MgO System Research Articles

Phase formation in the CaO–Al2O3–ZnO system as an analogue to CaO–Al2O3–MgO in spinel containing refractories

AbstractRecently, gahnite (ZnAl2O4) is gaining attraction as a potential refractory ceramic because of the similarity of its structure and properties with those of magnesium aluminate (MgAl2O4) spinel refractories. Formation of MgO and hibonite solid solution (CaMgxAl12−xO19−0.5x; 0 ≤ x ≤ 0.18), CAM‐I (Ca2Mg2−3xAl28+2xO46 (0 ≤ x ≤ 0.3), and CAM‐II (CaMg2−3xAl16+2xO27, 0 ≤ x ≤ 0.2) phases with platelet and interlocking microstructure in the CaO–Al2O3–MgO ternary system significantly enhances the high temperature mechanical properties of refractory castables. The CaO–Al2O3–ZnO ternary system has been studied, for the first time to our knowledge, in a selected compositional range with reference to the CaO–Al2O3–MgO system from 1650°C to 1700°C. The formation of ZnO and hibonite solid solution (CaZnxAl12−xO19−0.5x; 0 < x < 0.18), CAZ‐I (Ca2Zn2−3xAl28+2xO46; 0 ≤ x ≤ 0.3), and CAZ‐II (CaZn2−3xAl16+2xO27; 0 ≤ x ≤ 0.2) phases with platelet and interlocking morphology have been found. The crystal structures and lattice parameters of ZnO and hibonite solid solution, CAZ‐I, and CAZ‐II are comparable, respectively, with MgO and hibonite solid solution, CAM‐I, and CAM‐II. Furthermore, CAZ‐I and CAZ‐II phases also form due to reaction between hibonite (CaO·6Al2O3) and ZnAl2O4.

Analysis of Microstructure Molecular Dynamics and Slag–Metal Reaction of Low‐Basicity CaOSiO2Al2O3MgO System Refining Slag

To clarify the effect of slag composition changes on the slag–metal interface reaction, the microstructure of the CaOSiO2Al2O3MgO system molten refining slag is analyzed using molecular dynamics simulation. In the simulation results, it is shown that in the slag, the SiO bond and AlO bond mainly exist in a tetrahedral coordination, mainly including five structural forms: Q0, Q1, Q2, Q3, and Q4. In addition, AlO also exists in a pentahedral and hexahedral coordination. With the increase of basicity, the proportion of aluminum–oxygen tetrahedral structure in the slag increases, the AlO bond length decreases, and the average diffusion ability of each atom in the slag increases, which can promote the reduction of aluminum in the slag into the steel melt. With the increase of Al2O3 content, the degree of slag polymerization increases, the proportion of pentacoordinated and hexacoordinated aluminum increases, the AlO bond length increases, and the average diffusion ability of each atom in the slag decreases, which can inhibit the reduction of aluminum in the slag into the steel melt.

A Diazeniumdiolate Signal in Pseudomonas syringae Upregulates Virulence Factors and Promotes Survival in Plants.

Pseudomonas syringae infects a wide variety of crops. The mangotoxin-generating operon (mgo) is conserved across many P. syringae strains and is responsible for producing an extracellular chemical signal, leudiazen. Disruption of the mgoA gene in P. syringae pv. syringae (Pss) UMAF0158 alleviated tomato chlorosis caused by this bacterium. We showed that deletion of the entire mgo reduced Pss UMAF0158 population in tomato leaflets. Leudiazen restored the signaling activity of the deletion mutant at a concentration as low as 10 nM. Both the diazeniumdiolate and isobutyl groups of leudiazen are critical for this potent signaling activity. Transcriptional analysis showed that mgo and leudiazen induce the expression of mangotoxin biosynthetic operon as well as an uncharacterized gene cluster, RS17235-RS17245. We found that this cluster enhances the survival of Pss UMAF0158 in planta and is widely distributed in P. syringae strains. Our results demonstrate that mgo plays prominent roles in the virulence and growth of P. syringae. The mgo and mgo-like signaling systems in different bacteria likely regulate diverse microbe-host interactions. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Viscosity of titanium slag in separating electric melting of a metallized mixture of perovskite and ilmenite concentrates

