The influence of partial substitution of iron by Al in TiFe compound on the hydrogenation characteristics was systematically investigated. The composition of alloys corresponds to the formula $TiFe_{1-x} Al_x$ with x increasing from 0 to 0.10 with 0.02 by intervals.
Activation properties were enhanced with the Al content and crack formation during hydrogen absorption-desorption cycles was increased for the Al containing compound.
The pressure-composition isotherms were made to see the difference in the thermodynamic properties. The hydrogen storage capacity was drastically decreased and the ｒ-phase was not appeared. The plateau pressure was inclined and was higher for $TiFe_{0.98} Al_{0.02}$ and $TiFe_{0.96} Al_{0.04}$ and lower for $TiFe_{0.94} Al_{0.06}$ and $TiFe_{0.90} Al_{0.10}$ than for pure TiFe. The ΔH˚,ΔS˚, ΔG˚ values were obtained from the plot of $l_n$ P v.s. 1/T by the van't Hoff relation. The Hysteresis energy loss was decreased with the Al content.
The kinetic properties were investigated for the $TiFe_{0.94} Al_{0.06}$ compound from the pressure sweeps. The dependence of hydrogen absorption rate on driving force and reacted fraction showed that the chemisorption of hydrogen molecules on sample surface is rate controlling at the initial stage and the apparent activation energy of the chemisorption is about 1.7Kcal/mole $H_2$. At later stage (F70.15), rate controlling step changed from chemisorption to hydrogen diffusion through the hydride phase.
