THE CHARACTERIZATION OF MULTICOMPONENT METAL-HYDRIDES USING REACTION CALORIMETRY

Enthalpies have been determined calorimetrically for the reaction of H -2(g) with the technologically important multicomponent intermetallic compounds: Ti0.8Zr0.2Fe0.1V0.4Mn1.5 (AB2) and La0.8Nd0.2Ni2.5Co2.4Si0. 1 (AB5). The heats of reaction with H-2 have been measured using a twi n-cell, heat leak calorimeter. The measured heats are converted to rel ative enthalpies when expressed per mole 1/2H-2(g) and these enthalpie s have been determined as a function of n (= H/AB2 or = H/AB5) from 0 to 3.0 for AB2 and from 0 to 4.9 for AB5. The H-2(g) pressures, which give relative H chemical potentials, have also been determined over th ese intervals. The relative entropies are derived from the enthalpies and chemical potentials at given H contents. The average magnitude of the enthalpy along the plateau region is 15.5 kJ/mol 1/2H-2 for AB2 an d 17.8 kJ/mol 1/2H-2 for AB5 but for both the magnitudes decrease with increase of n.