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The Effect of Calcium Fluoride on Slag Viscosity
Abstract
The effect of CaF(2) on the viscosity of high-basicity Al(2)O(3)-CaO-MgO-SiO(2) (-CaF(2)) slags for secondary steelmaking was studied using a Brookfield digital viscometer. The addition of approximately 3 mass pct CaF(2) could decrease the liquidus temperature substantially in the case of high CaO containing slags, leading to good flowability of the slag at the temperature of the ladle treatment. The addition of CaF(2) had the strongest effect on the viscosity of liquid slag with high SiO(2) content. DOI:10.1007/s11663-011-9546-x (C) The Minerals, Metals & Materials Society and ASM International 2011
... 8,15) Therefore, effect of CaF 2 content on the viscosity of some metallurgical slags has been extensively investigated. Wu et al. 16) found that addition of less than 5% CaF 2 effectively decreases the viscosity of highly basic CaO-Al 2 O 3 -SiO 2 -MgO (C/S = 1.95-8.0) slags containing 25% Al 2 O 3 especially at low temperatures. ...
... Moreover, solid precipitation in molten slags was mostly neglected in previous studies on slag viscosity, even for highly basic slags. 16,17) In this work, we also focused on the effect of CaF 2 on the precipitation behaviors of the highly basic slags and further made clear the extent of solid precipitation in affecting slag viscosity. ...
... Such a phenomenon is consistent with previous studies. [16][17][18][19][20][21][22][23][24][25][26] Physical properties of slags including viscosity intrinsically depend on ionic structure of molten slags. Therefore, to clarify the mechanism of fluorine (F) ions in decreasing slag viscosity, various spectroscopic instruments, such as nuclear magnetic resonance (NMR) spectroscopy, 42) Raman spectroscopy, 25,30) X-ray photoelectron spectroscopy (XPS) 22,43) and Fourier transform infrared (FTIR) spectroscopy, 44,45) as well as molecular dynamics simulation method [45][46][47] have been used to explore the effect of F ions on the structural changes of molten slags. ...
To optimize CaF2 content in highly basic CaO-18%Al2O3-SiO2-10%MgO-CaF2 (%CaO/%SiO2=6, denoted as C/S=6) refining slags used for the production of Al-killed duplex stainless steel with high cleanliness demand, the effect of CaF2 content on the viscosity and refining ability of the slags were studied and compared with typical CaF2-free highly basic CaO-30%Al2O3-SiO2-10%MgO (C/S=6) slag. The effect of CaF2 addition in decreasing slag viscosity becomes less obvious with increasing temperature and CaF2 content. When CaF2 content exceeds 10%, slag viscosity only marginally decreases with further increasing CaF2 content. Both monoxide-CaO and monoxide-MgO phases are precipitated in all the CaF2-bearing slags. CaF2 addition slightly increases monoxide-MgO precipitation, but dramatically decreases monoxide-CaO precipitation. Viscosities of the CaF2-bearing slags were also theoretically calculated and good agreement with the measured values was observed. Moreover, the 6% CaF2-bearing slag has very close viscosities above 1833 K but much lower viscosities below 1833 K, compared with the CaF2-free highly basic slag. Further evaluation of the 6% CaF2-bearing slag on steel cleanliness confirms that 6% CaF2 addition is sufficient for the highly basic CaO-18%Al2O3-SiO2-10%MgO-CaF2 (C/S=6) slag. The mechanism of CaF2 in decreasing the viscosity of CaF2-bearing slags was discussed from the viewpoints that CaF2 behaves as a network breaker and that CaF2 suppresses the precipitation of solid phases. The first aspect was identified to play a much greater role in decreasing slag viscosity.
... In the CSAM slag system, the apparatus for viscosity measurement adopted by Pengcheng and Xiaojung (2016), Shankar et al. (2007) and Tang et al. (2011) were made by the rotating cylinder method at 1723 K (1450 °C) to 1823 K (1550 °C). This measurement method was also applied in other studies (Ji et al., 1997;Wu et al., 2011;Zhang and Chou, 2012;Chen and Zhao, 2015) in the CSAK, CSAMF and CAFeO slag systems. In the Zhang and Chou (2012) study, the temperature range was 1713 K (1440 ºC) to 1813 K (1540 ºC) and in the Wu et al. (2011) study, the temperature range was 1697 K (1424 ºC) to 1905 K (1632 ºC). ...
... This measurement method was also applied in other studies (Ji et al., 1997;Wu et al., 2011;Zhang and Chou, 2012;Chen and Zhao, 2015) in the CSAK, CSAMF and CAFeO slag systems. In the Zhang and Chou (2012) study, the temperature range was 1713 K (1440 ºC) to 1813 K (1540 ºC) and in the Wu et al. (2011) study, the temperature range was 1697 K (1424 ºC) to 1905 K (1632 ºC). Lastly, in the CAFeO system (Ji et al., 1997;Chen and Zhao, 2015) a range of 1423 K (1150 °C) to 1773 K (1500 °C) was used. ...
... CaO-SiO 2 -Al 2 O 3 -MgO (70 slags (Machin et al.,1952) CaO-SiO 2 -Al 2 O 3 -K 2 O (13 slags) (Zhang and Chou, 2012) CaO-SiO 2 -Al 2 O 3 -MgO-CaF 2 (9 slags) (Wu et al., 2011) CaO-SiO 2 -FeO (18 slags) (Ji et al., 1997) (Chen and Zhao, 2015) CaO-SiO 2 -MgO (4 slags) (Schumacher et al., 2015) CaO-SiO 2 -Al 2 O 3 (48 slags) (Chopra and Taneja, 1964) (Machin and Yee, 1948) (Urbain et al., 1982) Table 2 Systems adopted in viscosity calculations and their references. ...
This study focuses on the viscosity calculation of molten slags using computational thermodynamics. Different slag systems and their measured viscosities from different references were used and compared with those obtained through FactSage software. To calculate the viscosity of each slag the Viscosity module available in FactSage 6.4 was used. In order to perform the evaluation of computational thermodynamics in viscosity calculation, six different slag systems were presented, all of which were formed of calcium-silicate melts. In total, 162 slags, in temperatures ranges from 1423 K (1150 ºC) to 2089 K (1816 °C) were presented for all slag systems. The software showed a tendency to produce viscosity values lower than those found in the literature measured by an experimental method. The relative deviation between the measured and calculated viscosity values is in the range of 13.31 to 37.53% for evaluated systems. Considering all references and systems, the average deviation between measured and calculated viscosities is 23.61%, which, according to literature, is an acceptable value. The CaO-SiO2-Al2O3 and CaO-SiO2-FeO systems showed the best agreement between the experimental method and the method calculated through FactSage 6.4 with a very good fitting between viscosity values.
... In order to meet these requirements, it is necessary to consider and quantify the effect of fluorspar (CaF 2 ) addition on the viscosity of MnO-containing slags at high temperatures, because the CaF 2 is well known to decrease the viscosity of silicate melts. [3][4][5][6][7][8][9][10][11][12]15,19,20,24) The experimental study of the effect of CaF 2 on the viscosity of various silicate melts has been investigated by several researchers for CaO-SiO 2 (-MgO)-CaF 2 , [3][4][5][10][11][12]24) FeO(-CaO)-SiO 2 -CaF 2 , [6][7][8] CaO-SiO 2 -Na 2 O-Li 2 O-CaF 2 , 19) and CaO-Al 2 O 3 -SiO 2 -MgO-CaF 2 systems. 20) From the above studies, the viscosity itself and the activation energy of Newtonian flow of silicate melts generally decrease with increasing content of CaF 2 due to depolymerization reactions of silicate networks, indicating that the addition of CaF 2 is more effective in higher silica content region. ...
