KINETICS OF OXIDATION OF CARBON IN LIQUID IRON-CARBON-SILICON-MANGANESE-SULFUR ALLOYS BY CARBON-DIOXIDE IN NITROGEN

The oxidation of carbon with the simultaneous oxidation of silicon, ma nganese, and iron of liquid alloys by carbon dioxide in nitrogen and t he absorption of oxygen by the alloys from the gas were studied using 1-g liquid iron droplets levitated in a stream of the gas at 1575 degr ees C to 1715 degrees C. Oxidation of carbon was favored over oxidatio n of silicon and manganese when cast iron (3.35 pct C, 2.0 pct Si, 0.3 6 pct Mn, and 0.05 pct S) reacted with CO2/N-2 gas at 1635 degrees C. An increase in the flow rate of CO2/N-2 gas increased the decarburizat ion rate of cast iron. The rate of carbon oxidation by this gas mixtur e was found to be independent of temperature and alloying element conc entrations (in the range of silicon = 0 to 2.0 pct manganese = 0 to 0. 36 pct and sulfur = 0 to 0.5 pct) within the temperature range of the present study. Based on the results of a kinetic analysis, diffusion o f CO2 in the boundary layer of the gas phase was found to be the rate- limiting step for the reactions during the earlier period of the react ion when the contents of carbon, silicon, and manganese are higher. Ho wever, the limiting step changed to diffusion of the elements in the m etal phase during the middle period of the reaction and then to the di ffusion of CO in the gas phase during the later period of the reaction when the content of the elements in the metal were relatively low. Fo r the simultaneous oxidation reactions of several elements in the meta l, however, the diffusion of CO2 in the gas phase is the primary limit ing step of the reaction rate for the oxidation of carbon during the l ater period of reaction.