MgO SiO2 System Research Articles

Experimental Determination of Slag Emissivities for Enhanced Slag Control by Infrared‐Based Systems

For today's high‐quality steel production, good control of slag composition is essential in secondary steelmaking. However, the conventional slag analysis practice, involving sampling, sample preparation, and analysis, is very time‐consuming. This work is the first step toward an investigation of infrared (IR)‐based systems and can be used for online slag composition monitoring using the principle that different slag compositions have different emissivities in the IR wavelength range. Therefore, this work experimentally determines emissivity values of slags as a function of composition at steelmaking temperature, since available data for slags are very limited in the literature. The emissivities of three different slag compositions belonging to the Al2O3–CaO–SiO2–MgO system are investigated at 1773 K. The investigated emissivities are in the range of 0.75–0.87, with the best repeatability seen in the slag which is fully liquid at 1773 K. Variations in emissivities are observed within the other slags due to the presence of solid phases. Although the data clearly indicate a difference of emissivities as a function of slag composition, further experiments must be performed to evaluate the emissivities of other characteristic slags at different temperatures in order to further assess the applicability of IR‐based systems for slag composition control.

Evaluation of rheo-viscoelasticity of magnesium-silicate-hydrate mixes incorporating different superplasticizers

This study investigated rheo-viscoelastic behaviors of MgO-SiO2 pastes with three phosphate additives (sodium hexametaphosphate (SHMP), sodium trimetaphosphate (STMP), and sodium orthophosphate (SOP)) as superplasticizers. Static yield stress, dynamic yield stress, median differential viscosity, thixotropic loop area, structural recovery rate, and non-destructive structural build-up were analyzed. Furthermore, assessment of hydration and particle dispersion stability was facilitated by employing isothermal calorimetry, XRD, DTG, and zeta potential techniques. SHMP significantly decreased the static and dynamic rheology, thixotropy, and viscoelastic evolution. Samples incorporating 2 wt% SOP exhibited enhanced rheological parameters, particularly static yield stress, owing to increased brucite formation and a denser microstructure in the fresh paste. Adsorption of phosphate additives on MgO surfaces inhibited formation of brucite and improved interparticle electrostatic repulsion, thereby increasing suspension stability. High-efficiency adsorption of SHMP on MgO surfaces, coupled with the retardation of brucite nucleation-and-growth, and enhancement in suspension stability, greatly restrained the rheo-viscoelastic evolution of MgO-SiO2 system.

First principles thermodynamic assessment of the MgO–SiO2 system

First principles thermodynamic assessment of the MgO–SiO2 system

Phase diagrams of oxide system FeO–MnO–MgO–SiO2. Report 2. Triple state diagrams FeO–MnO–SiO2, FeO–MgO–SiO2, MgO–MnO–SiO2

The knowledge of the thermodynamics and phase equilibria of silicate melts FeO–MnO–MgO–SiO2 and solid solutions of silicates of the MnO–MgO–SiO2 system allows us to predict the appearance of non-metallic inclusions in steel. The FeO–MnO–MgO–SiO2 system includes six double and four triple state diagrams of oxide systems. Previously, the state diagrams of binary FeO–MnO, FeO–MgO, FeO–SiO2, MnO–MgO and ternary FeO–MnO–MgO oxide systems were studied. In this work, state diagrams of the FeO–MnO–SiO2, FeO–MgO–SiO2 and MgO–MnO–SiO2 systems were constructed. The calculations used the theory of subregular ionic solutions, which takes into account the dependence of the coordination number on the composition of the melt, quite accurately describes diagrams with two immiscible liquids and is consistent with the experimental data presented in the literature. In the work, the energy parameters of this theory were selected to calculate the activities of the components of the oxide melt of each of the systems under study, as well as the parameter of the theory of regular ionic solutions to calculate the activities of the components of the magnesium-manganese orthosilicate solution |Mg2SiO4, Mn2SiO4|. The data obtained on the state diagrams of the systems included in the FeO–MgO–MnO–SiO2 system will make it possible to establish non-metallic inclusions in equilibrium with the liquid metal in the Fe–Mg–Mn–Si–O system

Magnesium-silicate-hydrate cement pastes: Rheological behavior and strength development

