Carbide ultra-high temperature ceramics (UHTCs) have emerged as ideal coating materials for the thermal protection systems of hypersonic vehicles due to their high melting point (>3000 ℃), high hardness, low thermal conductivity, excellent heat resistance, and good chemical stability. This review provides a comprehensive overview of structure and properties of carbide UHTCs, namely TiC, ZrC, HfC, NbC, and TaC. Furthermore, it summarizes recent developments in preparation of carbide UHTC coatings using various methods, including chemical vapor deposition, plasma spraying, and solid-phase reaction. Effects of coating microstructure, composition, structural design, and heat flux on the ablation behavior are analyzed. Data from recent literature corroborate that the added second phase can facilitate formation of complex oxides, generate an oxidation layer during ablation to undergo moderate sintering, protect structural integrity, and enhance oxygen barrier properties. Multi-layer structural designs utilize gradient layering and multi-functional structures, which effectively alleviate thermal stress within the coating, suppress crack propagation, and facilitate synergistic enhancing effects among different layers. Finally, the challenges and opportunities in development of carbide UHTC anti-ablation coatings are prospected.

Microstructural design is a promising strategy to enhance the toughness and plasticity of structural ceramics while maintaining their inherently excellent hardness, which can facilitate their applications in extreme environments. In this work, the possibility of establishing a symbiotic structure with metal atomic-layer phase-separation (MALPS) in carbide structural ceramics was investigated. The carbide ceramic samples were synthesized from raw materials comprising transition metals with different component numbers, graphite powders, and a small amount of aluminum by spark plasma sintering at 1900 ℃ and under a pressure of 30 MPa. It was found that Al-MALPS structure was observed exclusively in the high-entropy (TiZrHfNbTa)C ceramic, which was not a MAX phase with long-range-order but rather a composite featuring a non-periodic cross-stacking of single metal atomic layers within the carbide matrix. Characterization by spherical aberration correction transmission electron microscopy and energy dispersive spectroscopy from nanometer to atomic scales revealed that the single Al atomic layers were sparsely embedded onto the {111} planes of the carbide face-centered cubic structure. Combined with the first-principles calculations, the formation of MALPS structure was found to be driven by thermodynamic stability, lattice distortion, and sluggish-diffusion effect of high entropy, rather than the differential diffusion of Al in various carbide lattices. This work could promote the design and regulation of atomic-scale microstructures in structural ceramics, aiming for high performance with synergetic high hardness-strength-toughness.

As aeroengines operate in gradually harsher service environments, enhancement of the service temperature and stress tolerance of SiCf/SiC is in great demand to ensure its proper work in high-temperature air/water-oxygen environments. Previously, researchers have initiated efforts to modify the matrix through self-healing techniques to enhance the oxidation resistance and creep resistance of SiCf/SiC composites, but whether it can be modified for more severe conditions remained unknown. Here, SiYBC modified SiCf/SiC composites (MI SiCf/SiC-SiYBC) were prepared by melt infiltration (MI), and their tensile creep properties and damage mechanisms in air at temperatures of 1300, 1350, and 1400 ℃ with applied stresses ranging from 60 to 120 MPa were explored. The composites were reinforced with plain woven fabric of silicon carbide fibers, while the matrix was prepared by melt infiltration process. The results demonstrate that the creep rupture time ($t~~{\mathrm{u}}$) is significantly influenced by stress and temperature, exhibiting a decrease with increasing temperature or stress. When test creep stress exceeds the proportional ultimate stress ($\sigma~~{\mathrm{PLS}}$), the matrix cracking facilitates oxygen ingress into the material, leading to erosion of the fiber and BN interfaces and subsequent oxidative degradation, which markedly reduces $t~~{\mathrm{u}}$. As a result, the matrix is fully fractured, and the load is mainly supported by the fibers, whose creep resistance becomes the principal factor influencing performance. Conversely, when the creep stress is below $\sigma~~{\mathrm{PLS}}$, $t~~{\mathrm{u}}$ is extended, with the load being borne by the fibers and the matrix, which is controlled by the combined creep resistance of fibers and matrix. Additionally, as the temperature increases from 1300 to 1400 ℃, the generated oxides fill the gap of the matrix/fiber interface, enhancing interfacial bonding and facilitating crack propagation and growth.

Ti2AlC is considered to be one of the compounds with the best antioxidant properties in MAX phase materials, with potential application prospects in the field of high-temperature structural materials and high-temperature antioxidant protective coatings. However, the low hardness and strength of single phase Ti2AlC limit its wide application in the field of high-temperature material. In order to improve the properties of Ti2AlC, Ti2AlC-20%TiB2 (in volume) composites (referred to as Ti2AlC-20TiB2) were synthesized by the in-situ solid-liquid phase reaction/hot pressing method. Besides, the high temperature oxidation behavior in the temperature range of 1000-1300 ℃ was studied, and the oxidation resistance mechanism at high temperature was analyzed. The results show that the oxidation kinetics of Ti2AlC-20TiB2 composites is logarithmic, exhibiting superior oxidation resistance compared to single phase Ti2AlC. Below 1200 ℃, the oxide scale is mainly composed of an inner layer of Al2O3 and an outer layer of TiO2, while the outer layer of oxide scale is a mixture of TiO2 and Al2TiO5 at 1300 ℃. The Al2O3 protective layer formed in the composite is denser than that in single-phase Ti2AlC, which is the key to its excellent antioxidant performance. The addition of TiB2 reduces the grain size of the material and increases the number of grain boundaries for short-circuit diffusion, which facilitates the selective oxidation of Al and accelerates the formation of Al2O3 protective layer. Additionally, B2O3 produced during the oxidation of TiB2 can effectively fill the micropores and repair microcracks, thereby preventing the internal diffusion of O and further enhancing the antioxidant properties of the composites.

