Preparation and Ablation Properties of LaB6-Modified C/C-ZrC-SiC Composites

LaB6-C/C preform containing 9.73wt% LaB6 was prepared by slurry impregnation combined with resin infiltration pyrolysis, and then LaB6-modified C/C-ZrC-SiC composites were obtained by reactive melt impregnation ( RMI). The microstructure and ablative behavior of the composites were studied, and the effect mechanism of LaB6 on the ablation properties of the composites was investigated. The results show that after oxyacetylene ablation at the heat flux of 2380 kW/ m(2) for 120 s, the mass ablation rate and linear ablation rate of LaB6-modified C/C-ZrC-SiC composites are 1.05x10(-3) g/ s and 2.17x10(-3) mm/s, which are 74.8% and 61.9% lower than those of unmodified C/C-ZrC- SiC composites, respectively. During ablation, LaB6 is oxidized to La2O3 and B2O3, the solid solution and chemical reaction occur between La2O3 and ZrO2, and the liquid B2O3 can promote mass transfer in solid phase reaction. These phenomena jointly result in the formation of a large area of continuous and stable ZrO2La2Zr2O7-La0.1Zr0.9O1.95 molten protective layer on the material surface, which is the main reason for the excellent ablation performance of the material.