UV/VIS-spectroscopy of aluminates in liquid and solid oxide slags

Structural information of liquid oxide melts including statements concerning their basicity are important not only for the metallurgy of steelmaking but also for the refractory industry, for ceramic productions and for glass manufacturing. After the introduction of infrared emission spectroscopy of liquid melts up to 1600°C it is now possible to receive UV/VIS-spectra of these melts in different atmospheres. The comparison to already published spectra is possible by recording spectra of quenched samples at room temperature with the same optical system as the high temperature ones. The suitability of the Fe- and Cr-Ions as test-ions for the indications of the features of liquid aluminate melts is discussed. A new spectroscopical method for the investigation of melts above 1450°C was developed. Octahedral-coordinated Fe³⁺ causes intensive charge-transfer (CT) absorptions in the melts. These CT-bands shift towards higher wavelengths and get broader and more intensive at higher temperatures; the results are discussed by the use of the Urbach-approximation. The CT-bands of Cr(VI) are attached to various chromate species. The properties of liquid silicates will be the subject of a later investigation.     

UV/VIS-spectroscopy of molten and solid CaO-MgO-SiO2 - slags

The previously developed high temperature set-up has been used to monitor the redox state of molten slags at 1500°C directly by UV/VIS spectroscopy. Slags of the CaO-MgO-SiO₂-system were doped with Fe₂O₃ mass contents of 0.80 and 5%. Spectroscopical results at different oxygen partial pressures of the investigated Fe³⁺ charge-transfer (CT) transitions in the wavelength range between 200 and 800 nm were found to be representative for the redox state of the slag. The peak positions and shifts give further information about the optical basicity and the structure of molten slags. The time dependence of the oxidation/reduction equilibrium process was measured and evaluated concerning diffusion mechanisms. In Cr₂O₃-doped silicate-slags in the liquid state CrO₃ - and Cr³⁺- species occur. The different CrO₃-species (CrO₄^2- and Cr₂O₇^2-) in silicate slags have been indicated spectroscopically and registed quantitatively. Further investigations on Cr₂O₃-doped slags uncovered the well known evaporation of chromium out of molten slags as a decrease in the CrO₃ concentration in time. In the molten slag the CrO₃ slowly evaporates, which can be seen spectroscopically as a decrease in the CT-band intensity. The results obtained on numerous optical parameters of molten slags will establish the application of reflection spectroscopy at high temperatures.     

Diffusion of copper in liquid fayalite slags

Abstract

A modified version of the capillary reservoir technique was used to determine the diffusivity of Cu in silica-saturated fayalite slag. Values of the diffusion coefficient increased from 1.0% × 10^?5 to 7.0 × 10^?5 cm²/sec over the temp. range 1150–1300°C. From a series of diffusion experiments conducted at constant copper activity, the calculated activation energy for diffusion was 39,000 ± 12,000 cal/mole. Under isothermal conditions, the diffusion coefficient was found to be independent of the , oxygen partial pressure over the slag phase. The range of oxygen partial pressures investigated was from 10^?8 to 10^?12 atm.

Résumé

Par une version modifyée de la technique du réservoir capillaire les auteurs ont déterminé la diffusion du cuivre dans des laitiers de fayalite saturé en silice. Dans l'intervalle de tempérapture de 1150 à 1300°C, le coefficient de diffusion augmente de 1.0 × 10^?5 à 7.0 × 10^?5 cm²/sec. L' énergie d'activation pour la diffusion, calculée à; partir d'une série d'expériences faites à une activité du cuivre constante, est de 39,000 ± 12,000 cal/mole. Dans des conditions isothermes il a été trouvé que le coefficient de diffusion était indépendant de la pression partielle d'oxygene au dessus du laitier. Le domaine des pressions partielles d'oxygene étudié était de 10^?8 à 10^?12 atm.     

