MgO Al2O3 Research Articles

Effect of TiO2 on crystallization and mechanical properties of MgO–Al2O3–SiO2 glasses containing P2O5

MgO–Al2O3–SiO2 glass-ceramics have been widely used in military, industrial, and construction applications. The nucleating agent is one of the most important factors in the production of glass-ceramics as it can control the crystallization temperature or the grain size. In this study, we investigated the effect of replacing P2O5 with different amounts of TiO2 on the crystallization, structure, and mechanical properties of an MgO–Al2O3–SiO2 system. The crystallization and microstructure were investigated by differential scanning calorimetry, Raman spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The mechanical properties were investigated by measuring the Vickers hardness, Young's modulus, and fracture toughness. The results showed that adding TiO2 favored the precipitation of fine grains and significantly increased the Vickers hardness, Young's modulus, and fracture toughness of the glasses. Introducing an appropriate amount of TiO2 can make a glass structure more compact, promote crystallization, and improve the mechanical properties of MgO–Al2O3–SiO2 glass-ceramics.

Nanostructured Gd2Zr2O7: a promising thermal barrier coating with high resistance to CaO–MgO–Al2O3–SiO2 corrosion

Nanostructured Gd2Zr2O7: a promising thermal barrier coating with high resistance to CaO–MgO–Al2O3–SiO2 corrosion

Unpacking Intermineral Synergies and Reactions During Dust Deposition in an Impingement Coolant Jet

Abstract This paper seeks to unpack synergies that exist between minerals during deposition of the heterogeneous AFRL02 mixture in gas turbine engines and demonstrate that the contributions of each mineral cannot be considered independently. In each experiment, one gram of mineral dust (0–10 µm particle diameter distribution) was injected into an 894 K, 57 m/s coolant flow impinging normally on a Hastelloy X plate with a surface temperature of 1033 K, 1144 K, or 1255 K. Capture efficiency measurements, deposit morphology analyses, and X-ray diffraction results are reported. Besides AFRL02, single mineral dusts, dual mineral dusts, and AFRL02-like dust blends lacking in one mineral were tested. The results of the experiments elucidate that the deposition behavior of single minerals indeed cannot explain the composite deposition of heterogeneous mixtures. For example, gypsum had the highest capture efficiency of any single mineral in ARFL02, and yet removing gypsum from AFRL02 counterintuitively raised the capture efficiency of that blend when compared to AFRL02. Quartz was found to erode albite deposits but stick to and build upon dolomite and halite deposits, even though quartz did not deposit significantly as a single mineral. Quartz also chemically reacted with gypsum and dolomite to form wollastonite and diopside, respectively. Finally, we found that the capture efficiency of each blend increased with plate temperature, but not according to the same trend. Results are interpreted through the lens of CaO–MgO–Al2O3–SiO2 eutectic chemistry, but the chemical pathways by which these eutectics come into existence is found to be of equal importance.

Sol-Gel Synthesis of MgO–Al2O3–ZrO2–SiO2 Coatings on Quartz Ceramics

Sol-Gel Synthesis of MgO–Al2O3–ZrO2–SiO2 Coatings on Quartz Ceramics

Effect of Cr2O3 on Crystallization of Diopside Glass–Ceramics

CaO–MgO–Al2O3–SiO2–Cr2O3 diopside glass–ceramics were prepared from blast furnace slag, low-carbon ferrochromium alloy slag, and quartz sand by the melting method. The prepared glass–ceramics were characterized by differential thermal analysis (DTA), X-ray diffraction (XRD),scanning electron microscopy (SEM), energy-dispersive spectrometer (EDS), and X-ray photoelectron spectroscopy (XPS). The effect of Cr2O3, a nucleating agent, in the crystallization process of diopside glass–ceramics was studied. The results show that chromium is present in glass–ceramics as Cr3+ and Cr6+, and Cr3+ accounts for more than 80% of the chromium contents. When the mass percentage of Cr2O3 in glass–ceramics is less than 1.60%, a small amount of diopside phase is precipitated during heat treatment, and Cr3+ is dispersed in the diopside phase. When the mass percentage of Cr2O3 reaches or exceeds 1.60%, Cr3+ preferentially forms the magnesia chrome spinel phase, which further induces the in situ growth of diopside. The leaching concentration of chromium meets the Chinese national standard, indicating that diopside glass–ceramics can effectively solidify the heavy metal chromium, and this fact makes the application of glass–ceramics feasible.

