Primary Phase Field Research Articles

Experimental Phase Equilibria Studies in the FeO-Fe2O3-CaO-SiO2 System in Air: Results for the Iron-Rich Region

New experimental data are reported on the liquidus and sub-liquidus phase equilibria in the FeO-Fe2O3-CaO-SiO2 system in air. The study was undertaken using equilibration/quenching and microanalysis techniques enabling the compositions of the liquid and solid phases in equilibrium at temperature to be accurately measured. The limits of stability and associations of the primary phase fields of hematite (Fe2O3), dicalcium silicate (Ca2SiO4), silico-ferrite of calcium solid solution (SFC), dicalcium ferrite (Ca2Fe2O5), calcium ferrite (CaFe2O4), calcium diferrite (CaFe4O7) have been characterized in the high iron, high CaO/SiO2, low melting temperature region of the system. The full extent of the primary phase field of SFC has been determined, as have the conjugate lines joining the SFC and the corresponding liquid phase over the range of SFC compositions at sub-liquidus temperatures.

Effect of Cooling Rate on the Controlled Solidification of “Fe<sub>2</sub>O<sub>3</sub>”–CaO–SiO<sub>2</sub> Liquids in Air in Synthetic Iron Ore Sinter

The cooling rate of the liquid oxide can be controlled in industrial sintering processes through the draft pressure and has the potential to influence microstructure formation. The solidification of a liquid within the hematite primary phase field in the ternary FeO-CaO-SiO system in air was undertaken at different cooling rates to determine the impact of cooling rate on the formation of product microstructures. Samples with a bulk composition of 72.7 wt% FeO and a CaO/SiO ratio of 3.46, were cooled from 1623 K (1350°C) at 2 K/s, 0.5 K/s, 0.1 K/s and 0.01 K/s and quenched at 5 K temperature intervals from 1533 K (1260°C) to 1453 K (1180°C). During cooling, four stages of phase assemblage formation were consistently observed at all cooling rates; in order of formation these are, Liquid +hematite (I), Liquid+hematite+dicalcium silicate(CS)(II), Liquid+CS+calcium diferrite (CF)(III) and CS+CF+calcium ferrite (CF)(IV). An intergrowth of silico-ferrite of calcium and aluminium-I (SFCA-I) and CaFeFeO was observed to form in some conditions in regions free of hematite, present in liquids solidifying at 0.5 K/s and 0.1 K/s. The sizes and shapes of microstructures were observed to systematically change with cooling rate, with a slower cooling rate typically resulting in coarser coupled microstructures and larger individual crystals. A larger proportion of coupled microstructures are observed at slower cooling rates, this appears to be related to the degree of undercooling prior to the nucleation of new phases. The equilibrium silico-ferrite of calcium (SFC) phase was not observed at any of the cooling rates investigated.

Effects of the Bulk Fe<sub>2</sub>O<sub>3</sub> Concentration on the Controlled Solidification of “Fe<sub>2</sub>O<sub>3</sub>”–CaO–SiO<sub>2</sub> Liquids in Air

The solidification of FeO-CaO-SiO liquids in air at a controlled cooling rate of 2.0 K/s for a range of FeO concentrations in the bulk has been investigated. The compositions investigated were selected such that the bulk compositions were within the hematite primary phase field and had a CaO/SiO ratio of 3.46 wt/wt. Non-equilibrium phase assemblages were formed for all bulk compositions investigated. Specifically, the silico ferrite of calcium (SFC) phase was not formed on cooling. The microstructures and proportions of the phase assemblages formed were found to vary with the FeO concentration in the bulk.

Thermodynamic optimization of the binary PbO-“Cu2O”, “Cu2O”-SiO2 and ternary PbO-“Cu2O”-SiO2 systems

Liquidus phase equilibrium data obtained in the recent study by the authors for the binary PbO–“Cu2O”, “Cu2O”–SiO2 and the ternary PbO–“Cu2O”–SiO2 systems in equilibrium with metallic Cu or Pb–Cu alloy (as a part of research program on the characterization of the multicomponent PbO–ZnO–FeO–Fe2O3–“Cu2O”–CaO–SiO2 system), combined with phase equilibrium and thermodynamic data from the literature, have been used to obtain a self-consistent set of parameters of the thermodynamic models for all phases. The modified quasichemical model is used for the liquid slag phase. From these model parameters, the optimized ternary phase diagram is back calculated. Liquidus surface with cristobalite, tridymite and quartz (SiO2), two immiscible liquids, cuprite (Cu2O), lead silicates (PbSiO3, Pb2SiO4, Pb11Si3O17, Pb5SiO7), massicot (PbO) and copper plumbite Cu2PbO2 primary phase fields has been constructed. Available experimental data are described within uncertainties. Oxygen partial pressures and distribution of lead between slag and metal have been calculated.

