Kinetics of hydrogen absorption and thermodynamics of dissolved hydrogen in Tb1−xZrxFe3 system

The kinetics of hydrogen absorption in the PuNi3 type rhombohedral Tb1−xZrxFe3 (x=0.1, 0.2, 0.3) system are studied in the temperature range 75≤T(°C)≤150 at an initial pressure of 20 bar. By fitting the experimental kinetic data to a second order rate equation, the different phases [α, (α+β), β] and phase boundaries [α→(α+β), (α+β)→β] of the alloy-hydrogen system are identified. The thermodynamical parameters viz. the relative molar enthalpy (ΔHH) and the relative molar entropy (ΔSH) of dissolved hydrogen are evaluated using the vant Hoff equation and are found to be in the ranges −(8 to 28) kJ (mol H)−1 and −(32 to 66) J K−1 (mol H)−1 respectively. From the dependence of ΔHH with hydrogen concentration of the alloy-hydrides, the different phases [α, (α+β), β] and phase boundaries [α→(α+β), (α+β)→β] of the alloy-hydrogen system are identified. The different phases identified by both kinetic and thermodynamic studies confirm those seen in the hydrogen absorption isotherms of the respective alloy.