Iron isotopic variations in basalts from oceanic crust due to low-temperature seawater alteration

Iron (Fe) isotopic compositions of seafloor basalts can provide important insights into high-temperature processes in the upper mantle. However, low-temperature seawater alteration (i.e., seafloor weathering) may significantly affect the primary Fe isotopic compositions. In this paper, we report whole-rock Fe isotopes, major and trace elements, and SrNd isotopes, along with in situ elemental maps for slightly altered Site U1434 basalts collected on IODP Expedition 349 from the South China Sea. We use these data to investigate the influence of low-temperature seawater alteration on the Fe isotopic compositions of seafloor basalts. The basalts have δ57Fe values of +0.12‰ to +0.27‰. No correlation between δ57Fe values versus Sr or Nd isotopes that are source-sensitive and no correlation between δ57Fe values and La/Yb ratios that are melting-sensitive indicate the δ57Fe values have not been affected by mantle source heterogeneity and partial melting. The negative correlations of MgO versus CaO and Al2O3 contents suggest limited clinopyroxene and plagioclase fractionation during magmatic evolution. Possible influence of olivine fractionation on the Fe isotopic variations can further be ruled out by a positive correlation between MgO and SiO2 contents and a weak negative correlation between δ57Fe values and SiO2 contents because olivine fractionation can form basalts with increasing SiO2 and δ57Fe with decreasing MgO. The strong correlations between δ57Fe values and MgO, Al2O3, and TiO2 contents indicate the Fe isotopic variations were caused by low-temperature seawater alteration. This is also evident from in situ elemental mapping of representative Site U1434 basalt sample, which shows that low-temperature alteration was characterized by decreases in MgO and SiO2 contents, and increases in Al2O3 and TiO2 contents. We propose a two-stage alteration model to explain the Fe isotopic variations of the Site U1434 basalts. The alteration appeared to occur under oxidizing conditions: Fe2+-rich external fluid likely derived from the progressive alteration inside the oceanic crust was oxidized at the surface of the oceanic crust, which caused the alteration, Fe isotopic fractionation, and increase in δ57Fe values of the seafloor basalts. This study highlights how low-temperature seawater alteration under oxidizing conditions can modify the Fe isotopic compositions of slightly altered oceanic crust, with critical implications for understanding the Fe cycle in the oceans.

Mixed alkaline earth effect on the structure and elastic modulus of CaO–MgO–Al2O3–SiO2 glasses: A molecular dynamics simulation

The influence of mixed alkaline earth effect on the atomic structure and elastic modulus of the CaO–MgO–Al2O3–SiO2 glasses were studied by molecular dynamics simulation. The elastic modulus values obtained from the simulation of uniaxial tension and stiffness tensor methods showed the same trend with the change of composition, while the simulated results of the former were closer to the measured data. The variation trend of Qn species obtained by the simulation and Raman spectroscopy was consistent. Ca and Mg cations were more inclined to form non-bridging oxygen when the Ca/Mg ratio exceeded 1, which damaged the tetrahedral connection and further reduced the degree of network polymerization. The ratio of non-bridging oxygen to tetrahedrally coordinated cations (NBO/T) used to characterize the degree of polymerization was found to have a linear relationship with the elastic modulus. In addition, the local cluster of modifier atoms was beneficial to increase the elastic modulus values.

