CaO Al2O3 SiO2 Research Articles

Effect of MgO–CaO–Al2O3–SiO2 glass additive on dielectric properties of Ba0.95Sr0.05Zr0.2Ti0.8O3 ceramics

MgO–CaO–Al2O3–SiO2 glass-added Ba0.95Sr0.05Zr0.2Ti0.8O3 ceramics were prepared via a wet chemical route. The effect of the glass additive on the structure and dielectric properties of the ceramics was studied. The glass additive was confirmed to be effective in promoting sintering and refining microstructure. The addition of the glass additive led to a crossover from a diffusion phase transition (DPT) to relaxor behavior. The dielectric constants of the glass-added specimens under bias electric field deviated from the behavior as predicted by the phenomenological Johnson model in a manner different from Ba0.95Sr0.05Zr0.2Ti0.8O3 specimen. Furthermore, adding the glass additive resulted in a decline of energy storage capability and an enhancement of energy efficiency. These dielectric phenomena were qualitatively interpreted in relation to the polarization response of polar nano-regions (PNRs) embedded in the specimens. By balancing the energy storage capability and energy efficiency of the specimens, the preferred content of the glass additive was determined to be 5wt.%. At an electric field of 140kV/cm, the specimen with 5wt.% glass additive showed an energy density of 0.42J/cm3 and an energy efficiency of 82.8%.

Evaluation of Sulfur Addition to the High Basicity Slag on the Sulfur, Aluminum, and Cleanliness of High Sulfur Al‐Killed Molten Steel

AbstractIn the present work, the influence of sulfur addition to the high basicity slag on the Al‐killed molten steel with high sulfur content was investigated by using a vacuum induction furnace at 1873 K in MgO crucibles. CaO–SiO2–Al2O3–MgO–CaS slags were used to study the effect of high basicity slags with different CaS contents on sulfur loss, aluminum loss, and total oxygen content in the molten steel. It is shown that the sulfur content in the molten steel decreased with the time, and the addition of CaS into the slag can reduce the sulfur loss in the molten steel. Moreover, there was a decreasing tendency of the aluminum content in the molten steel with the time, and the addition of CaS into the slag can reduce the aluminum loss in the molten steel. Total oxygen content in the molten steel first increased and then decreased with the time when no CaS was added into the slag. However, it decreased monotonically with the time when the addition of CaS was made into the slag.

Effect of Na2O and heat-treatment on crystallization of glass–ceramics from phosphorus slag

Na2O–CaO–Al2O3–SiO2–MgO glass was prepared from phosphorus slag as the raw materials and subsequently converted to glass–ceramics. The effects of both heat-treatment system and Na2O content on crystallization and microstructure were investigated by XRD and SEM. For the glass–ceramics with 15 mass% Na2O (A), Na2Ca2Si3O9 appears initially at 850°C, then the dominant β-CaSiO3 from 850°C to 1050°C, which further transforms into α-CaSiO3 from 1050°C to 1150°C. The existing phases are α-CaSiO3 and Na2Ca2Si3O9 at above 1150°C. For the glass–ceramics with 17 mass% Na2O (B), the primary and second phases are β-CaSiO3 and Na2Ca2Si3O9 in the range of 750°C–950°C, respectively. The transformation from β-CaSiO3 to Na2Ca2Si3O9 occurs from 950°C to 1050°C. Na2Ca2Si3O9 gradually transforms into Na2Ca2Si3O9 solid solution from 1050°C to 1150°C, and Na2Ca2Si3O9 solid solution becomes the predominant crystal phase above 1150°C. Surface crystallization is dominant mechanism in glass–ceramics A, while volume crystallization mechanism is predominant in glass–ceramics B.

