Hydrogen uptake characteristics of mischmetal based alloy

Hydrogen storage properties of Mm39.2Ni42.1Mn4.9Al1.25Co10.2Fe2.35 alloy have been systematically studied in the present work. An attempt is made to relate the content of hydrogen with change in resistance. It is found that the resistance of material increases with the increase in value of H/M due to hydrogen absorption. Pressure composition (P-C-T) isotherm using water displacement method has been investigated in the temperature and pressure ranges of 308 ≤ T ≤ 338 K and 0.5 ≤ P ≤ 10 bar, respectively. The P-C isotherms show the presence of two single α and β regions one mixed α + β phase. The maximum H (wt%) was found to be around 1.53 at 308 K and around 6 bar. Since enthalpy is an index of thermochemical stability of metal hydride the thermo dynamical parameters viz., the relative partial molar enthalpy (ΔH) and relative partial molar entropy (ΔS) of dissolved hydrogen have been calculated by plotting the Van’t Hoff plot. The variation of ΔH and ΔS with the hydrogen concentration confirm the phase boundaries.