Effect of Water Vapor on Mass Transfer in Polycrystalline Yb2Si2O7 under Oxygen Potential Gradients at High Temperatures. (December 2020) - Wada, Masashi
Abstract: The effect of water vapor on mass transfer in polycrystalline Yb2 Si2 O7 (YbDS) wafers under oxygen potential gradients (d µ O ) at high temperatures was investigated using an oxygen permeation technique. The oxygen permeation under dry d µ O (high oxygen partial pressure ( P O2 (hi))/low P O2 ( P O2 (lo)) of 10 5 Pa/10 −9 Pa) is controlled by the inward and outward diffusion of oxide and Yb ions through the YbDS grain boundaries (GBs), in which the contribution of oxide ions is very large. In contrast, under wet d µ O conditions, with the introduction of H2 O at the partial pressure of 10 4 Pa to the P O 2 (hi) surface, the interdiffusion of oxide and Yb ions was accelerated, but no oxygen permeation was detected. The inwardly diffused oxide ions were consumed by the formation of Yb2 SiO5 (YbMS) with the generation of charged jogs. O2 molecules released from the P O2 (lo) surface and H2 in the atmosphere were consumed by reaction with SiO2 at the P O2 (lo) surface, which was formed by the outward diffusion of Yb ions, to generate Si(OH)4 . In addition, when the treatment conditions were switched from wet to dry d µ O, YbMS formed on the P O2 (hi) surface and inside the wafer was reconverted to YbDS, and oxygen permeation was not detected during the regeneration step (self-healing). The formation of YbMS inside the YbDS wafer is considered to contribute to the progress of the self-healing reaction. Graphical Abstract: Image, graphical abstract