Effect of Al2O3 and TiO2 on Viscosity,Surface Tension,and Density of Blast Furnace Slag with CaO/SiO2 = 1.13

The influence of Al₂O₃ in the range of 10–20 mass% and TiO₂ in the range of 0.55–5 mass% on the flow behavior, viscosity, density, and surface tension of molten industrial blast furnace slag with CaO/SiO₂ = 1.13 is investigated using a high-temperature microscope, a rotating viscometer, and the maximum bubble pressure method. The measurement results show that Al₂O₃ acts as a network former in the studied CaO–SiO₂–MgO–Al₂O₃–TiO₂ slags. With an increase in the Al₂O₃ content from 10 to 20 mass%, the viscosity and surface tension of the slags increase and the density decreases. In contrast to Al₂O₃, the TiO₂ acts as a surfactant and network breaker in the range of up to 15 mass%. The addition of TiO₂ up to 15 mass% results in a decrease in the viscosity in the liquid-dominated region and a decrease in the surface tension of the studied slags. Therefore, the density increases with the addition of TiO₂ due to increasing molar volume. The behavior of the breakpoint temperature on all the viscosity curves is in complete agreement with the behavior of the flow point temperature and crystallization temperatures of melilite and perovskite.     

Viscosity of low silica CaO–5MgO–Al2O3–SiO2 slags

Abstract

The viscosity of CaO–5MgO–Al₂O₃–SiO₂ slag with low silica was measured by rotating cylinder method up to 1823 K. Slag compositions were chosen based on five different levels of SiO₂ content between 0 and 11·80%. The MgO content was 5·0%. The mass ratio of CaO/Al₂O₃ was varied from 0·66 to 1·95. It was shown that viscosity decreased with increasing temperature and decreased with increasing the mass ratio of CaO/Al₂O₃, following by an increase with further increasing the mass ratio of CaO/Al₂O₃. The viscosity decreased with the NBO/T ratio increasing, and the trend that flow activation energy changes with the NBO/T ratio of slag was the same as the trend that viscosity changes with the NBO/T ratio. Based on the experimental data as the boundary of the homogenous phase region, the mass triangle model was used to calculate the viscosity of low silica region.     

A Study on the Viscous Behaviour with K2O Additions in the CaO?SiO2?Al2O3?MgO?K2O Quinary Slag System

The viscosities of CaO? SiO₂? 20wt%Al₂O₃? 10 wt%MgO‐K₂O quinary slags with CaO/SiO₂ from 0.8 to 1.2 at 1773 K with 1–5 wt% K₂O additions were measured to estimate the effect of K₂O on the viscous behaviour of the slags. The measured viscosity at 1773 K increased with K₂O addition at a fixed CaO/SiO₂, which is contrary to the effect of Na₂O on the viscosity of BF slags. To qualitatively verify the changes in slag structure, FT‐IR spectroscopy was used. It was found that K₂O induces Al₂O₃ to behave as an acidic oxide by forming [AlO₄]^5?‐tetrahedral units by the ionic compensation effect of K⁺ cations. However, regarding the effect of K₂O on the silicate structure, it is observed that K₂O has a negligible effect due to the consumption of O^2? with the formation of [AlO₄]^5?‐tetrahedral units. Furthermore, it is also found that Si? O? Al bending became more complicated with K₂O additions, which supports the selective effect of K₂O on the aluminate structure of the slag. In spite of the more complicated structure with K₂O additions, the critical temperature (T_CR) decreased due to the gradual reduction of the liquidus temperature (T_LQ) of the slags.     

Influence of MgO,Al2O3 and CaO/SiO2 on the viscosity of blast furnace type slag with high Al2O3 and 5 wt-% TiO2

The effect of MgO, Al₂O₃ and CaO/SiO₂ on the viscosity of CaO–SiO₂–Al₂O₃–MgO–5 wt-% TiO₂ slag was studied in the temperature range of 1673–1773?K. At a fixed CaO/SiO₂ ratio of 1·17 and 12 wt-% Al₂O₃, the viscosity of the slag decreased with increasing MgO content because of depolymerisation of the silicate structures. At a fixed CaO/SiO₂ ratio of 1·17 and 8 wt-% MgO, the viscosity of the slag increased with increasing Al₂O₃ content. At 8 wt-% MgO and 12 wt-% Al₂O₃ wt-%, increasing the CaO/SiO₂ ratio from 1·07 to 1·50 resulted in lower slag viscosity. The temperature dependencies of the viscosity on MgO addition, Al₂O₃ addition, and CaO/SiO₂ ratio were analyzed, and the apparent activation energies of each system were found to be between 178 and 232?kJ/mol, 273 and 360?kJ/mol, and 204 and 233?kJ/mol, respectively. Five different viscosity models were employed to predict slag viscosity, and the Riboud model was found to be the best for predicting this parameter.     

