Pressure-composition and electrical resistance-composition isotherms of a palladium-hydrogen system

Abstract

The equilibrium hydrogen pressure and the relative electrical resistance as a function of composition of a Pd-H system have been measured by a gas phase method at temperatures of 75, 100, 130 and 160 °C with hydrogen pressure up to 3.3 MPa. On the absorbtion process, the R Ro value in the α phase region increased significantly with increasing H Pd content up to α max composition. Achievement of ( R Ro)α max values required a long holding time. In the (α + β) two-phase region, R Ro showed almost a constant value up to β min, which seems to be related to the degree of saturation of the α phase with hydrogen. Entering the β single phase region, R Ro increased monotonously. On desorbtion, R Ro decreased with the decrease of H Pd content down to β min. In the (α + β) two-phase region, initially R Ro remained constant and then showed a small increase near the α (α + β boundary, where a maximum R Ro value was attained when the β phase completely disappeared. In the α phase region, R Ro decreased abruptly with the decrease of H Pd content. The change in R Ro in the α and β single phase regions, was mainly caused by the change in the scattering of conduction electrons associated with the expansion and contraction of lattice. ( R Ro)α max , R Ro α + β and R Ro max values tend to decrease with increasing temperature.