Experimental study of phase equilibria and thermodynamic optimization of the Fe-Zn-O system

The Fe-Zn-O phase diagram in air was studied over the temperature range from 900 °C to 1500 °C. The compositions of the phases in quenched samples were obtained by electron probe X-ray microanalysis (EPMA). This experimental technique is not affected by zinc losses resulting from vaporization of zinc at high temperatures. The model for the spinel solid solution was developed within the framework of the compound-energy formalism (CEF). The choice of parameters of the CEF and the sequence of their optimization can have a major influence on the predictions in multicomponent phases. These choices can only be made rationally by reference to the specific model being represented in the CEF. This is discussed for the case of the two-sublattice spinel model. In the limiting case, the proposed model reduces to the model by O’Neill and Navrotsky for spinels. When the CEF is used in combination with the equation of Hillert and Jarl to describe the magnetic contribution to thermodynamic functions of a solution, it is necessary to assign certain values of magnetic properties to all pseudocomponents and to magnetic interaction parameters to obtain the most reasonable approximation of the magnetic properties of a solution. It was shown how this can be done based on very limited experimental data. The same equations can be used when the Murnaghan or the Birch-Murnaghan equation is combined with the CEF to describe the pressure dependence of thermodynamic functions. The polynomial model was used to describe the properties of wustite and zincite, and the modified quasichemical model was used for the liquid slag. All thermodynamic and phase-equilibria data on the Fe-O and Fe-Zn-O systems were critically evaluated, and parameters of the models were optimized to give a self-consistent set of thermodynamic functions of the phases in these systems. All experimental data are reproduced within experimental error limits. These include the thermodynamic properties of phases (such as specific heat, heat content, entropy, enthalpy, and Gibbs energy); the cation distribution between octahedral and tetrahedral sites in spinel; the oxygen partial pressure over single-phase, two-phase, and three-phase regions; the phase boundaries (liquidus, solidus, and subsolidus); and the tie-lines.     

Phase equilibria in the system Fe-Zn-O at intermediate conditions between metallic-iron saturation and air

The phase equilibria in the FeO-Fe₂O₃-ZnO system have been experimentally investigated at oxygen partial pressures between metallic iron saturation and air using a specially developed quenching technique, followed by electron probe X-ray microanalysis (EPMA) and then wet chemistry for determination of ferrous and ferric iron concentrations. Gas mixtures of H₂, N₂, and CO₂ or CO and CO₂ controlled the atmosphere in the furnace. The determined metal cation ratios in phases at equilibrium were used for the construction of the 1200 °C isothermal section of the Fe-Zn-O system. The univariant equilibria between the gas phase, spinel, wustite, and zincite was found to be close to pO₂=1 · 10⁻⁸ atm at 1200 °C. The ferric and ferrous iron concentrations in zincite and spinel at equilibrium were also determined at temperatures from 1200 °C to 1400 °C at pO₂ = 1·10⁻⁶ atm and at 1200 °C at pO₂ values ranging from 1 · 10⁻⁴ to 1 · 10⁻⁸ atm. Implications of the phase equilibria in the Fe-Zn-O system for the formation of the platelike zincite, especially important for the Imperial Smelting Process (ISP), are discussed.     

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.     

Experimental study of the phase equilibria in the Fe-Mn-Al system

The isothermal sections with lower Al content at 800 ‡C, 900 ‡C, 1200 ‡C, and 1300 ‡C and two vertical sections of 4 wt pct Al and 8 wt pct Al in the Fe-Mn-AI system were determined by means of the diffusion couple technique, metallographic method, and differential thermal analysis (DTA). It is shown that the results of isothermal and vertical sections coincide with each other, and the twophase (α + γ) region and three-phase (α + γ + β) region trend toward the Fe-Mn side and Mn corner with the rise of temperature, respectively. The experimental results are in agreement with those calculated by the present authors. Formerly Graduate Student, Department of Materials Science and Engineering, Northeastern University     

Experimental study of phase equilibria in the systems PbO x -CaO and PbO x -CaO-SiO2

The reported experimental work on the systems PbO _x -CaO and PbO _x -CaO-SiO₂ in air is part of a wider research program that combines experimental and thermodynamic computer modeling techniques to characterize zinc/lead industrial slags. Extensive experimental investigation by high-temperature equilibration and quenching techniques followed by electron probe microanalysis was carried out in the temperature range 640 °C to 1500 °C (913 to 1773 K) and in the composition ranges 0 to 65 mol pct SiO₂ and 0 to 42 mol pct CaO. Liquidus and solidus data were reported for most of the primary phase fields. Liquidus surfaces in the systems CaO-Pb-O and PbO _x -CaO-SiO₂ in air were completely reconstructed. Extensive solid solutions of PbO in α′ dicalcium silicate and Ca₂Pb₃Si₃O₁₁ were measured.     

