The effect of thermal cycling of FeTi on the degradation was investigated to increase the understanding of intrinsic degradation mechanism by measuring of P-C-Isotherm curves and hydrogen absorption rate in the isothermal condition.
The reversible hydrogen absorption capacity was decreased about 19% after 2000 cycles and about 23% after 5000 cycles respectively.
In activated FeTi, the rate controlling steps of hydriding reaction changed from surface chemisorption to hydrogen diffusion process through hydride phase sequentially as reaction proceeded.
As the numbe of cycle was increased, the sequential change of rate controlling step was same as activated FeTi. However, the transition point of rate controlling steps from surface chemisorption to diffusion process was shifted to lower reacted fraction and the intrinsic hydrogen absorption rate was significantly decreased.
It is suggested that the intrinsic degradation of FeTi can be interpreted with coring model, the formation of stable hydride at the particle surface is a cause of changes of kinetic behavior.
