As one of the few thermal structural materials that can be used at temperatures exceeding 2 500 K, carbon/carbon composites (C/C composites) have excellent properties such as low density, ablation resistance, high temperature resistance, and small coefficient of thermal expansion [1-5], and they have occupied an increasingly important position in aerospace, aviation, and national defense fields. However, C/C composites are easily oxidized in high temperature and oxygen-rich environment, and oxidative ablation leads to the degradation of their original excellent performance, which in turn leads to material failure. Therefore, it has become a research hotspot to improve the properties of C/C composites such as oxidation resistance, thermal shock resistance, ablation resistance and high temperature resistance, in order to prolong the service life of the materials in the extreme harsh environments such as higher temperatures and stronger heat flux densities [6-8]. The preparation of ceramic coatings with excellent high-temperature oxidation and ablation resistance on the surface of C/C composites is a simple and effective protection method. Among them, silicon-based ceramic coatings are widely used as antioxidant coatings, thanks to the Si element in the process of ablation and oxidation can generate glassy SiO2 with good high-temperature self-healing effect, and at high temperatures, SiO2 has a low oxygen diffusion coefficient (10-13 g/(cm2-s) at 1,200 ℃, 10-11 g/(cm2-s) at 2,200 ℃), and a low oxygen diffusion coefficient (10-11 g/(cm2-s) at 2,200 ℃). YANG et al. [11] used the chemical vapor reaction method to prepare a thick SiC coating on the graphite surface, which could provide oxidation protection for the graphite substrate under oxyacetylene flame for more than 50 s. However, at 1,200-1,700 ℃, SiO2 was found to have a low oxygen diffusion coefficient (10-13 g/(cm2-s) at 1,200 ℃ and 10-11 g/(cm2-s) at 2,200 ℃) [9-10]. However, the viscosity of SiC decreases with increasing temperature in an air environment from 1 200 to 1 700 ℃. Studies have shown [12-14] that when the temperature exceeds 2 000 ℃, the viscosity of SiO2 decreases dramatically, and its exfoliation and vaporization are intensified; and when the temperature is further elevated above 2 700 ℃, the SiC decomposes by direct sublimation. The introduction of ultra-high temperature ceramics (UHTCs) in the coating to further improve the ablation resistance and oxidation resistance of SiC coatings at high temperatures has become a new research direction.
UHTCs have a melting point higher than 3 000 °C and maintain stable physical and chemical properties under extreme environments. Among them, IVB and VB transition metal carbides (ZrC, TaC, HfC, TiC, etc.), borides (ZrB2, TaB2, HfB2, TiB2, etc.), which have good ablation, corrosion resistance and mechanical properties [15-19], are considered ideal candidates for extreme environments. Tantalum carbide (TaC) has an extremely high melting point (up to 3,880 °C), and its oxidation product Ta2O5 [20-22] has a melting point of more than 1,800 °C. It has a lower vapor pressure and higher viscosity than the SiO2 glass phase in medium and high temperature environments, but oxygen can diffuse into the coating through the Ta2O5 glass layer during the ablation process and continue to react with the coating. Reaction. As the degree of oxidation increases, defects such as pores, bubbles, and cracks are produced due to excessive depletion of the coating, especially penetrating cracks that form preferentially along the defects, leading to coating failure. At the same time, the thermal expansion coefficient difference between single TaC coating and C/C substrate is large, and it is easy to crack and peel off the coating due to the mismatch of the thermal expansion coefficient in the process of temperature rise and fall of the etching. Therefore, TaC is introduced into SiC coating as the second phase, and TaC-SiC composite coatings are prepared, and the defects on the surface of the coating are sealed by the flow of Ta2O5 liquid phase in the process of the etching to promote the formation of a continuous glass protective layer, which is similar to the formation of thermal barrier coating. During the ablation process, Ta2O5 liquid phase flows to seal the defects formed on the surface, thus promoting the formation of continuous glass protective layer, which produces the oxygen barrier effect similar to that of the thermal barrier coating, and is conducive to the improvement of high-temperature ablation resistance of SiC coating. In this study, C/C composites were embedded in Si powder and Si-Ta2O5 powder, and SiC coatings and TaC-SiC composite coatings were generated on the surfaces of C/C composites by redox reaction, and the effects of TaC on the microstructure and high-temperature ablative corrosion resistance of SiC coatings were investigated, as well as the mechanism of the effects. The TaC-SiC composite coatings will be used as the transition layer in the multilayer coatings to study the ablation resistance of the multilayer coatings at high temperature for a long period of time (more than 120 s), and to prolong the service life of C/C composites at higher temperatures and higher heat flux densities in the extremely harsh environmental conditions.


Room termperature curing polysilazane, pls check IOTA 9150, IOTA 9150A. 
High termperature curing polysilazane, pls check IOTA 9108, IOTA 9118.