... [3][4][5][6][7][8][9][10][11][12]15,19,20,24) The experimental study of the effect of CaF 2 on the viscosity of various silicate melts has been investigated by several researchers for CaO-SiO 2 (-MgO)-CaF 2 , [3][4][5][10][11][12]24) FeO(-CaO)-SiO 2 -CaF 2 , [6][7][8] CaO-SiO 2 -Na 2 O-Li 2 O-CaF 2 , 19) and CaO-Al 2 O 3 -SiO 2 -MgO-CaF 2 systems. 20) From the above studies, the viscosity itself and the activation energy of Newtonian flow of silicate melts generally decrease with increasing content of CaF 2 due to depolymerization reactions of silicate networks, indicating that the addition of CaF 2 is more effective in higher silica content region. However, the effect of CaF 2 on the viscosity of the FeO-SiO 2 slags was not found to be as significant as in the case of the CaO-SiO 2 slags. ...
... [10][11][12]19) Also, for the highly basic slags, of which silica content is lower than about 10 mass%, CaF 2 suppresses the precipitation of solid phases at lower temperatures, whereas the effect of CaF 2 on viscosity itself is negligible when the slags are completely liquid at high temperatures. 20) From solidstate 19 F nuclear magnetic resonance (NMR) spectroscopic analyses of CaO-SiO 2 -CaF 2 (-Na 2 O) systems, it was reported that Fwas dominantly coordinated with Ca 2+ in alkali-free ternary system, whereas it predominantly bonded with Na + rather than Ca 2+ in quaternary system. In both cases, however, Fions were commonly believed not to break the Si-O-Si bonds. ...
The viscosity of the CaO-SiO2-MnO(-CaF2) slags (CaO/SiO2 = 1.0, MnO = 10, 40 mass%) was measured to clarify the effect of CaF2 on the viscous flow of molten slags at high temperatures. Furthermore, the Raman spectra of the quenched glass samples were quantitatively analyzed to investigate the structural role of CaF2 in a depolymerization of silicate networks. The critical temperature of the slags abruptly increased at 15 mass% CaF2, which was confirmed to originate from a crystallization of cuspidine using XRD analysis. The viscosity of the slags continuously decreased by CaF2 addition in the 10 mass% MnO system, whereas the viscosity of the 40 mass% MnO system was not significantly affected by CaF2 addition. The activation energy for the viscous flow of silicate melts decreased by CaF2 addition and its tendency became less significant in the more basic composition, i.e. in the 40 mass% MnO system. The effect of CaF2 on the viscosity of the slags was quantitatively analyzed using micro-Raman spectra of quenched glass samples accompanying with a concept of silicate polymerization index, Q(3)/Q(2) ratio. A polymerization index continuously decreased with increasing content of CaF2 in the 10 mass% MnO system, whereas it was not affected by CaF2 in the 40 mass% MnO system. Consequently, the bulk thermophysical property of the CaO-SiO2-MnO-CaF2 slags was quantitatively correlated to the structural information.
... As an additive material in steelmaking, CaF 2 usually decreases the viscosity of the slag. 7,8,[17][18][19][20] This is especially notable with slags containing SiO 2 . 8,20) CaF 2 has also been observed to affect the crystallization temperature of the slags 7,8,18) and the activity coefficient of FeO. ...
... 7,8,[17][18][19][20] This is especially notable with slags containing SiO 2 . 8,20) CaF 2 has also been observed to affect the crystallization temperature of the slags 7,8,18) and the activity coefficient of FeO. 21) On the other hand, in high MnO concentrations it is not recommended to add large amounts of CaF 2 due to corrosion of refractory material. ...
With the strict standards for steel quality and high production rates, the demand for faster and more convenient slag composition analysis for both electric arc and ladle furnaces has become a major issue in industrial steel plants. To overcome the time-delay between slag sampling and results of the slag composition analysis, an on-line slag composition analysis is required. Such a method that can be used in on-line analysis and is also chemically sensitive to the slag composition is optical emission spectroscopy. In this work, the optical emissions from the arc have been measured in an industrial ladle furnace and used for slag composition analysis. This article focuses on CaF2 and MgO, since the CaF2 is a common additive material in the ladle treatment and high MgO content means that the ladle refractory lining is dissolving into the slag. The analysis has been carried out by comparing emission line ratios to the XRF analyzed ratios of CaF2/MgO and MnO/MgO, respectively. The results show that several atomic emissions lines of calcium, magnesium, and manganese can be used to evaluate the CaF2/MgO and MnO/MgO ratios in the slag. It was found out that the plasma temperature derived from Ca I emission lines has a non-linear relation with the CaF2 content of the slag. Additionally, the dissociation pathways of molecular slag components were determined and studied in different plasma temperatures with equilibrium composition computation in order to determine the relations between the slag and plasma compositions.
... The CaF 2 is well known to decrease the viscosity of silicate melts, because fluorine is a network modifier which could rearrange the glass network by forming non-bridging fluorine to replace nonbridging oxygens. Consequently, adding CaF 2 to the glass batch affects the glass crystallization mechanism and the type of crystalline phases formed [19][20][21][22]. The effects of CaF 2 on viscosity of various silicate melts have been experimentally investigated by several researchers for different systems [20][21][22][23][24][25][26]. ...
... Consequently, adding CaF 2 to the glass batch affects the glass crystallization mechanism and the type of crystalline phases formed [19][20][21][22]. The effects of CaF 2 on viscosity of various silicate melts have been experimentally investigated by several researchers for different systems [20][21][22][23][24][25][26]. Further, CaF 2 can be used as a nucleation agent and is frequently added in small portions to LD glasses to stimulate the internal nucleation through phase separation [27]. ...
... Traditional mold fluxes are based on the CaO-SiO2-Al2O3 ternary system with the addition of fluorides to improve the physical properties and the heat transfer control in the mold [1,2]. The addition of fluorite can, for example, significantly reduce the melting temperature and viscosity of the mold fluxes and promote the crystallization of the slag film by cuspidine precipitation [3][4][5][6]. ...
... The viscosity data of CaO-Al 2 O 3 -SiO 2 -MgO-CaF 2 systems for comparison are from the research of Kim et al. [56], Wu et al. [57] and Yu [58] et al. and Jiao et al. [59] at various temperatures. The specific values of the selected 56 groups of data are listed in Table 5. ...
Model prediction is an effective method to obtain the physicochemical properties data of molten slags, which is difficult to test experimentally due to their high melting points. Empirical models are prevalent at present; however, it needs large amount of experimental data to fit the empirical parameters with narrow application scope. In this paper, the Kriging interpolation method modified with oxide property weights, is firstly introduced into the viscosity prediction of multicomponent slags. The prediction results of CaO–Al2O3–SiO2, CaO–Al2O3–CaF2, CaO–Al2O3–SiO2–MgO and CaO–Al2O3–SiO2–MgO–CaF2 systems showed that the predicted errors by the Modified Kriging Interpolation (MKI) method are smaller than those by various empirical models. It is anticipated that the MKI method can be extended to predicting the continuous physicochemical properties of multicomponent slags.
... In order to reduce the oxidation of Fe 2+ , shorten measurement time and obtain the relationship between viscosity and temperature over a wide range of intervals, viscosity measurements were conducted under continuous cooling cycles. Some other literature has also used continuous cooling methods for viscosity testing [10,27,28]. In the viscosity determination experiments, the resistance furnace was ramped up to 1673 K and then cooled with a rate of 3 K·min −1 . ...