In contrast to Portland cement (PC), magnesium-silicate-hydrate (MgO-SiO2) cement mixes offer a significant advantage due to their lower calcination temperature requirement during production, reduced carbon footprint and energy consumption linked with the manufacturing process. This study presents a detailed investigation of the rheological characteristics and strength development of magnesium-silicate-hydrate cement mixes, along with a series of microstructural analyses to examine the hydration process and phase compositions of the prepared mixes. Results indicated that an increase in the water-to-binder (w/b) ratio decelerated the growth rate of both storage and loss moduli over time. Samples with magnesia-to-silica (m/s) ratios of 4:6 exhibited not only the highest modulus during the initial stages of hydration, but also the most rapid increase. The reaction of MgO and dissolution of SiO2 were limited in the fresh state, initially resulting in low brucite and M-S-H contents. Although samples with m/s ratios of 5:5 exhibited the highest 28-day compressive strength (38.5 MPa), those with m/s ratios of 4:6 had the highest M-S-H content at 28 days. These findings contributed to existing knowledge by revealing the relationship between rheological characteristics, reaction mechanisms and strength development within MgO-SiO2 system and highlighted the impact of key factors such as w/b and m/s ratios on both the fresh and hardened properties.

Metamorphic reaction kinetics at anhydrous to water-saturated conditions in the binary MgO-SiO2 system

Metamorphic reaction kinetics at anhydrous to water-saturated conditions in the binary MgO-SiO2 system

To study the synthesis and characterization of SrO–MgO–SiO2 system in biological and dielectric applications

Ternary ceramic samples comprising SrO–MgO–SiO2 with varying element concentrations were synthesized using the solid-state method and sintered at 800°C. To characterize the properties of the samples, several analysis techniques were employed. X-ray Diffraction (XRD) was utilized for structural analysis, FTIR spectroscopy was used to identify bonds, SEM provided morphological analysis, biocompatibility was assessed through Vitro testing, microhardness was evaluated using Vickers testing, and dielectric analysis was performed to investigate electrical properties. The XRD spectra confirmed the presence of a ternary phase known as Magnesium Strontium Di-silicate [MgSr2Si2O7], with no impurity peaks detected. FTIR spectroscopy indicated the formation of Magnesium silicate, displaying vibrational bands corresponding to SiO4 and MgO, which further confirmed the existence of MgSr2Si2O7 in the samples. The Vitro test results revealed that all samples exhibited biocompatible behavior, with moderate pH and weight loss. SEM images provided insights into the morphology of the system and confirmed the development of an appetite layer on the sample surfaces. The particle size of the samples was measured to be approximately 116.48±9 nm. Vickers hardness testing yielded microhardness values ranging from 378.1 to 400.2 HV. Dielectric constant measurements demonstrated that the AC conductivity of the SrO–MgO–SiO2 system increased as the percentage of Mg doping increased.

Phase diagrams of oxide system FeO–MnO–MgO–SiO2. Report 1. Binary oxide systems MnO–SiO2 and MgO–SiO2

Manganese and silicon are present in almost any steel, and magnesium can enter the metal from the lining and magnesian slags or be introduced in the form of an alloy, so knowledge of the thermodynamics and phase equilibria of liquid and solid silicate solutions allows to predict the appearance of non-metallic inclusions in steel. The FeO–MnO–MgO–SiO2 system includes six double and four triple phase diagrams of oxide systems. The binary phase diagrams of FeO–MnO, FeO–MgO, FeO–SiO2, and MnO–MgO oxide systems were previously studied. In this work, the phase diagrams of the MnO–SiO2 and MgO–SiO2 systems were considered, the liquidus lines and thermodynamic data on the melting of manganese and magnesium silicates – the enthalpies and entropies of melting of ortho- and metasilicates of manganese (Mn2SiO4 and MnSiO3) and magnesium (Mg2SiO4 and MgSiO3) were calculated. The theory of subregular ionic solutions, which takes into account the dependence of the coordination number on the melt composition, is used to calculate the activities of the components of the oxide melt and accurately describes the diagrams with two immiscible liquids and is consistent with the experimental data presented in the literature. The obtained data on the energy parameters of the theory of subregular ionic solutions for the systems MnO–SiO2 and MgO–SiO2, as well as the thermodynamic data on the formation of manganese and magnesium silicates, make it possible to proceed to the study of ternary oxide systems belonging to the FeO–MgO–MnO–SiO2 system.