To assess the possibility of joint processing of ilmenite (FeTiO3) and perovskite (CaTiO3) concentrates using a duplex process involving solid-phase reduction of iron (metallization) and subsequent separating melting into pig iron and titanium slag, the properties of slag melts were studied. The crystallization beginning point (liquidus temperature) and the corresponding viscosity of titanium slag depend on its chemical composition. The increase in titanium oxides content results in increase of these properties, while the presence of iron and calcium oxides leads to their decrease. During the joint processing of ilmenite (IC) and perovskite (PC) concentrates, the CaO content in the slag can be adjusted by changing their PC/IC ratio, and the FeO fraction is determined by the degree of iron metallization during the preliminary reduction roasting of a concentrate mixture with a carbon reducing agent. To select the optimal PC/IC ratio the temperature dependences of the viscosity of model oxide melts of the TiO2–FeO–CaO–Al2O3–MgO system, similar in composition to the slags formed as a result of melting mixtures of perovskite and ilmenite concentrates within the range of PC/IC ratios equaling to 0.6÷1.4, and the metallization degree from 75 to 95% were determined. According to the results obtained, within the entire range of studied compositions and temperatures, the viscosity of slag melts does not exceed 0.8 Pa·s. That is to say, such slags will be sufficiently fluid at the tapping point if the melt temperature is higher than liquidus temperature — the crystallization beginning point. Increasing the PC/IC ratios when decreasing the metallization from 95 to 75%, results in a monotonous decrease in liquidus temperature and its corresponding viscosity from 1490 оC and 0.79 Pa·s up to 1270 оC and 0.17 Pa·s, respectively. It is recommended to use a charge containing equal mass fractions of concentrates (PC/IC equal to 1) at the consumption of carbon reducing agent based on metallization of 85% iron. In this case, slags with a relatively low iron oxide content (3.1%) will be fluid (0.38 Pa·s), and have liquidus temperature of 1400 оC which will allow carrying out top and bottom melt at operating temperatures of 1500–1550 оC.

Study on Transformation of Glassy and Crystalline Inclusions in Cord Steel during Heat Treatment at 1100 °C

To clarify the transformation of the glassy and crystalline inclusions in cord steel during heat treatment, four groups of MnO–SiO2–Al2O3 systems with different MgO contents are designed to obtain samples with both glassy and crystalline inclusions by slow‐cooling, and then the samples are isothermal held at 1100 °C for 120 min. The results of X‐ray diffraction and scanning electron microscope and energy dispersive spectrometer indicate that after isothermal holding, the MgMnSiO4 crystalline phase transforms into MgAl2O4 and MnSiO3 phases in 5 wt% MgO system, while partial MgMnSiO4 phase transforms into MgSiO3 phase in 10 wt% MgO system. Besides, the MgMnSiO4 crystalline phase transforms into MgSiO3 and Mg2SiO4 phases in 15 wt% MgO system, while the Mg2SiO4 crystalline phase partially transforms into MgSiO3 phase in 20 wt% MgO system. Combined with the calculation results of FactSage 8.1, it shows that the higher the MgO content in the system, the stronger the crystallization ability and the easier the formation of the crystalline phase. During the isothermal holding process, the elements in inclusions continuously diffuse and migrate, so that the glassy phase transforms into crystalline phase, while the crystalline phase grows further and the internal glassy phase disappear, accompanied by the transformation of the crystal type.

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.

Materials for improved lifetime of saggar in production of Li‐ion cathode powders

AbstractCeramic saggars of mullite‐cordierite are currently used to produce cathode powders for lithium‐ion batteries. Strong interactions occur between the LiNi0.8Mn0.1Co0.1O2 (NMC) precursor in the temperature range of calcination (750–1000°C) leading to corrosion and formation of cracks in the saggar. The frequent failure of saggar causes a lot of waste, which could be reduced by choosing corrosion‐resistant materials. To understand the corrosion mechanism in the system MgO–Al2O3–SiO2, the materials MgO, Al2O3, MgAl2O4, and SiC (instead of SiO2) were embedded in premixed NMC precursor and calcined at T = 780°C for 50, 100, 150 and 200 h. The formed phases were determined by phase and microstructure analysis. Finally, the formation of LiAlO2 and Li5AlO4 is associated with a lower growth rate of the corrosion layer compared with Li4SiO4, while MgO is inert. The reactivity with NMC can be ordered as follows: SiO2 > Al2O3 > MgO.

