A study of the reaction of CO on liquid iron alloys
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INTRODUCTION
THE rate of formation or dissociation of the CO molecule on liquid and solid iron surfaces is important in many steelmaking operations. The formation of CO is relevant in vacuum carbon deoxidation, the rimming of steel, and in the steelmaking reaction itself. Due to its importance, it has been the subject of numerous experimental investigations. One of the earliest investigations was by Parlee e t al. using a constant volume Sieverts' type apparatus in which it was concluded that for their experimental conditions of induction stirred melts, the rate of absorption and desorption of CO was controlled primarily by diffusion of oxygen in the metal. Schenck e t al. 2 ran similar experiments and showed that sulfur had no effect on the rate; they also concluded that the chemical rate was fast and that the overall rate was controlled by liquid phase mass transfer. Similar results were reported by Rathke and T a r b y . 3 They showed that for vacuum desorption of CO the rate was controlled by mass transfer, while at low oxygen levels melt reactions with the crucible became important but diffusion was still controlling the rate. King e t a l . 4 carried out absorption and desorption experiments with only natural convection for stirring and they also concluded that the rate was controlled by oxygen mass transfer. Solar and Guthrie 5 made Sieverts type measurements for CO absorption in stagnant iron and showed that the rate could be explained in terms of an "apparent diffusion coefficient" of CO in iron. This "apparent diffusion coefficient" essentially took into account both carbon and oxygen diffusivity. Suzuki and Mori 6 ran Sieverts' type experiments and refined the interpretation to include mass transfer of both carbon and oxygen. Several investigators used levitated drop experiments to eliminate the effect of the crucible on the rate and they also found the rate to be controlled by liquid phase mass transfer. 7'8 Therefore, in all of the previous studies, the rate was controlled by liquid phase mass transfer and in no case was the rate controlled by chemical kinetics. Several recent R. J. FRUEHAN is Professor and Director of Center for Iron and Steelmaking Research, Department of Metallurgical Engineering and Materials Science, Carnegie Mellon University, Pittsburgh, PA 15213. S. ANTOLIN, formerly Graduate Student at Carnegie Mellon University, is with LANXIDE Corporation, Newark, DE 19711. Manuscript submitted July 11, 1986.
METALLURGICAL TRANSACTIONS B
studies concerning the kinetics of gas-liquid metal reaction have applied the isotope exchange technique: 9-12 for example, the nitrogen reaction on iron 9'1~and iron chromium alloys, 11 and the CO2 reaction 12 with iron. With the isotope exchange technique the measurement is made at chemical equilibrium and the isotope exchange reaction is not influenced by liquid phase mass transfer. For example, for investigating the nitrogen reaction, nitrogen gas enriched with about 1 pct of the isotope N 3~ is used. The gas is reacted with the surface and the foll
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