (816 pC/N) is greater than that of random PSN-PMN-PT ceramics (402 pC/N). Based on the analysis of the dielectric loss at room temperature, the dielectric loss of the textured ceramics reduces to 0.008, which is lower than that of randomly oriented ceramics and most soft piezoelectric ceramics (i.e., >0.020). The high d33, Spositive, Stotal, and d33* of textured ceramics are all related to the "4R" domain engineering state. Only a transition from tetragonal to cubic phase occurs in the textured ceramics, indicating that the textured ceramics have a good temperature stability. The results of annealed piezoelectric constant test show that the d33 change of 3% BT-PSN-PMN-PT ceramics at 30-160 ℃ is only 12%, further proving a good temperature stability of textured ceramics.ConclusionsThe [001] oriented texture PSN-PMN-PT ceramic with a texture degree F001 of 98.6% was synthesized by the TGG method, obtaining the high piezoelectric properties (i.e., d33 = 816 pC/N, d33* = 1 080 pm/V) and high Curie temperature (i.e., TC = 185 ℃). This enhanced piezoelectric response was attributed to the grain orientation characteristics. Furthermore, the 3% BT-PSN-PMN-PT texture ceramic exhibited an improved temperature stability, compared with previously reported lead-based ceramics with the similar piezoelectric constants. These results showed that the textured PSN-PMN-PT ceramics had high piezoelectric properties and good temperature stability, having the application prospects of textured ceramics in electromechanical devices.

IntroductionZnO varistor ceramics have some advantages of high nonlinear coefficient, low leakage current and low production cost, which are widely used in the protection of power systems and electronic equipment. With the development of electronic devices in the direction of better performance and miniaturization, the electrical performance of ZnO varistor ceramics needs to be further improved. It is thus necessary to prepare ZnO varistor ceramics with a high breakdown voltage and a uniform fine grain size. In common ZnO-Bi2O3-Sb2O3 varistor ceramics, Bi2O3 and Sb2O3 are the two most important elements, and Bi2O3 and Sb2O3 doped in a certain proportion play an important role in the optimization of electrical properties and microstructure regulation of ZnO varistor ceramics. The melting point of Bi2O3 is 825 ℃ and the melting point of Sb2O3 is 655 ℃ in the high-temperature sintering process volatile, resulting in the loss of components and the increased porosity, structural uniformity, deterioration of electrical properties of ZnO varistor ceramics. Therefore, reducing the sintering temperature of ZnO varistor ceramics (i.e., below 1 000 ℃) is a necessity, which is expected to provide the experimental basis for the realization of pure silver internal electrode co-firing of multi-layer chip ZnO varistor elements.MethodsZnO-Bi2O3 based varistor ceramics with a Bi:Sb molar ratio of 4:1 were prepared by a traditional electronic ceramics process. ZnO powder was mixed with Bi2O3, Sb2O3 powder, agate ball and deionized water in a certain proportion and then the mixed slurry was ground in a planetary ball mill. The ground mixed slurry was dried at 110 ℃, then ground and passed through the 100 mesh screen. 5% polyvinyl alcohol (PVA) solution was used as a binder for granulation, and then pressed into green billets with a diameter of 13 mm and a thickness of 2 mm. The green billet was firstly discharged in a muffle furnace at a rate of 2 ℃/min to 500 ℃, and then sintered in a sintering furnace at different temperatures (i.e., 880, 900, 920, 950, and 980 ℃, respectively). The obtained sample was polished and silvered. The final sample size was 10 mm×1 mm. The phase was analyzed by X-ray powder diffraction (XRD). The backscattering mode of field emission scanning electron microscopy (FESEM) was used to characterize the surface morphology of the samples, and the distribution of elements on the surface of the samples was analyzed by X-ray energy spectroscopy (EDS). The electrical properties of the samples were measured by a varistor tester, and the grain boundary characteristic parameters were measured by wideband dielectric impedance spectrometry.Results and discussionIn this experiment, 800 ℃ is selected as a turning point. When the temperature is higher than 800 ℃, the sample is heated at a lower rate and the sintering temperature is below 1 000 ℃, obtaining fully developed ZnO grains. The grain size of the two groups of samples is small and evenly distributed. The molar ratio of Bi2O3 and Sb2O3 of the two groups of samples is 4:1. When the sintering temperature is 920 ℃ or above, the breakdown voltage of the two groups of samples is similar. At the Bi2O3:Sb2O3 molar ratio of 4:1, the breakdown voltage of the sample is more related to the Bi2O3:Sb2O3 molar ratio rather than to the total doping amount of Bi2O3 and Sb2O3. This means that the breakdown voltage regulation can be achieved with less doping of Bi2O3 and Sb2O3. The high breakdown voltage ZnO varistor ceramics can be prepared by sintering at a low temperature, and the breakdown voltage of doped with the same proportion of Bi2O3 and Sb2O3 is similar in the less addition of Bi2O3 and Sb2O3, thus providing an effective way for the low-carbon preparation of ZnO varistor ceramics.ConclusionsLow-temperature sintering could effectively inhibit the growth of ZnO grains. The breakdown voltage of the two groups of samples was high, ranging from 599-1 154 V/mm. ZnO grains of all the samples were fully developed, and the average size of ZnO grains of the samples was 2.7-3.6 m. In addition, the grain size distribution and microstructure of the sample were more uniform. The optimum comprehensive electrical performance of the sample sintered at 900 ℃ was obtained (i.e., the breakdown voltage of 1 154 V/mm, the nonlinear coefficient of 13.7, and the leakage current of 39 A).

