The interfacial kinetics of the reaction of CO2 with liquid nickel

Measurements of the rate of dissociation of CO2 on liquid nickel have been made by the¹⁴CO2-CO isotope exchange technique between 1490 and 1670 °C at CO2/CO ratios between 0.01 and 7. Apparent first order rate constants are given by the expression:ka = (1 + 2pCO₂/pCO)⁻¹exp(−12700/T - 0.65) mol cm⁻² s⁻¹ atm⁻¹. It is shown that the results are consistent with blockage of the surface by oxygen which exhibits ideal Langmuirian adsorption over the conditions of the experiments. The adsorption coefficient of oxygen with respect to the infinitely dilute solution with 1 wt pct as the standard state is deduced to be given by the equation: logK′_o = 11880/T - 4.6. It is deduced that the interfacial rate of oxidation of nickel by CO₂ is given by the rate of dissociative chemisorption of CO₂. Measurements of the rate of decarburization of liquid nickel are reexamined in the light of the present results.     

The influence of sulfur on interfacial reaction kinetics in the decarburization of liquid iron by carbon dioxide

The kinetics of decarburization of continuously carbon-saturated liquid iron by CO₂ have been studied between 1280 and 1600?C at sulfur concentrations between 0.01 and 1 wt pct. The results are consistent with a surface blockage mechanism by chemisorbed sulfur which shows an essentially ideal adsorption isotherm. The adsorption coefficient of sulfur, in (wt pct)^-1, is given by the equation logK = 3600/T + 0.57 for carbon-saturated alloys. A small residual rate at apparent surface saturation is observed. This leaves about 1.4 pct of the active surface sites available for reaction, essentially independent of temperature. Studies with varying carbon concentration suggest that to a first approximation, and above about 3 wt pct C, the adsorption equilibrium for sulfur depends only on the thermodynamic activity of sulfur.     

The influence of sulfur on interfacial reaction kinetics in the decarburization of liquid iron by carbon dioxide

The kinetics of decarburization of continuously carbon-saturated liquid iron by CO₂ have been studied between 1280 and 1600‡C at sulfur concentrations between 0.01 and 1 wt pct. The results are consistent with a surface blockage mechanism by chemisorbed sulfur which shows an essentially ideal adsorption isotherm. The adsorption coefficient of sulfur, in (wt pct)^-1, is given by the equation logK = 3600/T + 0.57 for carbon-saturated alloys. A small residual rate at apparent surface saturation is observed. This leaves about 1.4 pct of the active surface sites available for reaction, essentially independent of temperature. Studies with varying carbon concentration suggest that to a first approximation, and above about 3 wt pct C, the adsorption equilibrium for sulfur depends only on the thermodynamic activity of sulfur. DR. SAIN was formerly a Graduate Student.     

Studies of the interfacial kinetics of the reaction of CO2 with liquid iron by the14CO2-CO isotope exchange reaction

The rate of dissociation of CO₂ on liquid iron between about 1540 and 1740 °C and at CO/CO₂ ratios of 6.7 to 100 has been studied by means of the¹⁴CO₂-CO exchange reaction. It is shown that for essentially pure iron the rate constant at low oxygen potential is consistent with that for the decarburization of liquid iron by CO₂, indicating a common rate determining step. The influence of the gas composition on the rate is found to be consistent with surface blockage by adsorbed oxygen which obeys an ideal Langmuir adsorption isotherm over the experimentally accessible conditions. The adsorption coefficient for oxygen with respect to the infinitely dilute solution with 1 wt pct as standard state is deduced to be given by: logK′_o = 11270/T – 4.09 The value of K′_o at 1550 °C is found to be in good accord with the available data for the depression of the surface tension of liquid iron by oxygen. A. W. Cramb, Formerly with the Department of Materials Science and Engineering, University of Pennsylvania     

CO2 conversion and decarburization kinetics of CO2 gas and liquid Fe-C alloy at 1873 K

The reactions between CO2 gas and liquid Fe-C alloy with different initial carbon concentrations at 1873 K were investigated using experimental results,thermody...     

Interfacial reaction kinetics in the decarburization of liquid iron by carbon dioxide

The kinetics of decarburization of liquid iron have been studied between 1160 and 1600°C under conditions where mass transport of reactants is not rate determining. Studies with continuously carbon-saturated iron and of iron with varying carbon concentration have been used to show that the slow step at high concentrations of carbon is independent of carbon concentration and is first order with respect to the pressure of CO₂. For high purity iron, the forward rate constant, in mole cm² s^-1 atm^-1, is given by the equation ln k_f = -11,700/T-0.48. It is concluded that the data are consistent with the chemisorption process as the rate limiting step. A marked sensitivity of the rate to trace amounts of sulfur has been found and it is shown that this is consistent with ideal adsorption of sulfur and is in fair accord with the existing measurements of the depression of the surface tension of iron-carbon alloys by sulfur. D. R. Sain was formerly a Graduate Student.     