Effect of chlorine on the viscosities and structures of blast furnace slags

The viscosity of CaO–SiO₂–Al₂O₃–MgO–CaCl₂ slags (C/S?=?1.12) were investigated to elucidate the effects of chlorine ranging from 0.02 to 0.53?mass% on the blast furnace slags at high temperatures. Moreover, the Raman spectra of the quenched slags and the X-ray diffraction patterns of the slags cooled in air after viscosity measurement were thoroughly analysed to interpret the transformation of the structures of the slags with increasing the content of chlorine. The viscosity was found to decrease slightly with the increase of chlorine at a given temperature higher than 1673?K, and the critical temperature (T_CR) decreased from about 1660 to 1590?K simultaneously which was possibly deriving from the precipitation of Ca₂Al₂SiO₇, Ca₃Al₂(SiO₄)₃–xCl₄ x and SiO₂ in higher chlorine content. The degree of polymerisation for silicon–oxygen tetrahedra was found to decrease estimating from the decrease of the average amount of bridging oxygen calculated from the deconvolution results of the Raman spectra of the quenched slags, which provided the explanation for the decrease in viscosity. And that the apparent activation energy of the slags was commonly reduced by chlorine increasing demonstrated the decrease in the degree of polymerisation of molten slags simultaneously.     

Molecular dynamics simulations of microstructural properties of CaO–SiO2–TiO2 fluorine-free slag systems

The microstructural properties of F-free slag, the CaO–SiO₂–TiO₂ (CST) systems, are investigated by molecular dynamics (MD) simulations. The results show that in the CST system, the average bond length of Si–O remains in 1.61?Å. The addition of TiO₂ contributes to the increase in the concentrations of 4-coordinated Si and 4-coordinated Ti. Increasing the amount of CaO decreases the proportion of bridging oxygen (BO) atoms and the degree of network connectivity (Q³ and Q⁴), suggesting the simplification of melt polymerisation. Substituting CaO with SiO₂ and maintaining a constant TiO₂ level causes the microstructure of the slag to become more complex. Both SiO₂ and TiO₂ contribute to the more complex structures of the melts. Simultaneously, Si–O–Ti linkages are more favourable than Si–O–Si or Ti–O–Ti linkages. Thus, TiO₂ is regarded as network former in terms of its structure within CST system when the content of TiO₂ excessed 28 mass%.     

Viscosities of the Quaternary Al2O3‐CaO‐MgO‐SiO2 Slags

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.     

Viscosity of copper slags from chalcocite concentrate smelting

The viscosity of smelting slags from the Glogow copper plant in Poland was measured using a concentric cylinder viscometer. These slags contain typically 45 pct SiO₂, 16 pct CaO, 8 pct MgO, 11 pct Al₂O₃, and only 5 to 7 pct total iron. The viscosity was measured as a function of the CaO, MgO, SiO₂, Cu₂O, Cr₂O₃, and Fe₃O₄ contents in the temperature range from 1473 to 1623 K. Silica and chromium oxide additions increased the viscosity, while small additions of the other oxides decreased the viscosity. However, at large additions of CaO or MgO, cooling resulted in a rapid increase in the viscosity upon reaching the transition temperature. This critical transition temperature increased with increasing additions of CaO and MgO. This was explained by the precipitation of solid particles upon reaching the saturation limit. Depending on the slag composition, the activation energy for viscous flow was found to be in the range from 200 to 370 kJ/mol.     

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.     

