Lead solubility in FeO x -CaO-SiO2 slags at iron saturation

Experiments have been carried out to determine the equilibria between FeO _x -CaO-SiO₂ slag and lead metal in iron crucibles at temperatures ranging from 1473 to 1573 K. It has been found that the highest lead solubilities are observed in the silica-saturated iron silicate slags, while the lowest solubilities are observed in the CaO-saturated calcium ferrite slags. The activity coefficient of PbO varies from 0.15 to 3, depending on the slag composition. Changes in temperature do not have a significant impact on the activity coefficient. The activity of FeO and pct Fe³⁺/pct Fe²⁺ ratios have been determined as a function of slag composition. These new experimental data have been incorporated into an optimized thermodynamic slag model using the computer package FACT.     

Permeability,diffusivity, and solubility of oxygen gas in liquid slag

An experimental procedure for measurement of the permeability of dissolved oxygen gas in liquid slag has been developed using an oxygen concentration cell. The small amount of oxygen gas which penetrated through the liquid oxide from a pure oxygen compartment to a pure argon compartment was determined by the galvanic cell. The permeabilities of oxygen through liquid PbO-SiO₂ and FeO-PbO-SiO₂ were found to be in the range 3 x 10^-8 to 3 x 1O^-7 moles/cm s. The permeabilities were little influenced by temperature but more influenced by the composition. In separate experiments, the oxygen pressure change at the bottom of a column of slag was detected by another galvanic cell. By this method, it is not necessary to quench the specimen to determine the concentration profile of dissolved oxygen and to determine its diffusivity. Liquid oxides in the PbO-SiO₂, CaO-SiO₂-Al₂O₃and FeO-PbO-SiO₂ systems were studied. The oxygen diffusion coefficients (5 x 10^-5 to 3 x 10^-3 cm²/s) were found to increase with temperature for a fixed composition of slag, and with an increase of network-modifier oxide content at constant temperature. The solubility of oxygen gas in PbO-SiO₂ melts was estimated to be 2 x 10^-4 to 2 x 10^-5 moles/cm³ from the determined diffusivities and permeabilities. The solubilities decreased with increasing temperature in the composition range studied. Physical solubilities of gases and metals in slags determined by other investigators are compared with the present results.     

Thermochemistry of calcium oxide and calcium hydroxide in fluoride slags

Calcium oxide activity in binary CaF₂-CaO and ternary CaF₂-CaO-Al₂O₃ and CaF₂-CaO-SiO₂ slags has been determined by CO₂-slag equilibrium experiments at 1400 °C. The carbonate ca-pacity of these slags has also been computed and compared with sulfide capacity data available in the literature. The similarity in trends suggests the possibility of characterizing carbonate capacity as an alternative basicity index for fluoride-base slags. Slag-D₂O equilibrium experi-ments are performed at 1400°C with different fluoride-base slags to determine water solubility at two different partial pressures of D₂O, employing a new slag sampling technique. A novel isotope tracer detection technique is employed to analyze water in the slags. The water solubility data found show higher values than the previous literature data by an order of magnitude but show a linear relationship with the square root of water vapor partial pressure. The activity of hydroxide computed from the data is shown to be helpful in estimating water solubility in in-dustrial electroslag remelting (ESR) slags. Formerly Graduate Student, University of British Columbia.     

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.     

