Kinetics of hydrogen absorption in Ho<inf>1-x</inf>Mm<inf>x</inf>Co<inf>2</inf> alloys

The hydriding kinetics of cubic Laves phase Ho1-xMmxCo2 (x = 0, 0.1 and 0.2) have been investigated in the pressure range 100-1000 mbar and in the temperature range 100-200 °C. The experimental results are interpreted from the time dependent hydrogen absorption curves using Johnson-Mehl-Avrami model. The existence of three different phase regions, α-phase, (α + β)-phase and β-phase, have been identified from hydriding kinetic reactions and corresponding reaction rate constants. The dependence of the reaction rate constants on hydriding pressure and temperature in the (α + β) region have been discussed and the equilibrium pressures for hydrogen absorption have been calculated. The mechanism of hydriding reactions in different phase regions has been analyzed, which proceeds quite differently in different phase regions. The activation energy in the (α + β)-phase region is 13 ± 0.6, 22 ± 2 and 28 ± 3 kJ/mol H for Ho1-xMmxCo2 (x = 0, 0.1 and 0.2), respectively. © 2006 Elsevier B.V. All rights reserved.