CaO Al2O3 SiO2 Research Articles

Relation between Electrical Conductivity and Viscosity of CaO–SiO<sub>2</sub>–Al<sub>2</sub>O<sub>3</sub>–MgO System

Alternating current impedance method has been used to measure the electrical conductivity of CaO–SiO2–Al2O3–MgO system and viscosity of this system has been measured by high temperature rheometer at the same time. It is found that measured data of electrical conductivity and viscosity showed a relatively high accuracy. A relation between the two parameters has been estimated using a formula which showed a relatively lower deviation compared to the precious work. Ionization theory of molten slag has been used to explicate the electrical conductivity and viscosity of molten slag.

Effect of Al Content on the Evolution of Non‐Metallic Inclusions in Si–Mn Deoxidized Steel

Industrial trials and thermodynamic calculations are performed to investigate the effect of Al content on the evolution of non‐metallic inclusions in Si–Mn deoxidized spring steel by using scanning electron microscope (SEM) equipped with energy dispersive spectrometer (EDS) and FactSage thermodynamic software. Sulfide type inclusions and CaO–Al2O3–SiO2–MgO type complex inclusions are two major non‐metallic inclusions. The effect of Al content on the evolution of CaO–Al2O3–SiO2–MgO system inclusions is discussed. The stability diagram of Fe–Mn–Si–Al–Mg–O system inclusions is calculated in liquid steel at 1873 K. In practice, to achieve the liquid inclusions in molten steel, both the amount of magnesium and aluminum should be considered simultaneously.

Composition-dependent reactive wetting of molten slag on coke substrates

The reactive wetting behavior of molten CaO–SiO2–Al2O3–MgO slag drops on a coke substrate was investigated using the sessile drop method at 1500 °C in flowing Ar. The wetting behavior of slags in blast furnaces is known to affect the energy efficiency of ironmaking, but has not yet been sufficiently characterized. In this study, the ratio of MgO to CaO was varied from 0.01 to 0.56, while the concentrations of SiO2 and Al2O3 were fixed at 34 and 17 wt%, respectively. The contact angle between slag and coke remained constant for a certain period of time, and then suddenly decreased remarkably. The time until this dramatic contact angle change increased with increasing the ratio of MgO to CaO. Chemical analysis revealed that the reduction of SiO2 in the slag improved the wettability by forming SiC on the coke substrate, while MgO in the slag was preferentially reduced and prevented the reduction of SiO2. Consequently, with increasing MgO content, the wettability of the molten slag on the coke substrate decreased.

Fundamental investigations on the high temperature corrosion of ZrSiO4-containing andalusite refractories in cement kiln preheater

ZrSiO4-containing andalusite brick after service in cement kiln preheater was analysed by means of XRF, XRD and SEM/EDS techniques in order to determine the corrosion mechanism during 8-months industrial-scale corrosion test in high-alkaline environment at 1100°C. The detailed investigation of the wear mechanism through “post-mortem studies” of the ZrSiO4-containing andalusite brick showed that the K-aluminosilicate phases were formed along with a liquid phase as a consequence of reactions between potassium and andalusite. Ca-aluminosilicate and CaZrO3 phases were also formed.In this paper, a new model of the refractory corrosion was proposed. In modelling the corrosion of zircon-containing andalusite refractory material, ZrSiO4 and Al2SiO5 single grains were used to represent the refractory, so that in all cases the isothermal sections of CaO–Al2O3–SiO2, K2O–Al2O3–SiO2 and CaO–ZrO2–SiO2 systems at 1100°C were used to identify the equilibrium phases and also to explain the mechanism of corrosion.

