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Dense Si3N4 hot-pressed with the aid of 9 wt% Y2O3 was oxidized in 'dry' synthetic air at both 1000 and 1200?C for up to 500 hours under thermal cycling conditions. The experiments revealed that thermal cycling has little effect on oxidation kinetics although the morphology of surface oxidation products is affected by the cycling frequency. Cracks formed in the oxide layers on cooling healed immediately on re-exposure to high temperature, and there was no apparent change in the oxidation rate controlling mechanism over the time period investigated. The exposure of the material at 1000?C did not result in catastrophic oxidation as observed for some other Y2O3-doped hot-pressured Si3N4 compositions. Additionally, it was observed that crystallization of the oxide layer with time (assisted in part by the outward diffusion of intergranular phase actions from the bulk ceramic to the surface scale) leads to non-parabolic kinetics owing to reduced rates of diffusion through crystalline phases in the surface scale.

Additional information

Authors: COASTA F, INETI, Lisbon (PT);BAXTER D, IAM, JRC-Petten (NL)
Bibliographic Reference: Article: Journal of the European Ceramics Society (1999)
Record Number: 199911396 / Last updated on: 1999-09-17
Original language: en
Available languages: en