Thermogravimetric analysis of the H/D isotope effect on hydration thermodynamics of Y-substituted BaZrO3

The isotopic difference in the thermodynamics of hydration of 20 mol% Y-substituted BaZrO 3 with H 2 O or D 2 O has been investigated by thermogravimetry. Average standard entropies and enthalpies of hydration were extracted from linear regressions of van ‘t Hoff plots of hydration over the range 400–900 °C, further validated by the fit of the associated isothermal net mass changes. The thermodynamic parameters for hydration by H 2 O and D 2 O are very similar: by using the nominal acceptor level of 0.20 in the fitting, we find Δ H hyd , H 2 O 0 = −89.5±1.2 kJ/mol and Δ S hyd , H 2 O 0 = −97.5±1.4 J/molK for H 2 O and Δ H hyd , D 2 O 0 = −89.4±1.4 kJ/mol, Δ S hyd , D 2 O 0 = 98.2±1.7 J/molK for D 2 O. An effective lower acceptor level of 0.16 yields marginally more negative enthalpies and entropies. The thermodynamic isotope effects appear small but yield significant differences in hydration level under conditions of partial hydration. They are sufficient to cause considerable errors in attempts to measure total proton contents by mere isotope mass changes unless properly taken into account.