Fundamental thermodynamic aspects of the CaO–Al2O3–SiO2 system

The most important metallurgical effects of ladle treatment of aluminium-killed steels with calcium, are associated with the modification of alumina inclusion. For the development of the deoxidation-control model for inclusions, the thermodynamic slag model, based on the Gibbs energy minimization and modelling approaches postulated from J. Hastie et al., was used to calculate component oxide activities in the system CaO–Al₂O₃ and part of systems 3CaO · Al₂O₃ – SiO₂, 12 CaO · 7Al₂O₃ – SiO₂ and CaO · Al₂O₃ – SiO₂ at 1600°C.     

Dephosphorization equilibria between pure molten iron and CaO-saturated FeOn–CaO–SiO2 and FeOn–CaO–Al2O3 slags

Metal-slag refining reactions have been investigated to determine dephosphorization equilibria in steelmaking using CaO-saturated slags, low in P₂O₅–content, based on the systems FeO_n–CaO–SiO₂ and FeO_n–CaO–Al₂O₃. Slag compositions have been optimized with respect to basicity and oxygen potential to achieve maximum partition ratios wt.%(P₂O₅)/wt.%[P] and minimum phosphorus contents in pure molten iron at 1550, 1600 and 1700°C. Both slag systems prove to be effective dephosphorizers. Optimal slag compositions are around 10 wt.% SiO₂ near the CaO–3CaO · SiO₂ double saturation in the case of FeO_n–CaO–SiO₂ slags and at Al₂O₃ contents tending to zero in the case of FeO_n–CaO–Al₂O₃ slags. Attempts were also made to present phosphate capacities C_PO4^3?, fractions of free oxygen ions x_O^2? and theoretical optical basicities Λ as a function of the FeO_n content of slags.     

Gleichgewichte zwischen flüssigem Eisen und gesättigten Schlacken des Systems CaO–FeO–MnO–SiO2 bei 1600 °C unter Berücksichtigung der Schwefelverteilung

Tiegelversuche im Tammannofen bei 1600 °C zur Ermittlung der Schlackengleichgewichte. Zusammensetzung und Aufbau der Versuchsschlacken bei Sättigung an Dikalziumsilikat, Trikalziumsilikat und Kalkmischkristallen. Zusammensetzung der Kalkmischkristalle. Darstellung des Systems CaO–FeO–MnO–SiO₂ bei 1600 °C. Sauerstoffgehalt des flüssigen Eisens. Verteilung des Mangans und des Schwefels zwischen Schlacke und Eisen. Schlußfolgerungen zum Einfluß von Manganoxyd im System CaO–FeO–SiO₂.     

Verlauf der Kalksättigung im System FeO–Fe2O3–CaO–SiO2–P2O5–MgO–MnO beim Gleichgewicht mit einer Eisenschmelze

Durch Auswertung zahlreicher, in Laborversuchen bei 1580–1650°C erschmolzener kalkgesättigter Schlacken mit gleichzeitigen Gehalten an FeO, Fe₂O₃, SiO₂, P₂O₅, MgO und MnO ist die aus metallurgischen Gründen angestrebte Kalksättigung komplexer Schlacken der Stahlerzeugung für 1600°C neu festgelegt worden. Ausgehend von der Beschreibung der Schlackenzusammensetzungen in den Grundsystemen CaO′–FeO′_n–SiO′₂ und CaO′–FeO′_n–P₂O₅ wird dabei die Beeinflussung der Kalksättigung durch MgO und MnO sowie qualitativ durch dreiwertige Eisenanteile angegeben. Die untersuchten Schlacken lassen in beiden Grundsystemen einen stetigen, von hohen FeO′_n-Gehalten bis hinunter zu Massengehalten von 8% gültigen Verlauf der Kalksättigung ohne einsetzende Dicalciumsilikat- bzw. Tetracalciumphosphatausscheidung erkennen. Durch die bewertende Umrechnung der P₂O₅-, MgO- und MnO-Gehalte wird eine nahezu alle Komponenten erfassende Darstellung komplexer kalkgesättigter Schlacken in einem einfachen Quasidreistoffsystem CaO^*–FeO^*-SiO^*₂ erreicht und die resultierende, dicht belegte Kalksättigungslinie mathematisch beschrieben. Der Einfluß von Al₂O₃-Gehalten auf die Kalksättigung wird abgeschätzt sowie das maximale Lösungsvermögen der kalkgesättigten Schlacke für MgO durch die Berechnung der Schnittlinie zwischen der Kalk- und der Magnesiowüstitsättigungsfläche festgelegt. Ein Ansatz zur Erfassung des Temperatureinflusses auf die Kalksättigung erlaubt schließlich eine vollständige mathematische Beschreibung der Kalksättigungsgehalte im System CaO^*–FeO^*_n–SiO₂ sowohl in Abhängigkeit von der Schlackenzusammensetzung als auch von der Temperatur. Damit können die Kalkgehalte komplexer Betriebsschlacken unterschiedlicher Temperatur mit den erreichbaren Gleichgewichtssättigungswerten verglichen und die Sättigungszustände der Schlacken nach Berechnung eines Sättigungsgrades S_CaO beurteilt werden.     

