Kinetics and Mechanism of Hydrogen Sorption in Yttrium-Silicon D88- Structure Phases, Part I


AbstractA relationship between the size of the z-axis lattice parameter and the rate of hydrogenation of D88 phases has been established. Materials with c-axis in the range 0.632-0.642 nm are most resistant to hydrogen content increase whilst maintaining a fast sorption capability for 0.9-10 H (fu)-1. From this Y5Si2Ge and Y5Si2GeN0.1 have been prepared and used to establish the hydrogen sorption kinetics at a range of temperatures and pressures of hydrogen. The effect that nitrogen has on the alloy is to increase reaction rates by a factor of approximately 3. Thermogravimetric plots were first analysed by the J-M-A equation as used by Goudy (6). Arrhenius representation of the first and second order equations indicate a significant change in reaction mechanism at 740-745 K. Activation energies are in the range 84-166 kJ (mol)-1 depending on order and temperature.