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, $$\log (P_{O_2 } /atm) = 6.35 - 27,600 (T/K)$$      

Experimental liquidus in the PbO-ZnO-“Fe2O3”-(CaO + SiO2) System in Air,with CaO/SiO2 = 0.35 and PbO/(CaO + SiO2) = 3.2

Experimental studies on phase equilibria in the multicomponent system PbO-ZnO-CaO-SiO₂-FeO-Fe₂O₃ in air have been conducted to characterize the phase relations of a complex slag system used in lead and zinc smelting. The liquidus in the pseudoternary section ZnO-“Fe₂O₃”-(PbO + CaO + SiO₂) with a CaO/SiO₂ weight ratio of 0.35 and a PbO/(CaO + SiO₂) weight ratio of 3.2 has been constructed to describe liquidus temperatures as a function of composition in the range of commercial operating conditions employed by the Lead Isasmelt smelting process. The section contains the primary phase fields of spinel (zinc ferrite, Zn _x Fe_3−y O_4+z ), zincite (Zn _u Fe_1−u O), melilite (Pb _v Ca_2−v Zn _w Fe_1−w -Si₂O₇), hematite (Fe₂O₃), magnetoplumbite (PbFe₁₀O₁₆), and wollastonite (CaSiO₃).     

Experimental study of phase equilibria in the “FeO”-ZnO-(CaO + SiO2) system with the CaO/SiO2 weight ratio of 0.71 at metallic iron saturation

The pseudoternary section “FeO”-ZnO-(CaO + SiO₂) with a CaO/SiO₂ weight ratio of 0.71 in equilibrium with metallic iron has been experimentally investigated in the temperature range from 1000 °C to 1300 °C (1273 to 1573 K). The liquidus surface in this pseudoternary section has been determined in the composition range of 0 to 33 wt pct ZnO and 30 to 70 wt pct (CaO + SiO₂). The system contains primary-phase fields of wustite (Fe _x Zn_1−x O_1−y ), zincite (Zn _z Fe_1−z O), fayalite (Fe _w Zn_2−w SiO₄), melilite (Ca₂Zn _u Fe_1−u Si₂O₇), and pseudowollastonite (CaSiO₃). The phase equilibria involving the liquid phase and the solid solutions have also been measured.     

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.     

Experimental study of phase equilibria in the “FeO”-ZnO-(CaO + SiO2) system with CaO/SiO2 weight ratios of 0.33, 0.93, and 1.2 in equilibrium with metallic iron

The pseudoternary sections “FeO”-ZnO-(CaO + SiO₂) with CaO/SiO₂ weight ratios of 0.33, 0.93, and 1.2 in equilibrium with metallic iron have been experimentally investigated in the temperature range from 1000 °C to 1300 °C (1273 to 1573 K). The liquidus surfaces in these pseudoternary sections have been experimentally determined in the composition range from 0 to 33 wt pct ZnO and 30 to 70 wt pct (CaO + SiO₂). The sections contain primary-phase fields of wustite (Fe _x Zn_1−x O_1+y ), zincite (Zn _z Fe_1−z O), fayalite (Fe _w Zn_2−w SiO₄), melilite (Ca₂Zn _u Fe_1−u Si₂O₇), willemite (Zn _v Fe_2−v SiO₄), dicalcium silicate (Ca₂SiO₄), pseudowollastonite and wollastonite (CaSiO₃), and tridymite (SiO₂). The phase equilibria involving the liquid phase and the solid solutions have also been measured.     

Experimental study of phase equilibria in the PbO-ZnO-“Fe2O3”-CaO-SiO2 system in air for high lead smelting slags (CaO/SiO2=0.35 and PbO/(CaO + SiO2)=5.0 by weight)

Experimental studies on phase equilibria in the multicomponent system PbO-ZnO-CaO-SiO₂-FeO-Fe₂O₃ in air have been conducted to characterize the phase relations of a complex slag system used in commercial lead oxidation smelting. The liquidus in the pseudo-ternary section ZnO-“Fe₂O₃”-(PbO + CaO + SiO₂) with the CaO/SiO₂ weight ratio of 0.35 and the PbO/(CaO + SiO₂) weight ratio of 5.0 has been constructed using results of over 100 high-temperature equilibration and quenching experiments followed by electron probe X-ray microanalysis. The liquidus in this pseudoternary section contains primary phase fields of spinel (zinc ferrite) Zn _x Fe_3−x O_4+y , zincite Zn _u Fe_1−u O, melilite Pb _v Ca_2−v Zn _w Fe_1−w Si₂O₇, hematite Fe₂O₃, magneto-plumbite PbFe₁₀O₁₆, and dicalcium silicate Ca_2−t Pb _t SiO₄. The laboratory results are compared with the slags obtained from an industrial reactor.     

Reaction between CaO‐SiO2‐Al2O3 Slags and H2 + HCl + H2O Gas Mixtures

To better understand the thermodynamic behaviour of chlorine in blast furnaces, CaO‐SiO₂‐Al₂O₃ slags were brought into equilibrium with Ar + H₂ + HCl + H₂O gas mixtures at temperatures between 1673 K and 1798 K. The dissolution of chlorine into molten slags could be well interpreted through a reaction: (1/2) {CaO}_slag + (HCl) = {Ca_1/2Cl}_slag + (1/2) (H₂O). Conforming to this formula, a linear relation was observed between log (%CI) and log with an anticipated slope of 1/2.     

