Effects of the Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> Content on the Viscosity of CaO-SiO<Subscript>2</Subscript>-10 Pct Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> Quaternary Slag

The present study experimentally investigates the effect of Cr₂O₃ on the viscosity of molten slags. The viscosities of CaO-SiO₂-10 pct Al₂O₃-Cr₂O₃ quaternary slags with two different binary basicities (R, basic slag with R = 1.2 and acidic slag with R = 0.8) were measured by the rotating cylindrical method from 1813 K to 1953 K (1540 °C to 1680 °C). The results showed that the viscosity of both types of slag decreased as the Cr₂O₃ content increased, but the viscosity of acidic slags exhibited a greater decrease. The slags showed good Newtonian behavior at such high temperatures. Cr₂O₃ could act as a network modifier to simplify the Si-O-Si tetrahedral structure, as verified by the Raman spectral analysis, which was consistent with the decreasing trend of viscosity. The activation energy of viscous flow decreased slightly with increasing Cr₂O₃, but increasing the basicity seemed to be more effective in decreasing the viscosity than adding Cr₂O₃.     

Effects of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and CaO/SiO<Subscript>2</Subscript> Ratio on Phase Equilbria in the ZnO-“FeO”-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-CaO-SiO<Subscript>2</Subscript> System in Equilibrium with Metallic Iron

The phase equilibria and liquidus temperatures in the ZnO-“FeO”-Al₂O₃-CaO-SiO₂ system in equilibrium with metallic iron have been determined experimentally in the temperature range 1383 K to 1573 K (1150 °C to 1300 °C). The experimental conditions were selected to characterize lead blast furnace and imperial smelting furnace slags. The results are presented in a form of pseudoternary sections ZnO-“FeO”-(Al₂O₃ + CaO + SiO₂) with fixed CaO/SiO₂ and (CaO + SiO₂)/Al₂O₃ ratios. It was found that wustite and spinel are the major primary phases in the composition range investigated. Effects of Al₂O₃ concentration as well as the CaO/SiO₂ ratio on the primary phase field, the liquidus temperature, and the partitioning of ZnO between liquid and solid phases have been discussed for zinc-containing slags.     

Phase Equilibria in the System “FeO”-CaO-SiO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-MgO at Different CaO/SiO<Subscript>2</Subscript> Ratios

The “FeO”-containing slags play an important role in the operation of an ironmaking blast furnace (BF), in particular the primary slags such as the system “FeO”-CaO-SiO₂-Al₂O₃-2 mass pct MgO with CaO/SiO₂ weight ratios of 1.3, 1.5, and 1.8 saturated with metallic iron. To investigate the characteristics of such a slag system and its behavior in BF, the phase equilibria and liquidus temperatures in the slag system have been experimentally determined using the high-temperature equilibration and quenching technique followed by an electron probe X-ray microanalysis (EPMA). Isotherms between 1553 K and 1603 K (1280 °C and 1330 °C) were determined in the primary phase fields of dicalcium silicate, melilite, spinel, and monoxide [(Mg,Fe²⁺)O]. Pseudo-ternary phase diagrams of (CaO + SiO₂)-Al₂O₃-“FeO” with a fixed MgO concentration at 2 mass pct and at CaO/SiO₂ ratios of 1.3, 1.5, and 1.8 have been discussed, respectively, simplifying the complexity of the slag system for easy understanding and applying in BF operation. It was found that the liquidus temperatures increase in melilite and spinel primary phase fields, but decrease in dicalcium silicate and monoxide primary phase fields with increasing Al₂O₃/(CaO + SiO₂) ratio. In addition, the liquidus temperatures decrease with increasing “FeO” concentration in dicalcium silicate and melilite primary phase fields, while showing an increasing trend in the spinel and monoxide primary phase fields. The data resulted from this study can be used to improve and optimize currently available database of thermodynamic models used in FactSage.     