Effect of Basicity on Electroreduction with Controlled Oxygen Flow of Molten Slag Containing FeO

This paper reports on electroreduction with controlled oxygen flow (COF) for extraction of iron along with oxygen by-product from molten slags containing iron oxide at 1723 K. An electrolytic cell with COF was constructed by an iridium wire cathode and a porous platinum anode sintered on a one-end-closed magnesia-stabilized zirconia-based solid electrolyte tube. Effect of basicity of SiO2–CaO–Al2O3–MgO–FeO slag on electroreduction behavior of FeO was investigated by means of the linear sweep and the potentiostatic electrolysis. The possibility of the zirconia membrane as conductive noncorrosive anode material was also discussed. The results indicate that both cathode alloying and increasing slag basicity are helpful to the FeO electrolytic reduction in the molten slag. With the iridium wire as a cathode and an applied voltage at 2.5 V, higher slag basicity results in higher electrolysis rate and higher reduction ratio of the FeO; however, silicon is also precipitated during electrolysis. The applied voltage can cause the increased porosity in the zirconia membrane. The corrosion of the molten slag to the zirconia membrane during electrolysis is evidently aggravated when the slag basicity reaches 0.8. In order to minimize the corrosion of the molten slag to the zirconia membrane during electrolysis, the slag basicity of 0.6 is relatively advisable for extraction of iron under conditions of experimentation.

Production of added-value materials from a hazardous waste in the aluminium tertiary industry: Synergistic effect between hydrotalcites and glasses

The powdered solids trapped in filter sleeves in the aluminium tertiary industry are currently disposed of in secure landfills as a result of environmental considerations. Their classification as a hazardous waste is due to their high aluminium content as metallic aluminium or in compounds such as aluminium nitride. These compounds can react with a very low moisture content to release toxic or hazardous gases such as hydrogen and ammonia. This paper presents a low-cost process for the full recovery of this hazardous waste in three steps leading to the production of two different added-value materials. In the first step, mild acid hydrolysis of the waste is carried out to obtain a concentrated aluminium solution and an inert cake. The following steps consist of hydrotalcite synthesis with the resulting solution, and the production of transparent glasses in the CaO–Al2O3–SiO2 system with the cake. Characterisation of the products obtained indicates that the hydrotalcites can adsorb anionic pollutants (molybdates) in a simple way, while the glasses afford improved optical properties in comparison with those prepared by direct vitrification of the waste.

Structure and optical band gap study of transparent oxyfluoride glass-ceramics containing CaF2 nanocrystals

Oxyfluoride glass-ceramics containing CaF2 nanocrystals were prepared by one-step crystallization of SiO2–Al2O3–CaO–CaF2 glasses at different temperatures. X-ray diffraction (XRD) results have revealed that CaF2 was the only precipitated crystalline phase in glass-ceramic samples. Fourier transform infrared spectroscopy (FT-IR) study of the samples showed the effect of crystallization temperature on the structure. According to DTA and XRD results, suitable glass and its associated glass-ceramics were selected as the best sample in order to study the effect of crystallization on the optical properties. UV–Vis spectra of samples were recorded to determine optical properties. Fermi energy level decreased for glass-ceramics due to the increment of semiconducting behavior. Urbach energy, optical band of the specimens have been reduced by increasing of nanocrystals in glassy matrix which could be attributed to increasing of the order of the structural and formation of crystals and dangling bonds, respectively.

Vapor pressure measurement of lead and lead chlorides in FeOT–CaO–SiO2–Al2O3 system

Vapor pressure of lead and lead chlorides from FeOT–CaO–SiO2–Al2O3 slag system was measured by using Knudsen effusion method. The results suggest that the vapor pressures of lead and lead chlorides increase with increasing temperature. For the slag systems without chlorine, the logarithm of vapor pressure (lnp) shows highly linear dependency on the reciprocal of temperature (1/T), and higher vapor pressure is observed in the condition where more metallic lead vapor is formed. In this case, the vapor pressure of lead increases with increasing slag basicity (w(CaO)/w(SiO2)), increasing FeO content and w(Fe2+)/w(Fe3+) ratio. For the case of slag system with chlorine addition, the total pressures of PbCl2 and PbCl increase with decreasing basicity and FeO content of slag.

