PHASE-TRANSITIONS IN THE PALLADIUM-RICH PD-LI ALLOY SYSTEM AND HYDROGEN SOLUBILITY IN THE SOLID-SOLUTION ALLOYS

The phase boundaries of the solid solution of Li in alpha-Pd, alpha-Pd(Li), and the ordered Pd7Li phases in Pd-Li alloys have been examined by X-ray, electron diffraction and electrical resistance measurements. The solubility limit of lithium in the alpha-Pd phase is about 4 at.% Li at room temperature, and there is an almost linear decrease in the lattice parameters with Li content in the alpha-Pd phase up to about 4 at.% Li. In the composition range between about 4 and 10.3 at.% Li, there is a two-phase mixture of a saturated Pd-Li solid solution phase, alpha-Pd(Li,s), and an ordered Pd7Li phase (25-degrees-C). Hydrogen absorption characteristics of Pd-Li solid solution alloys with 1.6 and 3.1 at.% Li have been investigated by measurements of pressure-composition isotherms at temperatures between 273 K and 433 K and hydrogen pressures up to 1000 Torr. The low pressure hydrogen solubilities increase with Li content, and the (alpha + beta) hydrogen plateau pressures decrease with the Li content, despite the lattice contraction upon alloying with Li. The Pd-Li alloys absorb considerable amounts of hydrogen, and their higher pressure solubilities are comparable to that of pure Pd. The hydrogen absorption characteristics of these Pd-rich alloys are quite similar to those that have been observed for the "expanded" alloys, despite the lattice contraction upon Li substitution.