非酸化物セラミックスの高温水蒸気酸化(<小特集>セラミック材料小特集)

概要

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Nonoxide ceramics of hot-pressed AlN, hot-pressed Si_3N_4, sintered Si_3N_4, hot-pressed sialon and hot-pressed B_4C were oxidized in wet nitrogen and/or wet air atmosphere at 1.5 to 20 kPa of water vapor pressure and in dry air at 900-1400℃. All specimens were oxidized by both dry air and water vapor at high temperatures. AlN formed α-Al_2O_3 film on the surface above 1150℃. 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. Si_3N_4 and sialon formed oxide films consisting of SiO_2, Y_2Si_2O_7 and YAlO_3. 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 Y_2O_3 content. The apparent activation energy for the oxidation of Si_3N_4 based ceramics was about 800 kJ/mol. On the other hand, since the oxidation of B_4C by water vapor and dry air above 900℃ resulted in weight loss, the formation of BO or HBO_2 seemed to be the main reaction. The oxidation rate of B_4C by water vapor above 900℃ could be expressed by the surface chemical reaction controlled kinetics with the apparent activation energy of 200 kJ/mol.
社団法人日本材料学会の論文
1988-01-15