Synthesis of ZrB2-SiC-ZrC composite powders with core-shell structure via sol-gel molecular modulation

In this study, ZrB2-SiC-ZrC (ZSZ) composite powders with molar ratios C/(B + Zr + Si) = 1.5, 1.9 and 2.4 were obtained by sol-gel method and boro/carbothermal reduction reaction. Meanwhile, the impact of heat treatment temperature (1100 degrees C-1600 degrees C) and holding time (1 h-2.5 h) on the resulting powders were studied. The results showed that the ZSZ powder precursors were first completely converted to ZrO2, SiO2, B2O3 and pyrolytic carbon after heat treatment at 1200 degrees C under the optimized molar ratio (2.4) and holding time (2.5 h). Then, the transformed oxidation products and pyrolytic carbon were completely transformed into ZSZ composite powders after optimized heat treatment at 1500 degrees C. The synthesized ZSZ composite powders are characterized by the core-shell structure, in which ZSZ particles act as the inner core are encapsulated by the low-crystalline ZrB2 phase as the outer shell to form a core shell structure. The ZSZ composite ceramic materials prepared using the core-shell structural powders have excellent ablative properties in the range of 2000 degrees C, with the mass and line ablation rate of -3.5 x 10(-4) g/cm(3) and 2.39 x 10(-3) mm/s, respectively.