Cr Effect on Hydrogen Interactions with Intrinsic Point Defects and Hydrogen Diffusion in alpha-Al2O3 as Tritium Permeation Barriers

摘要

Hydrogen transport in the outer Al2O3 scale is the rate-limiting step for H-permeation resistance of FeAl/ Al2O3-type aluminide tritium permeation barriers (TPBs) in fusion reactors. With first-principle calculations, the effects of Cr, a main impurity element in the Al2O3 scale, on intrinsic point defect formation, hydrogen interactions with intrinsic point defects, and hydrogen diffusion in alpha-Al2O3 have been investigated under the working conditions of aluminide TPBs. It is found that Cr addition is favorable for the formation of V-O, yet unfavorable for V-Al formation in alpha-Al2O3. Compared with the alpha-Al2O3 H case, Cr is beneficial for the formation of H-related defects in alpha-Al2O3, whereas it is unfavorable for the H-i trapping ability of V-Al and V-O. H-O(-) will dominate among H-i(-), V-Al(3-), V-O(0), and [V-Al(3-)-H+](2-), and only one step of H-i reorientation will be involved for the Hi diffusion in Cr-doped alpha-Al2O3. H-i is the dominant diffusion species in both pure and Crdoped alpha-Al2O3, whereas the activation energy of H diffusion in Cr-doped alpha-Al2O3 is sharply reduced, which is unfavorable for H-permeation resistance of aluminide TPBs. The Cr effect on hydrogen behaviors in alpha-Al2O3 can be attributed to the chemically unstable electron structure of Cr3+ and a relatively stronger bonding interaction between H and Cr than that between H and Al or O atoms.