Experimental study of phase equilibria in the PbO-MgO-SiO2 system

An experimental study of the PbO-MgO-SiO₂ system has been carried out using high-temperature equilibration and quenching techniques, followed by electron probe X-ray microanalysis (EPMA). The phase equilibria were determined in the temperature range from 973 to 1673K. Nine primary phase fields have been investigated in this system, including three monoxides (PbO, MgO, and SiO₂), five binary compounds (MgSiO₃, Mg₂SiO₄, PbSiO₃, Pb₂SiO₄, and Pb₄SiO₆), and one ternary compound Pb₈Mg(Si₂O₇)₃. Two other ternary compounds, PbMgSiO₄ and PbMgSi₃O₈, were observed in some experiments; however, further experiments indicated that these two compounds are unstable in the temperature range investigated.     

Experimental study of phase equilibria in the system PbO-ZnO-SiO2

An experimental study on the ternary system PbO-ZnO-SiO₂ in air by high-temperature equilibration and quenching techniques followed by electron probe X-ray microanalysis was carried out as part of the wider research program on the six-component system PbO-ZnO-SiO₂-CaO-FeO-Fe₂O₃, which combines experimental and thermodynamic computer modeling techniques to characterize zinc and lead industrial slags. Liquidus and solidus data were reported for all primary phase fields in the system PbO-ZnO-SiO₂ in the temperature range 640 °C to 1400 °C (913 to 1673 K).     

Experimental and theoretical study of the phase equilibria in the fe-ni-w system

Experimental data on the Fe-Ni-W phase diagram have been obtained at 1273, 1373, 1473, 1573, and 1673 K by means of the diffusion-couple technique and electron microprobe analysis. These data were combined with selected literature information on the liquidus surface and the complete Fe-Ni-W phase diagram was evaluated. The evaluation was performed by analyzing the experimental data in terms of thermodynamic models for the Gibbs energy of the various phases and by computer-optimizing the model parameters involved. The optimized phase diagram satisfactorily describes the available data.     

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.     

Experimental investigation and thermodynamic calculation of the phase equilibria in the Cu-Sn and Cu-Sn-Mn systems

The phase equilibria in the Cu-rich portion of the Cu-Sn binary and Cu-Sn-Mn ternary systems have been determined using the diffusion-couple method, differential scanning calorimetry (DSC), high-temperature electron diffraction (HTED), and high-temperature X-ray diffraction (HTXRD) techniques. The present experimental results on the binary Cu-Sn system show the presence of the two-stage, second-order reaction A2 → B2 → D0₃ in the bcc-phase region, rather than a two-phase equilibrium between the disordered bcc (A2) and the ordered bcc (D0₃) phases, as reported before. Phase equilibria in the Cu-Sn-Mn ternary system in the composition range of 0 to 30 at. pct Sn and 0 to 30 at. pct Mn at 550 °C, 600 °C, 650 °C, and 700 °C have been determined, and a ternary compound (Cu₄MnSn) with a very small solubility has been detected. A thermodynamic analysis of the Cu-Sn-Mn ternary system including the Cu-Sn and Mn-Sn binary systems has also been carried out by the CALPHAD (Calculation of Phase Diagrams) method, in which the Gibbs energy of the bcc phase is described by the two-sublattice model in order to take into account the second-order A2/B2 ordering reaction. A consistent set of optimized thermodynamic parameters for the Cu-Sn-Mn system for describing the Gibbs energy of each phase results in a better fit between calculation and experiment.     

Monosilicide-disilicide-silicon phase equilibria in the nickel-platinum-silicon and nickel-palladium-silicon systems

Bulk-phase equilibria in Ni-rich/Si-rich alloys of the Ni-Pt-Si and Ni-Pd-Si systems were investigated. Results suggest that a bulk monosilicide solid solution, containing up to at least 11 at. pct Pt, exists in the Ni-Pt-Si system. Monosilicides containing more than 11 at. pct Pt were not examined. Results from both ternary systems point convincingly to the existence of a NiSi+Si↔NiSi₂ eutectoid reaction near 700 °C in the Ni-Si binary system; data from the Ni-Pt-Si system, which yield the more accurate determination of the eutectoid temperature, place it at roughly 710 °C. The Pt and Pd concentrations of monosilicide in equilibrium with disilicide and Si were measured using energy-dispersive spectrometry (EDS) and were found to increase with temperature.     

Estimating terminal phase equilibria in ternary systems

Abstract

An analytical method for the estimation of terminal two-phase equilibria in ternary systems is presented. The method utilizes thermodynamic solution parameters, free energies of transformation of pure components and phase equilibria of the relevant binary systems.

At low solute concentrations or at higher concentrations in systems where solute interactions are weak, it is shown that ternary isotherms are characterized by approximately linear phase boundaries and constant solute partition coefficients.

