Hydrogen permeability in (CeO 2) 0.9(CaO) 0.1 at high temperatures

Abstract

It was found that hydrogen permeated the bulk of the fluorite-type (CeO 2) 0.9(CaO) 0.1 at 1075–1800 K. Two tube shaped specimens of different lengths were prepared. The hydrogen source gas was H 2(7.8%)+N 2 which was humidified at 293 K and supplied to the outside of specimens. Ar gas was let flow to the inside of specimens and the permeated hydrogen in the outlet Ar gas was analyzed by a gas chromatograph. Measurements were made at the same conditions on the specimens to eliminate the hydrogen permeated through Pt rings, which were used to fix the specimen, the alumina tube and disk, and the alumina supporting materials. The permeability, J H, in log( J H/mol h −1 cm −1) was almost proportional to 1/ T ( T: temperature). The gradient of the line changes at 1525 K. The activation energy, E, of conductive protons or electrons was estimated from the Arrhenius' relation, log J H= A− E/2.303 kT. A is constant and E is the activation energy, which is 1.07±0.03 eV above 1525 K and 0.73±0.06 eV below 1525 K, respectively. The electronic activation energies, which were determined from the oxygen permeability, were higher than the above values, and they might be the activation energy of protons. There is a possibility that (CeO 2) 0.9(CaO) 0.1 is an electron–proton mixed conductor under H 2–H 2O atmosphere at high temperature.