Wettability of Silicon Carbide by CaO-SiO2 Slags

The wettability of silicon carbide by liquid CaO-SiO₂ slags that contain 47 to 60 wt pct SiO₂ was studied using the sessile drop wettability technique. The experiments were carried out in Ar and CO atmospheres. A small piece of slag was melted on SiC substrates under different heating regimes up to 1600 °C. It was found that the wetting is not significantly dependent on the temperature and the heating rate. However, the wettability is relatively high, and the wetting is higher for slags that contain lower SiO₂ concentrations. Moreover, the wettability between the slags and SiC is dependent on the gas phase composition, and it is higher in Ar than that in CO. When the SiO₂ concentration changes from 47 pct wt to 60 pct wt, the wetting angle changes from 20 deg to 73 deg in Ar and from 58 deg to 87 deg in a CO atmosphere. The formation and bursting of gas bubbles also was observed after some contact time, which indicates that the wetting system is a reactive type. However, microscopic studies indicated that no metal phase exists at the slag/silicon–carbide interface. Therefore, it was concluded that chemical reactions between the slag and SiC take place and that SiO₂ is slowly reduced to form CO and SiO gases. Based on the experimental data, the dependence of the Girifalco–Good coefficient on the slag composition and the relationship between the interfacial tension of CaO-SiO₂ slags and SiC also were estimated.     

Effect of Physicochemical Properties of Slag and Flux on the Removal Rate of Oxide Inclusion from Molten Steel

The slag-metal reaction experiments were carried out using a high-frequency induction furnace to confirm the effect of slag composition on the removal rate of inclusions in molten steel through the CaO-based slags. The apparent rate constant of oxygen removal (k _O) was obtained as a function of slag composition. It increased with increasing basicity, and the content of MgO and CaF₂, whereas it decreased by increasing the content of Al₂O₃ in the slag. The removal rate of inclusions was strongly affected not only by the driving force of the chemical dissolution but also by the viscosity of the slags and fluxes.     

Experimental simulations of primary slag formation in blast furnace

Abstract

Primary slag formation of the blast furnace ferrous burden was experimentally simulated using synthetic MgO-Al₂O₃-CaO-SiO₂ slags with FeO, Na₂O, or FeS additions. The combined effect of FeO and Na₂O or FeS was also examined. The melting behaviour and viscosity of five different base slags (sinter, pellet, or lump ore) were investigated using optical dilatometry, thermogravimetric-differential thermal analysis (TGA-DTA), and viscometric analysis. The results indicate the importance of FeO (wüstite) in the formation and nature of liquid primary slags. Solidus temperature, fusion temperature, solidus-fusion interval, and viscosity were all significantly affected by FeO. A clear, but not simple or linear, tendency showed a lowering of the solidus and fusion temperatures and a concomitant decrease of the viscosity with increased FeO addition. The presence of Na₂O or FeS in the slag system, alone or combined with the FeO addition, created an initial melting at lower temperatures, but the liquid volume produced was limited. The effect of the added components was distinctly different on different base slag systems. It is proposed that the effect is fundamentally dependent on the chemical or, more exactly, on the mineralogical composition of the base slag systems at the initial stage of the melting. The results of the experiments are considered to represent reasonable simulations of the melting behaviour of the corresponding primary slags of the blast furnace ferrous burden in the cohesive zone.     

Multicomponent diffusion in molten slags

A method for investigating the diffusion of metal cations in multicomponent slag systems was developed. This method used microprobe analysis and allowed the analysis of the diffusion of multiple species within a single system. This project focused on the diffusion behavior of manganese, iron, calcium, and silicon in silicate slags, in order to simulate industrial steel and ferromanganese production. The molecular structure of CaO-Al₂O₃-SiO₂ slags was investigated with Raman spectroscopy, and oxidation states of manganese and iron in slags of varying composition were determined. This study identified the variation in diffusivity of slag components with changes in composition and temperature of multicomponent slag systems. An empirical model based on the correlation between optical basicity and diffusivity was developed to predict the multicomponent diffusivity of ionic species in molten silicate slags. The model takes into account properties of the bulk slag and the network forming ability of the diffusing species. The relative rate of diffusion of metal cations is proportional to the optical basicity coefficient of that species, while the rate of diffusion of all species increases exponentially with the calculated optical basicity of the bulk slag.     

