To evaluate the capability of candidate materials such as alumina (Al
2O
3) and yttria stabilized zirconia (YSZ) ceramics for use as environmental barrier coatings (EBCs) on C/C composites, the oxygen and water permeability through each oxide ceramic were measured in dry and/or wet atmospheres at ultra-high temperatures. The oxygen permeability constant of Al
2O
3 was much smaller than that of YSZ, and was found to be in good agreement with previous values. The surface morphology of Al
2O
3 after the test displayed significant dependence on the oxygen potential gradients during the test. Deep grain boundary grooves were formed on those surfaces exposed to lower Po
2 ; however, on the opposite surface under a higher Po
2, the grain boundaries rose, forming ridges. The dependence of the Al
2O
3 oxygen permeability constant on the Po
2 in the testing environment displayed p-type semiconductivity. Therefore, the unique morphological change may be related to the migration of aluminum ions from the lower to the higher Po
2 side by the substitution of cation vacancies that segregate at the grain boundaries. The water permeability constant of Al
2O
3 was under the detection limit (10
-10mol/(m·s) at the temperature of 1923K.
抄録全体を表示