IntroductionTransparent ceramics are a kind of ceramic materials integrating structural and functional properties. A variety of ceramic materials such as oxides, nitrides, oxynitrides and fluorides are developed. Among them, spinel transparent ceramics are suitable for transparent armor, mid-wave infrared windows and fairings due to their low density, high hardness, high strength, high temperature stability, especially the wide transmittance range and high transmittance from near ultraviolet to mid-infrared. The development of transparent ceramics becomes a hot research spot. The design and performance optimization of new transparent ceramics are mainly realized through composition design because transparent ceramics have some strict requirements for microstructure and phase purity.In recent years, the novel properties of the high-entropy effect in materials provide an approach for the development of materials. In this paper, a spinel-type (Li,Mg,Zn,Al,Ga)3O4 (LMAZGO) compound was designed with MgAl2O4, MgGa2O4, ZnAl2O4, ZnGa2O4, LiGa5O8 and LiAl5O8 as components. The sintering process of LMAZGO high-entropy transparent ceramic materials was investigated, and the microstructure of transparent ceramics was optimized. In addition, the optical transmittance and mechanical properties of LMAZGO high-entropy transparent ceramic materials were also analyzed.MethodsCommercial powders of Li2CO3, MgO, -Al2O3, ZnO, and Ga2O3 (purity of 99.99%) were used as raw materials, and the proportion of each raw material was calculated according to the elemental composition of LMAZGO. After mixing evenly, the high-entropy ceramic was synthesized in air by a high-temperature solid-state reaction method, and then ground to the target powder. LMAZGO blanks with a diameter of 20 mm were prepared via axial compression combined with cold isostatic pressing. Subsequently, the transparent ceramic pre-sintered body was prepared via pressureless pre-sintering in a muffle furnace, and the residual pores were further removed by hot isostatic post-treatment. The prepared LMAZGO transparent ceramics were ground and polished on the both sides for further characterization.The phases of LMAZGO powders and bulk were characterized by a model X'Pert PRO X-ray diffractometer under Cu target at 40 kV and 40 mA. The density of ceramics was measured based on the Archimedes drainage principle. The thermal behavior of the blank was determined by a model DIL402SE thermodilatometer at different temperatures from room temperature to 1 500 ℃ at a heating rate of 10 ℃/min. The microstructure of powders and ceramics was characterized by a model S-3 400 scanning electron microscope, and the average grain size of the grains was determined by a linear intercept method. The linear transmission spectra of the samples were measured by a model Lambda 750S UV-NIR spectrophotometer and a model 6 700 Fourier transform infrared absorption spectrometer. The Vickers hardness was measured by a model 430SVD hardness tester. The flexural strength of high-entropy transparent ceramics was determined based on a three-point flexure test by a model MTS810 universal materials testing machine. The elastic properties of transparent ceramics were determined by a model MK7 elastic modulus meter.Results and discussionThe spinel LMAZGO compounds were synthesized at 1 100 ℃ for 2 h. Based on the XRD and SEM results, the synthesized powder has a spinel phase, uniform and fine grains and little agglomeration, and the average grain size is 290 nm. The configuration entropy of LMAZGO is 3.18R, calculated by the sublattice model, which has a high crystal structure stability.The results of thermal expansion show that the shrinkage densification rate of LMAZGO ceramic blank is further accelerated from 1 200 ℃, and the maximum densification rate of LMAZGO ceramic blank occurs at 1 380 ℃ in the middle stage of sintering. According to the thermal expansion analysis of LMAZGO, 1 300, 1 350, 1 400 and 1 450 ℃ were selected as the pressureless pre-firing temperatures, and the pre-firing process of the green body was optimized. The optical transmittance of the transparent ceramic samples obtained by subsequent HIP sintering firstly increases and then decreases with the increase of pre-firing temperature. Based on the results of the sintering curve, the pressureless sintering process of LMAZGO transparent ceramics can be optimized at a sintering temperature of 1 400 ℃ for holding time of 6 h. The average grain size of the prepared LMAZGO transparent ceramic pre-burned body is 1.81 m, and the density is 98.7%. The superior optical transparency is obtained after hot isostatic sintering (sintering conditions: argon atmosphere, incubation at 1 550 ℃for 5 h), and there is no abnormal growth of grain size.The optical transmittance range of the obtained high-entropy spinel LMAZGO transparent ceramics is 0.23-7.35 m, the maximum linear transmittance is 85.2%, the Vickers hardness (HV1) is 12.7 GPa, the Young modulus is 265 GPa, and the flexural strength is (332±30) MPa.ConclusionsA spinel LMAZGO high-entropy compound with a configuration entropy of 3.18R and a high crystal structure stability was synthesized. The preparation process of LMAZGO high-entropy transparent ceramics was systematically optimized via pressureless sintering combined with hot isostatic post-treatment, and the prepared LMAZGO transparent ceramics had an excellent optical transparency, with an optical transmittance range of 0.23-7.35 m, the maximum linear transmittance of 85.2%, the Vickers hardness (HV1) of 12.7 GPa, the Young modulus of 265 GPa, and the flexural strength of (332±30) MPa. The results showed that the high-entropy spinel LMAZGO transparent ceramic material exhibited broad spectral transparency and excellent mechanical properties, having a promising application in the field of mid-infrared transparent window. This study provided some ideas for the development of new transparent ceramics.

