Comparing hydriding kinetic equations derived from a theoretical model with experimental data, the kinetic mechanism of hydriding reaction of pure Mg and Mg in a Mg-$Mg_2$Cu hypo-eutectic alloy is analyzed. And experimental data of Mg-$Mg_2$ Cu eutectic, published by Rudman et al.[6] is reanalyzed.
As Mg particle has the uniform radius and eutectic structure of the alloy has the uniform interlamellar spacing, shrinking core model is assumed for the hydriding of both Mg.
In both cases the diffusion of hydrogen through the hydride phase is the rate controlling step.
Apparent activation energy of surface chemisorption is about 16-17Kcal/mole $H_2$ for both cases, then we know that surface chemisorption is mainly controlled by Mg.
Comparing hydriding reaction rate of pure Mg with that of Mg in a Mg-$Mg_2$ Cu hypo-eutectic alloy, the catalytic effect of $Mg_2$ Cu is that $Mg_2$ Cu phase provides hydrogen with diffusion path, resulted in reduction of reaction thickness.
