Preparation of SiC coated graphite composite powders by nitriding combustion synthesis

Ceramics-coated graphite powders are considered an effective raw material to fabricate the three-dimensional continuous ceramics skeleton reinforced graphite matrix composites which can overcome their inherent poor densification, mechanical and antioxidation properties. However, the morphology and thickness regulation of the 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 the promoter. The effects of PTFE content and Si/MCMB molar ratio on the phase composition and coating morphology were investigated. The phase transition and microstructure evolution of the CS process were revealed by a gas-released quenching experiment. When the Si/MCMB molar ratio was 1:3 and 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 a relative density of 99.2% and a 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 application in nuclear industry and other extreme fields.