CaO MgO Al2O3 Research Articles

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.

Strontium carbonate in glazes from the SiO2–Al2O3–CaO–MgO–Na2O–K2O system, sintering and surface properties

In this study, the influence of the addition of SrO on sintering and selected parameters of the surface of the glazes from the SiO2–Al2O3–CaO–MgO–Na2O–K2O system were examined. The novelty is introducing strontium oxide through strontium carbonate without using frits, which lowers the cost of the raw material input. To describe the sintering process the most important techniques were used, i.e. differential scanning calorimetry DSC, dilatometric measurements DL, hot-stage microscopy HSM, and viscosity as a function of temperature (VFT equation). Additionally, based on the data from DSC measurements, tests of the phase composition were carried out at temperatures at which thermal effects occurred. The crystal phase of Sr-feldspar is observed right after the SrCO3 decarbonization, but after the entire firing cycle, its quantity is below the XRD detection threshold. The glaze containing 7.5 mol% addition of SrO is completely amorphous. In order to examine surface physicochemical properties, laser confocal microscopy and spectrophotometry were used. An important conclusion is that the use of strontium carbonate does not cause a visual deterioration of the surface quality of the fired material.

Plasma-sprayed CeO2 overlay on YSZ thermal barrier coating: Solution for resisting molten CMAS infiltration

In high-temperature turbine engines, the components face severe interaction with airborne particles of CaO–MgO–Al2O3–SiO2 (CMAS). Generally, YSZ based TBCs are used in these applications to protect the components. Although, the YSZ coatings enhance the properties of the components, but were found to be vulnerable to the molten CMAS penetration. To tackle this serious issue, we report the performance of an atmospheric plasma sprayed CeO2 overlay on the YSZ coating (CYSZ) against CMAS and compared it with the established YSZ coatings. The hot corrosion test with CMAS was performed on the coatings at different temperatures viz. 1200 °C, 1300 °C and 1400 °C for 4 h. The evolution of microstructure after the CMAS infiltration and the depth of penetration for both YSZ and CYSZ coatings were studied in greater details. The molten CMAS reacts with the CeO2 overlay coat in the CYSZ coatings and forms a compound phase of CeAlSiO, which acts as a sealant and prevents the further infiltration of the melted CMAS towards YSZ coating. The thermal insulation of CYSZ coatings was also found to be improved by 45% as compared to the conventional YSZ coatings. This work suggests the application of CeO2 overlayed YSZ coating for CMAS infiltration resistance as well as a good thermal insulating coating.

Kinetic study on the reaction between Incoloy 825 alloy and low-fluoride slag for electroslag remelting

Abstract A kinetic model for the reactions between the low-fluoride slag CaF2–CaO–Al2O3–MgO–Li2O–TiO2 and Incoloy 825 alloy was proposed based on the two-film theory. The applicability of the model was verified to predict the variation of components in the slag–metal reaction process. The results show that the controlling step of the reaction 4[Al] + 3(TiO2) = 3[Ti] + 2(Al2O3) is the mass transfer of Al and Ti in the liquid alloy and the controlling step of the reactions 4[Al] + 3(SiO2) = 3[Si] + 2(Al2O3) and [Si] + (TiO2) = [Ti] + (SiO2) is the mass transfer of SiO2 in the molten slag. With increasing TiO2 content in the slag from 3.57% to 11.27%, the Al content in the alloy decreased whereas the Ti content increased gradually. The Si content continued to decrease during the slag–metal reaction. Soluble oxygen in the alloy reacts with Al, Ti, and Si, resulting in a decrease of the oxygen content in the alloy. The variations of TiO2 content were in good agreement with the calculated results by the kinetic model whereas the measured results of Al2O3 and SiO2 in the slag were lower than the calculated results, which is mainly due to the volatilization of fluoride.