The method has been employed to calculate several tie-lines of the 1510°C isotherm in the iron-rich comer of the Fe-Mn-S diagram. In this moderately rich solution system typifying fairly strong solute interaction, the curvature of the phase boundaries and variation of the partition coefficients throughout the two-phase region are found to be minimal (for the parameters used in the calculations).

Résumé

Cette communication fait part d'une méthode de calcul des lignes de conjugaison dans les régions terminales d'un diagramme de phases ternaire. La méthode utilise les paramètres thermodynamiques de solution, les énergies libres de transformation des composants, et les diagrammes de phases binaires qui limitent le diagramme ternaire.

On démontre que les isothermes sont linéaires et les coefficients de partage invariables lorsque les interactions entre solutés sont faibles.

La méthode a servi au calcul des lignes de conjugaison de la région fer δ + liquide du système Fe-Mn-S à 1510°C. On constate que la courbure des isothermes et la variation des coefficients de partage d'un bout à l'autre de la région bi-phasée sont minimes.     

Experimental study of phase equilibria in the PbO-Al2O3-SiO2 system

Equilibrium phase relations in the PbO-Al₂O₃-SiO₂ system have been investigated experimentally by means of high-temperature equilibration, quenching, and electron probe X-ray microanalysis (EPMA). The system has 21 primary phase fields including three monoxides (PbO, Al₂O₃, and SiO₂), seven binary compounds (Al₆Si₂O₁₃, PbAl₂O₄, PbAl₁₂O₁₉, Pb₂Al₂O₅, PbSiO₃, Pb₂SiO₄, and Pb₄SiO₆), and eleven ternary compounds (PbAl₂Si₂O₈, Pb₃Al₁₀SiO₂₀, Pb₄Al₂Si₂O₁₁, Pb₄Al₄SiO₁₂, Pb₄Al₄Si₃O₁₆, Pb₄Al₄Si₅O₂₀, Pb₅Al₂Si₁₀O₂₈, Pb₆Al₂Si₆O₂₁, Pb₈Al₂Si₄O₁₉, Pb₁₂Al₂Si₁₇O₄₉, and Pb₁₂Al₂Si₂₀O₅₅). Three new ternary compounds, Pb₄Al₄SiO₁₂, Pb₄Al₄Si₅O₂₀, and Pb₁₂Al₂Si₁₇O₄₉, were observed and characterized by EPMA. No extensive solid solution in any of the compounds was found in the present study. The liquidus isotherms were experimentally determined in most of the primary phase fields in the temperature range from 923 to 1873 K, and the ternary phase diagram of the PbO-Al₂O₃-SiO₂ system has been constructed.     

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.     

An experimental and theoretical study of the phase equilibria in the Fe-Mo-Ni system

New experimental data on the Fe-Mo-Ni phase diagram have been obtained at 1223, 1273, 1373, 1473, and 1543 K using a diffusion couple technique. A number of tie lines were determined using a scanning electron microscope with energy-dispersive X-ray analysis equipment. In a few cases, the phases were identified by X-ray diffraction. The experimental data obtained in the present work, and previously published data, were analyzed by the use of thermodynamic models describing the Gibbs energy of the various phases. The model parameters were calculated using a computerized optimization procedure. The intermetallic phases stable at temperatures above 1223 K were included in the calculations using a three-sublattice model. Experimental data on solidus and liquidus temperatures were used to evaluate properties for the liquid phase. A number of calculated isothermal sections are presented and compared with experimental data. The calculations satisfactorily describe the available experimental data. KARIN FRISK, formerly with the Division of Physical Metallurgy, Royal Institute of Technology, Stockholm.     

Application of the diffusion couple to study phase equilibria in the Fe-Cr-S ternary system at 600 °C

The sulfidation of Fe-Cr alloys has a large financial significance for industries that use fossil fuels, such as the electric utility industry. Therefore, the sulfidation of a series of Fe-Cr alloys was studied at 600 °C using a solid-state diffusion couple technique. The diffusion couple technique combined Fe_0.95S powder and FeCr binary alloys together in a configuration that allowed for post-heat-treatment microanalysis using an electron probe microanalyzer (EPMA). The results showed that only two different diffusion couple microstructures formed in samples spanning the entire Fe-Cr binary range. The Fe-rich alloy diffusion couples contained a surface αFeCr layer and an internal sulfide precipitate layer that contained three different sulfide phases. The Cr-rich alloy diffusion couples also possessed an internal precipitate layer, as well as a thick, triplex interfacial scale. The ternary elemental diffusion was described using diffusion paths plotted on the 600 °C isothermal section of the Fe-Cr-S phase diagram. The results also showed that samples with less than 51 wt Pct Cr were more sulfidation resistant. The accuracy of the existing Fe-Cr-S 600 °C isothermal section was assessed, and it was determined that the τ phase field had a larger composition than previously published.