R. J. Fruehan

The rate of reduction of iron oxides by carbon

The rate of reduction of Fe2O3 and FeO by coconut charcoal, coal char and coke, in an inert atmosphere within the temperature range 900 to 1200°C was investigated. The effects of pressure, particle size, and the amount of carbon were determined. The results indicate that the reaction takes place by means of the gaseous intermediates CO and CO2, and that the overall rate is controlled by the oxidation of the carbon by CO2. The rates of reduction of FeO and Fe2O3 by CO are relatively fast, and the CO2/CO ratio for the oxidation of carbon is determined by their equilibria. The reduction of Fe2O3 by carbon is accomplished in two stages, with FeO forming first. The reduction of Fe2O3 to FeO is faster than that of FeO to Fe because its CO2/CO equilibrium ratio is higher and hence the rate of oxidation of carbon is faster. A direct comparison was made between the rate constants for the reduction of FeO by carbon and those for the oxidation of carbon in the appropriate CO2-CO gas mixtures, and they are in good agreement. Apparently the iron formed by the reduction does not significantly catalyze the oxidation of carbon; whereas for the reduction of NiO by carbon, the Ni formed does catalyze the oxidation of carbon.

Activities in liquid Fe-V-O and Fe-B-O alloys

The activities in liquid Fe-V-0 and Fe-B-O alloys have been determined using the following galvanic cells Cr-Cr2O3(s) | ZrO2(CaO) | Fe-V-O (l, saturated with oxide) Cr-Cr2O3(s) | ThO2(Y2O3) | Fe-V-O (l, saturated with oxide) Cr-Cr2O3(s) | ZrO2(CaO) | Fe-B-O (l, B2O3 saturated with Al2O3) The solubility of oxygen in Fe-V alloys at 1600°C decreases with increasing vanadium content to a minimum of about 180 ppm at 3 wt pct V, and then increases to over 4000 ppm at 36.3 wt pct V. Vanadium was found to decrease the activity coefficient of oxygen and the value of the interaction coefficient eoV at infinite dilution of vanadium is -0.14. The activity of vanadium was calculated from the measured electromotive force, and log γv was found to be represented well by the quadratic formalism for Nv < 0.4: log γV = -0.70N2Fe -0.30 At 1550°C boron decreases the solubility of oxygen down to about 80 ppm at 0.67 wt pct B in Fe-B melts in equilibrium with B2O3 saturated with A12O3 (NAl2 O3 = 0.087). The boron deoxidation product, ’K′ = (wt pct B)2(wt pct 0)3 at infinite dilution of boron is 4.4 × 10-9 and 1.5 × 10-8 at 1550° and 1600°C, respectively. Boron decreases the activity coefficient of oxygen in liquid iron, and the value of the interaction coefficient eoB is -2.6 at infinite dilution of boron. The activity coefficient of boron at infinite dilution (γ°B) is 0.083 at 1550°C relative to solid boron.

The rate of absorption of nitrogen into liquid iron containing oxygen and sulfur

The rate of nitrogen absorption into and desorption from liquid iron containing sulfur and/or oxygen was measured by employing a constant-volume technique with a highly sensitive pressure transducer. Critical evaluation of the results demonstrated conclusively that the chemical rate at high oxygen or sulfur contents is second order with respect to nitrogen content in the metal and probably controlled by the dissociation of the nitrogen molecule on the surface. The effect of sulfur on the rate is complex because of the influence of 1) liquid-phase mass transfer at low sulfur contents, 2) the chemical rate on vacant iron sites at intermediate sulfur contents, and 3) the rate on the adsorbed sulfur layer or the limiting rate at high sulfur contents. However, at intermediate concentrations the limiting case for the adsorption isotherm for sulfur is adhered to and the rate is inversely proportional to the sulfur concentration. For Fe-O melts the rate is inversely proportional to the oxygen content except at low oxygen levels where mass transfer affects the rate. The rate for Fe-S-O melts can be calculated reasonably well from the results for the Fe-S and Fe-0 alloys, assuming that oxygen does not effect the adsorption of sulfur andvice versa and that there is nearly complete coverage of the surface with oxygen and sulfur atoms.

