OXYGEN SOLUBILITY IN LIQUID SILICON

The oxygen solubility in liquid silicon equilibrated with solid silica (cristobalite) was determined in the temperature range between 1693 and 1823 K. Silicon was melted in a silica crucible with oxygen gas flowing. Oxygen in a quenched sample was analyzed by the inert gas fusion-IR absorption method. The optimum furnace power and bath composition for oxygen extraction were determined. The temperature dependence of oxygen solubility in liquid silicon could be expressed as the following equation. log (C-O under bar/mass%)= -4620/T+0.332(+/-0.06)(T:1693 similar to 1823 K) The oxygen solubility in liquid silicon at the melting point (1685 K) was calculated to be 39 ppm (3.4 x 10(18) atoms . cm(-3)). Using the temperature dependence of oxygen solubility in the present work and the standard free energy of formation of silica in the literature, the standard free energy change follows: 1/2O(2)(g)=(O) under bar(mass%, in liquid silicon) Delta G degrees= -3.88 x 10(5)+95.6 T(J) According to the previously reported correlations between the standard enthalpy change for oxygen dissolution in liquid metals and the standard enthalpy of the formation of the metal oxides at 298 K per mol of oxygen, and the standard enthalpy change and the standard entropy change for oxygen dissolution in liquid metals, it was suggested that the present Delta G degrees value, i.e., the oxygen solubility in liquid silicon, was reasonable.