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I. I N T R O D U C T I O N

THE

authors in previous publications tt'2'31 have reported on the sulfur partition ratio between Na20-SiO2 slags and carbon saturated iron and the sulfide capacity of slags. As shown in Figure 1, Na20-SiO2 slags have excellent sulfide capacities when compared to common CaO-based slags.J4-9] It is of interest to determine whether additions of Na20 to conventional CaO-based slags will significantly increase the sulfide capacity. If Na20 additions significantly increase the sulfide capacity, this could be a possible method for improving sulfur removal in steelmaking processes. The sulfide capacities and sulfur partition ratios with carbon saturated iron melts and CaO-Na20-SiO2 slags with less than 20 wt pct Na20 at 1400 ~ were measured. Measurements also were performed on a 48 pct CAO-45 pct A1203-7 pct S i O 2 s l a g with and without small amounts (less than 2 pct) of Na20. This is a typical ladle slag for an aluminum-killed steel and if Na20 additions increase the sulfide capacity, the desulfurization by ladle slags may be improved. It is also of interest to determine if the concept of optical basicity can be used to describe the sulfide capacity of Na20 based slags. Sommerville and Sosinsky t~~ correlated a vast amount of sulfide capacity data to the optical basicity (A). The optical basicity is proportional to the mole fraction of various oxides with each oxide having a particular value of optical basicity. Previous work by the authors on Na20-SiO2 slags indicated that the sulfide capacity correlated to A, but the correlation was somewhat different than previously obtained f~~ for CaO-based slags. II. E X P E R I M E N T A L P R O C E D U R E

The experimental procedure was similar to that described previously, m Briefly, for the partition ratio meaA.H. CHAN, formerly Graduate Student at Carnegie Mellon University, is with Union Carbide Corporation, Linde Division, Tarrytown Technical Center, Tarrytown, NY 10591. R.J. FRUEHAN is Professor and Director, Center for Iron and Steelmaking Research, Department of Metallurgical Engineering and Materials Science, Carnegie Mellon University, Pittsburgh, PA 15213. Manuscript submitted January 27, 1988. METALLURGICAL TRANSACTIONS B

surements, approximately 8 grams each of slag and metal were equilibrated in graphite crucibles. Several adjustments had to be made for the higher temperature used in this study. The capped crucible system used for the sulfur partition ratio experiments was modified by drilling a small hole less than 1 mm in diameter in the cap to allow some gas to escape. Caps without the small hole would pop off soon after introduction into the furnace. The hole did not greatly affect slag evaporation at low Na20 and CaO contents. The Nichrome basket system used in the previous work could not withstand the temperature used in this study. Therefore, holes were drilled near the bottom of the crucible so that removable iron rods could be used to raise and lower the crucible. The holes were placed so that the sample chamber was not pie