Thermodynamics of Ti in liquid steels and slags

Thermodynamics of Ti in liquid steels and slags was studied in order to establish a data base for the prediction of TiO_x and TiN formation in liquid steels.The interaction parameters between Ti and i（i = Cr,Ti,Al, Si,Ni,Mo,Nb,N,O） in liquid iron and the equilibrium constants for the formation of TiN and TiO_x in liquid iron were determined as a function of temperature.In view of high Ti yield during ladle treatment,thermodynamics of titanium oxides in ladle slags was studied as well.Activity coefficient and redox equilibrium of TiO_x in MgO saturated CaO-Al₂O₃ slag are also discussed by measuring the distribution ratio of Ti between slag and iron melts and the Ti³⁺/Ti⁴⁺ ratio in slag at 1 873 K.     

Processing of liquid steelmaking slags to obtain commercial products

The processing of liquid steelmaking slags to obtain a commercial product with specified properties and maximum iron extraction is considered. The performance of existing systems for liquid-phase reduction of the metal from slag and methods of liquid-slag processing is compared. Prototype equipment for slag processing is developed and tested at OAO OMK-Stal’ (Vyksa) on liquid electrofurnace slag and ladle (refining) slag.     

Reduction kinetics of liquid iron oxide-containing slags by carbon monoxide

The reduction of iron oxides from liquid slags is important in the nonferrous as well as the ferrous industry. In the primary smelting of copper, the trend is to produce copper mattes with increasing contents of copper. This is accomplished by increasing the degree of oxidation, leading to more oxidized slags with higher copper contents. To recover this copper, the high magnetite content of these slags has to be reduced in a separate slag cleaning process. Laboratory reduction experiments on commercial copper slags using carbon monoxide-containing gases show that the reduction rate increases with increasing injection depth and slag temperature. The reduction rate was found to follow the relationship $$Rate(\frac{{molO}}{{m^2 \cdot s}}) = 7.9 \cdot 10^5 \cdot e^{\frac{{ - 43,300}}{{T(K)}}} \cdot p_{CO} (Pa)$$ with an activation energy of 360±20 kJ/mol.     

Equilibria between liquid Mn-Si alloys and MnO-SiO2-CaO-MgO slags

The activity of silicon in manganese-silicon melts was determined at 1500°C. The results are in general agreement with the thermodynamic data of the iron-silicon system. Equilibria between manganese-silicon melts and slags containing MnO, SiO₂, CaO, and MgO were studied at 1400 and 1500°C in silica and magnesia crucibles. An empirical relationship easy to use in practice was derived, expressing the manganese and silicon distribution ratio between slag and metal as a function of the slag basicity. This relationship describes equilibria pertinent to the silicothermic reduction of manganese oxide and the production of silicomanganese. The present knowledge of the activities in the slag and metal phase is adequate to explain the experimental results. The presence of up to about 10 pct CaF₂ in the slag makes it possible to maintain a higher slag basicity and therefore a lower activity of silica, resulting in lower silicon contents in the metal. Iron contents of up to about 20 pct in the metal cause a slight increase in the silicon content of the metal under otherwise similar conditions. The effect of 1 to 2 pct carbon in the metal on the equilibrium was roughly estimated and found to be almost negligible.     

Measurement of the thermal diffusivity of liquid oxides and metallurgical slags

The methods of heat transfer in stagnant bodies of glass and slag are reviewed, and it is shown that the effective thermal diffusivity determines the rate at which heat is transferred in glasses similar in composition to metallurgical slags. A new experimental apparatus is also described for measuring the effective thermal diffusivity of these glasses. The results of experiments performed on glasses containing between 10.9 and 26.8 pct FeO, with lime/ silica ratios,B, of 1.0 and 1.5, and at temperatures ranging from the liquidus temperatures of the glasses to 1750 K are represented by A theoretical basis is used to develop the form of this relationship, and consequently, it should yield reasonable estimates for glasses of other composition and at other temperatures. H. Allan Fine and T. Engh were formerly Research Assistant and Visiting Scientist, respectively.     

Thermodynamic data for liquid Ca-CaF2 and Ca-CaCl2 slags

Activities of calcium in the systems Ca-CaF₂ and Ca-CaCl₂ were measured as a function of concentration with help of the distribution method between slag and Ca-Ag alloys. Activity coefficients greater than 1 were found for both systems at 1 425°C and 995°C. The liquidus of CaO for the Ca-CaO phase diagram was remeasured with respect to mixtures of lime with calcium halogenide slags. Influence of the activity of calcium on the distribution of impurities between steel and halogenide slags are discussed.     