Rheological behavior and constitutive equations of heterogeneous titanium-bearing molten slag

Experimental studies on the rheological properties of a CaO–SiO2–Al2O3–MgO–TiO2–(TiC) blast furnace (BF) slag system were conducted using a high-temperature rheometer to reveal the non-Newtonian behavior of heterogeneous titanium-bearing molten slag. By measuring the relationships among the viscosity, the shear stress and the shear rate of molten slags with different TiC contents at different temperatures, the rheological constitutive equations were established along with the rheological parameters; in addition, the non-Newtonian fluid types of the molten slags were determined. The results indicated that, with increasing TiC content, the viscosity of the molten slag tended to increase. If the TiC content was less than 2wt%, the molten slag exhibited the Newtonian fluid behavior when the temperature was higher than the critical viscosity temperature of the molten slag. In contrast, the molten slag exhibited the non-Newtonian pseudoplastic fluid characteristic and the shear thinning behavior when the temperature was less than the critical viscosity temperature. However, if the TiC content exceeded 4wt%, the molten slag produced the yield stress and exhibited the Bingham and plastic pseudoplastic fluid behaviors when the temperature was higher and lower than the critical viscosity temperature, respectively. When the TiC content increased further, the yield stress of the molten slag increased and the shear thinning phenomenon became more obvious.

Effect of sludge addition to coal on Na, K and S volatilisation in ashing process and ash fusibility

The effect of the addition of three types of sludge (L, O and F) on both the Na, K and S volatilisation and the slagging behaviour of a bituminous coal (H) was studied. Na, K and S volatilise in the coal, the sludges and their blends partially, and there exist linear relationships between their contents in ashes and the ratio sludge ash/blend ashes for each coal–sludge blend ash series. However, in blends with F (treated with FeCl3 and lime), S relationship is not linear due mainly to the following effects: a) sulphur retention by CaO to form CaSO4, and b) decrease of free CaO due to the formation of ferrites, silicates and phosphates. To determine the slagging tendency, the ash fusion temperatures (AFTs) were related with ash chemical and mineral composition by using the slagging factor, the base/acid ratio, the Fe2O3/CaO ratio, the P2O5 content, and the ternary equilibrium phase diagram SiO2–Al2O3–CaO. Sludge addition to coal produces a decrease in AFTs that depends on the percentage of sludge added, the sludge phosphorus content and additives (FeCl3 and/or lime), the fact that ash composition is near to those of the eutectics, and the formation of Si and P amorphous compounds.

RH-Degasser Refractory Corrosion Mechanism by Lime-Silica Slags of Different Basicity

Results are provided for a laboratory study of the reaction of industrial self-dissociating slag after steel treatment in an OAO NTMK furnace-ladle unit and synthetic slag of the system CaO–SiO2–Al2O3 with five forms of periclase-spinelid refractories produced by enterprises of Gruppa Magnezit in Russia and Slovakia (Slovmag), and also two Chinese producers. Refractory slag resistance is compared, and their mineral and phase compositions are studied before and after testing.

Viscosity model for oxide melts relevant to fuel slags. Part 2: The system SiO2–Al2O3–CaO–MgO–Na2O–K2O

The viscosity model recently developed for fully liquid pure oxides and binary systems is extended to describe the viscosity of multicomponent systems, based on the thermodynamic modified associate species model. In the model the viscosity is linked to the distribution of associate species as well as the connectivity of associate species. To describe the viscosity for multicomponent systems, the ternary associate species are introduced. The focus of the present paper is to describe the viscosity of the system SiO2–Al2O3–CaO–MgO–Na2O–K2O and its ternary or higher order subsystems. The model shows a good performance in describing the viscosity using only one set of model parameters, which all have a clear physico-chemical meaning. The viscosity behavior when substituting one network modifier for another at constant SiO2 contents is well described. The Al2O3-induced viscosity maximum is also well described, in which the position and magnitude of the viscosity maximum as a function of composition and temperature (charge compensation effect) are properly predicted. Another viscosity maximum when replacing Al2O3 with SiO2 for constant contents of the network modifiers is well presented. Moreover, the current model is self-consistent, in which the extension of viscosities from lower order systems to higher order systems works well, and vice versa.

