Synthesis of a Thin Metal Hydride Mg2NiH4 Film on a Nickel Substrate

This work is a continuation of the previous study of the synthesis of intermetallic hydride compound Mg₂NiH₄ in the reaction between a nickel foil and magnesium hydride MgH₂ in a hydrogen atmosphere at pressures exceeding the decomposition pressures of both MgH₂ and Mg₂NiH₄. The synthesis was performed at temperatures of 400 and 475°С. With allowance for the results obtained previously at a temperature 450°С, it was found that, after some incubation time, the thickness of grown Mg₂NiH₄ film depends linearly on time. During incubation, a sublayer of intermetallic compound MgNi₂ is synthesized. The set of these data validates the previously proposed synthesis mechanism, where the limiting factor is the diffusion entry of nickel atoms with a constant rate over the MgNi₂ sublayer. Based on the analysis of X-ray diffraction (XRD) data, it was concluded that the MgNi₂ sublayer thickness is approximately the same for all three synthesis temperatures. The film growth rates were found for all three temperatures using thermal desorption spectroscopy, and the kinetic parameters of the diffusion of nickel atoms in the sublayer of intermetallic compound MgNi₂ were determined based on these data.