Liquidus surface of MgO–CaO–Al2O3–SiO2 glass-forming systems

Alkaline earth aluminosilicate systems are of widespread technological importance, and it is therefore essential to have accurate phase equilibrium diagrams available. While the phase equilibria for the single alkaline earth CaO–Al2O3–SiO2 and MgO–Al2O3–SiO2 systems are fairly well established, the mixed MgO–CaO–Al2O3–SiO2 systems have received little attention despite their important role in the high-tech glass industry. Here, the liquidus surface (liquidus temperature Tliq and primary devitrification phase) is determined by x-ray diffraction phase analyses of isothermally reacted samples from powder mixtures. The phase equilibrium diagrams are presented based on measurements on a total of 120 compositions. In the composition range of interest for industrial glasses, Tliq tends to increase with increasing silica content and decreasing alkaline earth-to-alumina ratio. Cristobalite, mullite, anorthite, and cordierite are found to be the dominant devitrification phases for the compositions with high SiO2, Al2O3, CaO, and MgO contents, respectively. Anorthite extends further into the cristobalite and mullite fields for the [CaO]/[MgO]=3 system compared to the cordierite behavior in systems with [MgO]/[CaO]=3. For systems with [MgO]=[CaO], the liquidus temperatures are shifted to lower values since the formation of anorthite and cordierite requires some critical concentration of CaO and MgO, respectively.

Effect of Na2O on formation of calcium aluminates in CaO–Al2O3–SiO2 system

The formation characteristics of calcium aluminates in the CaO–Al2O3–SiO2 system with sodium oxide was investigated by XRD, SEM–EDS and DSC–TG technologies. The main phases in the clinker after sintering at 1350 °C are 12CaO·7Al2O3, 2CaO·Al2O3·SiO2 and 2CaO·SiO2 when the mass ratio of Al2O3 to SiO2 is 3.0 and the molar ratio of CaO to Al2O3 is 1.0. The proportion of 12CaO·7Al2O3 increases with the increase of Na2O addition when the molar ratio of Na2O to Al2O3 is from 0 to 0.4, while the proportion of 2CaO·Al2O3·SiO2 decreases with the increase of Na2O addition. Na2O forms solid solution in 12CaO·7Al2O3, which increases the volume of elementary cell of 12CaO·7Al2O3. The formation temperature of 12CaO·7Al2O3 is decreased by 30 °C when the molar ratio of Na2O to Al2O3 increases from 0 to 0.4 determined by DSC. The alumina leaching property of clinker increases obviously with the increase of Na2O addition.

Effects of CaCO3 on slag flow properties at high temperatures

Experiments were conducted on the selected ashes with different additions of CaCO3 for understanding the effects on slag flow properties including ash fusion temperatures, slag viscosity, temperature of critical viscosity and type of slag. ICP-AES, XRD and FTIR analyses were applied to determine the component and structure of the slags. Factsage was used to calculate liquidus temperatures in the SiO2–Al2O3–CaO–FeO system and to predict formed mineral matters and proportion of solid phase as a function of temperatures. The results show that the liquidus temperature calculated by Factsage well predicts the variation of ash fusion temperatures. Slag viscosity behavior changes with increasing addition of CaCO3 because the formation process of solid phase is different. The Fourier transform infrared (FTIR) spectrum indicates that Ca2+ leads to break polymerized Si–O–Si into Si–O, so the increasing Ca2+ in slag results in the decrease of viscosity above liquidus temperature. Below liquidus temperature, solids content decreases with increasing addition of CaCO3 above the temperature of critical viscosity (Tcv). Meanwhile, it is found that the rate of solid formation is related with Tcv and a new prediction method of Tcv based on that was proposed. Moreover, the type of slag changed with addition of CaCO3 was predictable by XRD analysis. The prediction on ash fusion temperature, Tcv and type of slag is expected to serve as a reference for adding flux to regulate coal/ash properties suitable for slag tapping gasification technology.

Theoretical calculations of the thermal expansion coefficient of glass-ceramic sealing materials in solid oxide electrolysis cell

Three series of glasses, BaO–CaO–SiO2–Al2O3, SrO–SiO2–Al2O3 and SrO–CaO–SiO2–Al2O3 were prepared. The coefficients of thermal expansion (CTE) of as-cast glasses were measured using dilatometer from room temperature to their glass transition. A new method — Average Field Strength Method was developed to accurately calculate the CTEs of all glasses and compared with traditional method (Appen method). Through comparison between calculated results and experimental results, the relation between the average field strength and the average field strength coefficient was found. With the increase of average field strength, the CTE of glasses calculated by the Average Field Strength Method of glass decreases smoothly. The CTEF were very close to the experimental results. The errors between them were smaller than 3%. The error between the CTE of glasses calculated by traditional method and the experimental CTE was near 40%. The average Field Strength Method can be used to accurately calculate the CTE, and estimate the change trends of CTE.

