Magnetic study of the activation energy of the phase transition kinetics between nickel and nickel hydride

Abstract

The phase transition of Ni to non‐ferromagnetic nickel hydride (NiHβ) is followed by measurements of the saturation magnetization Ms of 2 to 12 μm thick Ni foils during their cathodic charging with hydrogen at temperatures between 15 and 38°C. The linear decrease of Ms hereby in a quadratic time scale confirms the picture of a maintenance of a trapezoidal concentration profile of the advancing NiHβ‐fronts up to their meeting in the middle of the foils. Some corresponding measurements are performed during the decomposition of NiHβ. The difference between the activation energies found for the formation (Ea = (6.5 ± 1.2) kcal/mol) and for the decomposition (Ed = (13.7 ± 0.6) kcal/mol) of NiHβ indicates different mechanism and supports the conception of a precipitation‐like character of the decomposition process.