Calorimetric Study of Heats of Mixing in SnxTi1−xO2Rutile Solid Solutions

Abstract

Despite the SnO2–TiO2 system being a classical example of immiscibility and spinodal decomposition for over 50 years, the enthalpies of mixing in this rutile‐structured solid solution have not been measured previously because of the refractory nature of the oxides. We report new measurements of enthalpies of drop solution in molten 2PbO·B2O3 at 800°C of the SnxTi1−xO2 solid solutions system. The data show a nearly symmetrical deviation from linearity, supporting regular solution behavior with an interaction parameter of 27.0 ± 2.6 kJ/mol. The calculated miscibility gap has a critical temperature of 1351°± 156°C. These calorimetric data are in reasonable agreement with those calculated from phase equilibria and suggest that the regular solution model, which implies random mixing of the cations and no excess (vibrational) entropy of mixing, indeed adequately describes the thermodynamic behavior. The interaction parameter is more positive than that for oxide systems of lower cation charge and similar volume mismatch.