Liquidus Temperatures in the “Cu<Subscript>2</Subscript>O”-FeO-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-CaO System at Molten Metallic Copper Saturation

Calcium ferrite slags, which are represented by the “Cu₂O”-FeO-Fe₂O₃-CaO system at copper saturation, have been applied successfully to existing copper-converting processes. Because of the industrial importance of this system, the characterization of the effects of oxygen partial pressure and silica on the phase equilibria is necessary to improve the control of process parameters, which include fluxing and operating temperatures. In the current study, experimental methods, which use the equilibration/quenching/electron probe X-ray microanalysis (EPMA) techniques with primary phase substrate support, were subsequently developed to incorporate fixed oxygen partial pressure experiments. Experiments were carried out at 1200 °C and 1250 °C both with and without silica additions; both liquidus and solidus data were reported for the primary phase field of spinel and dicalcium ferrite between the oxygen partial pressures of 10^−5.0 and 10^−6.5 atm. The analyzed compositions of the liquid and solid phases are used to construct the phase diagram of the pseudoternary “Cu₂O”-“Fe₂O₃”-CaO system in equilibrium with metallic copper at fixed oxygen partial pressures and with additions of silica. The maximum solubility of silica within the liquid slag phase, prior to dicalcium silicate precipitation, was measured at specific conditions. Two empirical equations used for the calculation of the copper oxide concentration in calcium ferrite slag are evaluated with the new experimental data defined in the current study.     

Effect of MgO on Liquidus Temperatures in the ZnO-“FeO”-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-CaO-SiO<Subscript>2</Subscript>-MgO System in Equilibrium with Metallic Iron

The phase equilibria in the ZnO-“FeO”-Al₂O₃-CaO-SiO₂-MgO system have been determined experimentally in equilibrium with metallic iron. Synthetic slags were equilibrated at a high temperature, quenched, and then the compositions of the phases in equilibrium were measured using electron probe X-ray microanalysis. Pseudoternary sections of the form ZnO-“FeO”-(Al₂O₃ + CaO + SiO₂) for CaO/SiO₂ = 0.71, (CaO + SiO₂)/Al₂O₃ = 5 and fixed MgO concentrations of 2, 4, and 6 wt pct have been constructed. Wustite (Fe²⁺,Mg,Zn)O and spinel (Fe²⁺,Mg,Zn)O·(Al,Fe³⁺)₂O₃ are the major primary phases in the temperature and composition ranges investigated. The liquidus temperatures are increased by 140 K in the wustite primary phase field and by 70 K in the spinel primary phase field with the addition of 6 wt pct MgO in the slag. The partitioning of MgO and ZnO between the solid and liquid phases has been discussed.     

Effect of Sulfur on Liquidus Temperatures in the ZnO-“FeO”-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-CaO-SiO<Subscript>2</Subscript>-S System in Equilibrium with Metallic Iron

The phase equilibria in the ZnO-“FeO”-Al₂O₃-CaO-SiO₂-S system have been determined experimentally in equilibrium with metallic iron. A pseudoternary section of the form ZnO-“FeO”-(Al₂O₃+CaO+SiO₂) for CaO/SiO₂ = 0.71 (weight), (CaO+SiO₂)/Al₂O₃ = 5.0 (weight), and fixed 2.0 wt pct S concentration has been constructed. It was found that the addition of 2.0 wt pct S to the liquid extends the spinel primary phase field significantly and decreases the size of the wustite primary phase field. The liquidus temperature in the wustite primary phase field is decreased by approximately 80 K and the liquidus temperature in the spinel primary phase field is decreased by approximately 10 K with addition of 2.0 wt pct S in the composition range investigated. It was also found that iron-zinc sulfides are present in some samples in the spinel primary phase field, which are matte appearing at low zinc concentrations and sphalerite (Zn,Fe)S at higher zinc concentrations. The presence of sulfur in the slag has a minor effect on the partitioning of ZnO between the wustite and liquid phases but no effect on the partitioning of ZnO between the spinel and liquid phases.     