Preparation of an experimental glass-ionomer cements and evaluation of their properties

The preparation of glass-ionomer cements based on the composition of SiO2–Al2O3–CaO–SrO–F and evaluation of their properties is described. Cements were prepared via the sol–gel method and characterized by XRD, BET, SEM, and EDAX analysis. The effect of various concentrations of Sr on in vitro bioactivity of the glass speciments was investigated. In vitro bioactivity of the samples was evaluated by soaking them in simulated body fluid followed by structural characterization using SEM and atomic absorption analysis. A glass specimen with 0.5 mol of Sr exhibited appropriate bioactivity.

Viscosity, fragility and structure of Na2O–CaO–Al2O3–SiO2 glasses of increasing Al/Si ratio

The research and development of a new float glass with higher content of Al 2 O 3 is essential for the commercial flat glass. The study on the workability and kinetic fragility of Na 2 O–CaO–Al 2 O 3 –SiO 2 glass melts with different Al/Si ratios has been linked with the structure. The viscosities as a function of temperature for glass melts were derived on the basis of Vogel–Fulcher–Tamman (VFT) equation. Some characteristic temperatures and four characteristic temperature intervals of forming process in tin bath were estimated. The results showed that: adding 12 wt% Al 2 O 3 substitute for SiO 2 , the melting point ( Tm ) increased about 35 K, entire temperature interval in tin bath narrowed down about 20 K, the shortening of workability was mainly reflected in the viscosity range of 10 5.75 –10 10 Pa s, the fragility index m increased by 15%. It reveals an inverse correlation between the workability and the fragility. The structural changes on the tetrahedron structural unit Q n ( n =1, 2, 3, 4) were obtained by using Raman spectroscopy. Our analysis indicates that: the number of NBO reducing and a more polymerized structure with adding Al/Si ratios are responsible for the increase of viscosity; the tetrahedral distortion, a decrease of Q 3 / Q 2 in the Q n species, is responsible for the increase of fragility.

Thermodynamic investigation of the CaO–Al2O3–SiO2 system at high P and T through polymer chemistry and convex-hull techniques

The system CaO–Al2O3–SiO2 (CAS) is explored in the pressure–temperature (P, T) range 0–2GPa and 1000–3000K with the aim of defining the complex topology of the liquidus surface at various isobaric conditions and assessing the role of P on the stability fields and melting behavior of the various solids nucleating in the system. Calculations are carried out by coupling a generalized polymeric approach that reduces the system to two interacting sub‐lattices (Network Formers and Network Modifiers; NF, NM) with an improved and generalized convex-hull procedure that conforms mathematically the equipotential loci at the various T, P conditions. The thermodynamic model operates through a Toop's asymmetric deconvolution (interactions within the NM sub‐lattice unaffected by NF; interactions within the NF sub‐lattice affected by NM) of the bulk Gibbs free energy of mixing. Mixing energies (chemical and strain) are calculated with a polymeric model where the individual properties of the oxides composing the NF and NM matrixes are determined by their Lux–Flood acid–base properties and weighted on the basis of their electrical equivalent fractions. The convex-hull procedure locates points on the liquidus by lifted Delaunay triangulation. The isobaric liquidus at P=1bar (105Pa) is in reasonable agreement with the experimental observations. As far as we know isobaric sections at higher P conditions based on calculus have never been produced in literature. Our results indicate that the primary phase fields of anorthite and gehlenite shrink progressively with increasing P and a primary phase field of grossular appears at high P predating on the fields of the neighboring phases (gehlenite, rankinite, anorthite and wollastonite). Increasing P also causes the progressive disappearance of the liquid miscibility gap at high SiO2 content. Moreover the congruent melting of anorthite becomes incongruent. The fields of rankinite (Ca3Si2O7), tri-calcium aluminate (Ca3Al2O6) and grossite (CaAl4O7) disappear at P≥1GPa.

