UV/VIS-spectroscopy of liquid slags

UV/VIS-spectroscopical methods have been applied to investigate the absorption behaviour of CaO-Al₂O₃-SiO₂-slags in a wide temperature range from 20 to 1655°C. The observations reveal a strong temperature dependence of the absorption bands, which can be explained by means of a newly developed theoretical model. The model also correlates the observed long-frequency UV cutoff-wavelength with the optical basicity. The definition of the optical basicity has been corrected for higher temperatures, since there are remarkable deviations between the solid and the liquid state, which have not been taken in consideration yet. Further investigations on a CaO-Al₂O₃-slag containing CaF₂ at 1500°C show that no Fe³⁺… F-complexes like Fe³⁺(F^?)₄ or Fe³⁺(F^?)₆ are formed. F^? reacts with Al³⁺ forming Al-O-F-complexes. The F^?-ions displace the O^2--ions from the Al³⁺. This causes the basicity to increase.     

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.     

Settling of copper drops in molten slags

The settling of suspended metal and sulfide droplets in liquid metallurgical, slags can be affected by electric fields. The migration of droplets due to electrocapillary motion phenomena may be used to enhance the recovery of suspended matte/metal droplets and thereby to increase the recovery of pay metals. An experimental technique was developed for the purpose of measuring the effect of electric fields on the settling rate of metallic drops in liquid slags. Copper drops suspended in CaO−SiO₂−Al₂O₃−Cu₂O slags were found to migrate toward the cathode. Electric fields can increase the settling rate of 5-mm-diameter copper drops 3 times or decrease the settling until levitation by reversal of the electric field. The enhanced settling due to electric fields decreases with increasing Cu₂O contents in the slag.     

Investigation into rheological characteristic and foaming behaviour of molten slags

The rheological characteristic and foaming behaviour of molten slags have been investigated at different temperatures and with different additives, such as coke, coal and CaO. In the experiment of rheological characteristic, a modified rotational viscometer with variable revolution's speed was applied. Therefore, constitutive equations and rheological parameters of molten slags have been established. The tolerance-analysis method is applied to judge whether a molten slag belongs to Newtonian fluid or not. The results of foaming behaviour in the blowing gas show that addition of coarse grain coke and coal decreases the foam height. However, the carbonaceous materials of fine grain and CaO powder can cause the increase in foam height. It has also been found from the experimental results that the foam index ∑ is only available for slag of Newtonian fluid in blowing gas. The reason may be well explained with the rheological characteristic of molten slags.     

Calculation for density of molten slags using optical basicity

Abstract

A model for density calculation of multicomponent slags was developed in the present work. This model is an extension of a previous model proposed by the present author. Density values of molten slags were calculated from molar volume values, which were calculated from molar volume of pure component and mixing molar volume. Mixing molar volume is correlated to differences between reciprocals of optical basicities of network forming oxides and those of network modifying oxides. Charge compensation for AIO₄^5? was taken into consideration explicitly. An increase in molar volume due to Al coordination shift from sixfold to fourfold was modelled by defining molar volume of a hypothetical state of alumina in fourfold coordination in the present work. Density values of M₂O–SiO₂ (M?=?Na, K), CaO–Na₂O–SiO₂, MgO–Na₂O–SiO₂, Al₂O₃–CaO–SiO₂, Al₂O₃–Na₂O–SiO₂ and Al₂O₃–CaO–MgO–SiO₂ system were calculated by employing the present model. Comparisons between calculated and experimental values in literature were also made. The calculated values are in good agreement with experimental data with a mean deviation within 2%. The present work also showed that the addition of network modifying oxide with high optical basicity values would lead to a remarkable negative deviation of molar volume from ideal mixing, which could be interpreted by considering larger Si–O shortening caused by metal cations with lower electronegativity. In addition, the positive deviation for metal oxide and alumina join was also well explained in terms of molar volume increase due to Al coordination change in the present work.     

Preparation of CeNi2 intermetallic compound by direct electroreduction of solid CeO2-2NiO in molten LiCl

Electrochemical reduction of solid CeO 2 -2NiO to produce CeNi 2 was conducted in molten LiCl at 650 oC. The electrochemical reduction behaviors of NiO, CeO 2 and their mixture were investigated by cyclic voltammetric measurements. Moreover, a series of electrolysis experiments of different electrolysis cell voltages and electrolysis duration were performed to evaluate the reduction mechanism of the mixed oxides pellet cathode as well as the energy efficiency of the process. Homogeneous CeNi 2 was prepared by electrolysis at the constant cell voltage of 3.5 V with a graphite anode. The results demonstrated that the NiO was preferentially reduced to Ni and it subsequently promoted the reduction of CeO 2 . The electrolysis energy consumption for preparation of the CeNi 2 could be as low as 6.5 kWh/kg-CeNi 2 .     