Reduction of iron oxides from liquid slags using a graphite rotating disc

Research work has been carried out on the reduction of FeO from liquid slags of the CaO‐FeO‐SiO₂ ternary system using a graphite rotating disc technique. The investigations were conducted on slags with a basicity of CaO/SiO₂ = 1.27 and FeO contents of 20 and 60%, at temperatures of 1350 and 1420°C. The calculated viscosity range for these slags is within 2.53 – 0.43 dPa·s. It has been found that the factor controlling the reduction process is diffusion of FeO towards the disc surface, both in the case of the reduction from the slag with 20% FeO and in the case of the reduction from the slag with 60% FeO fraction. The diffusion coefficient of FeO at the reduction temperature of 1350°C is of the order of magnitudes of 10^?7 cm²/s, while at 1420°C it reaches the order of 10^?6 cm²/s. The calculated thickness values for the limiting diffusion layers range from 8.54·10^?3 to 0.70·10^?3 cm. It has been found that with increasing reduction rate also Boudouard's reaction starts to be important to the overall reduction rate. The limiting reduction rate at which Boudouard's reaction starts to be important to the entire process is dependent on temperature, being approximately 10.0·10^?6 mol FeO/cm² s at 1350°C, and approximately 15.0·10^?6 mol FeO/cm² s at 1420°C.     

Kinetics of simultaneous reactions between liquid iron-carbon alloys and slags containing MnO

The oxidation rates of carbon, phosphorus, and silicon; the desulfurization rate of liquid iron; and the simultaneous reduction rate of MnO from slag were examined at 1450 °C to 1550 °C by using high carbon iron alloys and CaO-SiO₂-CaF₂ slags containing MnO and FeO. The reaction rates were well reproduced by a kinetic model describing the reaction between the slag and multicomponent iron alloys. The controlling steps applied for the reactions considered in the present kinetic simulation were as follows. The rate of decarburization is controlled by the chemical reaction at the slag-metal interface, and those of the other reactions are controlled by the transport in slag and metal phases. Both observation and simulation results showed that MnO was not a strong oxidizer compared with FeO in the slag, but was an effective component for desulfurization. The simulation results also showed that the interfacial oxygen activity using MnO-based slag was much lower than that using FeO-based slag. The apparent equilibrium constants of phosphorus and sulfur, which were obtained by the kinetic modeling of experimental results, were found to increase with increasing the (MnO + CaO)/SiO₂ ratio of the slag. The controlling step(s) of each element transport across the slag-metal interface was discussed with the aid of the kinetic model.     

Kinetics of mass transfer of manganese and silicon between liquid iron and slags

The kinetics of mass transfer of Mn and Si between liquid iron and slags were investigated in laboratory experiments at 1600°C in MgO crucibles with 1500 g iron and 250 g slag. Three different slags consisting of CaO-MgO-MnO-SiO₂, MgO-MnO-SiO₂ and MgO-MnO-Al₂O₃-SiO₂ were used. The concentration-vs.-time curves, experimentally measured under defined flow conditions generated by gas stirring, were evaluated by application of a multi-component transport model in order to obtain the mass transfer coefficients. The numerical values of the thus determined measured mass transfer coefficients were compared with values calculated by a theory of mass transfer at liquid-liquid interfaces. The measured and theoretical values were in good agreement with each other in the case of reduction of MnO from the slag by Si in the metal, provided that the measurements had been carried out below a critical stirring intensity, above which metal droplets were emulsified in the slag. Experiments, where sulphur was dissolved in the metal melt and where the sulphur contents were systematically varied, showed no changes of the mass transfer coefficient in comparison to sulphur-free melts. The experimental mass transfer coefficients for the reduction of silica from the slag by manganese in the metal were smaller than those calculated by the mentioned mass transfer theory. This could be explained by inhibition of surface renewal under the influence of solid reaction products precipitated at the interface.     

