Hydrogen absorption and desorption properties of Ho1-xMmxCo2Ho1-xMmxCo2 alloys

The hydrogen absorption–desorption pressure-composition (PC) isotherms and kinetics of Ho1-xMmxCo2Ho1-xMmxCo2 (x=0,0.1,0.2,0.3x=0,0.1,0.2,0.3 and 0.4, Mm=mischmetalMm=mischmetal) have been carried out in the temperature and pressure ranges 50–200∘C and 0.001–1 bar using Sieverts-type apparatus. The effect of Mm on the equilibrium plateau pressure and hydrides stability has been discussed. The kinetics of hydrogen absorption at near equilibrium plateau region have been analyzed by a rate function. The reaction rate constants in the two-phase coexistence region and diffusion coefficient in the hydride phase region were calculated and its pressure and temperature dependence have been discussed. The hydrogen desorption from interstitial sites of Ho1-xMmxCo2HHo1-xMmxCo2H has been performed using differential scanning calorimetry (DSC) and thermogravimetry (TG) analysis. The results are explored to identify the preferential occupation of different interstitial sites of hydrogen atoms and complete desorption temperature. The observed phase transformations as a function of hydrogen concentration and temperature have been discussed.