The Viscous Behavior of FeO<Subscript>t</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> Copper Smelting Slags

Understanding the viscous behavior of copper smelting slags is essential in increasing the process efficiency and obtaining the discrete separation between the matte and the slag. The viscosity of the FeO_t-SiO₂-Al₂O₃ copper smelting slags was measured in the current study using the rotating spindle method. The viscosity at a fixed Al₂O₃ concentration decreased with increasing Fe/SiO₂ ratio because of the depolymerization of the molten slag by the network-modifying free oxygen ions (O²⁻) supplied by FeO. The Fourier transform infrared (FTIR) analyses of the slag samples with increasing Fe/SiO₂ ratio revealed that the amount of large silicate sheets decreased, whereas the amount of simpler silicate structures increased. Al₂O₃ additions to the ternary FeO_t-SiO₂-Al₂O₃ slag system at a fixed Fe/SiO₂ ratio showed a characteristic V-shaped pattern, where initial additions decreased the viscosity, reached a minimum, and increased subsequently with higher Al₂O₃ content. The effect of Al₂O₃ was considered to be related to the amphoteric behavior of Al₂O₃, where Al₂O₃ initially behaves as a basic oxide and changes to an acidic oxide with variation in slag composition. Furthermore, Al₂O₃ additions also resulted in the high temperature phase change between fayalite/hercynite and the modification of the liquidus temperature with Al₂O₃ additions affecting the viscosity of the copper smelting slag.     

The effect of CaF2 on the viscosities and structures of CaO-SiO2(-MgO)-CaF2 slags

The viscosities of CaO-SiO₂(-MgO)-CaF₂ slags were measured to clarify the effect of CaF₂ on the viscous flow of molten slags at high temperatures and the solidification behavior of slags. Furthermore, the infrared (IR) spectra of the quenched slags were analyzed to understand the structural role of CaF₂ in the modification of slag structure. The CaF₂ affects the critical temperature (T _CR) of the slags; that is, the higher the content of CaF₂, the lower the T _CR of the slags. It is suggested that some extent of undercooling as a driving force is needed for the precipitation of solid particles in the melt. In the composition of B (≡(mass pct CaO)/(mass pct SiO₂)) = 1.0, the T _CR was decreased about 150 to 200 K by addition of 10 mass pct MgO, while the T _CR was increased about 100 K by MgO addition at B = 1.3. The effect of CaF₂ on the viscous flow of molten slags can be understood based on a decrease in the degree of polymerization by F⁻ as well as by O²⁻ ions and this was confirmed by the IR spectra of the quenched slags. The relative intensity of the IR bands for [SiO₄]-tetrahedra with low NBO/Si decreased, while that of the IR bands for [SiO₄]-tetrahedra with high NBO/Si increased with increasing CaF₂ content. The decrease in viscosity of the CaO-SiO₂-MgO-CaF₂ (B = 1.0) system by CaF₂ addition was negligible, while the effect of CaF₂ on the viscosity was significant in the more basic system (B = 1.3).     

The Effect of MgO on the Viscosity of the CaO‐SiO2‐20 wt%Al2O3‐MgO Slag System

The viscosities of CaO‐SiO₂‐20 wt%Al₂O₃‐MgO slags (CaO/SiO₂ = 1.0–1.2, wt%MgO = 5–13) were measured to estimate the effect of MgO on the viscous behaviour at elevated temperatures. The slag viscosity at 1773 K decreased with increasing MgO contents, which was typical of a basic oxide component at relatively low basicity (CaO/SiO₂) of 1.0. The FT‐IR spectroscopic analysis of the slag structure seems to verify this behaviour. However, an unexpected contradiction with the temperature dependence was observed above 10 wt%MgO and above CaO/SiO₂ of 1.2. Although the apparent activation energy was expected to decrease with additions of the basic oxide component MgO, the apparent activation energy increased. This unexpected behaviour seems to be related to the change in the primary phase field correlating to the phase diagram corresponding to the slag composition. Therefore, in order to understand the viscosity at both high Al₂O₃ and MgO, not only should the typical depolymerization of the slag structure with high MgO content be considered but also the primary phases of which the molten slag originates.     

