THERMODYNAMIC STUDIES OF THE LANI5-XSNX-H SYSTEM FROM X=O TO 0.5

Hydrogen isotherms have been measured for the ternary intermetallic sy stem LaNi5-xSnx-H with x = 0, 0.10, 0.20, 0.25, 0.32, 0.40 and 0.50 at a series of temperatures from 300 to 423 K. The plateau pressures dec rease with increase in x. The magnitudes of the enthalpy for the plate au reaction, as determined from the van't Hoff plots, increase steadil y with x while the corresponding entropies are nearly constant. Thus t he observed decrease in the plateau pressures can be attributed to the changes in Delta H-plat with x. The extent of the two-phase plateau r egions decrease with x and hysteresis also decreases, nearly vanishing at x = 0.5.