The rate of chlorination of metals and oxides: Part I. Fe, Ni, and Sn in chlorine

The rates of chlorination of Fe (528 to 921 K), Ni (890 to 1249 K), and Sn (340 to 396 K) in Cl2-He andCl2-Ar mixtures were measured. In the temperature range of the respective investigations the overall reaction products are gaseous: (FeCl3)2, NiCl2, and SnCl4. Transport through the gas film boundary layer at the surface of the sample plays a major role in controlling the rate of the reactions over large temperature ranges for all three metals. In the high-temperature range for iron (> 680 K) and nickel (> 993 K) as well as for the entire temperature range studied for tin, the transport of Cl22(g) through the gas film boundary layer to the surface of the sample controlled the rates for the experimental conditions in the present work. The transport of NiCl2(g) controlled the rate of the Ni-Cl2 reaction at lower temperatures. The rate of the Fe-Cl2 reaction at lower temperatures is controlled by a slow surface reaction between Cl2(g) and FeCl2(s) which covers the surface of the iron. The overall activation energy for the formation of the activated complex (FeCl3)2‡ is 23 kcal/g-atom Fe.

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 Effect of Zirconium, Cerium, and Lanthanum on the Solubility of Oxygen in Liquid Iron

The effect of zirconium, cerium, and lanthanum up to about 1 wt pet on the solubility of oxygen in liquid iron in equilibrium with an oxide phase at 1680°C was measured. All three elements are strong deoxidizers of iron, and the oxygen solubility minimums were 10 ppm or less at 0.05 to 0.1 wt pet of the alloying element. The interaction coefficients were estimated from the results giving eozr = −3, eoCe = −3, and eoLa = −5. When the concentration of the alloying element is expressed in wt pet, the effect of each of the three elements (Zr, Ce, and La) on the activity and solubility of oxygen in liquid iron is similar to that of aluminum.

The free energy of formation of Ce2O2S and the nonstoichiometry of cerium oxides

The free energy of formation of Ce2O2S was determined by equilibrating CeO2with COCO2-SO2 gas mixtures in the temperature range 900 to 1400°C. There was no significant sulfur solubility in cerium oxide and the free energy of formation of Ce2O2S was considerably less than previously estimated; it is 12 kcal (50 kJ) lower at 1300°C The oxygen dissociation pressures for the nonstoichiometric cerium oxide was also measured by equilibrating CeO2 with CO-CO2 gas mixtures in the temperature range 1000 to 1450°C and oxygen pressures from 10-6 to 10-18 atm. The results indicate a very large range of nonstoichiometry from CeO2 to at least CeO1.72. The new thermodynamic information was used to estimate the phase equilibria for the Fe-Ce-S-O system. The calculations indicate that for a steel with normal sulfur levels treated with aluminum and rare earth deoxidizers very little Ce2O3will form but rather Ce2O2S or cerium Sulfides. Also the stability range of Ce2O2S is smaller than previously believed.

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.

The rate of chlorination of metals and oxide: part II. iron and nickel in HCL(g)

The rates of chlorination of iron (810 to 1175 K) and nickel (850 to 1340 K) in HC1 (g) have been measured. For all conditions in this work the rates are controlled by transport through the gas film boundary layer at the surface of the sample. At low temperatures and high pressures of HC1 the condensed chlorides form, FeCl2 (s or l) and NiCl2(s), and the steady state weight loss is controlled by diffusion of metal chlorides through the gasfilm boundary layer; the temperature dependence of the rates is essentially the same as for the vapor pressure of the chlorides: 37 kcal for iron and 53 kcal for nickel. At high temperatures the condensed chlorides do not form and the rates are controlled by the countercurrent diffusion of HC1 and the gaseous chlorides through the boundary layer for both metals.

The rate of carburization of iron in CO-H2 atmospheres: Part I. Effect of temperature and CO and H2-pressures

The rates of carburization of iron strips in CO-He and CO-H2 atmospheres at 1188 and 1273 K have been investigated. The rates in CO-He and the initial rates in CO-H2 mixtures are controlled by a slow chemical reaction on the surface of iron. The rate controlling reaction in CO-He atmospheres is interpreted to be the formation of the activated complex (CO)‡2 and the results indicate that CO and carbon are adsorbed on solid iron and affect the rates. The rate of carburization in CO-H2 is significantly faster than in CO-He mixtures and the maximum rate occurs at the equimolar composition. The rate controlling reaction for the CO-H2 reaction is the formation of (H2CO)° and the rate constant is about a factor of five greater than that for carburization in CO alone.