HYDROGEN STORAGE PROPERTIES OF THE MMNI4.6SN0.4 SYSTEM

The hydrogen absorption and desorption characteristics of cast and annealed MmNi4.6Sn0.4 intermetallic have been investigated in the temperature range 278-308 K. Hydride formation pressure is in the range of 4-10 atm in the above temperature range. The ease of hydriding of MmNi4.6Sn0.4 has been related to an increase in the unit cell volume of MmNi5 with Sn substitution. The enthalpies of hydride formation for the as-cast and annealed conditions are -26.33 kJ mol-1 H-2 and -25.53 kJ mol-1 H-2, respectively. The entropies of hydride formation are -108.21 J K-1 mol-1 H-2 and -105.49 J K-1 mol-1 H-2 for the as-cast and annealed intermetallic, respectively. Annealing markedly flattened the plateau pressure and increased the hysteresis at any fixed temperature. Hysteresis reduced with increasing temperature for both the cast and annealed conditions. The hydrogen storage capacity (i.e. the maximum H/M) was limited to 0.6.