HfC and TaC are typical ultra-high temperature ceramics (UHTCs), which are important candidate materials for thermal protection components in high-speed aircraft. However, their oxidation resistance at medium and low temperatures is relatively poor. Due to the similar crystal structures of HfC and TaC, and the close atomic radii of Hf and Ta (rHf = 1.585 ?, rTa = 1.457 ?, Δr < 0.15), theoretically, they can form an infinitely miscible substitutional solid solution (HfxTa1–x)C (0 < x < 1). Among them, Hf0.2Ta0.8C has a melting point as high as 4 300 K, which is recognized as the highest melting point carbide. Compared with single-component HfC and TaC, (HfxTa1–x)C exhibits higher initial oxidation temperature and lower oxidation rate, indicating significantly improved oxidation resistance. In this work, a series of processable liquid single-source precursors (SSPs) were successfully prepared by introducing HfCl4 and TaCl5 into allylhydridopolycarbosilane (AHPCS). Through the polymer-derived ceramic (PDC) method, SiC/(HfxTa1–x)C/C nanocomposites with core–shell structured SiC@C and (HfxTa1–x)C@C nanoparticles were obtained, and the evolution of phase composition and microstructure during the ceramic transformation process was investigated.Combining PDC and spark plasma sintering (SPS) technology, nearly dense SiC/(HfxTa1–x)C/C bulk materials were prepared, and the mechanical properties of the resulting bulk ceramic were investigated.

Uniform distribution in molecular level of ceramics could be achieved by polymer-derived method. Comparing to other methods, fewer crystal seeds existed in microstructure of polymer-derived ceramics, which made it more difficult to sinter. Up to now, few reports focused on the direct sintering of the polymer-derived ceramics. For silicon nitride sintering, the introduction of metal oxide additives caused defects in the lattice of silicon nitride because of oxygen atoms, which could affect the properties of thematerial. This work focused on the sintering behavior of polymer-derived ceramics and the issue of performance degradation caused by introducing oxygen elements in sintering additives. The metal elements were connected to the precursor molecule and formed the metal nitride sintering additives during pyrolysis process. The method could help to achieve the in-situ non-oxygen addition and uniformly mixing of sintering additives, and the followed low-temperature sintering could achieve the high-purity silicon nitride ceramics.

With the rapid development of high-technology fields, advanced aerogel acts as the thermal insulation materials under high-temperature environment attracted extensive attention. Polymer derived ceramic (PDC) aerogels were considered to be a promising thermal protection materials due to its low density, high porosity, excellent thermal insulation performance and high-temperature stability. Silicon oxycarbide (SiOC) ceramic aerogels, one kind of typical representative PDC materials, were mainly formed by partial substitution of C atoms for O atoms in SiO2 tetrahedra. Compared the traditional silica aerogels, silicon oxycarbide (SiOC) aerogels exhibited better thermal and chemical stability as well as higher mechanical strength. Previously research reported that SiOC aerogels were mainly prepared by sol-gel method and PDC route, exhibited a higher density, which limited its applications and development in lightweight thermal insulation filed. Moreover, the obtained SiOC aerogels exhibited a necklace-like structure, poor high-temperature stability and mechanical strength due to the weak contact between nanoparticles. And most researches on SiOC aerogels focused on its high-temperature pyrolysis behavior. In this paper, a lightweight and high-strength SiOC aerogel were prepared using polyhydromethylsiloxane (PHMS) as precursor and tetramethyltetravinylcycletetrasiloxane (D4Vi) as crosslinker through solvothermal, freeze casting and pyrolysis. The influence of D4Vi content on the microstructure and thermal stability of SiOC aerogels were discussed. The evolution of phase composition, mechanical strength and thermal insulation performance was further explored via high-temperature heat treatment and oxidation treatment.

SiC ceramics, known for their lightweight, high strength, high temperature resistance and oxidation resistance, find extensive applications in aerospace, energy and transportation industries. The polymer-derived ceramics (PDC) method is an important method for the preparation of SiC ceramics, employing special polymers as raw materials and converting them into inorganic ceramics via high-temperature pyrolysis. This method offers advantages such as controllable elemental composition, ease of molding, and lower processing temperatures. As one of the most important raw materials in the PDC method, hyperbranched liquid polycarbosilanes, synthesized via the Grignard coupling reaction and the subsequent reduction reaction, are prized for their low viscosity, high ceramic yield, and ease of processing and molding. Therefore, it has been widely used in the fabrication of ceramic matrix composites, coatings and membrane materials. A large number of articles have been published on the synthesis and applications of polycarbosilanes. The molecular structure of SiC polymer precursors not only influences their curing and pyrolysis processes, including weight loss and gas release behavior, but also plays an important role in determining the elemental composition(e.g., C/Si ratio), crystallization behavior and oxidation resistance. There are many studies conducted to investigate the structure of precursors affecting their curing and pyrolysis properties. However, it is very necessary to investigate the relationship between molecular structures of different types of liquid polycarbosilanes with varying C/Si ratios and their curing, pyrolysis and crystallization behaviors. In this work, the curing and pyrolysis behaviors as well as the crystallization behavior of two major types of liquid hyperbranched polycarbosilanes vinylhydridopolycarbosilane (VHPCS) and allylmethylhydridopolycarbosilane (AMHPCS)) with different carbon-to-silicon ratios and molecular structures were comprehensively characterized by a variety of testing methods.The relationship between the molecular structure and the ceramization process, as well as the properties of the ceramic products, was established using five types of liquid polycarbosilanes with varying C/Si ratios and molecular structures.

