Effect of Water Vapor on Mass Transfer in Polycrystalline Yb2Si2O7 under Oxygen Potential Gradients at High Temperatures

Abstract

The effect of water vapor on mass transfer in polycrystalline Yb2Si2O7 (YbDS) wafers under oxygen potential gradients (dµO) at high temperatures was investigated using an oxygen permeation technique. The oxygen permeation under dry dµO (high oxygen partial pressure (PO2(hi))/low PO2 (PO2(lo)) of 105 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 dµO conditions, with the introduction of H2O at the partial pressure of 104 Pa to the PO2(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 Yb2SiO5 (YbMS) with the generation of charged jogs. O2 molecules released from the PO2(lo) surface and H2 in the atmosphere were consumed by reaction with SiO2 at the PO2(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 dµO, YbMS formed on the PO2(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.