Structural, hydrogen storage and thermodynamic properties of some mischmetal–nickel alloys with partial substitutions for nickel

Abstract

Mischmetal–nickel (Mm–Ni) alloys with single (Al) and multiple (Al, Co, Mn, Fe) substitutions for Ni are studied for their structural, hydrogen storage and thermodynamic properties. The alloys considered are MmNi 5, MmNi 4.7Al 0.3, MmNi 4.5Al 0.5, MmNi 4.2Al 0.8 and MmNi 4Al for single substitution, and MmNi 3.9Co 0.8Mn 0.2Al 0.1, MmNi 3.8Co 0.7Mn 0.3Al 0.2, MmNi 3.7Co 0.7Mn 0.3Al 0.3, MmNi 3.6Co 0.6Mn 0.3Al 0.3Fe 0.2 and MmNi 3.5Co 0.4Mn 0.4Al 0.4Fe 0.3 for multiple substitutions. The XRD patterns of all the alloys show single phase with the reflection peaks related to the CaCu 5 hexagonal structure. All the multiple substituted alloys absorb and desorb hydrogen at sub-atmospheric pressures. The equilibrium pressure and hysteresis decrease, while enthalpy of formation (Δ H) and plateau slope increase with increase in unit cell volume, indicating an increase in the stability of the alloys.