Discussion of “thermodynamic activity of Na2O in Na2O-CaO-SiO2, Na2O-MgO-SiO2, and Na2O-CaO-SiO2-Al2O3 melts at 1400 ‡C≓

D.N. REGO, G.K. SIGWORTH, and W.O. PHILBROOK: Metall. Trans. B, 1988, vol. 19B, pp. 655-61.     

Study of Interfacial Tension between Molten Steel and Na2O-Li2O-SiO2-B2O3 Slag

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The sulfur partition ratio and the sulfide capacity of Na2O-SiO2 slags at 1200 °C

The sulfur partition ratio between carbon-saturated iron and Na₂O-SiO₂ slags and the sulfide capacity of these slags have been measured at 1200 °C. The two measurements are consistent with each other and the results are compared with other investigations. These slags have higher sulfide capacities and partition ratios than equivalent CaO-based slags and are thus attractive desulfurizers. Both the sulfide capacity and the partition ratio increase with increasing Na₂O. The activity coefficient of Na₂S has been calculated; it also increases with increasing Na₂O. The solubility of sulfur in a slag of 0.4 mole fraction Na₂O is estimated to be 5 pct.     

Density of Na2O-Li2O-SiO2-B2O3 Molten Slag at 1 803——1 873 K

The density of three kinds of molten slags was measured by modified sessile dropmethod at 1 803 1 873 K. The density of molten slag is found to decrease with increasing tem-perature. The temperature coefficients of Na2 O-Li2--SiO2 and Li2O-SiO2-B2O3 slag are smallerthan that of Na20-B2O3 slag. The molar volume of slags increases with increasing temperature.     

Dissolution of carbon dioxide in CaO-CaF2-Al2O3 based melts containing Na2O or K2O oxide

The influence of Na₂O or K₂O on the solubility of CO₂ in CaO-CaF₂-Al₂O₃ based melts is measured by a thermogravimetric technique over a temperature range of 1250–1350°C. The values of the carbonate capacities (C'_c = wt. % ) are calculated by data on the dissolution and partial pressure of carbon dioxide. The replacement of CaO by Na₂O leads to an increase of the carbonate capacity to a maximum at 3–3.5 wt. % Na₂O and then to a decrease. The addition of Na₂O or K₂O up to 2 wt. %, to CaO-CaF₂-Al₂O₃ increases the carbonate capacity at 1300°C by 30%.     

Thermodynamic study of Fe2O3-Fe2(SO4)3 equilibrium using an oxyanionic electrolyte (Na2SO4-I)

The emf of the cell, Pt, Ar + O₂ + SO₂ + SO₃/Na₂SO₄-I/Fe₂O₂ + Fe₂(SO₄)₃, Pt, has been measured in the temperature range 800 to 1000 K, using a gas mixture of known input composition as the reference electrode. The equilibrium composition of the reference gas at the measuring temperatures was computed using the thermodynamic data on the gaseous species reported in the literature. A mixture of ferric oxide and sulfate was kept in a closed system to ensure establishment of equilibrium partial pressure at the electrode. The cell was designed to avoid physical contact between Fe₂(SO₄)₃ and Na₂SO₄ electrolyte. Uncertainties arising from the formation of sulfate solid solution were thus eliminated. The Gibbs’ energy of formation of ferric sulfate calculated from the emf is discussed in comparison with data reported in the literature. There is no evidence for the formation of oxysulfates in the Fe-S-0 system. Based on the results obtained in the present study for Fe₂(SO₄)₃ and literature data for other phases, chemical potential diagrams have been constructed for the Fe-S-O system at 900 and 1100 K.     

The effect of chlorine on the kinetics of oxidation of cobalt in environments containing 0.5 atmosphere of oxygen between 900 K and 1200 K

The corrosion of cobalt metal in gas mixtures containing argon, chlorine, and 0.5 atmosphere of oxygen has been studied by measuring the kinetics of the reaction using thermogravimetric techniques and by examination of the corrosion products using scanning electron microscopy. The corrosion products include both oxides and chlorides. The formation of volatile cobalt chloride plays a critical role in the corrosion process by attacking and penetrating the condensed oxide scale. At 1200 K, the Tedmon equation describes the kinetics of the corrosion process. At lower temperatures the corrosion behavior is more complex, and under some conditions the formation of a porous, nonprotective oxide scale can lead to rapid consumption of the metal. Formerly Graduate Research Assistant     

Reoxidation of Aluminum in Fe-Al-M (M = C,Mn, and Ti) melts with CaO-Al2 O3-Fe t O (3 mass pct) slags

An Fe-0.01 to 0.5 mass pctAl alloy and an Fe-0.003 to 0.71 mass pctAl-1 mass pctM (M = C, Mn, and Ti) alloy were reoxidized with the CaO-Al₂O₃-Fe_tO (3 mass pct) slags at 1873 K in an Al2O3 or CaO crucible for 5 and 60 minutes. The contents of acid-insoluble Al, total O, and alloying element M in metal as well as those of M and FetO in slag were measured as a function of total Al content. On the basis of the present and previous results for Fe-Al-Te alloys, the effect of alloying elements on the degree of supersaturation with respect to the Al2O3 precipitation was studied. As a result, the supersaturation phenomenon was observed in all experiments at 5 minutes, but in the experiments at 60 minutes, it was observed only in Fe-Al and Fe-Al-Ti alloys. No supersaturation was observed in the reoxidation of Si in Fe-0.13 to 0.98 mass pctSi alloys with the CaO-SiO2-FetO (3 mass pct) slags in a CaO crucible at 5 and 60 minutes.     