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

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

Effect of composition on the crystallisation behaviour of blast furnace slag using single hot thermocouple technique

When the content of glass in blast furnace slag is over 95%, it can be used as a raw material in the manufacture of cement. The critical cooling rate required for the formation of glassy slag is one of the important characteristics for molten BF slag. The crystallisation behaviour of molten BF slag has been studied by in situ observation with the single hot thermocouple technique. The isothermal and non-isothermal experiments were performed to construct time–temperature-transformation and continuous-cooling-transformation diagrams. The effect of MgO, Al₂O₃ and binary basicity (CaO/SiO₂) on the critical cooling rate of the CaO–SiO₂–MgO–Al₂O₃ slags were studied under conditions of CaO/SiO₂?=?1.1–1.4, 6–12?mass% MgO and 10–16?mass% Al₂O₃. The following finding are reported in the present paper: (i) Higher MgO content increased the critical cooling rate; higher Al₂O₃ content decreased the critical cooling rate; higher CaO/SiO₂ increased the critical cooling rate. (ii) The crystallisation temperature of molten BF slag lowers as the cooling rate increases, the slag have larger critical cooling rate, higher crystallisation temperature. The results could be used to design proper cooling path of molten BF slag for the formation of glassy.     

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.     

Amphoteric behavior of alumina in viscous flow and structure of CaO-SiO<Subscript>2</Subscript> (-MgO)-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> slags

The viscosity of CaO-SiO₂ (-MgO)-Al₂O₃ slags was measured to clarify the effects of Al₂O₃ and MgO on the structure and viscous flow of molten slags at high temperatures. Furthermore, the infrared spectra of the quenched slags were analyzed to understand the structural role of Al₂O₃ in the polymerization or depolymerization of silicate network. The Al₂O₃ behaves as an amphoteric oxide with the composition of slags; that is, the alumina behaves as a network former up to about 10 mass pct Al₂O₃, while it acts as a network modifier, in parts, in the composition greater than 10 mass pct Al₂O₃. This amphoteric role of Al₂O₃ in the viscous flow of molten slags at the Newtonian flow region was diminished by the coexistence of MgO. The effect of Al₂O₃ on the viscosity increase can be understood based on an increase in the degree of polymerization (DOP) by the incorporation of the [AlO₄]-tetrahedra into the [SiO₄]-tetrahedral units, and this was confirmed by the infrared (IR) spectra of the quenched slags. The influence of alumina on the viscosity decrease can be explained on the basis of a decrease in the DOP by the increase in the relative fraction of the [AlO₆]-octahedral units. The relative intensity of the IR bands for the [SiO₄]-tetrahedra with low NBO/Si decreased, while that of the IR bands for [SiO₄]-tetrahedra with high NBO/Si increased with increasing Al₂O₃ content greater than the critical point, i.e., about 10 mass pct in the present systems. The variations of the activity coefficient of slag components with composition indirectly supported those of viscosity and structure of the aluminosilicate melts.     

The equilibrium partitioning of titanium between Ti3+ and Ti4+ valency states in CaO-SiO2-TiO x slags

The redox behavior of titanium in CaO-SiO₂-TiO _x melts was investigated using a slag-gas equilibrium technique. Titanium partitioning between Ti³⁺ and Ti⁴⁺ valency states and the ratio of activity coefficients of TiO_1.5 and TiO₂ were determined as functions of oxygen partial pressure, temperature, and slag composition. The equilibrium experiments were carried out at temperatures between 1783 and 1903 K under CO-CO₂-Ar gas atmosphere with oxygen partial pressure ranging from 10⁻¹² to 10⁻⁷ atm (1.01×10⁻¹⁰ kPa to 1.01×10⁻⁵ kPa). The slags had CaO/SiO₂ ratios between 0.55 and 1.35 and total titanium oxide concentrations from 7 to 50 mass pct. Experimental results showed that the Ti³⁺/Ti⁴⁺ ratio in CaO-SiO₂-TiO _x slags, containing up to 50 mass pct TiO _x , increased with decreasing oxygen partial pressure and decreased with increasing CaO/SiO₂ ratio and decreasing temperature. Measured variation of the redox ratio Ti³⁺/Ti⁴⁺ with oxygen partial pressure closely followed the ideal behavior. Increasing the CaO/SiO₂ ratio increased the ratio of activity coefficients of TiO_1.5 and TiO₂. The effect of total titania content on this ratio was more complex and in accord with Raman spectroscopy data.     