IntroductionZirconium dioxide (ZrO2) ceramics have superior properties such as high hardness, high thermal expansion coefficient and low thermal conductivity, which are widely used in high-temperature components like aircraft engines, gas turbines and combustion power plants. However, ZrO2 ceramics in the use can be CMAS (i.e., CaO, MgO, Al2O3 and SiO2) and other small particles corrosion, resulting in the decrease of ZrO2 ceramics performance. The problem of CMAS corrosion becomes a challenge. The technologies used to protect the CMAS corrosion of ZrO2 ceramics are the use of a non-permeable protective layer, the use of a top layer of laser glazing treatment, a thermal spray nanostructure coating and a rare-earth co-doped coating. Although these methods have a certain anti-CMAS corrosion effect, they still have some shortcomings of complex preparation process and high cost. To further investigate and improve the high-temperature corrosion resistance of ZrO2 ceramics, Al2O3-ZrO2 prestressed ceramics were prepared with Al2O3 as a coating and ZrO2 as a matrix. The flexural strength at different temperatures and the behavior of CMAS penetration and element diffusion were investigated via comparative analysis of Al2O3-ZrO2 prestressed ceramics and ZrO2 ceramics. The effect of prestressed enhancement, the CMAS penetration and the corrosion mechanism of Al2O3-ZrO2 prestressed ceramics against CMAS at a high temperature were analyzed.MethodsThe thermal corrosion experiment was carried out in a high-temperature sintering furnace. The samples of ZrO2 ceramics and Al2O3-ZrO2 prestressed ceramics with CMAS powder were heated at different temperatures (i.e., 1 200, 1 250, 1 300, 1 350 ℃ and 1 400 ℃), respectively, for 10 h, and then cooled in the furnace. In the analysis of corrosion resistance of ZrO2 ceramics and Al2O3-ZrO2 prestressed ceramics, the mechanical properties of ZrO2 ceramics and Al2O3-ZrO2 prestressed ceramics before and after corrosion were tested by a model C45 machine controlled electronic universal testing machine. During the test, the span of 30 mm and the loading rate of 0.5 mm /min were set, and the data of 5 samples in each group were collected to obtain the three-point flexural strength of the samples affected by corrosion. The corrosion and morphology characteristics of the sample in a macro-scale were determined by a model KEYENCE VHX-970F optical microscope. The depth of CMAS corrosion of ZrO2 ceramics and the change of the state of Al2O3 coating at different corrosion temperatures were analyzed via adjusting different magnifications. The microstructure of the sample was characterized by a model QUANTA 250FEG scanning electron microscope in order to further analyze the corrosion mechanism of CMAS. The morphology and distribution area of corrosion products generated by Al2O3-ZrO2 prestressed ceramics were determined, and the corrosion mode of ZrO2 ceramics was analyzed. Also, the element composition ratio and distribution of the sample cross-section were analyzed by an EDS scanning system. The phase of Al2O3 ceramic particles corroded by CMAS was analyzed by a model Rigaku SmartLab SE X-ray diffractometer.Results and discussionBefore corrosion, the flexural strength of Al2O3-ZrO2 prestressed ceramics reaches (1 038±41) MPa, which is 35.6% higher than that of ZrO2 ceramics. After CMAS corrosion, the flexural strength of Al2O3-ZrO2 prestressed ceramics decreases with the increase of corrosion temperature, but it is still higher than that of ZrO2 ceramics. This is because the residual stress formed during the cooling process enhances the strength of ZrO2 ceramics after sintering Al2O3 coating and ZrO2 ceramics.In the high-temperature service environment, the EDS analysis results show that CMAS exists an element diffusion in ZrO2 ceramics. Based on the analysis of the cross section of ZrO2 ceramics after corrosion, the corrosion mode of ZrO2 ceramics is a grain boundary corrosion. The penetration depth of CMAS gradually increases from 24 m to 143 m with the increase of corrosion temperature, thus bringing a serious harm to ZrO2 ceramic components. Al2O3 coating in Al2O3-ZrO2 prestressed ceramics effectively blocks a direct contact between CMAS and ZrO2 ceramics, avoids the diffusion of elements Ca, Mg, Al and Si in CMAS to ZrO2 ceramics, and effectively protects the microstructure of ZrO2 ceramics. The results indicate that Al2O3 coating can improve the strength and CMAS corrosion resistance of ZrO2 ceramics.Based on the analysis of the corroded section of Al2O3-ZrO2 prestressed ceramics as well as the analysis of EDS and XRD results, Al2O3 coating reacts with CMAS at a high temperature. The high melting point compounds calc feldspar (CaAl2Si2O8), spinel (MgAl2O4) and a small amount of calc aluminite (Ca2Al2SiO7) are generated. The diffusion channel is clogged and the penetration depth of CMAS is greatly reduced due to these substances with a high melting point and a good chemical stability as well as the increased viscosity of molten CMAS, thus having a positive effect on preventing CMAS corrosion. In addition, the compressive stress in the Al2O3 coating can also inhibit the expansion of cracks, prevent the deep oxidation effect entering through cracks, and improve the service life of ZrO2 ceramic components in CMAS corrosion environment.ConclusionsThe mechanism of resistance of Al2O3-ZrO2 prestressed ceramics to CMAS corrosion at a high temperature was investigated, and ZrO2 ceramics were taken as a reference sample. The results showed that in Al2O3-ZrO2 prestressed ceramics, Al2O3 coating with compressive stress could effectively improve the flexural strength of ZrO2 ceramics, and help to slow down the action of CMAS corrosion, thus having the superior resistance to CMAS corrosion. This was mainly attributed to that the compressive stress of the surface layer of the material could improve the strength and toughness of the ceramic, effectively inhibiting the crack propagation; and at high temperatures, Al2O3 coating in Al2O3-ZrO2 prestressed ceramics could react with CMAS, producing a high melting point calcium feldspar, spinel and a small amount of calcium-aluminum feldspar at the interface, and forming a stable and dense reaction layer, which inhibited the continuous penetration of CMAS melt.