Sulfide capacity of high alumina blast furnace slags

Sulfide capacities of high alumina blast furnace slags were experimentally determined using the gas-slag equilibration technique. Two different slag systems were considered for the current study, namely, CaO-SiO₂-MgO-Al₂O₃ quaternary and CaO-SiO₂-MgO-Al₂O₃-TiO₂ quinary system. The liquid slag was equilibrated with the Ar-CO-CO₂-SO₂ gas mixture. Experiments were conducted in the temperature range of 1773 to 1873 K. The effects of temperature, basicity, and the MgO and TiO₂ contents of slags on sulfide capacity were studied. As expected, sulfide capacity was found to increase with the increase in temperature and basicity. At the higher experimental temperature, titania decreases the sulfide capacity of slag. However, at the lower temperature, there was no significant effect of titania on the sulfide capacity of slag. Sulfide capacity increases with the increase in MgO content of slag if the MgO content is more than 5 pct.     

The thermodynamic behavior of sulfur in BaO-BaF2 slags

A gas-slag-metal equilibration technique was used to determine the sulfide capacity of the BaO-BaF₂ system at 1473 and 1573 K. The dependence of carbonate capacity on the slag composition was also measured at these temperatures. It was found that the BaO-BaF₂ system has the highest sulfide capacities among the fluxes which are of metallurgical interest. The dependence of sulfide and carbonate capacities on the partial pressure of O₂ and CO₂ was also investigated. The partial pressure of CO₂ proved to have a strong effect on these values at the investigated temperatures. The influence of temperature on the sulfide and carbonate capacities was studied in the temperature range between 1423 and 1623 K. The data for sulfide and carbonate capacities were correlated in order to check if the carbonate capacity can be used as a measure of basicity of slags. It was found that the carbonate capacity can be used as a representative measure of the slag basicity at low contents of BaO and at temperatures higher than 1623 K when the carbonate dissolution into the slag is low and the ratio of the activity coefficient of a sulfide ion to that of a carbonate ion is independent of slag composition. on leave from the Department of Metallurgy, Higher Institute of Chemical Technology, Sofia, Bulgaria     

Kinetics of CO-CO<Subscript>2</Subscript> reaction with CaO-SiO<Subscript>2</Subscript>-FeOx melts

Measurements of the rate of interfacial reaction between CO₂-CO mixtures and CaO-SiO₂-FeOx slags have been made using the ¹³CO₂-CO isotope exchange technique. Ranges of slag compositions from 0 to 100 wt pct ‘FeO’ and CaO/SiO₂ between 0.3 and 2.0 were examined in the experiments. For each slag, the dependence of the apparent rate constant on temperature and equilibrium oxygen potential was studied. The relationship between the rate constant and oxygen potential was found to be in the form k _a=k _a ^o (a_o)^-α. The parameter a, with values between 0.5 and 0.9, was dependent on the slag composition. The activation energy of the reaction was independent of iron oxide content and dependent on slag basicity.     

Oxidation State of Titanium in CaO‐SiO2‐TiOx Slags at 1873K

Oxidation state of titanium was determined in CaO‐SiO₂‐TiO_x slags in the composition range 25‐53 percent CaO, 27‐46 percent SiO₂, 10‐55 percent TiO_x at 1873K using gas equilibration method. In the experiments, slags with different titanium oxide contents were equilibrated with a known carbon monoxide and carbon dioxide ratio. The results were used to determine the Ti³⁺ and Ti⁴⁺ contents as well as the activity coefficient ratio of corresponding oxides in the slag. The dependence of the activity coefficient ratio as a function of oxygen partial pressure was determined.     

Effect of slag composition on the cleanliness of drill rod steel

In order to obtain the 55SiMnMo drill rod steel with a high cleanliness, the slag refining has been simulated by laboratory experiments. More desired spherical-shaped complex inclusions with an average diameter of about 2.7?μm, total oxygen of 4?ppm and Mg of 10?ppm after refining were obtained with initial slag basicity of 2.1 and Al₂O₃ 15?wt-%. The relationship between the slag composition and the melting temperature and viscosities of slag was achieved based on a calculation by Factsage Software and Einstein–Roscoe Equation. The refractory–slag–metal–inclusion multiphase reactions were investigated from the viewpoint of thermodynamics and kinetics by the estimation of viscosities, MgO solubility, Al₂O₃ activity in slag and sulphur capacity of slags. It is experimentally confirmed that the corrosion of MgO crucible by slag was affected by the MgO solubility and viscosity of slag. The factors facilitating to obtain low oxygen and control sulphur content were also analysed. Finally, the composition transformation of inclusions during slag refining and cooling process was discussed based on thermodynamic calculation.     