The SiCxOy phase in SiC fibers will decompose at high temperature, which results in the loose structure, declining mechanical performance, and lowing the high temperature resistance of the fibers. Introduction of some elements can play the role of sintering assistant at high temperature. Nearly stoichiometric polycrystalline SiC fibers can improve the oxidation resistance of fibers at high temperature. Al and Y are commonly used as sintering additives for SiC ceramics. Al and Y can form yttrium aluminum garnet (YAG) liquid phase at high temperature. The YAG liquid phase is conducive to reduce the sintering temperature and improve the densification of SiC ceramics. If the SiC fibers can form YAG phase at high temperature, the performance of SiC fibers can be improved. In this work, the both Y and Al are introduced for the fabrication of high performance SiC fibers.

SiC ceramic matrix composites have excellent mechanical properties and high-temperature resistance, and hence attracts increasing research attentions in aerospace and other fields. Precursor infiltration and pyrolysis (PIP) is one of the most common methods for the preparation of SiC ceramic matrix composites. The synthesis of organic precursors is the basis of the PIP process. Liquid polycarbosilane (LPCS) is an ideal precursor for the preparation of SiC ceramic matrix composites by PIP process.LPCS can be prepared using the Grignard coupling reaction, while this method suffers from the problem of long synthesis route and high cost. The Wurtz reaction, as another method for synthesizing LPCS, has a shorter route and less cost. However, it is difficult to directly synthesize LPCS containing active groups because of the severe reaction conditions. Ultrasound can significantly promote the effective contact between sodium and chlorosilanes and reduce the reaction conditions in the Wurtz reaction, and some ether additives can improve the activity of the reaction groups. Therefore, the introduction of ultrasound and ether additives is expected to realize the efficient synthesis of LPCS containing active groups. In this work, an active LPCS was prepared directly from chlorosilane monomer containing active groups by using ultrasonic and ether additives in Wurtz reaction. The basic structure of the product, ceramic yield and pyrolytic properties of the transformed ceramics were characterized.

In recent years, with the rapid development of the flexible displays and wearable electronic devices, higher requirements have been placed on the performance of electronic devices, such as lightweight and flexible. Polymer films such as transparent polyimide (CPI) and polyethylene terephthalate (PET) have gained widespread attention in the field of flexibleoptoelectronic materials owing to their high transparency, light weight, good bendability and high mechanical strength. However, due to the characteristics of their molecular structure, polymer films generally have the problems of low surface hardness and poor abrasion resistance. Therefore, enhancing the surface hardness and abrasion resistance of polymer films without compromising theircharacteristics such as transparency, light weight and flexibility become an urgent problem to be solved. Among the various enhancement strategies that have been developed, applying optically transparent coatings with abrasion and bending resistance to the surface of polymer films is one of the most effective and promising approaches. Hard flexible coatings are mainly achieved by organic–inorganic hybridization to achieve both hardness and flexibility. Organic polysilazanes can retain their organic groups while forming the Si—O—Si network structure by hydrolysis condensation reaction, which can realize organic-inorganic hybridization and providing a basis for constructing hard flexible coatings. In this work, an organic–inorganic hybrid hard flexible coating was prepared at 80 ℃ 90%RH by hybridizing organic polysilazane OPZ181 with triethoxysilane (KH550). The effect of KH550 content on the conversion process of OPZ181 was investigated, and the structure and properties of the hard flexible coatings were systematically characterized.

Polymer-derived ceramics (PDCs) have attracted great attention in the applications of high-temperature harsh environments due to its excellent high-temperature semiconductive properties, corrosion/ oxidation resistance, high thermal stability, et al. Therefore, PDCs as sensing material exhibits great potential to be applied in high-temperature harsh environments. This article summarized the research progress on PDCs sensors both domestically and internationally in recent years. The sensing mechanism and related parameters of PDCs sensors were summarized also focusing on temperature sensors, pressure sensors, and strain sensors. At the same time, the performance of relevant ceramic sensors was compared, and the future development of PDCs sensors was discussed finally.Summary and prospects PDCs as sensing material is one of the most promising materials for high-temperature extreme environment applications. This paper summarized the development of PDCs sensors and elaborated the corresponding sensing mechanism. According to the connection type, the properties of existed wired/wirelesses PDCs sensors was compared, results exhibited that the PDCs sensors possess excellent sensitivity, repeatability, stability and fast response, exhibiting competitive performance in high temperature. Meanwhile, PDCs sensor can be prepared on complex surfaces based on the distinctive liquid precursor. Temperature, pressure and strain signals of PDCs sensor can be monitored in-situ and long-distance.However, the development of PDCs sensors is still in infancy stage, and it still exists many obstacles to be overcome. Firstly, it is necessary to eliminate the sensor transmission signal interference through the structural design, and improve the anti-interference ability; Secondly, it is still a challenge to realize the application of PDCs sensors at higher temperature and more complex environments; Finally, the repeatability of wireless PDCs sensors needs to be enhanced by attenuating the interference of wireless transmission signals so that the longer distance transmission can be achieved. In a summary, to realize the practical application of PDCs sensors, some parameters need to be optimized such as structural components, material properties, and production costs.