Phase diagrams of oxide system FeO–MnO–MgO–SiO2. Report 1. Binary oxide systems MnO–SiO2 and MgO–SiO2

Manganese and silicon are present in almost any steel, and magnesium can enter the metal from the lining and magnesian slags or be introduced in the form of an alloy, so knowledge of the thermodynamics and phase equilibria of liquid and solid silicate solutions allows to predict the appearance of non-metallic inclusions in steel. The FeO–MnO–MgO–SiO2 system includes six double and four triple phase diagrams of oxide systems. The binary phase diagrams of FeO–MnO, FeO–MgO, FeO–SiO2, and MnO–MgO oxide systems were previously studied. In this work, the phase diagrams of the MnO–SiO2 and MgO–SiO2 systems were considered, the liquidus lines and thermodynamic data on the melting of manganese and magnesium silicates – the enthalpies and entropies of melting of ortho- and metasilicates of manganese (Mn2SiO4 and MnSiO3) and magnesium (Mg2SiO4 and MgSiO3) were calculated. The theory of subregular ionic solutions, which takes into account the dependence of the coordination number on the melt composition, is used to calculate the activities of the components of the oxide melt and accurately describes the diagrams with two immiscible liquids and is consistent with the experimental data presented in the literature. The obtained data on the energy parameters of the theory of subregular ionic solutions for the systems MnO–SiO2 and MgO–SiO2, as well as the thermodynamic data on the formation of manganese and magnesium silicates, make it possible to proceed to the study of ternary oxide systems belonging to the FeO–MgO–MnO–SiO2 system.

Dissolution of Magnesia in Silicate Melts and Diffusivity Determination from CLSM Studies

Magnesia is one of the vital and extensively used refractory components. In this study, the dissolution of magnesia is investigated at 1450, 1500, and 1550 °C in three silicate slags in the CaO–Al2O3–SiO2–MgO system using high-temperature confocal laser scanning microscopy to determine its effective binary diffusivity. The pore-free fragments of single-crystal fused magnesia particles were used, and the effects of experimental parameters and slag properties on the dissolution of magnesia were assessed. The ranking of dissolution times in the three slags at the three temperatures did not agree with the trend expected from the CaO/SiO2 ratio of each slag. Instead, several quotients serving as reference numbers were tested. The effective binary diffusivities were calculated considering all the impacting phenomena and parameters. The diffusivities of magnesia at 1500 °C in the slags with CaO/SiO2 weight ratios of 0.65, 0.93, and 1.17 are 2.67 × 10−10, 1.81 × 10−10, and 3.20 × 10−10 m2/s, respectively. The diffusivity of magnesia in one of the three slags was compared with rotating finger test results, which showed good agreement. The plausibility of diffusivity was checked using an Arrhenius plot.

Аналіз структурно-хімічного стану дуплекс-систем силікати-силіциди лужно-земельних металів. Повідомлення 1.

The classification and structuring of oxide and metallic phases of binary duplex systems of silicates-silicides of alkaline earth metals are carried out in the work. This will determine the optimal composition of alkaline earth metal alloys based on silicon in the refining of ferrocarbon melts and modification of non-metallic inclusions. The ionic-molecular complexes of magnesium, oxygen and silicon are constructed in the work, which determine the mechanism of formation of non-metallic inclusions (magnesium silicates) in steel when using silicomagnesium alloys for refining. The parameters of chemical bonding for oxides with ionic bond type, for liquid silicomagnesium alloys having a metallic type of chemical bonding and for hard alloys with metal-covalent bond are determined. The presented results of structural and chemical analysis of the duplex system MgO–SIO2–Mg–Si allow to reveal the mechanisms of desulfurization processes and to develop technologies of blast furnace desulfurization in smelting and ladle treatment with furnace slag, magnesium and its alloys with silicon. Keywords: polygonal diagram, magnesium oxides, alkaline earth metal silicides, quantum mechanical parameters, classification and structuring.