Phase Equilibrium Study of the CaO-SiO2-MgO-Al2O3-TiO2 System at 1300\xb0C and 1400\xb0C in Air

Due to the importance of the physicochemical properties of slag in the recovery of low-titanium ores and by-products, the equilibrium phase relationships of the CaO-MgO-Al2O3-SiO2-TiO2 system were experimentally determined using a high-temperature equilibration and quenching method at 1300°C and 1400°C. The equilibrium information was obtained by scanning electron microscope–energy dispersive x-ray spectrometer. Perovskite, spinel and pseudobrookite solid solution phases with MgO·2TiO2 and Al2O3·TiO2 end members were found to be coexisting with the liquid phase. The 1300°C and 1400°C isotherms were then constructed on a CaO-SiO2-TiO2-8 wt.% MgO-14 wt.% Al2O3 quasi-ternary section. Comparisons with predictions by Factsage and MTDATA indicated that the computational results agreed well only in the primary phase field of perovskite, while clear deviations existed within other primary phase fields. Therefore, the present results improve our knowledge about the utilization of titanium resources, and are also significant in providing novel equilibrium data for updating the related thermodynamic databases.

Liquidus Phase Diagram of CaO-SiO2-La2O3-Nb2O5 System with w(La2O3) = 15 to 25 Pct

The thermodynamic information of the CaO-SiO2-Nb2O5-La2O3 system is of great significance for the utilization of Nb and RE resources from minerals. In this article, the phase equilibria of the CaO-SiO2-Nb2O5-La2O3 system were investigated by equilibrium experiments. Twelve kinds of phase equilibria were determined, and then a spatial liquidus phase diagram was constructed. The primary phase fields of SiO2, CaNb2O6, LaNbO4, Ca2Nb2O7 and CaSi3La4O13 were determined, respectively. Meanwhile, the liquidus surfaces in the primary phase fields of SiO2, Ca2Nb2O7 and LaNbO4 were determined. Finally, the CaO-SiO2-Nb2O5-(17.5, 20, 22.5, 25 pct)La2O3 pseudo-ternary phase diagrams were also obtained. In addition to the experimental results, two theoretical rules applicable for the spatial quaternary phase diagram were also proposed to obtain indirect information on the bivariate interface between two adjacent primary phase fields. The first rule was the “tangent line rule” for judging related precipitation reaction types, and the second rule was the “highest temperature rule” for judging related temperature trends. The present work will be helpful for the utilization of Nb and RE resources and for the establishment of related thermodynamic databases.

Development of Ferrous-Calcium Silicate Slag for the Direct to Blister Copper-Making Process and the Equilibria Investigation

To mitigate possible environmental pollutions, the direct to blister (DTB) route is an important process for copper making because a single, SO2-concentrated stream can be produced. In this study, the ferrous-calcium silicate (FCS) slag system for the DTB process with a CaO content of ~ 15 wt pct was studied, as well as its equilibria with spinel, blister, and gas phases. The investigation was targeted in the spinel primary phase field with accurately controlled P(SO2) and P(O2) to be 0.4 and 1 × 10−5 atm, respectively. The equilibrium chemical compositions of various phases in the samples after high-temperature experiments were quantified using an electron probe X-ray microanalyzer (EPMA). Accordingly, the relationship between the liquidus temperature of slags and Fe/SiO2 was established, as well as that between the equilibrium “Cu2O” content and temperature. The solid solubilities in the spinel phase were also identified, including the concentrations of S, CaO, SiO2, and “Cu2O.” Last, the present results on FCS slags were compared with those on iron silicate (IRS) slags and the FactSage predictions, which provided more clues for further slag development and thermodynamic modeling.

Effect of CaO on the liquid/spinel/matte/gas equilibria in the Si–Fe–O–Cu–S system at controlled P(SO2) 0.3 and 0.6 atm

Herein the phase equilibria in the Si–Fe–Ca–O–S–Cu system in equilibrium with matte at controlled P(SO2) of 0.3 and 0.6 atm and fixed matte grade of 72 wt % Cu were experimentally investigated in the spinel primary phase field. The high-temperature equilibrations were realized in spinel substrate and the sample after quenching were characterized using Electron Probe Micro-analysis (EPMA). The effect of CaO on the liquidus temperature of slags was quantified with varying CaO content from 0 to 6 wt %. It was found that, the presence of CaO increased the liquidus temperature of slags and moreover, the increment effect got enhanced with increasing CaO content in the present range. The influence of P(SO2) was further clarified and it was found that, the equilibrium SiO2 content in the liquid phase, at the same temperature, remarkably increased with increasing P(SO2). The present study will not only deepen the understanding of the equilibration in the present liquid/spinel/matte/gas system, but also provide useful guidance for the industrial operations.