Thermodynamics of Composition Control of CaO‐MnO‐Al2O3‐SiO2 Inclusions in Tire Cord Steel

The effect of oxide component content on the low melting point zone (simplified as LMP) in the CaO‐MnO‐Al₂O₃‐SiO₂ system has been analysed by FactSage. The contents of [Si], [Mn], [O] and [Al] in liquid steel which are in equilibrium with the LMP inclusions in the CaO‐MnO‐Al₂O₃‐SiO₂ system have been calculated. The results show that the CaO‐MnO‐Al₂O₃‐SiO₂ system has the largest LMP zone (below 1400°C) when the Al₂O₃ content is 20% or the CaO content is 15%, and that the LMP zone becomes wider with increase in SiO₂ and MnO contents (within the range of 0~25%). To obtain LMP inclusions (below 1400°C), [Si] and [Mn] can be controlled within a wide range, but [Al] and [O] must be controlled within the range of 0.5~5 ppm and 50~120 ppm, respectively.     

A Thermodynamic Model for Prediction of Iron Oxide Activity in Some FeO‐Containing Slag Systems

A thermodynamic model for calculating the mass action concentrations of structural units in CaO–SiO₂–MgO–FeO–MnO–Al₂O₃–CaF₂ slags, i.e., the IMCT‐N_i model, has been developed based on the ion and molecule coexistence theory (IMCT). The calculated comprehensive mass action concentration of iron oxides $N_{{\rm Fe}_{t} {\rm O}} $ has been compared with the reported activity of iron oxide $a_{{\rm Fe}_{t} {\rm O}} $ in 14 FeO‐containing slag systems from literatures. The good agreement between the calculated $N_{{\rm Fe}_{t} {\rm O}} $ and reported $a_{{\rm Fe}_{t} {\rm O}} $ indicates that the developed IMCT‐N_i model can be successfully applied to predict the activity of iron oxide $a_{{\rm Fe}_{t} {\rm O}} $ as well as the slag oxidation ability of CaO–FeO (s1), SiO₂–FeO (s2), CaO–SiO₂–FeO (s3), CaO–FeO–Al₂O₃ (s4), SiO₂–MgO–FeO (s5), SiO₂–FeO–Al₂O₃ (s6), CaO–SiO₂–FeO–Al₂O₃ (s7), CaO–SiO₂–MgO–FeO–Al₂O₃ (s8), SiO₂–FeO–MnO (s9), SiO₂–FeO–MnO–Al₂O₃ (s10), FeO–MnO (s11), FeO–MnO–Al₂O₃ (s12), CaO–FeO–CaF₂ (s13), and CaO–SiO₂–FeO–CaF₂ slags (s14) in a temperature range of 1473–1973 K.     

Activity of MnO in MnO‐CaO‐MgO‐SiO2‐Al2O3 Slags at 1500 °C

A thermodynamic study was made on the MnO‐CaO‐MgO‐SiO₂‐Al₂O₃ slags that are typical of the production of ferromanganese in submerged arc furnaces. The Al₂O₃ content of the slags was kept constant at 5 per cent by mass. The activity‐composition relationship in Pt‐Mn binary alloys were re‐determined for calibration purposes at 1300, 1400 and 1500°C and po₂ values between 5.40×10^?6 and 4.54×10^?13 atm. A linear regression equation was derived to predict the activity coefficients of manganese, in Pt‐Mn alloys at 1500°C. The effect of concentration, basicity ratio and CaO‐to‐MgO ratio on MnO activities in above mentioned complex slags was investigated at 1500 °C and at two different po₂ values of 4.76×10^?7 and 5.80×10^?8 atm. It was found that a_Mno values increase with increasing MnO, and tend to increase with an increasing CaO‐to‐MgO ratio. The a_MnO values also increase with increasing basicity ratio. The activity coefficient of MnO increases with an increase in its mole fraction in the slag. Quadratic multivariable regression model equations which represent the activity data successfully and which can be used to predict the MnO activities in the compositional range of this study were developed. The MnO activity data was interpreted in terms of a slag model which describes the thermodynamic properties of the slag successfully.     