Crystallization Behavior of the CaO–SiO2–Al2O3–MgO System Inclusions

The crystallization process of low melting point CaO–SiO2–Al2O3–MgO system inclusions during the continuous casting and hot rolling process greatly affects the deformability of inclusions. The effect of Al2O3 and MgO contents on the crystallization characteristics of CaO–SiO2–Al2O3–MgO system melts representing the typical oxide inclusions in Si–Mn deoxidized steels is systematically investigated. The continuous cooling transformation and time–temperature transformation experiments are carried out. The results reveal that the increase of Al2O3 contents restrains the crystallization process of the melt, whereas the crystallization tendency of the melt is promoted with the increase of MgO contents. The precipitated phases are predominately 2CaO·MgO·2SiO2 and 3CaO·MgO·2SiO2, and the primary crystalline phase is unaffected by the changes of Al2O3 and MgO contents. To obtain low melting point plasticized inclusions with limited crystallization ability, it is recommended to control the Al2O3 and MgO contents greater than 15 wt% and below 5 wt%, respectively. The isothermal treatment is suggested to be controlled within a proper temperature range (1175–1250 °C) to decrease the crystallization kinetics. The oxide system's viscosity change is the limiting kinetic factor in the crystallization process, and it can be utilized to predict the system's crystallization tendency.

Insight into the TiO2 on transport behavior and heat transfer of the CaO–SiO2–FeO–MgO system at different basicities: Molecular dynamics simulation and thermodynamics

In order to promote the resource utilization of Ti-containing converter slag and reduce the loss of metallic Ti, it is necessary to clarify the relationship between the oxygen network structure and thermophysical properties of the slag. The present work uses classical molecular dynamics (CMD) simulation to study the effects of basicity (1.0–3.0) and TiO2 content (0%–10 %) on the local structural properties, viscosity, and thermal conductivity of the CaO–SiO2–FeO–MgO–TiO2 (CSFMT) system at 1873 K. The M − O (M = Ca, Si, Fe, Mg, and Ti) bond length calculated based on CMD is consistent with the experimental results, and the [SiO4] tetrahedron and [TiO6] octahedron are the basic structural units of the CSFMT system. The increase in basicity promotes the break of bridging oxygen (BO) Si–O–Si and the formation of non-bridging oxygen Si–O-M. The increase in TiO2 content promotes the formation of Ti–O–Si in the system. The basicity and TiO2 content affect the thermophysical properties of the CSFMT system by promoting and inhibiting the depolymerization of the oxygen network structure, respectively. The diffusion abilities of different atoms in the CSFMT system are in descending order of Fe > Mg > Ca > O > Si > Ti. The viscosity of the CSFMT system decreases with increasing basicity and increases with increasing TiO2 content. Increasing the proportion of BOs can weaken the anharmonicity in the polyhedral structural units and reduce phonon scattering. With increasing basicity and TiO2 content, the effective phonon mean free path decreases and increases, respectively, resulting in a decrease and an increase in the thermal conductivity of the CSFMT system. The changes in the microstructure properties of the CSFMT system can be reasonably explained by the changes in its thermodynamic properties such as enthalpy. It is worth noting that the basicity has a greater effect on the viscosity, while the TiO2 content has a more significant impact on the thermal conductivity of the CSFMT system.

Nanomechanical properties of ceramic materials from the SiO2–Al2O3-(Na2O)–K2O–MgO system with an addition of SrO

The ceramic materials studied in this paper consist of finely dispersed crystalline phases embedded in a glassy matrix, which is similar to glass-ceramic materials, porcelain, and VC products. The strength depends then not only on the properties of the individual crystalline phases but also on their interactions and the matrix. Differences in mechanical properties for materials with similar chemical compositions are most likely related to diverging microstructures. Crystal orientation, grain-size distribution and shape, the ratio of the glass matrix to the crystalline phase, and homogeneity control the flexural strength of glass-ceramic materials. The subject of the study is whiteware ceramic materials from the SiO2–Al2O3–Na2O–K2O–MgO–SrO system, fired similarly to the regime used for VC products. The effect of the type of alkali oxide and the share of SrO were tested. This paper presents the results of hot-stage microscopy, X-ray diffraction (XRD), scanning electron microscopy with a micro-analyzer (SEM-EDS) and biaxial flexural strength measurements. Additionally, nanoindentation technique was used to access local mechanical properties.

Phase equilibria of TiO2–SiO2–CaO–10%Al2O3-7.5%MgO at 1773 K and effects of MgO on the distribution of phase fields

The 1773 K phase diagram of the TiO2–SiO2–CaO-10 wt%Al2O3-7.5 wt%MgO system was constructed experimentally using the quenching method, focusing on the composition range of high TiO2 content. The obtained isothermal section contains four phase fields: the liquid phase field, the primary phase field of pseudo-brookite, the primary phase field of perovskite, and the liquid + perovskite + pseudo-brookite phase field. The pseudo-brookite particle precipitated in its primary phase field is more suitable for the efficient selective enrichment and separation of titanium resources. The increase of MgO from 5 % to 7.5 % in the TiO2–CaO–SiO2-10 wt%Al2O3–MgO system leads to a decrease of the liquidus temperature and an expansion of the liquid + pseudo-brookite + perovskite phase field. The increase of MgO promotes the enrichment of TiO2 into the pseudo-brookite phase and reduces the TiO2 level in the glass phase.

