Abstract
Oxidation kinetics provide essential baseline information on the performance of silicon-based ceramics for high temperature structural applications. A study of the oxidation kinetics of a hot-pressed Si3N4 densified with 9wt% Y2O3 was carried out by thermogravimetry in ‘dry’ synthetic air over the temperature range 800 to 1200°C for 50h. Data obtained clearly show that oxidation kinetics are mostly non-parabolic suggesting that the oxidation mechanism is more complex than simple diffusion. At 800°C, the kinetics are approximately parabolic, but a linear contribution to the process possibly indicates that the oxidation product is non-protective, allowing internal oxidation to occur. In the temperature range 900 to 1200°C, kinetics are better described by an arctan model suggesting that either SiO2 devitrification or nitrogen bubble formation reduce the cross-sectional area for diffusion.
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