Effects of crystallisation behaviour of mould fluxes on properties of liquid slag film

Abstract

During the continuous casting of medium carbon steel slabs, stable liquid slag film performance is necessary to ensure that the process runs smoothly. In this paper, the effects of mould flux crystallisation behaviour on the properties of leftover liquid slag films were examined. First, the compositions of the leftover liquid slags of high fluorine, CaO–SiO₂–TiO₂ and CaO–SiO₂–Na₂O based mould fluxes after a single crystalline phase was separated were calculated. Then, the viscosity, melting temperature, break temperature and degree of crystallisation of each leftover liquid flux were measured. The results revealed that the properties of leftover liquid slag films of CaO–SiO₂–TiO₂ and CaO–SiO₂–Na₂O based mould fluxes are not as stable as those of high fluorine films after crystallisation. This paper provides a new method for developing fluorine free mould fluxes and for determining the most suitable type of crystalline phase that should be utilised in the continuous casting of medium carbon steel slabs.     

A thermodynamic model for calculating manganese distribution ratio between CaO–SiO2–MgO–FeO–MnO–Al2O3–TiO2–CaF2 ironmaking slags and carbon saturated hot metal based on the IMCT

A thermodynamic model (IMCT-L_Mn) for calculating manganese distribution ratio between CaO–SiO₂–MgO–FeO–MnO–Al₂O₃–TiO₂–CaF₂ slags and carbon saturated liquid iron have been developed based on the ion and molecule coexistence theory. The predicted manganese distribution ratio shows a reliable agreement with the measured ones. With the aid of the IMCT-L_Mn model, the respective manganese distribution ratio of (Mn²⁺?+?O^2?), MnO·SiO₂, 2MnO·SiO₂, MnO·Al₂O₃, MnO·TiO₂, and 2MnO·TiO₂ are investigated. The results indicate that the structural units SiO₂?+?FeO play a key role in CaO–SiO₂–MgO–FeO–MnO–Al₂O₃–TiO₂–CaF₂ slags in demanganisation process in the course of hot metal treatment at 1673?K. The manganese distribution ratio at a given binary basicity range increases with CaF₂ content, while that decreases with TiO₂ content at different binary basicity scopes, which demonstrate that high Mn in the metal is favoured by TiO₂ content. In the present study, various critical experiments are carried out in an effort to clarify the effect of temperature on demanganisation ability, indicating that the lower temperature of molten metal is, the faster the rate of demanganisation reaction is and the shorter the thermodynamic equilibrium time is and the lower end-point Mn content is. It can be deduced from the obtained experimental results that the greater oxygen potential of slags or iron-based melts, lower content of basic oxides in slags, and lower temperature at reaction region is benefit for demanganisation reaction.     

Effect of TiO2 on the crystallisation behaviour of CaF2–CaO–Al2O3–MgO slag for electroslag remelting of Ti-containing tool steel

The crystallisation characteristics of CaF₂–CaO–Al₂O₃–MgO slags with various TiO₂ contents from 0 to 9.73 mass% were studied using a single hot thermocouple technique, SEM-EDS and X-ray diffraction. The crystallisation mechanism of TiO₂-bearing slag was identified based on kinetic analysis. It was found that increasing TiO₂ from 0 to 6.43 mass% inhibited the crystallisation ability of electroslag remelting-type CaF₂–CaO–Al₂O₃–MgO slag, whereas further increasing TiO₂ content up to 9.73 mass% enhanced the slag crystallisation signally. When increasing TiO₂ content to 6.43 mass%, the crystalline phase shift from CaO to Ca₁₂Al₁₄O₃₂F₂ and CaTiO₃ at high temperatures. At lower temperatures, the crystalline phase change from polygonal Ca₁₂Al₁₄O₃₂F₂ to need-like CaTiO₃. Further increasing TiO₂ content to 9.73 mass%, the crystalline phase are Ca₁₂Al₁₄O₃₂F₂ and CaTiO₃ in the range of 1473–1613?K. The crystallisation of crystalline phase in the isothermal crystallisation is surface nucleation and controlled by interface reaction when TiO₂ content is lower than 6.43 mass% in the slag. It is bulk nucleation and diffusion-controlled one-dimensional growth in slag with 9.73 mass% TiO₂.