Solubility of RH/sub 2-x/ in Gd, Er, Tm, Lu, and Y from ambient to 8500C

The solubility of hydrogen in Gd, Er, Tm, Lu, and Y was determined from 25 to 8500C when the metal was in equilibrium with RH/sub 2-x/ (x varies between 0.1 and 0.2 depending on the rare earth metal). The room temperature solubilities determined by the lattice parametric method were found to be less than 0.1, 3.6, 7.7, 20.6, and 19.0 at. percent H in Gd, Er, Tm, Lu, and Y, respectively. The change in unit cell volume for each atomic percent hydrogen added was nearly the same for all metals. The solubility of hydrogen increases more rapidly with temperature in those metals with low solubility at room temperature. Thus the solubility of hydrogen at 8500C is nearly the same in all five of the metals studied, that is, 35.0, 36.2, 36.0, 36.0, and 37.3 at. percent H in Gd, Er, Tm, Lu, and Y, respectively. The equilibrium pressure of H2 in these studies was the equilibrium pressure of hydrogen in contact with RH/sub 2-x/ at the temperature concerned. A change in slope was observed in the solubility curves of the Gd--, Er--, Tm--, and Lu--H systems. The log C (at. percent H in R) was plotted vs 1/T for each system. Straight lines were obtained at temperatures above and below the changes in slope of the solubility curves. A calculation of the approximate ΔH of solution of RH/sub 2-x/ in the metals from the slope of the lines gave 4.35, 1.88, 1.28, 0.61, and 0.55 kcal/mole for Gd, Er, Tm, Lu, and Y, respectively in the low temperature portion. The change in slope which occurs at some point between 350 and 6500C, depending on the metal, indicates a lower heat of solution of RH/sub 2-x/ in these metals at the higher temperatures. In Lu there appears to be yet another change in slope in the neighborhood of 2500C. (auth)