Activities of FexO in CaO + CaF2 + SiO2 + FexO quaternary slags by disposable electrochemical oxygen probes

The activities of Fe_xO in CaO + CaF₂ + SiO₂ + Fe_xO quaternary slags were measured by means of solid-oxide galvanic cell. The Fe_xO activities in the slags are influenced by CaF₂ as well as SiO₂. At constant Fe_xO mole fractions, e.g., , at low SiO₂ mole fractions i.e., , the substitution of CaF₂ for CaO has an effect of raising the Fe_xO activity. At higher SiO₂ mole fractions, e.g., , however, such an effect becomes insignificant.     

A thermodynamic study of SrO + SrCI2 + FexO fluxes by means of solid-oxide galvanic cell

Electrochemical measurements of the solid-oxide galvanic cell, Mo / Mo + MoO₂ // ZrO₂(MgO) // Fe + (SrO + SrCI₂ + Fe_xO) / Ag / Fe, have been made at temperatures of 1473 and 1623 K in order to obtain the activities of Fe_xO in SrO + SrCI₂ + Fe_xO fluxes. The Fe_xO activities showed a significant dependence upon the molar ratio of SrO/SrCI₂; within homogeneous liquid region the substitution of SrCI₂ for SrO has an effect of raising the Fe_xO activities. From these activity data, the phase diagrams of the system SrO + SrCI₂ + Fe_xO have been drawn at 1473 and 1623 K. The temperature dependence of the activity coefficient of Fe_xO at a fixed SrO/SrCI₂ molar ratio can be expressed by the formula R T In constant.     

A thermodynamic study of the system CaO + Al2O3 + FexO at 1673 K

Electrochemical measurements of the solid-oxide galvanic cell: Mo/Mo + MoO₂/ZrO₂(MgO)/(CaO + Al₂O₃ + Fe_xO) + Fe(s) + Ag/Fe have been conducted at 1673 K in order to obtain the activities of Fe_xO) in CaO + Al₂O₃ + Fe_xO slags. By using the activity data for Fe_xO, the isothermal section of the phase diagram for the system CaO + Al₂O₃ + Fe_xO was derived.     

A thermodynamic study of silica-saturated iron silicate slags in equilibrium with liquid copper

The thermodynamic properties of silica-saturated iron silicate slags in equilibrium with liquid copper have been studied from oxygen partial pressure measurements in the temperature range from 1490 to 1580 K by means of a solid electrolyte galvanic cell. The following cells were used: Pt, Ni-NiO/O⁼/slag-Cu(l), Cr₂O₃, Pt; Pt, Fe-FeO/O⁼/slag-Cu(Fe sat.), Fe. A strong correlation was found between oxygen pressure and the copper content of the slag; the copper content increased from less than 1 pct near iron saturation to about 4 pct at an oxygen partial pressure of 7.2 x 10^?3 Pa. A similar correlation was found between the ferric iron/total iron ratio and the oxygen pressure. The oxygen content in liquid copper decreased with increasing iron content in liquid copper and increased slightly near iron saturation. This behavior could be explained qualitatively by using the standard free energy of formation of FeO and the activities of components.     

A thermodynamic study of the system FexO + AI2O3 + SiO2 at 1673 K

Electrochemical measurements of the solid-oxide galvanic cell Mo/Mo + MoO₂/ZrO₂(MgO)/Fe + (Fe_xO + A1₂O₃ + SiO₂)_slag/Ag/Fe have been made at 1673 K in order to obtain the activities of Fe_xO in Fe_xO + A1₂O₃ + SiO₂ slags. Activities of A1₂O₃ and SiO₂ were also determined by virtue of Gibbs-Duhem integration. By using the activity data, the free energies of formation of hercynite and mullite were also obtained. Leave of absence from the Steelmaking Research Section, Iron and Steel Research Laboratories, Kobe Steel Ltd.     

Petrographic and thermodynamic study of slags in EAF stainless steelmaking

Abstract

A study of the typical characteristics of electrical arc furnace (EAF) slags in the production of the stainless steel (AISI 304L) was carried out. Twenty-eight slag samples were taken from 14 heats. Simultaneously with each slag sampling, the temperature of the steel was measured, and one steel sample was taken. The selected slag samples were studied both using SEM–EDS and light optical microscopy. Computational thermodynamics was used as a tool to predict the equilibrium phases in the top slag as well as the amount of these phases at the process temperatures. It was observed that, at process temperature, the stainless EAF slag generally consists of liquid oxides, spinel particles and metallic droplets. Under normal operation, the amount of spinel particles is 2–6 wt-%. In addition, the influence of the slag temperature, basicity, MgO content and Cr₂O₃ content on the amount of spinel precipitates and thereby on the foaming index of the top slag is also illustrated and discussed. More specifically, it was found that, within the compositional range of the slag samples, the critical parameter affecting the amount of solid spinel particles in the slag is the chromium oxide content.     

