Transition from interfacial to diffusional growth during hydrogenation of Mg

The transition from interfacial to diffusional growth during hydrogenation of Mg→MgH2 (hydride) at 210 °C for 300 min is studied using Johnson-Mehl-Avrami-Kolmogorov equation (α=1−exp(−ktn)). The growth dimensionality (n) decreases from 0.73 to 0.23. 1D (hydride/metal) interfacial growth occurs when n>0.50, suggested by constant interface velocity (U). Diffusional growth at n<0.50 is confirmed by the core-shell (Mg-MgH2) structure, drop in U by ~2-orders and the diffusion coefficient (D) of H-atom through hydride. The transition from 1D interfacial to diffusional growth occurs at n≈0.50.