The nitrogen reaction between carbon saturated Iron and Na 2 O-SiO 2 slag: Part II. Kinetics
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INTRODUCTION
THEthermodynamics of the nitrogen reaction between FeC-Si alloys and Na20-SiO2 slag were presented in a previous paper. 1The thermodynamics indicate nitrogen removal from hot metal by Na20-SiOz slags or by Na2CO3 treatment is possible. However, to assess the possibility of such a process, information on the kinetics of reactions is essential. Although hot metal treatments have been developed for soda ash removal of sulfur and phosphorus and many kinetic studies have been made, there is no information on the kinetics of nitrogen reaction between an iron alloy and Na20-SiO2 slags. It is the purpose of this work to determine the kinetics of nitrogen transfer between carbon saturated iron and Na20-SiOz slags. In addition, nitrogen transfer from a NazO-SiO2 slag to an inert gas phase at 1200 ~ was also investigated. Finally, the possibility of nitrogen removal from hot metal by NazCO3 was demonstrated.
II.
EXPERIMENTAL
Several different types of experiments were conducted in order to investigate the kinetics of nitrogen transfer from carbon saturated iron to Na20-SiO2 slags, transfer from a Na20-SiO2 slag to an inert gas phase, and the overall rate of nitrogen removal from carbon saturated iron by Na2CO3.
A. Nitrogen Transferfrom Carbon Saturated Iron to Na20-Si02 Slag In one set of experiments, 250 grams of an Fe-C-N-Si alloy was reacted with 250 grams of an equimolar Na20-SiO2 slag contained in a 38 mm I.D. graphite crucible at 1200 ~ F. TSUKIHASHI is Research Associate, Department of Metallurgical Engineering and Materials Science, Carnegie Mellon University, Pittsburgh, PA 15213, and is on leave of absence from the Department of Metallurgical Engineering and Materials Science, Faculty of Engineering, The University of Tokyo. E. OKTAY, formerly with the Department of Metallurgical Engineering and Materials Science, Carnegie Mellon University, is with the Department of Metallurgical Engineering, Purdue University, West Lafayette, IN 47907. R.J. FRUEHAN is Professor, Department of Metallurgical Engineering and Materials Science, Carnegie Mellon University, Pittsburgh, PA 15213. Manuscript submitted March 10, 1986. METALLURGICALTRANSACTIONSB
in an argon atmosphere flowing at 0.1 liter per minute. The crucible was lowered into the hot zone of the SiC resistance furnace and after allowing about 3 minutes for the sample to reach the experimental temperature, samples of the slag were taken periodically with a copper rod and of the metal by suction into silica tube. In the second set of experiments, each experimental time was a separate experiment. Six grams of the iron alloy and the Na20-SiO2 slag were reacted in an 18 mm I.D. graphite crucible at times varying from 0 to 120 minutes. The temperature was 1200 ~ and the atmosphere was flowing argon at 0.1 liter per minute. The iron alloy was prepared from electrolytic iron, graphite powder, and ferrosilicon in a graphite crucible and saturated with nitrogen at one atmosphere pressure. The initial nitrogen and silicon contents were 0.0077 and 0.1 pct, respec
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