Water Vapor‐Enhanced Diffusion in Alumina

Abstract

Experimental results indicate effective faster diffusion of oxygen in polycrystalline alumina when exposed to water vapor at high temperatures. α‐Al2O3 containing Ni metal particles was exposed to dry air or humid environments at 1300°C for up to 20 h. Oxidation of Ni in α‐Al2O3 to form NiAl2O4 was used to determine oxygen diffusion depth from the surface. The apparent kinetic rate constant for oxygen diffusion in the presence of water vapor was 79% higher compared with that in a dry atmosphere at 1300°C (1.4 × 10−13 m2/s for 0.2 atm versus 7.9 × 10−14 m2/s for dry air). (OH)− ions are smaller and more polarizable than O2−, which would be expected to lead to faster diffusion. This effect may impact sintering, creep, corrosion, oxidation, and the performance of thermal barrier coatings (TBC).