Dephosphorization equilibria between pure molten iron and CaO-saturated FeOn–CaO–CaF2 slags

Metal-slag refining reactions have been investigated to determine dephosphorization equilibria in steelmaking using CaO-saturated FeO_n–CaO–CaF₂ slags low in P₂O₅ content. Slag compositions have been optimized to achieve maximum partition ratios wt.%(P₂O₅)/wt.%[P] and minimum phosphorus contents in pure molten iron at 1 550 and 1 600°C. FeO_n–CaO–CaF₂ slags prove to be most effective dephosphorizers. Optimal slag compositions are between 10 and 20 wt.% FeO_n. Attempts were also made to present phosphate capacities fractions of free oxygen ions and theoretical optical basicities Λ as a function of the FeO_n content of slags. Dephosphorization capacity of FeO_n–CaO–CaF₂ slags is compared with that of FeO_n–CaO–SiO₂ and FeO_n–CaO–Al₂O₃ slags.     

冶金熔渣混合制备微晶玻璃的组成及性能优化

以电炉镍铁渣和普通高炉渣为主要原料,采用Petrurgic一步法制备了微晶玻璃,并结合力学性能测试,对样品进行了X射线衍射(XRD)、扫描电镜(SEM)等分析,讨论了电炉镍铁渣和普通高炉渣配比、Mg2+含量以及晶核剂Ti O2对成品微观结构及性能的影响规律.结果表明:将熔渣冷却至900℃结晶和650℃退火,能够制备出性能优良的微晶玻璃.当Mg2+含量增加且析出晶体为单一辉石族矿物时,微晶玻璃具有较高的力学性能.电炉镍铁渣或Mg2+含量增加,会导致其辉石族矿物含量增加,当两种渣混合掺量达到90%(镍铁渣质量分数50%,高炉渣质量分数为40%)且外掺2%MgO时,所制备微晶玻璃结构致密,仅含有单一辉石族矿物,包括透辉石、普通辉石和斜顽辉石,从而具有最优的力学性能,其抗折强度达210 MPa,抗压强度达1162 MPa.电炉镍铁渣或者MgO含量进一步增加,会导致镁橄榄石析出,此时微晶玻璃的力学性能显著下降.Ti O2含量的增加不改变微晶玻璃晶体种类,合适掺入Ti O2(本实验为质量分数2%)能够增强透辉石含量,提升性能;但过量掺入会抑制晶体生长,导致其性能下降.     

Thermodynamic assessment of the CaO-MgO-SiO2 system

The phase equilibrium and thermodynamic information of the CaO-MgO-SiO₂ system at 1 atm was reviewed and assessed by using thermodynamic models for the Gibbs energy of all the phases. The assessment was based on recent assessments of the CaO-MgO, CaO-SiO₂, and MgO-SiO₂ systems. Two thermodynamic models were used: the two-sublattice model for ionic liquids for the liquid phase, and the compound energy model for the solid solution phases. The model parameters were evaluated by fitting to the selected experimental data by means of a computer program, which can accommodate a variety of experimental data. A consistent set of parameters was obtained that sat-isfactorily described most of the experimental information. The models were found to be well-suited for the present system, and only a small number of adjustable parameters were needed. Extensive comparisons were made between the calculations and experimental data. Formerly Research Associate, Royal Institute of Technology     

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.     

Kinetic model for reduction of iron oxide in molten slags by iron-carbon melt

Rate of reduction of iron oxide in iron and steelmaking slags by mass contents of dissolved carbon (>3%) in molten iron depends upon activity of FeO, temperature, mixing of bulk slag and other experimental conditions. A general kinetic model is developed by considering mass transfer of FeO in slag, chemical reaction at gas-metal interface and chemical reaction at gas-slag interface, respectively, as the three rate controlling steps. A critical analysis of the experimental data reported in literature has been done. It is shown that in the case of slags containing mass contents of less than 5% FeO, the reduction of FeO is controlled by mass transfer of FeO in slag plus chemical reaction at gas-metal interface; when slags contain more than 40% FeO, the reduction of FeO is controlled by chemical reaction at gas-metal interface plus chemical reaction at gas-slag interface; at intermediate FeO mass contents (between ～ 5 and 40% FeO), the reduction of FeO is controlled by all three steps, namely, mass transfer of FeO in slag, chemical reaction at gas-metal interface and chemical reaction at gas-slag interface. The temperature dependence of rate constant for the gas-slag reaction is obtained as: In k₂ = –32345.4(&6128)/ T + 19.0(&3.42); σ_lnk2,1/T = &0.3. where k₂ is expressed in mol m^-2 s^-1 bar^-1. The mass transfer coefficient of iron oxide in bulk slag is found to vary in the range 1.5 × 10^-5 to 5.0 × 10^-5 m/s, depending upon the slag composition as well as experimental conditions.     