IntroductionEnvironmental protection and sustainable development have attracted recent attention. Especially, the lead-free reproduction of ancient ceramic glazes with rich historical and cultural values becomes a common concern for both academia and industry. Jizhou kiln is one of the well-preserved ancient kiln sites in China, and is one of the famous folk firing kilns during the Song and Yuan dynasties. Jizhou kiln green glaze is colored in addition to the chemical composition as well as coloring mechanism. The sintering temperature is also one of the key factors influencing the ceramic glaze color, microstructure, and physical properties. However, the current research on the sintering process of copper-green glaze is still insufficient. The lead-free preparation of green glaze from the Jizhou kiln was achieved using the conventional ceramic raw materials in the Jingdezhen area and Cu2+ coloring. The influence of sintering temperature on the formation of glaze color, microstructure, and color-presenting mechanism of lead-free green glazed ceramics, as well as the mechanism of the effect of sintering temperature on the glaze's physical properties were systematically investigated. This study provides a scientific guidance and a technical support for the lead-free reproduction of green-glazed porcelain of Jizhou kiln to further promote the protection and inheritance of traditional ceramic culture, and to provide an important reference basis for the sintering behavior of other types of glazes.MethodsA base glaze was prepared using 23% (in mass fraction, hereinafter the same) wollastonite, 9% talc, 20% feldspar, 26% quartz, 10% kaolin, 8% smelter's ash, and 4% zinc oxide (ZnO) from mineral raw materials originating in the Jingdezhen area of Jiangxi Province, China, with 4% CuO as a coloring agent. ZnO (99% analytically pure), CuO (99% analytically pure), and glazes were applied to blanks by an impregnation method (blanks were already 900 ℃ plain firing), and the impregnation time was 20 s. Subsequently, the samples were put into a box-type resistance furnace and sintered in air. Six lead-free green glaze samples sintered at different temperatures (i.e., 1 250, 1 260, 1 270, 1 280, 1 290 ℃ and 1 300 ℃) were obtained.The chemical composition of the mineral raw materials was analyzed by energy-dispersive X-ray fluorescence spectrometry. The phase structure of the sample glazes was analyzed by X-ray diffraction and micro-confocal laser Raman spectrometry. The optical photography of the sample surfaces was carried out using a super depth of field microscope. Scanning electron microscopy was used to observe the microstructure of the samples after etching with 5% HF solution for 20 s as well as the fractional phase structure in the glaze. The chromaticity values and reflectance spectra of the glazes were determined by benchtop spectrophotometry as well as a UV-Vis-IR reflectance spectrophotometry. The elemental valence states were analyzed by X-ray photoelectron spectroscopy.Results and discussionThe optical analysis indicates that the glaze surface changes from greenish blue to light green and green with the increase of sintering temperature, and reaches the optimum effect of glaze surface at 1 280 ℃, at which time the glaze surface of the samples is smooth and uniformly colored, with a strong sense of glassy feeling. The results of XRD patterns and Raman spectra show that the glaze layer is composed of a glassy phase and trace SiO2 crystals, and the phase of glaze layer is not a main factor of color presentation. The structural analysis shows that the glaze layer is not a homogeneous material, it is composed of two kinds of phase separation structures, i.e., round and worm-like. The phase separation structure shrinks and grows further to form a large-size round phase separation droplet, and the incident light undergoes Mie scattering with the increase of sintering temperature and the gradual decrease of high-temperature viscosity of the glaze layer, which produces a white opalescence and deepens the glaze surface coloration. Lead-free green glaze is mainly due to the effect of Cu2+ color presentation. As the sintering temperature increases, the Cu2+ concentration gradually increases, and copper ions and six bridging oxygen (Ob) form a six-coordinated structure, mainly presented in green. The coloration of lead-free green glaze is a result of the synergistic coupling of the phase separation structure and the valence state of copper ions, and the lead-free green glaze with a stable coloration and a good glaze quality can be prepared via optimizing the sintering temperature.Conclusions The viscosity of the glaze layer gradually decreased, and the glaze surface showed greenish blue, light green, and green in turn, and the optimum effect of the glaze surface reached at 1 280 ℃ as the sintering temperature increased. The glaze was mainly dominated by the green coloration of Cu2+, and the molar ratio of Cu+/Cu2+ gradually increased, while the glaze changed from blue-green to lime green as the sintering temperature increased The round and worm-like phase-separated structures both appeared in the samples, and the phase-separated structures contracted at higher sintering temperatures and grew further into large-sized round phase-separated droplets, with Mie scattering occurring to produce a white opalescence that deepened the glaze coloration; The color-presentation mechanism of the lead-free green glaze was a result of the synergistic coupling of copper ion valence and phase-separated structures.

IntroductionThe purity of the Ni-based superalloy is directly related to the alloy-crucible interaction during induction melting. It is thus of great significance to clarify the interaction mechanism for the achievement of preparing the high-purity superalloys. In this study, pure Ni and Ni-based superalloys were melted in MgO crucibles, respectively. The phase composition, microstructure of the crucible and the oxygen concentration of the metals were analyzed by scanning electron microscopy, X-ray diffractometry and O/N analyzer. The interaction between the metals and the crucibles were investigated, and the interaction mechanism was elucidated. The results indicate that after melting pure Ni in MgO crucible, pure Ni melt exhibits a good wettability to the crucible, but little interaction occurs. However, a significant interaction between the superalloy melt and MgO crucible occurs. This reaction primarily involves the dissolution and decomposition of MgO in the alloy melt. The decomposed element O reacts with element Al to form Al2O3 products, which can float to the surface of the superalloy. Also, some Al2O3 can further react with MgO crucible matrix to generate MgAl2O4 product, which can attach to the inner surface of the crucible, and float into the slag, respectively. A slag layer with the thickness of approximately 80 m composed of Al2O3, MgAl2O4, and a portion of the alloy can be formed on the surface of the alloy.MethodsIn this study, an industrial grade MgO (purity>99.5%) was used as a raw material. The MgO powder was mixed and ground in ethanol in a concrete mixer with yttria stabilized zirconia (YSZ) balls at a speed of 300 r/min. The mass ratio of powders, YSZ balls and ethanol were 3.0 : 5.0 : 0.8. The ground powder was then dried in an oven for 12 h. The MgO crucible green body was fabricated via cold isostatic pressing at 150 MPa for 3 min. Subsequently, the green body was sintered in a high-temperature silicon molybdenum rod sintering furnace at 1 750 ℃ for 6 h. The outer diameter, inner diameter, and height of the sintered crucible are 60, 50 and 70 mm, respectively.An electrolytic pure Ni and DD419 alloy was used as an experimental metal. Pure Ni of 100 g was ground and acid pickled. The DD419 alloy was cut into 2 cm×2 cm×4 cm block caret, and its weight was 120 g. After grinding and acid pickling, the alloy was used as an experimental metal. The sintered MgO crucible was placed in a coil of a vacuum induction melting furnace, and filled with fused MgO sand around the crucible. It