The mobile use of metal hydrides suffers from the high mass density and the relatively high costs of the currently used hydrides that are all formed from transition metal alloys. Our goal is to develop light weight hydrides, possibly based on light and cheap metals like Al, Ba, Ca, Mg, Ti, etc., with a plateau pressure of about 1 atm at room temperature, which corresponds to an enthalpy of formation DELTAH between - 14 and - 25 kJ/mole H depending on the exact value of the entropy of formation DELTAS. Assuming that the component metals should be as light as or lighter than V (density rho = 6.1 g/cm3) then there are no less than 595 alloys to investigate, according to the phase diagrams of binary alloys [1]. Clearly, there is a need for models for predicting the enthalpies of formation of ternary hydrides. Furthermore, in order to be practical, and since the structures of the new hydrides to be found are not known, total energy calculations are ruled out. One has to rely on semiempirical models instead. We compared the bandstructure model of Griessen and Driessen [2] and Miedema's macroscopic atom model [3, 4], on the ensemble of all 21 hydrides for which both groups gave model values. Our success in improving Miedema's values [4] (by inserting experimental instead of model values for the heats of formation in the rule of reversed stability) encouraged us to apply his model to find new hydrides containing simple metals (which is not possible with the bandstructure model). Thermodynamic results for the seven new predicted hydrides are tabulated.