Low-temperature crystallization and microwave dielectric properties of forsterite generated in MgO–SiO2 system following LiF addition

The crystallization and microwave dielectric properties of forsterite (Mg2SiO4) produced in (1-x)2MgO–SiO2(MS)-xLiF mixtures were characterized. High-temperature XRPD for a 0.91MS-0.09LiF specimen indicated the crystallization of forsterite above 800 °C, although MgSiO3, MgO and SiO2 were also detected due to the short heating duration. The XRPD patterns for (1-x)MS-xLiF ceramics sintered at 900 °C for 4 h in a covered crucible demonstrated the formation of forsterite as a single phase in compositions having x values less than 0.08. The activation energy for the crystallization fraction of forsterite was estimated from the DTA curves by using Kissinger-Akahira-Sunose method and decreased from 1382.4 to 474.0 kJ/mol, suggesting that the LiF addition enhances the nucleation and crystallization of forsterite. Refinement of the crystal structures of the (1-x)MS-xLiF ceramics by Rietveld analysis showed that the patterns acquired from samples having x values of 0.03–0.08 corresponded to a forsterite single phase with a decrease in the lattice parameters, confirming the substitution of Li and F for Mg and O in the forsterite. 7Li and 19F solid-state NMR spectroscopy analyses also confirmed the presence of 7Li and 19F signals for the sintered ceramics. The Q・f values for the ceramics increased from 22,800 to 104,800 GHz as x was increased to 0.08, due to the improvement in the crystallinity of forsterite. Although a near zero TCf value was achieved by CaTiO3 addition for (1-y)(0.92MS-0.08LiF)-yCaTiO3 ceramics at y = 0.10 (εr = 8.2, Q・f = 25,050 GHz, TCf = −5 ppm/°C), the Q・f values were drastically decreased due to the lower crystallinity of the forsterite and the presence of SiO2 and Li2MgSiO4 as secondary phases.

Analysis of chemical weathering trends across three compositional dimensions: applications to modern and ancient mafic-rock weathering profiles

Chemical weathering indices (one-dimensional/1D index values) and accompanying ternary plots (two-dimensional/2D compositional space) facilitate quantitative comparison of whole-rock and mineral major-element data, and empirical chemical trends with predicted weathering vectors. However, data analysis in ternary plots is restricted by poles grouping elements that are hosted in different minerals or that are influenced selectively by later alteration (e.g., diagenesis/metasomatism). Tetrahedral plots (three-dimensional/3D compositional space) offer enhanced analytical utility of major-element data by shifting elements across four poles and (or) incorporating additional proxy elements. Tetrahedral space can better reveal combined effects on major-element compositions from independent mineralogical controls and post-depositional alteration via curvilinear trends that are otherwise simplified and linear in ternary space. This study focuses on mafic-rock weathering and first reviews applications and limitations of the 1D mafic index of alteration (MIA) and index of lateritization/bauxitization (IOL/IOB) that integrate into molar Al2O3–CaO*–Na2O–K2O–(FeO(T)/Fe2O3(T))–MgO and SiO2–Al2O3–Fe2O3(T) ternary compositional space, respectively. Analysis in tetrahedral space is then demonstrated with Phanerozoic weathering profile and Precambrian paleosol data in two plots of the molar Al2O3–CaO*–Na2O–K2O–(FeO(T)/Fe2O3(T))–MgO system (A–CN–K–FM and AF–CN–K–M plots) and one plot of the molar Al2O3–CaO*–Na2O–K2O–(FeO(T)/Fe2O3(T))–MgO–SiO2 system (A–L–F–S plot). Common chemical weathering indices are integrated into these 3D tetrahedral spaces or onto some of their 2D ternary faces. However, the tetrahedral compositional space is a key to (1) assessing integrative effects from labile element loss while accounting for the variable, redox-dependent behaviour of Fe, (2) better exposing, and correcting for, overprinting effects of diagenesis/metasomatism, and (3) tracking Si loss across all stages of chemical weathering.

