1-3 piezoelectric single crystal composites with relaxor ferroelectric single crystals and composites as ideal piezoelectric elements in high-frequency transmitting transducers possess the superior characteristics including high piezoelectric constants, ultrahigh electromechanical coupling factors, and low acoustic impedance. A high-frequency wideband transmitting transducer based on 1-3 piezoelectric single crystal composite was designed and manufactured. The properties of piezoelectric single crystal composites were analyzed theoretically, and the transducer structure was optimized via simulation by finite element method. The 1-3 piezoelectric single crystal composite transducer produced has a bandwidth of 160 kHz, while the ripple of the transmitting voltage response does not exceed 3 dB in the frequency range from 250 kHz to 410 kHz. The maximum transmitting voltage response is 178.4 dB. The underwater transmitting performances of the single crystal composite transducer are superior to those of the ceramic composite transducer with the same structure and size. Fabricating high-frequency transmitting transducers using 1-3 piezoelectric single crystal composites can broaden the operating bandwith effectively, and improve the ability of acoustic emission underwater.

Rare-earth calcium oxyborate crystals (i.e., RECa4O(BO3)3, RECOB, RE:Y and rare-earth elements) are promising piezoelectric materials for high-temperature sensing application due to their high melting point, highs electrical resistivity, low dielectric loss and moderate piezoelectric activity. Single crystal growth of RECOB crystals was introduced, the characterization of electro-elastic properties and the research progress of RECOB piezoelectric crystals in the high-temperature sensing field were represented. High-temperature surface acoustic wave sensor for temperature sensing, high-temperature piezoelectric transducers and vibration sensors were described. The potential applications and technical advantages of RECOB crystals and related sensors were introduced.

The micro-displacement actuators based on the electrostriction are widely used in precision positioning and machining technology due to the merits of high accuracy, high sensitivity, low hysteresis and easy realization of the micro displacement in a submicron order. The electrostriction refers to a phenomenon that the strain is proportional to the square of electric field (or polarization) in dielectrics, which plays a crucial role in the electromechanical behavior of piezoelectric and ferroelectric materials. With particular emphasis on the sustainable development of environment, the electrostriction in lead-free perovskite ceramics has attracted a lot of attentions. In this review, recent development on the electrostriction was represented, and the design idea of materials with a low strain hysteresis and a large electrostrictive strain was discussed. Several kinds of lead-free electrostrictive ceramics were described, and their advantages and disadvantages were pointed out. Besides, the relationships among the electrostriction, piezoelectric effect and electrocaloric effect were discussed, providing an opportunity for further enhancing the piezoelectric and electrocaloric properties for piezoelectric and ferroelectric ceramics. In addition, the existing problems, challenges, and prospects were put forward to promote the development and practical application of electrostrictive ceramics and relative devices.

High-performance environmentally-benign (K,Na)NbO3-based (KNN) lead-free piezoceramics has been the spotlight in the search for functional oxides. The KNN-based piezoceramics with the multiscale structures have the superior piezoelectricity, thermal stability, fatigue resistance, mechanical properties, and reproducibility, for the practical applications. In this review, recent development on the multiscale structural engineering of piezoelectricity, thermal stability, fatigue resistance, mechanical properties, and reproducibility, and the emerging applications of KNN-based lead-free piezoceramics was summarized. In addition, the future perspective for the development of KNN-based piezoceramics was also presented.

Textured piezoelectric ceramics have received considerable recent attention due to their superior electromechanical properties, low cost, uniform composition, shape-controlled fabrication process, etc.. In this review, the principles of design and preparation techniques of textured piezoelectric ceramics were introduced. The characteristics and advantages of textured ceramics were compared to those of single crystals and non-textured ceramics. Recent work on the fabrication of microcrystalline templates and textured lead-based piezoelectric ceramics was represented. In addition, the present issues and challenges of textured lead-based piezoelectric ceramics were also discussed.

