Water Vapor‐Enhanced Diffusion in Alumina

Experimental results indicate effective faster diffusion of oxygen in polycrystalline alumina when exposed to water vapor at high temperatures. α‐ Al 2 O 3 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‐ Al 2 O 3 to form NiAl 2 O 4 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 m 2 /s for 0.2 atm versus 7.9 × 10 −14 m 2 /s for dry air). ( OH ) − ions are smaller and more polarizable than O 2− , 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 ).