Ultra-high temperature ceramics are a new type of heat-resistant materials that could withstand extreme service environments such as long periods of ultra-high sound speeds, atmospheric flight, and re-entry. It usually refers to advanced ceramics with a melting point above 3 000 ℃ and the ability to resist ablation in an oxidizing atmosphere above 2 000 ℃, mainly including carbides,nitrides, and borides of transition metals in the IVB and VB groups. As thermal protection materials used in extreme environments, single-phase ultra-high temperature ceramics exhibit extremely poor antioxidant performance in extreme environments. In this paper,the development of ultra-high temperature ceramics is moved towards diversification and multiphase, and ultra-high temperature ceramic matrix composites are formed by compounding with fibers and other materials.Polymer conversion methods mainly include two types: the first type is metal hybrid polymer method, which use alcohol oxides(such as alcohol organic compounds, acetate, acetylacetone, salicylic acid, etc.) to modify and obtain polymer precursors with M (Ti,Zr, Hf, Ta, Nb, etc.) and O acted as the main chains; The second type is the metal organic polymer method, which choose alkyl,alkenyl, alkynyl or aryl ligands to realize the chemically modified organic metal compounds (such as metallocene compounds, methylamine metal compounds, etc.) to obtain polymer precursors containing M and C or B bonds. With the diversification and multiphase development of ultra-high temperature ceramics, the multi-component nanocomposite ceramics obtained by reacting metal with polycarbosilane, polysilazane, polyborosilicate, etc. were significantly better than those obtained by traditional ultra-high temperature ceramics. The polymer conversion ultra-high temperature ceramic technology could realize the control of the composition, microstructure, properties, etc., which could exhibit a revolutionary significance in the preparation of structure function integrated ceramics.

Polymer-derived ceramics (PDCs) are a kind of advanced materials prepared by high-temperature pyrolysis of silicon-based precursors, and they exhibit a series of excellent properties, such as outstanding physical and chemical stabilities, flexible designability and easy processability. Furthermore, suitable modification of the precursors leads to multiphase ceramics known as polymer-derived ceramic nanocomposites (PDC-NCs), which in some cases exhibit enhanced properties compared to those of the original materials. Nowadays, the application of PDC-NCs is no longer limited to the high-temperature and high-strength structural materials, by doping different metals, a series of heterogeneous catalysts with unique microstructures and excellent catalytic properties can be synthesized via PDC approach. This article proposed an overview of the research progress on the preparation of PDC-NCs and their catalytic properties in the last 20 a. The main topics is related to the chemical composition design of polymeric precursors, the construction of porous structure, and the characterization of catalytic properties. Finally, the current challenges and perspectives on the field of porous PDC-NCs preparation and their application in catalysis are discussed.The properties of PDC-NCs were directly affected by the composition and the architecture of the precursors, which provided enormous potential in tuning the microstructure and properties of the PDC-NCs via the various dopants. Metal containing PDC-NCs can be conveniently synthesized via the chemical modification of the precursors and physical blending, the obtained ceramics were endowed with different catalytic properties. In chemical modification, metal elements were linked to silicon-based precursor molecules via chemical reactions between precursors and metallic compounds. Three typical of metallic compounds have been summarized here: metal chlorides, acetylacetonate metal compounds and metal complex. Active groups like Si—H, N—H and C=C of precursors were convenience to the chemical modification. The metallic elements were homogeneously introduced into single-source precursors at the molecular level, which of great significance to prepare heterogeneous catalysts with high activity and stability. In physical blending, metallic compounds have been simply mixed with precursors through ultrasound, ball milling, or impregnation,and then PDC-NCs can be obtained via a simply pyrolysis process of these mixtures. Although there were still some drawbacks such as nonuniform element dispersion and relatively low catalytic performance, the physical blending approach is still a promising route to produce catalysts owing to the simple technologic process, cheap and wide source of raw materials, etc.Additionally, the porous structure in heterogeneous catalysts exhibited a crucial influence on its properties, as high porosity could increase the specific surface area (SSA) of ceramics, and more catalytic active sites can be exposed, which is beneficial for improving catalytic efficiency. While appropriate pore size and porous structure are conducive to the diffusion and transport of reactants and products. Mesopores can be constructed in PDC-NCs via the introduction of hard/soft templates and even template-free method. The porous morphology and pore size can be regulated at the meso-scale by changing the templates and pyrolysis program, thereby further promoting the catalytic performance.Many studies indicated that PDC-NCs with precise composition and structure design could be used as heterogeneous catalysts and showed excellent catalytic performance in the fields of catalytic synthesis, pollution treatment and new energy development. The polymeric precursors can be modified easily by various metallic compounds due to its superior molecular designability, after high-temperature pyrolysis, the ceramic skeleton can be applied as robust support materials to disperse and anchor active metallic nanoparticles. Moreover, the distinct characteristics such as adjustable SSA, pore volume, surface hydrophilicity or lipophilicity, as well as chemical resistance towards reaction medium, making porous PDC-NCs showed significant advantages for catalysis in harsh environments.

