The influence of transition elements (M ≡ V, Fe, Co, Ni) in ZrMn2 - xMx alloy systems on the equilibrium hydrogen pressure and lattice parameters was studied in order to develop metal hydride materials for use in heat storage and heat transportation systems operating at temperatures between 100 and 250 °C, for which there is great demand in industrial heat processes. The equilibrium characteristics and lattice parameters of as-cast pseudobinary alloys ZrMn2 - xMx (M ≡ V, Fe, Co, Ni; 0 ≤ x ≤ 0.6) were evaluated by measuring pressure-composition isotherms at 200 °C and by analysing X-ray diffraction patterns using Rietveld's method. The crystal structures of all the pseudobinary alloys were the C14-type Laves phase. The decrease of the unit cell volume increased the equilibrium hydrogen pressure in the alloys modified by vanadium, iron or cobalt, but the alloys modified by nickel showed an opposite tendency. These results were interpreted in terms of Miedema's rule. Consequently, cobalt and vanadium were found to be the most effective elements for control of the equilibrium hydrogen pressure and therefore for extension of the available temperature range of pseudobinary ZrMn alloy systems of the C14-type Laves phase.
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