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 1250° and 1500°C, 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 kJ/mol, comparing favorably to other studies. Microstructural examination of tested sapphire coupons revealed surface rearrangement consistent with a volatilization process.