Kinetics of the reaction of H 2 O gas with liquid iron
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k-
+kr 1 + Ksas
where k~ kr, Ks, and as are the rate constant for pure iron, residual rate constant, the adsorption coefficient of sulfur, and the activity of sulfur in the metal relative to 1 mass pct in carbonsaturated liquid iron, respectively. The rate constants and adsorption coefficient were determined to be logk~
log k r - - log Ks -
I.
-4860
(mol/cm2satm)
T -5350
1.03
T 3870 T
+ 0.51
INTRODUCTION
THE reaction o f water vapor with liquid iron plays an important role in several steelmaking processes. In particular, in the iron bath smelting process, the H20 content in the highly postcombusted gas in the reactor could be as high as 30 pct. LI,2}H20 could react with iron droplets containing carbon in suspension in the slag as C + H 2 0 (g) = CO (g) + H 2 (g)
[1]
Fe (1) + H20 (g) = H2 + FeO (1)
[2]
Reaction [1] is endothermic, whereas Reaction [2] causes iron reoxidation. Both of these reactions are harmful to the process, and the reaction of water vapor with Fe-C droplets in the iron bath smelting reactor may limit the degree of postcombustion. Another example of the reaction of water vapor is hydrogen pickup in steel according to the reaction H20 (g) = 2H + O
[3]
For deoxidized steel, Reaction [3] is thermodynamically favorable and can cause substantial hydrogen pickup. T. NAGASAKA, formerly Research Associate, presently Associate Professor, Department of Materials Science and Engineering, Carnegie Mellon University, is with Tohoku University, Sendal, Japan. R.J. FRUEHAN, Professor, is with the Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA 15213. Manuscript submitted June 11, 1993. METALLURGICALAND MATERIALSTRANSACTIONS B
(mol/cm2s atm)
In spite of the importance of the water vapor reaction with liquid iron, little information is available on the interfacial chemical kinetics of this reaction. 13'4'5J Shigeno et al.[3] measured the rate of the decarburization of an Fe-C melt by H20-H2 gas mixtures between 1573 and 1873 K. They concluded that the chemical rate of this reaction was very fast, and most of their measurements were influenced significantly by gas phase mass transfer even at high sulfur concentrations. Sasaki and Belton, t4] using Shigeno et a l . ' s results, estimated the interfacial chemical kinetics of this reaction. They assumed the existence of the residual rate at high sulfur concentrations, and a mixed control model was used to eliminate the effect of mass transfer. However, their correction for mass transfer was excessively large, and the authors concluded that in order to establish a more reliable chemical rate constant of this reaction, additional precise measurements must be made under welldetermined experimental conditions. Recently, Fruehan et al. t51 studied the kinetics of the reaction at 1523 and 1873 K under a condition where the gas phase mass transfer was small or corrected. They confirmed that sulfur acted as a strong surface active element and retarded the rate of the H20 reaction significantly. Using a mixed cont
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