Secondary copper smelting is an effective means of treating waste resources. During the smelting process, the viscous behavior of the smelting slags is essential for smooth operation. Therefore, the effects of Fe/SiO2 ratio and Fe2O3 contents on the viscous behavior of the FeO−Fe2O3−SiO2−8 wt%CaO−3 wt%MgO−3 wt%Al2O3 slag system were investigated. The slag viscosity and activation energy for viscous flow decrease with increasing Fe/SiO2 from 0.8 to 1.2, and increase as the Fe2O3 content increases from 4 wt% to 16 wt% at Fe/SiO2 ratio of 1.2. However, under the conditions of Fe/SiO2 of 0.8 and 1.0, the viscosity and activation energy for viscous flow show a minimum value at Fe2O3 content of 12 wt%. Fe2O3 exhibits amphoteric properties. In addition, the increase in Fe2O3 content raises the breaking temperature of the slag, while the Fe/SiO2 ratio has the opposite effect. Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy show that increases in Fe/SiO2 ratio lead to simplification of the silicate network structure, while increases in Fe2O3 content improves the formability of the network. This study provides theoretical support for the related research and application of secondary copper smelting.
... In China, the adopted production of axle steel is generally the electric arc furnace (EAF) → ladle furnace (LF) → vacuum degassing or Ruhrstahl-Heraeus process (VD or RH) → continuous casting (CC) route. The LF slag of axle steel is mainly designed based on a high-basicity CaO-Al 2 O 3 slag system [6], and the mass ratio of CaO to Al 2 O 3 is usually in the range w(CaO)/w(Al 2 O 3 ) = 1.0-2.0 [7]. ...
Fluorine-bearing refining slag (FBS) is used to produce axle steel for electric multiple unit vehicles. To avoid environmental pollution caused by fluorine, a fluorine-free ladle furnace slag (FFS) was designed based on an industrial FBS. The effects of main components on the physical and metallurgical properties of slag were investigated via theoretical analysis and laboratory tests. The composition range of components of the designed FFS are w(CaO) = 40–55 wt.%, w(SiO2) = 2–6 wt.%, w(Al2O3) = 30–40 wt.%, w(MgO) = 6–8 wt.%, and w(CaO)/w(Al2O3) = 1.25–1.50. Industrial-scale test results indicate that the FFS has similar deoxidation and desulfurization capabilities to industrial FBS.
... According to earlier studies, 2,20) the infiltration rate of slag into refractory increased with the decreasing of slag viscosity. The slag viscosity decreased with the addition of CaF 2 , [21][22][23] which could improve the slag fluidity and promote the penetration of slag into the corundum brick sample. Furthermore, it accelerated the mass transfer rate of the reactants at the reaction interface and provided more opportunity to make components of the refractory in contact with the slag, then resulted in the formation of compound such as MgO·Al 2 O 3 and aggravated the brick disintegration. ...
The corrosion behaviors of corundum brick and carbon composite brick used in blast furnace hearth by CaO–SiO2–MgO–Al2O3–Cr2O3(-CaF2) slags were studied in the present work. The degradation of the corundum brick in slag was a result of slag infiltration and brick dissolution, and the corrosion of the brick became more serious with the addition of CaF2 due to the decrease of slag viscosity. The disintegration of carbon composite brick in CaF2-containing slag was caused by the combination of slag penetration, brick dissolution and reaction between slag and brick. By comparing the corrosion behavior in CaF2-containing slag between the corundum brick and carbon composite brick, the corrosion degree of the corundum brick was greater than that of the carbon composite brick. To the blast furnace operation in which a low grade iron ore such as laterite ore and CaF2 containing slag (about 2 wt%) are used, it was found that the carbon composite brick with better slag corrosion resistance can be selected as a hearth refractory so as to improve the operation performance and ensure the longer campaign life of blast furnace.
... It has been revealed that the addition of CaF 2 to various calcium silicate melts decreases the viscosity of the melts due to depolymerization of silicate networks, indicating that CaF 2 modifies silicate networks with high silica contents. [9][10][11][14][15][16][17][18][20][21][22][23][27][28][29]32 The addition of a limited amount of CaF 2 has an effect on the depolymerization of the silicate networks in MgO-and Na 2 O-containing calcium silicate melts because basic oxides, such as MgO and Na 2 O, act as network modifiers in the silicate melts. 15,16,22 However, the addition of over 10 wt% CaF 2 to highly basic MnO-containing calcium silicate melts causes precipitation of solid phase, which increases the apparent viscosity of the calcium silicate melts. ...
The effect of CaF2 on the viscosities of the MO‐SiO2‐xMnO‐yCaF2 melts (M[=Ca or Ba]O/SiO2 = 0.4‐0.5, x = 10[±1] or 40[±2] mol%, y = 0‐15 mol%) have been studied at high temperatures. At MnO = 40[±2] mol%, the viscosity of Ba‐Mn‐silicate melts is lower than that of Ca‐Mn‐silicate melts because Mn²⁺ is a strong network modifier in the former system. However, the viscosities of both alkaline earth silicate melts with MnO = 10[±1] mol% are not affected by cation type because MnO activity is too low to affect the viscosity of the melts. The CaF2 addition decreases the viscosities of the Ba‐Mn‐silicate melts with low‐MnO contents, while it has less impact on the viscosities of the melts with high‐MnO contents. The effect of CaF2 on the relationship between viscosity and the structure of the silicate melts is quantitatively analyzed using the micro‐Raman spectra of quenched glass samples. The NBO/Si ratio of alkaline earth silicate melts, which indicates the degree of polymerization of the silicate networks, has a linear relationship with the activation energy for the viscous flow of the melts.
... Since changing the slag composition has a strong effect on its viscosity, it is common to use slags containing fluorite (CaF 2 ), as this reduces their viscosity and melting point. The addition of alumina (Al 2 O 3 ) should amplify this effect and produce slags with higher liquid fraction 3,[10][11][12][13][14][15] . The impact of top slag viscosity has been investigated by many researchers. ...
Secondary refining slag samples with different chemical compositions (45-54 % CaO, 7-13 % Al2O3, 20-29 % SiO2, 9-16 % MgO, 0-5 % CaF2) were investigated to verify the influence of their effective viscosity on inclusion cleanliness of DIN 38MnS6 in a steelmaking plant. The steel samples were collected during the production process for analysis of inclusions. Using the commercial software FactSage 6.4, thermodynamic calculations were performed to determine the effective viscosity, solid fraction, liquid fraction and MgO saturation point of these slags at 1560ºC. The results showed that all the slags were saturated in MgO, revealing a better protection of the ladle refractory. The addition of 2 to 5 % of CaF2 reduced the effective viscosity values for the analyzed slags from 0.45 Pa∙s to 0.10 Pa∙s , in comparison to the slags without the addition of CaF2, with an effective viscosity of 0.40 Pa∙s, 0.27 Pa∙s and 0.22 Pa∙s, decreasing the level of non-metallic inclusions for some of the analysed heats. However, it was detected during the manufacturing process that high slag fluidity and re-oxidation events continue to be a challenge associated with reducing the level of non-metallic inclusions.
... In practice, the viscosity is decreased further by the presence of some unreduced FeO, as well as the addition of lime CaO and fluorspar CaF 2 . Fluorspar is known to markedly reduce the viscosity of high-silica slags (Wu et al. 2011). However, the use of aluminium as reductant involves a high ED; ...
Ferromolybdenum, used in alloy steel production, is made by the batch reduction of molybdenum oxide by silicon and aluminium at high temperatures. In this work, the technology of the process has been reviewed and representative charge mixes compared. A computational thermodynamics model was developed and used to investigate the relationships between charge composition and ferroalloy grade and quality, indicated by its silicon content. The model predicted satisfactorily the composition of the ferromolybdenum and waste slag from a typical charge mixture. The silicon content depended on the ratio of silicon to molybdenum oxide in the charge and was not sensitive to the assumed smelting temperature or activity coefficient of silicon in the alloy. Losses of molybdenum to slag as dissolved oxide were predicted to be much lower than published industrial data, suggesting that losses in practice are mostly due to the inclusion of unsettled ferromolybdenum droplets.
