Activity of Calcium in Dilute Liquid Si-Ca Alloy

The activity coefficient of calcium in dilute silicon solutions was measured by equilibrating a CaO-SiO2 slag, at silica saturation, with electronic grade silicon, inside a vitreous silica crucible, heated at 1823 K (1550°C) and 1923 K (1650°C). The equilibrium was reached starting with pure silicon as well as with calcium-silicon alloys having calcium content above the equilibrium concentration. At 1823 K (1550°C), the value of (gamma)(ca) was determined as 0.00059 ± 0.00002 and at 1923 K (1650 °C) as 0.00091 ± 0.00005. With these values, a temperature dependence expression of (gamma)(ca) was proposed. The results were shown to be consistent with values measured by other authors in the range 0.30 < XCa < 1 through the use of the alpha function.