1988 年 37 巻 412 号 p. 77-82
Nonoxide ceramics of hot-pressed AlN, hot-pressed Si3N4, sintered Si3N4, hot-pressed sialon and hot-pressed B4C were oxidized in wet nitrogen and/or wet air atmosphere at 1.5 to 20kPa of water vapor pressure and in dry air at 900-1400°C. All specimens were oxidized by both dry air and water vapor at high temperatures. AlN formed α-Al2O3 film on the surface above 1150°C. The oxidation rate of AlN increased with increasing water vapor pressure. The oxidation rate of AlN in wet nitrogen was much greater than that in wet air. Si3N4 and sialon formed oxide films consisting of SiO2, Y2Si2O7 and YAlO3. The oxidation kinetics obeyed the usual parabolic law. The oxidation rate in wet nitrogen, however, was unaffected by water vapor pressure and increased with increasing Y2O3 content. The apparent activation energy for the oxidation of Si3N4 based ceramics was about 800kJ/mol. On the other hand, since the oxidation of B4C by water vapor and dry air above 900°C resulted in weight loss, the formation of BO or HBO2 seemed to be the main reaction. The oxidation rate of B4C by water vapor above 900°C could be expressed by the surface chemical reaction controlled kinetics with the apparent activation energy of 200kJ/mol.