Pressure-composition isotherms of hydrogen and deuterium in vanadium films measured with a vibrating quartz microbalance

Abstract

Thin films of vanadium produced by vapour deposition on vibrating quartz crystals were used to determine thermodynamic parameters of hydrogen occlusion from the gas phase in the pressure range 10^-10H^x=-26 kJ (mol H)^-1, Delta H_D^x=-28 kJ (mol H)^-1 and Delta S_H,D^{x nc}/R=-6. The pressure-composition isotherms indicated various phase transitions in agreement with the known phase diagram. Values of the enthalpies of transition Delta H (in kJ (mol H)^-) and the entropies of transition Delta S/R were -35 and -5 for VH_{x<( alpha )-VH0.5( beta ); -36 and -6 for VDx<( alpha )-VD0.5( beta ); -37 and -7 for VD0.5( beta )-VD0.7( alpha '); -21 and -8.5 for VH( beta ')-VH2( epsilon ); and -23 and -8 for VD( alpha ')-VD2( epsilon ). The hydriding-dehydriding kinetics were dominated by surface effects.}