... It is known that the addition of fluoride results in a decrease in the viscosity. [16][17][18][19][20][21][22][23] However, there have been reports contradicting this. Hence, the effect of anions, particularly fluoride anion, on the viscous behavior of slags is ambiguous. ...
The effect of the addition of CaX (X=Cl2, F2 and S) on the viscous behavior and structure of CaO–SiO2–Al2O3–MgO–CaX slag was investigated by measuring its viscosity. The viscosity of the slag without CaX gradually decreased with an increase in the C/S ratio because of the depolymerization of the silicate groups in the slag. While the viscosity of the CaX-bearing slag decreased with an increase in the CaX content, depolymerization was not observed in this case. Three distinct compositional regions for the activation energy of the viscous flow were observed because of the effect of the equilibrium of the polymeric silicate groups. The relaxation effect of the CaX groups on the activation energy was also observed. Raman spectroscopic analysis indicated that the relaxation in the viscosity and activation energy by CaX addition stemmed from the breaking of the NBO-M2+-NBO linkage to form NBO-M2+-F−, NBO-M2+-Cl−, or M2+-S2−. All these results are discussed in detail with the help of a viscous flow model based on the ionic interactions.
... Increase in both glass transition temperature and onset crystallization temperature of BaPF glasses with increase in CaF 2 content can be attributed to the increase in compactness of the glass structure [26,27]. Incorporation of Ca 2+ ions into the glass matrix, which is having larger field strength (0.69) compared to Ba 2+ (0.51) results in more tightened and compact glass structure due to shortening of phosphate chains and increase in both cross-link density and bond strength between phosphate chains [3,28,29], whereas the lower melting temperature of glasses with higher CaF 2 content may be due to the action of CaF 2 as a flux to reduce the viscosity of glass melt [30]. ...
... One of the most common means of decreasing the viscosities of slags and their melting temperatures is the addition of some fluorite to the slag. [14] It is especially important for cases of the dephosphorization or desulfurization [15] of pig irons containing chromium to keep the process temperature low and to minimize chromium losses. In slags of high basicity with CaO, fluorite increases the phosphate capacity and stabilizes the slag, forming the following fluorophosphates: 3Ca 3 (PO 4 ) 2 AECaF 2 . ...
The most up-to-date trends in stainless steel production—aiming at the reduction of production costs—consist of the substitution of steel scrap by hot metal, coming from the reduction of iron-chromium ores. This process requires a more extensive dephosphorization. The dephosphorization process, when applied to chromium steels, requires slag with high dephosphorization properties, as either chromium or chromium oxide entering the slag decreases distinctly the efficiency of the process. The results of laboratory investigations on the dephosphorization of liquid iron solutions containing chromium and nickel are presented. In particular, the study was focused on the selection of the optimal slag composition and the way the slag should be added. The slags based on calcium and fluorite with cryolite additions were considered. It was shown that the variables with the greatest impact on the dephosphorization process include chromium and nickel levels, temperature, and slag basicity. A statistical analysis was performed and regression equations were set. The results may be of use for the design of new methods of production of high-chromium steels.
To guide the development of CaO–Al2O3-based non-reactive mold flux for low-density high-strength steel production, CaO–Al2O3–CaF2 slags were calculated by first-principles molecular dynamics. The results showed that the stability order of corresponding bonds was Al–O > Ca–F > Ca–O > Al–F. With F− addition, the stability of Al–O and Al–F bonds enhanced, and that of Ca–O bond decreased while Ca–F bond almost did not change. Furthermore, although lower CaO/Al2O3 ratio increased the structure complex, the depolymerization and dilution of F played a dominant role to reduce the viscosity. Al–O and Al–F were charge-transfer bond, while Ca–O and Ca–F were ionic bond. The unstable hexahedron AlO4F evolved into tetrahedral AlO3F and AlO4 dynamically. In addition, the low content of F mainly formed AlO3F structure to depolymerize and stabilize the Al–O network structure, while the high content of F promoted AlO4F structure to reduce the symmetry and stability of slag.
Accurate viscosity of molten blast furnace (BF) slag is indispensable for the development of centrifugal-granulation-assisted thermal energy recovery (CGATER) to decarbonize the iron and steel industry. Yet, direct experimental measurement of this quantity remains a formidable task due to the high temperature of 1600 Kelvin or above. Empirical models, if with high fidelity, are ideal to enable a fast and accurate prediction of the high-temperature viscosity of molten blast furnace slag. In this communication, we embark on a new effort to develop an artificial neural network (ANN)-based model to provide accurate viscosity prediction of molten blast furnace slag. This model was established based on a grid search method with approximately 4000 experimental measurements collected as the train and validation datasets. The viscosities of three types of molten blast furnace slag were measured above 1600 K as cross validation for the ANN model. Our ANN model agrees well with the experimental measurement with a small uncertainty of < 6%. Finally, an open-source artificial neural network code with a graphical user interface (GUI) was developed to provide a user-friendly portal for high-fidelity viscosity prediction. The present study not only enables a definitive, unified viscosity determination but also provides a flexible tool for the database establishment of the thermophysical properties of molten BF slag.Graphical Abstract
We developed an ANN-based model to enable fast and accurate viscosity prediction of molten blast furnace slags at high temperatures and provided a user-interfaced open-source program, i.e. X-slag: Thermophysical Property.
Resource and harmless treatment of spent cathode carbon (SCC) in aluminum electrolysis and copper slag is a great significance in the environmental protection and sustainable development of resources. This study proposes to use SCC as a reductant for copper slag cleaning and CaO as an additive to recover copper from the slag while achieving fluorine fixation. After adding 2.4 pct CaO at 1220 °C, fluorine exists in the form of CaF2 in slag, and the fluorine fixation rate and copper recovery are 81.32 and 94.04 pct, respectively. When excessive CaO is added, the fluorine phase in the slag is transformed into Ca4Si2O7F2. The leaching toxicity of fluorine after co-treatment is 8 mg/L, which meets the national emission standard (100 mg/L). The co-treatment of SCC and copper slag improves the utilization of industrial waste and achieves harmless treatment of hazardous waste.Graphical Abstract
Ti-bearing blast furnace slag (TBFS) and diamond wire saw silicon powder (DWSSP) waste are solid wastes that have been investigated by researchers. In this paper, the possibility of metal thermal reduction of TBFS is determined by calculating the component activities using the molecular interaction volume model (MIVM). The metal thermal reduction and electromagnetic separation technique was used to simultaneously recover titanium (Ti) and silicon (Si) from waste. DWSSP and Al were used as the reducing agents for the high-temperature reduction of TBFS in an induction furnace. The reduced Ti was alloyed with a small amount of Al and residual Si in DWSSP. The alloy and slag were separated by electromagnetic stirring because they were subjected to forces in opposite directions. The effects of CaF2 addition and holding time on the recovery rate of Ti were studied. It was found that the addition of CaF2 to the raw materials improved the separation of the alloy from the slag. Si and TiSi2 were the main phases in the recovered alloy. This simple process provides a new method to recover Ti and Si from TBFS and DWSSP.
