Effect Of Surface Concentration Of Lu On Oxygen Permeation Of Polycrystalline Alumina At High Temperatures

摘要

The effect of Lu surface concentration on oxygen permeation in polycrystalline α-alumina wafers was determined at 1773 K under limited oxygen potential gradients (ΔPo_2), where the two surfaces of the wafer were deliberately subjected to different oxygen partial pressures [Po_2 (Ⅰ) « Po_2 (Ⅱ)]. When oxygen permeation occurred mainly by oxygen GB diffusion under a ΔPo_2 generated by a combination of low Po_2 values, the Lu-coating on the Po_2 (Ⅰ) [Po_2 (Ⅱ)] surface decreased [increased] the oxygen permeability constants. When ΔPo_2 was the result of a combination of high Po_2 values, where oxygen permeation proceeded mainly by aluminum GB diffusion, the oxygen permeability constants were decreased only by the Lu-coating on the Po_2 (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-Po_2 environments, leading to a change in oxygen permeability.