Chemical potentials of components of the system CaO + P2O5 + FexO at 1673 K

Electromotive force (emf) measurements were conducted with a solid oxide galvanic cell of the type Mo/Mo + MoO₂/ZrO₂ (MgO)/Fe (s) + Fe_xO (in slag)/Ag/Fe at 1673 K in order to obtain the activities of Fe_xO in CaO + P₂O₅ + Fe_xO ternary slags. By using the Gibbs-Duhem integration, the activities of P₂O₅ and CaO were also obtained.     

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.     

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.     

Activities of Phosphorus in Copper‐Iron Liquid Alloys Saturated with Copper‐Iron Solid Solutions

In order to determine the activities of phosphorus and iron in liquid {Cu‐Fe‐P} alloys, the two coexisting phases of liquid {Cu‐Fe‐P} alloys + <Cu‐Fe‐P> solid solutions were brought into equilibrium with a mixture of Al₂O₃ + AlPO₄ + Fe_xAl₂O₄ at temperatures of 1416K and 1526K. The oxygen partial pressures were measured with the aid of a solid‐oxide galvanic cell of the type: (+)Mo / Mo + MoO₂/ ZrO₂(MgO) / {Cu‐Fe‐P} + <Cu‐Fe‐P> + <Al₂O₃> + <AlPO₄> + <FeAl₂O₄> / Fe(‐) The equilibrium reactions underlying the experiments can be expressed by 2[P]_cu + (5/2) (O₂) + <Al₂O₃> = 2 <AlPO₄> and x[Fe]_Cu + (1/2) (O₂) + <Al₂O₃> = <Fe_xAl₂O₄> The Henrian activity coefficient referred to 1 wt pct solution in pure liquid copper could be well expressed by the formula log f_P° = (4.46±0.40) ‐ (8.67±0.59)/(T/K). The iron activities referred to pure solid iron could be formulated as log a_Fe =‐ (0.37 ± 0.12) + (500 ±200) /(T/K).     

Chemical potentials of oxygen for three-phase assemblages of CaSiO3(s) + Ca3Si2O7(s) + {CaO + SiO2 + FexO} melt and Ca3Si2O7(s) + Ca2SiO4(s) + {CaO + SiO2 + FexO} melt

By employing an electrochemical technique involving stabilized zirconia as solid electrolyte and Mo + MoO₂ mixture as reference electrode, the equilibrium oxygen partial pressures for three-phase assemblages of CaSiO₃(s) + Ca₃Si₂O₇(s) + {CaO + SiO₂ + Fe_xO} melt and Ca₃Si₂O₇(s) + Ca₂SiO₄(s) + {CaO + SiO₂ + Fe_xO} melt were determined as: - log {P_O2 (CS + C₃S₂ + L)/bar} = - 3.22 13000/(T/K) ± 0.05 - log {P_O2 (C₃S₂ + C₂S + L)/bar} = - 0.92 16400/ (T/K) ± 0.04. respectively, where CS, C₃S₂ and C₂S indicate CaSiO₃(s), Ca₃Si₂O₇(s). and Ca₂SiO₄(s), respectively.     

Chemical potentials of oxygen for mixtures of CaO (s) + Ca4P2O9 (s) + {CaO + P2O5 + FexO} melts and Ca4P2O9 (s) + Ca3P2O8 (s) + {CaO + P2O5 + FexO} melts

Electrochemical measurements involving stabilized zirconia as solid electrode and Mo + MoO₂ as reference electrode were conducted in order to determine the chemical potentials of oxygen for threephase assemblages of CaO (s) + Ca₄P₂O₉ (s) + liquid and Ca₄P₂O₉ + Ca₃P₂O₈ + liquid within the system CaO + Fe_xO + P₂O₅. The results for the former are $$\log (P_{O_2 } /atm) = 6.22 - 27,900 (T/K)$$ while for the latter, $$\log (P_{O_2 } /atm) = 6.35 - 27,600 (T/K)$$      

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.     

Activities of FexO in CaO‐(Na2O)0.1875(K2O)0.0625(Al2O3)0.25(SiO2)0.5‐FexO Pseudo‐Ternary Slags

Activities of Fe_xO in CaO‐(Na₂O)_0.1875(K₂O)_0.0625(Al₂O₃)_0.25(SiO₂)_0.5‐Fe_xO pseudo‐ternary slags were determined at 1673K by using a solid‐oxide galvanic cell; The substitution of (Na₂O)_0.1875(K₂O)_0.0625(Al₂O₃)_0.25(SiO₂)_0.5 for CaO has an effect of raising the Fe_xO activities.     

