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

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 degrees C with hydrogen pressure up to 3.3 MPa. On the absorbtion process, the R/Ro value in the a phase region increased significantly with increasing H/Pd content up to alpha(max) composition. Achievement of (R/Ro)alpha(max) values required a long holding time. In the (alpha + beta) two-phase region, R/Ro showed almost a constant value up to beta(min), which seems to be related to the degree of saturation of the alpha phase with hydrogen. Entering the beta single phase region, R/Ro increased monotonously. On desorbtion. R/Ro decreased with the decrease of H/Pd content down to beta(min). In the (alpha + beta) two-phase region, initially R/Ro remained constant and then showed a small increase near the alpha/(alpha + beta) boundary, where a maximum R/Ro value was attained when the beta phase completely disappeared. In the alpha phase region, R/Ro decreased abruptly with the decrease of H/Pd content.The change in R/Ro in the alpha and beta 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)alpha(max), (R/Ro)(alpha + beta) and (R/Ro)(max) values tend to decrease with increasing temperature. (C) 1998 International Association for Hydrogen Energy.