Steady-state studies of the reactions of H 2 O-CO and CO 2 -H 2 mixtures with liquid iron
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I.
INTRODUCTION
THE interfacial rate constants for the decarburization of carbon-saturated liquid iron alloys by CO2 were first reasonably well established by the work of Sain and Belton[1,2] who used jets of CO2-containing gas mixtures impinging onto the surfaces of inductively stirred iron-carbon alloys, maintained near to carbon saturation by means of highpurity graphite discs cemented inside the reaction crucibles. Reaction rates were determined from the weight losses of the crucibles and contents. Mannion and Fruehan[3] used a similar technique but determined the rates from the rates of production of CO, measured by continuous mass-spectrometric analysis of the reacted gas stream. As has been discussed elsewhere,[4] all the data are consistent with the first-order rate constants, k1, in units of mol cm22 s21 atm21, being given by the expression log k1 5 2 5080/T 2 0.21
[1]
for very pure iron. The profound effect of sulfur in depressing the rate is closely described by the expression ka,1 5
k1 (1 1 0.014KS aS) 1 1 KS a S
[2]
where ka,1 is the apparent first-order rate constant and KS is the adsorption coefficient[5] (apparent Langmuir isotherm constant) of sulfur with respect to the activity of sulfur, aS, with a standard state of 1 wt pct S in carbon-saturated iron. Values of KS were deduced to be given by log KS 5 3600/T 1 0.57
[3]
over the temperature range of the kinetic studies, 1280 7C to 1600 7C. Cramb and Belton[6] used the 14CO2-CO isotope exchange technique to determine the rates of dissociation of CO2 on
liquid iron and showed that the first-order rate constants for essentially sulfur- and oxygen-free iron were closely consistent with those from the decarburization studies, i.e., given by Eq. [1] for temperatures of 1550 7C to 1700 7C. The influence of dissolved oxygen was found to be closely described by the ideal surface blockage expression: ka,1 5
k1 1 1 KOaO
where KO is the adsorption coefficient of oxygen and aO is the activity of oxygen. Values of KO, with respect to a standard state for oxygen of the 1 wt pct ideal solution, were deduced to be given by log KO 5 11,370/T 2 4.09
METALLURGICAL AND MATERIALS TRANSACTIONS B
[5]
Rates of decarburization of liquid iron by H2O were first studied by Shinego et al.[7] under conditions where gaseous phase mass-transfer limitations were significant. Sasaki and Belton[8] applied approximate mass-transfer corrections and deduced that the apparent first-order rate constants for the interfacial reaction were from about 9 to about 5 times those for the CO2 reaction over the temperature range 1300 7C to 1500 7C at given sulfur concentrations. Fruehan et al.[9] have measured the rates of reaction of H2O with continuously carbon-saturated iron under conditions where gaseous phase mass transfer limitations were either negligible or where small corrections could be made. They confirmed that the reaction was first order with respect to the pressure of H2O and deduced that the ratio of the apparent rate constants for H2O and CO2, at given sulfur concen
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