High Mach precision guided aircraft has the important advantages of successful penetration with high level, presenting a strategic deterrent force to safeguard national core interests and maintain world peace. Its extremely high flight speed (>5 Ma) is an important guarantee of breakthrough capability, but causing severe aerodynamic erosion, heating, and ablation. Thus, it is a serious challenge to the communication, precise guidance, detonation and other combat tasks of the front-end antenna cover and antenna window. Therefore, the development of high-temperature transparent materials for antenna covers/windows that integrate various functions such as load-bearing, high-temperature resistance, and wave transmission is an urgent bottleneck problem to be solved.High temperature resistance is an important indicator of transparent materials. The service speed of low-speed aircraft is low, and organic transparent materials such as phenolic resin and epoxy resin with lower temperature resistance can meet the usage requirements. With the continuous improvement of aircraft flight speed, higher temperature requirements are also expected for the use of transparent materials. The selection of transparent materials has transitioned from organic polymer systems to inorganic ceramic systems. Traditional inorganic transparent ceramics mainly include oxide ceramics such as quartz and glass-ceramics, with short-term usage temperatures around 1 000 ℃. With the development of aircraft flight speed towards high Mach numbers, there is a higher demand for the high-temperature resistance of transparent ceramic materials. Nitride ceramics, represented by silicon nitride (Si—N),boron nitride (B—N), silicon boron nitrogen (Si—B—N), and silicon nitrogen oxide (Si—N—O), exhibit superior high-temperature resistance than oxide ceramics. They are the most promising high-temperature transparent materials to meet the requirements of high Mach number aircraft and have become a research hotspot both domestically and internationally.In recent years, researchers have conducted a detailed review of the research progress on nitride high-temperature transparent ceramic materials, which are a type of inorganic materials bonded by strong covalent bonds. They have the characteristics of high brittleness, high melting point and high hardness. Most nitride ceramics undergo obvious thermal decomposition reactions before melting, making it more difficult to sintering compared to carbide and boride ceramics. Typical sintering methods such as hot pressing or pressureless sintering have obvious shortcomings when preparing complex and precise structure antenna covers.The precursor conversion method has the advantages of low processing temperature, controllable composition, easy processing and plasticity, and has become the preferred method for the preparation of high-performance antenna covers. The precursor conversion method first requires the synthesis of organic polymers containing target ceramic elements, which can be transformed into target ceramics after high-temperature (>1 000 ℃) pyrolysis. By utilizing the soluble and fusible properties of polymers, it is possible to prepare complex and precise antenna radomes through close prototyping.At present, the development of new equipment is increasingly urgent for the precursor of nitride transparent ceramics, and the performance indicators of the precursor are also clearer. Driven by demand, systematic research has been carried out both domestically and internationally on the synthesis, transformation, and applications of nitride wave transmitting ceramic precursors.This not only provides rich material selection schemes for the development of high-temperature performance antenna covers, but also greatly enriches the development of precursor ceramics. This review mainly summarized the research progress in the precursor of nitride wave transmission ceramics in recent years, involving silicon nitride, boron nitride, silicon nitrogen oxide and other nitride wave transmission ceramic precursors, and proposes research directions in the future. It is expected that the work can provide certain reference for relevant researchers, and also look forward to more researchers paying attention to the research of nitride wave transmission precursors, supporting the development of wave transparent materials at high temperature.

Boron nitride fibers have attracted significant research interest due to their low density, high strength, high temperature resistance, strong insulation and wave transparent properties, making them promising high-performance wave transparent composites required for aerospace applications. The polymer-derived ceramics (PDCs) method is one of the most potential approaches for preparing boron nitride fibers. Currently, developing high performance boron nitride fibers remains a major challenge in the field. Controlling the structure of polyborazane precursor and structure-property relationships between polymer and ceramic have been gained widespread attention. Numerous studies were focused on optimizing the boron nitride fiber fabrication process, including precursor molecular structure design, thermal treatment process, and fiber microstructure regulation. However, reviews from the perspective of precursor molecular structures for boron nitride fiber preparation via PDCs were still rarely, and the relationship between precursor molecular structure and boron nitride fiber performance requires further in-depth analysis.The molecular structure of precursors plays a critical role in determining its physicochemical properties. in this paper, authors firstly analyzed the different molecular structures of boron nitride precursors to elucidate the structure-property relationships between polymer and ceramic. Based on the flexibility and molecular weight of the chains, boron nitride precursors can be divided into rigid chain structures, flexible chain structures, and small molecule boron nitride precursors. The synthesis methods, properties, and applications of precursors with corresponding chain structures were summarized. Directly synthesizing a precursor that simultaneously satisfies all performance requirements of thermal stability, solubility, meltability, high ceramic yield, and spinnability was highly challenging. To overcome this challenge, this paper summarized common approaches for modulating the elemental composition and molecular structure of precursors to improve its overall properties. Methods for modulating precursor molecular structures primarily include substitution group modification, mixing/copolymerization modification, and bridge-linking structure modification. Through structural modulation of precursor molecules, spinnability and crosslinking characteristics could be realized.The molecular structural transformation process from polymer to boron nitride ceramic during PDCs was rather complex and significantly impacts the properties of boron nitride fiber. This paper reviews the heat treatment and microstructural control techniques employed during boron nitride fiber fabrication. Fiber heat treatment currently included inert atmosphere thermal crosslinking, ammonia (NH3) atmosphere thermal crosslinking, air heat treatment, and BCl3-assisted heat treatment with different mechanisms for crosslinking and solidifying precursor. Methods for controlling microstructure mainly included molecular symmetry modulation, heat treatment, and secondary phase induction. The goal of these operations is to achieve an intimate structure and crystalline orientation within fibers for optimal mechanical performance. Overall, a systematic understanding of structure-property relationships and process-microstructure-property correlations of boron nitride precursors is important for continued advances in high-performance boron nitride ceramic fibers.

Photocatalysis is an effective technology to solve environmental pollution. Ferroelectric ceramics, as a new type of catalyst, have been received widespread attention mainly attributed to the ability to reduce the recombination rate of photo–induced carriers and to improve catalytic performance by building a built-in electric field. In order to avoid the decrease of remanent polarization in ceramic bulks during the traditional poling technology and simplify the poling process, corona poling technology has been used for the poling of powders. Several researches indicated that corona poling could significantly improve the catalytic performance, while the relationship among the particle size, phase structure, and piezo–photocatalytic performance was still not so clear. Therefore, BaTiO3 (BT) nanoparticles with different particle sizes were prepared via sol-gel method and then polarized these powders for 1 h under a voltage of 6.56 kV. The phase structures and the lattice distortion before and after poling were carefully explored. In addition, the effect of corona poling on the piezo–photocatalytic performance of BT powders was investigated, Rhodamine B (RhB) was utilized as the target pollutant.

