PRESSURE-COMPOSITION AND ELECTRICAL-RESISTANCE COMPOSITION ISOTHERMS OF A PALLADIUM-HYDROGEN SYSTEM

The equilibrium hydrogen pressure and the relative electrical resistan ce 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 increasin g H/Pd content up to alpha(max) composition. Achievement of (R/Ro)alph a(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), whi ch seems to be related to the degree of saturation of the alpha phase with hydrogen. Entering the beta single phase region, R/Ro increased m onotonously. On desorbtion. R/Ro decreased with the decrease of H/Pd c ontent down to beta(min). In the (alpha + beta) two-phase region, init ially R/Ro remained constant and then showed a small increase near the alpha/(alpha + beta) boundary, where a maximum R/Ro value was attaine d when the beta phase completely disappeared. In the alpha phase regio n, R/Ro decreased abruptly with the decrease of H/Pd content.The chang e in R/Ro in the alpha and beta single phase regions, was mainly cause d by the change in the scattering of conduction electrons associated w ith 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.