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

The solubility of H in Gd, Er, Tm, Lu, and Yt 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 determinedparametric 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 H added was nearly the same for all metals. The solubility of H increases more rapidly with temperature in those metals with low solubility at room temperature. Thus, the solubility of H 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 H 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 approx. 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 temperature. In Lu there appears to be yet another change in slope in the neighborhood of 2500C