The effects of graphite substrate properties such as the density and the pore size distribution on the conversion behavior of graphite surface were investigated. Graphite substrates and silica powder in graphite crucible were treated by a chemical vapor reaction method. In this process, SiO vapor was created, infiltrated into the graphite substrate, and the β-SiC conversion layer was formed. The XRD patterns of conversion layers produced from vapor-solid (SiO-C) reaction were identified as β-SiC (3C type, zinc blende structure). In the cross-sectional microstructure, the B specimen showed simply an interface, whereas the A specimen showed an interlayer with an average SiC : C ratio of 1 : 3 in chemical composition. It seemed that the formation of the interlayer in the A specimen was caused by a high nucleation rate due to the low density or the pore size distribution during the CVR process. Ultimately, the microstructural features of conversion layers reveal that the pore size distribution and the density of substrates were important factors in the formation of conversion layer.

Keywords: SiC conversion layer, Graphite substrate, Chemical conversion