Dielectric energy storage materials as "the blood of modern industry" are the key components of various pulse power electronic systems. These materials are attracted extensive attentions because of the high dielectric constant, low loss, high power density, fast charge/discharge speed and excellent reliability. However, dielectric materials for multi-fields applications still have some problems, such as low energy storage density, poor efficiency. Therefore, improving the energy storage performances of dielectric materials becomes one of the research hotspots in recent years. This review represented the performance advantages of inorganic dielectric energy storage materials, summarized the energy storage principle and the main parameters of energy storage performance, and analyzed the energy storage performance of linear dielectrics, relax or ferroelectrics and antiferroelectrics from the viewpoint of component design and multiple material forms (i.e., ceramics, films and multilayer ceramic capacitors). The performance control methods and enhancement mechanisms from the aspects of material composition, structure and preparation technology were discussed. Finally, the opportunities and challenges for inorganic dielectric energy storage materials were given, and the development trend for pulse power capacitors in the future was prospected.

Piezoelectric materials are widely used in sensors and actuators due to their unique electromechanical coupling capability. However, the tradeoff between flexibility and high piezoelectric performance restrains their application into flexible electronic technology, which is an important underpinning for the future intelligent technology. In this review, we summarized the flexible piezoelectric materials currently available and their design and preparation strategies. Also, the application of flexible piezoelectric materials in pressure sensing, energy harvesting and biomedicine was outlined. Finally, we gave the challenges and perspectives of developing the flexible piezoelectric materials.

Electrocaloric effect, i.e., the entropy and temperature changes arising from phase transition and dipole orientation induced in electric fields, can realize heat transport and refrigeration. The electrocaloric cooling eliminates the use of environmentally harmful coolants, possesses high cooling efficiency, small size and low weight as a promising environmental-friendly and high-efficiency cooling. One key point for electrocaloric cooling toward practical cooling is to enhance the performance of the electrocaloric effect of ferroelectrics. Ferroelectric ceramics have attracted much attention due to their high polarization, rich phase structures and variety of regulation methods. In this review, we introduced the electrocaloric effect of ferroelectric ceramic thin films, bulks and multilayer thick films with various compositions, and discussed the internal relations among electrocaloric effect, compositions, phase transition behaviors and microstructures. Furthermore, we concluded the modulation approaches of the electrocaloric effect of ferroelectric ceramics, and gave the future development of electrocaloric materials.

For crystalline materials, atomistic local structures are deviations from their long-range average crystal structures. With the recent development of experimental techniques and in-depth investigation methods for probing local structures, it has been realized and understood that local structures have profound influences on the physical properties of functional materials, and the understanding of local structures provides theoretical instructions for the improvements of materials performances as well as development of novel applications. This review summarized the well-established X-ray and neutron scattering techniques, data analysis and model refinements mothods in the local-structure investigation researches; in addition, examples of local structural investigations for several classical ferroelectric perovskites are reviewed.

The ceramics of 0.96K0.48Na0.52Nb(1-x)TaxO3-0.04BaZrO3-0.3%MnCO3 were prepared via solid-state reaction and subsequent sintering in air and reducing atmospheres. The effects of Ta doping and sintering atmosphere on the microstructure and piezoelectric properties of ceramics were investigated. The results demonstrate that all the ceramics sintered in different atmospheres exhibit a pure perovskite structure. The phase structure of KNN-based ceramics is the coexistence of rhombohedral and orthorhombic phases. Also, the generation of oxygen vacancies is suppressed as Ta doping content is increased. When x = 0.1, the ceramics sintered in a reducing atmosphere exhibit the optimum electrical properties (i.e., d33=172 pC/N, d*33=294 pm/V, kp=24.9, εT33=820, and tanδ=0.021), which are superior to the counterparts sintered in air atmosphere (i.e., d33=142 pC/N, d*33=220 pm/V, kp=21.1, εT33=593, and tanδ=0.022). It is indicated that sintering in a reducing atmosphere can suppress the grain growth, thus facilitating the densification of ceramics and improving the piezoelectric properties.

3-1 type and 3-3 type porous PZT ceramics were fabricated by the alginate ionotropic gelation process and gelcasting technology respectively. The resultant samples were sintered at different temperatures and characterized in terms of both microstructure and piezoelectric properties. It was noted that the porosity and grain size of porous PZT ceramics increased with the sintering temperature increasing from 1 150 to 1 250 ℃, which resulted in the increase of relative permittivity, piezoelectric efficient, thickness coupling coefficient kt and compressive strength, the corresponding decrease of hydrostatic voltage coefficient and hydrostatic figure of merit (HFOM). Under the joint effects of unidirectionally aligned channels and the incorporation of Ca2+ into PZT matrix, the 3-1 type PZT ceramics possessed higher εr and compressive strength, lower d33 and HFOM than that of 3-3 type PZT ceramics. However, the maximum HFOM value of 3-1 type PZT ceramics achieved 4 755×10-15 Pa-1, which makes it suitable for the application of underwater sonar detectors.

