Investigation into the Cause of Spontaneous Emulsification of a Free Steel Droplet; Validation of the Chemical Exchange
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MANY steps in the process of steel making rely on the transfer of elements from metal to slag; a few examples are silica removal in the blast furnace,[2] sulfur in the desulfurization pre-treatment,[3] and phosphorus removal during steelmaking in the basic oxygen furnace (BOF).[4] In the case of phosphorus refining in the BOF, much work has been carried out on the thermodynamic equilibrium between the metal and slag,[5–7] giving evidence to the kinetic inhibition of the potential partition possible.[8] This lack of equilibrium could either be caused by lack of homogeneity in the slag layer of the BOF, (reducing the local driving force for phosphorus partition into the slag), or through kinetic restrictions through a deficiency of required interface for refining to transpose across/mass transfer controlling delivery of impurities to the interface.[8–10] Due to the inherent high temperatures, the transfer of material at the interface tends to be fast in comparison to the kinetically restricting mass transfer of materials in their respective bulk phases.[8–10] Current levels of understanding have extended beyond equilibrium conditions STEPHEN SPOONER, Ph.D. Researcher, JASON WARNETT, Research Fellow, and MARK A. WILLIAMS and SEETHARAMAN SRIDHAR, Professors, are with the University of Warwick, Coventry, UK. Contact e-mail: [email protected] ANDRE N. ASSIS, formerly Researcher with Carnegie Mellon University, Pittsburgh, PA, is now R&D Project Manager with Vallourec Research Center, Aulnoye-Aymeries, France. RICHARD FRUEHAN, Professor, is with Carnegie Mellon University. Manuscript submitted January 21, 2016. Article published online May 31, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B
to include the description of mass transport in the slag and metal phases.[11–14] It is however known that under dynamic conditions the interface between phases can display significant perturbation in comparison to a relaxed planar state, and may even lead to emulsification.[15–20] A proper description of the slag/metal reaction necessitates an elucidation of the dynamic change of interfacial area and the coupling of this change to the interfacial reactions. As such this work intends to investigate the effects of refining performance on interface morphology between Fe alloys and slags where mixing of phases may intrinsically occur to reduce the kinetic restrictions of mass transfer. Understanding when and by how much areas change during a reaction would be critical when describing the transient trajectory towards equilibrium in metallurgical processes. In this study the specific case of the transient interface in the BOF emulsion phase is considered, which has previously been attributed to offering large contributions to the overall refining performance seen within the BOF.[21] The emulsion phase of the BOF is a mix of slag, gas (O2, CO, CO2), and metal droplets caused by the impinging oxygen jet delivered to the bulk bath surface overcoming the surface tension of the molten metal and sheering material away to form discrete d
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