Abstract
Six kinds of pressureless sintered Si3N4 with three different additives (CeO2-Al2O3-MgO, Y2O3-Al2O3, Y2O3-Al2O3-MgO) were rapidly heated up to 1400°C and then held at this temperature for 15h in pure oxygen. During the oxidation, N2, NO and CO2 concentrations in the exhaust gas were continuously measured by a mass spectrometer. In every sample, a good correlation was observed between the amount of N2 formed and weight gain. The amount of N2 formed and weight gain after oxidation of Si3N4 increased with decreasing sintering temperature. The rates of N2 and NO formation increased rapidly for 5min after the heating temperature reached 1400°C and then decreased rapidly. After rapid decrease, the N2 formation curve showed different behavior with three additives. The maximum N2 formation rate was in the order Y2O3-Al2O3-MgO>CeO2-Al2O3-MgO>Y2O3-Al2O3. The total amount of N2 formed was in the order Y2O3-Al2O3-MgO>CeO2-Al2O3-MgO≈Y2O3-Al2O3. From the Si3N4 with CeO2-Al2O3-MgO, a large amount of CO2 was released and the surface of oxide scale was rough.
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