Structural, morphological and mechanical insights from La2O3 doped machinable silicate glass ceramics for biomedical applications

Machinable glass ceramics attracted much attention in recent years due to its improved mechanical and therapeutic performances. La2O3 doped SiO2–Al2O3–MgO–K2CO3–CaO–MgF2 glass and glass ceramics (GCs) were synthesized using melt-quenching and solid-state reaction methods. Herein, doping impact of La2O3 on physical, optical, morphological, mechanical, and biological properties were studied. XRD reveals the major phase formation of monoclinic cuspidine, Ca4F2Si2O7 with some minor phases. 3 mol% of La2O3 GCs shows a new major crystalline phase of akermanite, Ca2MgSi2O7. FTIR study shows that La2O3 acts as a network modifier and non-bridging oxygens presented in the glassy structure tends to be increased. Optical band gap and particle size were lies in the range of 4.18–4.10 eV, and 50–57 nm, respectively. Rod-like morphology and their elemental distributions were confirmed via SEM and EDS techniques. TEM studies suggested that the lattice planes agreed with the XRD results and confirmed a major phase formation of Ca2MgSi2O7. Enhanced mechanical properties were observed using Universal Testing Machine. The cell viability and cell cytotoxicity, were performed by MTT and ALP assay.

Evolution of inclusion populations in Al-killed steel during the steelmaking process

The increasing demand for higher steel inclusion cleanliness has motivated control over the formation and evolution of inclusions during the production process. To generate knowledge of the formation and evolution of inclusions during the production of Al-killed steel slabs, the evolution of the chemical composition and size distribution of inclusions throughout the process, including ladle furnace (LF) treatment and continuous casting (CC), was studied. Liquid steel sampling was conducted throughout the process. The chemical composition was measured using the EDS technique, and the size distribution analysis was performed with the population density function (PDF) approach. The upper tail of the size distributions was analyzed by generalized extreme value (GEV) theory. Evolution of the chemical composition of inclusions involved the following path: solid Al2O3 solid Al2O3-MgO partly liquid Al2O3–MgO–CaO fully liquid Al2O3–MgO–CaO. The PDF analysis accounted for the evolution of the size distribution, which was supposed to be driven by the balance of the coalescence/growth and collision/breakage of inclusions and their removal. Finally, the GEV approach allowed us to describe the evolution of large inclusions and compare inclusion populations in terms of survival probability.

Thermodynamic Modeling of the Carbothermic Reduction of Manganese from the MnO–Fe2O3–CaO–SiO2–MgO–Al2O3 Oxide Melt

Thermodynamic Modeling of the Carbothermic Reduction of Manganese from the MnO–Fe2O3–CaO–SiO2–MgO–Al2O3 Oxide Melt

Synthesis of Solid Acid Catalysts of MgO–Al2O3 Mixed Oxide Containing Oxyanions by Thermal Decomposition of Anion-Exchanged Hydrotalcites

Solid acid catalysts of MgO–Al2O3 mixed oxides containing B4O72−, HPO42−, Mo7O246−, MoO42−, WO42−, and SO42− were synthesized by anion exchange with Cl− located in the space between anionic layers of hydrotalcite, followed by heat treatment at 773 K. The distance between the hydroxide layers was expanded by the intercalation of oxyanions larger than Cl−. The exchange of oxyanions in the interlayer space was confirmed by IR spectroscopy. Acid sites were generated on the obtained mixed oxides of MgO–Al2O3 by the electron withdrawing effect of the oxyanions. The acid catalyzed ethanol dehydration into ethylene and diethyl ether took place on the obtained catalysts. The effect of exchanged anions in the generation of acid sites was the largest in SO42−.

Effect of metastable phase on the crystallization and mechanical properties of MgO-Al2O3-SiO2 glass-ceramics without nucleating agents

Glass-ceramics without nucleating agents usually undergo surface crystallization, which deteriorates the overall performance of the products. In this paper, we evaluated the effects of the metastable MgAl2Si3O10 crystalline phase on the crystallization behavior of a MgO–Al2O3–SiO2 (MAS) glass without nucleating agents and mechanical properties of the glass-ceramics obtained. The results demonstrated that the precipitation of metastable MgAl2Si3O10 crystallites promotes the crystallization mechanism transformed from surface crystallization into volume crystallization with two-dimensional crystal growth. Furthermore, the grain size of MgAl2Si3O10 near the surface of the prepared glass-ceramics was larger than that of MgAl2Si3O10 inside, which helps to generate compressive stress and improves its mechanical properties. The glass-ceramics containing metastable MgAl2Si3O10 phase exhibited an enhanced hardness in the range of 7.6 GPa–9.5 GPa for indentation loads ranging from 2.94 N to 98 N, and indentation size effect behavior was observed in Vickers hardness tests of both MAS glass and glass-ceramics. The load-independent hardness values for MAS glass and glass-ceramics were reliably evaluated by the modified proportional specimen resistance (MPSR) model of 7.1 GPa and 7.6 GPa, respectively, with a high correlation coefficient of more than 0.9999. This work reveals the unexploited potential of the metastable phase in improving the crystallization ability and mechanical properties of glass-ceramics.

