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 N_(2)reached 1.14μm.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.