Near net size preparation of porous mullite ceramics with controllable shrinkage was achieved via gel casting and pore-forming agent process With Al2O3 and kyanite as raw materials, PMMA microspheres as a pore-forming agent, and isobutylene/maleic anhydride copolymer (Isobam104) as a gelling/dispersing agent. The effect of sintering temperature on the phase composition and the effect of solid loading on the microstructure, phase composition, shrinkage, porosity, and compressive strength of samples were investigated. The results show that the shrinkage of samples sintered at 1 500 ℃ firstly decreases and then increases as the solid loading increases. At the solid loading of 30%(in volume fraction) and the content of pore forming agent of 30%(in mass fraction), the total shrinkage of the samples is close to zero, realizing the near net size preparation of porous mullite ceramics. The prepared porous mullite ceramics exhibite a higher porosity (i.e., 60.4%), a smaller average pore size (i.e., 3.75 μm) and a higher compressive strength (i.e., 8.3 MPa). The shrinkage of porous ceramics can be effectively controlled by the volume expansion effect in the preparation process, and the near net size preparation of porous mullite ceramics is of great significance for the preparation of large-size and complex porous ceramic parts and the reduction of processing cost.

Alumina ceramics were joined with Ag-10CuO-10B2O3 filler via reactiver air brazing for the formation of whiskers (Cu2Al6B4O17) in the joints. The effects of brazing temperature and holding time on the microstructure, properties of the joints and the whisker structure were investigated. The results show that Al2O3 reacts with CuO and B2O3 to form Cu2Al6B4O17 whiskers in the brazing process, thus obtaining a reliable joint with the superior performance. At the holding time of 60 min and the brazing temperature of > 950 ℃, an effective connection of Al2O3 ceramic joint can be realized. The center area of the brazing joint is mainly Ag, while the interface at the both sides of the joint is composed of CuO、Cu3B2O6 phase and Cu2Al6B4O17 whiskers. The shear strength of the joint increases with the increase of the brazing temperature. The whiskers become thick and the adhesion occurs when the brazing temperature is > 1 050 ℃, thus reducing the strengthening effect on the joint and the shear strength of the joint. The whiskers decompose into some lamellar products, and the shear strength of the joint decreases when the brazing temperature is > 1 100 ℃. The shear strength of the joint prepared under optimum process parameters (i.e., at 1 000 ℃ for 60 min) can reach 86.7 MPa, and the fracture occurs in the weld nearby alumina ceramic base material.

Porous ceramics were prepared by a high-temperature melting foaming method with red mud and high-aluminum fly ash as main raw materials. The effects of raw material composition and foaming process on the cellular structure and properties were investigated. The results show that the cellular structure of porous ceramic obtained after melt foaming at 1 200 ℃ for 1 h changes from closed to open, eventually forming a composite cellular structure. Also, the average pore size and porosity increase, while the bulk density and thermal conductivity decrease with increasing the mass ratio of SiO2/Al2O3 from 1.2 to 1.9 in the raw material composition. At the blowing agent of 5% (in mass fraction) SiC and the melting agent of albite and microcline of 35%, a composite cellular structure porous ceramic with the bulk density of 0.63 g/cm3, average pore size of 0.98 mm and bulk porosity of 70% is obtained, and its flexural strength and thermal conductivity are 7.17 MPa and 0.34 W/(m·K), respectively.

Single-phase anorthite porous ceramics were in-situ prepared by a foam gel-casting method with CaCO3, α-Al2O3 and SiO2 as raw materials and environmental-friendly gelatin as a gel. The influence of gelatin amount on the phase composition, microstructure and properties (i.e., porosity, density, compressive strength, and thermal conductivity) of the samples was investigated. The amount of gelatin has no effect on the phase composition of the prepared material, but it affects the properties. The total porosity decreases from 89.7% to 88.0%, the bulk density increases from 0.28 g/cm3 to 0.33 g/cm3, the compressive strength increases from 1.02 MPa to 2.54 MPa, and the thermal conductivity increases from 0.038 W/(m·K) to 0.059 W/(m·K) as the gelatin amount increases from 6% to 12%. It is indicated that porous anothite ceramics with a low density, a high strength and a low thermal conductivity could be prepared by this promising method.