Thermodynamic analysis of the reactions of diopside phase formation during synthesis of ceramic pigments from granulated blast-furnace slag

The purpose of this study is to perform the thermodynamic analysis of the reactions of diopside phase (CaOMgO2SiO2) formation during the synthesis of ceramic pigments based on the granulated blast-furnace slag. Thermodynamic analysis is of great practical importance in studying solid-phase interactions, which are involved in the pigment technology. At the same time, the scope of energy-intensive experimental studies of ceramic pigments is significantly reduced. When performing thermodynamic calculations, we assessed the fundamental possibility and direction of occurrence of chemical reactions by determining the changes in the Gibbs energy. In order to verify the calculation data, the change in the mineralogy of the diopside compositions was evaluated with the use of X-ray phase analysis at different firing temperatures. It was found that the diopside phase in the CaO–MgO–Al2O3–SiO2 system is formed in several stages. The merwinite (3CaOMgO2SiO2) mineral is formed first. Further, merwinite, along with blast-furnace slag minerals, is involved in the diopside formation. The formation of diopside is completed at the temperature of 12000С. The findings of the study will provide a reasonable approach to the choice of compositions of ceramic pigments using complex raw materials, including the wastes of various industries.

Xenoliths of High-Alumina Pyroxenites in the Basalts of the Sigurd Volcano, Spitsbergen Island (Svalbard Archipelago), as Indicators of the Paleozoic Geodynamics of the Regional Lithosphere

Abstract—Xenoliths of high-alumina pyroxenites in the Quaternary basalts of the Sigurd Volcano of West Spitsbergen are spinel and spinel–garnet clinopyroxenites, spinel–garnet websterites, and websterites. The granoblastic texture with relics of subhedral magmatic texture, the change of mineral assemblages, and the signs of partial melting in the xenoliths reflect their multistage formation. The goal of our study was to determine the sequence and thermodynamic conditions of the change of mineral assemblages and to establish their age by Re–Os, U–Pb, Sm–Nd, and Rb–Sr isotope dating. It has been established that the primary assemblage in the pyroxenites, which included high-alumina Opx, Cpx, and Spl, was transformed in several stages: (1) Spl→Grt replacement with the formation of garnet-containing websterites and clinopyroxenites, (2) development of kelyphitic Opx–Spl rims over Grt grains, (3) formation of Amph, (4) exsolution with the formation of Cpx and Opx, and (5) partial melting. Comparison of the obtained results with published data shows that the primary assemblage is similar in Al2O3/MgO ratio to Opx + Cpx ± Spl cumulates resulted from the crystallization of basaltic melts at 1.2 GPa and the degree of crystallization of ~15%, i.e., in the lower crust (at 2.0 GPa, Grt and Cpx crystallize from the solution). The equilibrium parameters of the Grt–Opx assemblage in the pyroxenites are 1060–1310 ºC and 2.2–3.3 GPa; in the P–T diagram, their points are localized below the Spl→Grt phase transition curve, in the system CaO–MgO–Al2O3–SiO2, thus corresponding to the model continental geotherm with a surface heat flow density of 60 mV/m2 and somewhat higher. This indicates the Spl→Grt replacement and the formation of garnet-containing pyroxenites in the shallow-depth upper mantle. The formation of kelyphitic Opx–Spl rims over the Grt grains indicates a subsequent temperature and pressure decrease to values above the Grt→Spl phase transition curve. This is confirmed by the presence of exsolution structures in pyroxene, which formed when the temperature decreased by 100–150 ºC. The Re and Os isotope composition in the bulk samples of Spl–Grt websterites that did not undergo partial melting corresponds to an age of 457.0 ± 3.5 Ma, which reflects the time of transformation of the primary Cpx–Opx–Spl assemblage into a garnet-including one. A similar value (488.6 ± 5.9 Ma) was obtained by U–Pb dating of zircon from Spl–Grt websterite, also without signs of melting. Zircon crystals from Spl–Grt clinopyroxenite with clear signs of partial melting have typomorphic features of autochthonous magmatic zircons. They form a single age cluster of 310.7 ± 3.3 Ma, which marks the age of melt crystallization in the pyroxenites. Thus, Spl pyroxenites are, most likely, Opx + Cpx ± Spl cumulates, products of crystallization of basaltic melts in the lower crust. The subsequent Spl→Grt replacement and the formation of garnet-containing websterites and clinopyroxenites in the shallow-depth upper mantle can be regarded as an indicator of the delamination of the continental crust into the mantle, and the Re–Os isochron date of 457.0 ± 3.5 Ma is the most likely upper age bound of the crust delamination into the mantle. The subsequent uplifting of the Spitsbergen lithosphere, which was expressed as the formation of kelyphitic Opx–Spl rims over garnet, exsolution in pyroxene, and partial melting, was not far in time from the delamination stage and lasted ≤ 300 Ma.

