OXYGEN SOLUBILITY IN LIQUID SILICON

The oxygen solubility in liquid silicon equilibrated with solid silica (cristobalite) was determined in the temperature range between 1693 a nd 1823 K. Silicon was melted in a silica crucible with oxygen gas flo wing. 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 o xygen 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 si milar to 1823 K) The oxygen solubility in liquid silicon at the meltin g 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 pre sent work and the standard free energy of formation of silica in the l iterature, the standard free energy change follows: 1/2O(2)(g)=(O) und er 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 stan dard enthalpy change for oxygen dissolution in liquid metals and the s tandard 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 liqu id silicon, was reasonable.