Interfacial Tension in the CaO-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript>-(MgO) Liquid Slag–Solid Oxide Systems

Interfacial phenomenon is critical in metal processing and refining. While it is known to be important, there are little data available for key oxide systems in the literature. In this study, the interfacial tension (σ _LS) of liquid slag on solid oxides (alumina, spinel, and calcium aluminate), for a range of slags in the CaO-Al₂O₃-SiO₂-(MgO) system at 1773 K (1500 °C), has been evaluated. The results show that basic ladle-type slags exhibit lower σ _LS with oxide phases examined compared to that of acid tundish-type slags. Also, within the slag types (acid and base), σ _LS was observed to decrease with increasing slag basicity. A correlation between σ _LS and slag structure was observed, i.e., σ _LS was found to decrease linearly with increasing of slag optical basicity (Λ) and decrease logarithmically with decreasing of slag viscosity from acid to base slags. This indicated a higher σ _LS as the ions in the slag become larger and more complex. Through a work of adhesion (W) analysis, it was shown that basic ladle slags with lower σ _LS result in a greater W, i.e., form a stronger bond with the solid oxide phases examined. This indicates that all other factors being equal, the efficiency of inclusion removal from steel of inclusions of similar phase to these solid oxides would be greater.     

Liquidus Temperatures in the “Cu<Subscript>2</Subscript>O”-FeO-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-CaO-SiO<Subscript>2</Subscript> System at Metallic Copper Saturation,at Fixed Oxygen Partial Pressures,and in Equilibrium with Spinel or Dicalcium Ferrite at 1200 °C and 1250 °C

Calcium ferrite slags, which are represented by the “Cu₂O”-FeO-Fe₂O₃-CaO system at copper saturation, have been applied successfully to existing copper-converting processes. Because of the industrial importance of this system, the characterization of the effects of oxygen partial pressure and silica on the phase equilibria is necessary to improve the control of process parameters, which include fluxing and operating temperatures. In the current study, experimental methods, which use the equilibration/quenching/electron probe X-ray microanalysis (EPMA) techniques with primary phase substrate support, were subsequently developed to incorporate fixed oxygen partial pressure experiments. Experiments were carried out at 1200 °C and 1250 °C both with and without silica additions; both liquidus and solidus data were reported for the primary phase field of spinel and dicalcium ferrite between the oxygen partial pressures of 10^?5.0 and 10^?6.5 atm. The analyzed compositions of the liquid and solid phases are used to construct the phase diagram of the pseudoternary “Cu₂O”-“Fe₂O₃”-CaO system in equilibrium with metallic copper at fixed oxygen partial pressures and with additions of silica. The maximum solubility of silica within the liquid slag phase, prior to dicalcium silicate precipitation, was measured at specific conditions. Two empirical equations used for the calculation of the copper oxide concentration in calcium ferrite slag are evaluated with the new experimental data defined in the current study.     

Stabilization of the fluorite phase in the ZrO<Subscript>2</Subscript>–Y<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The calculated and experimental vertical ZrO₂–Y₂O₃ sections of the Zr–Y–O system are compared to find the region of a stable fluorite structure of yttrium-stabilized zirconia (YSZ). X-ray diffraction (XRD) and Raman scattering are used to study the crystal and local structures of mixed oxide 0.82ZrO₂ · 0.18Y₂O₃ (18YSZ) powders prepared by isothermal annealing of a precursor precipitated from a salt solution. The formation of a fluorite-type fcc structure (space group \(Fm\overline 3 m\)) in the powders is detected by XRD. Raman scattering study of the local structure of the cubic 18YSZ powders revealed traces of the tetragonal phase in them.     

Thermodynamic Modeling of Metal Desulfurization with Boron-Containing Slags of the CaO–SiO<Subscript>2</Subscript>–MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript> System

