Rare earth hydrides formed by reaction of rare earth metals with water vapor

The reaction of Pr, Gd, Dy, and Er with water vapor has been studied in the temperature interval 100 to 1400C. There was corroboration of the earlier observations of J. Dexpert-Ghys. et al. (J. Less Common Metals, 41, 105, 1975) to the effect that (1) DyH2 forms when Dy is treated with water vapor and (2) there is no evidence by x-ray diffraction of the formation of Dy(OH)3 and Dy2O3. Since the free energy change involved in forming DyH2 and O2 from Dy and H2O is about + 17 kcal, the reaction was carried out under radiation in an effort to ascertain whether the missing energy was being photochemically supplied. Results were negative. Mass spectrometric examinations of the reacting system using O18-enriched water showed no oxygen in the gaseous products. Study of the solid using Auger spectroscopy gave clear indication of large amounts of oxygen in the sample after reaction with water. Presumably the incorporation of oxygen in the lattice permits the thermodymamic requirements to be satisfied. Oxygen is not present in Dy in a phase with sufficient long-range order to give a detectable x-ray diffraction pattern. Pr and Gd in the form of filings react with H2O to give dihydride and hydroxide. Er is unreactive as judged from x-ray diffraction measurements. 2 figures, 1 table