Thermodynamic Properties of Selected Glasses in the Cao-Al2o3-Tio2 System

The thermodynamic properties of a Ca12Al14O33 (C12A7) binary glass and the impact of titania additives were studied for the first time using three different calorimetric techniques: low-temperature adiabatic, high-temperature drop and drop solution calorimetry. The enthalpy of formation from oxides at 298.15 K of Ca12Al14O33 and Ca12Al14O33+7wt.% TiO2 glass samples obtained by drop solution calorimetry in a lead borate bath is 15.9±1.8 kJ/mol and 14.8±2.4 kJ/mol, respectively. A close value (11.9±2.3 kJ/mol) was obtained for the same C12A7 glass by drop calorimetry. The investigation of the impact of TiO2 additions on the thermodynamic properties of glasses shows that there is no influence on heat capacity of C12A7 up to 7wt.% of TiO2. In contrast to this, the enthalpy of mixing of C12A7 and TiO2 as components of a solution phase under the assumption of a regular solution behavior in the amorphous state was estimated as g00 = -54.3 kJ/mol.