It is of great practical significance to develop thermal insulation materials with integrated load bearing and thermal insulation for energy saving and emission reduction in high-temperature engineering. In this work, SiO_2f/SiO₂ composites were prepared by a precursor impregnation heat-treatment method with quartz fiber needled felt as a reinforcement and silica sol as a precursor. The effect of heat-treatment temperature on the density, porosity, mechanical properties and thermal properties of SiO_2f/SiO₂ composites was investigated. The composition and microstructure of the composites were characterized by X-ray diffraction and scanning electron microscopy. The coefficient of thermal expansion and thermal conductivity of composites were measured by a push rod method and a transient hot-wire method. The results indicate that the apparent porosity and mechanical strength firstly increase and then decrease with the increase of heat-treatment temperature. The sample after heat-treatment at 450 ℃ has the optimum overall performance (i.e., the flexural strength of 23.5 MPa, and the compressive strength of 61.9 MPa). The fracture mechanism is a ductile fracture. At 300-700 ℃, the thermal expansion coefficient of the sample is 0.564×10^-6/℃. The thermal conductivity of the samples decreases with the increase of temperature, and it is as low as 0.096 W/m·K at 700℃. The SiO_2f/SiO₂ composite prepared has some advantages in the integrated application of load bearing and thermal insulation, and meets the harsh requirements of hot pressing and sintering, non-ferrous metallurgy and other industries.

Reducing the operational temperature for high-temperature solid oxide fuel cell (SOFC) is of great significance to improve the stability of materials, increase the operation life of the system and reduce the fabrication and operation cost of the cell. This aspect has therefore attracted recent research attention. So far, different research strategies were proposed to reduce the operational temperature. This review represented recent research progress on the composite electrolyte in low-temperature solid oxide fuel cell (LT-SOFC). The carbonate materials as the second phase for composite preparation of molten carbonate-like SOFCs and the transition metal oxide materials as the second phase for composite preparation were introduced. The single-component fuel cell for eliminating the interface resistance between electrode and electrolyte and improving the fuel cell performance and the stability of the peroxide composite electrolyte was elaborated. The semiconductor composites to enhance LT-SOFC's electrochemical performance were described. In addition, this review also represented the preparation of novel nanocomposites to further enhance the electrolyte ionic conductivity and the interfacial compatibility, and the explorations of the electrochemical performance of LT-SOFC with respect to the effect of novel electrode materials.

The photocatalytic reduction of CO₂ is a green, environmental-friendly energy conversion way to realize the carbon cycle of ecosystem. This method can effectively convert greenhouse gases into renewable fuels, thus alleviating energy crisis and global warming problems. This review represented recent research work on the semiconductor composites in photocatalytic reduction of CO₂ and the reaction conditions and photocatalytic mechanism of photocatalytic reduction of CO₂. Based on the previous reports, the main types of semiconductor composites of photocatalytic reduction of CO₂ were summarized, i.e., pure semiconductor photocatalysts, metal and nonmetal doped semiconductor photocatalysts, composite semiconductor photocatalysts, and carbon-based semiconductor photocatalysts. In addition, the advantages and disadvantages of various photocatalytic materials and some factors affecting photocatalytic activities were also analyzed. The future research aspects on the catalytic reduction of CO₂ by semiconductor composites were prospected.

With the rapid development of absorbing materials due to the demand for stealth technology in the military and national defense field and the increasingly serious electromagnetic pollution in life, various types of absorbing materials emerge. Compared with the conventional carbonaceous absorbing materials, biomass-derived carbonaceous materials improve the absorbing performance due to their advantages like light weight, low cost and sustainability. This review briefly represented the synthesis methods of biomass carbon materials, systematically introduced the application of edible and non-edible biomass derived materials in the preparation of carbonaceous composite absorbing materials, and described recent work on the biomass-derived carbonaceous materials. Recent research progress on the composite materials in the field of wave absorption was given. The differences in the microstructure and microwave absorption properties of different biomass-derived carbonaceous composites were mainly analyzed, and the microwave absorption mechanism of different biomass-derived carbonaceous composites was summarized. The current challenge and the directional perspective of biomass-derived carbonaceous composites absorbing materials with efficient microwave absorption properties were discussed. This review provides a comprehensive theoretical and applied knowledge background for the investigation of biomass-derived absorbing materials, which can promote the development and application of biomass-derived carbon-based composite absorbing materials.

