Hydrogen-absorbing characteristics of 15 rare earth elements

The amounts of absorbed hydrogen and the rates of hydrogen-absorption reaction were measured for 15 rare earth elements. The cohesive energy and energy fluctuation of metal clusters were also calculated by using the extended-Hückel method. The characteristics of each rare earth element in the capacity of hydrogen absorption and the reaction rate were discussed by comparing the experimental results with the calculated ones. The major results are as follows. (i) Hydrogen/metal ratios (H/M) of rare-earth metals are nearly constant, ∼3, except for Eu and Yb; (ii) the rate of hydrogen-absorption reaction may be determined by the product of (magnitude of energy fluctuation) and (density of states); (iii) the 15 rare-earth elements would be classified into four groups: Group 1 (Ce, Pr, Nd), Group 2 (Sm, Gd, Tb, Dy, Ho, Er), Group 3 (Tm, Yb, Lu) and Group 4 (Y, La, Eu) and (iv) the rate of hydrogen-absorption reaction is remarkably promoted by pre-heating the metals before the reaction.