Several research projects are currently focused on the search for new sources of scandium due to its expected increasing demand in advanced technology applications. The Kiviniemi Fe-Sc-enriched mafic intrusion is a potential primary source for Sc. According to the recent investigations on the FeO component reduction in the Kiviniemi magnetic Sc concentrate at various end temperatures, complete FeO reduction is achieved at the highest experimental temperature (1500 °C). However, efficient separation of metal from the Sc2O3-enriched slag is hindered by the high viscosity of the slag. In this study, investigations of the Kiviniemi-type concentrate reduction characteristics are complemented from three perspectives: (1) slag modification with CaF2 and/or CaO to promote the reduction of the FeO component and metal separation, (2) reduction characteristics of the concentrates with a slightly different modal mineralogy and chemical composition, and (3) description of the main features of the progression of reduction at selected temperatures (950, 1050, 1150, 1250, and 1350 °C) with CaO addition. Both CaF2 and CaO increase conversion rates at a lower temperature region and promote the separation of metal from the slag. High-temperature behavior of the concentrates used in this study is essentially similar, although the main reduction stage is initiated at a slightly higher temperature for concentrates with less amphibole and a higher amount of nonferrous gangue minerals. Only after the complete decomposition and melting of clinopyroxene and nonferrous minerals of the concentrate, the final reduction of the FeO component from the slag can take place.
The present study investigated the effects of Fe/SiO2 and MgO content on the viscous behaviors of the slag formed by the charging of secondary resources into the copper-smelting furnace. It is determined that the increase of Fe/SiO2 (0.8–1.2) and the addition of MgO (1–7 wt pct) both reduce the slag viscosity. The addition of MgO accelerates the transition of breaking temperature of slags to higher temperatures, while the effect of Fe/SiO2 on that is relatively complicated. Fourier transform infrared spectroscopy (FTIR) and Raman spectra indicate that increases in either Fe/SiO2 or MgO content contribute to depolymerization of silicate network structures in high-temperature melts. The [AlO6]9− octahedra in the melt tended to increase with increasing Fe/SiO2 and MgO content, while the opposite change is observed for [FeO4]5− tetrahedra. Moreover, an increase in Fe/SiO2 or MgO content also leads to a gradual decrease in the activation energy of slag viscous flow, except in the case of Fe/SiO2 of 1.2 and MgO content of 7 wt pct. This unexpected discrepancy can be accounted for different types of flow units that arise in the slag at high temperatures.
The laboratory-scale experiments between the CaF2-CaO-Al2O3-SiO2-B2O3 slag and 9CrMoCoB steel were carried out in alumina and magnesia crucibles at 1823 K to investigate the oxidation behavior of boron (B) during the electroslag remelting (ESR) process. The activities of SiO2 and B2O3 in the slag and the activities of Si and B in the molten steel were calculated by the ion and molecule coexistence theory (IMCT) and the Wagner formalism, respectively. The results showed that both SiO2 and B2O3 have a significant influence on the equilibrium B content. The calculated content of B was in good agreement with the experimental value when the SiO2+B2O3 content in the slag is more than 3.3 wt%. The temperature had little influence on the equilibrium B content when the SiO2, B2O3 and CaO content were in the ranges of 3 to 5 wt%, 0 to 1 wt%, and 20 to 30 wt%, respectively. However, the Si is more prone to oxidation than is B as the temperature increases, indicating that more SiO2 should be added in the slag to reduce the oxidation of Si. From the 80 tonnes industrial tests, the distribution of B and Si content along with the radial direction of the remelted ingot was almost uniform, which is in line with the calculated B content (approx. 30 ppm) under conditions of the Si content in the liquid steel and the (%B2O3)/(%SiO2) ratio are 0.07% and 0.05, respectively, at 1973 K.
CaO and CaF2 are important slag constituents and additive materials in secondary metallurgy. Optimization of the quantity of these compounds has a key role in adjusting the slag chemistry for optimal refining properties. In this study, the CaO and CaF2 content of the slag has been analyzed with optical emissions from an industrial ladle furnace measured through the casting spout. Molecular optical emissions from CaO and CaF were observed directly from the molten bath and the arc, whereas atomic emission lines from the slag components were detected in the arc spectra. Optical emissions from CaO, CaF, and atomic calcium lines have been correlated with the CaO and CaF2 content of the slag. The CaO and CaF2 content of the slag could be evaluated from the spectra ranging from 10 to 41 min before the X-ray fluorescence (XRF) analysis was finished. The mean differences between the OES and XRF analysis were 0.59 % and 0.61 % for CaF2, and 2.19 % and 0.67 % for CaO when using the spectra from the molten bath and the arc, respectively. The method has the potential to work as an in situ online measurement system due to real-time data acquisition and fast computation times.
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Traditional ESR technology using the slag with high CaF2 content is faced with high specific power consumption and fluoride pollution. Under the double pressure, it is therefore very important to have a good understanding of the ESR process. The energy utilization η of the ESR is depended on both the electrical ηE and thermal efficiency ηH. Tailoring slag composition is one of the useful techniques to enhance the energy utilization, because of the slag is very important to generate Joule heat for melting electrode, control horizontal heat transfer, maintain uniform distribution of alloy elements from the bottom to top of the remelted ingots in the ESR process. Therefore, this paper aims to review the effects of slag composition, especially CaF2 content, and temperature on the electrical conductivity and thermal conductivity, which further influences the heat balance during the ESR process. The volatilization mechanism of the liquid fluoride‐containing slag at elevated temperature are introduced in this article from the perspective of thermodynamics and kinetics. Meanwhile, some of the recent advances and technology improvements in energy utilization and productivity enhancements for the ESR process have been summarized in this article, which will provide benefits to achieve sustainable development for the ESR process. This article is protected by copyright. All rights reserved.
The viscosity of Al 2 O 3 /SiO 2 melts is important because it affects secondary steelmaking. In this study, the effect of the Al 2 O 3 /SiO 2 ratio on the viscosity was investigated for a CaO-Al 2 O 3 -SiO 2 -CaF 2 -MgO slag system. Softening point determination, structural analysis, and thermodynamic analysis were carried to explain and confirm the viscosity results. The lowest viscosity of 19 mPa · s was observed for 14Al 2 O 3 -18SiO 2 . An increase in the Al 2 O 3 /SiO 2 ratio to 27Al 2 O 3 -5SiO 2 resulted in an increase in the viscosity to 83 mPa · s at 1600 8C. In the case of 6Al 2 O 3 -26SiO 2 , the main structural unit was [SiO 4 ] ⁴ - (tetrahedral) stretching vibration bands, whereas for 14Al 2 O 3 -18SiO 2 , the dominant [SiO 4 ]- (tetrahedral) stretching vibration bands decreased after Si-O-Al vibratio4n bands became dominant. [AlO 4 ] ⁵ - (octahedral) bands were observed with increasing Al 2 O 3 / SiO 2 ratio in the CaO-Al 2 O 3 -SiO 2 -CaF 2 -MgO slag system.
In China, two typical vanadium–titanium magnetite ores were used as raw materials in iron making. In order to obtain the differences in the high temperature metallurgical properties of these ores, the phase and microstructure of on-site sinter, pellet, slag and laboratorial non-dripped slag were analyzed by XRD and SEM–EDS. The results show that the phases of two typical sinter and pellet have no significant changes, but the microstructures are different. The softening start temperature and softening zone of high chromium vanadium–titanium magnetite (HCVTM) burden are higher than ordinary vanadium–titanium magnetite (VTM) burden. The melting start temperature of HCVTM burden is higher and melting–dripping zone is smaller than VTM burden, which is beneficial to the blast furnace smelting. In addition, the calculation results using Factsage 7.0 are in accord with the experimental results. The primary crystal field of slag of HCVTM is the melilite, and the liquidus temperature is 1409.81 °C; the primary crystal field of slag of VTM is CaTiO3, and the liquidus temperature is 1418.51 °C.
