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. -Al2O3 containing Ni metal particles was exposed to dry air or humid environments at 1300 degrees C for up to 20h. Oxidation of Ni in -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 degrees C (1.4x10(-13)m(2)/s for 0.2 atm PH2O versus 7.9x10(-14)m(2)/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).