Porous alumina (Al2O3) beads were prepared via gel-dripping and pressureless sintering with α-Al2O3 as a raw material, nontoxic sodium alginate as a gelation reagent, and the calcium ions were introduced in the preparation using a calcium chloride solution. The effects of coagulation time and sintering temperature on the porosity, compressive strength and microstructure of porous Al2O3 beads were investigated. The results show that calcium ions can transfer and react readily with sodium alginate as the coagulation time increases. Alumina particles are solidified to form a bead green body by a three-dimensional network. The number of meso-pores decreases and the microstructure becomes well-distributed with increasing the sintering temperature. The porosity and compressive strength are 47.7%-78.1% and 1.2-36.0 MPa, respectively. The porosity, pore structure and compressive strength can be tailored by optimizing the coagulation time, sintering temperature and calcium ion concentration. The diameter, sphericity and property of porous alumina beads can be controlled through the simple gel-dripping method. The porous alumina beads can be used in many fields, such as catalyst support, adsorption, separation, purification, etc..

Rapid preparation of dense BiFeO3-BaTiO3 lead-free piezoelectric ceramics at low temperatures is beneficial to preventing the Bi volatilization, reducing the energy consumption and developing novel materials with some unique properties. In this paper, dense BiFeO3-BaTiO3 ceramics with good ferroelectric and piezoelectric properties were prepared in an electric field of 200 V/cm with a current limit of 280 mA via reactive flash sintering of multiphase precursor powders (i.e., Bi2O3, Fe2O3, TiO2 and BaCO3) at 415 ℃ for 30 s. The solid-state reaction in sintering occurs during the flash event. The current limit has an effect on the phase transformation and densification. It is indicated that the reactive flash sintering technology could prepare the single-phase and dense ceramic material through flash sintering of starting precursors in one step, thus providing an effective approach for the rapid production of ceramic materials.

ZTA composite ceramics were prepared via pressureless sintering, and the influence of Cr2O3 doping on the microstructure and mechanical properties of ZTA ceramics was investigated. The results show that Cr2O3 can promote the growth of Al2O3 grains and obtain elongated Al2O3 grains. The density, hardness and fracture toughness of ZTA ceramics firstly increase and then decrease with the increase of Cr2O3 addition. ZTA ceramics with 0.6% Cr2O3 addition exhibit the optimum properties. However, the properties of ZTA ceramics with the excessive addition of Cr2O3 can be impaired due to the increased internal porosities. The mechanical properties of ZTA composite ceramics with Cr2O3 nano-sized particles are superior to those with Cr2O3 micron-sized particles. The addition of Cr2O3 nano-sized particles results in greater density and hardness of ZTA ceramics due to the smaller average grain size of Al2O3. Besides, the fracture toughness of ZTA ceramics improves due to the formation of more elongated grains and the consumption of more energy for crack propagation.

A holmium molybdate ceramic pigment with ‘allochroic effect’ was prepared via mechanical activation-assisted solid-state reaction. The effects of mechanical activation mode and time as well as sintering temperature on the properties of synthesized holmium molybdate pigment were investigated by laser particle size analysis, simultaneous thermal analysis, X-ray diffraction and scanning electron microscopy, respectively. The color properties and allochroic effect of the synthesized pigments were evaluated by ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis) and colorimetry. In addition, the high-temperature stability and chemical stability of the pigments were also investigated. The results show that a sole phase of holmium molybdate can be obtained from mixed precursors ground at 1 h and sintered at 900 ℃ for 3 h, and the sintering temperature is reduced by 100 ℃, compared to that from each precursor ground separately for 2 h and then mixed or the mixed precursors unground. This is because mechanical activation pretreatment can effectively reduce the size and crystallinity of mixed precursor particles and enhance its solid-phase reaction activity, thus leading to the decrease of solid-phase reaction temperature. In addition, the pigment obtained from mixed precursors ground for 2 h has better color performance and allochroic effect under different illuminants. It is indicated that the allochroic effect of holmium molybdate pigment occurs due to the rich energy level structure of holmium ions in the visible range and the difference between relative spectral power distributions under different light sources. Meanwhile, holmium molybdate pigment can be used as a potential functional pigment in ceramic decoration and other related fields due to its high-temperature stability and chemical stability.