The influence of composition on the local structure around yttrium in quenched silicate melts — Insights from EXAFS

The structural environment around Y in silicate and aluminosilicate glasses containing 5000ppm Y was investigated as a function of melt composition and polymerization using Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. The used glass compositions were taken from Prowatke and Klemme (2005) varying in the aluminum saturation index (ASI, molar ratio of Al2O3/(Na2O+K2O+CaO)) from 0.115 to 0.768. Furthermore, a set of glass compositions from the system CaO–Al2O3–SiO2 (CAS) was used, for which structural data from computer simulations are available (Haigis et al., 2013--this issue). Structural parameters of the Y–O pair correlation of the first coordination shell were determined from the EXAFS based on a gamma-like distribution function that accounts for the large static disorder and non-Gaussian pair distributions. The analysis shows an increase in the coordination number from 6 to 8, along with an increase of the average Y–O distance by 0.13Å for the composition of Prowatke and Klemme (2005). For the CAS-composition an increase of the coordination number from 6 to 7, along with an increase of the average Y–O distance by 0.06Å is obtained. The change of these parameters is associated with a considerable increase in the asymmetry and width of the Y–O pair distribution. Due to its size and charge, 6-fold coordinated Y will preferentially bond to non-bridging oxygens of the polymeric melt network to form a stable configuration, as is the case for the less polymerized melts with low ASI. In highly polymerized melts with ASI values close to one, 6-fold coordination of Y is not possible because almost only bridging oxygens are available. Consequently, over-bonding of bridging oxygens around Y is counterbalanced by an increase of coordination number and Y–O distance to satisfy local charge balance requirements.

Compositional dependence of the rheology of halogen (F, Cl) bearing aluminosilicate melts

The rheology of three melt compositions containing different amounts of fluorine (F) and chlorine (Cl) or both was investigated with micropenetration and parallel-plate techniques. The heat capacity and configurational entropy of the melts were also determined. The observed viscosity range is between 105.5 and 1013Pas. The melts were produced in a 1atm furnace at temperatures between 1523 and 1923K using oxide and carbonate compounds. The halogens were incorporated using halides and halogen-bearing ammonium compounds. The first composition is a peraluminous Na2O–CaO–Al2O3–SiO2 melt (ANCS) with an apparent NBO/T of ~−0.08, the second composition is a peralkaline Na2O–CaO–Al2O3–SiO2 melt (NACS) (NBO/T=~0.24), which is an analogue for phonolites, and the third is an aluminium-free Na2O–CaO–SiO2 melt (NCS) (NBO/T of ~0.68). Five halogen-bearing ANCS melts with up to 1.10mol% Cl and 18.25mol% F, 6 halogen-bearing NACS melts with up to 1.38mol% Cl and 2.58mol% F and 3 halogen-bearing NCS melts with up to 2.15mol% Cl and 2.04mol% F were investigated in this study.Fluorine was found to decrease the viscosity for all compositions, but not with equal strength. Interpolated to 1mol%, F decreases the viscosity by 0.31±0.08 log units in the peraluminous melt (ANCS), 0.57±0.11 log units in the peralkaline melt (NACS) and 0.47±0.14 log units in the NCS melt.The effect of Cl on rheology depends on the melt composition. Interpolated to 1mol%, Cl decreases the viscosity by 0.57±0.13 log units in the peraluminous melt, but increases viscosity by 0.87±0.10 log units in the peralkaline melt. There is no measurable effect on viscosity due to the addition of chlorine to the aluminium-free melt.In the peraluminous melts the effects of F and Cl add almost linearly to decrease viscosity. In the peralkaline melts, Cl increases the viscosity while F decreases it, if both are present, the effects appear to balance each other; resulting in no change in viscosity for the addition of equal amounts (in mol%) of fluorine and chlorine. The results were obtained from samples with higher and more varied halogen contents than in the most previous studies, therefore they hold true for a wide range of concentrations of both elements and should be taken into account for modelling magmatic processes.

