FORMATION AND OXIDATION RESISTANCE OF THE COATING FORMED ON CARBON MATERIAL COMPOSED OF B4C-SIC POWDERS

The formation and oxidation resistance of surface oxide layers formed on carbon-B4C-SiC composites with two different B4C-SiC ratios were investigated at elevated temperatures in dry and moist atmospheres. From SEM observation, X-ray diffraction analysis, EPMA, and ESCA measurements of the samples before and after oxidation, it was found that the oxidation resistance depended on the oxidation temperature, the presence of moisture, and the B4C-SiC ratio. The surface oxide layer was very weak for oxidation at a temperature range of 800 degrees-1000 degrees C, while a dense and homogeneous surface layer formed on the composite with higher B4C-SiC ratio on oxidation at 1200 degrees C. This coating was found to be a suitable protective SiO2-rich borosilicate layer with a self-healing property that was remarkably stable against oxidation, even in moist air of about 900 degrees C.