Phase Equilibrium Studies of Iron Silicate Slag in the Liquid/Spinel/White Metal/Gas System for Copper Converting Process

The phase equilibria of iron silicate slags in liquid/spinel/white metal/gas system for the copper converting process were studied, for the first time, under controlled P(SO2) 0.4 atm and P(O2) 10−6 atm in the spinel primary phase field. The liquidus temperatures of slags in the “FeO”-SiO2-“Cu2O” system were determined, and the solubilities of “Cu2O” in the spinel phase were also quantified. The results would be beneficial for the industrial copper converting operations, and thermodynamic modeling development.

Viscosity of Spinel Primary Phase Field Slags from Australian Brown Coals

The achievement of a steady rate of slag tapping in entrained-flow gasifiers relies on their continuous, smooth operation. In turn, this requires the viscosity of coal ash slags to be within 5–25 P...

Phase equilibria and liquid phase behavior of the K2O-CaO-SiO2 system for entrained flow biomass gasification

Experimental data of solid-liquid phase equilibria in the K2O-CaO-SiO2 systems vital for many technologies and industrial applications are very limited and even not available at some primary phase fields. In the present study, by using Equilibration-Quenching-Phase compositional analysis (EPMA/EDS) method, liquidus compositions in equilibrium with pure solid SiO2, CaO·SiO2, 3CaO·2SiO2, 2CaO·SiO2, K2O·6CaO·4SiO2 and K2O·2CaO·2SiO2 compounds and 2CaO·SiO2 solid solution were measured. By knowing the evaporation behavior of K2O during the equilibration process, specific initial mixtures could be selected to obtain liquidus data for targeted final equilibrium assemblages. EPMA and EDS analysis results were compared. The experimental data obtained in the present study were discussed and compared with the results from previous experimental investigations and the assessed ternary phase diagrams. Some novel experimental data of the liquid at single and double solid phase saturations were obtained in the present study and they can be used to correct and support the predictions and thermodynamic assessments of the K2O-CaO-SiO2 system. Present investigation reports liquidus projections and detailed phase relations among the phases in isothermal sections at 1000, 1100, 1200, 1300 and 1400 °C. Viscosity calculations of the liquid at different compositions between 1000 and 1400 °C also have been made. A combination of phase equilibria study and the viscosity predictions in the present investigation provides suitable temperature and ash composition regions for optimal flow properties of the slag in entrained flow biomass combustion or gasification processes.

Application of phase equilibrium studies of CaO–SiO2–Al2O3–MgO system for oxide inclusions in Si-deoxidized steels

In the steelmaking process, the compositions of the oxide inclusions could be modified by refining slags to a large extent. The chemistries of the oxide inclusions and refining slags can be described by the system CaO–SiO2–Al2O3–MgO. Phase equilibria and liquidus temperatures in this system have been experimentally investigated in the composition and temperature ranges related to the oxide inclusions and refining slags by means of high-temperature equilibration, quenching and electron probe X-ray microanalysis. Isotherms in the interval of 20 °C between 1260 and 1560 °C were determined in the primary phase fields of wollastonite, anorthite, spinel, and melilite. Effects of the mass ratio of (Al2O3+SiO2)/((Al2O3+SiO2)+(CaO + SiO2)) and MgO content on the liquidus temperatures have been discussed to assist inclusion control. To obtain the lowest liquidus temperature of Al2O3–SiO2–CaO–MgO system inclusions, refining time ought to be properly controlled.

Phase Equilibrium Studies of Iron Silicate Slag Under Direct to Blister Copper-Making Condition

Direct to blister (DTB) accounts for a significant process for copper making due to its simplified process chain and the production of a single stable SO-concentrated off-gas. In this study, the phase equilibria of iron silicate slags in the Cu-Fe-Si-S-O system at controlled atmosphere were, for the first time, experimentally investigated in the spinel primary phase field. The liquidus temperatures were quantified, including the equilibrium “CuO” content as well as the solid solutions in spinel.

