Corrosion of silicon nitride ceramics in aqueous HCl and HF solutions at 27-80°C

The corrosion behaviour of a hot isostatically pressed (HIP)-Si3N4 containing 2.7 wt.% Y2O3 and a sintered (S)-Si3N4 containing 12.5 wt.% Y2O3 + 1.1 wt.% Al2O3 in HCl and HF solutions with various molarities, at the temperature range 27-80 degrees C, have been studied. Corroded surfaces and the specimen cross sections were examined by the SEM and EDAX. The activation energies for the dissolution of HIP- and S-Si3N4 in HCl and HF solutions were determined. The results of the corrosion tests indicated that there is a significant difference in the corrosion resistance of the HIP- and S-Si3N4 specimens in HCl and HF solutions. This difference depended on the sintering additives used to form dense Si3N4 as well as the molarity and temperature of the corrosive solutions. (C) 1998 Elsevier Science Ltd. All rights reserved