DETERMINATION OF THE EXCESS THERMODYNAMIC FUNCTIONS IN TERNARY CS2O-SIO2-NA2O MELTS BY KNUDSEN EFFUSION MASS-SPECTROMETRY

The enthalpy and the free enthalpy of formation of the melts in the sy stem Cs2O-SiO2-Na3O are measured by mass spectrometry coupled with a K nudsen effusion cell. The measurements are performed through four quas i-binary sections at the constant SiO2 molar fraction 0.5, 0.667, 0.75 and 0.85 in the temperature range (950-1600 K) using the intensity ra tio method. Some phase limits have been determined. The thermodynamic behaviour of the melt is characterised by a slightly negative deviatio n from ideality and a symmetrical effect between Na and Cs regarding t o SiO2.