Effect of Dopants on the Distribution of Aluminum and Oxygen Fluxes in Polycrystalline Alumina Under Oxygen Potential Gradients at High Temperatures

Abstract

The oxygen permeability of Lu‐, Y‐, and Hf‐doped polycrystalline alumina wafers under steep oxygen potential gradients was evaluated at temperatures above 1773 K. Oxygen permeation occurred by the grain‐boundary (GB) diffusion of oxygen from the higher oxygen partial pressure (PO2) surface to the lower PO2 surface, and was coincident with GB diffusion of aluminum in the reverse direction. Lu‐ and Y‐doping both suppressed oxygen permeation to the same extent, owing to the decrease in oxygen mobility, but neither had any significant effect on aluminum mobility. Hf‐doping had the opposite effect. The fluxes of oxygen and aluminum at the inflow side in all wafers were significantly smaller than those at the outflow side, regardless of whether or not these dopants were added. Consequently, the intersection of the fluxes shifted to the lower PO2 side upon Lu‐ and Y‐doping, and to the higher PO2 side upon Hf‐doping. Furthermore, the effect of dopants on the mass transfer in scales formed by oxidation of FeCrAl‐based alloys at 1300–1500 K was analyzed through predictions of the flux distributions of oxygen and aluminum in the scales.