Thermodynamic properties of geikielite (MgTiO3) and ilmenite (FeTiO3) derived from vibrational methods combined with Raman and infrared spectroscopic data

We present a model for the lattice vibrational density of states of MgTiO3 (geikielite) and FeTiO3 (ilmenite) that predicts thermodynamic properties, in agreement with observational data. The model is based on Kieffer’s method combined with spectroscopic data. For both substances experimental data sets are influenced by non-stoichiometry. For geikielite that affects the volume, whereas for ilmenite volume and bulk modulus are affected. We show that Kieffer’s method enables predicting bulk moduli in pressure–temperature space. We demonstrate that intrinsic anharmonicity or electronic effects significantly affect the heat capacity of ilmenite, whereas that is not the case for geikielite. We use Kieffer’s method to derive multiple-Einstein models, from which we demonstrate that thermodynamic properties are insignificantly influenced by dispersion in Grüneisen, mode-q and anharmonicity parameters for both substances. We show that our results enable predicting thermodynamic properties and shear modulus of the solid solution formed from geikielite and ilmenite. Geikielite and ilmenite are added to our thermodynamic database for the system MgO–SiO2–FeO, to enable modeling phase stability and physical properties of titanium-rich reservoirs in the Earth’s Moon.

Integrated experimental and thermodynamic modeling study of phase equilibria in the ‘CuO0.5’-MgO-SiO2 system in equilibrium with liquid Cu metal for characterizing refractory-slag interactions

An integrated experimental and thermodynamic modeling study of the phase equilibria in the ‘CuO0.5’-MgO-SiO2 system in equilibrium with liquid Cu metal has been undertaken to better understand the reactions between MgO-based refractories and liquid slag in copper converting and refining processes. New experimental phase equilibria data at 1250–1680 °C were obtained for this system using a high-temperature equilibration of synthetic mixtures with predetermined compositions in silica ampoules or magnesia crucibles, a rapid quenching technique, and electron probe X-ray microanalysis of the equilibrated phase compositions. The system has been shown to contain primary phase fields of cristobalite (SiO2), tridymite (SiO2), pyroxene/protoenstatite (MgSiO3), olivine/forsterite (Mg2SiO4), periclase (MgO), and cuprite (Cu2O). Three regions of 2-liquid immiscibility were found—two in the high-silica range of compositions above the cristobalite primary phase field (close to ‘CuO0.5’-SiO2 and MgO–SiO2 binaries) and one in the low-SiO2, high-‘CuO0.5’ compositional region above the periclase and olivine phase fields. The results obtained in this study indicate that silica in high-copper refining slags likely led to olivine and pyroxene phase formation, increased solubility of MgO in liquid slag, and decline in the performance of MgO-based refractories. New experimental data were used in the development of a thermodynamic database describing this pseudo-ternary system.

Integrated Experimental and Thermodynamic Modeling Investigation of Phase Equilibria in the PbO\u2013MgO\u2013SiO2 System in Air

Magnesium oxide-based refractory materials are used industrially to contain the chemically aggressive slags present in lead smelting systems. In the present study an integrated experimental and thermodynamic modeling approach was taken to provide fundamental information on the chemical reactions taking place in these systems. New experimental phase equilibria and liquidus data were obtained for the PbO–MgO–SiO2 system in air in the temperature range 750 °C to 1740 °C. In the MgO–SiO2 binary, new experimental results were obtained at 1550 °C to 1740 °C and compared to the available thermodynamic data in the literature. The experiments were carried out using the high-temperature equilibration of oxide powder mixtures followed by rapid quenching of the samples. Electron probe X-ray microanalysis (EPMA) was used to determine the compositions of the solid and liquid phases present at equilibrium conditions. Phase equilibria and liquidus isotherms in the cristobalite and tridymite (SiO2), pyroxene (protoenstatite MgSiO3), olivine (forsterite Mg2SiO4), barysilite (Pb8MgSi6O21), massicot (PbO) and periclase (MgO) primary phase fields were measured, and the extent of the high-silica two-liquid immiscibility gap in equilibrium with cristobalite was determined. The experimental results were used to optimize the parameters in a thermodynamic database that was subsequently used to describe this multi-component, multi-phase system and predict the liquidus for the PbO–MgO–SiO2 system. The new data were used to characterize the chemical interactions of magnesia-based refractory with PbO–MgO–SiO2 slags.