In thermodynamic modeling of the desulfurization of steel by CaO–SiO₂–MgO–Al₂O₃–B₂O₃ slag on the basis of HSC 6.12 Chemistry software (Outokumpu), the influence of the temperature (1500–1700°C), the slag basicity (2–5), and the B₂O₃ content (1–4%)1 on the desulfurization is analyzed. It is found that the sulfur content is reduced with increase in the temperature from 1500 to 1700°C, within the given range of slag basicity. At 1600°C, the sulfur content in the metal is 0.0052% for slag of basicity 2; at 1650°C, by contrast, its content is 0.0048%. Increase in slag basicity from 2 to 5 improves the desulfurization, which increases from 80.7 to 98.7% at 1600°C. If the B₂O₃ content in the slag rises, desulfurization is impaired. At 1600°C, the sulfur content in the metal may be reduced to 0.0052 and 0.0098% when using slag of basicity 2 with 1 and 4% B₂O₃, respectively; in the same conditions but with slag of basicity 5, the corresponding values are 0.00036 and 0.00088%, respectively. Note that desulfurization is better for slag without B₂O₃. According to thermodynamic modeling, metal with 0.0039 and 0.00019% S is obtained at 1600°C when using slag of basicity 2 and 5, respectively, that contains no B₂O₃. The results obtained by thermodynamic modeling for the desulfurization of metal by CaO–SiO₂–MgO–Al₂O₃–B₂O₃ slag of basicity 2–5 in the range 1500–1700°C are consistent with experimental data and may be used in improving the desulfurization of steel by slag that contains boron.     

Phase Equilibria Studies in the System ZnO-“FeO”-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-CaO-SiO<Subscript>2</Subscript> Relevant to Imperial Smelting Furnace Slags: Part I

The phase equilibria and the liquidus temperatures in the system ZnO-“FeO”-Al₂O₃-CaO-SiO₂ have been determined experimentally in equilibrium with metallic iron. Specifically, the effects of Al₂O₃ concentrations in Imperial Smelting Furnace slags are identified, and the results are presented in the form of pseudo-ternary sections ZnO-“FeO”-(Al₂O₃ + CaO + SiO₂) in which CaO/SiO₂ = 0.93 and (CaO + SiO₂)/Al₂O₃ = 5.0 and 3.5, respectively. It was found that, in the presence of Al₂O₃, the spinel phase is formed, the spinel primary phase field expands, and the wustite and melilite primary phase fields are reduced in size with an increasing Al₂O₃ concentration. The implications of the findings to industrial practice are discussed.     

Phase Equilibria Studies in the System ZnO-“FeO”-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-CaO-SiO<Subscript>2</Subscript> Relevant to Imperial Smelting Furnace Slags: Part II

The phase equilibria and the liquidus temperatures in the system ZnO-“FeO”-Al₂O₃-CaO-SiO₂ have been determined experimentally in equilibrium with metallic iron. Specifically, the effects of Al₂O₃ concentrations in Imperial Smelting Furnace slags are identified, and the results are presented in the form of pseudo-ternary sections ZnO-“FeO”-(Al₂O₃ + CaO + SiO₂) in which CaO/SiO₂ = 0.93 and (CaO + SiO₂)/Al₂O₃ = 5.0 and 3.5, respectively. It was found that, in the presence of Al₂O₃, the spinel phase is formed, the spinel primary phase field expands, and the wustite and melilite primary phase fields are reduced in size with an increasing Al₂O₃ concentration. The implications of the findings to industrial practice are discussed.     

A Study of the Viscous Properties with NaF Additions in the CaO-SiO<Subscript>2</Subscript>-12 mass pct Na<Subscript>2</Subscript>O Based Slags

The viscous behavior of the CaO-SiO₂-12 mass pct Na₂O based slag system with various concentrations of NaF has been studied using the rotating spindle method. NaF additions decreased the viscosity by interacting with bridged oxygens in the complex silicates and depolymerizing the network structure of the molten slag. NaF was particularly effective at lowering the viscosity in small amounts, but beyond 8 mass pct NaF, the effect was not as pronounced. A comparison between additions of NaF and CaF₂ revealed NaF to be more effective at decreasing the viscosity for 1523 K and 1573 K (1250 °C and 1300 °C). From the slopes of the Arrhenius relationship for viscosity, the activation energy of viscous flow was found to be between 128 kJ/mol to 115 kJ/mol, which were lower than the values for the same amount of CaF₂ additions. Both a temperature effect and a compositional effect on the molten slag structure and subsequently the viscous behavior were observed. The Fourier transformed infrared (FTIR) spectra taken for the CaO-SiO₂-12 mass pct Na₂O-8 mass pct NaF slag samples quenched from 1623 K to 1773 K (1350 °C to 1500 °C) revealed that the temperature effect on the viscosity was observed at temperatures below 1673 K (1400 °C).     