Reduction of MnO from molten slags with liquid steel of high carbon content

This work estimated the reduction of MnO in slags of the CaO‐SiO₂‐FeO‐CaF₂‐MnO system and liquid steel with the initial composition (mass contents) 0.75 %Mn, 0.16 % Si and 0.5 to 2.0 % C, as an alternative to introducing Mn to the steel melt. The slag basicities (CaO/SiO₂) In the experiments were 2 and 3. MnO was obtained from manganese ore. The experiments were carried out in an open 10 kg induction furnace using Al₂O₃‐based refractory at 1873 K. The oxygen potential was measured throughout the experiments with a galvanic cell (ZrO₂‐solid electrolyte with a Cr/Cr₂O₃ reference electrode). The MnO reaction mechanism was analysed in terms of the slag basicity, the silicon and the initial carbon contents in the melt. The rate and the degree of MnO reduction were found to increase with the increasing of initial carbon content; however, the effect of slag basicity was less important. A kinetic analysis of the process was performed using a coupled reaction model.     

A thermodynamic study of silica-saturated iron silicate slags in equilibrium with liquid copper

The thermodynamic properties of silica-saturated iron silicate slags in equilibrium with liquid copper have been studied from oxygen partial pressure measurements in the temperature range from 1490 to 1580 K by means of a solid electrolyte galvanic cell. The following cells were used: Pt, Ni-NiO/O⁼/slag-Cu(l), Cr₂O₃, Pt; Pt, Fe-FeO/O⁼/slag-Cu(Fe sat.), Fe. A strong correlation was found between oxygen pressure and the copper content of the slag; the copper content increased from less than 1 pct near iron saturation to about 4 pct at an oxygen partial pressure of 7.2 x 10^?3 Pa. A similar correlation was found between the ferric iron/total iron ratio and the oxygen pressure. The oxygen content in liquid copper decreased with increasing iron content in liquid copper and increased slightly near iron saturation. This behavior could be explained qualitatively by using the standard free energy of formation of FeO and the activities of components.     

Distribution of vanadium between SiO2 rich slags and carbon saturated liquid iron

In order to determine optimal slag compositions for the extraction of vanadium from hot metal to SiO₂ rich slags, vanadium distributions were determined between slags of the following systems: FeO*–SiO₂ [(%V) ã 1.7] FeO*–SiO₂(sat)-CaO,Na₂O,MgO,Al₂O₃,TiO₂ [(%V) ã 1.7] FeO*–SiO₂–VO_n [(%FeO*)/(%SiO₂) = 1.5–1.7] and carbon saturated liquid iron at 1 300°C using the solid iron foil technique. The distribution increased with FeO* content in the binary FeO*–SiO₂ system, while additions of CaO, Na₂O, MgO and Al₂O₃ to FeO*–SiO₂ based slags under SiO₂ saturation caused the distribution to decrease. A slight decrease in distribution was also observed with increasing vanadium oxide content in FeO*–SiO₂ based slags having a constant (%FeO*)/(%SiO₂) ratio. The highest vanadium distributions were found in SiO₂ saturated slags with high TiO₂ contents. Vanadium valencies in the slags were determined by a wet analytic titration technique and the results showed that V^III+ is predominant. It was suggested that the predominating ionic species of vanadium in SiO₂ saturated slags are V³⁺ and VO⁺ while a change towards VO^?₂ may occur for FeO rich slags.     

Silicon-Oxygen equilibrium and nitrogen distribution between CaO-SiO2 slags and liquid iron

Silicon-oxygen equilibria in an Fe-0.003 ~ 27 mass pct Si alloy in equilibrium with the CaO-SiO₂ slags were studied in the temperature range of 1823 to 1923 K using a lime crucible. At the same time, nitrogen distribution ratios, L_N, between slag and metal were measured, and from these results and the reported values for activities of SiO₂, nitride capacities, , defined by (mass pct N). were evaluated. It was found that the values for L_N decreased, whereas those for increased with an increase in temperature. Activities of SiO₂ were determined using the values for L_N and obtained in previous gas-slag experiments. These values were compared with the previous results.