Mass spectrométrie determination of activity coefficients of dilute aluminium and calcium in liquid silicon and ferrosilicon alloys

The vaporisation of liquid Fe-Si-Al-Ca alloys was studied with a Knudsen-cell mass spectrometric technique. A single graphite effusion cell was used and silicon was chosen as thermodynamic reference. In the studied ranges of temperature [1523-1923K] and composition (wt%Fe 0-55: wt%Al 0-0.5: wt%Ca 0- 0,5), activities of Al and Ca were derived from measured Al+ Ca+ Si+ ionic intensities and from Si activity in the melt. The results in tenus of activity coefficients at infinite dilution are : [math] and [math] in liquid Si and [math] and [math] si in liquid Fe-Si alloys at 1723K (T: °K, XSi : Si molar fraction). A good agreement is found with previous results derived from metal/slag equilibria.