Kinetics of Transformation of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> to MgO·Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Spinel Inclusions in Mg-Containing Steel

During ladle furnace refining, initial Al₂O₃ inclusions generally transform into MgO·Al₂O₃ spinel inclusions; these generated spinel inclusions consequently deteriorate the product quality. In this study, the transformation from Al₂O₃ to MgO·Al₂O₃ was investigated by immersing an Al₂O₃ rod into molten steel, which was in equilibrium with both MgO and MgO·Al₂O₃ spinel-saturated slag. A spinel layer, with a thickness of 4 μm, was generated on the Al₂O₃ rod surface just 10 s after its immersion at 1873 K (1600 °C). The thickness of the formed spinel layer increased with the immersion period and temperature. Moreover, the MgO content of the generated spinel layer also increased with the immersion period. In this study, the chemical reaction rate at 1873 K (1600 °C) was assumed to be sufficiently high, and only diffusion was considered as a rate-controlling step for this transformation. By evaluating the activation energy, MgO diffusion in the generated spinel layer was found to be the rate-controlling step. In addition, this estimation was confirmed by observing the Mg and Al concentration gradients in the generated spinel layer. The results of this study suggest that the MgO diffusion in the spinel inclusions plays a substantial role with regard to their formation kinetics.     

A new experimental technique for determinations of the activities of P<Subscript>2</Subscript>O<Subscript>5</Subscript> and Fe<Subscript>x</Subscript>O—the system CaO-P<Subscript>2</Subscript>O<Subscript>5</Subscript>-Fe<Subscript>x</Subscript>O

An experimental technique was applied for simultaneous determinations of the activities of P₂O₅ and Fe_xO in slags. With this technique, phosphorus-containing liquid copper was heated inside an iron crucible at temperatures below 1600 K. When copper is melted, the iron crucible dissolves into liquid copper, to a small extent, to form ternary {Cu-Fe-P} liquid alloy, while 〈Cu-Fe-P〉 solid solutions are formed on the inner wall of the iron crucible. Slags containing tri-calcium phosphate were then brought into equilibrium with {Cu-Fe-P} liquid alloy. By measuring the equilibrium oxygen partial pressures with the aid of a zirconia electrolyte cell, activities of P₂O₅ and Fe_xO were obtainable. Between 1553 and 1593 K, the P₂O₅ activities could be expressed as

Construction of viscosity diagrams for CaO–SiO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–8% MgO–4% B<Subscript>2</Subscript>O<Subscript>3</Subscript> slags by the simplex lattice method

The simplex lattice method of planning experiments is used to study the viscosities of CaO–SiO₂–Al₂O₃–8% MgO–4% B₂O₃ slags in a wide chemical composition range. For each viscosity, we developed an adequate mathematical model in the form of a reduced third-order polynomial. The results of mathematical simulation are presented in composition–viscosity diagrams. Composition regions with a high fluidity of slags, the viscosities of which are 0.8–1.2 Pa s in the temperature range 1500–1600°C, are indicated in the diagrams.     

Deformation Behavior of Inclusion System CaO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> with Different Compositions During Hot Rolling Processes

The present study was aimed at exploring the influence of compositions on the deformation behavior of inclusion system CaO–Al₂O₃–SiO₂, during hot rolling processes. The plastic deformations of four inclusions with different compositions, at different rolling temperatures (800, 850, 900, 982 and 1100 °C), were simulated using a finite element model. The equivalent plastic strain distributions and the shapes of the inclusions after rolling were obtained via the model. The influences of rolling temperature, flow stresses of inclusions and matrix, reduction, etc., on the void length and the deformation degree of inclusions were analyzed. The critical temperatures of the four inclusions during hot rolling were different. No voids occurred above the critical temperature. Voids only occurred along the length direction, but not the width and thickness directions, below the critical temperature. Low rolling temperatures led to long void length and small deformation of inclusions. The inclusion with high SiO₂ content had a high critical temperature and a high risk of void formation. Results generated by the experiment on deformation behaviors of inclusions with different SiO₂ content, were in good agreement with the simulated results.