Effect of Minor Additives on Bead Geometry and Shape Relationship Using Submerged Arc Welding Fluxes

AbstractSubmerged arc welding (SAW) is extensively used because of its ability of metal refinement, deep penetration and protection from atmospheric contamination. In this study 20 base fluxes having CaO–SiO2–Al2O3 were prepared by agglomeration technique and CaF2, FeMn and NiO were added to study their effects on bead geometry (weld width, reinforcement and penetration) and shape relationship parameters (weld penetration shape factor and weld reinforcement form factor). The bead on plate welds was made on 18 mm thick MS plates using submerged arc welding. Welding parameters voltage, current and travel speed were kept constant. Design expert 8.0.7.1 has been used to develop mathematical models and ANOVA was used to check the accuracy and significance of the developed models. In this study the elements transferred to the welds during submerged arc welding have been correlated with the bead geometry.

Phase and chemical equilibria in the melt (Fe–Si–C)–Slag (CaO–Al2O3–SiO2)–Gas (O2–SiO–CO) system

The equilibrium compositions of high-silicon metallic melts coexisting with CaO–Al2O3–SiO2 slag are determined. The dependence of the activity a of silicon in ferrosilicon melts is formulated as activity isolines on the Fe–Si phase diagram. The dependence of log \({P_{{O_2}}}\) on xSi and T is determined at 1823, 1873, and 1973 K. The influence of \({a_{Si{O_2}}}\) which depends on xSi and T, on the equilibrium composition of the gas phase \({P_{{O_2}}}\) is studied. Data on the activity of silicon dioxide in CaO–Al2O3–SiO2 slags is analyzed and corrected. At fixed temperature, each alloy of specified composition corresponds to only one value of \({a_{Si{O_2}}}\) represented on the concentration diagram by an activity isoline. In the presence of carbon, all the high-silicon alloys may be obtained at T ≥ 1973 K, with \({a_{Si{O_2}}}\) > 0.8. At 1873 K, when \({a_{Si{O_2}}}\) > 0.9, only alloys with 0.5).

Dissolution behaviour of MgO based refractories in CaO–Al2O3–SiO2 slag

Magnesium oxide (MgO) based refractories are widely used in secondary refining processes, and their dissolution into refining slag is the primary cause of their shortened lifespan. The dissolution rate was investigated for sintered MgO and commercial MgO–C and MgO–Cr2O3 refractories in a synthesised 50CaO–45Al2O3–5SiO2 liquid (mass-%) slag. The change in slag composition was measured after a refractory sample was placed into the molten slag that was stirred by flowing argon gas at 1773 K. The dissolution rate of the sintered MgO was above those of the MgO–C and MgO–Cr2O3 refractories under the same gas flowrate, although the dissolution rate of all samples increased as the gas flowrate was increased from 25 to 75 mL·min− 1. The slag containing 5 mass-% FeO considerably promoted the dissolution of the MgO–C refractory because of the oxidation of carbon by FeO. The dissolution of all the refractories was greatly affected by penetration of the liquid slag, with the mass transfer of MgO in the penetrating slag at lower gas flowrates likely being the rate controlling step. At high gas flowrates, Ar bubbles covered the surface and blocked the contact between the liquid slag and the solid phase, reducing the dissolution rate.

Low-temperature-sintering characteristic and microwave dielectric properties of (Zn0.7Mg0.3)TiO3 ceramics with LBSCA glass

(Zn0.7Mg0.3)TiO3 (ZMT) powders were synthesized by a traditional solid-state preparation process. Meanwhile, the effects of adding Li2O–B2O3–SiO2–CaO–Al2O3 (LBSCA) glass on the microstructure, phase formation, and microwave dielectric properties of ZMT ceramic were investigated. The LBSCA glass as a sintering agent can effectively reduce the sintering temperature of ZMT ceramic from 1100°C to 900°C, which can be attributed to its liquid-phase effect. Only 0.5wt% LBSCA-doping contributed to a 20.2% increase in relative density. XRD patterns indicated that ZnTiO3 was the major crystalline phase. Scanning electron microscopy images demonstrated that low LBSCA-doping (≤2.5wt%) promoted the grain densification and uniformity of specimens. A dense microstructure with uniform grain size could be obtained with 1wt% LBSCA and sintered at 900°C. The ceramic also exhibited excellent microwave dielectric properties: εr=21.6; Q×f=62,000GHz; and τf=−60ppm/°C.