A glaze with a good quality and a unique decorative pattern was prepared with purple clay as a source of iron, Ca3(PO4)2 and SnO2. The effect of addition agents on the glaze color, microstructure and artistic textures was investigated by ultraviolet-visible spectroscopy, X-ray diffraction and scanning electron microscopy, and the color mechanism was analyzed. The results illustrate that the introduction of addition agents changes the chemical state of iron, and contributes to the formation of blue fancy glaze. The introduction of Ca3(PO4)2 can cause the partial reduction of iron ions, leading to the glaze appearing blue and yellow, and Ca2+ ions promoting the separation of liquid phase to produce blue patterns. Also, the introduction of Ca3(PO4)2 and SnO2 for the increased reducibility of iron ions can increase the ratio of Fe2+ and Fe3+ ions, resulting in the glaze being blue-green, and the greater pattern and lightness value L*. The presence of Fe3+―O―Fe2+ in the vitreous is one of the color factors. The liquid separation forming the structure of the color is the auxiliary color of glaze color. The combined chemical color with structural color on the glaze becomes more colorful.

Tantalum (Ta) doped Li7La3Zr2O12 (Ta-LLZO) ceramics were prepared via conventional solid-state reaction. LiOH was used as a lithium source and a sintering additive for ceramics. The effect of LiOH on the microstructure and ionic conductivity of Ta-LLZO ceramics was investigated. The results show that LiOH as a lithium source can promote the formation of cubic Ta-LLZO, and LiOH as a sintering additive can effectively improve the densification of ceramics. The dense cubic garnet Ta-LLZO ceramics were obtained by sintering at 1 200 ℃ for 5 h. When the amount of the sintering additive is 6% (in mass fraction), the ionic conductivity of ceramics reaches 6.23×10-4 S·cm-1. It is indicated that Li7La3Zr2O12 prepared via solid-state reaction has a great potential in the application of all-solid-state lithium ion batteries.

In order to solve the problem for high initial frequency of unilateral lightweight phononic crystals, a phononic crystal structure of bilateral hollow asymmetric scatterers was proposed based on the local resonance mechanism. The energy band structure, transmission loss spectrum and intrinsic displacement field of phononic crystals with bilateral hollow asymmetric scatterers were calculated by the finite element method. The ultra-wide first complete band gap with an initial frequency of 79.4 Hz and a bandwidth of 1 065.2 Hz was obtained. Combined with an equivalent spring mass system, the vibration modes of the intrinsic displacement field of the marked points were analyzed, and the mechanism of band gap formation in phononic crystals of bilateral hollow asymmetric scatterers was revealed. Furthermore, effects of the geometric parameters such as notch angle of cladding, width of connecting short plate and height of hollow cylindrical scatterer on the first complete band gap were analyzed, and the geometric parameters of the phononic crystal were adjusted to control the band gap frequency. The results show that the initial frequency of the first complete band gap of the proposed bilateral asymmetric two-dimensional hollow scatterer phononic crystal effectively reduces to less than 80 Hz, and the bandwidth exceeds 1 000 Hz. Adjusting the structural parameters of phononic crystals can realize the coexistence of local resonance and the Bragg scattering band gap in a phononic crystal, which makes it possible for a single phononic crystal to regulate the low-frequency and high-frequency band gaps simultaneously.

The influences of pH value, Fe3+ mass concentration, and stirring rate and their interactions on the ammonium sulfate crystallization were investigated via cooling crystallization and sieving based on a response surface methodology. An average particle size quadratic orthogonal model and a variation coefficient 2FI orthogonal model were proposed. The interactions among the various factors were analyzed. The results show that pH value (A) > stirring rate (C) > Fe3+ ions concentration (B) is a decreased order for the parameter effects on the average particle size and variation coefficient. Their interactions have a decreased effect order (i.e., AC > BC > AB) on the average particle size and variation coefficient. When pH value is 5.5, stirring rate is 150 r/min, and Fe3+ ions concentration is 0.3 g/L, the average particle size and variation coefficient of the ideal crystals is 0.985 mm and 793.719, respectively.