The kinetics of S35 exchange between SO2/CO/CO2 gas mixtures and copper sulfide melts at 1523 K

The kinetics and mechanisms of oxidation of copper sulfide melts have been investigated using a radioisotope exchange technique. Copper sulfide melts were doped with S³⁵. The transfer of the radioisotope between the melt and SO₂/CO/CO₂ gas mixtures in chemical equilibrium with the melt was monitored by analyzing the changes in radioactivity of the gas. Analysis of the results indicates that the rate-limiting chemical reaction involves the formation of an activated complex SO, and the rate of exchange of the sulfur isotope at 1523 K is described by the relationshipR = 6.4(±2) (P _CO /P _CO2 )P _SO2 g atom S m⁻² s⁻¹. formerly Research Assistant, University of Queensland formerly Postdoctoral Fellow, University of Queensland     

Oxidation kinetics of niobium in the temperature range of 873 to 1083 K

Oxidation kinetics of niobium (columbium) in oxygen are investigated in the temperature range of 873 to 1083 K. The observed abnormal dependence of the linear oxidation rate on temperature is suggested to be due to the relative amount of NbO₂ in the oxide scale. The amount of oxygen dissolved in the metal is calculated and it constitutes a small fraction of the total oxygen uptake. From hardness measurements, the oxygen diffusion coefficient in Nb can be expressed as:D = 2.72 × 10⁻³ exp ( − 95.4/R T) with the activation energy in kjoule/mole.     

Nitridation kinetics of niobium in the temperature range of 873 to 1273 K

The kinetics of Nb (Cb) nitridation and ε-NbN growth obey a parabolic relationship and their temperature dependence can be expressed ask _p = 5.19 × 10⁻⁷ exp (−125,500/RT) and (k _{p ξ} = 1.15 × 10⁻⁴ exp (−61,500/RT), respectively, with the activation energies in joules/mole. The nitrogen diffusion coefficient in niobium, obtained from microhardness traverses, is given byD = 1.02 × 10⁻⁵ exp (−77,000/RT). A diffusion model accounting for the partition of nitrogen between ε-NbN and Nb is proposed. The total nitrogen uptake calculated from the model is compared to that obtained experimentally.     

Identification of ions present in LiF-DyF3 melts and the mechanism of Dy2O3 dissolution therein

Herein, the present paper were attempted to identify ions in LiF-DyF_3 melts according to the law of decreasing primary crystallization temperature and model analysis. Specifically.the primary crystallization temperatures of LiF-DyF_3 and LiF-DyF_3-Dy_2O_3 melts with various DyF_3 and Dy_2O_3 contents were determined by differential scanning calorimetry(DSC), and reactions occurring in the above melts were investigated using ideal dilute solution(Temkin and Flood) models. Moreover, crystal phases produced by rapid solidification of LiF-DyF_3, LiF-Dy_2O_3, DyF_3-Dy_2O_3, and LiF-DyF_3-Dy_2O_3 melts were identified by X-ray diffraction(XRD) analysis. The primary crystallization temperature of LiF-DyF_3 melts exhibits an approximately linear decrease with increasing molar fraction of DyF_3, and the general formula of complex ions in these melts is expressed as DyF_x~((3-x)),e.g., DyF_4~-. Finally, we investigated the dissolution of Dy_2O_3 in LiF-DyF_3 melts, showing that it was chemical in nature and afforded Dy_(1+x)O_(3x)F_(3-3x) and DyOF.     

Thermodynamic properties of the V2O3−V4O7 system at temperatures from 1400° to 1700°K

Phase equilibria in the V₂O₃−V₄O₇ system were studied at 1400°, 1500°, 1600°, and 1700°K by varying the oxygen partial pressure. Besides the three phases of V₂O₃, V₃O₅, and V₄O₇ which were stable in this system, the vanadium sesquioxide has an extensive range of solid solution at the above mentioned temperatures. The standard free energies of oxidation of both V₂O₃ to V₃O₅ and V₃O₅ to V₄O₇ were precisely determined on the basis of equilibrium oxygen partial pressures at each above temperature. The standard enthalpy and the entropy changes of these reactions were also calculated from the free energy data.     

Solubilities of Pb+2, Bi+3, Sb+3, and Cu+1 sulfides in (NaCl+KCl+Na2S) melts

Solubilities of common metal sulfides have been determined in the (NaCl+KCl) eutectic melt with and without Na₂S. A novel gas-phase equilibrium technique has been used for PbS, Bi₂S₃, and So₂S₃, and an improved liquid phase equilibrium technique for Cu₂S, which eliminates the errors due to physical entrapment of the sulfide phase and segregation on quenching, enabling precise measurements to be made. Solubilities in the (NaCl+KCl) eutectic melt were determined as a function of temperature in the rante 700° to 950°C, and were found to be small. The partial molar heats of mixing of the sulfides in the eutectic melt have been calculated from the solubility measurements, to be 13.3, 31.4, 37.1, and 49.0 kcal for PbSs), Sb₂S₂(l), and Cu₂S(s), respectively. Sodium sulfide addition was observed to enhance these solubilities, the effect being largest for Cu₂S followed by Sb₂S₃, Bi₂S₃, and PbS. This effect is explained qualitatively. It was observed that PbS and Sb₂S₃ obey Henry's law up to saturation in (NaCl+KCl+Na₂S) melts. O. P. MOHAPATRA, formerly Graduate Student, University of Toronto