CaO MgO SiO2 Research Articles

Phase Equilibria Study of the MgO–CaO–SiO2 Slag System with Ferronickel Alloy, Solid Carbon, and Al2O3 Additions

Phase Equilibria Study of the MgO–CaO–SiO2 Slag System with Ferronickel Alloy, Solid Carbon, and Al2O3 Additions

Phase equilibria in the low-TiO2 part of the CaO–MgO–SiO2–Al2O3–TiO2 system at a fixed MgO/CaO mass ratio of 0.2 and Al2O3/SiO2 mass ratio of 0.4

Adding titanium oxide has become a common practice in modern blast furnace operating procedures. The blast furnace slag is based on the CaO–MgO–Al2O3–SiO2–TiO2 low titanium slag system rather than CaO–MgO–Al2O3–SiO2 system. Phase equilibria in the CaO–SiO2–Al2O3–MgO–TiO2 system in the low-TiO2 part have been experimentally determined by means of high temperature equilibration and quenching technique followed by electron probe X-ray microanalysis. Introducing a small quantity of titanium-bearing materials can lower the liquidus temperature. The TiO2 content in the slag should be controlled below 4.6 wt%, otherwise it will enter the perovskite phase region where the liquidus temperatures increases rapidly. The compositions of the solid solutions corresponding to the liquidus have been precisely measured and should be utilized for developing the thermodynamic database.

Effect of CaO/MgO on rheological properties and structure of CaO–MgO–SiO2–Al2O3-50 % TiO2 slag with SiO2/Al2O3=1.0

The rheological properties, including viscosity, melting temperature, surface tension, density, and viscous activation energy (Eη) were systematically investigated in the CaO–MgO–SiO2–Al2O3-50 % TiO2 slag system with SiO2/Al2O3 = 1.0. The effect of CaO/MgO on the structure and phase composition of the slag was studied using Raman spectroscopy and X-ray diffraction (XRD). The results of viscosity properties indicate that as the CaO/MgO ratio in the slag increase, viscosity and the viscous activation tend to decrease. Melting temperature and surface tension decreases with increasing CaO/MgO, while density increases. As the CaO/MgO ratio in the slag increases, polymerization decreases, leading to the dissociated basic oxides into metal cations and oxygen anions. This addition of basic oxides provides more O2−, increasing the O/Si ratio, disintegrating complex silica-oxygen composite ions into simple silica-oxygen composite anion, and reducing viscosity. Anosovite (MgTi2O5), CaAl2Si2O8, Mg (Al, Ti)2O4, spinel (MgAl2O4), augite (Ca (Mg, Fe, Al) (Al, Si)2O6) and Ca12Al14O33 were identified as the primary phases in slag. The appropriate CaO/MgO should not exceed 0.76. These findings will serve as a valuable technical foundation to support the development of the direct reduction smelting process for the comprehensive utilization of vanadium titanomagnetite.

Electrical Conductivity and Structure of CaO–MgO–SiO2–Al2O3–BaO Slag with Different BaO/Al2O3 Molar Ratios

Electrical Conductivity and Structure of CaO–MgO–SiO2–Al2O3–BaO Slag with Different BaO/Al2O3 Molar Ratios

Dissolution behavior of Al2O3 inclusions into CaO–MgO–SiO2–Al2O3–TiO2 system ladle slags

Dissolution behavior of Al2O3 inclusions into CaO–MgO–SiO2–Al2O3–TiO2 system ladle slags

Wetting of Graphite and Platinum Substrate by Oxide System with Graded B2O3 Content

This work focuses on wetting two types of substrates (a platinum substrate and a polished graphite substrate) by molten polycomponent oxide system CaO–MgO–SiO2–Al2O3–B2O3 to test the level of interaction at high temperatures. The tested systems were subjected to high-temperature wetting tests in the temperature range from liquidus temperature to 1550 °C using the sessile drop method. A total of four oxide systems were tested with graded boron oxide contents ranging from 0 to 30 wt%. The experiments were conducted in a CLASIC high-temperature resistance observation furnace and an inert atmosphere of high-purity argon. Droplet silhouettes were obtained with a CANON EOS 550D high-resolution camera during heat treatment, with reactive and non-reactive wetting occurring depending on the substrate type. The dependence of the average wetting angles on temperature and time was evaluated, and it was found that boron oxide decreased the average wetting angles of molten oxide droplets. The analyses were accompanied by the SEM/EDX analysis of the substrate and FTIR analysis of the droplets after high-temperature experiments. The phase composition of the oxide systems was evaluated by XRD analysis.

Wollastonite-containing glass-ceramics from the CaO–Al2O3–SiO2 and CaO–MgO–SiO2 ternary systems

Glass-ceramics (GCs) are polycrystalline materials produced from parent glasses by the controlled crystallization that results in crystalline phase(s) embedded in a residual amorphous matrix. Typically, GCs are produced by a conventional glass route with subsequent crystallization for which two heat treatments are usually applied, the former to generate nuclei and the latter being a crystal growth stage. Alternatively, another technically viable route for manufacturing GCs involves sintering of glass-powder compacts followed by crystallization (sinter-crystallization).Wollastonite-containing GCs from the CaO–Al2O3–SiO2 and CaO–MgO–SiO2 systems find a wide variety of uses in different technological fields, including construction, architecture, medical and high-tech fields. For example, a special type of wollastonite-containing GC marketed under the name of Neoparies®, which is stronger and lighter than natural stone, features high resistance to weathering/chemical attack and is manufactured on a large scale for construction and architectural applications. In the biomedical field, the well-known Cerabone® products have been used in bone-contact applications for many years.The main goal of this brief review is to provide a critical analysis of the experimental trials focusing on the synthesis of wollastonite-containing GC materials and to discuss the various fields of their application. Constitution of phase diagram of CaO–Al2O3–SiO2 and CaO–MgO–SiO2 systems are comprehensively discussed with connection to melt crystallization path and crystalline phase formation. Furthermore, special emphasis will be given to the production of wollastonite-containing GCs for construction and architectural purposes from natural raw materials and wastes, as well as to the recent advancement in developing wollastonite-containing GC biomaterials for bone repair.

Factors Affecting Microscopic Basicity of Silicate Glasses from the Perspective of O1s Binding Energy

The factor affecting the microscopic basicity of oxygen in the SiOSi bond are investigated on the basis of the O1s binding energy measured by X‐ray photoelectron spectroscopy (XPS). The samples used are SiO2, Na2OSiO2, CaOSiO2, CaOMgOSiO2, and CaOAl2O3SiO2. For analysis on clean surfaces, samples are finally prepared by fracturing in a vacuum in an XPS system. From the O1s spectra, derived are the centers of gravity of the O1s spectra and the binding energies of O1s in the SiOSi, SiOAl, AlOAl, SiONa, SiOCa, and SiOMg bonds. A good linear relationship is found between the center of gravity of the O1s spectra and the optical basicity, suggesting that the center of gravity of the O1s spectra is a reasonable basicity index of silicate glasses used in this work. It is also found that there is a linear relationship between the binding energy of O1s in the SiOSi bond and the optical basicity, irrespective of the glass systems. This indicates that the experimental microscopic basicity of oxygen in SiOSi bond is affected not only by the first neighboring ions of oxygen but also by the composition of the sample.

Rheological behaviour of CaO–MgO–SiO2–Al2O3–B2O3 system with varying B2O3 content up to 30 wt% at basicity of 0.4

A comprehensive theoretical and experimental study describing the effect of B2O3 (0–30 wt%) on softening, liquidus, and crystallization temperatures, flow behaviour, and dynamic viscosity of the glass-based oxide system SiO2(64.64–43.21 wt%)-MgO(10 wt%)-CaO(15.86–7.29 wt%)-Al2O3(9.50 wt%)-B2O3 with a constant basicity of 0.4 was carried out. The experimental data was obtained up to 1550 °C using a high-temperature rheometer and were supported by the study of the internal structure by means of scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray powder diffraction analysis, and Fourier transform infrared spectroscopy. The increasing addition of boron oxide caused a decrease in the start and end softening and liquidus temperatures. At 1550 °C, the systems exhibited Newtonian behaviour, with a dynamic viscosity increasing exponentially with a decreasing temperature and decreasing with increasing B2O3 content. The amorphous character of the samples and the formation of structural units [BO2O−] and [BO3] and [BO4], confirmed by complementary analyses, led to a decrease in the degree of polymerization of the silicate structure. The theoretical insight into the dependence of dynamic viscosity on the temperature and composition was realized based on molecular dynamics. Furthermore, the prediction of viscosity as a function of temperature (1230–1550 °C) and the change in chemical composition (0–30 wt% B2O3) was performed using artificial neural networks.

An experimental study on the phase equilibria of the CaO–MgO–SiO2–13%Al2O3–50%TiO2 system in air at 1450 °C

This study systematically investigates the phase equilibrium relations of the CaO–MgO–SiO2–13%Al2O3–50%TiO2 system in air at 1450 °C. Within the composition range, the coexistence of the liquid phase with anosovite and rutile, liquid-rutile (TiO2), liquid-anosovite (M3O5), liquid phase with anosovite and spinel, liquid-spinel, liquid phase with perovskite and spinel, and liquid-perovskite (CaTiO3) were found. Additionally, the 1450 °C isotherm in this system was obtained by comparing the experimental liquid phase results with the predicted results by FactSage 8.1. The experimental findings indicated that an increase in MgO content contributed to a higher concentration of MgTi2O5 in the anosovite solid solution. Notably, the predicted liquidus temperature was much lower than the experimentally determined liquidus temperatures within the primary of M3O5 and spinel area. This work would contribute to further refining the phase diagram of the titania-containing systems.

Mechanism of Al Coordination Change in Alkaline-earth Aluminosilicate Glasses: An Application of Bond Valence Model

Aluminum cations are generally present in four-fold ([4]Al3+) or five-fold coordination ([5]Al3+) in aluminosilicate slags, where the concentration of [5]Al3+ varies depending on the type of charge compensator, for example, Mg2+ and Ca2+. Although it has been reported that the amount of [5]Al3+ species increases with the replacement of CaO with MgO in the CaO–MgO–SiO2–Al2O3 system, the detailed mechanism underlying the change in the local structure near the aluminum cations remains unclear. Because the residual negative charge on the bridging oxygen between [4]Si4+ and [5]Al3+ ([4]Si4+–OBO–[5]Al3+) is larger than that of [4]Si4+–OBO–[4]Al3+, it is essential to understand the positive charge contributions of alkaline-earth cations to compensate for these negative charges on the bridging oxygens. In the present study, the valence of a single chemical bond near Mg2+ and Ca2+ cations in the chosen aluminosilicate glasses was determined using a simple empirical model, which enabled calculation of the bond valence from the observed interatomic distance of near alkaline-earth cations by synchrotron X-ray total scattering. Magnesium cations had a larger average bond valence (+0.39) than calcium cations (+0.31). The difference in the positive charge contribution from Mg2+ and Ca2+ should explain the variation in the coordination number of aluminum cations.

Forecast of Crystallizing Phases and Modeling of Chemical Interaction in the System CaO–MgO–SiO2

Forecast of Crystallizing Phases and Modeling of Chemical Interaction in the System CaO–MgO–SiO2

Effect of Al Content in Steel on Interfacial Interaction between Molten Steel and MgO Substrate

The apparent contact angles between the molten steel with different [Al] contents (w[Al]) from 0.002% to 0.831% (mass fraction) and the microporous MgO (MM) substrates are measured at 1823 K using the sessile drop method. In particular, the contact angles of No. 1 (w[Al] = 0.002%) and No. 5 (w[Al] = 0.831%) molten steels gradually increase with time at the initial stage. As w[Al] increases from 0.002% to 0.831%, the transformation route of interfacial products between molten steel and the MM substrate is MgO–FeO → MgO·Al2O3 → CaO·2Al2O3 + MgO·Al2O3. The w[Al] of No. 1 molten steel is small, and the dissolution of CaO·ZrO2(s) in the substrate is mainly affected by FeO. As w[Al] increases gradually, [Al] consumes the (MgO) contained in CaO·MgO·SiO2 (CMS), and turns the CMS into (CaO·SiO2) slag layer, which promotes the CaO·ZrO2(s) dissolving and thus increasing the interaction area percentage. When w[Al] is 0.831%, [Al] can react with (CaO·SiO2) slag layer or CaO·ZrO2(s) to form CaO·2Al2O3(s).

Cathodoluminescence imaging for rapid identification of low-melting CaO–MgO–SiO2 phases in MgO-based refractories involving the steelmaking process

For MgO–C refractories used in the steelmaking process, identifying low-melting CaO–MgO–SiO2 phases is crucial because they accelerate the corrosion of the refractories. However, electron probe microanalysis, a conventional method for identifying such phases, is time-consuming. Herein, cathodoluminescence (CL) imaging is proposed for the rapid identification of low-melting CaO–MgO–SiO2 phases at the reaction interface between MgO-based refractory and steelmaking slag. Monticellite, merwinite, and melilite were identified as the low-melting phases, emitting green, red, and violet luminescence, respectively, in the CL images. Other mineral phases emitted luminescence whose colors differed from those of the low-melting phases (3CaO·2SiO2 and 2CaO·SiO2) or no luminescence (magnesiowüstite, MgO·Al2O3, Ca2Fe2O5, 3CaO·SiO2, MnS, and FeS). The CL images (area: 0.5 ×0.3 mm2) were obtained in 30 s. Therefore, CL imaging is effective for the rapid identification of mineral phases, which limit the service life of MgO–C refractories during steelmaking.

Study the structural, physical, and optical properties of CaO–MgO–SiO2–CaF2 bioactive glasses with Na2O and P2O5 dopants

A new bioactive CaO–MgO–CaF2–SiO2 glass system with Na2O/MgO and P2O5/SiO2 substitutions was produced by the melting and quenching methods. Different properties of synthesized glasses, such as structural, mechanical, physical, and optical were conducted. The characterization was achieved by employing XRD, DTA, FTIR, and UV–visible techniques. The variation in density values (ρ), molar volume (Vm), oxygen molar volume (Vo), oxygen packing density (OPD), and micro-hardness showed the influence of Na2O and P2O5 dopants on the glass structure and associated physical properties. The amorphous nature of the tested glasses was confirmed using XRD, while FTIR proved the existence of [SiO4]4- and [PO4]3- in glassy networks. The optical band gap determined using the absorbance spectrum fitting (ASF) model was found to increase under substitution processes. The impact of P5+ on the bonding mechanisms by scavenging metal cations and enhancing polymerization of the silicate network, whereas increasing Na+ ions causes charge balance in the glassy network. The results revealed that the density values of the studied glasses increased from 2.76 g/cm3 to 2.86 g/cm3 by introducing Na+ and P5+ ions, whereas increasing the molar ratio improved the mechanical properties with little effect on the Poisson's ratio of multicomponent glass systems. The data also shows that the random distribution of two dissimilar Na+ and P5+cations within the silicate network leads to structural and property modifications in the developed glass. The results could pave the way for a new brake application in the biomaterials industry as an effective anti-caries agent in preventive dentistry.

Variation in viscosity of aluminosilicate melts with MgO/CaO molar ratio: Influence of five-fold coordinated aluminum

Viscosity of aluminosilicate melts is important for estimating transport phenomena in industrial processes. Viscosity variations with increasing MgO/CaO molar ratio have been reported for CaO–MgO–SiO2 (CMS) and CaO–MgO–Al2O3–SiO2 (CMAS) systems; however, the viscosity variation was not clearly correlated with the change in the melt structure. The present study investigated the influence of the MgO/CaO molar ratio on the viscosity of CMAS melts at temperatures higher than the liquidus using the rotating crucible method. The viscosity decreased with increasing substitution of CaO by MgO in the chosen CMAS system, whereas the opposite behavior has been reported for the CMS system. Aluminum-27 magic-angle spinning nuclear magnetic resonance spectra of the CMAS glasses show that the fraction of aluminum atoms in five-fold coordination ([5]Al) increased with increasing substitution of CaO by MgO. Our findings indicate that the formation of [5]Al reduces the viscosity of aluminosilicate melts.

Relationship between interaction under non-load condition and softening & melting behaviour of typical blast furnace feed

ABSTRACT The evolution of slag phases and interaction between sinter and acid pellet in cohesive zone were systematically investigated, as well as the relationship between microstructure, thermal calculation and S&M behaviour. The results indicate that both ‘component interaction’ and ‘formation interaction’ will be hindered before the formation of liquid phases. The effect of network iron at the interface on the interaction is more apparent than that of the relative position of materials. The main slag phases detected at the interface are FeO–CaO–SiO2, FeO–CaO–MgO–SiO2, FeO–CaO–Al2O3–SiO2 and FeO–CaO–MgO–Al2O3–SiO2. The relationship between interaction without load and S&M behaviour has been revealed through breaking down the complex process into the reaction between P–P, S–S and P–S. The main area that affects the pressure drop in cohesive zone is the melting region. Mixed burden is beneficial to enhance the interaction and promote the melting behaviour.

Effect of Al2O3 on the molten slag microstructure information by molecular dynamics simulation and experimental analysis

The metallurgical properties of blast furnace slag changed when high alumina iron ore was used extensively due to the resulting changes of the molten slag microstructure. In the study, based on typical CaO–MgO–SiO2–Al2O3 slag systems with different w(Al2O3) content, molecular dynamics simulation was used to calculate the microstructural properties of particles in the high-temperature slag system, such as bond length, partial radial distribution function, coordination numbers, and diffusion coefficient. In addition, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and 27Al solid-state magic angle spinning nuclear magnetic resonance (27Al SS MAS NMR) were used to detect and analyze the samples. The comprehensive calculations and experimental results show that increasing w(Al2O3) can enhance the structural stability of each ion pair, and the strength of the structural stability is such that Si–O > Al–O > Mg–O > Ca–O. The self-diffusion coefficients are as follows: Mg2+ > Ca2+ > Al3+ > Si4+, which leads to the transformation of the [SiO4]4−(Q0), [Si2O7]6−(Q1) and [Si2O6]4−(Q2) structural units to [Si2O5]2−(Q3). The degree of polymerization of slag increased as well as the stability of the structural units. Moreover, the coordination of Al will change from the [AlO6]9−octahedral structure of six-coordinated Al to the [AlO5]7−pentahedral structure of five-coordinated Al and the [AlO4]5−tetrahedral structure of four-coordinated Al. It was also found that the content of non-bridge oxygen in the whole slag system decreased continuously, leading to the increasing degree of polymerization of slag, and the experimental results were consistent with the molecular dynamics calculation.

Three routes for the synthesis of the bioceramic powder of the CaO-MgO-SiO2 system

We report three routes for the synthesis of CaO-MgO-SiO2 (CMS) bioceramic powder using different Si sources and synthesis procedures. The ceramic powders were synthesized from Na2SiO3 waste solution by the sol-gel process combined with co-precipitation (synthesis route I and synthesis route II), and from TEOS (tetraethyl orthosilicate) by conventional sol-gel (synthesis route III). Ceramic powders of the CMS multiphase system were obtained, including diopside, wollastonite, akermanite, monticellite and merwinite, which are suitable for application as biomaterial. These powders were sintered at 1200 °C for 2 h to obtain the CMS ceramics. The ceramics mostly contained diopside and wollastonite crystalline phases. Those ceramics when submitted to cytotoxicity tests revealed to be non-cytotoxic, according to ISO10993-5:2009. The ceramics were tested for in vitro bioactivity while soaked in simulated body fluid (SBF) solution. After 14 days, the presence of hydroxyapatite particles on the surface of ceramics was confirmed by Fourier Transform Infrared (FTIR) spectroscopy and Scanning Electron Microscopy (SEM) micrographs. The surfaces were completely covered with hydroxyapatite, after 21 days. In summary, CaO-MgO-SiO2 (CMS) ceramic powder derived from three routes of synthesis have potential application in the biomedical area. However, further in-vitro and in-vivo studies are needed.

Effect of MgO Grade in MgO–C Refractories on the Non‐metallic Inclusion Population in Al‐Treated Steel

Steelmaking processes require high‐performance lining materials with high refractoriness and thermal shock resistance, such as MgO–C bricks. Therefore, the interactions between three industrially fabricated MgO–C bricks differing in the used MgO grade and liquid steel are investigated by immersion tests in an Al‐deoxidized 42CrMo4 steel at 1600 °C, herein. The trials are carried out in a steel casting simulator. Macro‐ and microstructure of immersed specimens are characterized using light microscopy, scanning electron microscopy, and X‐ray diffraction, while the inclusion population in the solidified steel is analyzed using an automated feature analysis to determine the frequency, geometric characteristics, and elemental composition of the inclusions. Newly formed structures consisting mainly of MgO are observed on the immersed specimens differing in their superficial appearance and the frequency of phases assigned to the system Al2O3–CaO–MgO–SiO2 in dependence on the MgO grade. Based on the inclusion species occurring in the solidified steel, a specific rulefile is developed to classify the non‐metallic inclusions by their elemental composition. Significant differences in the frequency of detected inclusions and their distribution according to the developed rulefile depending on the MgO grade are identified by keeping the processing in the steel casting simulator constant.