Micro-displacement actuators are widely used in micromachining, precision measurement, aerospace and biomedical. The performance of micro-displacement actuators can be evaluated in terms of displacement, hysteresis, linearity and temperature stability. For a long time, researchers have been hoping to obtain a ferroelectric material with high field-induced strain, low hysteresis and good temperature stability for a variety of different applications. Pb(Mg1/3Nb2/3)O3 (PMN) is a typical perovskite type relaxor ferroelectric, and PMN–PbTiO3 (PT) solid solution possesses a morphotropic phase boundary (MPB) region from PT mole fractions of 0.27 to 0.35. The field-induced strain and hysteresis of PMN–PT could meet the requirements of high-performance micro-displacement actuators. However, the temperature stability of field-induced strain still needs to be improved before practical application. In this work, effect of Sm3+ doping on the temperature stability of field-induced strain in PMN–0.32PT ceramics was investigated.

Microwave dielectric ceramics are widely used in microwave frequency (i.e., 300 MHz–300 GHz) circuits as communication electronic components such as resonators, filters, and antennas. The dielectric permittivity (εr), quality factor (Q×f) and the temperature coefficient of resonant frequency (τf) are the main performance index to measure the quality of microwave dielectric ceramics. However, there is a constraint relationship between the performance parameters. In general, the giant εr may cause a large dielectric loss and a low Q×f, and the volatility of εr originates an enormous τf value. Therefore, materials with superior intrinsic microwave dielectric properties are rare. The existing methods of controlling microwave dielectric properties mainly include ion substitution, composite control, laminated control and non-stoichiometric ratio control. These methods often require sacrificing one parameter to satisfy other parameters. High-entropy strategy is a novel regulation method used in inorganic materials.High-entropy ceramics refer to a ceramic system with a configuration entropy (Sc) of 1.5R. The high-entropy effect, sluggish diffusion effect, lattice distortion effect and synergy in components (i.e., cocktail effect) are four special effects of high-entropy ceramics. The high-entropy strategy shows a great potential in dielectric ceramics due to these unique effects. In this paper, high-entropy strategy was used to design rare-earth vanadate ceramics. The impact of high-entropy structure on the microwave dielectric properties was investigated.

High-entropy zirconate ceramics (HEZCs) have been studied extensively in recent years for the potential applications in thermal barrier coatings and high-level nuclear waste immobilization. While these HEZCs have the issue of poor toughness, which impedes their applications. The toughness of HEZCs can be improved by decreasing its grain size. While preparation of ultrafine-grained or nanocrystalline HEZCs is a challenge because the rapid grain growth inevitably occurred at high temperature densification process (typically above 1 500 ℃).In this work, the challenge of preparing dense ultrafine-grained high-entropy ceramics through conventional pressureless sintering process was addressed via a simple two-step sintering method. Ultrafine-grained (Ce0.2Nd0.2Sm0.2Gd0.2Y0.2)2Zr2O7 high-entropy zirconate with 99.0% theoretical density and 162 nm grain size was fabricated. Compared to the conventional method,two-step sintering provided the high-entropy zirconate with finer grain size and better microstructural uniformity, and excellent comprehensive mechanical properties including high hardness of 12.5 GPa and high fracture toughness of 2.4 MPa·m1/2. This workcould help to understand the sintering kinetics of HEZCs, and also supplied a guidance to prepare the ultrafine-grained or nanocrystalline HEZCs by pressureless sintering method.

Compared with the preparation process of blade turbine using precision investment casting (PIC), additive manufacturing technology, especially binder jetting additive manufacturing (BJAM), possess many advantages such as the decreased cost, simplified process, easily preparation of complex porous materials, and diversified selectivity of binder types, therefore, it has been widely used to fabricate the core parts. Al2O3 ceramic owns better oxidation and corrosion resistance, highly serviced temperature and high hardness, is widely used as the core materials. However, the solid sintering method is hard to meet the mechanical requirement of Al2O3 ceramic cores. Therefore, a solid-liquid sintering additives, such as CuO and TiO2, was added to assist the sintering of Al2O3 ceramic. In this work, influence of sintering additives contents ranged from 0 to 10% (mass fraction) and layer thickness ranged from 60–100 μm on the porosity, microstructure, and mechanical properties of Al2O3 ceramic cores were investigated. the results could construct a theoretical foundation for the rapid and low-cost printing of high-performance ceramic cores,and further expand the application scope of Al2O3 ceramics.

Silicon nitride (Si3N4) ceramics are considered to be one of the most promising ceramic substrate materials due to their good insulation, low coefficient of thermal expansion and high mechanical properties. However, the thermal conductivity of Si3N4 ceramics prepared by conventional methods is low (< 50 W·m–1·K–1), which greatly affects the reliability of chips and even causes the failure of electronic devices. New methods such as gas pressure sintering (GPS), and sintered reaction-bonded silicon nitride (SRBSN) have been employed to fabricate Si3N4 ceramics with high thermal conductivity and high bending strength. Nevertheless, the sintering temperature of both GPS and SRBSN is high and the holding time is too long, which lead to the high cost and limit its applications. Spark plasma sintering (SPS) can produce ceramics with high density in a relatively short time, while the short soaking time is not suitable to improve the thermal conductivity. High-temperature heat treatment can promote the growth of Si3N4 grains, and thus improves the thermal conductivity of Si3N4 ceramics. Therefore, it is expected that Si3N4 ceramics with highbending strength and high thermal conductivity can be prepared at a lower temperature and a shorter time by the combination of SPS and high-temperature heat treatment processes.