This paper presents the idea of increasing the effectiveness of slag decopperisation in an electric furnace in the "Głogów II" Copper Smelter by replacing the currently added CaCO3 with a less energy-intensive technological additive. As a result of this conversion, one may expect improved parameters of the process, including process time or power consumption per cycle. The incentives to optimize the process are the benefits of increasing copper production in the company and the growing global demand for this metal. The paper also describes other factors that may have a significant impact on the optimization of the copper production process. Based on the literature analysis, a solution has been developed that improves the copper production process. The benefits of using a new technology additive primarily include increased share of copper in the alloy, reduced production costs, reduced amount of power consumed per cycle and reduced time it takes to melt. At the conclusion of the paper, the issues raised are highlighted, stressing that mastering the slag slurry process in electric furnaces requires continuous improvement.
The viscosity of SiO2–Al2O3–CaO–MgO system and its subsystems are of fundamental importance for control and optimization of metallurgical, material, energy and geological phenomena. In this work, an accurate and simple viscosity model suitable for use in numerical simulations was established for SiO2–Al2O3–CaO–MgO system and its subsystems, based on the physically meaningful MYEGA equation. The model was calibrated by 4403 viscosity data measured in non-graphite crucibles. It was found current model calculates the viscosity with a remarkable overall accuracy of 15.8%. For each of the subsystems, current model also results in very good accuracy lower than 20%. The model could calculate the viscosity very reliably over the entire composition, temperature and viscosity value ranges studied in the work, even for viscosity value as low as 10⁻² Pa·s. The composition dependences of viscosity for binary, ternary and quaternary systems were derived using established model. The effects of each component on viscosity were interpreted according to the concept of network “former” and “modifier” and the charge compensation effect of Ca²⁺ on the tetrahedral-coordinated structure of Al³⁺.
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An effective process for recycling lead from hazardous waste cathode ray tubes (CRTs) funnel glass through traditional lead smelting has been presented previously. The viscous behavior of the molten high lead slag, which is affected by the addition of funnel glass, plays a critical role in determining the production efficiency. Therefore, the viscosities of the CaO–SiO2–“FeO”–12wt%ZnO–3wt%Al2O3 slags were measured in the current study using the rotating spindle method. The slag viscosity decreases as the CaO/SiO2 mass ratio is increased from 0.8 to 1.2 and also as the FeO content is increased from 8wt% to 20wt%. The breaking temperature of the slag is lowered substantially by the addition of FeO, whereas the influence of the CaO/SiO2 mass ratio on the breaking temperature is complex. The structural analysis of quenched slags using Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy reveals that the silicate network structure is depolymerized with increasing CaO/SiO2 mass ratio or increasing FeO content. The [FeO6]-octahedra in the slag melt increase as the CaO/SiO2 mass ratio or the FeO content increases. This increase can further decrease the degree of polymerization (DOP) of the slag. Furthermore, the activation energy for viscous flow decreases both with increasing CaO/SiO2 mass ratio and increasing FeO content.
Introduction Materials and Methods Results and Discussion Conclusions Acknowledgments
Density and viscosity components of multifunction Γ(T,ρ,η,к) which for requested working temperature (T), density (ρ), viscosity (η) and electrical conductivity (к) defines all six-component (CaF2, CaO, MgO, AI2O3, TiO2, SiO2) slags of requested properties have been defined. The seven parameter correlation parameters describing molten flux density were calculated using Gauss-Jordan multivariable regression analysis approach and literature data. Mills and Sridhar method for estimating molten flux viscosity, has been used. The brute force algorithm for solving Γ has been updated and tested. Our results showed, despite of the exploratory nature of our work, that the calculated compositions included slags manufactured at American Flux & Metal, both: containing fluorspar and those composed only of oxides. The developed numerical algorithm for solving multifunction Γ is powerful enough to give us solutions in reasonable time so in the future additional components of ESR slags (MgF2, MnO2, LaF3, La2O3, and ZrO2) will be also included in the set of solutions.
The viscosity of the CaO-SiO2-xMnO-yCaF2 slags (C/S=1.0; x=10, 40%; y=0 to 15%) was measured to clarify the effect of CaF2 on the viscous flow of molten slags at high temperatures. Furthermore, the Raman spectra of the quenched glass samples were quantitatively analyzed to investigate the structural role of CaF2 in a depolymerization of silicate networks. The critical temperature of the slags abruptly increased at 15%CaF2, which was confirmed to originate from a crystallization of cuspidine using XRD analysis. The viscosity of the slags continuously decreased by CaF2 addition in the 10%MnO system, whereas the viscosity of the 40%MnO system was not significantly affected by CaF2 addition. The effect of CaF2 on the viscosity of the slags was quantitatively analyzed using micro-Raman spectra of quenched glass samples accompanying with a concept of silicate polymerization index, Q3/Q2 ratio. A polymerization index continuously decreased with increasing content of CaF2 in the 10%MnO system, whereas it was not affected by CaF2 in the 40%MnO system. Consequently, the bulk thermophysical property of the CaO-SiO2-MnO-CaF2 slags was quantitatively correlated to the structural information.
Density and viscosity components of multifunction Γ(T, ρ, η,κ) which for requested working temperature (T), density (ρ), viscosity (η) and electrical conductivity (κ) defines all six-component (CaF 2 , CaO, MgO, Al 2 O 3 , TiO 2 , SiO 2) slags of requested properties have been defined. The seven parameter correlation parameters describing molten flux density were calculated using Gauss-Jordan multivariable regression analysis approach and literature data. Mills and Sridhar method for estimating molten flux viscosity, has been used. The brute force algorithm for solving Γ has been updated and tested. Our results showed, despite of the exploratory nature of our work, that the calculated compositions included slags manufactured at American Flux & Metal, both: containing fluorspar and those composed only of oxides. The developed numerical algorithm for solving multifunction Γ is powerful enough to give us solutions in reasonable time so in the future additional components of ESR slags (MgF 2 , MnO 2 , LaF 3 , La 2 O 3 , and ZrO 2) will be also included in the set of solutions.
The effects of MgO and TiO2 on the viscosity, activation energy for viscous flow, and break-point temperature of titanium-bearing slag were studied. The correlation between viscosity and slag structure was analyzed by Fourier transform infrared (FTIR) spectroscopy. Subsequently, main phases in the slag and their content changes were investigated by X-ray diffraction and Factsage 6.4 software package. The results show that the viscosity decreases when the MgO content increases from 10.00wt% to 14.00wt%. Moreover, the break-point temperature increases, and the activation energy for viscous flow initially increases and subsequently decreases. In addition, with increasing TiO2 content from 5.00wt% to 9.00wt%, the viscosity decreases, and the break-point temperature and activation energy for viscous flow initially decrease and subsequently increase. FTIR analyses reveal that the polymerization degree of complex viscous units in titanium-bearing slag decreases with increasing MgO and TiO2 contents. The mechanism of viscosity variation was elucidated. The basic phase in experimental slags is melilite. Besides, as the MgO content increases, the amount of magnesia–alumina spinel in the slag increases. Similarly, the sum of pyroxene and perovskite phases in the slag increases with increasing TiO2 content.
In the Blast Furnace (BF) process, the viscous behaviors of molten slags are essential to the efficiency and the productivity of operations. In this work, the effects of CaO/SiO2 and Al2O3 on the viscosity, activation energy for viscous flow, and break point temperature of titanium-bearing BF slags are analyzed. To connect the viscosity and the slag structure, Fourier transform infrared spectroscopy (FTIR) is performed on the as-quenched slags. It is found that the viscosity and the activation energy for viscous flow of slags decrease as the CaO/SiO2 content increases from 1.00 to 1.20 and increase with increasing the Al2O3 content from 11.00 to 15.00 wt%. As for the break point temperature, it raises when the CaO/SiO2 and the Al2O3 content increases. FTIR results reveal that the polymerization degree of complex viscous units in the slag decreases as the CaO/SiO2 increases. However, it is opposite when the Al2O3 content increases. The variation of viscosity and activation energy for viscous flow for the different CaO/SiO2 and Al2O3 content slags are explained.