could prevent the short circuit of the induction coil due to the leakage of the molten metal. The experimental metal was inserted into the crucible, and the furnace was evacuated with a mechanical pump and a molecular pump to approximately 1×10-2 Pa. The furnace was backfilled with high-purity argon to 0.06 MPa, and repeated for three times in order to eliminate the influence of the residual oxygen. The melting experiment was conducted in high vacuum. The metal temperature was raised slowly until the appearance of the liquid at the bottom of the metal. The temperature of the molten metal rapidly increased to 1 550 ℃, and hold at this temperature for 20 min. Finally, the molten melts were cooled in the crucibles to obtain the corresponding samples. After melting, the samples were cut via wire-electrode cutting and polished for the coming use.Results and discussionThe surface of pure Ni after melting in the MgO crucible is smooth without the appearance of the impurities. However, the surface of the superalloy has a black slag layer with a thickness of 80 m, indicating that the slag is formed during the interaction between the alloy and the crucible. The surface of the slag can form a wrinkled shape due to the difference in the cooling rate between the slag and the alloy melt. No corrosion phenomenon occurs on the surface of the crucible after melting pure Ni. However, some Ni melt is residual on the surface of the crucible due to the wettability. In contrast, after melting the alloy in the crucible, the grain morphology and grain boundaries on the surface of the crucible disappear, indicating that the surface of the crucible is corroded by the alloy melt, thus leading to the generation of MgAl2O4 products. The slag primarily consists of Al2O3 and MgAl2O4 as well as some residual alloy melt, respectively. The generation of Al2O3 and MgAl2O4 products is attributed to the reaction at the melt-crucible interface. These products can float into the surface of the alloy melts under the electromagnetic stirring because Al2O3 and MgAl2O4 products have a lower density than that of the alloy melts. The thermodynamic stability for Al2O3, MgO, Cr2O3 and NiO indicates that element Al in the alloy has an intense affinity for element O, leading to the dissolution of MgO refractory and the oxygen contamination of the alloy melt. The uneven distribution of MgAl2O4 in both the inner surface of the crucible and the slag exhibits that the interaction and electromagnetic stirring significantly affect the formation of the slag.ConclusionsPure Ni did not react with MgO crucible. However, DD419 alloy could exhibit a significant interaction with the crucible, resulting in the alloy contamination and the formation of a slag layer. The thickness of the slag layer was 80 m, and it consisted of Al2O3, MgAl2O4 and some alloy. In addition, Al2O3 and MgAl2O4 were the interaction products between the alloy melt and the crucible. The dissolution of MgO refractory could result in the release of elements Mg and O, respectively. Element Al reacted with element O to generate Al2O3 products. A portion of the products could float, and another part could react with MgO matrix on the inner wall of the crucible to form MgAl2O4. Meanwhile, some of the generated MgAl2O4 was adhered to the inner wall of the crucible, and another portion was floated into the slag layer.

IntroductionCopper is a kind of strategic resource to support low carbon transition and economic development. The main sources of raw materials for copper smelting are copper concentrate and recycled copper resources. The existing researches on the damage mechanism of refractories that are used in copper smelting mainly focus on the smelting furnace, converter, anode furnace and other furnace types for copper concentrate pyrometallurgical copper refining process. However, there is little research on the damage mechanism of refractory, used in recycled copper refining furnace. Nerin-Gutai-Lu (NGL) has a great significance for the recycled of waste copper and alleviates the shortage of copper concentrate resources. The copper smelting process is characterized by intense chemical reactions, fast speed, high heat intensity and complex furnace atmosphere (i.e., O2 and SO2) in the furnace, which can easily damage the furnace lining refractories. The magnesia-chrome refractories have extensive applications in coppers smelting because of its excellent slag corrosion resistance. In this study, the damage mechanism of magnesia-chrome brick used in NGL recycled copper refining furnace was investigated. The macroscopic morphology, phase composition, and microstructure of the used magnesia-chrome brick were analyzed.MethodsThe sample was selected from magnesia-chrome brick used in the NGL furnace of a copper plant in Jiangxi Province, China, and their corrosion behavior and mechanism were analyzed. The residual brick was horizontally cut and divided into different areas according to the degree of corrosion, which were the reaction layer, infiltrated zone and the similar original brick zone. The chemical and phase composition of different areas of the residual brick were characterized by X-ray fluorescence (XRF) and X-ray diffraction (XRD), and the bulk density and apparent porosity were measured based on the Archimedes principle using water as a medium. The degradation on mechanism and microstructure of the sample were analyzed by scanning electron microscopy (SEM), and the composition of the sample was identified by attached energy dispersive spectrometry (EDS).Results and discussionThe magnesia-chrome brick is destroyed through chemical damage by NGL slag and copper melt due to the forsterite phase and the dissolution of periclase grains. The crude copper and copper oxides exhibit an intense permeability due to the penetration of slag (containing gas) and dissolution of periclase particles. With a large number of crude copper and copper oxides melting, the direct combination of fused magnesia-chrome, and periclase is destroyed. This metal melt can penetrate into the internal structure of magnesia-chrome brick and reach over 260 mm, which distributes in the matrix around the chromite particles and the grain boundaries, and pores or cracks of magnesia aggregate. Subsequently, SO2 and O2 are diffused to the similar original brick layer on the cold face of the residual brick due to the dissociation of monticellite at the grain boundary. SO2/SO3 in gas-phase medium reacts with CaO in brick to form CaSO4. The XRD patterns indicate that the main component of the reaction layer on the cold face of the residual brick is CaSO4 phase. The related reaction under the gas diffusion of SO2-O2 can cause a volume expansion, leading to the structural looseness and exacerbating the melting corrosion of refractories.ConclusionsThe diffusion of metal elements in NGL refining slag, i.e., ferrum, nickel and zinc, led to the interaction between slag and periclase grains, resulting in the formation of forsterite (containing Fe) and (Mg, Fe, Ni)O solid solutions, which reacted with chromite to form (Mg, Fe, Ni)(Cr, Al, Fe)2O4 multiphase spinel. The reasons of chemical damage in magnesia-chrome refractories included the formation of forsterite phase and the dissolution of periclase grains. The corrosion of refractories by metal melts, such as Cu-CuxO, was mainly infiltrated. The gases containing SO2-O2 diffused into the similar original brick layer of the residual brick cold surface, generating low melting point alkaline earth metal sulfides mainly composed of MgSO4 and CaSO4. The relevant reactions under the action of SO2-O2 could cause a volume expansion, resulted in a loose structure of magnesia-chrome refractories and exacerbating the melting corrosion of refractories. The uniform microstructure of the fused magnesia-chrome block in the furnace lining was a mixture of magnesia-chrome spinel and periclase, which could effectively resist the infiltration of copper melt. In addition, the high-Fe spinel ring formed at the edge of chromite particles also enhanced the slag corrosion resistance.

