THE THERMODYNAMICS OF HYDROGEN ABSORPTION DESORPTION BY PD-CO ALLOYS/

The thermodynamics of Pd-Co-H(D) systems have been investigated using H-2(D-2) pressure-composition isotherms and reaction calorimetry. The enthalpies for hydrogen solution and hydride formation decrease in mag nitude with increase of X-Co and, because of this, the hydrogen pressu res at a given value of H/M increase with X-Co. This behavior is consi stent with the decrease of the unit cell size with increase of X-Co fo r these random solid solution fcc Pd-Co alloys. Repeated hydride forma tion and decomposition at ambient temperature without intermediate ann ealing treatments, causes the plateau pressures to converge thereby de creasing the extent of hysteresis.