Experimental Determination of the Effect of CaO and Al2O3 in Slag Systems Related to the Conversion Process of High Copper Matte Grade

The slags generated in the conventional copper conversion process are mainly composed of Cu2O–Fe2O3–SiO2 with CaO, Al2O3, and MgO compounds—in concentrations up to 10 wt %. The present work contributes to the knowledge of the conversion process, generating experimental data for the phase diagrams of the Cu2O–Fe2O3–SiO2–Al2O3 and Cu2O–Fe2O3–SiO2–CaO systems. The experiments were carried out in a tubular furnace at temperatures of 1150 °C and 1200 °C, under a condition of saturation with tridymite and spinel. Once the equilibrium was reached, the samples were immediately quenched in water. The phases in the samples were observed through a scanning electron microscope (SEM) and the elemental composition of the phases were analyzed by means of energy-dispersive X-ray spectroscopy (EDS) detectors. The addition of Al2O3 and CaO into the Cu2O–Fe2O3–SiO2 system resulted in an appreciable displacement of the liquidus lines, corresponding to an expansion of the liquid in the tridymite primary phase field. The addition of CaO and Al2O3 combined was evaluated on industrial slags and from samples obtained in a Peirce–Smith furnace, with increasing amounts of CaO in the flux.

Controlled Solidification of Liquids Within the SFC Primary Phase Field of the “Fe2O3”-CaO-SiO2 System in Air

To provide fundamental information on the phases and microstructures formed during sintering, a liquid with a bulk composition within the silico ferrite of calcium (SFC) primary phase field in the ternary “Fe2O3”-CaO-SiO2 system in air was solidified at a controlled rate. Samples of a bulk composition with a CaO/SiO2 ratio of 4.00 and 69.24 wt pct Fe2O3, were cooled from 1623 K (1350 °C) at 2 K/s, with samples quenched at temperatures between 1513 K (1240 °C) to 1453 K (1180 °C). The silico ferrite of calcium and aluminium I (SFCA-I) and Ca7.2Fe 0.8 2+ Fe303+O53 phases were observed to form an intergrowth (‘SFC-I’) rather than the anticipated SFC phase. Solidification was found to occur in three stages, Liquid + ‘SFC-I’, Liquid + ‘SFC-I’ + C2S + CF2, and C2S + CF2 + CF, where C2S denotes dicalcium silicate, CF denotes calcium ferrite and CF2 denotes calcium diferrite. The phases formed and the solidification sequence differ from those predicted under equilibrium and Scheil–Gulliver Cooling. Although not directly applicable to industrial operations, this research clearly shows that the formation of both the SFCA and SFCA-I phase in iron ore sinters is controlled by kinetic processes rather than equilibrium conditions.

Experimental Liquidus Studies of the Binary Pb-Cu-O and Ternary Pb-Cu-Si-O Systems in Equilibrium with Metallic Pb-Cu Alloys

Phase equilibria of the Pb-Cu-Si-O system have been investigated in the range 933-1938 K (660-1665 °C) for oxide liquid (slag) in equilibrium with solid Cu metal, liquid Pb-Cu alloy, or both solid and liquid metals, and solid oxide phases: (a) quartz, tridymite, cristobalite (SiO2); (b) cuprite (Cu2O); (c) lead silicates (PbSiO3, Pb2SiO4, Pb11Si3O17); (d) lead oxide (massicot, PbO); and (e) copper plumbite (Cu2PbO2). High-temperature equilibration on silica or copper substrates, followed by quenching and direct measurement of Pb, Cu and Si concentrations in the liquid and solid phases with the electron probe x-ray microanalysis (EPMA) has been used to accurately characterize the system in equilibrium with Cu or Pb-Cu metal. All results are projected onto the PbO-“CuO0.5”-SiO2 plane for presentation purposes. The present study is a continuation of the previous investigation of this system by the authors in a part of the silica and cuprite primary phase fields. Present data were later used to develop the thermodynamic models for all phases in this system.

Viscosity of slags with solids: The effect of solids morphology and concentration

