Determination of sulfide capacities of CaO-SiO2 slags containing CaF2 and B2O3 by an encapsulation method

The sulfide capacities of CaO-SiO₂ melts containing CaF₂ and B₂O₃ have been measured by simultaneous equilibration of samples within quartz capsules at 1503°C. In this method, the compositions of both the condensed phases and the static gas environment adjust to es-tablish a mutual equilibrium. Although the sulfurizing potential,P _{S 2}/P _{O 2}, is neither preset nor directly measured, the sulfide capacities,C _s, of all samples within the capsule are related by the following equation:C _S(j)=(pct S)j/(pct S)i · C_S(i)· Hence, the sulfide capacities of all samples may be calculated from the measurement of the final sulfur content of each sample and the inclusion of a “reference” slag sample for which C_S is known from previous measurements. In the present study, quartz capsules containing as many as fifty slag samples including several reference samples have been equilibrated. With considerable difficulty the encapsulation-equilibration method atl503°C has been developed into an acceptable procedure. The influences of CaF₂ and B₂O₃ on the sulfide capacities of several CaO-SiO₂ melts have been measured. The results may be summarized as follows: 1) for melts of fixed CaO/SiO₂ ratio, the addition of CaF₂ increases sulfide capacity and the addition of B₂O₃ decreases sulfide capacity, 2) the substitution of CaF₂ for CaO does not alter sulfide capacity significantly, and 3) the substitution of B₂O₃ for SiO₂ increases sulfide capacity slightly. These results have been obtained for melts with CaO/SiO₂ mass ratios ranging from 1.00 to 1.28 and with flux additions up to 10 wt pct.