Thermodynamics of iron oxide in FexO‐dilute CaO + Al2O3 + SiO2 + FexO slags at 1873 K

The ferrous and ferric ion capacities, and , for the slag of CaO + Al₂O₃ + SiO₂ are determined at 1873 K by means of the distribution equilibrium of iron between Fe_xO dilute slags of the system and Pt + Fe alloys under a controlled atmosphere. Compared with the values of for CaO + Al₂O₃ binary slag at a constant ratio of Al₂O₃ to decreases with an increase in SiO₂ content. Nearly linear relationships are observed between the logarithm of the ferrous and ferric ion capacities and the optical basicity. Applying these capacities, the relationship between (%Fe^T) and PO₂ under iron saturation, as well as the iron redox equilibrium in slag in relation to the optical basicity were discussed.     

A thermodynamic study of BaO + BaCl2 + Cr2O3 fluxes used for the removal of phosphorus from chromium-containing iron melts

Electrochemical measurements with solid-oxide galvanic cell of the type Mo/Mo + MoO₂//ZrO₂(MgO)//{Cu + Cr}_alloy + (Cr₂O₃)_slag/Mo were conducted at 1473 K in order to obtain the activities of Cr₂O₃ in BaO + BaCl₂ + Cr₂O₃ slags used for dephosphorization of chromium-containing iron melts. Based on the activity measurements, it is concluded that in the system BaO + BaCl₂ + Cr_{2 O3} at 1473 K, there are 1 two-phase region in saturation with pure Cr₂O₃(s) and 3 three-phase regions. The activities of Cr₂O₃ within such three-phase regions decrease with an increase in BaO/BaCl₂ mole ratios. The Cr₂O₃ activities in BaO + BaCl₂ + Cr2O3 fluxes are, in general, greater than those in CaO + CaCl₂ + Cr₂O₃, corresponding to much more effective dephosphorization by BaO + BaCl₂ + Cr₂O₃ fluxes rather than CaO + CaCl₂ + Cr₂O₃ slag.     

A thermodynamic study of copper-iron and copper-cobalt liquid alloys by mass spectrometry

The thermodynamic activities in the liquid Cu-Fe and Cu-Co binary systems were measured by a high temperature mass spectrometric technique. From the obtained data, the heats of mixing in the Cu-Co liquid binary were calculated. Both the Cu-Fe and Cu-Co systems are thermodynamically similar, with large positive deviations from ideality in the activities. The activity coefficients in the liquid Cu-Co system at 1823 K were found to be symmetrical and can be expressed by lnγ_Cu= 1.76X _Co ² The heat of mixing in the liquid Cu-Co system was found to be described by a cubic function δH_m = −17.9 _Co ³ − 7.6X _Co ² + 25.5_Co (kJ/mol) The activity coefficients in the liquid Cu-Fe system at 1873 K were found to satisfy two quadratic formalisms in the binary In γ_Cu = 2.10X _Fe ² − 0.13 0.65 ≤X _Fe ≤ 1 In γ_Fe = 1.79X _Cu ² + 0.04 0 ≤X _Fe ≤ 0.65     

Quantitative analysis of the relative basicity of CaO and BaO by silver solubility in slags

The solubility of silver in molten CaO-B₂O₃ and BaO-B₂O₃ slags at high temperatures was measured to seek a new measure of the basicity of slags. The B₂O₃-bearing fluxes, which have wide range of liquids at the temperature of interest, have been applied to investigate the effects of flux composition on the solubility of silver from the saturation of acidic or basic components. The solubility of silver in slags has a minimum value as a function of flux composition, and it is suggested that silver behaves as an amphoteric substance and dissolves by different mechanisms in acidic and basic fluxes. The solubility of silver decreased with the increasing temperature and content of basic oxides in the acidic region, and vice versa in the highly basic region. In the acidic region, BaO is more basic than CaO by, at most, about 33 pct, based on the difference of the solubility of silver in both slags, indicating that BaO is not a much-stronger basic oxide than CaO in the acidic slags. In the highly basic region, BaO is about 5 times more basic than CaO. The solubility of silver in slags was compared to the nitride capacity, showing that the dissolutions of silver and nitrogen into the melts are similar to each other. The relationship between Ag solubility and theoretical optical basicity was also discussed.     