Interfacial reactions between impurities and slag onset of Si purification by slag addition

The interfacial reactions between impurities (Al and Ti) and slag onset of Si purification by 51 mol% SiO2–34 mol% CaO–15 mol% MgO slag addition were studied to enhance impurity removal efficiency from Si. The Al distribution behavior at the Si/Slag interface was investigated; a short reaction time (10 s) resulted in the formation of successive SiO2–CaO–MgO–Al2O3 layers in the slag with a thickness of 10 µm; increasing the reaction time (60 s) resulted in the entire ternary slag being changed into SiO2–CaO–MgO–Al2O3 quaternary slag due to the diffusion of Al2O3. It was shown that the highest impurity removal rate of Al could be achieved at the onset of the slag refining process. Based on the Ti distribution at the Si/slag interface, the slag refinement with 51 mol% SiO2–34 mol% CaO–15 mol% MgO had no effect on Ti removal.

A comparative study of Ni catalysts supported on Al2O3, MgO–CaO–Al2O3 and La2O3–Al2O3 for the dry reforming of ethane

CO2 utilization through the activation of ethane, the second largest component of natural and shale gas, to produce syngas, has garnered significant attention in recent years. This work provides a comparative study of Ni catalysts supported on alumina, alumina modified with CaO and MgO, as well as alumina modified with La2O3 for the reaction of dry ethane reforming. The calcined, reduced and spent catalysts were characterized employing XRD, N2 physisorption, H2-TPR, CO2-TPD, TEM, XPS and TPO. The modification of the alumina support with alkaline earth oxides (MgO and CaO) and lanthanide oxides (La2O3), as promoters, is found to improve the dispersion of Ni, enhance the catalyst's basicity and metal-support interaction, as well as influence the nature of carbon deposition. The Ni catalyst supported on modified alumina with La2O3 exhibits a relatively stable syngas yield during 8 h of operation, while H2 and CO yields decrease substantially for Ni/Al2O3.

Effect of Tundish Flux on Compositional Changes in Non-metallic Inclusions in Stainless Steel Melts

The effect of the tundish flux on the evolution of non-metallic inclusions in Si-killed 304 (18%Cr-8%Ni) stainless steel has been investigated at 1773 K. The interfacial reaction between molten steel and the CaO–Al2O3–MgO flux causes the aluminum pick-up from the liquid slag into the steel melt, resulting in a decrease in the oxygen content in the steel. The aluminum originating from the slag modifies the pre-existing Mn-silicate inclusions into alumina-rich inclusions in the steel. Because the oxygen content in the steel decreases as it reacts with the CaO–Al2O3–MgO flux, the degree of supersaturation for alumina formation is too low to precipitate new-born alumina particles in the steel. By analyzing the population density function (PDF) results for inclusions, it can be observed that the growth of spinel-type inclusions occurs by the diffusion of aluminum and magnesium in the steel. On the other hand, the composition of the steel, as well as the evolution of inclusions, is negligibly changed when the CaO–SiO2–MgO flux is added to the molten steel. Furthermore, the computational simulation for predicting the evolution of inclusions in molten steel during a continuous casting tundish process was carried out based on a refractory-slag-metal-inclusion (ReSMI) multiphase reaction model.

Development of structural descriptors to predict dissolution rate of volcanic glasses: Molecular dynamic simulations

AbstractEstablishing the composition–structure–property relationships for amorphous materials is critical for many important natural and engineering processes, including the dissolution of highly complex volcanic glasses. In this investigation, we performed force field molecular dynamics (MD) simulations to generate detailed structural representations for 10 natural CaO–MgO–Al2O3–SiO2–TiO2–FeO–Fe2O3–Na2O–K2O glasses with compositions ranging from rhyolitic to basaltic. Based on the resulting atomic structural representations at 300 K, we have calculated the partial radial distribution functions, nearest interatomic distances and coordination number, which are consistent with the literature data on silicate‐based glasses. Based on these structural attributes and classical bond valence models, we have introduced a novel structural descriptor, that is, average metal–oxygen (M–O) bond strength parameter, which has captured the log dissolution rates of the 10 glasses at both acidic and basic conditions (based on literature data) with R2 values of ∼0.80–0.92 based on linear regression. This structural descriptor is seen to outperform several other structural descriptors also derived from MD simulation results, including the average metal oxide dissociation energy, the average self‐diffusion coefficient of all the atoms at 2000 K, and the energy barrier of self‐diffusion. Furthermore, we showed that the MD‐derived descriptors generally exhibit better predictive performance than the degree of depolymerization parameter commonly used to describe glass and mineral reactivity. The results suggest that the structural descriptors derived from MD simulations, especially the average M–O bond strength parameter, are promising structural descriptors for connecting composition with dissolution rates of highly complex natural glasses.