The viscosity of the CaO-SiO2-xMnO-yCaF2 slags (C/S=1.0; x=10, 40%; y=0 to 15%) was measured to clarify the effect of CaF 2 on the viscous flow of molten slags at high temperatures. Furthermore, the Raman spectra of the quenched glass samples were quantitatively analyzed to investigate the structural role of CaF2 in a depolymerization of silicate networks. The critical temperature of the slags abruptly increased at 15%CaF2, which was confirmed to originate from a crystallization of cuspidine using XRD analysis. The viscosity of the slags continuously decreased by CaF2 addition in the 10%MnO system, whereas the viscosity of the 40%MnO system was not significantly affected by CaF 2 addition. The effect of CaF2 on the viscosity of the slags was quantitatively analyzed using micro-Raman spectra of quenched glass samples accompanying with a concept of silicate polymerization index, Q 3/Q2 ratio. A polymerization index continuously decreased with increasing content of CaF2 in the 10%MnO system, whereas it was not affected by CaF2 in the 40%MnO system. Consequently, the bulk thermophysical property of the CaO-SiO2-MnO-CaF2 slags was quantitatively correlated to the structural information.
Addition of CaF2 to the CaO-SiO2-MnO (CaO/SiO2 = 0.5) system, which corresponds qualitatively to a silicomanganese ferroalloy smelting slag, affected not only the critical (crystallization) temperature (T
CR) but also the viscosity at high temperatures, and its influence on slag properties was strongly dependent on the content of MnO in the slag. The viscosity of CaF2-free 10 mass pct MnO slag was relatively high, i.e., about 10 dPa s at 1773 K (1500 °C), but decreased continuously upon addition of CaF2 to the system. In contrast, the viscosity of the 40 pct MnO system was very low, i.e., 1 dPa s at 1773 K (1500 °C), and CaF2 did not have a large effect. This indicates that Mn2+ is a strong network modifier in manganese ferroalloy smelting slags. Nevertheless, CaF2 addition was very effective at decreasing the viscosity of low MnO slags at low temperatures. The activation energy for the viscous flow of silicate melts decreased linearly in response to CaF2 addition, but this tendency was less pronounced in the more basic composition of the slag. The effect of CaF2 on the viscosity and activation energy for viscous flow of melts was analyzed quantitatively using micro-Raman spectra of quenched glass samples and the silicate polymerization index, i.e., Q3/Q2 ratio. The polymerization index decreased continuously with increasing CaF2 content in less basic (10 pct MnO or C/S = 0.5) slags, whereas it was not affected by CaF2 content in highly basic (40 pct MnO and C/S = 1.0) slags. Bulk thermophysical properties of the CaO-SiO2-MnO-CaF2 slags were quantitatively correlated with the structural information of the slags.
The structure-viscosity relationship of the low-silica (SiO2 <= 10 wt%) calcium aluminosilicate melts, which represent the secondary refining ladle slag systems, was investigated by employing the rotatingcylinder viscosity measurement in conjunction with the Raman spectroscopy measurement for linking the macroscopic thermophysical property and molecular (ionic) structural information. Furthermore, the influence of CaF2 on the structure-property relationship was explored. The viscosity of low-silica calcium aluminosilicate melts decreased with increasing both CaO/Al2O3 and CaO/SiO2 ratios. However, the effect of the former on the viscosity of low-silica calcium aluminosilicate melts was larger than that of the latter. By employing the Neuville's structure model, in which the silicate structural units with various NBO, i.e. Q(n)si are located at the boundary of the AlO4 aluminate, and the Raman scattering data of the glass samples, it was demonstrated that the aluminate and silicate units are more effectively modified by increasing the CaO/Al2O3 ratio at fixed silica content. The addition of small amounts of CaF2 (similar to 5 wt%) to the low-silica calcium aluminosilicate melts decreased the viscosity of the melts. From the analysis of Raman scattering data, the liberation of SiO44- (Q(Si)(0)) units from the AlO4 aluminate structure by addition of CaF2 was understood. However, the effect of CaF2 addition on the viscosity became less discernible at higher CaF2 content (>= 10 wt%) region, where the F ions simply substitute for the non-bridging oxygen ions in AlO4 tetrahedra.
An equation has been proposed for predicting the viscosities of industrial mold fluxes for steel casting, on the basis of relationships between the network parameter and the reciprocal of the basicity index. The viscosities of mold fluxes have been calculated using the equation proposed by the authors and several representative equations, and compared with experimental data. The proposed equation provides the most satisfactory results for predicting the viscosities of multicomponent mold fluxes used in continuous casting of steels.
In an effort to systematize the knowledge of the viscosities of slags containing CaF2 and to enable the prediction of the change of viscosities of mould flux slags, viscosity measurements of synthetic slags in the system "FeO"-SiO2-CaF2 were carried out in the temperature range 1450-1763 K. Five different fayalite slag compositions with "FeO" contents varying between 55-65 mass% in the homogeneous liquid range were chosen for the studies. The CaF2 content was varied between 5 and 15 mass%. Due to the reactions between the slag components and CaF2, some CaO was formed during the premelting of the slags. Through analysis, it was found that, compositional changes due to fluoride evaporation occurred during the long premelting period. The libration of the volatile components SiF4 and FeF2 during sample preparation was the main source for compositional changes. DTA experiments were carried out in order to determine the liquidus points of the slags studied. CaF2 was found to decrease the liquidus temperatures. The viscosities were measured by the rotating cylinder method using spindles and crucibles made of iron in an argon atmosphere. The results showed the effect of the CaF2 content on viscosity. The activation energy for viscous flow was generally dependent on the "FeO"/SiO2 ratio and viscosity increased with decreasing temperature. The effect on the viscosities of "FeO"-SiO2 slags due to CaF2 additions was not found to be as significant as in the case of CaO-SiO2 slags.
This article considers the viscous-flow phenomenon in molten silicate melts in the vicinity of their liquidus temperatures.
An agglomeration of ionic species occurs in the liquid slag with decreasing temperatures and results in an increase in the
viscosity and the activation energy for viscous flow. The latter was found to be nonlinear, increasing rapidly as the temperature
is approached wherein a solid phase is likely to separate from the liquid. The second derivative of the activation energy
for viscous flow with respect to temperature was found to show a discontinuity in the vicinity of the liquidus temperature.
This has been verified in the case of viscous flow for both pure water and CaOSiO2 melts. Experimental data for the viscosities of complex silicate melts and mold fluxes have also demonstrated the occurrence
of a discontinuity in the second-derivative function, which is in accordance with the liquidus temperature as determined by
differential thermal analysis (DTA). Thus, the second derivative offers a useful way of estimating the liquidus temperatures
of multicomponent silicates, which are often difficult to determine due to supercooling effects.
A correlation to predict the viscosities of ternary silicates using the Gibbs energies of mixing of the silicate melts has
been developed. This correlation has been employed to predict the viscosities of liquid slags in the systems FeO-MnO-SiO2, FeO-MgO-SiO2, CaO-FeO-SiO2, CaO-MnO-SiO2, and CaO-MgO-SiO2. The good agreement between the calculated viscosities and the experimental data in the ternary silicate systems has indicated
that this approach can be successfully employed to predict the viscosities of ternary silicate melts.
In the present work, information on the integral molar Gibbs energies of mixing is employed to calculate the viscosities of
binary substitutional metallic melts. A correlation has been established between the second derivative of the integral molar
Gibbs energy of mixing with respect to composition and the corresponding function for the Gibbs energy of activation for viscosity.