Growth of multiferroic γ-BaFe2O4 thin films by Pulsed Electron Deposition technique

Multiferroic materials have attracted significant attention due to their potential to revolutionize logic and memory devices by reducing energy consumption or increasing information density. Barium monoferrite (γ-BaFe2O4 or BaFeO) is a promising lead- and bismuth-free multiferroic material with a stuffed tridymite-like structure, exhibiting both ferroelectricity and antiferromagnetism at room temperature. BaFeO thin films with engineered grain orientation, composition, elastic strain, and magnetic interlayer couplings could open new avenues for novel devices. However, synthesizing the stoichiometric "1–2–4" phase in the BaO-Fe2O3 system remains a challenge. This study focuses on the deposition of pure and crystalline γ-BaFe2O4 thin films using the Pulsed Electron Deposition (PED) method. An analysis of the plasma plume revealed that two main mechanisms govern the dynamics of BaFeO deposition: a congruent ablation process occurring far from thermodynamic equilibrium and an incongruent low-energy evaporation process. The regions of the film with maximized ablative/evaporative ratios are free from the secondary Ba2Fe2O5 phase, suggesting that the thermal evaporative contribution is the primary factor responsible for the out-of-stoichiometry composition. The influence of the substrate type on the structural properties of BaFeO films was also evaluated. It was confirmed that (h00)-oriented BaFeO tends to grow on amorphous quartz and polycrystalline Pt-coated quartz in the 700–800°C temperature range. Conversely, the growth on SiO2/Si leads to the preferential grain orientation along the (0k0) and (0kl) directions by increasing the temperature. These findings demonstrate the potential of PED for producing high-quality γ-BaFe2O4 polycrystalline thin films. A fully heteroepitaxial (h00)-BaFeO/(111)-MgO system was even achieved by depositing on a single-crystal MgO substrate. This unprecedented result paves the way for utilizing such thin films in multiferroic applications, where phase purity, structural orientation, and defect-free structures can be exploited to enhance the magnetoelectric properties of the device.

Effect of Cr2O3 on properties of CaO–SiO2–FetO–MgO system and dissolution behavior of lime

Effect of Cr2O3 on properties of CaO–SiO2–FetO–MgO system and dissolution behavior of lime

Study on the Influence of Low Temperatures on the Physicochemical Properties of Xerogels, Powders and Ceramics Based on ZrO2

By using the method of coprecipitation of hydroxides in the ZrO2–CaO–MgO system, xerogels, powders, and ceramics based on them are obtained. The effect of low temperatures during the preparation of precursors on the phase composition and physicochemical properties of the materials is studied. It is shown that the use of precipitate’s cryotreatment makes it possible to reduce the open porosity and water absorption of the ceramics.

Alkali ionic state behavior in γ-Irradiated borate glasses for medical ultrasonic transducer fabrication

Lenses could be added to ultrasonic transducers used in medical applications to improve them. They may solve some limiting factors, like the acoustic impedance mismatch between the transducer and the tissues, the wave collimation difficulty, the wave scattering, etc. Novel ultrasonic transducers were developed that contained lenses made from new glass systems. Al2O3, MgO, and Li2O alkali-borate glass systems were prepared via the melt-quenching technique. Structural, electrical, and ultrasonic measurements were done with regard to the effect of gamma radiation. The XRD pattern showed the glassy, amorphous nature of the lenses. FTIR absorption spectra revealed the large stability of the main structural units of borate. Electron spin resonance (ESR) spectra clarified the low distortions caused by irradiation with g-values ∼ 2.025–2.026 and recognized the formation of oxygen hole centers (OHC) caused by breaking B–O connectivity. Al ions produced the most compact glass network, resulting in the highest ultrasonic velocity and wave passage. The characteristics of transducers with and without the lens were measured. The transducers with Al2O3 lenses demonstrated the lowest signal-to-noise ratio, the greatest beam diameter, and the highest sensitivity. The results ensured the effectiveness of the prepared glass as a lens in high-frequency ultrasonic transducers that are mainly used in medical applications.

