Thermodynamics of the Ni-H system

Thermodynamic properties of the Ni-H system have been analyzed by means of the CALPHAD method. Thermodynamic models have been defined to describe the Gibbs energy of the individual phases, and the model parameters have been o ptimized from the original experimental hydrogen solubility data. Magnetic ordering in solid nickel has also been considered. The nickel hydride that only forms at very high hydrogen pressure has not been included. No seconda ry values, such as the hydrogen solubility data at 1 bar derived from those values measured at lower pressures, were used in optimization. The heat of solution of hydrogen in nickel is calculated in dependence of temperature. The effect of the magnetic ordering in solid nickel on the heat of solutio n of hydrogen and, consequently, on the hydrogen solubility, is discussed. The CALPHAD method is demonstrated to be a powerful tool for determining th e heat of solution of gaseous atoms in metals. (C) 1999 Elsevier Science S. A. All rights reserved.