Hydrothermal corrosion of alumina ceramics under static and quasi-dynamic conditions

Corrosion resistance of solid state (SSS) and liquid phase sintered (LPS) alumina under hydrothermal conditions (subcritical water and sodium chloride solution at temperatures up to 290 degrees C, and pressures up to 7 MPa) was evaluated. The influence of sintering additives as well as the conditions of the test (temperature, corrosion medium) on dissolution of ceramics was studied. For evaluation of the corrosion mechanisms special attention was paid to determination of the eluate chemistry combined with the chemical and phase analysis of corroded surfaces. Corrosion of LPS alumina in both media was controlled by dissolution of calcium aluminosilicate grain boundary glass. Corrosion rates of SSS ceramics were several times lower and were largely controlled by dissolution of highly resistant alumina matrix. Corrosion of the ceramics was moderately faster in sodium chloride solution. The data are supplemented by calculations of phase equilibria in the corrosion solutions.