Das Hochofenschlackensystem Al2O3–CaO–MgO–SiO2 bei 1600, 1500 und 1400 °C

Beschreibung von Sättigungsflächen im System Al₂O₃–CaO–MgO–SiO₂ durch isotherme Schnitte im Konzentrationsbereich der Hochofenschlacken für 1600, 1500 und 1400 °C. Räumliche Tetraederdarstellungen und quantitative Grundrißprojektionen nach Überprüfung und Neufestlegung der Grenzflächen des homogenen Schlackenraumes durch Sättigungsschmelzen. Vollständige Darstellung des Grundsystems Al₂O₃–CaO–SiO₂ für 1600, 1500 und 1400 °C. Beispiel für die Anwendung der quantitativen Grundrißprojektion zur Einschätzung der Heterogenität von flüssigen Hochofenschlacken.     

Atomizing molten metals — a review

Abstract

Data from the literature were used to construct activity diagrams for the systems Mn–Fe–C, MnO–CaO–SiO₂ and CaO–Al₂O₃–SiO₂ with 10% MnO. Assuming that the reduction temperature is close to slag melting point, the MnO content required to obtain a 75% Mn alloy can be found. One can also calculate the Si content corresponding to the slag composition. Fixing the allowable %Si it is found that the slag will contain more than 25% MnO in the MnO–CaO–SiO₂ system. The effect of CO pressure is minor. If it is practical to add Al₂O₃ to the slag, its melting point can be lowered sufficiently to obtain slags with 10% MnO in the CaO–Al₂O₃–SiO₂ system while keeping Si in the metal low.

Résumé

Des données de la littérature ont été employées pour construire les diagrammes d'activité des systèmes Mn–Fe–C, MnO–CaO–SiO₂, et CaO–Al₂O₃–SiO₂ it 10% de MnO. En admettant que la température de la zone de réduction est proche de celle de fusion du laitier, on trouve la teneur en MnO nécessaire pour obtenir l'alliage à 75% de Mn. La quantité de Si réduit a également été déterminée. Le calcul montre qu'en fixant la teneur finale silicium à moins de 0.5% la teneur en MnO doit être supérieure à 25% . dans les laitiers MnO–CaO–SiO₂. La pression de CO n'a guere d'effet. S'il est pratique d'ajouter du Al₂O₃ au laitier pour en abaisser le point de fusion on peut obtenir avec un laiter it 10 % de MnO un alliage pour lequelle Si ne dépasse pas les bornes permises.     

Aktivität des Eiseni(ll)-oxids in Schlacken

Elektrochemische Aktivitätsbestimmung des Eisen(ll)-oxids in den Systemen FeO–SiO₂, FeO–MnO–SiO₂ und FeO–CaO–SiO₂ im Temperaturbereich von 1250 bis 1350 °C durch Messung der Sauerstoffaktivität einer mit der flüssigen Schlacke im Gleichgewicht stehenden Silberschmelze mit Hilfe eines ZrO₂(CaO)-Festelektrolyten. Ermittlung der freien Standardenthalpie der Reaktion Fe(γ) + 1/2 O₂ (g) = FeO (I). Erörterung über das Oxydationsvermögen von Schlacken sowie über die Möglichkeiten zur Berechnung der Basizität von Schlacken.     

Manganese Distribution between FeO‐MnO‐SiO2–CaO–MgO‐Al2O3 Slags and Molten Iron

Pretreatment of high manganese hot metal is suggested to produce hot metal suitable for further processing to steel in conventional LD converter and rich manganese slags satisfy the requirements for the production of silicomanganese alloys. Manganese distribution between slag and iron represents the efficiency of manganese oxidation from hot metal. The present study has been done to investigate the effect of temperature, slag basicity and composition of oxidizer mixture on the distribution coefficient of manganese between slag and iron. Ferrous oxide activity was determined in molten synthetic slag mixtures of FeO‐MnO‐SiO₂–CaO–MgO‐Al₂O₃. The investigated slags had chemical compositions similar to either oxidizer mixture or slags expected to result from the treatment of high manganese hot metal. The technique used to measure the ferrous oxide activity in the investigated slag systems was the well established one of gas‐slag‐metal equilibration in which molten slags contained in armco iron crucibles are exposed to a flowing gas mixture with a known oxygen potential until equilibrium has been attained. After equilibration, the final chemical analysis of the slags gave compositions having a particular ferrous oxide activity corresponding to the oxygen potential of the gas mixture. The determined values of ferrous oxide activity were used to calculate the equilibrium distribution of manganese between slag and iron. Higher manganese distribution between slag and iron was found to be obtained by using oxidizer containing high active iron oxide under acidic slag and relatively low temperature of about 1350°C.     

