Hot Corrosion Behavior of SiC in Molten Na₂SO₄

Abstract

The hot corrosion behavior of SiC specimens prepared by solid phase sintering and CVD was examined in molten Na₂SO₄ at 1223 K under argon and oxygen atmospheres. Measurement of mass change, and surface observation and analysis of specimens after corrosion experiment were carried out. Particular attention was paid to the effect of sintering additives in SiC and gas atmosphere on the corrosion behavior. The SiC prepared by CVD showed the best corrosion resistance in the molten salt under argon atmosphere. For the SiC specimens prepared by solid phase sintering, the SiC containing lower content of sintering additives showed better corrosion resistance than that containing higher content of sintering additives. Many small holes were observed on the SiC specimens prepared by solid phase sintering after corrosion experiment. However, the SiC specimens did not corrode under oxygen atmosphere regardless of the kinds of specimens. The formation of cristobalite SiO₂ film was observed on the specimen surfaces after corrosion experiment under oxygen. The pre-oxidation treatment led to a stop of corrosion for the SiC specimens with and without sintering additives in the molten salt even under argon atmosphere. The formation of cristobalite SiO₂ film was also observed for the pre-oxidized specimens after the corrosion experiment. Consequently, it was found that the SiO₂ film formed on SiC stopped corrosion of SiC in molten Na₂SO₄.