Optimizing RH refining process to maximize cleanliness of low-carbon low-silicon Al killed steel

ABSTRACT In the LD–RH–CC process for producing low-carbon low-silicon steel, the cleanliness level of the slab was studied by optimizing the compositions of the refining slag and oxygen blowing flow in trial heats through judicious control. In order to realize RH without oxygen blowing, the oxygen content of molten steel should reach 475–525 ppm before RH degassing to guarantee that the free oxygen is in the range of 100–150 ppm after the carbon–oxygen reaction. When the slag compositions were controlled to CaO = 41–50 wt-%, Al2O3 = 29–36 wt-%, SiO2 = 5–11 wt-% and MgO = 6–10 wt-% in the RH treatment without feeding calcium, the total oxygen content in the plate was 18 ppm, and the nitrogen content decreased to 17 ppm in the improved process. The micro-inclusions in the slab mainly consisted of MgO–Al2O3–(MnS) and Al2O3–(MnS), and the particle size was mainly concentrated below 3 μm. The average total amount of large electrolytic inclusions in the slab was 1.384 mg kg steel−1. The large inclusions were mainly SiO2, Al2O3, SiO2–Al2O3–(K2O), and MgO–Al2O3.

Post-mortem analysis of MgO–Al2O3–C bricks containing bauxite used in steel ladle walls

A serious problem with integrated masonry linings ladle was that the ladle wall bricks were difficult to be partially replaced. Thus, the service life of the ladle was determined by the properties of ladle wall bricks. In this study, the new generation of MgO–Al2O3–C bricks with bauxite aggregates was tested in a ladle lining of an integrated steel ladle for 103 cycles, and the corroded microstructure of the used brick was investigated. A multilayered structure of bauxite aggregates could be observed in the used brick, which inhibited the slag penetration along the boundary of the magnesia aggregates and reduced the degree of the aggregates fall off from the used bricks. Besides, during the process of slag penetration, bauxite aggregates could melt into the slag, which increased the viscosity of the slag and weakened the penetration ability of the slag. The MgO–Al2O3–C bricks with bauxite addition could improve the service life of the ladle to a certain extent.