Oxidation of titanium-vanadium slags with the participation of Na2O and its effect on the behavior of vanadium

The oxidation of titanium-vanadium slags with the participation of Na₂O is studied by X-ray diffraction. The slags have the following phase compositions: anosovite, anosovite-spinellide, and spinellide. An alkaline component in the form of Na₂CO₃ is introduced into a slag either before oxidizing roasting or during slag production from a concentrate (alkaline slag forms). The general laws of the processes of slag oxidation in the temperature range 600–1100°C and the effect of these processes on the behavior of vanadium are found. The degree of formation of watersoluble vanadium compounds during roasting is shown to depend substantially on the SiO₂ content in the slag. When the slags are roasted, SiO₂ intensely combines with Na₂O to form sodium silicates or aluminosilicates depending on the slag composition, which restricts the formation of sodium vanadates. In anosovite-spinellide slags (with a high Al₂O₃ content), the maximum degree of vanadium oxidation with the formation of water-soluble sodium vanadates is achieved at a temperature of about 1000°C. In anosovite slags (with a low Al₂O₃ content), the maximum degree of formation of water-soluble vanadium compounds is achieved at a temperature below 900°C. At higher temperatures, the major portion of vanadium transforms into an acid-soluble form.     

Metal loss to slag: Part II. oxidic dissolution of nickel in fayalite slag and thermodynamics of continuous converting of nickel-copper matte

FeO-Fe₂O₃-SiO₂ slags were equilibrated in pure nickel crucibles under a CO-CO₂ atmosphere. The Fe/SiO₂ ratios in the slag were fixed at 1.51 and 1.97 at temperatures of 1200 and 1300°C. The CO₂/CO ratios were varied up to values corresponding to magnetite saturation. On the basis of solubility data obtained, a computer model was developed to predict the solubilities of nickel and copper in slag during the continuous converting of nickel-copper matte. These are given as a function of five parameters: temperature, iron content and Cu/Ni ratio in the matte, partial pressure of SO₂ in the gas phase, and magnetite activity in the slag. The model is helpful in comprehending converting reactions and of practical applicability in optimizing the conventional as well as continuous converting processes. Noranda Research Centre, Pointe Claire, Quebec.     

Thermodynamic Model and Database for Sulfides Dissolved in Molten Oxide Slags

A thermodynamic model has been developed in the framework of the modified quasichemical model in the quadruplet approximation to permit the calculation of solubilities of various gaseous species (sulfide, sulfate, nitride, carbide, water, etc.) in molten slags. The model calculates the solubilities solely from knowledge of the thermodynamic activities of the component oxides and the Gibbs energies of the pure liquid components (oxides, sulfides, sulfates, etc.). In the current article, it is shown that solubilities of sulfur as sulfide in Al₂O₃-CaO-FeO-Fe₂O₃-MgO-MnO-SiO₂-TiO₂-Ti₂O₃ multicomponent slags, which are predicted from the current model with no adjustable model parameters, are in good agreement with all available experimental data. The article also provides a thorough review of experimental sulfide capacity data for this system. The model applies at all compositions from pure oxides to pure sulfides and from basic to acidic slags. By coupling this database with other evaluated databases, such as those for molten metal and gaseous phases, and with general software for Gibbs energy minimization, practically important slag/metal/gas/solid equilibria can be computed such as S-distribution ratios.     