Densely sintered carbide-silicon ceramics on a glass-crystal binder of cordierite composition

The high density of silicon carbide ceramics is a prerequisite for obtaining materials with high strength. A promising technology for preparation of such materials at relatively low temperatures is the use of glass crystal bonds. The paper presents the results of studies on ceramic materials based on silicon carbide using glass in the pseudoternary system MgO–Al2O3–SiO2 as a glass binder. The composition of the glass corresponds to a ternary eutectic with a temperature of 13650C, which is located at the boundary of the primary crystallization fields, where one of the phases is cordierite. It has been determined that it is necessary to mechanically activate the components of the raw material mixture to obtain densely sintered ceramics. In this case, the most rational ratio between SiC filler and glass binder, which provides the maximum mechanical compressive strength (up to 700 MPa), is 60:40. It has been established that the crystallization of the glass binder plays a decisive role in determining the formation temperature of dense silicon carbide materials. The compaction occurs due to the movement of dispersed silicon carbide particles in the softened glass melt under the influence of thermal vibrations. The subsequent process of fine-dispersed crystallization of the glass binder during cooling during firing provides strengthening of the structure of the synthesized materials. The proposed integrated approach to the intensification of the sintering process is promising for obtaining durable silicon carbide ceramics with low synthesis temperatures (up to 16000C). A sufficiently high strength of the experimental ceramics will ensure its competitiveness with respect to traditional materials, including those used as wear and impact resistant.

A Green Approach to Obtaining Glycerol Carbonate by Urea Glycerolysis Using Carbon-Supported Metal Oxide Catalysts.

The results of sustainable and selective synthesis of glycerol carbonate (GC) from urea and glycerol under ambient pressure using carbon-fiber-supported metal oxide catalysts are reported. Carbon fibers (CF) were prepared via a catalytic chemical vapor deposition method (CCVD) using Ni as a catalyst and liquefied petroleum gas (LPG) as a cheap carbon source. Supported metal oxide catalysts were obtained by an incipient wetness impregnation technique using Zn, Ba, Cr, and Mg nitrates. Finally, the samples were pyrolyzed and oxidized in an air flow. The obtained catalysts (10%MexOy/CFox) were tested in the reaction of urea glycerolysis at 140 °C for 6 h under atmospheric pressure, using an equimolar ratio of reagents and an inert gas flow for NH3 removal. Under the applied conditions, all of the prepared catalysts increased the glycerol conversion and glycerol carbonate yield compared to the blank test, and the best catalytic performance was shown by the CFox-supported ZnO and MgO systems. Screening of the reaction conditions was carried out by applying ZnO/CFox as a catalyst and considering the effect of reaction temperature, molar ratio of reagents, and the mode of the inert gas flow through the reactor on the catalytic process. Finally, a maximum yield of GC of about 40%, together with a selectivity to glycerol carbonate of ~100%, was obtained within 6 h of reaction at 140 °C using a glycerol-to-urea molar ratio of 1:1 while flowing Ar through the reaction mixture. Furthermore, a positive heterogeneous catalytic effect of the CFox support on the process was noticed.

Development of Numerical Analysis Model for New Magnesium Electrolysis Process Using COMSOL

Magnesium (Mg) has good physical properties including light weight, excellent specific strength and high stiffness, and Mg is used in many fields. But current production methods of Mg have disadvantages, such as the generation of sulfur oxide and chlorine gas. In this situation, The Korea Institute of Geoscience and Mineral Resources (KIGAM) developed a Molten Salt Electrolysis Using Liquid Metal Cathode (MSELMC) method to produce high-purity magnesium. The MSE-LMC method can obtain 99.998-99.999% highpurity magnesium by the electrolysis of MgO dissolved in (MgF2)-LiF molten salt at 1053-1083 K, and by vacuum distilling an alloy generated by reacting with a metallic liquid cathode at 1200-1300 K. This study developed a numerical analysis model using COMSOL Multiphysics electrodeposition module to optimize the design of the electrolysis process. The model temperature was 1053K and molten salt was 54MgF2-46LiF with a 0.6wt% MgO system. 10A constant current was applied at the anode. This model uses the Butler-Volmer equation and the Nernst equation for the electric reaction. The Stokes-Einstein equation and Nernst-Einstein relation were used to calculate the diffusivity and electric mobility of salts. Unlike the experiment, in this model chlorine gas was generated. However, this model satisfied Faraday’s law. Therefore we define a new parameter using electric flux and voltage to conduct a quantitative evaluation according to the electrode shape, and compared that parameter by the changing angle of the anode.

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.

Phase Equilibrium Relationship of CaO–Al2O3–Ce2O3–MgO System at 1573 K

Phase Equilibrium Relationship of CaO–Al2O3–Ce2O3–MgO System at 1573 K