Nitrogen solubility in CaO-SiO2, CaO-MgO-SiO2, and BaO-MgO-SiO2 melts

Nitrogen solubility in molten CaO-SiO₂, CaO-MgO-SiO₂, and BaO-MgO-SiO₂ silicate systems was measured as functions of nitrogen and oxygen partial pressures and composition at 1823 K. Experimental findings indicate that nitrogen exists as a free nitride ion or is associated with silicate networks, depending principally on the slag composition. A special analytical technique was developed to separately determine the two species. Its dissolution mechanism, which is similar to that for hydrogen, was proposed, being supported by the detection of a Si-N bond by infrared spectroscopy. Neither the content of free nor incorporated nitrogen was demonstrated to have a very good correlation with the CaO or SiO₂ activity in the melts, probably because the activity coefficient of nitrogen is affected by the slag composition. Formerly Graduate Student, Department of Metallurgy, The University of Tokyo.     

Surface interactions between fayalite slags and synthetic spinels and solid solutions

To obtain a better understanding of the complex corrosion mechanisms occurring at the interface, the surface and interfacial properties between fayalite-type slags and homogeneous, synthetic spinels and solid solutions of these spinels were investigated. These oxides represent the conventional refractory components. The sessile drop technique incorporating high-temperature X-ray radiography was employed for this purpose. The experimental temperature was 1200 °C and the oxygen potential was 10⁻⁹ atm controlled by CO/CO₂ gas mixture. The contact angles between the solid substrates and molten silica-rich fayalite slag ranged from 0 deg for MgFe₂O₄ to 23 deg for MgAl₂O₄. When iron-rich slags were employed, the contact angles ranged from 15 deg for MgCr₂O₄ to 22 deg for MgAl₂O₄. The interfacial reactions between the slags and the various spinel materials and the dissolution of the solids into the slags are discussed.     

Benetzbarkeit von festen CaO-MgO-SiO2 - und Al2O3-SiO2-CaO-Oxiden durch flüssigen Stahl

Ermittlung der Benetzbarkeit von gesinterten Oxidmischungen der Systeme CaO–MgO–SiO₂ und Al₂O₃–SiO₂–CaO durch eine hochlegierte Eisenschmelze mit rd. 20 % Ni und 25 % Cr zur Simulation der Verhältnisse bei der Stahlerzeugung beim Kontakt zwischen Schmelze und feuerfester Zustellung. Aussagen zum Einfluß der Oberflächenrauheit des Oxids. Erörterung des Verhaltens exogener Einschlüsse aus den untersuchten Oxiden in der Schmelze.     

Equilibria between silica-saturated iron silicate slags and molten Cu-As,Cu-Sb,and Cu-Bi Alloys

The solubilities of copper, arsenic, antimony, and bismuth in silica-saturated iron silicate slag, equilibrated with molten copper which included the corresponding element, were measured at temperatures 1473 and 1523 K under oxygen pressures ranging from 10⁻¹ to 10⁻⁷ atm. The results confirm that copper is dissolved as CuO^0.5 in silica-saturated fayalite slag. Dissolution of As, Sb, and Bi was found to be dependent upon the oxygen potential, suggesting oxidic rather than atomic dissolution. The data obtained also support models in which these elements exist in the slag mainly as two different types of oxides, but occasionally these oxides coexist with neutral atoms. Based on these models, equations were obtained that related the solubilities of these elements in the slags to the oxygen potential in them. The knowledge obtained in this investigation will be helpful in eliminating deleterious minor elements in copper smelting.     

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.     

Chemical state of fluorine in fluoroaluminosilicate slags in glassy and molten states from perspective of electronic polarisability

Abstract

The electronic polarisability of F α _F has been determined for fluoroaluminosilicate slags from density and refractive index data measured to investigate the chemical state of F in the slags and the effect of CaF₂ additions on depolymerisation of the aluminosilicate network. To simulate commercial mould fluxes, synthetic slags with compositions of xCaF₂–5Na₂O–6Al₂O₃–(89–x)CaO.SiO₂ were prepared as samples, where x ranged between 5 and 12·5 mol.-%. Densities and refractive indices of the slags were measured in glassy and molten states; for the melts, the sessile drop method and ellipsometry were applied to density and refractive index measurements respectively. Values of α _F determined for the slags are on the whole in good agreement with those for CaF₂, irrespective of temperature, which suggests that F ions in the slags are in ionic bonding of Ca–F with a possibility of a Na–F bond. However, only a glassy slag with a lower concentration of CaF₂ exhibits a slightly smaller α _F than CaF₂, which would be a sign of Al–F and/or Si–F bonds being produced. From the value of α _F, F ions are likely to terminate silicate anions by forming Ca–F bonds in the slags and depolymerisation of the network by this termination would be responsible for lowering the viscosity of molten slags with CaF₂ additions.