Hydrogen absorption characteristics in Zr0.2Ho0.8Fe0.5Co1.5

Hydrogen absorption studies have been carried out on the C15 cubic Laves ph ase alloy of Zr0.2Ho0.8Fe0.5Co1.5. The p-c data were collected in the press ure and temperature ranges of 0.05 less than or equal to P (bar) less than or equal to 45 and 27 less than or equal to T (degrees C) less than or equa l to 100, respectively. A maximum hydrogen uptake of 3.6 hydrogen atoms per formula unit at 33 bar and 27 degrees C is observed. The p-c isotherms sho w one plateau (alpha + beta) region. This is confirmed from the dependence of the thermodynamics of dissolved hydrogen as a function of hydrogen conce ntration. Delta H-H and Delta S-H are found to be in the ranges -(5-15) kJ (mol H)(-1) and -(23-48) J K-1 (mol H)(-1), respectively. Volume expansion of about 20% is found at the maximum hydrogen concentration at RT, without a change in its crystal structure. (C) 2000 International Association for H ydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.