To efficiently decrease the ablation heat accumulation and improve the ablation protective ability of ZrC-SiC/TaC coating on carbon/carbon composites, a thermally conductive nano-network with ceramic@carbon core-shell structure was designed and constructed. Polymer-derived SiC/TaC with graphene carbon shell was synthesized and introduced into ZrC coating by supersonic atmospheric plasma spraying. Graphene shell paths were benefitted in increasing the heat transfer capability by lowering the surface temperature of about 200 °C during oxyacetylene ablation. The heat dissipation of the graphene shell in ZrC-SiC/TaC@C coating reduced the volatilization of low-melting-point phases and delayed the sintering of ZrO₂ particles. Thus, the graphene shell in ZrC-SiC/TaC@C coating decreased the mass and linear ablation rates by 91.4 % and 93.7 % compared to ZrC-SiC/TaC coating, respectively. This work provided a constructive idea to improve the ablation resistance of the coatings by incorporating carbon nanomaterials with a function of heat dissipation.

Polysiloxane (PSO) was adopted as the matrix of the repair agents, and SiC-ZrB₂ powder was used as the filler, to repair the prefabricated defects on the SiC-ZrB₂/SiC (SZS) coating of carbon/carbon (C/C) composites. The repair agents were brushed on the defect areas and then underwent preoxidation (PR) or heat-treatment (HR) in a vacuum. The effects of different treatment processes on the chemical composition, microstructure of the repair agents, and the oxidation resistance behavior of the repaired coating were investigated. The repaired agents after both processes were pyrolyzed and generated SiOC ceramics, and they were well combined with the original coating. The thermal stability of PSO after preoxidation is poorer than that after heat-treatment, resulting in a weight loss rate of 5.88% after oxidation at 1500 ℃ for 270 min, while that of the HR coating is only −0.87%, yet both have been great improvement compared with the unrepaired coating. This work provides an effective and simple approach to repairing damaged coatings for high-temperature applications.

Core–shell structured SiC@SiO₂ nanowires and Si@SiO₂ nanowires were prepared on the surface of carbon/carbon (C/C) composites by a thermal evaporation method using SiO powders as the silicon source and Ni(NO₃)₂ as the catalyst. The average diameters of SiC@SiO₂ nanowires and Si@SiO₂ nanowires are about 145 nm, and the core–shell diameter ratios are about 0.41 and 0.53, respectively. The SiO₂ shells of such two nanowires resulted from the reaction between SiO and CO and the reaction of SiO itself, respectively, based on the model analysis. The growth of these two nanowires conformed to the vapor–liquid–solid (VLS) mode. In this mode, CO played an important role in the growth of nanowires. There existed a critical partial pressure of CO (p_C) determining the microstructure evolution of nanowires into whether SiC@SiO₂ or Si@SiO₂. The value of p_C was calculated to be 4.01×10⁻¹⁵ Pa from the thermodynamic computation. Once the CO partial pressure in the system was greater than the p_C, SiO tended to react with CO, causing the formation of SiC@SiO₂ nanowires. However, the decomposition of SiO played a predominant role and the products mainly consisted of Si@SiO₂ nanowires. This work may be helpful for the regulation of the growth process and the understanding of the growth mechanism of silicon-based nanowires.

Ultra-high temperature ceramics (UHTCs) are generally referred to the carbides, nitrides, and borides of the transition metals, with the Group IVB compounds (Zr & Hf) and TaC as the main focus. The UHTCs are endowed with ultra-high melting points, excellent mechanical properties, and ablation resistance at elevated temperatures. These unique combinations of properties make them promising materials for extremely environmental structural applications in rocket and hypersonic vehicles, particularly nozzles, leading edges, and engine components, etc. In addition to bulk UHTCs, UHTC coatings and fiber reinforced UHTC composites are extensively developed and applied to avoid the intrinsic brittleness and poor thermal shock resistance of bulk ceramics. Recently, high- entropy UHTCs are developed rapidly and attract a lot of attention as an emerging direction for ultra-high temperature materials. This review presents the state of the art of processing approaches, microstructure design and properties of UHTCs from bulk materials to composites and coatings, as well as the future directions.