Effect of Surface Concentration of Lu on Oxygen Permeation of Polycrystalline Alumina at High Temperatures


Author to whom correspondence should be addressed. e-mail: kitaoka@jfcc.or.jp


The effect of Lu surface concentration on oxygen permeation in polycrystalline α-alumina wafers was determined at 1773 K under limited oxygen potential gradients (Δmath formula), where the two surfaces of the wafer were deliberately subjected to different oxygen partial pressures [math formula (I) ≪ math formula (II)]. When oxygen permeation occurred mainly by oxygen GB diffusion under a Δmath formula generated by a combination of low math formula values, the Lu-coating on the math formula (I) [math formula (II)] surface decreased [increased] the oxygen permeability constants. When Δmath formula was the result of a combination of high math formula values, where oxygen permeation proceeded mainly by aluminum GB diffusion, the oxygen permeability constants were decreased only by the Lu-coating on the math formula (I) surface. The analysis of mass transfer parameters, such as the chemical potentials, GB diffusion coefficients, and fluxes of aluminum and oxygen in the wafers, suggested that ambient oxygen molecules were effectively attracted toward Lu-coated surfaces exposed to low-math formula environments, leading to a change in oxygen permeability.