The kinetic studies of the hydrogen induced amorphization in $ErCo_2$ Laves phase is observed by the internal standard method using X-ray diffraction intensities. The activation energy and rate constant exponent for the amorphization in $ErCo_2$ are found to be 26 kcal/mole and 0.78, respectively. From these results, it is believed that the mechanism of the hydrogen induced amorphization in $ErCo_2$ is related to the motion of Co atoms.
Though there are many similar physical properties between $ErCo_2$ and $ErNi_2$, the activation energy for the amorphization in $ErCo_2$ is larger than that in $ErNi-2$ and the amorphization rate in $ErCo_2$ is slower. It is suggested that these differences of activation energy for the hydrogen induced amorphization and the amorphization rate between $ErCo_2$ and $ErNi_2$ is due to the occurence of structural change on forming crystalline hydride.
As the hydrogen induced amorphization reaction in $ErCo_2$ is thermally activated process, the amorphization temperature is related to the activation energy for amorphization. From the investigations of the amorphization temperature of $Er(Co_{0.9}M_{0.1})_2$ compounds (M = Cr, Mn, Fe, Ni, Cu ), the amorphization temperature is proportional to the atomic radius of substituted transition element. This indicates that the atomic radius of transition metal which is a measure of diffusion is the factor affecting the hydrogen induced amorphization.
