INFLUENCE OF CHROMIUM AND NICKEL ON THE DISSOCIATION OF CO2 ON CARBON-SATURATED LIQUID-IRON

At 1600 degrees C, under conditions where the rate was not significant ly affected by liquid-phase or gasphase mass transfer, the rate of dis sociation of CO2 was determined from the rate of decarburization of ir on-based carbon-saturated melts containing varying amounts of chromium and nickel, The rate was determined by monitoring the change in react ed gas composition with an in-line spectrometer. The results indicate that neither chromium nor nickel had a strong effect on the kinetics o f dissociation of CO2 on the surface of the melt. Sulfur was found to significantly decrease the rate, as is the case for alloys without chr omium or nickel, and the rate constant is given by k = k(0)/1+K(s)a(s) + k(r) where k(0) denotes the chemical rate on pure iron, K-s is the adsorption coefficient of sulfur, a(s) is the activity of sulfur corre cted for Cr, and k(r) represents the residual rate at a high sulfur le vel, The rate constants and adsorption coefficient were determined to be: k(0) = 1.8 X 10(-3) mol/cm(2) s atm k(r) = 6.1 X 10(-5) mol/cm(2) s atm K-s = 330 +/- 20 Experiments run at lower carbon contents showed that only a very small quantity of chromium was oxidized, immediately forming a protective layer. However, this oxidation occurred at a hig her carbon content (2 pct) than what was expected from the thermodynam ics.