Electrochemical properties of intermetallic compounds Mg2Ni, MgNi2, and the hydride Mg2Nih4 in 30% KOH solution

Using the potentiodynamic polarization curve method, x-ray phase analysis, and Auger electron spectroscopy, we have studied the mechanisms for cathodic and anodic processes occurring in a 30% KOH solution on the surface of the intermetallic compounds Mg2Ni, MgNi2 and the hydride Mg2NiH4. In contrast to MgNi2, we observed hysteresis of the cathodic polarization curve for Mg2Ni due to formation of a surface layer (a mixture of the hydride phases beta-Mg2NiH4 and Mg2NiH3.85) on the sample, as a result of reaction between Mg2Ni and atomic hydrogen. We have shown that the surface of the samples is considerably enriched in magnesium and depleted of nickel, and their corrosion resistance in the indicated electrolyte is determined by active dissolution of nickel and formation of a surface layer (similar to25 nm) on the electrodes consisting of MgO and Mg(OH)(2) in the case of Mg2Ni and Mg2NiH4, and also of MgO, Mg(OH)(2), and NiO in the case of MgNi2. The intermetallic compound MgNi2 was the most corrosion-resistant, probably because of the presence of a monolayer of the oxides MgO and NiO on the original surface.