DECOMPOSITION KINETICS OF PALLADIUM NICKEL HYDRIDE

The kinetics of the decomposition of beta-Pd0.85Ni0.15Hx were determined under isothermal conditions. The experiments were carried out with a suspension of alloy particles in liquid undecane. The rate-limiting process is the solid state transformation taking place at the interface between the hydride and the hydrogen solid solution phase. The activation energy was 78 kJ mol-1; the pre-exponential in the Arrhenius expression is 4.38 x 10(9) s-1. The results are discussed in terms of the Polanyi-Wigner expression and the activated complex theory. It is proposed that the decomposition proceeds by the conversion of a group of approximately ten whole beta-phase unit cells to a corresponding group of whole alpha-phase unit cells.