The viscosity of slags containing crystallized solids is always of great interest for materials scientists working in high-temperature slag processing, as it strongly affects slag flow behavior. Different slag characteristics, such as liquid phase composition, concentration of solid phases, and crystal morphology, have different impacts on the slag viscosity. However, the effect of crystal shape and size is hard to demonstrate directly in high-temperature slag experiments, because other slag characteristics may also change. The present work provides experimental results for the viscosity of two slags from the olivine primary phase field, which have slag assemblies with different olivine shapes and sizes, while the other slag characteristics remain the same. The results clearly demonstrate that the crystal morphology has a pronounced effect on the slag viscosity. A detailed analysis of the slag microstructure also provides insight into their Newtonian and non-Newtonian flow behavior. The experimental results were used to evaluate different models of the effective viscosity of classical/archetypal suspensions. Based on this evaluation, we suggest that elongated olivine crystals, which are randomly oriented in the melt at rest and at lower rotation speeds, can become aligned to shear at higher rotation speeds. The Powell model adequately describes such a rheological behavior of slags containing elongated olivine crystals, while the Krieger–Dougherty model is applicable to slags with polyhedral olivine crystals, with the intrinsic viscosity being close to theoretical values obtained for cuboids and prisms of various sizes.The viscosity of slags containing crystallized solids is always of great interest for materials scientists working in high-temperature slag processing, as it strongly affects slag flow behavior. Different slag characteristics, such as liquid phase composition, concentration of solid phases, and crystal morphology, have different impacts on the slag viscosity. However, the effect of crystal shape and size is hard to demonstrate directly in high-temperature slag experiments, because other slag characteristics may also change. The present work provides experimental results for the viscosity of two slags from the olivine primary phase field, which have slag assemblies with different olivine shapes and sizes, while the other slag characteristics remain the same. The results clearly demonstrate that the crystal morphology has a pronounced effect on the slag viscosity. A detailed analysis of the slag microstructure also provides insight into their Newtonian and non-Newtonian flow behavior. The experimental resul...

Effect of H2 addition on process of primary slag formation in cohesive zone

Based on the technology of gas-injection blast furnace (BF), the characteristics of primary slag formation with H2 addition were researched. The results indicate that, compared with traditional BF, the primary melt is formed at a lower temperature, which promotes the deformation of the solid burden particles. With the increase in temperature and H2 content, the quantity of formed melt containing FeO decreases sharply, corresponding to the crystallization of solid 2CaO·SiO2 during reduction. A wider softening range and narrower melting zone could be found in the gas-injection BF with a higher reduction potential. The permeability of burden layer is ameliorated as a result of decreased melt quantity. The influence of H2 on the high-temperature properties of burden is not so conspicuous when the H2 addition is from 10 to 15 vol.% against 5 to 10 vol.%. What is more, the slag shows a better liquidity with the decrease in basicity, owing to the transformation of melt composition from a primary phase field with high melting point to that with low melting point. The process of slag forming in gas-injection BF is characterized by earlier melt formation, less primary slag, higher melting temperature, better permeability and better liquidity, and the phase compositions of primary slag are close to those of final slag.

Experimental liquidus studies of the Zn–Fe–Si–O system in air

AbstractThe liquidus of the ternary system ZnO–“FeO1.5”–SiO2 in air has been experimentally investigated in the tridymite and cristobalite, spinel, and zincite primary phase fields in the temperature range 1623–1923 K (1350–1650°C). Slags containing up to 65 mol.% “FeO1.5” have been studied for the first time. The slag–spinel–zincite eutectic in the binary ZnO–“FeO1.5” system in air has been estimated by extrapolation of the low-SiO2 part of the ternary system to x(SiO2) = 0. High-temperature equilibration on primary phase (silica) or inert metal (platinum) substrates, followed by quenching and direct measurement of Zn, Fe and Si concentrations in the equilibrium phases with electron probe X-ray microanalysis has been used to accurately characterize the system in equilibrium with air. The discrepancies of the previous experimental work in this system have been resolved. The obtained data have been used to reoptimise the existing thermodynamic model.

Phase equilibria in low basicity region of CaO-SiO2-Nb2O5-(5 wt%, 10 wt%, 15 wt%) La2O3 system

The lack of thermodynamic information, such as primary phase fields and liquidus temperatures, in the CaO-SiO2-Nb2O5-La2O3 quaternary system phase diagram has restricted the comprehensive utilization of the niobium (Nb) and rare earth (RE) resources. In this work, the phase equilibria in low basicity region (w(CaO)/w(SiO2)<1) of CaO-SiO2-Nb2O5-(0–15 wt%)La2O3 system at 1373–1873 K were experimentally studied by thermodynamic equilibrium experiment, and then, the results were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectrometry (EDS). Additionally, an optimized method was proposed to process the compositions of equilibrium liquid phases at different temperatures. According to the experimental results, the univariate line between CaNb2O6, SiO2 and LaNbO4 primary phase fields, interface between CaNb2O6 and SiO2 primary phase fields and isothermal liquidus surfaces in SiO2 primary phase field were determined. Finally, the spatial phase diagram of CaO-SiO2-Nb2O5-La2O3 within specific region was constructed, and furthermore, the phase diagram was also presented in CaO-SiO2-Nb2O5 pseudo-ternary system with w(La2O3) = 5 wt%, 10 wt% and 15 wt%. The research results have guiding significance for the improvement of related phase diagram and the comprehensive utilization of Nb and RE resources.