The effect of surfactants on the interfacial rates of reaction of CO2 and CO with liquid iron oxide

The ¹⁴CO₂-CO isotope exchange technique has been used to measure the rates of dissociation of CO₂ on liquid iron oxide containing the surface active components P₂O₅ or Na₂O, principally at 1673 K. The apparent first-order rate constant is found to decrease monotonically with small additions of P₂O₅ up to a factor of about 4 at 3.5 mol pct. Vaporization losses prevented detailed studies of the effect of Na₂O, but it is shown that there is probably a twofold increase in the rate constant at a concentration of about 0.2 wt pct and a fivefold increase at a concentration between 0.5 and 1.6 wt pct. A smoothed surface potential model, based upon the Vol’kenshtein model for catalysis by semiconductors, is developed, and it is shown that the required surface potential changes due to the segregation of P₂O₅ and Na₂O are physically reasonable.     

The rate of decarburization of liquid iron by CO2 and H2

The rate of decarburization of liquid iron in CO-CO₂ mixtures and hydrogen at 1800 K has been investigated. The effect of sulfur on the rate in CO-CO₂ was also determined. Two experimental techniques were employed, one with the gas flow parallel to the surface of the melt, the other with gas flow perpendicular to it. The rate of decarburization in both CO-CO₂ mixtures and hydrogen at high carbon contents is controlled primarily by diffusionsion in the gas film boundary layer near the surface of the liquid. The presence of 0.3 wt pct sulfur reduced the rate of decarburization in CO-CO₂ by about 10 pct indicating that a slow chemical reaction on the surface is effecting the rate slightly when the surface is covered with sulfur atoms. The rate of decarburization at low carbon contents in CO-CO₂ is controlled primarily by carbon diffusion in the metal. The mass transfer relationships for the experimental geometries employed were investigated by measuring the rate of oxidation of graphite in CO-CO₂ mixtures. Previous work in which it was concluded that a chemical reaction was controlling the rate were re-examined and it was concluded that gas phase mass transfer was in fact controlling the rate of the reaction.     

Oxidation kinetics of zinc vapor in CO:CO2 mixtures: Part II. Application of plug flow concepts

In the first of two articles on the subject, it was shown that the oxidation kinetics of Zn vapor in CO:CO₂ mixtures cannot be understood on the basis of previously proposed rate expressions. In this second article, an alternative interpretation, which appears capable of reconciling the apparent discrepancies of the past literature, is proposed. Evidence is provided to the effect that competing reactions occur in the system Zn−CO−CO₂ under the majority of conditions investigated. Analysis on the basis of a simple “plug flow” model reveals that oxidation by CO₂ can take place indirectly by a combination of the reactions Zn_(g)+CO_(g)→ZnO_(s)+C_(s) and C_(s)+CO_2(g)→2CO_(g) Zinc is also oxidized by direct reaction with both CO and CO₂. It is proposed that the distinctive morphologies observed (coarse, intermediate, and fine) can be related to the degree of direct and/or indirect oxidation occurring in the system.     

Rate of decarburization of iron-carbon melts: Part II. a mixed-control model

The observed retarding effect of sulfur on the decarburization of Fe-C melts has been interpreted by means of a mixed-control mechanism involving gas-phase mass transfer and dissociative adsorption of CO₂. A mathematical model formulated on the basis of the proposed mechanism gave an excellent fit to the experimental data. The application of the model to the data provided a value of 4.42 x 10⁻³ mole · cm⁻² · s⁻¹ · atm⁻¹ for the dissociative adsorption rate constant for CO₂ on liquid iron at 1973 K; the fraction of surface sites that cannot be occupied by sulfur, even at apparent surface-saturation, was found to be 0.085. The model predicts a residual rate of decarburization at high sulfur concentrations; this prediction is borne out by the experiment. The effect of convective motion within the levitated melt on the rate of decarburization below a characteristic carbon concentration was quantified. The liquid-phase mass transfer was greatly enhanced by the stirring effect of the electromagnetic field. The effective diffusivity of carbon in Fe-C melts under levitation conditions has been found to be 3.24 x 10⁻³ cm² · s⁻¹, a value ten times as large as that under stationary conditions.     

Oxidation kinetics of zinc vapor in CO∶CO2 mixtures: Part I. Comparison with past literature

The methods employed and the results obtained during a recent investigation of the oxidation of gaseous zinc by CO∶CO₂ mixtures are described. The kinetic data are tested against the predictive models derived and employed by previous investigators of this reaction. Although the experimentally determined reaction rates are highly reproducible, no consistent agreement can be found with the models presented in the prior literature. Efforts to account for the kinetics on the basis of the oxygen potential of the gas mixture are also unsuccessful. It is concluded that previous attempts to understand the kinetics in terms of the reaction Zn _(g) +CO _2(g) ⇒ZnO _(s) +CO _(g) are oversimplistic. A novel interpretation which appears to resolve the discrepancies of the literature is detailed in the second of two articles on the subject.     

