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

The kinetics of hydrogen absorption in the PuNi3 type rhombohedral Tb1-xZrx Fe3 (x = 0.1, 0.2, 0.3) system are studied in the temperature range 75 less than or equal to (degrees C) less than or equal to 150 at an initial press ure of 20 bar. By fitting the experimental kinetic data to a second order r ate equation, the different phases [alpha, (alpha+beta), beta] and phase bo undaries [alpha-->(alpha+beta), (alpha+beta)-->beta] of the alloy-hydrogen system are identified. The thermodynamical parameters viz. the relative mol ar enthalpy (Delta H-H) and the relative molar entropy (Delta S-H) Of disso lved hydrogen are evaluated using the vant Hoff equation and are found to b e 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 Delta H-H with hydrogen concentration of the alloy-hydrides, the different phases [alpha, (alpha+beta), beta] an d phase boundaries [alpha-->(alpha+beta), (alpha+beta)-->beta] of the alloy -hydrogen system are identified. The different phases identified by both ki netic and thermodynamic studies confirm those seen in the hydrogen absorpti on isotherms of the respective alloy. (C) 2000 International Association fo r Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.