Activities of MnO in CaO-SiO2-Al2O3-MnO (<10 Pct)-FetO(<3 pct) slags saturated with liquid iron

Activity coefficients of MnO and Fe,0 in CaO-SiO₂-Al₂O₃-MnO(<10 mass pct)-Fe,O(<3 mass pct) slags were determined at 1873 K in an Al₂O₃ or CaO crucible by using the reported values for the activities of Al₂O₃ and SiO₂ or the analyzed contents of oxygen. The activity coefficients of MnO and Fe_tO were found to be constant in the studied concentration range of MnO and Fe_tO. The former increased with an increase in the CaO content, while the latter increased with an increase in the SiO₂ content.     

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.     

Thermodynamics of manganese distribution between liquid iron and the CaO–Al2O3–SiO2–FeO–MnO system

The thermodynamics of distribution of constituents between liquid iron and the CaO–Al₂O₃–SiO₂–FeO–MnO system at 1600°C was studied using electrochemical indication of the equilibrium partial pressure of oxygen in both phases. The results show that oxidation potential of the Fe(l)–CaO–Al₂O₃–SiO₂–FeO–MnO system, expressed in terms of log p(O₂), is directly proportional to log (x(MnO) · x(FeO)/w| Mn |). Manganese distribution coefficient, L'_mn, in intersection CaO/Al₂O₃ = 1 decreases with increasing slag basicity expressed in terms of activity a(CaO) or 1/γ(MnO). Experimentally determined equilibrium constant K_Mn/Fe is equal to 2.7 for 1600°C. The number of exchanged electrons between Fe-O-Mn-Si electrode and the slag approaches the theoretical value.     

The Activities of FexO in {CaO‐SiO2‐Al2O3‐MgO‐FexO} Slags at 1723 K

In Japanese steelworks, hot metal is now produced by scrap melting process. With this process removal of sulphur is very much handicapped because of very high sulphur levels (0.04 to 0.09 pct by weight) and relatively low tapping temperatures (1623 to 1723 K). In order to overcome such disadvantages, the authors explored on the phase diagrams of {CaO‐SiO₂‐Al₂O₃‐MgO} slags, and this research revealed that those slags at 35 wt%‐Al₂O₃ would be good candidates as reagents for the removal of sulphur from high sulphur hot metal at relatively low temperatures. For better understanding of the thermodynamic properties of the candidate slags, in this study, activities of Fe_xO were determined by using solid‐state electrochemical cells incorporating MgO‐stabilized zirconia and Mo + MoO₂ reference electrode.     

Thermodynamics of iron oxide in Fe x O-dilute CaO+Al2O3+Fe x O fluxes at 1873 K

The distribution of iron between Fe _x O-dilute CaO+Al₂O₃+Fe _x O fluxes and Pt+Fe alloys, as well as the redox equilibrium of iron ions in these fluxes, was experimentally investigated in pressure-controlled CO₂/CO gas at 1873 K. Total iron content in flux (pct Fe ^T ) and the ratio of (pct Fe²⁺) to (pct Fe ^T ) in fluxes with constant can be related to the activity of iron, α _Fe, and the partial pressure of oxygen, a _Fe, using the following equation:

Thermodynamics of iron oxide in Fe x O-dilute CaO + Al2O3 + MgO + Fe x O slags at 1873 K

In order to determine the ferrous and ferric ion capacities: 3

A thermodynamic study of SrO + FexO and BaO + FexO liquid slags by disposable electrochemical oxygen probes

An electrochemical technique involving magnesia-stabilized zirconia as the solid electrolyte and a mixture of Mo + MoO₂ as the reference electrode for the measurements of the activities of Fe_xO in the SrO + Fe_xO and BaO + Fe_xO systems at 1673 K. Measurement of oxygen potentials established at the slag electrode by disposable solid state cells. Expression of the thermodynamic properties of SrO + Fe_xO and BaO + Fe_xO by the binary subregular model.     

