Formation mechanism of C/SiC/C multi-layers during self-propagating high-temperature synthesis

In order to study the formation mechanism of a silicon carbide layer during the self-propagating high-temperature synthesis (SHS) reaction between graphite and silicon layers, multi-layers of carbon–silicon carbide–carbon on UO2 pellets were prepared and analyzed. The carbon and silicon were deposited by thermal decomposition of propane in a chemical vapor deposition (CVD) unit and a microwave-pulsed electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR PECVD) unit using silane and propane gases, respectively. The activation energy for the formation of silicon carbide determined by differential scanning calorimetry (DSC) depended on the initial carbon precursors. The final product layer was a fine, crystalline beta-silicon carbide. The numerically estimated value of the combustion limit was 0.06 at an initial temperature of 1200 °C, which supported the finding that pre-heating above the temperature was required for the formation of the silicon carbide. From thermal analysis and microstructure observations, the formation mechanism of the silicon carbide layer included carbon diffusion at the interface between liquid silicon and silicon carbide.