Studies on the thermal characteristics of hydrides of Mg, Mg2Ni, Mg2Cu and Mg2Nil-x Mx (M = Fe, Co, Cu or Zn; 0 < x < 1) alloys

Abstract

X-ray results on the alloys of the composition Mg2Ni1-xMx. (M = Fe, Co, Cu or Zn, 0 < x < 1) suggest a Mg2Ni-type structure. The alloys, MgeNi0.75M0.25(M = Fe, Co, Cu or Zn) upon hydriding lead to the formation of quarternary hydrides while on dehydriding yield the starting ternary alloys except for copper containing alloys which show multi-phase regions and follow a different path way for the hydriding--dehydriding process. Thermal studies (TG-DTA) on the hydrides indicate the amount of hydrogen evolved as well as the desorption temperatures. The thermodynamic quantities, namely the enthalpies and entropies of formation of the hydrides were deduced from the DTA peak maximum temperature data. The kinetic parameters such as activation energies, reaction rates and orders of the reaction for the decomposition of the hydrides formed from Mg, Mg2Ni and Mg2Cu alloys were evaluated from the DTA data. As to the modified Mg,Ni system, the copper substituted alloys show lower thermal stability and also presents some interesting properties. Hence, it is considered as one of the promising ternary combinations (Mg-Ni-Cu) for hydrogen storage purposes.