G. R. Belton

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 kf = -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.

Langmuir Adsorption, the Gibbs Adsorption Isotherm, and Interfacial Kinetics in Liquid Metal Systems

The adsorption of strongly surface active solutes is considered in terms of the ideal site-fillage or Langmuir isotherm. The resulting equation for the depression of surface tension of a liquid metal by such a solute isσP- σ = RTΓio ln (1 +Kai where σP- σ is the depression of surface tension of the pure liquid metal, Γio is the satura-tion coverage by the solute, ai is the bulk activity of the solute, andK is a coverage inde-pendent adsorption coefficient. The isotherm is found to give a very good description of the available data for Group VI solutes on several metals. The derived values of the adsorp-tion coefficient are applied to several kinetic studies and they are found to give good rela-tive and possibly absolute measures of the interference by such solutes on interfacial re-action rates. The iron-sulfur system appears to differ, but only by a factor of two. The application of these adsorption coefficients in aiding the interpretation of kinetic studies is considered.

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 determination of activities by mass-spectrometry—some additional methods

Further consideration is given to the determination of the thermodynamic properties of metallurgical solutions by mass-spectrometric analysis of the equilibrium vapor effusing from a Knudsen cell. Equations are presented which permit the application of the integration of ion-current ratios to complex species, thus avoiding problems caused by fragmentation ionization. The method is applied to a limited study of the Bi-Te system at 750°C. Ternary systems are considered and the method for the determination of the properties from measurements of a pair of ion-currents is demonstrated. Equations are also derived for the treatment of a ternary system which is saturated with respect to an involatile component. Finally, a method is presented for correcting the monomer-dimer ratio technique of Berkowitz and Chupka for fragmentation ionization effects.

The thermodynamics of volatilization of chromic oxide: Part I. the species CrO3 and CrO2 OH

A study has been made, using the transpiration technique, of the volatility of chromic oxide in oxygen-argon and oxygen-water vapor-argon mixtures in the approximate temperature range 1300 to 1585° . Volatilization is shown to occur by the reactions r2O3(s) + 3/2O2(g) =3(g) and Cr2O3(s) + O2(g) + H2O(g) = 2CrO2OH(g). The standard Gibbs free energy changes are given byAG0 = 472,800 (±6200) - 118.5 (±3.6) andAG0 = 428,200 (±9400) — 119.4 (±5.6)TJ, respectively, where the reference state for the gases is one standard atmosphere.

The Interfacial Kinetics of the Reaction of CO2 with Nickel. Part I: The 14CO2-CO Exchange Reaction and the Influence of Sulfur

The rate of dissociation of CO2 on nickel has been studied by means of the 14CO2-CO exchange reaction. For pure polycrystalline nickel between 500 and 1240°C the forward rate constant, in mole cm−2 s−1 atm−1, is given by:

Thermodynamic properties of Mg−Ge alloys

\ln k_f = - 7300/T - 2.57.

Thermodynamics of mixing in molten sodium-potassium silicates at 1100°C: The effect of a calcium oxide addition

This is shown to be closely consistent with ideal chemisorption kinetics. Lower apparent rate constants when Ni3S2 is added to the surface or at bulk saturation with sulfur are consistent with a surface blockage mechanism by chemisorbed sulfur which shows a Langmuir adsorption isotherm. The adsorption coefficient of sulfur, in at. pet−1, is deduced to be given by the equation: