CaO Al2O3 SiO2 Research Articles

Structure of crystalline CaAl2Si2O8 precipitated in a CaO–Al2O3–SiO2 glass-ceramic

Metastable CaAl2Si2O8 crystalline phase was obtained via heat treatment of CaO–Al2O3–SiO2 glass with metallic molybdenum particles as nucleating agents. Its crystal structure was determined by aberration-corrected scanning transmission electron microscopy (Cs-STEM), Raman spectroscopy, and X-ray diffraction (XRD). Although the hexagonal structure was observed by Cs-STEM and Raman spectroscopy, Rietveld analysis revealed that a triclinic structure with space group P1 provided the best description of the crystal structure. The most appropriate lattice parameters were a = 5.1163(5) Å, b = 5.1155(5) Å, c = 15.0031(15) Å, α = 91.319(3)°, β = 88.172(3)°, and γ = 120.279(3)°. The c-axis layers composing the hexagonal plane were slightly distorted a few degrees from their arrangement in the hexagonal CaAl2Si2O8 crystal.

Induced Electro-Deposition of High Melting-Point Phases on MgO–C Refractory in CaO–Al2O3–SiO2 – (MgO) Slag at 1773 K

Abstract MgO–C refractory was polarized across the slag-refractory interface at a voltage of 8 V in a synthetic CaO–Al2O3–SiO2 – (MgO) Slag at 1773 K. A deposition layer mainly composed of dicalciumsilicate (2CaO.SiO2) or spinel (MgO.Al2O3) with several hundred microns thick was achieved by cathodic polarization. However, the anodic decay was accelerated in comparison to the cathodic refractories and nonpolarized reference MgO–C refractories. The electrodeposition layer was mainly caused by the reduction of silicate anions, in which a shift of slag composition to the dicalciumsilicate (C2S) or spinel (MA) primary phase field was induced. Furthermore, the rapid migration of mobile Ca2+ and Mg2+ ions can also lead to the enrichment of CaO and MgO at the slag/refractory interface. The present voltage level (8 V) is acceptable for the economic considerations and the slag component also need a careful section for the corrosion protection of MgO–C refractories.

Alumina–silica glass–ceramic sealants for tubular solid oxide fuel cells

In this work, we synthesized the glasses of the SiO2–Al2O3–CaO–Na2O–MgO–K2O–B2O3–Y2O3 system and investigated their thermal properties under changes in the ratios between the components in both modifying (MgO/CaO) and glass-forming (SiO2/B2O3) oxides. In addition, the effects of crystallization on both the properties of sealants and their behaviour at the boundary with ceramic yttria-stabilized zirconia (YSZ) electrolyte have been studied. X-ray diffraction analysis was used to determine the phase composition of the glasses both after quenching, dilatometric measurements and sealing of the glasses with the YSZ ceramic support. The thermal expansion coefficients (CTEs) found for the glasses and glass–ceramics are shown to be in good agreement with those of other cell components. The sealing temperatures of these materials are found to be lower than the operating temperature limit of the interconnector alloy. It is shown that Mg-rich glasses exhibit higher resistance to interaction with Cr compared to other compositions under study. The scanning electron microscopy and energy dispersive spectroscopy studies have confirmed the formation of gas-tight connections by the sealants under investigation. The glass demonstrating the highest stability in contact with the Crofer22APU alloy has been tested as a sealant for a tubular cell. This material is established to ensure a tight connection without cracks during operation at 850 °C for 250 h. The materials are thus found to be promising candidates for use as sealants for solid oxide fuel cells (SOFCs).

Influence of Composition of Technogenic Materials-sourced Alumininosilicate Binder onto Structural Formation and Performance Properties of Construction Composites

Analysis of data from studies of aluminum silicate binder-based construction composites allowed giving theoretical justification and then experimentally confirming a possibility to control synthesis of new growth to obtain composites with predefined characteristics by means of using shales of incomplete clay synthesis of various genesis. Employing aluminosilicate rocks of incomplete clay synthesis, which contain thermodynamically-unstable compounds make it possible to shift from traditional raw materials to production of composite materials on the basis of natural polyfunctional raw material, thus allowing to accelerate synthesis of new growth, change its morphology, optimize microstructure of binding materials and as a result, to improve performance properties of final products. Improvement of performance properties of silicate materials and reduction of their energy content are provided by producing hydrogarnets and other CaO–Al2O3–SiO2–H2O compounds in the binding material under condition of hydrothermal treatment without additional pressure.

Effect of Rb<sub>2</sub>O on Inclusion Removal in C96V Saw Wire Steels Using Low-Basicity LF Refining Slag

A novel Rb2O-containing synthetic LF refining slag has been developed in order to produce ultraclean C96V saw wire steel. In addition, the thermodynamic and kinetics mechanism of Rb2O on inclusion removal have been discussed fully. The results indicated that (1) Rb2O additions (≤10.00 wt%) seems to significantly enhance inclusion removal in steel melts. ① The average diameter of nonmetallic inclusions decreased significantly with the Rb2O addition in synthetic LF refining slag increasing. In particular, the diameter of most of inclusions was less than 3.0 × 10−6 m (3.0 µm) when Rb2O addition was 10.00 wt% ② The number of nonmetallic inclusions decreased sharply with the content of Rb2O in synthetic LF refining slag raising. ③ Both of the MnO–SiO2–Al2O3, CaO–SiO2–Al2O3 inclusions system mainly concentrated in the low melting point zone. (2) For the 15.00 wt% Rb2O-containing synthetic LF refining slag, not only the average diameter of inclusion increases slightly with reaction times increasing, but also the number. This is due to the fact that, the effect of Rb2O on the ability of refining slag to absorb inclusions is a double-edged sword: On the one hand, Rb2O addition would promote the thermodynamic conditions of inclusion removal, then, inclusions would enter the slag spontaneously easier. On the other hand, Rb2O addition could also exacerbate the kinetic conditions of inclusion removal by increasing the viscosity of slag at the same time.

Kinetics of hot metal desulfurization using CaO–SiO2–Al2O3–Na2O–TiO2 slag

Kinetics of hot metal desulfurization were studied using CaO–SiO2–Al2O3–Na2O–TiO2 slag in the range of 1400–1500 °C on a laboratory scale. The results of kinetic experiments indicate that the desulfurization rate increases as the temperature, Al2O3 content, Na2O content, and TiO2 content increase and basicity increases from 1.01 to 1.75, but decreases when basicity increases from 1.75 to 2.02. The melting effect of slag is promoted as the temperature, Na2O content, and TiO2 content increase and Al2O3 content increases from 12.13 to 17.17 mass%, but worsened as basicity increases and Al2O3 content increases from 17.17 to 22.27 mass%. A kinetic model of hot metal desulfurization has been developed to calculate the mass transfer coefficient and the mass transfer resistance of sulfur in slag. The mass transfer coefficient of sulfur increases as the temperature, Al2O3 content, Na2O content, and TiO2 content increase and basicity decreases. Total mass transfer coefficients of sulfur were in the range of (5.02–23.78) × 10−7 m s−1. The activation energy was estimated to be 464.06 kJ mol−1 at the temperature from 1400 to 1450 °C and 176.35 kJ mol−1 at the temperature from 1450 to 1500 °C. The sulfur distribution at the slag–metal interface was observed using a mineral liberation analyzer. The result shows that the mass transfer of sulfur in slag is the controlling step at high temperature during the desulfurization process.

Low-fire Processing and Dielectric Properties of a Binary Crystallizable Glasses+alumina System

Abstract Crystallization kinetics and dielectric properties of a low-temperature, cofirable binary crystallizable glasses (CaO-Al2O3-SiO2 (CAS) and CaO-B2O3-SiO2 (CBS)) with alumina have been investigated. With alumina present, the bloating is minimized and wollastonite formed in the binary crystallizable glasses is replaced by anorthite. With increasing amount of anorthite formed in the ternary alumina+CAS glass+CBS glass dielectric composite, the dielectric constant remains relatively unchanged but the dielectric loss decreases as sintering is extended.

Analysis of basic network structure of continuous casting mould powder in electromagnetic field

ABSTRACTIn the continuous casting process, the mould powder plays the role of insulator and heat insulator in the crystallizer, prevents molten steel from oxidizing, absorbs non-metallic inclusions, and controls lubrication and heat transfer between the casting billet and the mould. It is an important functional material that promotes the quality of a billet and ensures that the continuous casting process proceeds smoothly. Here in we analyse the changes in the microstructure of the protective flux from the aspect of the infrastructure of the flux slag. Additionally, using the classical molecular dynamics simulation method, the structure of the CaO–SiO2–Al2O3–MgO slag system was simulated in the presence of magnetic fields of various strengths. The magnetic field was found to have the following effects on the slag structure. The participation of the basic elements Si, Al, O, etc. in bond formation is independent of magnetic field strength. The magnetic field causes changes in the peaks, coordination numbers, and peak widths of the radial distribution functions of bonds such as Si–O, Al–O, and Mg–O. The greater the magnetic field strength, the more disordered the ionic clusters are, and the greater is the decrease in slag viscosity. Although the effect of the magnetic field influences the structure of the slag, there is not much change in the way the molecules and atoms are stacked in the slag.

Microwave dielectric properties of low-temperature-fired LiAlO2–Li2TiO3 composite ceramics with near-zero temperature coefficient

A series of LiAlO2–Li2TiO3 ceramics with near-zero temperature coefficient of resonant frequency was obtained by using a solid-state method in this study. Li2O–B2O3–SiO2–CaO–Al2O3 (LBSCA) glass was used to lower the sintering temperature of the ceramics to approximately 900 °C. Scanning electron microscope images illustrated the dense microstructures of the LiAlO2–Li2TiO3 ceramics when amount of LBSCA glass content exceeded 1.0 wt%. X-ray diffraction analyses indicated that LiAlO2 and Li2TiO3 were presented as separate phases in the composites and no any secondary phase was observed in the sintered samples. High-performance microwave dielectric properties with permittivity of ∼ 15.4, Q × f value of ∼ 52,740 GHz and τf value of ∼ + 1.37 ppm/°C were observed in the LiAlO2–Li2TiO3 ceramic sample sintered at 900 °C with 1.5 wt% LBSCA glass. The ceramic also exhibited excellent chemical compatibility with Ag, which indicated that the fabricated material could be a good candidate for low-temperature co-fired ceramic applications.

The crystallization kinetics of CaO–Al2O3–SiO2 (CAS) glass–ceramics system produced from pumice and marble dust

In the present work, CAS (CaO–Al2O3–SiO2)-based glass–ceramics were prepared by using Al2O3 (Seydisehir, Turkey) and pumice (Nevsehir, Turkey) as natural raw materials and marble dust (Sakarya, Turkey) as a waste source. CAS-coded composition (57.5 mass% SiO2, 27.5 mass% CaO, 15 mass% Al2O3) was selected in stoichiometric anorthite region according to the CAS ternary diagram. According to the DTA results at different heating rates, the crystallization activation energy of the glass that was prepared from the CAS-coded composition was calculated to be 373 ± 5 kJ mol−1 and the viscous flow activation energy to be 430 ± 8 kJ mol−1.

Experimental and thermodynamic analysis of MgO saturation in the CaO–SiO2–Al2O3–MgO slag system melted in a laboratory resistive furnace

Slags from the CaO–SiO2–Al2O3–MgO system (CSAM) are commonly employed for the secondary refining treatment of special steels. Those slags must be designed to work in the refining reactions, presenting properties that maximize their capability to capture impurities from the liquid steel. With this in context it becomes relevant to study the phases of those slags in the operating temperatures. In the present study, four slags from the CSAM system, with increments of MgO (5.98–23.43wt.%) and binary basicity (1.96–2.48), were melted in a high temperature resistive electric furnace. The objective was to analyze the phases present in the slags in secondary refining temperatures (1500°C (1773K) to 1600°C (1873K)), depending on their chemical composition. Fluorescence (XRF), X-ray diffraction (XRD) and scanning electron microscopy (SEM) with dispersive energy spectrometer (EDS) were used for the slag analyses. The experimental results were compared with thermodynamic calculations obtained by using the FactSage™ 7.1. As the MgO contents increased in the slag (>14.96wt.%), the precipitation of MgO solids were predicted by thermodynamic calculations, indicating the saturation of the slag in this compound. In the SEM/EDS analysis, this saturation was confirmed by the presence of dark and dendritic phases rich in MgO in the slag microstructure. However, for MgO contents up to 7.93wt.%, the microstructures obtained were mainly composed of C2S (dicalcium silicate) phases dispersed in the liquid matrix, identifying the unsaturated condition for the MgO compound.

Laboratorial Analysis of Inclusions Formed by Reoxidation in Tundish Steelmaking

In order to investigate the formation of inclusions by reoxidation in the tundish, an MgO–CaO gunning mass (GM1), an MgO gunning mass (GM2), a calcium aluminate tundish slag (TS), and a rice husk ash (RHA) silica based are evaluated. The interaction between the steel and these materials is analyzed under laboratory conditions. The experimental results for the chemical composition of steel and the types of inclusions formed satisfactory reach the thermodynamic equilibrium calculated by FactSage. GM1 presents better results for inclusion density and average size of inclusions compared to GM2. The experiment with TS presents a good steel cleanliness despite the formation of numerous alumina inclusions, caused by the reaction between the slag and the alumina crucible. The addition of RHA increases the inclusion density and average size of inclusions, and also the formation of CaO–Al2O3–SiO2 oxides inclusions is favored. RHA has harmful effects concerning reoxidation events, deteriorating the good cleanliness obtained with the TS. The experiments with GM1 and TS are less reoxidative and presents a better steel cleanliness. Thus, the usage of this gunning mass and a calcium aluminate slag without RHA is preferable in order to diminish reoxidation during the tundish steelmaking.

Effect of Fly Ash on the Properties of Ceramics Prepared from Steel Slag

In this study, SiO2–Al2O3–CaO–MgO steel slag ceramics containing 5 wt % MgO were used for the preparation of ceramic bodies, with the replacement of 5–20 wt % quartz and feldspar by fly ash. The effect of the addition of fly ash on the sintering shrinkage, water absorption, sintering range, and flexural strength of the steel slag ceramic was studied. Furthermore, the crystalline phase transitions and microstructures of the sintered samples were investigated by XRD, Fourier transform infrared (FTIR), and SEM. The results showed that the addition of fly ash affected the crystalline phases of the sintered ceramic samples. The main crystal phases of the base steel slag ceramic sample without fly ash were quartz, diopside, and augite. With increasing fly ash content, the quartz diffraction peak decreased gradually, while the diffraction peak intensity of anorthite became stronger. The mechanical properties of the samples decreased with the increasing amount of fly ash. The addition of fly ash (0–20 wt %) affected the optimum sintering temperature (1130–1160 °C) and widened the sintering range. The maximum addition amount of fly ash should be 15 wt %, for which the optimum sintering temperature was 1145 °C, water absorption was 0.03%, and flexural strength was 43.37 MPa higher than the Chinese national standard GBT 4100-2015 requirements.

Application of Alkali Oxides in LF Refining Slag for Enhancing Inclusion Removal in C96V Saw Wire Steel

A novel LF refining slag contains K2O has been developed in order to produce ultraclean saw wire steels. The diameter of ultrafine saw wire is between 50×10−6 m (50 µm) and 80 ×10−6 m (80 µm), any hard inclusion which diameter more than 5×10−6 m (5 µm) should be avoided because it probably will cause wire breaking. In order to enhance inclusion removal in C96V saw wire steel during LF refining process, fundamental work on the effect of alkali oxides (Li2O, K2O) on the absorption ability of inclusions in a typical LF refining slag for C96V saw wire steel has been investigated. The results indicated that K2O additions seems to significantly enhance inclusion removal in steel melts, instead, Li2O additions hindered inclusion removal. In details, K2O improve the cleanliness in the as quenched C96V saw wire steel melts compared to preexisting synthetic LF refining slag compositions: (i) The average diameter of nonmetallic inclusions was decreased sharply with the content of K2O in synthetic LF refining slag increasing. In particular, the diameter of most of inclusions was less than 2.5×10−6 m (2.5 µm) when the content of K2O in synthetic LF refining slag more than 10 wt%; (ii) The number of inclusions descend sharply with the content of K2O in synthetic LF refining slag raising. (iii) Both of the SiO2–MnO–Al2O3, SiO2–CaO–Al2O3 inclusions system mainly concentrated in the low melting zone when the composition of K2O in synthetic refining slag was less than 10 wt%. While the Li2O additions has the opposite effect.

Microwave dielectric properties of the low-temperature-fired Li2ZnTi3O8–Li2TiO3 ceramics for LTCC applications

In this work, 0.73Li2ZnTi3O8–0.27Li2TiO3 ceramics were prepared through a traditional solid-state process. The effects of Li2O–B2O3–SiO2–CaO–Al2O3 (LBSCA) glass addition on phase formation, microstructure, sintering characteristic and microwave dielectric properties of the ceramics were investigated. A small amount of LBSCA glass addition significantly reduced sintering temperature of the ceramics. X-ray diffraction analysis revealed that Li2ZnTi3O8 and Li2TiO3 phases coexisted without producing any other crystal phases in the sintered ceramics. Dielectric constant and Qf values were related to the amount of LBSCA addition and sintering temperatures. The specimens obtained near-zero temperature coefficient (τf) values through the compensation on the positive τf of Li2TiO3 and the negative τf of Li2ZnTi3O8. The 0.73Li2ZnTi3O8–0.27Li2TiO3 ceramic with 0.75 wt% LBSCA addition and sintered at 900 °C for 3 h exhibited excellent microwave dielectric properties of ɛr = 23.907, Qf = 63050 GHz and τf = 1.2 ppm/°C, which was very suitable for LTCC (low temperature co-fired ceramics) applications.

An Experimental Study on the Impact of Deoxidation Methods on the Fatigue Properties of Bearing Steels

Strong deoxidation and weak deoxidation are two kinds of deoxidation methods frequently applied in steelmaking. In the present study, high‐carbon chromium bearing steels are smelted with a strong deoxidizer and a weak deoxidizer, respectively in industrial trials. The generation mechanism of inclusions is analyzed, and the inclusion stability diagrams of the Fe–Si–Al–Mg–Mn–O system at 1873 and 1843 K are calculated. The very high cycle fatigue life of bearing steels deoxidized with different deoxidizers is also experimentally compared. The results showed that the evolution routes of inclusion in high‐carbon chromium bearing steels deoxidized by Si and Al are CaO–Al2O3–SiO2 → CaO–Al2O3–SiO2–MgO and Al2O3 → CaO–Al2O3–SiO2–MgO, respectively. The Al content in steel is controlled by different methods when different deoxidizers are applied. The effect of the oxide inclusions generated during Si deoxidization on the fatigue life is lower than that during Al deoxidization, even if the total oxygen content is slightly higher. This effect suggests that it is not accurate to evaluate the fatigue life of steels with the total oxygen content, and it is also desirable to produce bearing steels with the Si deoxidation method.

Study on the Interfacial Reactions between an Fe–Mn–Si Alloy and Complex Oxides Containing FeO during Isothermal Heating

To precisely control the characteristics of complex oxides by heat treatment, the effect of FeO on the interfacial reactions that occur between an Fe–Mn–Si alloy and CaO–SiO2–Al2O3–MgO–MnO–FeO oxide was studied and clarified. Eight types of diffusion couples with different compositions of oxides were produced using a confocal scanning laser microscope (CSLM). The morphologies of the alloy–oxide interfaces and the changes in their chemical compositions with isothermal heating at 1273 and 1473 K for 10 h were investigated. A modified dynamic calculation model was established and verified to achieve better understanding on the interfacial reaction mechanism between the Fe–Mn–Si alloy and the multicomponent oxide with different FeO content during isothermal heating. The results showed that during isothermal heating at 1273 and 1473 K, “solid–solid” and “solid–liquid” alloy–oxide reactions occurred in the A-1-x and A-2-x diffusion couples, respectively. The interfacial alloy–oxide reactions were enhanced by increasing the initial FeO content in the oxide and the heating temperature. The particle precipitation zone (PPZ), Mn-depleted zone (MDZ) and Si-depleted zone (SDZ) widths in the A-1-x and A-2-x diffusion couples after heating also showed a positive correlation with the increase in the initial FeO content in the oxide, as well as the size and number of MnO·SiO2 inclusions. The diffused oxygen from the oxide reacting with elemental Mn and Si in the alloy plays a dominant role in the A-1-x diffusion couple during heating, whereas for A-2-x, the dominant reaction is between elemental Si in the alloy and MnO in the oxide.

Kinetics of dissolution of sapphire in melts in the CaO–Al2O3–SiO2 system

The dissolution rate of sapphire in melts in the CAS system of varying silica activity, viscosity and degree of alumina saturation has been determined at 1600 °C and 1.5 GPa. After an initiation period of up to 1800 s, dissolution is controlled by diffusion of cations through the boundary layer adjacent to the dissolving sapphire. The dissolution rate decreases with increasing silica activity, viscosity and molar Al2O3/CaO. The calculated diffusion matrix for each solvent melt shows that CAS 1 and 9 which have molar Al2O3/CaO of 0.33 and 0.6 and dissolution rate constants of 0.65 × 10−6 and 0.59 × 10−6 m/s0.5 have similar directions and magnitudes of diffusive coupling: DCaO-Al2O3 and DAl2O3-CaO are both negative are approximately equal. The solvent with the fastest dissolution rate: CAS 4, which has a rate constant of 1.5 × 10−6 m/s0.5 and Al2O3/CaO of 0.31 has positive DCaO-Al2O3 and negative DAl2O3-CaO and the absolute values vary by a factor of 4. Although many studies show that aluminium is added to the melts via the reaction:Si4+=Al3++0.5Ca2+the compositional profiles show that this reaction is not the only one involved in accommodating the aluminium added during sapphire dissolution. Rather, aluminium is incorporated as both tetrahedrally coordinated Al charge balanced by Ca and as aluminium not charge balanced by Ca (termed Alxs). This reaction:AlIV–Ca=Alxs+CaNBOwhere CaNBO is a non-bridging oxygen associated with calcium, may involve the formation of aluminium triclusters. The shape of the compositional profiles and oxide-oxide composition paths is controlled by the aluminium addition reaction. When Alxs exceeds 2%, CaO diffusion becomes increasingly anomalous and since the bond strength of Alxs correlates with CaO/CaO + Al2O3, the presence of more than 2% Alxs leads to significantly slower dissolution than when Alxs is absent or at low concentration. Thus, dissolution is controlled by diffusion of cations through the boundary layer, but this diffusion is itself controlled by the structural modifications required by the addition of new components to the melt. Comparison of quartz dissolution rates in similar melts shows that dissolution is much faster for quartz than for sapphire and that dissolution rates show the same correlation with silica activity and viscosity. We suggest that diffusive fluxes are related to changes in melt structure and the nature of the reaction that incorporates the added component. For the slow eigendirection, SiO2 addition occurs by a single reaction whereas Al2O3 addition requires a more complex two part reaction in which Al is accommodated by charge balance with Ca until Al is in excess of that which can be charge balanced. The Alxs incorporation reaction, is slower than the Si incorporation reaction which inhibits sapphire dissolution relative to quartz in melts of the same composition.

Modeling reoxidation behavior of Al–Ti-containing steels by CaO–Al2O3–MgO–SiO2 slag

A kinetic model was developed using FactSage Macro Processing to simulate the reoxidation of Al–Ti-containing steels by CaO–Al2O3–SiO2–MgO slags. The calculated results show a good agreement with the experimental data. Thus, the developed kinetic model can be used to predict changes in slag, steel, and inclusion compositions during the reaction process. During the slag reoxidation process, the reactions occurring at slag–steel interface and in the bulk steel were confirmed to be the reduction of SiO2 by [Al] and [Ti] and the self-dissociation of SiO2 into [Si] and [O]. Increasing the ratio of CaO to SiO2 in the slag can significantly suppress the self-dissociation of SiO2 in the slag and lower the amount of inclusions produced during reoxidation. The formed inclusions changed from solid Al2O3 to Al2O3–TiO x inclusions, which was mainly dependent on the w([Al]) and w([Ti]). The amount of inclusions was obviously influenced by the composition of the top slag.

Influence of Al2O3 Content on the Melting and Fluidity of Blast Furnace Type Slag with Low TiO2 Content

The increasing usage of iron ores with high Al2O3 content significantly increases the amount of Al2O3 in blast furnace slag and consequently affects its performance. This work uses slag sampled on site to study the effects of changes in Al2O3 content on the fluidity of the CaO–SiO2–Al2O3–MgO–TiO2 slag system that is characterized by high Al2O3 and low TiO2 contents, as well as on the phase transition law during the cooling process. Slag viscosity exhibits a rising trend with an increase in Al2O3 content, and Al2O3 in the tested slag is alkaline. The viscous flow activation energy of molten slag rises from 157 kJ/mol to 172 kJ/mol with an increase in Al2O3 content, and the viscous flow units in the slag become large and complicated. When slag is cooled, the main precipitated phase is melilitite. Spinel, perovskite, and olivine are also observed. The crystallization amount of the melilitite phase decreases constantly with an increase in Al2O3 content.