Effect of FeO and Al2O3 on the MgO Solubility in CaO–SiO2–FeO–Al2O3–MgO Slag System at 1823 K

The MgO solubility in CaO–SiO₂–FeO–Al₂O₃–MgO quinary slag system at 1823 K was measured to evaluate the effect of FeO and Al₂O₃ on the MgO solubility. It was found that the MgO solubility was decreased with higher optical basicity, FeO concentration, and increased with higher Al₂O₃ concentration. The MgO solubility was affected by activity coefficient of Mg²⁺ ($\gamma _{{\rm Mg}_{{\rm 2 + }} } $ ). Increase of the activity coefficient of Mg²⁺ ($\gamma _{{\rm Mg}_{{\rm 2 + }} } $ ) with higher FeO or lower Al₂O₃ decreased the MgO solubility. The increment in MgO solubility is remarkably reduced beyond a critical $X_{{\rm Al}_{2} {\rm O}_{{\rm 3}} } /(X_{{\rm Al}_{2} {\rm O}_{{\rm 3}} } + X_{{\rm FeO}} )$ ratio. The significant decrease of the increment of MgO solubility is caused by the change of the molten slag structure. The excess stability function of Al₂O₃ and the Fourier transform infrared (FT‐IR) analysis were applied to indirectly verify the existence of the spinel structure in the CaO–SiO₂–FeO–Al₂O₃–MgO slag system.     

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.     

Contribution to the phase diagram CaF2–CaO–Al2O3

Critical review of the available data. Determination of the liquidus line of CaF₂-Al₂O₃ mixtures and of the CaO liquidus line in the CaF₂–CaO binary. Investigation of the heterogeneous equilibria in the CaF₂–CaO–Al₂O₃ ternary by using different techniques. Determination of the 1600°C liquidus isotherms of CaO, CaO · 2Al₂O₃, CaO · 6Al₂O₃, Al₂O₃ and of the miscibility gap.     

Critical assessment of activity coefficients of oxides in molten binary and ternary silicates,aluminates and aluminosilicates

Critical assessment is made of the activity coefficients of CaO, MgO, MnO, FeO, Al₂O₃ and SiO₂ in molten silicates, aluminates and aluminosilicates. In this assessment due consideration is given to the consistency of the free energies of formation of the interoxide compounds derived from the oxide activity data, compared with those derived from the compiled thermochemical data. For most oxides, it is found that by using an empirical formulation of the melt composition in ternary systems, the composition dependence of the oxide activity coefficient, γOX, can be represented by a single curve. For example, over a wide composition range in the FeO‐CaO‐SiO₂ system, the log(γCaO) is a single function of the melt composition in mol fraction as (?SiO₂ + 0.3xFeO); this relation being similar to that in the binary CaO‐SiO₂ melts. Therefore, with respect to γCaO, this ternary system is reduced to a pseudo binary system as xCaO ‐ (?SiO₂ + 0.3xFeO). With respect to γCaO, the ternary system CaO‐Al₂O₃‐SiO₂ is reduced to a pseudo binary system as xCaO ‐ (?SiO₂ + 0.4 xAl₂O₃). With γSiO₂, this ternary system is reduced to a pseudo binary system as (?CaO + xAl₂O₃) ‐ xSiO₂.     

Thermodynamic model calculations in multicomponent liquid silicate systems

Abstract

A thermodynamic model developed earlier in the present laboratory for oxidic melts was applied to some multicomponent systems, namely CaO–FeO–MgO–SiO₂ , Al₂ O₃–CaO–MgO–SiO₂ , Al₂ O₃–FeO–MnO–SiO₂ , and Al₂ O₃–CaO–FeO–MgO–MnO–SiO₂ . Model calculations were carried out using only the parameters corresponding to the binary systems, which, in turn, were based on the available thermodynamic information for these systems. The predicted thermodynamic activities of the component oxides in higher order systems were compared with the experimental data published in the literature. In general, the agreement between the model predictions and the experimental values was found to be satisfactory within the limits of experimental uncertainties and limitations of the model calculations. Examples of model predictions for some typical slag compositions, relevant to the Swedish steel industry and used in the blast furnace, electric arc furnace, and ladle furnace are also presented.     

