Johan Björkvall

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.

Thermodynamic description of Al2O3-CaO-MnO and Al2O3-FeO-MnO melts - a model approach

Assessments for the binary systems. Al2O3-CaO, Al2O3-FeO and Al2O3-MnO were carried out using a slag model developed at the present department. Calculations of the oxide activities in the homogenou ...

A new approach for the study of slag-metal interface in steelmaking

Abstract The main focus of the present work was to develop a sampler to obtain the physical description of the slag–metal interface in the presence of bulk flow. Industrial trial experiments were carried out in the ladles at Uddeholm Tooling, Hagfors, Sweden using the designed sampler. Samples of the slag–metal interface were successfully taken in both gas stirring and induction stirring modes. The similarities of the appearance as well as the micrographs of the samples suggested that the slag–metal interfaces in the two stirring modes were very similar except in the open eye area. In the case of both stirring modes, metal droplets were found in the slag bulk. On the other hand, no appreciable amount of slag was detected in the metal bulk. Further systematic investigation using a large number of samples is required to obtain a quantitative description of the interface.

A Model Description of the Thermochemical Properties of Multicomponent Slags and Its Application to Slag Viscosities

In view of the urgent need for an extrapolation of the thermochemical and thermophysical properties of multicomponent metallurgical slags, a semiempirical slag model has been developed at the Department of Metallurgy, Royal Institute of Technology, Stockholm. In this model, Temkins description of ionic melts is coupled with Lumsdens total dissociation of polymerized silicate and aluminate species. The excess Gibbs energies are described by means of Redlich–Kister polynomials. The model parameters that correspond to binary silicate systems are generated from available experimental data and used consequently to describe systems of higher order. The model is successful in extrapolating the thermodynamic data for a number of ternary and higher-order silicate systems. In view of the uncertainties in the literature data in the case of the Al2O3–SiO2system, Knudsen cell mass spectrometric measurements are conducted and the model parameters are assigned on the basis of these results. This enables reasonable predictions of the thermodynamic properties of multicomponent aluminosilicate slags. The model description is also used in linking thermodynamic data with slag viscosities. The viscosities of ternary silicates could be predicted from the binary viscosities and the thermodynamic data.

Investigation of iron losses during desulphurisation of hot metal utilising nepheline syenite

Abstract Iron losses during calcium carbide based hot metal desulphurisation have been studied via large scale investigations of slag from the slag pit as well as slag sampling during desulphurisation at SSAB EMEA in Luleå. The desulphurisation slag, after injection of calcium carbide, is normally solid and contains large amounts of iron. An alkali containing mineral, nepheline syenite, was mixed together with the calcium carbide to form a more fluid slag as the iron losses originate from enclosed metal droplets in the slag as well as drawn off hot metal during slag skimming. The slag amount after slag skimming decreased from 28·1 to 25·1 kg t−1 hot metal with addition of 5 wt-% nepheline syenite to the calcium carbide, and the magnetic fraction of the slag from the slag pit decreased from 2·5 to 1·9%. Finally, no negative effect on the reagent efficiency was observed during the trials with addition of nepheline syenite.

Vanadium oxide solubility in CaO–SiO2–VOX system

The solubility of vanadium oxide in the SiO2–CaO–VOX system was investigated as a function of basicity (CaO/SiO2) at a fixed temperature of 1600°C and oxygen partial pressure of 10−10 atm. Formed phases and microstructures of saturated samples were identified with SEM–EDS analysis and XRD. Maximum solubility of vanadium oxide was between 15 and 20% independent of basicity. Pure karelianite (V2O3) was formed in all samples at saturation of vanadium oxide. The morphology of karelianite changed with the change in basicity in the slag, where needles or threads were formed for slags with basicity B2 = 0.54 and B2 = 0.67 and stars or dendritic patterns were formed with basicity B2 = 1.0 and B2 = 1.22. Wollastonite (CaSiO3) was also formed in the slags with star or dendritic patterns.

Iron losses during desulphurisation of hot metal utilising co-injection of Mg and CaC2 combined with nepheline syenite

Abstract Iron losses during hot metal desulphurisation using magnesium and calcium carbide have been studied by large scale investigations of slag from the slag pit as well as slag sampling during desulphurisation at SSAB EMEA in Luleå. The desulphurisation slag after co-injection is normally solid and contains a large amount of iron. An alkali containing mineral, nepheline syenite, was mixed with calcium carbide to enhance the separation of iron from the slag. Even though the addition of nepheline syenite resulted in a more fine grained slag, no reduction of the iron content in the slag was observed before slag skimming. Nepheline syenite has a positive effect on slag skimming; however, the total magnetic iron losses have not decreased significantly. The increased turbulence during injection of magnesium could explain the lack of improved iron yield. The addition of nepheline syenite does not have a negative influence on the reagent efficiency.