Microstructure evolution and reaction mechanism of microporous carbon derived SiC ceramic

The process of reaction of silicon carbide ceramics derived from microporous carbon was investigated. The reaction mechanism was also analyzed. The ultimate microstructure of SiC ceramics are affected by the mass ratio of C to Si and infiltration time. Composite materials, which consist of SiC, Si and a small fraction of unreacted C, are obtained when the mass ratio of C to Si is higher whereas partial infiltration occurs when the mass ratio of C to Si is lower. Composite materials demonstrates many uniformly distributed strip-shaped SiC grains in certain region at transitional stage of reaction, and shows irregular SiC grains and an obvious bimodal distribution of grain size at terminal stage of reaction. The process of silicon-carbon reaction can be described as follows, melted Si ascends via capillary of micropore carbon and reacts with contacted carbon forming SiC. Size difference of pore and carbon wall induces difference of the infiltration deep of melted Si within micropore carbon and thicknesses of the dissolved carbon layer, respectively. As a result, some carbon particles are embedded in SiC grain and pore channel system is restructured. New pore channel with bigger pore size are formed, which accelerates infiltration rate of melted Si. Then the unreacted carbons embedded in SiC grain are firstly diffuse through the SiC layer and dissolved in the Si melt, and then deposits on the first SiC formed. Finally, liquid epitaxial growth of SiC causes coalescence of SiC grains and envelopment of some Si in SiC grains, resulting in change of microstructure of SiC ceramics.