THERMODYNAMICS AND HYSTERESIS FOR HYDROGEN SOLUTION AND HYDRIDE FORMATION IN PD-NI ALLOYS

Pd and its fee substitutional alloys which form hydride phases exhibit hysteresis. If Pd-Ni alloys have been hydrided and then dehydrided a number of times at a moderate temperature, the hysteresis is reduced. The reduction of hysteresis increases with increase of X(Ni) to 0.15 a nd, if the X(Ni) = 0.15 alloy is hydrided and dehydrided (298 K) a num ber of times, hysteresis disappears. Hydrogen isotherms have been meas ured for annealed Pd-Ni alloys from X(Ni) = 0.05 to 0.25 (273 K). Thes e show that the width of the plateau region decreases from X(Ni) = 0 t o approximate to 0.15 and then increases again. This trend is not appa rent from previous isotherm measurements but it is consistent with the x ray results available in the literature. Thermodynamic parameters f or hydrogen absorption/desorption have been measured in the dilute pha se and in the plateau region.