Wetting and interfacial tension of molten CaO–Al2O3–MgO–FeO slag and BN substrate

The interface characterization is one of the important properties of molten slag, which has a significant influence on the interface phenomenon of molten slag and the reaction between slag and metal. The wettability of molten CaO–Al2O3–MgO–FeO slag on BN substrate was investigated in a wide range of temperatures from 1673 to 1773K. The FeO content was varied from 0 to 15 wt%. The contact angle was measured by the sessile drop method, the surface tension and interfacial tension were calculated by Dorsey method and Young's equation, respectively. The effects of the FeO content and temperature on the contact angle, surface tension and interfacial tension were discussed. The results indicated that the initial contact angle decreases with the increase of temperature and FeO content. And the wetting reaction between BN substrate and the selected molten slag is non-reactive wetting. The surface tension of the selected molten slag is in the range of 586–616 mN/m, and the surface tension decrease with the increase of FeO content and temperature. The value of interfacial tension between the selected molten slag and BN substrate is close to that of the surface tension, and the interfacial tension is 211–375 mN/m. The trend that the interfacial tension changes with the FeO content and temperature was the same as the trend that surface tension changes with the FeO content and temperature. Changes in the interfacial tension were correlated with modifications in the slag structure when FeO is added. The interfacial tension linearly decreases with increasing the optical basicity, which can provide a global measure of the concentrations of free oxygen ion in molten slag.

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.

Optimizing Slag Content to Control Ds-Type Inclusions in 10B21 Cold Heading Steel

Ds-type inclusions during production are an important factor affecting the performance and quality of manufactured 10B21 steel. To minimize Ds-type inclusions in steel and improve the production qualification rate of steelmaking plants, a refining slag system optimization scheme was proposed based on the analysis of current inclusion evolution during the steelmaking process, and industrial tests were conducted to verify improvements resulting from application of the proposed scheme. The results showed that the composition of Ds inclusions in 10B21 steel are mainly CaO–Al2O3–MgO–CaS–TiN, which exists in the form of calcium–magnesium aluminate coated with titanium nitride and calcium sulfide. The main reason for the formation of Ds inclusions is the poor fluidity of the refining slag and its low capability to absorb inclusions. The poor coverage of the refining slag on the molten steel during refining can easily cause secondary oxidation of the molten steel. Thus, the formation and growth of Ds-type inclusions are aggravated after the calcium feeding line and soft blowing operation. Here, we propose to minimize Ds inclusions using our optimized refined slag system. The mass percentage of the optimized slag system is CaO: 55–60%, Al2O3: 20–35%, SiO2: 3–7%, MgO: 4–8%, (MnO + FeO) < 1%, and the basicity is controlled within the range of 7–11. We observed that our optimized refining slag system has a significantly improved ability to remove inclusions, particularly Ds inclusions, which improves the qualification rate of 10B21 steel.