Nanostructured amorphous materials represent a novel class of materials characterized by nanostructured amorphous particles and amorphous interfaces between particles. Due to the nanometer scales, amorphous disorder, controllable atomic and electronic structure, this kind of material exhibits numerous unique properties distinct from conventional materials. Recently, scholars discovered that composites composed of nanostructured amorphous materials as the matrix with precipitated nanocrystals exhibited excellent mechanical properties. However, densification of both nanostructured amorphous materials and nanostructured amorphous composites was primarily achieved through ultra-high-pressure forming. During ultra-high-pressure forming, the plastic deformation of nanostructured amorphous powder under high pressure enabled amorphous particles to contact each other, extrude pores, and diffused through interfaces to form new interfaces. However, these studies required high-pressure forming equipment, and the associated costs constrained further applications.In contrast to the ultra-high-pressure molding mentioned earlier, Rosenflanz et al. employed viscous sintering to consolidate amorphous powder within the supercooled liquid region. This method utilized amorphous powder with low viscosity above the glass transition temperature (Tg) and its viscous flowed under external pressure to fill the pores between particles, thereby achieving densification. This approach only required 34 MPa pressure, effectively circumventing the unrealistically high pressures previously required for amorphous material preparation. However, crystallization during viscous sintering may impede the viscous flow of amorphous powder, necessitating a sufficiently wide kinetic window between the glass transition temperature (Tg) and crystallization temperature (Tx) to achieve densification. To address this issue, Rosenflanz et al. again employed an alumina–rare earth oxide system (Al2O3–RE2O3) to modulate the polyhedral structure of Al–O, regulated the glass formation ability of the system, substantially widen the kinetic window of the oxide system, and fabricated a range of dense amorphous ceramics. Nonetheless, viscous sintering process has never been reported in the realm of nanostructured amorphous materials.

During the sintering process, porous ceramics undergo significant shrinkage with volume changes even half. Such volumetric alterations may lead to materials cracking or deformation, severely affecting the yield of the prepared products.Researchers have proposed several methods such as adjusting the sintering temperature, utilizing reactions and expansion phases during the sintering process to address these issues. The most commonly method was to utilize the expansion characteristics of the materials themselves to solve the shrinkage problem. However, this method requires complex raw materials and lacks universality.Recently, our group proposed an in-situ hollow sphere method with the addition of spherical metal powders, successfully preparing porous ceramics without sintering shrinkage. The main theoretical support for this process is the Kirkendall effect that occurs during two-phase diffusion. When metal spherical particles are oxidized, the difference in diffusion rates forms a hollow structure,effectively offsetting the shrinkage caused by sintering. In this work, hollow zinc oxide particles were successfully prepared using the direct oxidation of metallic zinc powders and applied in the preparation of zinc oxide porous ceramics. During the oxidation process of metallic zinc powder, its addition amount, particle size, and their effects on the properties and microstructure of porous ceramics were investigated. The relationship between the pore size of porous ceramics and the particle size of metallic zinc particles was analyzed. This study could broad the application scenarios of this process and hollow zinc oxide particles.

Ceramic foams is a kind of inorganic non-metallic material with a three-dimensional porous network structure after calcination at high temperatures. The mechanical properties are one of the important factor to evaluate the application of ceramic foams, which affected by the porosity, pore size, pore distribution and skeleton structure, etc. High porosity would reduce the bearing capacity of ceramic foams and limit its application fields. Therefore, this research is mainly focused on how to balance porosity and strength of ceramic foams, as compressive strength could be improved effectively by reducing the pore size, narrowing the pore size distribution or forming a closed pore structure.When coal gangue is used as raw materials to prepare ceramic foams, it still exists some problems, such as the low utilization, high energy consumption and unclear foaming principle. The key to producing a ceramic foam is to form a melt matrix with appropriate viscosity and to generate a certain amount of foaming gas in the matrix. Due to the complex composition of coal gangue,it is difficult to control the viscosity of the melt matrix at high temperatures, resulting in the pore structure distribution uneven and reducing the mechanical properties of ceramic foams.In this work, coal gangue was used as the main raw materials, and diatomite powder, talc powder, a small amount of silicon carbide (SiC) foaming agent were added to prepare the ceramic foams with high compressive strength. The effects of raw materials composition, SiC content (mass fraction) and particle size of feed mixture on the pore structure, apparent density and compressive strength and other properties of ceramic foams were investigated.

Porous ceramics are-widely used in a variety of environmental fields such as solid–liquid separation and hot gas filtration due to their high mechanical strength, excellent chemical resistance, and high thermal stability. Conventional porous ceramics are usually made of particle-packing of inorganic powders, which are usually characterized by a low porosity, a high self-weight, a low permeability and a high filtration resistance. It is thus necessary to develop novel porous ceramics with a high porosity, a high mechanical strength and a low packing density. Mullite whisker-based porous ceramics have attracted recent attention in the treatment of various wastewaters. Compared with porous ceramics prepared by conventional particle-packing, mullite whisker-based porous ceramics are constructed by whisker interlocking, resulting in fibrous structures with a high porosity, a high pore connectivity and a low packing density. However, these mullite porous ceramics are seldom used in industry due to the high cost of the high-purity starting materials. Fly ash is a major by-product of coal combustion. The elemental analysis shows that fly ash is mainly composed of unburned carbon, metal oxides (i.e., Si, Al, and Fe) and other inorganic materials. Fly ash can be used to prepare mullite porous ceramics due to the presence the high content of aluminum silicates. However, the effect of holding time on the growth of mullite whiskers and the permeance-selectivity of the fibrous structures is still unclear. In order to elucidate the growth mechanism of mullite whiskers based on gas-solid reaction, the effects of sintering temperature and holding time on the microstructure, phase composition and filtration properties of the porous ceramics were investigated.

