Oxygen permeability of Y2SiO5

The oxygen permeation through a wafer of Y2SiO5 has been measured in the te mperature range from 1973 to 2033 K and the oxygen permeability constant of Y2SiO5 has been determined, because Y2SiO5 is favorable for the outer laye r of our proposed oxidation protection double layered coating on C/C compos ites. We presented a data reduction, which can separate lattice diffusion t hrough the wafer from other contributions. The experimental data are in agr eement with previous data reported in the literature for Ca stabilized zirc onia and alumina in a maximum error of 10(-12) kg/(m.s). The oxygen permeab ility constant of Y2SiO5 at 1973 K is 10(-10) kg/(m.s). A 100 mum-thick Y2S iO5 outer layer would extend a life time of a 100 mum-thick SIC inner layer up to 70 hours, assuming that the SIC layer is consumed by oxygen permeate d through the Y2SiO5 layer. The mechanism of the oxygen transport is discus sed in accordance with the activation energy of the oxygen permeation and r elationship between the oxygen permeability constants and oxygen partial pr essure. Experimental results indicate that vacancy diffusion is dominant be low 1913 K and interstitial diffusion is dominant above 1913 K. It is estim ated that there is a mechanism to switch vacancy diffusion to interstitial diffusion with increasing temperature, because interstitial diffusion shoul d not be active at higher temperature.