Raw glass-ceramics glazes from SiO2–Al2O3–CaO–MgO–Na2O–K2O system modified by ZrO2 addition – Changes of structure, microstructure and surface properties

In this paper, raw glazes from the SiO2–Al2O3–CaO–MgO–K2O–Na2O system were examined. Zirconium oxide, in five different amounts – 1.5, 3, 6, 12 and 24 wt%, was added to the chosen system and heat treated at 1230 °C, where they were kept for an hour. The addition of zirconium oxide, especially in greater amounts, caused the crystalline phase of zirconium silicate and intact ZrO2 grains to appear. The amounts of these crystalline phases indicate that zirconium cations are present in the amorphous phase. Analysis of structural measurements showed that zirconium ions (Zr4+) have a depolymerizing effect on the glassy matrix of the glazes; however, it does not change subnets of an aluminum-silicon subnetwork. This is a new perspective on the matter, because it confirms that the addition of zirconium oxide causes those ions to be present not only in crystalline phases, but also some Zr4+ cations are located in the aluminosilicate subnetwork (Si–O–Si(Al)), in interstitial spaces, and it interacts only with silicon-oxygen bonds. Measurements of the color in the CIE L*a*b* system of the obtained glazes confirmed that the addition of zirconium oxide results in glaze with significantly higher whiteness (L* parameter increases) and a more monochromatic color (a* and b* parameters tend toward zero). The results of the surface smoothness were also presented, which clearly confirm that the higher content of zirconium crystalline phases results in obtaining a surface with higher roughness.

Conditional generative adversarial network driven approach for direct prediction of thermal stress based on two-phase material SEM images

A conditional generative adversarial network (cGAN)-driven approach for the direct prediction of thermal stress is proposed. Synthetic two-phase structure images of ceramic top coat (TC) with CaO–MgO–Al2O3–SiO2 (CMAS) inclusions are established, and the TC matrix and CMAS inclusions are semantically segmented by grayscale. The thermal stresses of the two-phase structure are calculated using image-restoration finite element models (FEMs) under the isothermal process. The training database is established based on a small-scale original dataset of integral structures and their stresses. Each integral TC–CMAS structure and its corresponding stress distribution are partitioned into many local images, using which the cGAN model is trained. The model stresses are generated by the trained cGAN directly from the structure images. The deviations between the predicted stress and the FEM stress are small in most areas of the images. In terms of computing time, the proposed approach has higher stress evaluation efficiency than does the FEM.

Evolution of Inclusions in Magnesium–Calcium-Treated Liquid Iron

With the development of clean steel technology, the control of non-metallic inclusions in steel is of increasing importance. Magnesium–calcium treatment can effectively balance the castability of molten steel and the control on inclusion size, which is an inclusion modification approach with application prospect. In view of this, how three addition methods (i.e., adding Mg before Ca, adding Mg after Ca, and adding Mg together with Ca) influenced the modification effect of inclusions in liquid iron was experimentally studied, and how these inclusions evolved with time was discussed in this paper. The results demonstrated that despite the sharp difference in their inclusion evolution, composite inclusions with a magnesium aluminate spinel (MAS) core and an outer CaO–Al2O3–MgO layer were formed by all the three addition methods, with the average inclusion size of 1–2 μm. Furthermore, thermodynamic calculation was adopted to reveal the transformation relationship between MAS and calcium aluminate in each of the three addition methods, and clarify the formation and disappearance mechanisms of the intermediate product CaS in the process of Mg–Ca treatment. The thermodynamic calculation results agreed well with the experiment data.

Glass‐ceramics in the CaO–MgO–Al2O3–SiO2 system as potential dental restorative materials

AbstractThis paper reports on development of novel alumina‐containing glass‐ceramics (GCs) with a high content of Al2O3 (12.5 wt.%) in the CaO–MgO–Al2O3–SiO2 system aimed for dental restorations. The thermal properties of the parent glasses, the microstructure and the mechanical properties of the produced sintered and crystallized GCs along with bio‐inertia performance were experimentally studied. Dense, white, and bio‐inert GCs, comprised of melilite, either as a single‐phase or with diopside, were produced. The values of flexural strength ranged between 120 and 171 MPa, the modulus of elasticity varied between 28 and 42 GPa, while the values of the hardness and the fracture toughness (measured by the indentation–Niihara equation) ranged from 6.3 to 7.0 GPa, and from 2.6 to 2.8 MPa m0.5, respectively. The mechanical properties of the produced GCs, after being meticulously compared with the mechanical properties of GCs of various compositions reported in literature, including commercial ones, are a good match to the properties of dental hard tissues, and satisfy the requirements of the ISO 6872 “Dentistry‐Ceramic Materials”.

