Abstract
The oxygen permeability of polycrystalline α-alumina wafers, which served as model alumina layers, under an oxygen potential gradient ΔPO2 was evaluated at a temperature of 1873 K. When mutual grain boundary (GB) diffusion of oxygen and aluminum occurred in wafers subjected to a steep ΔPO2, the oxygen and aluminum fluxes at the inflow side of the wafer were significantly smaller than those at the outflow side. It was noteworthy that Lu and Hf segregation at the GBs selectively reduced the mobility of oxygen and aluminum, respectively. It was found that a wafer with a bilayer structure, in which a Lu-doped layer was exposed to a low partial oxygen pressure (PO2) and a Hf-doped layer was exposed to a high PO2, exhibited excellent oxygen shielding properties at high temperatures.
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