Hydration of β″-alumina

Abstract

The results of infrared measurements on hydrated Na β″-alumina indicate that water molecules occupy mid-oxygen and vacant Na + ion sites in the conduction layers. At H 2O contents of about 0.2 molecules per formula unit, the ration of the number of molecules on the mid-oxygen and vacant sites at 25°C is close to the ratio of the numbers of the sites in the unit cell. Possible orientations of H 2O at these sites are suggested on the basis of the polarization characteristics of the OH stretching vibrations and electrostatic potential energy calculations. The diffusion coefficients of H 2O in Na β″-alumina were determined from infrared absorbance profiles measured at 70, 45, and 25°C. At 25°CD = 5×10 −10 cm 2/sec. Hydrogen (as protons and/or as a hydrogen-containing species) diffuses into β″-alumina simultaneously with Pb 2+ ions during ion exchange in PbCl 2 and is bound as OH - in the conduction layers. The hydrogen content is reduced on partial re-exchange in NaNO 3.