IntroductionOrganic compound formaldehyde (HCHO) is a toxic volatile gas with an irritating odour, which is mainly derived from building materials, furniture and various adhesive coatings. Living in an environment containing formaldehyde gas for a long time can cause a series of hazards to human health, such as headaches, allergies, nausea, and even genetic mutations and leukaemia. It is thus necessary to design a gas sensor with a superior sensing performance to detect formaldehyde in real time. ABO3 type chalcogenide metal oxides have attracted much attention in sensor research, but their application is restricted due to the drawbacks such as poor sensitivity and high operating temperature. Many studies indicate that the modification of metal oxides with two-dimensional transition metal dihalides (2D TMDs) is one of the effective strategies to improve the gas sensing performance, and among the 2D TMDs materials, WS2 has aroused much interest in sensor research because of its high specific surface area, good thermal stability and excellent electron mobility. The gas sensor performance of metal oxides can be improved via the combination of WS2 to form a novel nanocomposite material. Hence, in this paper, a series of WS2-CdSnO3 composites with different mass ratios were prepared by an ultrasonic mixing method. The microstructure, crystal structure, and valence state structure of WS2-CdSnO3 composite material were characterized, and the gas sensing performance of the composite material was analyzed.MethodsCdSnO3 was prepared with Cd(NO3)2·4H2O (AR, Shanghai Sarn Chemical Technology, China) and SnCl4·5H2O (AR) (Shanghai Aladdin Reagent Co., China). CdSnO3 was ultrasonically compounded with WS2 (99.9%) to obtain WS2-CdSnO3 composites. The physical phase composition, surface morphology, elemental composition, valence and pore size distribution and specific surface area of the composites were characterized by a model SmartLab SE X-ray diffractometer (XRD, Rigaku Co.,), scanning electron microscope (SEM, Tescan Mira Lms), a model K-Alpha X-ray photoelectron spectrometer (XPS, Thermo Scientific Co., USA), and a model ASAP 2460 fully automated specific surface and porosity analyser (BET, Micromeritics Co., USA).For the determination of gas sensing performance of WS2-CdSnO3 composite material, WS2-CdSnO3 composite material was put into a mortar with 1-2 drops of terpineol, and thoroughly mixed and ground. The paste was evenly applied to the outer wall of the alumina ceramic tube with a small brush, and an Ni-Cr heating wire put through the ceramic tube and welded firmly to the hexagonal base. The operating temperature was indirectly controlled via adjusting the amount of power added to the two sections of the heating wire. The sensitivity to gases is expressed as a ratio of the stable resistance value of the gas sensing material in air to a stable resistance value in the gas tested. The gas sensing performance of the composites was investigated at a relative humidity of 55% (except for humidity tests).Results and discussionFrom the SEM images, the microcube appeared is CdSnO3, and the cubes structure is agglomerated on the surface of layered WS2. Based on the EDS analysis, there are five elements Cd, Sn, O, W and S in the composites. It is indicated that WS2-CdSnO3 can be prepared. According to the XPS analysis, there are more oxygen vacancies in the sample WSC-2, which can provide more sites for oxygen adsorption, so that more target gases participate in the reaction on the surface of the material. The introduction of WS2 increases the specific surface area of the sample WSC-2, and the material with a larger specific surface area has more gas adsorption active sites, thus improving the gas sensing performance of the sensor. The sample WSC-2 has the maximum response value of 15.7 for 0.01% formaldehyde at 140 ℃. To check the potential practical application of the prepared WSC-2 sensor, the selectivity and sensitivity of the sensor to different gases were investigated at 140 ℃. The results show that the sample WSC-2 has the optimum selectivity for 0.01% formaldehyde, and the response value is 4.2 times higher than that of CdSnO3.ConclusionsA series of WS2-CdSnO3 composites with different ratios were prepared via ultrasonic dispersion mixing. WS2-CdSnO3 had a large specific surface area, which was beneficial for gas adsorption and diffusion. The gas sensing performance of CdSnO3 with different ratios of WS2-CdSnO3 composites were investigated, and the results showed that 3.5% WS2-CdSnO3 had the optimum selectivity for formaldehyde and the superior gas sensing performance at 140 ℃, and the sensitivity for 0.01% formaldehyde was 4.2 times higher than that of CdSnO3 material, and the detection limit was 0.0001%. Therefore, the 3.5% WS2-CdSnO3 composite had potential applications in indoor formaldehyde detection. This study indicated that the modification of metal oxides by two-dimensional TMD could be one of the effective strategies to improve the gas sensing performance.