The behaviour of chromium in reduced slag-metal systems

The equilibrium between slag and metal in the CaO-SiO₂-Al₂O₃-CrO_x-FeO/Fe-Cr-Si system was investigated and the results expressed in terms of the apparent equilibrium constants for the Cr/FeO and Cr/SiO₂ equilibria. The effect of slag composition and temperature on the apparent equilibrium constants is described. The predominant form of chromium in the slags was CrO and the thermodynamic properties of CrO in the slag are discussed. The equilibrium results are applied to the stainless steelmaking system in order to show the effect of slag composition, silicon content of metal and temperature on the equilibrium chromium content of the slag.     

Evaluation of Secondary Steelmaking Slags and Their Relation with Steel Cleanliness

Based on data provided from an industrial plant and FactSage commercial software use, a study of secondary refining slags and inclusion cleanliness was performed. Six heats of two slag series, namely, A and B, with average chemical composition (wt pct) of 43.00CaO-25.90SiO₂-12.96Al₂O₃-18.13MgO for series A and 49.98CaO-23.88SiO₂-10.11Al₂O₃-11.99MgO-4.03CaF₂ for series B, were used for the study. Both series used DIN 38MnS6 modified steel. The effective viscosity, solid fraction, composition of the liquid fraction, and slag saturation degree in MgO (calculated through thermodynamic software) were related to the experimental results obtained for the inclusion cleanliness. The B slags showed lower effective viscosity than the A slags, due to their high liquid fraction. Regarding the capacity of slags in the inclusion removal, slag B5 resulted in the lowest inclusion density and was considered as the best choice among the slags studied. The inclusion species formed using B slags are constituted especially of CaO-Al₂O₃-SiO₂ and MgO-Al₂O₃ and are Al₂O₃ rich. The presence of sulfide-type inclusions (AlMnS and CaS) were more pronounced among A slags.     

Determination and Prediction of Water Vapor Solubilities in CaO-MgO-SiO2 Slags

A thermogravimetric technique has been used to obtain accurate measurements of water vapor dissolution in molten CaO-MgO-SiO₂ slags. These measurements indicate that the solubility of water vapor is independent of temperature over a 200 °C range (1375 to 1575 °C) and varies directly with the square root of the water vapor partial pressure. Water vapor was observed to be amphoteric in nature with respect to dissolution in liquid silicates. A minimum in solubility was observed at approximately the metasilicate composition. Results obtained during the present study indicate that the empirically defined basicity index(N _Cao + N_Mgo)/N_sio2 is inadequate to describe the dissolution of water vapor in silicate melts. The activity of silica has been identified as a more accurate indicator. Based on this approach, ambiguous results from previous studies in the CaO-MgO-SiO₂ slag system have been rationalized. From a statistical evaluation of the data, a relationship in terms of the activity of silica has been obtained which permits calculation of water vapor contents in CaO-MgO-SiO₂ slags. M. Maeda, formerly Postdoctorate Fellow in Metallurgy and Materials Science, University of Toronto.     

Reaction equilibria in the production of manganese ferroalloys

A laboratory investigation has been carried out to determine slag/metal and slag/metal/gas equilibria relevant to production of manganese ferroalloys. The metal phase was normally composed of MnSi-C_sat alloys, but in some experiments, the alloys contained up to 15 wt pct Fe. Different slag systems were used: MnO-SiO₂, MnO-SiO₂-CaO, MnO-SiO₂-Al₂O₃, and quaternary MnO-SiO₂-CaO-Al₂O₃ with fixed CaO/Al₂O₃ weight ratios of 1.5 and 3. The experiments were normally made in CO gas atmosphere at temperatures ranging from 1450 °C to 1600 °C. The results give comprehensive information about equilibrium relations.Partial andcomplete equilibria are illustrated in equilibrium diagrams. Partial equilibrium is a situation in which equilibrium is established with respect to certain variables but not to others, in this case, between slag and metal but not with the gas phase. The effect of temperature was found to be of minor importance for the partial slag/metal equilibrium, whereas the complete slag/metal/gas equilibrium is considerably influenced by both temperature and CO pressure. As expected, increasing temperature and decreasing CO pressure will reduce the equilibrium MnO content of slags. The influence of alumina addition to the slag phase and of iron to the metal phase is also discussed.