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.     

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.     

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 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.     

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.     

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:

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.     

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.     

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

Influences of Al2O3/CaO and Na2O/CaO Ratios on Viscosities of CaO-Al2O3-SiO2-Na2O Melts

The influences of Al₂O₃/CaO and Na₂O/CaO ratios on viscosities of CaO-Al₂O₃-SiO₂-Na₂O melts are investigated by the rotating cylinder method in this study. It is indicated from the experimental results that viscosity first increases and then decreases as gradually increasing Na₂O/CaO ratio. As increasing Na₂O/CaO ratio while keeping the contents of Al₂O₃ and SiO₂ constant, the transformation of bridging oxygen (from being bonded with Al³⁺ ion charge compensated by Ca²⁺ ion to that compensated by Na⁺ ion, for the higher priority of Na⁺ ion relative to Ca²⁺ ion) increases the viscosity, whereas the transformation of non-bridging oxygen decreases the viscosity. These two factors lead to the appearance of viscosity maximum. The viscosity model proposed in our previous papers could well describe the viscosity variation tendency.     

Stability of silico-ferrite of calcium and aluminum (SFCA) in air-solid solution limits between 1240 °C and 1390 °C and phase relationships within the Fe2O3-CaO-Al2O3-SiO2 (FCAS) system

Quenching experiments were used to investigate the solid solution range, thermal stability, and selected phase relationships of silico-ferrite of calcium and aluminum (SFCA) within the Fe₂O₃-CaO-Al₂O₃-SiO₂ (FCAS) system. SFCA was found to be stable within a plane that connects the end members CF₃ (CaO·3Fe₂O₃), CA₃ (CaO·3Al₂O₃), and C₄S₃ (4CaO·3SiO₂). Chemical substitution in the four component system follows the coupled substitution mechanism 2(Fe³⁺, Al³⁺)↔(Ca²⁺, Fe²⁺)+Si⁴⁺ with the greatest range in chemical substitution occurring in the direction of the Al³⁺↔Fe³⁺ exchange (ranging from 0 wt pct Al₂O₃ to ∼31.5 wt pct Al₂O₃). The extent of Al³⁺↔Fe³⁺ substitution decreases with increasing temperature, and it was estimated that SFCA completely decomposes by ∼1480 °C. Coupled substitution involving Ca²⁺ and Si⁴⁺ for 2M³⁺ is not as extensive as the Al³⁺↔Fe³⁺ exchange, having a maximum range between 3 and 11 wt pct C₄S₃ component. Additional phases encountered in the experimental program included hematite; magnetite; quench liquid; dicalcium silicate; Fe-bearing gehlenite; calcium alumino-ferrite solid solutions, C(A, F)₆ and C(A, F)₂, plus an unidentified phase, possibly representing a solid substitution between SFCA-I and C(A, F)₃. Schematic phase diagrams have been constructed to show the relationship of SFCA with these surrounding phases.     

The effect of the CaO/SiO2 ratio on the phase equilibria in the ZnO-“Fe2O3”-(PbO + CaO + SiO2) system in air: CaO/SiO2 = 0.1, PbO/(CaO + SiO2) = 6.2, and CaO/SiO2 = 0.6, PbO/(CaO + SiO2) = 4.3

Experimental studies on phase equilibria in the multi-component system PbO-ZnO-CaO-SiO₂-FeO-Fe₂O₃ in air have been conducted to characterize the phase relations of a complex slag system used in the oxidation smelting of lead and in typical lead blast furnace sinters. The liquidus in two pseudoternary sections ZnO-“Fe₂O₃”-(PbO + CaO + SiO₂) with the CaO/SiO₂ weight ratio of 0.1 and the PbO/(CaO + SiO₂) weight ratio of 6.2, and with CaO/SiO₂ weight ratio of 0.6 and the PbO/(CaO + SiO₂) weight ratio of 4.3, have been constructed.     

Thermodynamic aspects of steel reoxidation behavior by the ladle slag system of CaO-MgO-SiO2-Al2O3-Fe t O-MnO-P2O5

The reoxidation behavior of steels by slag in the secondary steelmaking process was addressed by investigating the thermodynamic equilibria between the liquid iron containing Mn and P and CaO-MgO-SiO₂-Al₂O₃-P₂O₅-MnO-Fe _t O ladle slag at 1873 K. The activity coefficient of Fe _t O shows a maximum value in the vicinity of the basicity ((X _CaO + X _MgO + X _MnO)/(X _SiO2 + X _Al2O₃ + X _P2O₅)) = 2.5 at the specific mole fraction range of Fe _t O, while that of MnO seems to increase gradually with increasing the basicity. However, the values of and γ _MnO showed minima with respect to P₂O₅ content of slag. In addition, the values of and γ _MnO increased as (pct CaO)/(pct Al₂O₃) ratio increased at given SiO₂, MgO, and P₂O₅ contents. The conversion equations between the Fe _t O and MnO activities and their calculated activities via regular solution model were derived by the correlation between the measured and calculated activities over the limited ranges of Fe _t O and MnO contents. The regular solution model was used to estimate the oxygen potential in the slag. For MgO saturated slags, . For Al₂O₃ saturated slags, .