THE KINETICS OF HYDROGEN ABSORPTION IN ZR1-XHOXCO2 (X = 0.4, 0.6 AND 0.8) ALLOYS

The hydrogen absorption kinetics in the system Zr1-xHoCo2 (x = 0.4, 0.6 and 0.8) were studied in the temperature range 50-200-degrees-C. A change in slope is observed at the phase boundary as indicated in the first-order fit, which implies that different Tate controlling steps are involved during different stages of the reaction. It is believed that the surface process, the interface process and the diffusion of hydrogen in the product beta layer are the possible rate controlling steps in the alpha, alpha + beta and beta phases respectively. The diffusion coefficients obtained from the diffusion rate constants are found to be of the order of 10(-10) cm2 s-1 at 300 K. The average activation energy (E(a)) in the alpha + beta phase and the beta phase are found to be 20 and 16 kJ mol-1 respectively.