The viscosities predicted from available thermodynamic data in the case of a number of binary metallic systems using this
correlation show satisfactory agreement with the values reported from experimental measurements. The value of this correlation
in predicting the viscosities of complex metallic melts is also examined.
The viscosity of silicate melts and slags is a property difficult to measure accurately using sophisticated apparatus, it is both time consuming and expensive. The use of models to estimate the viscosity is the first step to be carried out, mainly with metallurgical slags involving numerous components. The proposed model is an experimental one based on accurate data for pure binary and ternary melts. From this data, using a simple hypothesis on the behaviour of unusual compounds, it is possible to estimate the viscosity of a complex melt. This estimation is used as a first approximation and can be amended, if necessary, by only a few direct measurements. Die Viskositätsmessungen von Schlacken und flüssigen Silikatschmelzen sind zeitaufwendig und schwierig. Um genaue Messungen zu erhalten, benötigt man komplizierte Geräte, da man bei hohen Temperaturen arbeiten muß. Für viele Anwendungen und ganz speziell für die metallurgischen Schlacken mit zahlreichen Komponenten können berechnete Werte genügen. Das Versuchsmodell für diese Werte beruht auf Viskositätsmessungen, die an binären und ternären Schmelzen vorgenommen wurden. Die berechneten Werte beziehen sich auf die Eigenschaften der Komponenten, für die es keine direkten Messungen gibt. Im allgemeinen ist der berechnete Wert ein erster Näherungswert, der allenfalls durch eine bestimmte Anzahl von direkten Messungen verbessert und vervollständigt werden muß.
An expression describing the excess viscosity of liquid binary alloys has been derived by use of some basic physical quantities, in order to estimate the viscosities of liquid alloys which are considered to be one of the most important properties in metallurgical processes, as follows;
Δη= (x1η1+x2η2) [-5x1x2 (σ1-σ2) ²/x1σ²1+x2σ²2+2 {√1+ (x1x2√m1-√m2) ²/ (x1√m1+x2√m2) ²-1} -0.12x1x2Δu/kT]
where, Δη: excess viscosity (cP), x: atomic fraction (x1+x2=1), η: viscosity of pure liquid metal, σ: diameter of the sphere (ionic radius after Pauling), m: atomic mass (m= M/NO, M: atomic weight, N0: Avogadro number), Δu: interchange energy (ΔH=x1x2NOΔu, ΔH: integral enthalpy of mixing), k: Boltzmann constant, T: absolute temperature. And the subscripts 1 and 2 refer to the components.
In the square bracket of the above equation, the first and the second terms show hard part and the third term represents soft part of friction constant for viscous movements.
Values calculated from the above equation for the excess viscosity of various liquid binary alloys coincided qualitatively with their experimental data, and in particular, for regular or nearly regular solutions, an excellent agreement has been found between those calculated and experimentally observed.
The viscosities of solid-liquid mixtures were experimentally determined for silicon oil-paraffin system at room temperature and solid-liquid oxide mixture at steelmaking temperature. The use of oil-paraffin systems was to confirm the results of high temperature measurements, the experimental conditions being very difficult to control. The silicon oil- paraffin mixtures behaved Newtonian until the particle fraction reached 0.15. At this fraction, the mixture started deviate from Newtonian flow; though some average values could still be collected with very high uncertainty. Liquid-2CaO.SiO2 mixtures and liquid-MgO mixtures were studied at steelmaking temperature with carefully prepared particle fractions and well controlled conditions. Liquid-2CaO.SiO2 mixture behaved Newtonian even when the particle fraction reached 0.1. The results of both room temperature measurements and steelmaking temperature measurements were used to examine the applicability of the existing models. Einstein-Roscoe equation was found to be the only model applicably for the systems studied. No modification of the model parameter was found necessary, though the particles were not spherical.
Calcium fluoride, known as fluorspar is a very good flux in steel making and also has been reported to increase the alloy yield and metal recovery in aluminothermic melts for production of ferrochrome. The present investigation is therefore carried out to study the effect of CaF2 additions on the viscosity of synthetically prepared aluminothermic slags pertaining to the production of ferrochrome, with the composition approximating that of ferrochrome slag generated in the industry. The viscosities of these slags have been measured at four different Al2O3/CaO ratios with the broad composition of the slags varying between 50-62 mass% Al2O3, at various temperatures. Calcium fluoride additions decreased the viscosity of aluminothermic ferrochrome slags at all temperatures. It is observed that the decrease in viscosity is different at different Al2O3/CaO ratios and that at all temperatures there is fast decrease in viscosity initially at lower CaF2 contents, the rate of decrease diminishing at higher mole percent of CaF2, The viscosity is found to obey the Arrhenius equation of viscous flow at two different temperature ranges and not throughout the temperature range above liquidus. The activation energy at the two temperature ranges have been estimated and it is found to be strongly dependent not only on the CaF2 content but also on the Al2O3/CaO ratio. From the analysis of results it is suggested that the decrease of viscosity with increasing additions of CaF2 content may be due to both depolymerisation and decreasing intensity of interactions among various anions and cations in the melt.
A model based on the optical basicity corrected for the cations required for the charge balance of AlO5-4 is investigated. This model has the advantage of being generally applicable and not limited to slags of a certain composition. The calculated results were in reasonable agreement with traceable experimental data for a range of synthetic slags and industrial iron- and steelmaking slags. The latter included mould fluxes and blast furnace, steelmaking and coal slags. For most slag compositions here, the viscosities predicted with the present model were in better agreement with the measured values than those predicted by the Riboud and Urbain models; coal slags were the only exception. In the case of CaF2 containing slags, the results indicate that an optical basicity of CaF2 of 1·2 provided the best fit to the viscosity data.A model based on the optical basicity corrected for the cations required for the charge balance of AlO5-4 is investigated. This model has the advantage of being generally applicable and not limited to slags of a certain composition. The calculated results were in reasonable agreement with traceable experimental data for a range of synthetic slags and industrial iron- and steelmaking slags. The latter included mould fluxes and blast furnace, steelmaking and coal slags. For most slag compositions here, the viscosities predicted with the present model were in better agreement with the measured values than those predicted by the Riboud and Urbain models; coal slags were the only exception. In the case of CaF2 containing slags, the results indicate that an optical basicity of CaF2 of 1·2 provided the best fit to the viscosity data.
In this investigation, the viscosity of slags containing 4 components, viz. CaO (4.48 wt% to 35.1wt%), FeO (16wt% to 50.9wt%), SiO2 (27.33 wt% to 47 wt%) and CaF2 (3.53 wt% to 13.2 wt%) were carried out with temperature range 1435 to 1749 K. For measuring the viscosity, a rotating cylinder method with iron spindle and crucible were used. The pre- as well as post-measurement samples of the slags were subjected to chemical and X-ray fluorescence analyses. The results indicated no significant change in composition during the measurements. In the temperature range of study, CaF2 additions had the expected effect of decreasing the viscosity of the slags. The effect was found to be particularly significant at lower temperatures. The slag viscosities were found to increase with increasing SiO2 contents and decreasing basicities. Arrhenius and Weymann activation energies for viscous flow have been evaluated from the present results.
Viscosities of some quaternary slags in the Al2O3-CaO-MgO-SiO2 system were measured using the rotating cylinder method. Eight different slag compositions were selected. These slag compositions ranging in the high basicity region were directly related to the secondary steel making operations. The measurements were carried out in the temperature range of 1720 to 1910 K. Viscosities in this system and its sub-systems were expressed as a function of temperature and composition based on the viscosity model developed earlier at KTH. The iso-viscosity contours in the Al2O3-CaO-MgO-SiO2 system relevant to ladle slags were calculated at 1823 K and 1873 K for 5 mass% MgO and 10 mass% MgO sections. The predicted results showed good agreement with experimental values and the literature data.
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