Oxidation of cobaltite: Part II. kinetics

A kinetics study has been performed on cobaltite to understand the oxidation processes over a temperature range of 573 to 1173 K using a thermogravimetric method. The results show that oxidation of cobaltite occurs in two stages. In the first stage, which occurs between 823 and 913 K, the majority of the sulfur is removed. However, the arsenic remains in the lattice of the reacted region. A pore-blocking kinetic model yields a satisfactory fit to these experimental data. At higher temperatures, there is a concurrent release of As and S from the crystal lattice of CoAsS. The shrinking-core kinetic model is applicable. Complementary X-ray diffraction and scanning electron microscopic analyses on these partially oxidized samples support the kinetic models. The effects of partial pressure of oxygen and particle size on roasting have been evaluated.     

The kinetics of the nitrogen reaction with liquid iron-Sulfur alloys

An experimental apparatus was designed and constructed which permits utilization of both the modified Sieverts' technique and the isotope exchange technique for study of the kinetics of ni-trogen reaction with liquid iron alloys. Experimental results from the two techniques are used in con-junction with the current knowledge in the field to readdress several persisting questions dealing with the nitrogen reaction. Results from this study have confirmed that N₂ dissociation is the rate lim-iting step in the intrinsic chemical reaction mechanism of nitrogen absorption. In addition, the ex-istence of a residual nitrogen absorption rate at high sulfur concentrations has been reaffirmed and possible reasons for the phenomenon are discussed. Lastly, results of an investigation into the in-fluence of carbon on the nitrogen reaction rate in liquid Fe-C-S alloys indicate that carbon has a negligible effect on the rate. Formerly with the Department of Metallurgical Engineer-ing and Materials Science, Carnegie-Mellon University, Pittsburgh, PA     

The kinetics of the nitrogen reaction with liquid iron-chromium alloys

The isotope exchange technique was employed to study the interfacial reaction kinetics of nitrogen with liquid iron-chromium and iron-chromium-sulfur solutions. Chromium was found to increase the rate of the nitrogen exchange reaction. The increase in the rate occurs, at least in part, through promotion of N₂ dissociation on the chromium surface sites. Although mass transport effects in the liquid are eliminated through the use of the isotope exchange technique, it was found that a correction for gas phase mass transfer was required for the determination of the interfacial reaction rate constant due to the faster exchange rates encountered in liquid iron solutions containing chromium. Formerly with the Department of Metallurgical Engineering and Materials Science, Carnegie-Mellon University, Pittsburgh, PA     

Studies of the interfacial kinetics of the reaction of nitrogen with liquid iron by the15N-14N isotope exchange reaction

The rate of dissociation of N₂ on high purity liquid iron and iron-sulfur alloys between 1550 and 1650 °C has been studied by means of the¹⁵N-¹⁴N exchange reaction. It is shown that the rate constants at given sulfur concentrations are consistent with those for the absorption of nitrogen into iron-sulfur alloys, indicating a common rate determining step. The rate constant for high purity liquid iron, in units of mol cm^?2 s^?1 aim^?1, is given by: logk _f = ?340/T ? 1.38. The rate constant is found to be independent of carbon concentration up to about 4.3 wt pct and to be closely consistent with ideal chemisorption kinetics. The results are combined with those of previously published studies to give rational equations for the apparent rate constants for Fe-S and Fe-O alloys. Consistent values for the adsorption coefficients at 1600 °C for sulfur and oxygen are deduced to be about 130 and 220, respectively, for a standard state of the 1 wt pct ideal solution.     

CO/CO2气氛下Fe-C合金气固反应脱碳

 为研究Ar-CO-CO₂气氛下Fe-C合金薄带的脱碳效果,通过热力学分析结合试验,确定脱碳气氛条件混合气体流量为850 mL/min,CO的体积分数为25%,PCO₂/(PCO+PCO₂)为0.26。以初始碳质量分数为4.2%左右的Fe-C合金薄带为研究对象,探索不同脱碳温度、薄带厚度、脱碳时间对脱碳效果的影响。研究结果表明,对厚度为2 mm的Fe-C合金薄带,脱碳温度分别为1 293、1 353、1 413 K,脱碳60 min后,平均碳质量分数分别为2.748%、1.870%、1.134%。厚度分别为1、1.5、2 mm的Fe-C合金薄带,脱碳温度为1 413 K,脱碳时间为60 min,对应的碳质量分数分别为0.32%、0.92%、1.05%。证明提高脱碳温度、延长脱碳时间、减少薄带厚度均有助于提高脱碳效果。     

Hydrogen transport during deformation in nickel: Part II. Single crystal nickel

Direct evidence for dislocation transport of hydrogen was observed in nickel single crystal slices using the electrochemical permeation technique modified to allow for simultaneous deformation. The hydrogen flux increased in the easy glide region of deformation even after accounting for the effects of a decrease in specimen thickness. At a fast strain rate the only explanation for this increase is dislocation transport. Formerly Graduate Student, The H. H. Uhlig Corrosion Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139.