Kinetics of metal/slag reactions during spontaneous emulsification
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I. INTRODUCTION
IT is well documented that during high-temperature reactions between liquid metal and liquid slag, dynamic interfacial phenomena may occur. In the case of a liquid iron alloy droplet reacting with liquid slag, the phenomena include interfacial turbulence, a decrease in apparent interfacial tension or droplet flattening/spreading, and spontaneous emulsification.[1–5] These phenomena are found in most liquid iron systems containing oxidizable alloying elements reacting with liquid slags, namely, Fe-Al, Fe-C-S, Fe-Ti, Fe-P, Fe-B, Fe-Cr, and Fe-Si alloys. There is interplay between dynamic interfacial phenomena, reaction kinetics, and interfacial area changes during high-temperature reactions. Reaction kinetics may induce dynamic interfacial phenomena, which in turn alter the interfacial area, for example, due to a lowering of interfacial tension and spontaneous emulsification. Further, this spontaneous increase of interfacial area will again affect the reaction kinetics. Ooi et al.[2] and Riboud and Lucas[3] have included some kinetic assessments of the reaction between Fe-Al alloy droplets and CaO-SiO2-Al2O3 slag. Ooi et al.[2] analyzed the kinetics of the reaction by assuming both steady and nonsteady-state diffusion of aluminum in the metal and with constant interfacial area. Riboud and Lucas analyzed the kinetics by evaluating the overall flux of Al leaving the metal droplets. The interfacial area was multiplied by a factor of 2 to take into account the irregularity of the interface, and the reaction rates were compared in terms of the equivalent flux of oxygen in the slag and assuming the stoichiometry of the reaction. However, both of these approaches are not sufficient to explain the kinetics in the presence of spontaneous emulsification as they do not take into account the interfacial area changes. In the event of spontaneous emulsification, the increase of interfacial area is very large, i.e., M.A. RHAMDHANI, Doctoral Student, and K.S. COLEY, Associate Professor, are with the Department of Materials Science and Engineering, McMaster University, Hamilton, ON, Canada, L8S 4L7. E-mail: rhamdhma@ mcmaster.ca G.A. BROOKS, formerly Associate Professor, Department of Materials Science and Engineering, McMaster University, is Principal Research Scientist, CSIRO Minerals, Clayton South, VIC 3169, Australia. Manuscript submitted July 21, 2004. METALLURGICAL AND MATERIALS TRANSACTIONS B
300 to 500 pct of the original value.[6,7] This creates difficulties in ascribing a reaction rate constant to a given system under a given set of conditions. A procedure in analyzing the kinetics of the reaction in the presence of spontaneous emulsification is not really defined, although recent work by the authors has attempted to address this issue.[8] In this study, an approach for accommodating the change in the reacting interface area is proposed and tested against experimental data obtained from the Fe-Al system. II. EXPERIMENTAL PROCEDURE The experiments involve reactions between Fe-Al alloy droplets, containing 3
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