A mass spectrometric study of Al(2)O(3)-SiO(2) melts using a Knudsen cell

The thermodynamic activities of SiO(2) in Al(2)O(3)-SiO(2) liquid slags were measured by the high-temperature Knudsen cell mass spectromeric method in the present work. The measurements were carried out in the temperature range 1863-2169 K. Tungsten crucibles were used to hold the slags. The system was calibrated using a CaF(2) standard. The mass spectra obtained for pure SiO(2) were in agreement with earlier data. The activities of silica, measured in the present work at 2150 K, show a slight negative deviation at very low alumina mole fractions which changed to a positive deviation at higher alumina contents. The activity values are in reasonable agreement with the assessment carried out by Hillert et al. The results were analysed on the basis of a slag model developed earlier at KTH, Stockholm. The present results are found to be compatible with the phase diagram proposed by Klug et al.