IntroductionGlass scintillators are commonly utilized for the detection of high-energy rays in various applications such as nuclear medicine imaging, industrial non-destructive testing, high-energy nuclear physics, safety inspection, and environmental monitoring. The scintillation glass with a high density is critical for improving the absorption and interception capabilities of rays and particles, thereby favoring the enhancement of the detector efficiency. This review represented recent development on high-density scintillation glass doped with rare-earth ions like Ce3+, Tb3+, and Eu3+. The critical parameters such as density, decay time, light output, and radiation resistance affecting the performance of the scintillation glass were discussed.Overall, the research delves into the scintillation mechanism of scintillation glass and presents an overview of the preparation process for high-density variants. The research progress on rare-earth ion-doped high-density scintillation glasses containing Ce3+, Tb3+, and Eu3+ ions was summarized, highlighting characteristics like density, light yield efficiency (LY), and decay time (). Some factors affecting these properties (i.e., substrate selection, energy transfer among ions, and reduction atmosphere) were also discussed.Ce3+-doped glass exhibits a nanosecond-level decay time. At the present, the density of Ce3+ doped scintillation glass can reach up to 6 g/cm3, but the light yield of this component is significantly low. The luminescence efficiency of the glass can be improved via introducing Gd2O3, which enhances the energy transfer between Gd3+ and Ce3+, while increasing the glass density. Also, incorporating fluoride into the oxide glass can lower the phonon energy, decrease the chances of non-radiative transition, and enhance the light yield. Ce3+ is prone to oxidation to non-luminescent Ce4+ during high-temperature melting. This oxidation process can be effectively controlled by using a reducing atmosphere (CO, H2) or adding reducing agents such as Si3N4, SiC, AlN, etc.The density of Tb3+-doped scintillation glass can reach 7.15 g/cm3, with a decay time in the millisecond range. Enhancing the luminescence efficiency of Tb3+ is achievable through the energy transfer between Gd3+-Tb3+, Ce3+-Tb3+, Dy3+-Tb3+, while the introduction of fluoride and reducing agents can effectively boost the light yield. Eu3+-doped scintillation glass can achieve a density of 6.60 g/cm3, and the addition of Gd3+ and Tb3+ can effectively enhance the emission intensity of Eu3+ ions.High density scintillating glasses doped with other rare-earth ions, such as Pr3+, Dy3+, Sm3+, and Er3+, can achieve a high density and exhibit distinct scintillation properties because of their unique energy level structures. However, the light yield of these glasses is too low to be used in practical applications.Summary and ProspectsA high-density and high-yield scintillation glass is needed. Despite the efforts of scientific research personnel, producing flashing glass with both a high density and a high yield remains a challenge. The main reason is that in high-density glass, although the introduction of heavy metal ions increases the density of the glass, it may lead to an increase in non-radiative transition channels, hindering the transfer of energy from the substrate to the luminescent center. Also, an increase in density can enhance the absorption and scattering of light, thereby reducing the effective amount of excitation light reaching the luminescent center. In addition, high density glass matrix may cause the local environment around rare-earth ions to become complex, affecting their energy level structure. To prepare scintillation glass that can meet both high-density and high light yield, several aspects can be considered. Firstly, the use of a reducing atmosphere such as H2 or CO and the addition of reducing agents like carbon powder can effectively control the valence of luminescent ions (i.e., Ce3+, Tb3+) during the melting process, preventing the formation of high valence ions. Using fluoride instead of partial oxides can reduce the melting point of the material and improve the light output via altering the band gap structure of the glass. The smaller volume of fluoride ions simultaneously contributes to the increased density of the glass. The utilization of energy transfer between ions can significantly enhance the light yield of glass. Some impurities and defects in glass can be minimized via utilizing high-purity raw materials and optimizing process steps such as melting and annealing. This can enhance the transparency and uniformity of the matrix, leading to a reduction in non-radiative transitions and an improvement in luminescence performance. It is possible to induce the formation of microcrystalline structures in glass via controlling the cooling rate or subsequent heat treatment. This optimization can enhance the energy transfer path, minimize scattering losses, and ultimately improve the luminescence efficiency.

With the development of electronic power devices towards high voltage, high current and high power density, they will generate more heat and bear greater thermal stress during the operation, which puts forward higher requirements for the heat dissipation ability and reliability of ceramic substrates used for devices. Conventional ceramic substrates such as alumina (i.e., low thermal conductivity, only 20-30 W·m&#87221·K&#87221) and aluminum nitride (i.e., poor mechanical property, such as bending strength of 300 MPa and fracture toughness of 3-4 MPa·m1/2) are difficult to meet the requirements of high power devices. Silicon nitride (Si3N4) ceramic becomes an ideal ceramic substrate for high power devices due to the high theoretical thermal conductivity and excellent mechanical properties. However, there is still a significant gap between the actual and theoretical values of thermal conductivity for Si3N4 ceramics, and the lattice oxygen content is a main affecting factor. Moreover, suitable sintering additives need to be added during the preparation of Si3N4 ceramics, and the microstructure (i.e., density, grain morphology, grain boundary phase content and distribution, and average thickness of grain boundary film) changes due to the introduction of sintering additives, which affects the thermal conductivity of Si3N4 ceramics. The microstructure evolution of Si3N4 ceramics is also closely related to the forming technology and sintering system. Therefore, the optimization of preparation processes of Si3N4 ceramics has a positive effect on its thermal conductivity improvement.In the review, the microstructures and thermal properties of Si3N4 ceramics were introduced. Some influencing factors of the thermal conductivity of Si3N4 ceramics were discussed and the related impact mechanism were illustrated. The -Si3N4 phase is metastable and transforms to -Si3N4 phase through the dissolution precipitation reaction at a high temperature. A lattice reconstruction also occurs at the same time. The -Si3N4 phase exhibits a high ideal thermal conductivity. The actual thermal conductivity of Si3N4 ceramics deteriorates gradually with increasing the lattice oxygen and grain boundary phase contents. Similarly, the continuous-distributed grain boundary phase is also harmful to the thermal conductivity of Si3N4 ceramics. These existed defects and microstructures lead to increased phonon scattering during the transmission process, which does not favor the thermal conductivity improvement. The large elongated -Si3N4 grains are beneficent to the thermal conductivity enhancement because of the decreased phonon scattering.The ways to improve the thermal conductivity of Si3N4 ceramics are to regulate their lattice oxygen and microstructures. In the review, the lattice oxygen regulation role, the microstructure evolution process and the thermal conductivity enhancement mechanism of Si3N4 ceramics could be elaborated from four aspects, i.e., raw material powder, sintering additives, sintering process and structural texture. The introduction of oxygen impurity content could be reduced with high purity silicon nitride powder as a raw material and the ball milling process optimization. And the microstructure and lattice oxygen content can be regulated via selecting rare-earth oxides with small ion radius and non-oxides as sintering additives and optimizing the sintering process (i.e., sintering temperature, soaking time, sintering atmosphere and so on), which are beneficial to promoting the thermal conductivity. In addition, the high thermal conductivity along the direction of Si3N4 grains orientation can be also obtained through a structural texture technology.The development status and challenges of high thermal conductive Si3N4 ceramics were discussed. The routes to realize the localization of high thermal conductive Si3N4 ceramics are to strengthen the source control of raw material production, thus improving the performance of production equipment and establishing the evaluation standard system of product performance.Summary and prospectsThe Si3N4 ceramic is an ideal substrate material for high power device, and its high thermal conductivity is essential. However, there is still a significant gap between the actual and theoretical values of the thermal conductivity of Si3N4 ceramics due to the influence of lattice oxygen impurity and microstructure composition. The approaches to obtain Si3N4 ceramics with a high thermal conductivity are to decrease the lattice oxygen content, reduce the grain boundary phase and obtain the double peak structure composed of fine grains and a high aspect ratio -Si3N4 grains through improving the purity of raw materials, selecting appropriate sintering aids and forming methods and optimizing the sintering system.To obtain high thermal conductive Si3N4 ceramics, a research on the raw material powder with a high purity and a low oxygen content should be strengthened. The high quality equipment for Si3N4 ceramics production should be developed through controlling the sintering and processing technology. The practical application research should be promoted continuously and the completed application closed loop should be formed among powder production companies, product manufacturing enterprises and users. The timely feedback and response about the problems discovered during this process should be provided quickly to improve the performance of high thermal conductive Si3N4 ceramic products.