Получение стеклокерамики системы MgO-SiO-=SUB=-2-=/SUB=- методом плазменной плавки

Results of experimental studies of the synthesis glass ceramics of the MgO–SiO2 system by plasma melting at atmospheric pressure are presented. According to electron microscopy data, during melt crystallization rate of 287 ± 5 K/s, the surface morphology is represented by dense packing of rhombic dodecahedral Mg2SiO4 crystals (there is no open porosity). In this case, the matrix is ​​characterized by the formation of dense framework with clear linear arrangement of spherical inclusions corresponding to the MgSiO3 phase. Result of synthesis by plasma melting, glass ceramics with density of 3.56 g/cm3 and microhardness of up to 15 GPa were obtained. It is assumed that glass-ceramics with such a composition can be considered as an excellent option for the development of economical high-quality refractory.

Obtaining glass ceramics of the MgO-SiO-=SUB=-2-=/SUB=- system by the plasma melting method

Results of experimental studies of the synthesis of glass ceramics of the MgO-SiO2 system by plasma melting at the atmospheric pressure are presented. Electron microscopy data showed that, during the melt crystallization with the rate of 287-5 K/s, the surface morphology is represented by a dense packing of rhombic dodecahedral Mg2SiO4 crystals (without open porosity). In this case, the matrix is characterized by the formation of a dense framework with a clear linear arrangement of spherical inclusions corresponding to the MgSiO3 phase. As a result of the plasma melting synthesis, glass ceramics with the density of 3.56 g/cm3 and microhardness of up to 15 GPa was obtained. It is assumed that glass ceramics with such a composition can be considered as an excellent option for the development of a cost-effective high-quality refractory. Keywords: forsterite, glass ceramics, electric arc synthesis.

Designing a novel CaO–MgO–SiO2-based multiphase bioceramic with adjustable ion dissolution behavior for enhancing osteogenesis

Many bioactive inorganic ions such as calcium (Ca), magnesium (Mg) and silicon (Si) have been confirmed to take part in bone regeneration through promoting the secretion of osteogenesis-related growth factors. However, it is not clear about the effective concentration range and action mechanism of ion combinations on synergistically facilitating osteogenesis. Besides, it is of great significance to design a novel bioceramic that could continuously release these effective inorganic ions to match the need for bone tissue repair. Thus, in this work, the concentration level of combined Ca, Mg, Si ions beneficial to osteogenesis of bone marrow-derived mesenchymal stem cells (BMSCs) was explored by orthogonal experimental design (OED) firstly. Meanwhile, eight single-phase ceramics in CaO–MgO–SiO2 system were synthesized, and the influences of their inherent properties on ion dissolution behaviors were systematically investigated. Finally, based on the above results, three multiphase bioceramics (named C1, C2 and C3) containing calcium silicate, diopside and akermanite as crystalline phase were designed and synthesized. It was found that the ionic extracts of bioceramic C1 were just within the above effective concentration range, displaying a predetermined ability of stimulating osteogenic differentiation of BMSCs through enhancing the expression of bone morphogenetic protein-2 (BMP-2) and vascular endothelial growth factor (VEGF). All the results indicated that this novel multiphase bioceramic with adjustable ion dissolution behavior has a great application potential in bone tissue engineering.

Addition of V2O5 and V2O3 to the CaO–FeO–Fe2O3–MgO–SiO2 database for vanadium distribution and viscosity calculations

Vanadium oxides were added to the existing GTOx database because of its important role in the ferro-titanium metallurgy as well as in petroleum coke gasification. The CaO–FeO–Fe2O3–MgO–SiO2 system is a part of GTOx database and is chosen because of the existence of experimentally determined vanadium distributions between vanadium ferroalloys and metallurgical slags. The CaO–FeO–Fe2O3–MgO–SiO2–V2O3–V2O5 system including all binary and ternary sub-systems was thermodynamically assessed using all available experimental data. Vanadium was introduced into the thermodynamic description of solid solution phases such as MeO, Spinel, Corundum and Ca2SiO4-α using available experimental information. Particular attention was given to the phase Spinel which forms the wide completely miscible solid solution Fe3O4–FeV2O4–MgV2O4–MgFe2O4. The thermodynamic description of the metallic vanadium containing systems was taken from the SGTE alloy database. With the knowledge about the complex behavior of vanadium in slags as well as in liquid metal alloys it is possible to calculate the vanadium distribution ratios (V)/[V] between iron melts and slags in a wide range of temperatures and compositions, corroborating the validity of the model under reducing conditions. The additionally developed viscosity model shows good agreement between the calculated and experimental values in vanadium-containing slags.