Viscosity model for oxide melts relevant to fuel slags. Part 1: Pure oxides and binary systems in the system SiO2–Al2O3–CaO–MgO–Na2O–K2O

Slag viscosity as a function of temperature and composition is a very important factor in determining the operating temperature, blended coals as well as fluxing agents for slagging gasification. A number of models for predicting the viscosity of fuel slags have been developed, however, most of them are only valid in a limited range of temperatures and compositions. This study aims at developing a new viscosity model for fully liquid slag systems in the Newtonian range, based on the thermodynamic modified associate species model. The viscosity model is a structurally-based model, which gives a reliable prediction over the whole range of compositions and a broad range of temperatures. The focus of the present paper is to collect and model the experimental data for pure oxides SiO2, Al2O3, CaO, MgO, Na2O, K2O and binary systems SiO2–Al2O3, SiO2–CaO, SiO2–MgO, SiO2–Na2O, SiO2–K2O, Al2O3–CaO, Al2O3–MgO, Al2O3–Na2O, Al2O3–K2O, which is the first step to develop a new viscosity model for the system SiO2–Al2O3–CaO–MgO–Na2O–K2O. A good agreement between experimental data and calculated data has been achieved using only one set of model parameters, which have a clear physico-chemical meaning. Moreover, the extrapolated viscosities to the regions where no experimental data are available in literature are reasonable.

Sintering behavior of aluminum nitride ceramics with MgO–CaO–Al2O3–SiO2 glass additive

In this study, MgO–CaO–Al2O3–SiO2 (MCAS) glass oxide fabricated by a conventional melting process was used as a sintering additive to prepare dense AlN ceramics at lower temperatures. AlN specimen with 5wt.% MCAS glass oxide was produced by sintering in a dilatometer and a conventional furnace. The sintering behavior of the glass-doped AlN was investigated by means of dilatometric analysis, X-ray diffraction analysis, and field-emission scanning electron microscopy microstructural observation. Results revealed that the melted glass phase had a significant effect on the densification of the AlN ceramics by a liquid-phase sintering. This led to a reduction in the sintering temperature by 200°C from the 1800°C required for conventional AlN–rare earth or –alkaline earth oxide system.

Luminescence properties of Dy3+ doped and Dy3+/Ce3+co-doped CaO–Al2O3–SiO2–B2O3 glass for LED applications

The Dy3+ doped and Dy3+/Ce3+ co-doped CaO–Al2O3–SiO2–B2O3 glass for light-emitting-diodes (LED) applications had been successfully prepared by the conventional melt-quenching method. Their photoluminescence properties were characterized by excitation and emission spectra. Under UV-light excitation, the Dy3+ doped CaO–Al2O3–SiO2–B2O3 showed a yellowish white light emission. To compensate for the lack of blue light emitting, Dy3+/Ce3+ co-doped CaO–Al2O3–SiO2–B2O3 glass with the compositions of 0.25Dy3+/zCe3+:CaAlSiB (z=0–0.35mol%) were prepared, and their photoluminescence properties were studied. The results showed that the white light could be achieved by varying excitation wavelengths and the concentration of Ce3+ ions. Furthermore, the energy transfer between Dy3+ and Ce3+ was also investigated.

Viscosity Model for Iron Blast Furnace Slags in SiO2–Al2O3–CaO–MgO System

Operational performance of ironmaking processes is determined to a great extent by its slag viscosity. A simple and accurate viscosity model for blast furnace (BF) slags has been developed based on the Urbain model using the critically evaluated experimental data reported by the authors and other researchers. A total number of 2958 viscosity measurements from 582 compositions in the SiO2–Al2O3–CaO–MgO system have been collected from 34 publications. These data have been critically reviewed for developing a viscosity model for ironmaking slags. The model has been significantly revised by consideration of alumina behavior in this system and re‐optimization of the parameters using large quantity and high quality data. The new model has less number of parameters, but better performance in the viscosity predictions. Applications of the new viscosity model on BF operation have been discussed.