Formation Mechanism of Large-size CaO–Al<sub>2</sub>O<sub>3</sub>–MgO–SiO<sub>2</sub> Inclusions in High Carbon Chromium Bearing Steel

Industrial experiments and thermodynamic analyses were carried out to investigate the formation mechanism of large-size (>30 µm) CaO–Al2O3–MgO–SiO2 (CAMS) inclusions in high carbon chromium bearing steel. It was found that the large-size CAMS inclusions existed during the whole refining process, most of which compositions were located in the liquid region. The average content of SiO2 in CAMS inclusions decreased from 27.5 mass% at argon-blowing station to 3.0 mass% in the hot-rolled bars. The results calculated by Factsage 7.3 indicated that the CAMS inclusions were originated from slag entrapment. During BOF tapping, the low basicity slag with 60 mass% SiO2 was entrapped into steel and combined with the deoxidation product Al2O3, forming a large amount of liquid CAMS inclusions. During LF refining process, [Al], [Ca] and [Mg] in molten steel were affected by the activities of corresponding slag components. The reaction between these three elements and SiO2 in CAMS inclusions originating from slag lead to the decrease of SiO2 in the inclusions. Due to the low interfacial energy between liquid CAMS inclusions and steel, a few large-size inclusions may be inherited to hot-rolled bars. In light of this, several optimization steps were conducted during BOF tapping and argon-blowing station. After the optimization, large-size CAMS originated form BOF tapping were effectively removed.

Influences of additives on crystal multiformity and composition in a CaO–Al2O3–MgO–SiO2–based glass–ceramics

Influences of additives on crystal multiformity and composition in a CaO–Al2O3–MgO–SiO2–based glass–ceramics

Optimization of Properties for Alumina-Spinel Refractory Castables by CMA (CaO-MgO-Al2O3) Aggregates.

Aiming at optimizing properties of alumina-spinel refractory castables, coarse corundum particles were replaced partially with the particles of a novel porous multi-component CMA (CaO-MgO-Al2O3) aggregate in the same size. Properties including the bulk density, apparent porosity, strength, slag corrosion resistance, thermal shock resistance and thermal fatigue resistance of alumina-spinel refractory castables containing CMA aggregates were evaluated contrastively. The results demonstrated that the incorporation of CMA aggregates can significantly improve thermal shock resistance and thermal fatigue resistance of castables, although companying with slight decrease in the bulk density and strength. Moreover, slag penetration resistance of castables can also be enhanced by CMA aggregates with appropriate particle size. The influence of CMA aggregates on properties of alumina-spinel refractory castables depended strongly on their particle size.

Effects of Fe2O3 on crystallisation and properties of R2O–CaO–MgO–Al2O3–SiO2–Fe2O3 glass ceramics

ABSTRACT The R2O–CaO–MgO–Al2O3–SiO2–Fe2O3 glass ceramics was prepared using granite wastes and Fe2O3. The effect of Fe2O3 on crystallisation and properties of glass ceramics was studied. Results show that the crystalline phases were Fe2TiO5 and K(NaCa)Mg5Si8O22F2 when the content of Fe2O3 was low. The main crystalline phase was Fe1.5Ti0.5O3 when the content of Fe2O3 was high. With the increase of Fe2O3, the crystal size of K(NaCa)Mg5Si8O22F2 reduced and the atomic ratio of Si to Mg increased. The colour of sample varied from greyish green to black with different additions of Fe2O3. The flexural strength with a maxim (101.02 MPa) when the content of Fe2O3 was 4.7 mol-%. Given the low cost of granite wastes and Fe2O3, this new type of black glass ceramics is expected to meet the increasing demand from the market of building decoration due to its excellent properties.