Oxygen Permeability for Selected Ceramic Oxides in the Range 1200 C - 1700 C

Abstract

Oxygen permeability as a function of temperature, was measured for several ceramic oxides over the range 1200 deg C-1700 deg F. Of the oxides tested, alumina, beryllia, yttria, lanthanum halfnate, and calcium zirconate exhibited the lowest permeabilities in order of decreasing resistance to oxygen transport. None of the permeability constants were less than the 10-10 to 10-12 gms 02 per cm.sec needed for a useful protective coating system above 1500 deg C. While oxygen permeability measurements on pure silica were not made during the course of this investigation, calculations indicate that silica is very impermeable to the diffusion of oxygen. In some of the mixed oxide compounds, cation segregation was observed to occur with the more rapidly diffusing specie segregating to the side of highest oxygen potential. Thus, segregation must be considered when selecting mixed oxides for high temperature applications.