Ortho to para hydrogen conversion catalyst (O-P catalyst) is integral for large-scale hydrogen liquefaction projects. However, factors that influence catalyst performance remain preliminary and unclear. In the mean time, the mechanical strength of the O-P catalyst is crucial for its efficacy and longevity, yet most related research has paid sufficient attention to the catalytic activity. In this work, an iron-based O-P catalyst was synthesized using a straightforward precipitation method. And effects of catalyst activation method, drying temperature, particle size, concentration ratio, and doping element on catalytic activity and mechanical strength were studied. Furthermore, the catalytic performance and structural characterization of the prepared catalyst and commercial catalyst were compared. The prepared catalyst achieved a para hydrogen (p-H2) content of 46.49% post-conversion at 77 K with a hydrogen flow rate of 1200 mL/min, surpassing the commercial catalyst by 2.9%. The maximum single particle crushing force of the prepared catalyst reached 4.75 N. Therefore, a preliminary mechanism for enhancing catalytic activity optimization was elucidated, offering valuable insights into ortho to para hydrogen conversion, and this study provides foundational data supporting the scaled production of domestic catalysts.

Ammonia decomposition is a promising approach for on-site hydrogen generation for fuel cells, and the development of a cost-effective and efficient catalyst is highly desired. In this study, a series of NixMg75-xAl25 hydrotalcite-like compounds (HTlc) with different Ni contents were synthesized by co-precipitation, followed by calcination and reduction treatments. Influences of Ni content and ammonia reduction on the catalytic performance for ammonia decomposition were investigated. The characterization results of the as-prepared samples showed that HTlc was decomposed into Mg(Ni, Al)O solid solution by calcination, which displayed a strong interaction between Ni species and support, while upon reduction with ammonia at 750 ℃, well-dispersed Ni metal nanoparticles with an average crystallite size range of 5.9-7.7 nm were formed. No nitrogen oxides (NOx) were produced during the NH3 reduction process as indicated by mass spectrometry analysis, and the catalyst reduced with ammonia showed comparable activity with that reduced with hydrogen, suggesting that ammonia can be used as a reductant gas. The catalyst activity increased with the increase of Ni content and reduction temperature. Among the catalysts, the Ni20Mg55Al25 catalyst reduced with ammonia at 750 ℃ showed the best activity, which afforded 98% ammonia conversion at 600 ℃ at a space velocity of 30000 mL·gcat-1·h-1, and no evident deactivation was observed during a 100 h test, demonstrating good activity, stability, and sintering resistance.

Dental resins are currently the most commonly used filling materials for dental caries clinically due to their advantages of aesthetics, safety, and easy operation. However, their service life is limited because of their low mechanical strength and insufficient antibacterial activity. In this study, radial mesoporous silica was prepared firstly, and then loaded nanosilver into its porous channels to obtain silver loaded radial mesoporous silica (Ag-RMS). Effects of different contents of Ag-RMS on antibacterial, mechanical, and physicochemical properties of dental composite resins were studied. The results showed that Ag-RMS could significantly improve the antibacterial performance of composite resins, achieving an antibacterial rate of 99.68% against Streptococcus mutans when the addition amount of Ag-RMS was 5% (mass fraction). Mechanical strength of the composite resin gradually increased with the increase of Ag-RMS content. When the addition amount of Ag-RMS reached 7% (in mass), the flexural strength of composite resins was 28.16% higher than that of resin matrix. Moreover, the addition of Ag-RMS had almost no obvious effect on their polymerization shrinkage rate, monomer conversion rate, curing depth, and surface hydrophobicity. These results indicate that the prepared Ag-RMS in this study can improve the comprehensive performance of the novel composite resins.

As one of the typical electrolyte materials for proton conducting solid oxide fuel cells, BaZr0.1Ce0.7Y0.2O3-δ (BZCY) possesses advantages such as high proton conductivity and stability. However, sintering activity of BZCY electrolyte is poor, usually requiring high sintering temperature for densification, which is inconducive to the preparation and application in cells. This study aimed to reduce the sintering temperature of BZCY electrolyte and explore the influence of sintering additives such as NiO, Fe2O3, ZnO, and CuO on the sintering characteristics of BZCY in detail. The results indicate that the oxides except Fe2O3 can effectively promote the grain growth of BZCY sintered body. Among them, the addition of CuO has the most significant promoting effect on the sintering process of BZCY. After adding 2% (in mass) CuO into BZCY (BZCY-2%CuO), even if the sintering temperature was reduced to 1250 ℃, the relative density of the sintered body still maintained higher than 98%. Additionally, the conductivity of BZCY-2%CuO was up to 2.7×10-2 S·cm-1 at 600 ℃ in wet H2 atmosphere, which was nearly 5 times higher than that in wet air. More importantly, BZCY-2%CuO electrolyte exhibits negligible electronic conductivity under cell operating conditions while maintaining excellent stability.

