The corrosion rate and changes in the microstructure and fracture strength of sintered α- and β-silicon carbides were studied in 0 to 25 m NaOH solutions and oxygen partial pressures of 0 to 10 MPa at 200°C to 300°C where m = mol(kg - H2O)-1. Silicon carbide ceramics were stable in 25 m NaOH solutions even at 300°C in the absence of oxygen, but susceptible to corrosive attack above 250°C in the presence of oxygen. The corrosion rate of α-silicon carbide was slightly higher than that of β-silicon carbide. The corrosion data could be adequately described by a surface chemical reaction controlled shrinking core model. The corrosion rate increased linearly with increasing NaOH concentration up to 0.35 m, but thereafter decreased strongly. The corrosion rate in 0.2 m NaOH increased linearly with increasing oxygen partial pressure up to 3 MPa and then remained almost constant, while in 25 m NaOH solutions it increased linearly up to 10 MPa. The apparent activation energy was 170 and 32 kJ · mol-1 in 0.2 m and 25 m NaOH solution, respectively. The corrosion resulted in surface roughening of the silicon carbide specimens and reduced the bend strength from ca. 500 MPa to ca. 250 MPa in the initial stage of corrosion up to 20% weight loss; the bend strength then remained almost constant up to 60% weight loss.
|Number of pages||5|
|Journal||British Ceramic Transactions|
|Publication status||Published - 1992 Dec 1|
ASJC Scopus subject areas
- Ceramics and Composites