Measurement of the partial molar volume and solubility of hydrogen in its dilute solutions in palladium-silver alloys

Linear expansion of thin-wall tubes of palladium silver alloys containing 10, 20. 27. and 40wt~ sihʹer was measured on absorption of small amounts of hydrogen (hydrogen-to-metal zttom ratio. 0.005 to 0,251 at temperattLres between 150~ 1423 K)and 350C 1623 K)lbr equilibration with gaseous hydrogen at presstLres up to around I bar, Hydrogen uptake by the test specimens was determined concurrently whh the expansion measurements. Thernaal expansion coefficients Iʹ~r the hydrogen-free materials were also obtained. Analysis of the data indicates that fractional length change is linearly dependent on hydrogen-tometal atom ratio within the experimental range of hydrogen concentrations. independent of temperature, and varies only slightly with alloy compositio~. Partial naolar volumes of hydrogen (with 95% confidence limits) vary from 1.77 +_ 0.0Bern 3 9( tool H ) -i I~)x the 10ʹ~o Ag alloy to 1.92 + 0.03cm 3 9( tool H ) - t Ibr the 40% Ag alloy. Hydrogen solubility results are correlated by a rek, tion that lhcilitates linear extrapolation Ibr determination of limiting values I\w equi* librium constants. Heats of solution of hydrogen at infinite dihttion and standard entropy changes are essentially independent of temperature within the range of experimental conditions.