Si_3N_4焼結体の高温酸化に及ぼす焼結助剤と不純物の影響

概要

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The high temperature oxidation behaviors of gas-pressure-sintered (GPS) Si_3N_4 containing small amounts of impurities in addition to 5 wt% Y_2O_3 and 0,2 or 5wt% Al_2O_3(A0,A2,A5) as the sintering aids were examied at 1400℃ for 15h in pure oxygen. For comparison, the GPS Si_3N_4 obtained from highly pure Si_3N_4 powder(B5) was examined. The oxidation reaction was followed every minute by measuring the evolved N_2 and NO using a quadrupole mass spectrometer. The weight changes of the bodies before and after the oxidation were measured and their oxidized surfaces were analyzed by SEM and EDX. The oxidation behavior of GPS Si_3N_4 with Y_2O_3 and Al_2O_3 additives obeyed an asymptotic kinetics possibly due to the formation of protective scales. The N_2 evolution rate, the parabolic rate constant of the initial oxidation stage, the amount of N_2 evolved, and the weight gain increased with an increase in the amount of Al_2O_3. The SEM observation of the oxidized surface revealed that the proportion of a crystalline phase identified as Y_2O_3・2SiO_2 decreased and a glassy phase increased with increaseing Al_2O_3 content. The oxidation behavior of B5 was fairly fitted with two stage parabolic kinetics. B5 exhibited a larger amount of N_2 evolved and larger weight gain than A5.
社団法人日本材料学会の論文
1993-05-15