Gallium nitride (GaN) thin films are typically obtained on foreign substrates. Hetero-epitaxial growth of GaN leads to high density of threading dislocations, which poses a significant challenge to promote high-performance electronic device and photoelectric device based on these films. This research used Ar-ion implantation pretreatment on sapphire substrates to induce high-quality nucleation, reducing the dislocation density in GaN epitaxial layers. By optimizing the dosage of Ar ions, it was found that when the Ar ion dosage was 1×1011 cm-2, the screw dislocation density was 5.26×107 cm-2, and the edge dislocation density was 1.95×108 cm-2, the total dislocation density decreased by 65% compared to GaN grown on traditional sapphire substrate. Photoluminescence spectra realized that the optical performance of the GaN epitaxial layer with induced nucleation was also improved. In contrast to the untreated sample, the photoluminescence strength increased by 152%. Therefore, all above results indicate that the Ar ion induced nucleation technique proposed in this study is a simple and effective method that can be used to improve the crystal quality of GaN layers. This is of great significance for achieving high-efficiency GaN-based LEDs and high-performance electronic devices.

Ceramic dielectric materials with high dielectric strength and mechanisms of their internal factors affecting dielectric strength are significantly valuable for industrial application, especially for selection of suitable dielectric materials for high-power microwave transmission devices and reliable power transmission. Pure magnesium oxide (MgO), a kind of ceramic dielectric material, possesses great application potential in high-power microwave transmission devices due to its high theoretical dielectric strength, low dielectric constant, and low dielectric loss properties, but its application is limited by high sintering temperature during preparation. This work presented the preparation of a new type of multiphase ceramics based on MgO, which was MgO-1%ZrO2-1%CaCO3-x%MnCO3 (MZCMx, x = 0, 0.25, 0.50, 1.00, 1.50, in molar), and their phase structures, morphological features, and dielectric properties were investigated. It was found that inclusion of ZrO2 and CaCO3 effectively inhibited excessive growth of MgO grains by formation of second phase, while addition of MnCO3 promoted the grain boundary diffusion process during the sintering process and reduced activation energy for the grain growth, resulting in a lower ceramic sintering temperature. Excellent performance, including high dielectric strength (Eb = 92.3 kV/mm) and quality factor (Q × f = 216642 GHz), simultaneously accompanying low dielectric loss (< 0.03%), low temperature coefficient of dielectric constant (20.3×10-6 ℃-1, 85 ℃) and resonance frequency (-12.54×10-6 ℃-1), was achieved in MZCM1.00 ceramics under a relatively low sintering temperature of 1350 ℃. This work offers an effective solution for selecting dielectric materials for high-power microwave transmission devices.

Currently, the carbothermal reduction-nitridation (CRN) process is the predominant method for preparing aluminum nitride (AlN) powder. Although AlN powder prepared by CRN process exhibits high purity and excellent sintering activity, it also presents challenges such as the necessity for high reaction temperatures and difficulties in achieving uniform mixing of its raw materials. This study presents a comprehensive investigation into preparation process of AlN nanopowders using a combination of hydrothermal synthesis and CRN. In the hydrothermal reaction, a homogeneous composite precursor consisting of carbon and boehmite (γ-AlOOH) is synthesized at 200 ℃ using aluminum nitrate as the aluminum source, sucrose as the carbon source, and urea as the precipitant. During the hydrothermal process, the precursor develops a core-shell structure, with boehmite tightly coated with carbon (γ-AlOOH@C) due to electrostatic attraction. Compared with conventional precursor, the hydrothermal hybrid offers many advantages, such as ultrafine particles, uniform particle size distribution, good dispersion, high reactivity, and environmental friendliness. The carbon shell enhances thermodynamic stability of γ-Al2O3 compared to the corundum phase (α-Al2O3) by preventing the loss of the surface area in alumina. This stability enables γ-Al2O3 to maintain high reactivity during CRN process, which initiates at 1300 ℃, and concludes at 1400 ℃. The underlying mechanisms are substantiated through experiments and thermodynamic calculations. This research provides a robust theoretical and experimental foundation for the hydrothermal combined carbothermal preparation of non-oxide ceramic nanopowders.

Perovskite quantum dots have unique advantages in display. However, their long-term stability at high brightness is still a huge challenge. Therefore, this article focuses on the progress of the regulation of perovskite quantum dots and their luminescent film morphology, explains the influence of long-range ordered perovskite quantum dot films on their electroluminescent properties, and looks forward to the development prospects in improving the electroluminescent stability of perovskite quantum dots.