Experimental evidence for electrochemical nature of the reaction between iron oxide in calcia-silica-alumina slag and ca
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RODUCTION
THE reaction between iron oxide in slag and carbon in liquid iron, FeO (slag sln) 1 C (1 Fe sln) → Fe (1 Fe sln) 1 CO (g)
[1]
†
is important in both iron- and steelmaking. In an early study of the kinetics of the reaction in Eq. [1] by Philbrook and Kirkbride,[2] it was suggested that molecular FeO might not be the true reactant. The authors suggested that FeO might be dissociated into atoms or ions in the slag, denoted by Fe* and O*, so that the overall reaction replacing Eq. †
States of aggregation are indicated using IUPAC notation.[1]
[1] would be Fe* (slag sln) 1 O* (slag sln) 1 C (1 Fe sln) → Fe (1 Fe sln) 1 CO (g)
[2]
In an article by Ramachandran et al.,[3] published at about the same time, it was proposed that sulfur transfer takes place when a cathodic partial reaction, S (1 Fe sln) 1 2e2 → S22 (1 slag sln)
[3]
is coupled with anodic partial reactions, such as the oxidation of liquid iron, Fe (1 Fe sln) → Fe21 (1 slag sln) 1 2e2
[4]
and of silicon, aluminum, manganese, or other elements in solution in liquid iron. They suggested that carbon participated in the reaction O22 (slag sln) 1 C (1 Fe sln) → CO (g) 1 2e2
[5]
DAVID E. WOOLLEY, Research Associate, and UDAY B. PAL, Associate Professor, are with the Department of Manufacturing Engineering, Boston University, Boston, MA 02215. Manuscript submitted October 29, 1998. METALLURGICAL AND MATERIALS TRANSACTIONS B
They also suggested that the liquid iron phase, or an electronically conducting crucible, could provide an electronic connection between the location of the cathodic and anodic reactions, so that when a graphite crucible was used, the reaction C (s) 1 O22 (slag sln) → CO (g) 1 2e2
[6]
might take place at the slag-crucible interface; the electrons would pass through the crucible and the metal phase to a location on the slag-metal interface, where they would be consumed in Reaction [3]. They noted that, if an electrochemical mechanism plays an important part in desulfurization of liquid iron, then an electrical potential should exist between cathodic and anodic reaction sites, and this should be measurable under appropriate experimental conditions. King and Ramachandran[4] and Wagner[5] worked on this problem, and it was later reported that Baak and King, studying sulfur transfer between a silver metal bath and a sodium borate slag, were able to measure an electric current passing through an external circuit connecting the slag and metal phases.[4,5] A number of studies have followed, focusing on electrochemical effects in different chemical systems and processes. These include studies on the reduction of silica by solid carbon and by carbon dissolved in liquid iron,[6,7] on the transfer of oxygen through PbO-SiO2 slag to liquid lead,[8,9] on the reaction between CO2 gas and Ag-S alloys through CaO-Al2O3-SiO2 slag,[10,11] on the desulfurization of liquid Fe-Cr-S alloy using CaO-Al2O3 and CaO-Al2O3-CaF2 slags,[12–15] on the reduction of solid NiO, MnO2, and Cr2O3 by solid carbon,[16] and on the reduction of MnO from SiO2MnO-Ca
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