Palladium Thermodynamic Properties Of Absorption And Desorption Of Hydrogen Isotopes

The adsorption and desorption pressure-composition isotherms of H₂ . D₂ and T₂ in sponge Palladium particle were experimentally measured at the range of 5 to 65℃. The thermodynamics of the reaction between Pd and hydrogen isotope were studied systemly. There is hysteresis effect in the Palladium-Hydrogen system, it can be decreased by ramping temperature, but cannot be eliminated. Accompanying with the hysteresis effect, the loss of Gibbs free energy is a constant below 50℃, for H, D and T, which is 1.28, 1.25 and 1.16 kJ·mol^-1,respectively. But when the temperature is higher than 50℃, the loss of Gibbs free energy decreases nearly 4% and 11% and 5%, respectively. At the same temperature, the hysteresis effect in Pd-H is the most prominent and decreases from Pd-D to Pd-T system in turn.The enthalpy and entropy of the reaction in the dilute phase, plateau region and hydride phase were derived from the P-C-T curve using the Sievert constant, Vant'Hoff equation and the equilibrium theory between gas and solid state, respectively. In the dilute phase, the enthalpy of adsorption â–³H_r-->>0= -6.5 kJ·mol^-1 the entropy of adsorption â–³S_r-->>0=-53.5 J·K^-1mol_-1 for H and â–³H_r-->>0=-5.6 kJ·mol^-1, â–³S_r-->>0=-53.7 J·K^-1·mol^-1 for D, respectively. In the plateau range, â–³H^a=-18.7, â–³H^d=21.3 kJ·mor^-1, â–³S^a=-46.4, â–³S^d=50.8 J·K^-1·mol^-1 for H and â–³H^a= -17.6, â–³H^d=18.7 kJ·mol^-1, â–³S^a=-49.6, â–³S^d=49.1 J·K^-1·mol^-1 for D and â–³H^a=-15.4, â–³H^d=18.4 kJ·mol^-1, â–³S^a=-45.2, â–³S^d=50.9J·K^-1·mol^-1 for T. In the β phase, â–³H^a=-2l.5kJ·mol^-1H, -25.3 kJ·mol^-1D, â–³S^a=-38.8J·K^-1·mol^-1H, -61.6J·K^-1'mol^-1D ; â–³H^d=29.1kJ·mol^-1H. 15.2kJ·mol^-1D, â–³S^d=62.6J·K^-1·mol^-1H, 22.4J·K^-1mol^-1DThe equation as following of the relationship between the adsorption and desorption pressure of Pd-Q system with the composition and temperature was fit out on the base of experiment data, which can be used to calculate the pressure at any composition and temperature.The effect of the total atomic ratio of protium and deautium to Pd(r), temperature (T) and the abundance of protium in solid state (XH) on the separation factor in Palladium hydrides was investigated respectively. The results show that the separation factor between H and D in Pd hydrides increases slightly as the total atomic ratio of protium and deautium to Pd increases while T and XH are kept constant, and decreases non-linearly as the abundance of protium in PdH_xD_1-x increases while T and r are kept constant, and decreases as expotenoryfunction accompanying with increasing temperature at the condition of keeping X_H and r as constant, respectively.The ideal solution model used for theoretical calculation of desorption P-C isotherms and isotopic separation factor of Pd- (H+D) system was derived. The desorption pressure of Pd-(H+D) system is lower than that Pd-D system and higher than that of Pd-H system through theoretical calculation. The solution behavior of binary hydrogen isotope in Pd does not obey the Raoults' law strictly and departures from ideal solution state. The desorption pressure of Pd-(H+D) system will become higher when the abundance of deautium in solid state increases and it will decrease non-linearly and presenting as hyperbolic function accompanying with the increasing of abundance of protium in solid state. In the plateau region, the desorption pressure of Pd-(H+D) system is independent of the total atomic ratio of protium and deautium to Pd. But the above decreasing trend of desorption pressure of Pd-(H+D) system with the increasing abundance of protium in solid state will become obvious while r≥0.6.The separation factor between H and D in PdH_xD_1-x decreases while x increasing and the decreasing trend will be evident accompanying with x getting closer to 1.0. In the plateau region, the separation factor is a constant and independent of r at the same x. When r≥0.6, the sep...