The heat contents of the LaNi5.25, CeNi5.13, PrNi4.65 and NdNi5.85 alloys were measured over the temperature range 800-1400 K using a drop calorimeter. The heat content and heat capacity equations were derived using the Shomate function. The heats of formation of these alloys were determined at 773 K from the heats of dissolution of these compounds and their components in a liquid tin solvent using a Calvet-type solution calorimeter. Heat balance was calculated for a reduction-diffusion process to make the RNi5 powders directly for use as hydrogen storage media by reducing the rare earth resources with metallic calcium, magnesium and lithium.
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