Heat content and heat of formation measurements of RNi_{5 ± x} alloys (R ≡ La, Ce, Pr or Nd) and heat balance in a reduction-diffusion process

The heat contents of the LaNi_5.25, CeNi_5.13, PrNi_4.65 and NdNi_5.85 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.