The aimed environmental barrier coatings (EBCs) need to meet the characteristics of low oxygen permeability, match thermal expansion coefficient, and keep phase stability under service conditions, which usually need to be designed as a multi-layer structures to avoid premature failure of gas turbine engines during operation. Yb2Si2O7 (YbDS) is considered the most promising candidate due to its excellent resistance to water vapor corrosion and damage tolerance, a similar coefficient of thermal expansion(4.1×10–6/K) to that of the matrix material (SiC, 4.7×10–6/K), and does not generate high thermal cycling stress in EBCs systems. However, when YbDS was exposed to an environment containing with high-temperature water vapor, corrosion transformation may occur, which would reduce the durability of EBCs. To analyze the corrosion process, stress characteristics, and crack propagation laws of YbDS under the coupling effect of water-oxygen corrosion and thermal cycling, the compositional and structural changes of YbDS under high-temperature water-oxygen action were determined through experiments, also the influence of water–oxygen corrosion on the stress evolution of the coating was explored using finite element software Abaqus. The extended Finite Element Method (XFEM) was used to simulate the propagation path of cracks in YbDS, and the accelerating effect of water–oxygen corrosion on crack propagation was discussed finally.

The modern gas turbines are constantly pursuing the development trend of high heat insulation and long service life, making the operating temperature of turbine blade continuously rising. Thermal barrier coatings (TBCs) have high temperature resistance and high heat insulation to protect metal alloy substrates. The ceramic topcoat layer is typically composed of yttria-stabilized zirconia (YSZ) material. However, the spallation failure of YSZ is easy to occur during high-temperature service.Gd2Zr2O7(GZO) is one of the candidate materials for the new generation of thermal barrier coatings，due to its low thermal conductivity and phase stability at high temperatures. The porous structure of ceramic coatings inevitably undergoes sintering and densification during high-temperature service, the hardness and elastic modulus of coating were decreased.Adjusting the spraying distance influence both the temperature and velocity of particles, thereby influencing the microstructure of the porous coating. In this work, three kinds of Gd2Zr2O7 (GZO) coatings deposited at different spraying distances were prepared by atmospheric plasma spraying (APS). The as-deposited coatings were thermal exposure to 1 300 ℃ for different hours. The phase structure, microstructure and mechanical properties of the obtained coatings were characterized. The relationships of pore structure and mechanical properties of GZO coatings were revealed during high temperature thermal exposure.

Magnesia, acted as a refractory material, is widely used in industrial metallurgical furnaces owing to its high refractoriness and excellent corrosion resistance to basic slag and metal melt. Generally, the fabrication of high-quality magnesia aggregates with high purity and high bulk densities (＞3.40 g/cm3) plays a critical role in producing MgO-based refractories that show satisfying mechanical properties and corrosion resistance. In China, magnesite is mainly used as a raw material to produce sintered magnesia at high-temperature. while, as the generally coarse-grained of magnesite, it is difficult to produce high density magnesia even sintered at high temperatures, being due to the poor sintering property. As reported that the introduction of oxides additives such as TiO2, Al2O3 ZrO2, etc. could effectively promote the sintering of magnesia. However, the additives also resulted in a low melting phase formation, which significantly reduced the high-temperature performance of magnesia. In fact, besides magnesite, China also has abundant magnesium resources in salt lakes. Compared to magnesite, magnesia derived from salt lake owns the advantage of higher purity and without CO2 emissions during the production process. In this work, magnesium hydroxide produced from salt lake was used as raw material to prepare the high-purity dense magnesia via a two-step method. Effects of calcination temperature and grinding time on the morphology and sintering activity of MgO were studied, microstructure and densification behavior of magnesia sintering at high-temperature were investigated also.

Chalcogenide glasses are primarily composed of elements from group VI of the periodic table, such as sulfur, selenium, and tellurium, and may include other non-oxide elements like germanium and arsenic. These glasses exhibit properties such as high refractive index (2–3.5), low phonon energy (<350 cm?1), and tunable performance. As the most popular chalcogenide glasses, As-Se and As-S glasses are widely used in the fields of mid- and far-infrared imaging, supercontinuum generation, infrared laser power transmission, etc. However, the soluble impurity absorption and insoluble particle impurities inside the glass lead to a lot of trouble. In particular, particle-induced scattering is one of the key factors for the decrease of the glass transmittance. Such particles may be sourced from various conditions, such as the original presence of raw materials and introduction during glass preparation. So, it is urgent to find the real source and remove these impurities. For example, Nguyen et al. prepared As2Se3 fiber with the lowest loss below 1 dB/m, but found that there are a large number of submicron particles-Al2SiO3-inside the fiber, which enhances the scattering loss of the glass. To address this challenge, this work investigated the optical properties of glass by adding deoxidizers and filter sheets to the dynamic distillation process.

Platinum group metals (PGM), including ruthenium (Ru), rhodium (Rh), and palladium (Pd) are enriched in high-level liquid waste (HLLW) during the reprocessing of spent nuclear fuels. Vitrification is currently the only practical technology to immobilize HLLW. However, the high density and low solubility of PGM in glass cause them to settle down during vitrification process, resulting in the increased viscosity and conductivity of the glass melt at the bottom of the melter. This would potentially lead to concerned issues such as blockages in the discharge port and damage of electrodes. Therefore, understanding the deposition of PGM during vitrification is quite crucial in the management of HLLW. However, few research focused on the deposition process and the spatial distribution of PGM particles in glass melts. Thus, this work took Ru as the representative of PGM and investigated spatial distribution of Ru precipitates in glass melts.