The multi-component ceramics of BaO-SrO-CaO-MgO-Al₂O₃-2SiO₂(BSCMAS) with different molar ratio of Ba, Sr, Ca, Mg were prepared by a conventional solid-state reaction. The fabrication procedure, CMAS corrosion resistance, and microstructures of BSCMAS were investigated. The results show that the multi-component ceramics of Ba_0.3Sr_0.3Ca_0.35Mg_0.05Al₂Si₂O₈ (B_0.3S_0.3C_0.35M_0.05AS) can form a single-phase solid solution by adjusting the concentration of MgO. The CMAS corrosion of B_0.3S_0.3C_0.35M_0.05AS were carried out at 1 250, 1 300 ℃ and 1 350 ℃. The B_0.3S_0.3C_0.35M_0.05AS showed better CMAS corrosion resistance than Ba_0.5Sr_0.5Al₂Si₂O₈. The sluggish diffusion of multi-component cations in B_0.3S_0.3C_0.35M_0.05AS leads to suppressing the interdiffusion of Ba—Sr with Ca—Mg, combined with the quick formation of anorthite to block the out-diffusion of Ba and Sr, resulting in the improved CMAS corrosion resistance of B_0.3S_0.3C_0.35M_0.05AS material.

To explore the application prospects of high-entropy carbide ceramics as wear-resistant parts, a high-entropy (TiVTaMoW)C ceramic with a uniform distribution of elements was prepared via ball milling and subsequent two-step sintering with metal carbides as raw materials. The friction and wear properties of (TiVTaMoW)C ceramic at room temperature and 800 ℃ sliding against Al₂O₃, SiC, and Si₃N₄ balls were investigated, respectively. The results show that (TiVTaMoW)C ceramic exhibits superior tribological properties with low friction coefficients and wear rates at room temperature. Especially for sliding against SiC ball, the friction coefficient and wear rate are (0.38±0.01) and (1.52±0.36)×10^-7 mm³/(N·m). The surface of (TiVTaMoW)C ceramic is severely oxidized during sliding and accompanied by aggravated wear when the temperature is 800 ℃. The wear rates of high-entropy carbide ceramic sliding against all of the friction pair balls can increase to 10^-4 mm³/Nm. The oxidation products of MoO₃ and V₂O₅ with low shear stress characteristics form self-lubricating and transferring films between the friction pairs, which made the friction coefficients maintain the same level as that at room temperature. In addition, SiC friction pair presents better tribological compatibility with (TiVTaMoW)C ceramic with a low friction coefficient and wear rate at room temperature and 800 ℃.

High-entropy oxides with complex compositions can be designed as novel ferroelectric materials with interesting physical consequences. A single-phase (K_0.5Bi_0.5)_0.2Ba_0.2Sr_0.2Ca_0.2Mg_0.2TiO₃ high-entropy ceramic with a perovskite structure was synthesized by a conventional high-temperature solid-state method, and the dielectric and ferroelectric properties of the ceramic were investigated. The results show that there are no relaxation peaks in the test temperature range because of the multi-element doping. The dielectric constant of ceramic has a high-temperature stability at < 300 ℃. The maximum dielectric constant of 8 887 is obtained at 100 Hz and 650 ℃. The introduction of high-entropy oxide in the ceramic can have high-entropy ferroelectrics in complex materials, and modify the properties of electronic ceramic.

The function of thermal barrier coating is to protect the hot components of advanced aero-engines from hot corrosion and ensures the hot components service in high-temperature environment safely. In general, a low thermal conductivity and a high fracture toughness are the key performance indexes for the selection of novel thermal barrier coating materials. In this work, a high-entropy rare-earth tantalate ceramic of (Y_0.2Dy_0.2Sm_0.2Yb_0.2Er_0.2)TaO₄ (i.e. (5RE_0.2)TaO₄) with the superior properties was synthesized via solid-state reaction. The results indicate that (5RE0.2)TaO4 exhibits a low thermal conductivity (i.e., 1.68 W·m^-1·K^-1@900 ℃) and a high thermal expansion coefficient (i.e., 10.0×10^-6 K^-1@1 200 ℃). (5RE_0.2)TaO₄ shows a high fracture toughness (i.e., 2.6 MPa·m^1/2) and a low brittleness index (i.e., 2.1 μm^-1/2) because of the unique ferroelastic toughening effect. In addition, (5RE_0.2)TaO₄ also has a promising application prospect as one of thermal barrier coating materials.

Based on the in-depth study of high-entropy alloys, a concept of configuration entropy stable single phase is introduced into inorganic non-metallic materials, thus developing high-entropy ceramics. The advantage of high-entropy ceramics is the diversity of composition and structure, which makes them have an application potential as functional materials. In this paper, high-entropy multiphase ceramics with a spinel structure and a perovskite structure were synthesized by a simple solid-state sintering method. The phase composition, microstructure, element content and valence state, and electromagnetic wave absorption properties were investigated. The microwave absorption properties of high-entropy multiphase ceramics sintered at different temperatures were analyzed. The results show that the high-entropy multiphase ceramics can be prepared, and two crystal structures (i.e., spinel structure and perovskite structure) can be formed due to the high-entropy effect. At 1 300 ℃, there exists a maximum dielectric constant. The high-entropy multiphase ceramics prepared have the optimum electromagnetic wave absorption performance when the frequency range is 8.2-12.4 GHz.