Kinetics of hydrogen absorption and thermodynamics of dissolved hydrogen in Tb_(1-x)Zr_xFe_3 system

摘要

The kinetics of hydrogen absorption in the PuNi_3 type rhombohedral Tb_(1-x)Zr_xFe_3 (x=0.1, 0.2, 0.3) ststem are studide in the temperature range 75≤T(~deg 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 systrem are identified. The thermodynamical paraameters viz. the relative molar enthalpy (ΔH_H) and the relative molar entropy (ΔS_H) of dissolved hydrogne are evaluated using the vant Hoff equation and are found to be in the ranges -(to 8 to 28)kJ (mol H)~(-1) and -(32 to 66) J K~(-1)(mol H_~(-1) respectively. From the dependence of ΔH_H 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.