Preparation of SiC coated graphite composite powders by nitriding combustion synthesis

Ceramic-coated graphite powders are considered as effective raw materials to fabricate three-dimensional continuous ceramic skeleton-reinforced graphite matrix composites which can overcome their inherent poor densification and improve their mechanical and antioxidation properties. However, the morphology and thickness regulation of ceramic coatings on graphite particles are still a great challenge. Herein, SiC-coated graphite (graphite@SiC) powders were prepared by nitriding combustion synthesis using Si and graphited mesocarbon microbead (MCMB) as raw powders with polytetrafluoroethylene (PTFE) as a promoter. The effects of the PTFE content and the Si/MCMB molar ratio on the phase composition and coating morphology were investigated. The phase transition and microstructure evolution of a combustion synthesis (CS) process were revealed by a gas-released quenching experiment. When the Si/MCMB molar ratio was 1 : 3 and the PTFE content was 10 wt%, the thickness of the SiC coating synthesized under 2 MPa N₂ reached 1.14 μm. The corresponding sintered graphite@SiC composite had relative density of 99.2% and flexural strength of 231 MPa, accompanied by a significant improvement in high-temperature antioxidation properties. The as-synthesized graphite@SiC powders with good sinterability and antioxidation properties show great promise for applications in the nuclear industry and other extreme fields.