Investigation of SiC formation on the graphite surface by CO-H₂-SiO gas

FINEX process, which utilizes hydrogen (H₂) as a part of reductants, has emerged as an environmentally sustainable ironmaking process to meet the upcoming carbon-neutral era. In the H₂-enriched atmosphere, local slag holdup in the carbonaceous particle bed may increase due to the increased melting temperature of slags by the rapid reduction of iron oxide and the resulting lower wettability of the carbonaceous materials by liquid slag. In-situ SiC formation on the carbon surface gains much attention as a method to reduce the slag holdup. In this study, as a fundamental study, we investigated the SiC formation on the surface of a graphite substrate under a CO-H₂-SiO gas environment at 1873 K. It was found that as the partial pressure of H₂ increased, the penetration depth of a SiC layer formed on the graphite surface increased, and the surface roughness became enhanced. A reaction rate analysis revealed that the H₂-CO gas mixture accelerated the SiC formation on the graphite surface compared to the N₂-CO gas mixture. This effect was attributed to the high bimolecular diffusivity of H₂-CO. Our results demonstrate that under a CO-H₂-SiO gas environment, the fast diffusion of H₂ gas through micropores in the graphite significantly enhances the formation of SiC on the graphite surface. The results obtained in this study show that the acceleration of SiC formation under an H₂-enriched atmosphere would improve the wettability of molten slag and reduce the slag holdup in the FINEX process.