Oxygen permeability of Y2SiO5

The oxygen permeation through a wafer of Y2SiO5 has been measured in the temperature range from 1973 to 2033 K and the oxygen permeability constant of Y2SiO5 has been determined, because Y2SiO5 is favorable for the outer layer of our proposed oxidation protection double layered coating on C/C composites. We presented a data reduction, which can separate lattice diffusion through the wafer from other contributions. The experimental data are in agreement with previous data reported in the literature for Ca stabilized zirconia and alumina in a maximum error of 10(-12) kg/(m.s). The oxygen permeability constant of Y2SiO5 at 1973 K is 10(-10) kg/(m.s). A 100 mum-thick Y2SiO5 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 permeated through the Y2SiO5 layer. The mechanism of the oxygen transport is discussed in accordance with the activation energy of the oxygen permeation and relationship between the oxygen permeability constants and oxygen partial pressure. Experimental results indicate that vacancy diffusion is dominant below 1913 K and interstitial diffusion is dominant above 1913 K. It is estimated that there is a mechanism to switch vacancy diffusion to interstitial diffusion with increasing temperature, because interstitial diffusion should not be active at higher temperature.