Aluminum oxycarbides were prepared via a carbothermal reduction of alumina in vacuum at 1 300 - 1 500 ℃. The results indicate that the temperature required for the formation of aluminum oxycarbides from the carbothermal reduction of alumina in vacuum is lower than that in argon, a large amount of Al4O4C can be formed at 1 300 ℃, and the main component of the condensation products is Al4O4C, which is independent of the reaction extent of the raw materials. The condensation products consisting mainly of Al4O4C with a small amount of Al4C3 can be obtained under optimum conditions (i.e., n(α-Al2O3):n(C) of 2:3, reaction temperature of 1 400 ℃ and reaction time of 20 min). It is confirmed that Al4O4C can be formed in two stages, i.e., alumina reacts with carbon to generate the gases containing aluminum Al2O, Al and CO at higher temperatures, and the condensates mainly consisting of Al4O4C form at lower temperatures.

KTa1-xNbxO3 crystal doped with 0.15% (in mole fraction) Fe was prepared by a top-seeded solution growth method. The dielectric properties, electric-field-induced strain distribution, component distribution and domain structure of Fe: KTN crystal were characterized. The results show that digital holography is a promising method to measure the spatial distribution of strain, and the electric-field-induced strain properties of KTN crystal present a uneven distribution. At room temperature, the maximum strain of crystal is 0.05% when the applied electric field is 435 V/mm, while the strain value is near 0.02% 3/4 area of crystal. There is a relationship among strain distribution, component distribution and domain structure of Fe:KTN crystal. The domain structure of crystal in the region with less Nb content is smaller and the electric-field-induced strain is greater when the room temperature is lower than the Curie temperature.

Hierarchical ZSM-5 zeolite was synthesized by a seed-assisted dry-gel conversion method, and the effects of seed amount, deionized water amount and crystallizing time on the structure and morphology of hierarchical zeolite were investigated. The results show that the crystallization rate of zeolite is increased with seed addition. Amorphous silica-aluminium gel can directly dissolve in the water film condensing on the seed surface and rapidly grew into ZSM-5 nano-zeolite near the seed. Simultaneously, nano-zeolites aggregate and some mesoporous channels are formed between the nano-crystals. The size of nano-zeolite and the resulting mesoporous pores can be adjusted by seed amount, deionized water amount and crystallizing time. The catalytic stability of the resulting hierarchical ZSM-5 zeolite is improved by nearly 5 times, compared with the conventional zeolite in the isomerization of styrene oxide to phenylacetaldehyde.

A ratiometric fluorescent probe was constructed with carbon quantum dots (CQDs) and europium ions (Eu3+) as a fluorophore for the visual detection of teracycline (TC). In this ratiometric probe, CQDs/Eu3+ has an intense blue fluorescence peak at 439 nm and a weak red fluorescence peak at 616 nm under the excitation of 380 nm wavelength. The fluorescence peak intensity of CQDs at 439 nm gradually decreases based on the inner filter effect. The fluorescence intensity of Eu3+ at 616 nm increases due to an antenna effect with the addition of TC. The experimental factors, such as CQDs and Eu3+ ratio, response time, stability, etc., were optimized. The results show that the ratio fluorescent probe has a specific recognition ability for TC. A linear relationship between the fluorescence intensity ratio(F616/F439) and different concentrations of TC (0-50 μM) was established with a detection limit of 0.68 ?倕 M. With the addition of TC, the color of the ratio fluorescent probe solution under ultraviolet light gradually changes from blue to red and is used for the detection of TC in milk with the recoveries ranging from 92.5% to 1 14.8%. In addition, a TC test paper was also prepared, which can be quickly used for a visual test paper detection of TC.

BaZrO3/Al2O3 composite molds were prepared via sintering at 1 600 ℃ for 8 h with BaZrO3 as a surface coating material and Al2O3 as a backup coating material. The phase composition and microstructure of the interfacial bonding layer between the face and back layers before and after hydration were investigated by optical microscopy, X-ray diffraction, and scanning electron microscopy with energy dispersive spectroscopy. The hydration process and damage mechanism of the interfacial bonding layer in the mold were analyzed. The effect of mold damage on the directional solidification of TiAl alloy was also investigated via directional solidification tests. The results show that BaZrO3 and Al2O3 generate BaAl2O4 at BaZrO3/Al2O3 interface during the high-temperature sintering process; and BaAl2O4 generates Ba(AlO(OH)2)2, Ba2Al4(OH)16 and Ba3(Al(OH)6)2 after hydration, leading to the grain volume change to destroy the intergranular bonding force, the generation of cracks in the mold and the failure of the mold. In the directional solidification process, the generated cracks become a channel for melt penetration of TiAl alloy, resulting in a melt leakage from the mold and the appearance of heterogeneous crystals in the directionally solidified TiAl alloy castings.