Sustainable H2 generation from water splitting by solar-driven photocatalysis has been proposed as a promising alternative to increasingly reduced fossil fuels. However, such techniques still face great challenges in dynamics and thermodynamics.Biomass as a hole sacrificial agent is conducive to the generation of H2. Local surface plasmon resonance (LSPR) can effectively use solar energy and convert it into high-energy "hot carriers", and realize high efficiency solar energy to chemical energy conversion. Copper alloy inherits the LSPR effect of copper particles. Palygorskite (Pal) is a natural hydrated magnesium silicate mineral with large surface area and certain acid sites. In this work, Pal-loaded plasma alloy nanocomposite was prepared for photocatalytic reforming cellulose for synergistic hydrogen production. The phosphate group-modified Pal provides a large number of acidic sites for cellulose hydrolysis and glucose. At the same time, the LSPR effect of CuNi alloy increases the reaction temperature, realizes the photothermal cooperative catalysis, and further enhances the catalyst activity.

With the continuous promotion of the "carbon neutrality" and "carbon peak" strategies, reducing carbon emissions from cement production is urgent. Replacing cement with a combination of one or multiple mineral materials can not only improve the physical properties of cement products, but also reduce the use of cement clinker, thereby reducing carbon emissions in cement production and saving resources. However, due to the complex properties and multiple interrelated properties of cement matrix composites, the optimization design of these materials in cement matrix composites faces challenges. Therefore, it is necessary to find more efficient and accurate methods for optimizing the design of cement matrix composites.

In recent years, mordenite molecular sieves with various properties have been successfully synthesized by template method. Although the template method has received a lot of attention, the addition of the templating agents especially organic templating agents, would increase the cost of raw materials, and could be harmful to environment. Therefore, the method without organic template is more economical and environmentally friendly. Recently, the synthesis and applications of mordenite modified by hetero-atom have getting more and more attentions, and the performance of modified mordenite molecular sieve shows better. The common methods for modifying mordenite molecular sieve include ion exchange method and impregnation method. Some researchers have synthesized monolithic iron-containing mordenite (Fe-MOR) by template-free method, which has excellent CO2/N2 separation performance and high carbon dioxide capture performance. In addition, Fe-MOR zeolite can catalytically decompose N2O into N2 and O2, which can effectively reduce the N2O content in the atmosphere. In this work, Fe-MOR zeolite was synthesized by hydrothermal method without organic template. A novel rod-cluster-shaped Fe-MOR zeolite was controllably synthesized by fine adjustment of pH and crystallization time, and its CO2 adsorption properties were investigated.

Supercapacitors (SCs) are known as one of the most promising energy storage devices due to their high-power density and excellent cycle stability. The performance of SCs is closely related to the electrochemical performance of electrode materials. The widely-used electrodes are carbon-based materials and their derivatives. Carbon materials contribute energy storage based on double layer capacitance associated with ion adsorption and desorption, achieving excellent power density and cycle stability. However, they lack in high capacitance because of limitation of surface area. Instead, Fe-based Prussian blue (PB) is a promising pseudocapacitive material with open frame structure and high theoretical capacitance, but the poor electrical conductivity limits its rate performance and cycle stability. Combining PB with carbon materials is considered as an effective solution to develop advanced electrode composites. Herein, nanoporous carbon (NPC) derived from lignite has been prepared with high specific surface area and good electrical conductivity. Then, Fe-Prussian blue was successfully loaded on NPC via co-precipitation method to obtain Fe-Prussian blue@ nanoporous carbon composite (PB@NPC). The fabricated PB@NPC composite possesses high specific surface area, high specific capacitance and excellent cycle stability.

Rare earth gypsum is an industrial by-product generated from the treatment of wastewater produced by the rare earth metallurgical process, and its recycling is a strategic measure for the current green metallurgy and cleaner production. In addition, the filler reinforcing agent for natural rubber in polymers is mainly carbon black or other materials such as calcium carbonate, which will cause a large amount of carbon emissions in the production process. Calcium sulfate whisker (CSW) is a new reinforcing agent in rubber composites, while its surface is hydrophilic and has poor compatibility with organic matrix. This work aims at the above problem by using inorganic trisodium phosphate-organic stearic acid composite modification, thus changing the surface polarity of CSW and improving the compatibility with organic matrix.

Ferroelectric materials are widely used in various electronic functional materials and devices due to their excellent energy conversion and storage functions, which mainly depends on the crystal structure gene of ferroelectric materials, named as polarization configuration. Traditional phase boundary construction strategies were not flexible enough in regulating polarization configuration, and the improvement on the electrical properties of materials was also limited for the requirements of miniaturization and integration of next-generation devices.Recently, researchers introduced the high-entropy strategy into ferroelectric materials and systematically studied the regulation mechanism of local polarization configuration. Theoretical and experimental results showed that, when retaining the traditional high-entropy effect, the high-entropy strategy could also fully utilize the comprehensive factors of atomic ferroactivity and radius for the directional design of ferroelectric functional elements (local polarization configuration and oxygen octahedron tilt), effectively improved the flexibility of external field response, and then significantly improved the related electrical properties. Materials with both high chemical disorder and high ferroelectric functional element disorder can be called “high-entropy FEs”. A series of researches have been carried on the ferroelectrics via the high-entropy strategy, and varieties of high-performance functional materials were designed and prepared.In this paper, the polarization configuration, acted as the core functional unit, is firstly introduced to achieve the diversity of physical properties in ferroelectric materials and the crucial role in regulating material’s properties. Then the mechanism of improving the performance of high-entropy FEs by adjusting the polarization configuration through the high-entropy strategy is discussed;Finally, the research on controlling the polarization configuration of ferroelectrics using the high-entropy strategy to enhance their performance is summarized and categorized, which demonstrated that the high-entropy strategy could improve the performance of ferroelectric materials in a feasibility and broad prospects. Finally, four directions of high-entropy strategy for enhancing material performance, including piezoelectric performance, large electrostriction, excellent energy storage, and refrigeration with large electrocaloric effect are introduced.