Preparation of silicon-based oxide layer on high-crystalline SiC fiber as an interphase in SiC/SiC composites

New silicon-based oxide layers, SiO2 and SiO2–MgO, as the interfacial materials of SiC/SiC composites were prepared on Hi-Nicalon Type S SiC fiber by sol–gel method. The fibers were completely coated by only dipping twice in a coating solution of [Si]=1.0 mol/dm3 or that of [Mg]=0.50 mol/dm3 and [Si]=0.25 mol/dm3. These coated layers were amorphous up to 1200 °C for the SiO2 coated fibers, or consisted of a mixture of SiO2 and MgxSizO up to 1400 °C in SiO2–MgO coated fibers. The tensile strength of coated Hi-Nicalon Type S SiC fiber after heating at 1200 °C was similar to that of unheated Hi-Nicalon Type S SiC fiber without heating and was reduced by 15% after heating to 1400 °C.