Über die Basizität flüssiger Schlacken der Systeme CaO–SiO2 und CaO–Al2O3

EMK-Messungen mit einer Diffusionszelle an flüssigen Schlacken der Systeme CaO–Al₂O₃ und CaO–SiO₂ bei 1600°C. EMK und Sulfidkapazität zeigen lineare Abhängigkeit. EMK-Werte können als relatives Basizitätsmaß gewertet werden.     

On the Formation of Vanadium Ferrites in CaO–SiO2–FeO–V2O5 Slags

Selective extraction of valuable elements (such as V, Cr, Mn, etc.) and their compounds from metallurgical slag is in a focus of many researchers. Although vanadium may be present in slag as oxides and/or complex spinels with Fe, Mn, etc. during an alloyed steel production, the majority of vanadium in metallurgical slags typically exists as V₂O₅, which comprises up to 3–5 wt% of the slag in some cases. Due to the vanadium toxicity, these slags are forbidden in many civil engineering applications. As a result, hundreds of thousand tonnes of V₂O₅‐bearing slags are landfilled every year. In the present work, the formation of vanadium ferrites (FeV₂O₄ and Fe₂VO₄) in synthesized CaO–SiO₂–FeO–V₂O₅ slags containing 5 wt% V₂O₅ was examined under different partial pressures of oxygen. For the current slag chemistry range, an XRD analysis confirmed the presence of vanadium ferrite in slag samples treated at 1773 K in an argon atmosphere (PO₂ = 10^?1–10^?2 Pa) while no solid was noted in samples treated in air. Results were discussed based on thermodynamic consistency.     

Effect of water vapour content in H2–H2O–CO–CO2 mixtures on activity of iron oxide in slags relevant to novel flash ironmaking technology

Abstract

As an integral part of developing a novel flash ironmaking technology at the University of Utah, the activity of iron oxide in the slag was studied under three different gas atmospheres: H₂/H₂O (H₂), CO/CO₂/H₂/H₂O (reformed natural/coal gas), and CO/CO₂. The conditions of the slags investigated were MgO-saturated CaO–FeO–Al₂O₃–SiO₂–MnO (0·2–0·8 wt-%)–P₂O₅ (0·1–0·9 wt-%) in the temperature range 1550–1600°C with wt-% CaO/wt-% SiO₂ of 0·8 to 1·2, and under pO₂?=?2×10^?10–2×10^?9 atm. Water increased the activity coefficient of FeO in the slag and accordingly lowered the FeO content. The average FeO content was found to be 10, 11 and 16 wt-% under H₂/H₂O (H₂), CO/CO₂/H₂/H₂O (reformed natural/coal gas), and CO/CO₂, respectively. An empirical correlation for γ_FeO in slags under H₂/H₂O atmospheres was formulated to givelog γ_FeO?=??3·0623 X_FeO?3·1421 X_CaO?2·5068 X_MgO+2·1957     

Dissolution of water vapour in ESR-slags of the systems CaO–Al2O3 and CaF2–CaO–Al2O3 by application of Fourier-Transform-Infrared-Spectroscopy

In CaO–Al₂O₃- and CaF₂–CaO–Al₂O₃-slags the soluted water vapour was quantitatively determined with Fourier-Transform-lnfrared-(FT-IR-)spectroscopy. The slags were equilibrated at 1500 and 1600 °C with definite H₂O- and H₂O/HF-partial pressures, respectively. The liquid slags were quenched in liquid D₂O. They solidified glassily. Water vapour exists in the slags soluted as OH^?-ion. For all slags investigated a linear dependence of the integral extinction upon the square root of the H₂O-partial pressure, respectively upon HF-partial pressure, was determined. The values of the integral extinction (CaF₂–CaO–Al₂O₃-slags) are calibrated by a H₂O-doping-technique. The solution enthalpy of H₂O in CaO–Al₂O₃-slags was estimated: endothermal reactions. Interpretation of the vibrational range yielded in a mainly tetrahedral coordination of Al³⁺ with O^2?- and F^? -ions in the glassy state. By heating the glassily solidified CaO–Al₂O₃-slags were transformed into their crystalline products: shifting of IR-peaks. The CaO–Al₂O₃- and CaF₂–CaO-slags were compared with a CaO–SiO₂–Al₂O₃-slag. The FT-IR-method is quick. The water content can be estimated with an uncertainty of less than ± 5% and is, therefore, suitable for process control of metallurgical procedures.