Thermodynamic behaviours of manganese and phosphorus between CaO‐MgOsat‐SiO2‐Al2O3‐FetO‐MnO‐P2O5 ladle slag and liquid iron

The thermodynamic equilibria of manganese and phosphorus between liquid iron and CaO‐MgO_Sat‐SiO₂‐Fe_tO‐MnO‐P₂O₅‐Al₂O₃ (0–33%) ladle slag have been investigated at 1873 K from the viewpoint of Mn and P yields for the production of high‐strength steels. The equilibrium distribution ratios of Mn and P were found to increase with increasing Fe_tO content; however, these ratios vary with basicity, but they do this the other way round. The addition of alumina into slag at a fixed basicity and Fe_tO content decreases both the equilibrium manganese and phosphorus distributions. The equilibrium distribution ratios were discussed in terms of the variation of activity coefficients of Fe_tO, MnO and PO_2.5, according to the slag basicity and Al₂O₃ content. The quantitative contributions of basicity and (%Fe_tO + %MnO) on L_Mn and L_P were empirically determined and their usefulness was discussed with the aid of plant data: To improve Mn and P yields in the practical RH operation, it is strongly recommended that Fe‐Mn and Fe‐P alloys be added after Al deoxidation treatment inducing relatively high Al₂O₃ in slag and maintaining low Fe_tO content. In addition, a ladle slag composition for the targeted Mn and P contents in liquid iron was substantially estimated using the empirical relationships.     

Experimental study of phase equilibria in the Al-Fe-Zn-O system in air

The phase equilibria in the Al-Fe-Zn-O system in the range 1250 °C to 1695 °C in air have been experimentally studied using equilibration and quenching techniques followed by electron probe X-ray microanalysis. The phase diagram of the binary Al₂O₃-ZnO system and isothermal sections of the Al₂O₃-“Fe₂O₃”-ZnO system at 1250 °C, 1400 °C, and 1550 °C have been constructed and reported for the first time. The extents of solid solutions in the corundum (Al,Fe)₂O₃, hematite (Fe,Al)₂O₃, Al₂O₃*Fe₂O₃ phase (Al,Fe)₂O₃, spinel (Al,Fe,Zn)O₄, and zincite (Al,Zn,Fe)O primary phase fields have been measured. Corundum, hematite, and Al₂O₃*Fe₂O₃ phases dissolve less than 1 mol pct zinc oxide. The limiting compositions of Al₂O₃*Fe₂O₃ phase measured in this study at 1400 °C are slightly nonstoichiometric, containing more Al₂O₃ then previously reported. Spinel forms an extensive solid solution in the Al₂O₃-“Fe₂O₃”-ZnO system in air with increasing temperature. Zincite was found to dissolve up to 7 mole pct of aluminum in the presence of iron at 1550 °C in air. A meta-stable Al₂O₃-rich phase of the approximate composition Al₈FeZnO_14+x was observed at all of the conditions investigated. Aluminum dissolved in the zincite in the presence of iron appears to suppress the transformation from a round to platelike morphology.     

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.     

Study on electrical conductivity of FexO–CaO–SiO2–Al2O3 slags

The composition dependences of electrical conductivity of Fe_xO–CaO–SiO₂–Al₂O₃ slags at different oxygen potentials and temperatures have been studied experimentally in the present work. From the experimental results, the total electrical conductivity and electronic conductivity for all the slags monotonously decrease as increasing CO/CO₂ ratio from about 0 to 1. With the increase of Fe_xO content, the total electrical conductivity and electronic conductivity increase at a fixed CO/CO₂ ratio. It is also found that the ionic conductivity of all the studied slags increases as increasing the CO/CO₂ ratio, which is resulted from the increase of Fe²⁺ ion concentration. In addition, the temperature dependences of ionic, electronic and total conductivity for different compositions obey the Arrhenius law. The electronic transference number exhibits a strong relationship with oxygen potential, but is independent of temperature.     

Activities of FexO in complex slags used during the final stages of external dephosphorization of hot metal

Measurements of the activities of Fe_xO in complex slags during the final stages of external dephosphorization by using a disposable electrochemical oxygen probe. Positive deviations of the Fe_xO activities from the Raoult law. Iso-activity curves drawn on the “ternary” diagram, (CaO + MgO + MnO + CaF₂) + Fe_xO + (SiO₂ + P₂O₅) at 1673 K. Calculations of the activities of P₂O₅ in complex slags with an assumption of thermodynamic equilibrium between slags and hot metal. Beneficial effect of CaF₂ in the slags with respect to lowering of the P₂O₅ activity.