For the improvement of the fluidity of castables with recycled aggregates of mullite-SiC bricks due to their high porosity, high water absorption and massive cracks, silica sol was used to impregnate mullite-SiC brick aggregates. The effect of silica sol concentration on the aggregate properties of mullite-SiC bricks was investigated. The microstructures and the element distributions of modified mullite-SiC bricks aggregate were analyzed by scanning electron microscopy coupled with energy dispersive spectroscopy. The water wettability of mullite-SiC brick aggregates was characterized via water contact angle measurement. The results show that after the impregnation of mullite-SiC brick aggregates, the water absorption of mullite-SiC brick aggregate reduces from 6.9% to 2.6%, and the water contact angle decreases from 55 ° to 7 °, thus improving the water wettability of the aggregate. The impregnated mullite-SiC bricks were used as recycled aggregates instead of brown corundum in Al2O3-SiC-C castables. In addition, the effect of aggregates on the properties of castables was also investigated. The results indicate that Al2O3-SiC-C refractory castables with silica sol concentration of 15% modified mullite-SiC bricks aggregates after heat-treated at 1 450 ℃ have the minimum apparent porosity of 17.1% and the maximum cold compressive strength of 73.7 MPa, which is 45.7% greater than the strength of castables with brown corundum as aggregates. Meanwhile, the residual strength and the residual strength ratio of castables after thermal shock are increased by 69.4% and 24.1%, respectively.

The residual mechanical properties and microstructure of UHPC mixed with 6, 8, 12 mm copolymer formaldehyde fiber and steel fiber after high temperature were studied. The test results show that at 400 ℃, only plain concrete bursts. At 500 ℃, the steel fiber UHPC specimen burst, while the UHPC specimen with single copolymer formaldehyde fiber and mixed with two kinds of fiber can still maintain relatively integrity, and the latter has higher residual strength at high temperature. SEM and pore structure show that the copolymer formaldehyde fiber in UHPC can be closely bonded to the matrix after steam curing at high temperature. The pore formed by fiber melting at 165 ℃ can effectively relieve and release steam pressure, keep the concrete matrix intact and prevent it from cracking at 500 ℃. The research results reveal the mechanism of the copolymer formaldehyde fiber on the high temperature performance of concrete, which has great reference value for its application in UHPC.

In addition to incandescent lamps, white light-emitting diode and nonlinear supercontinuum white light, recent studies focus on the production of continuum broadband white light by irradiating different active materials with near-infrared constant-wave lasers. In this review, we introduced and categorized different materials that exhibit NIR laser driven white light emission, i.e., inorganic phosphors, hybrid nanostructures, carbon-based materials, organometallic compounds and rare-earth complexes. The intrinsic photophysical behavior of this process in terms of spectral characteristics, temperature evolution and photoelectric response was discussed. In addition, the different mechanisms of while light generation and highlight potential applications of this process were also represented. Finally, the past results and point future research direction for this optical process were summaried.

Data-driven Machine Learning (ML) has been widely used in materials performance optimization and novel materials design due to its ability to quickly fit potential data patterns and achieve accurate prediction. However, the results of data-driven ML are often inconsistent with the materials basic theory or principle, which results mainly from the lack of the guidance of materials domain knowledge, e.g., the correlation among descriptors and the driving mechanism associated with the properties. Herein, by analyzing the characteristics of materials data and the modeling principle of data-driven ML methods, we clarify the three main contradictions occurring to the application of ML in materials science, i.e., the contradictions between high dimension and small sample, complexity and accuracy of models, learning results and domain knowledge. Following this, we propose the ML method embedded with materials domain knowledge to reconcile these three contradictions. Further, surrounding the whole ML process including target definition, data collection and preprocessing, feature engineering, model construction and application, we explore some key techniques to realize domain knowledge embedding by summarizing the related basic and exploratory efforts. Finally, opportunities and challenges facing the ML method embedded with domain knowledge are also discussed.