This review represents the research progress on the synthesis of aluminium nitride powder via carbon thermal reduction (CRN) in terms of the related reaction mechanism, Al2O3-C interface improvement, high specific surface area precursor preparation and reaction atmosphere regulation. In this review, the mass loss of the reaction process and the mass transfer process of whisker growth were discussed based on the gas-solid reaction, and the phenomenon of the continuation of the morphology of the synthesized products and precursors as well as the mechanism of the formation of the transformed intermediate state compounds such as Al2O3 from Al—O—C and Al—C—N were analyzed according to the solid-solid reaction control mechanism. Moreover, the solid-solid reaction mechanism indicates that C atoms act as electron exchange mediators to promote N2 decomposition, and the reaction proceeds in a positive direction due to their ability to both gain and lose electrons. Recent research work on the CRN method for the synthesis of AlN powder was summarized.Summary and prospectsThese researches involve 1) the introduction of organic dispersants to increase the dispersion of C and Al2O3 particles, and the formation of a uniform binding interface between particles, 2) the introduction of a binder (i.e., an organic carbon source) on the uniform coating of Al2O3 particles and pyrolysis to form a uniform combination of cracked carbon and Al2O3 particles, 3) the decomposition of organic matter, combustion synthesis and sol-gel and foam-injection coagulation to obtain precursors with a porous structure and a high specific surface area and the uniform mixing of aluminium and carbon sources in a micron scale, thus reducing the conditions for complete reaction and synthesizes high-quality nanopowders of AlN and 4) increasing the substitution (flow) efficiency of the reaction atmosphere, reducing the partial pressure of CO and increasing the partial pressure of N2 to promote the positive synthesis reaction. According to the existing research, the future industrial development can be based on the combination of key process technology and key equipment. The continuous precursor manufacturing and continuous high-temperature synthesis equipment, especially continuous high-temperature synthesis equipment to eliminate differences in temperature zones and in airflow fields, need to be developed for the enhanced performance and efficiency of AlN powder synthesized by the CRN method.

Aerogel is a kind of highly dispersed solid material with extremely low density, in which nano-scale particles aggregate to form a nanoporous network structure with a gaseous dispersed medium in the voids. This material has some superior characteristics such as high specific surface area and low thermal conductivity, having broad application prospects in aerospace, building insulation, energy, environmental protection and other fields.However, gelation process as a conventional preparation process of aerogel is mostly carried out in a liquid phase. The complex solvent replacement or sophisticated supercritical drying equipment is needed to avoid the influence of surface tension in the gel drying process, resulting in harsh preparation conditions, high cost, and cumbersome preparation process, and restricting the large-scale application of the aerogel in a certain extent.The direct construction of aerogel nanoskeleton in vapor phase environment by chemical vapor deposition process can avoid the drying stage, which can greatly simplify the process and reduce its cost. Also, the aerogel prepared by chemical vapor deposition process has good mechanical properties, and the vapor phase process is suitable for the preparation of some aerogels with a special structure. This review represents the latest research progress on the chemical vapor deposition processes for preparation of aerogels (i.e., template-less chemical vapor deposition and template-assisted chemical vapor deposition). In addition, the future research direction is also prospected.Summary and ProspectsThis review summarizes recent research progress on the preparation of aerogels by chemical vapor deposition. The template-free chemical vapor deposition (CVD) method of the aerogel preparation can produce carbon material aerogels and multifunctional silicon carbide nanowire aerogels with superior performances for several hours. The template-assisted CVD method can customize the microstructure of the aerogel according to the template in order to achieve some special functions (i.e., superelasticity, negative Poisson's ratio, etc.). The chemical vapor deposition process for the preparation of aerogel can completely avoid the influence of surface tension during the drying process and the preparation process is more efficient due to the absence of liquid phase, compared with the traditional aerogel liquid-phase preparation process. The existing research in the related field is not sufficient due to the presence of some problems. Some possible aspects of subsequent research include:1) To further simplify the process. The template-assisted chemical vapor deposition method in the chemical vapor deposition preparation process for aerogels usually requires the specialized preparation of templates with aerogel structures, which increases the complexity of the process and is not conducive to large-scale production. Industrially produced fumed silica or fumed alumina has a structure similar to that of an aerogel, and the use of fumed silica or fumed alumina as a template to grow the desired material on its nano-skeleton is expected to reduce the cost of preparation of partial oxide aerogels.2) To develop a chemical vapor deposition preparation process for aerogels with milder conditions. At present, the reaction temperature is mostly more than 1 000 ℃ when using chemical vapor deposition to prepare aerogels. The reaction conditions become milder and the requirements of equipment reduce through the introduction of catalysts and other methods, which is an important research aspect for the future development of chemical vapor deposition process of aerogel.3) To broaden the scope of application of the material type of aerogel chemical vapor deposition process. From the existing reports, the chemical vapor deposition process can be used for the preparation of some aerogel types (i.e., mainly carbon materials, carbides, borides and other aerogels). The reaction mechanism of the aerogel chemical vapor deposition preparation process needs to be further investigated. The chemical vapor deposition process can be used to prepare oxide aerogels (i.e., silica and alumina) via utilizing the advantages of the chemical vapor deposition process (i.e., short cycle time and no drying).