Alumina volatility in water vapor at elevated temperatures

The volatility of alumina in high-temperature water vapor was determined by a weight loss technique. Sapphire coupons were exposed at temperatures between 1250degrees and 1500degreesC, water partial pressures between 0.15 and 0.68 atm in oxygen, a total pressure of 1 atm, and flowing gas velocities of 4.4 cm/s. The water vapor pressure dependence of sapphire volatility was consistent with Al(OH)(3)(g) formation. The enthalpy of reaction to form Al(OH)(3)(g) from sapphire and water vapor was determined to be 210 +/- 20 Q/mol, comparing favorably to other studies. Microstructural examination of tested sapphire coupons revealed surface rearrangement consistent with a volatilization process.