Determination of standard gibbs energies of formation of MgO,SrO, and BaO

The standard Gibbs energy of formation of MgO was determined from the measurement of the ΔG° for the reaction ; by equilibrating Mg and Nb with a magnesia crucible and is expressed as follows: Mg(l)+ l/2O₂(g) = MgO(s) ΔG° = −657,000(±5000) + 141(±13)T [J/mol] (973 to 1323 K) The standard Gibbs energies of formation of SrO and BaO were determined by equilibrating silver and MO(M: Sr, and Ba) in a graphite crucible on the basis of the reactionM(in Ag) + CO (g) = MO (s) + C (s), yielding the following results:

Optical basicity and the thermodynamic properties of slags

Metallurgical and Materials Transactions B -     

A thermodynamic study on cobalt containing calcium ferrite and calcium iron silicate slags at 1573 K

Redox equilibria, activities of cobalt, iron and their oxides in calcium ferrite and calcium ironsilicate slags, were measured through metal-slag-gas equilibrium experiments under controlled oxygen potentials (10⁻⁷ to 3 × 10⁻⁷ atm) at 1573 K. Results on the redox equilibria show that addition of CoO to calcium ferrite slag increases the equilibrium Fe³⁺/Fe²⁺ ratio in these melts. Measured activities of CoO and FeO showed positive deviations from ideal behavior, while that of Fe₂O₃ showed negative deviation. Partial substitution of CaO by SiO₂, by up to 4 wt pct SiO₂ in the calcium ferrite based melts, resulted in increases in the activity coefficients of CoO and Fe₂O₃. Phase equilibria studies on the cobalt containing CaO-FeO-Fe₂O₃-SiO₂ slags were also carried out using the drop-quench technique. Good agreement between the activity data and the liquidus temperature with respect to magnetite solid solution containing CoO was observed.     

A thermodynamic study of MgO—P2O5 slags by means of solid-oxide galvanic cell at 1673 K

An electrochemical method was tested in order to find a suitable experimental technique for the determinations of the activities of P₂O₅ in molten fluxes used for external dephosphorization of hot metal. This technique consists of equilibrating phosphorus-containing copper with molten slag and measuring the equilibrium oxygen partial pressure by means of solid state galvanic cells. The activities of P²O₅ in MgO—P₂O₅ were determined with this technique.     

A solid electrolyte oxygen sensor for steelmaking slags of the basic oxygen converter

Oxygen pressure in the slag phase is an important parameter in steelmaking processes. Consequently, an in situ solid electrolyte oxygen sensor for the steelmaking slags was developed in the present work. EMF measurements, optical examination, and EPMA analysis of cross sections of the electrolyte tubes used in laboratory experiments indicated that magnesia-stabilized zirconia was suitable for this purpose. The oxygen sensor was also tested on slags of a 100,000 kg LD converter at the end of the normal blowing operation. The stable oxygen pressure in the slag was successfully obtained by the simultaneous measurements of EMF and temperature. By using the oxygen sensor, a simple empirical relation was obtained between the oxygen pressure and ratio of ferric to the total iron ion content in the slag. Also, the oxygen pressure in the LD converter slag was found an order of magnitude higher than that in the metal at the end of the normal blowing operation.     

Activities of oxygen in liquid thallium and indium from electrochemical measurements

Modified coulometric titrations on the galvanic cell;O in liquid Tl or In/ZrO₂(+CaO)/Air, Pt, were performed at 973, 1073, and 1173 K to determine the oxygen activities in liquid thallium and liquid indium. The standard Gibbs energies of solution of oxygen in liquid thallium and liquid indium for l/2 O₂ →O (1 at. pct) were determined respectively to be δG‡(in Tl) = -22000 + 0.74T (±300) cal/g-atom = -92000 + 3.10T (±1300) J/g-atom, δG‡(in In) = -42450+ 3.30T (±350) cal/g-atom = -177600 + 13.8T (±1500) J/g-atom, where the reference state for dissolved oxygen was an infinitely dilute solution. It was reconfirmed that the apparent initial oxygen concentration observed in the range of very low oxygen concentration in liquid metal was attributed to the oxygen released from the solid electrolyte.     

Activities of oxygen in liquid copper and silver from electrochemical measurements

Modified coulometric titrations on the galvanic cell:O in liquid Cu or Ag / ZrO₂( + CaO) / Air, Pt, were performed to determine precisely the oxygen activities in liquid copper and silver in the range of relatively low oxygen concentration. The present experimental results were remarkably reproducible in comparison with the published data. The standard Gibbs energies of solution of oxygen in liquid copper and liquid silver for 1/2 O₂(l atm) → O(l at. pct) were determined respectively to be ΔG° (in Cu) = −18040 −0.03 T(K) (± 120) cal · g-atom−1 = −75500 −0.12 T(K)(± 500) J · g-atom−1, ΔG°(inAg)= -3860+ 1.56 T(K) (±90) cal · g-atom−1 = −16140 + 6.52 T(K)(±380) J · g-atom−1 where the reference state for dissolved oxygen was an infinitely dilute solution. The present value of the partial entropy of oxygen dissolved in liquid copper differs significantly from that suggested by many investigators. Further, the present equation for liquid copper has been found to be consistent with a correlation proposed previously by the present authors. The equation for liquid silver is in good agreement with the published ones.