Effect of Cerium and Magnesium Addition on Evolution and Particle Size of Inclusions in Al-killed Molten Steel

To investigate the effect of Ce and Mg addition on the evolution of inclusions in Al-killed molten steel, both thermodynamic calculations and laboratory-scale experiments were carried out in the present work. The samples taken at different time after various addition amounts and order of Ce and Mg were analyzed by scanning electron microscopy and energy dispersive spectroscopy. The results show that Al2O3 was firstly modified to MgAl2O4 and then the transformation from MgAl2O4 to CeAlO3 with the addition order of Al → Mg → Ce. Under the addition order of first Ce followed by Mg, CeAlO3 was eventually modified to MgAl2O4 in the case of low Mg contents, and was modified to MgO with high Mg contents. The thermodynamic conditions were performed to discuss the mechanism of inclusions formation and transformation. More importantly, under the condition of Ce addition followed by Mg addition, due to the transformation from large-sized RE-inclusions to disperse MgO-containing ones, the average sizes of inclusions reduced from 3.12 µm and 3.28 µm to 1.99 µm and 1.83 µm, respectively. This evolution behavior of inclusions was firstly observed in-situ by a novel experiment, in which the large-sized CeAlO3 clusters were disaggregated to MgO–Al2O3 particles with smaller sizes. The control strategy of inclusions proposed in this study is expected to improve the casting process and the product quality of Al-killed steel containing rare earth element.

Effect of CaO/SiO2 mass ratio and Li2O on structure and phase precipitation behaviors of CaO–SiO2–MgO–Al2O3 oxide inclusions

The crystallization behaviors and structure of CaO-SiO2-MgO-Al2O3 melts representing the oxide inclusions in Si-Mn-killed steel were investigated. Raman spectroscopy analysis indicates that the degree of polymerization of oxide melts is lowered with increasing the CaO/SiO2 mass ratios or Li2O contents. Lowering the CaO/SiO2 mass ratios decreases the crystallization temperatures and suppresses crystallization of the oxide melts. Two crystalline phases precipitate (4CaO·MgO·Al2O3·3SiO2 and 3CaO·MgO·2SiO2 in sequence) during continuous cooling of oxide melts with the CaO/SiO2 mass ratios of 1.55 and 1.15. Only one crystalline phase (4CaO·MgO·Al2O3·3SiO2) was precipitated during the continuous cooling of the oxide melts with CaO/SiO2 mass ratio of 0.77. The crystallization ability of oxide melts was retarded with increasing the Li2O content. The crystalline phases precipitated sequentially are blocky 4CaO·MgO·Al2O3·3SiO2 and faceted 3CaO·MgO·2SiO2 irrespective of the Li2O content of oxide melts.

Inhibited Cr(VI) formation in Cr2O3-containing refractory castable using reactive MgO as hydraulic binder

Reactive MgO was used in the first time as alternative hydraulic binder of calcium aluminate cement (CAC) to prepare Cr2O3-bearing refractory castable. The formation of Cr(VI), and physical and mechanical properties of MgO-bonded refractory castables after heat-treating were investigated. Microstructural characterization and phase composition analyses on the heat-treated MgO-bonded refractory castable matrices resulted in a comprehensive understanding of the mechanism for the inhibition of Cr(VI), and of the strength development during firing. The results indicate that compared with CAC, Cr(VI) levels were 6.7–28.1 times lower using reactive MgO after firing at 700–1300 °C. The in situ Mg(Cr,Al)2O4 spinel formed from the preferential interactions among MgO and Cr2O3 and Al2O3 would be the main reason leading to the inhibited Cr(VI) formation and strength development during firing.

Some features of the surface modification of MgO–Al2O3–TiO2–SiO2 glass and glass ceramics by Ag diffusion

Diffusion of Ag species into the surface layers of the MgO–Al 2 O 3 –TiO 2 –SiO 2 glass stimulates the crystallization processes therein during subsequent thermal treatment. It was found that the silver doping significantly increases the microhardness of glass and glass ceramics. The effect of the Ag diffusion and the subsequent high-temperature treatment (T > T g ) on the structure and luminescence properties of the MgO–Al 2 O 3 –TiO 2 –SiO 2 glass was studied. The thermal evolution, structure and properties of the glass and glass ceramics were investigated by the DSC method, XRD analysis and luminescence spectroscopy. It was found that the Ag diffusion into the surface layers leads to the formation of numerous different luminescent molecular Ag n clusters. The MgO–Al 2 O 3 –TiO 2 –SiO 2 glass and glass ceramics subjected to the Ag diffusion can operate as effective down-converters of the radiation demonstrating the effective transformation of UV and blue light into the radiation of red and NIR spectral range.