Understanding the Crystallization Mechanism of a Wollastonite Base Glass Using Isoconversional, IKP Methods and Master Plots

The complex development of crystals found in the crystallization of SiO2–Al2O3–CaO–Na2O glass has been explained using Differential Thermal Analysis. The crystal growth process has been studied using isoconversional, invariant kinetic parameters, and master plots methods. The applied kinetic models have revealed activation energy values that are over 360 and 385 kJ/mol by employing the integral and differential kinetic methods, respectively. The crystallization process schedule that was previously observed using scanning electron microscopy has been corroborated in this study using the kinetic methods. The crystallization of wollastonite occurs through a complex two‐stage mechanism, with early three‐dimensional growth of crystals (A3 mechanism) on the surface of glass particles followed by one‐dimensional growth of needles (A3/2 mechanism) toward the interior of grains. The results presented in this article are in agreement with a previous paper that employed the Kissinger non‐isothermal method and the Ligero approximation.

SiO2–Al2O3–CaO glass-ceramics: Effects of CaF2 on crystallization, microstructure and properties

The effects of fluorine content on the nucleation and crystallization behavior of SiO2–Al2O3–CaO glass ceramics system have been investigated. The crystalline phases were determined by X-ray diffraction (XRD). The crystallization kinetics was determined by differential thermal analysis (DTA). The microstructures were examined by using scanning electron microscope (SEM). Fourier transformed infrared spectra (FTIR) analysis was used to study the glass structure. The results showed that by increasing the fluorine content, both the crystallization peak temperature (Tp) and activation energy (E) decreased. Wollastonite, anorthite and gehlenite are the main crystalline phases that exist in the glass ceramics system. The study shows that fluorine promoted initial crystallization of glass and can be used as an effective nucleating agent in the SiO2–Al2O3–CaO system.

Studies of dynamic mass transfer at the slag–metal interface – Interfacial velocity measurements

Abstract The dynamics of oxygen transport along the slag–metal interface of pure iron and alumina-saturated CaO–Al2O3–SiO2 slag was studied using high-temperature X-ray image analysis. The oscillations of the metal drop occurring due to the interfacial movement of oxygen atoms driven by Marangoni forces were studied in detail. The change in interfacial area during the oscillations was measured using a digitizing software and MATLAB. It was observed that the interfacial velocity as a function of oxygen exhibits insignificant variation with temperature. Further, the values obtained for the interfacial velocity using oxygen concentration difference at the interface were slightly lower in comparison to those using sulfur. The possible reason for this lower velocity could be that, although oxygen is a smaller atom compared to that of sulfur, the energy barrier at the free iron surface is higher for oxygen, thus hindering its motion along the interface.

Relationship between coal ash composition and ash fusion temperatures

Coal ash fusion characterization and the ash fusion temperatures (AFTs) are important parameters for coal industry. Previous research has proved that the AFTs are correlated with the chemical composition of coal ash samples. In this paper, a five-component SiO2–Al2O3–CaO–Fe2O3–K2O system is set. The AFTs of 34 synthetic ashes were measured in a carbon atmosphere, and the trends of the AFTs analyzed. Different from other studies, X-ray diffraction (XRD) and scanning electron microscope (SEM) were combined to explore the relationships between the measured AFTs and the mineral composition, morphology and microstructure of ash samples. Furthermore, the effect of the element valence state is also taken into account and X-ray photoelectron spectrometer (XPS) is used to analyze it firstly. The results show that the AFTs decrease with the increasing Fe2O3 content and silica-to-alumina (S/A) ratio. However, for the effect of CaO content, the AFTs reach a minimum value and then increase once again. Furthermore, the AFTs show no significant change as the K2O content varies. At last, all the conclusions found from the synthetic samples are also applicable for the seventeen bituminous coal ashes collected locally and abroad.

Reoxidation of Al‐Killed Steel by Ca(OH)2 in the High Basicity Slag

AbstractIn the present work, reoxidation of Al‐killed steel by Ca(OH)2 in high basicity slag was investigated by using laboratory experiments at 1873 K in MgO crucibles with various amount of Ca(OH)2 addition into slag. The CaO–SiO2–Al2O3–MgO–Ca(OH)2 slags were used to study the effect of Ca(OH)2 on total oxygen content, aluminum loss, and FeO content in the slag. It was shown that total oxygen content decreased with the time when no Ca(OH)2 was added into the slag, but it first increased and then decreased with the time when the addition of Ca(OH)2 was made. Moreover, aluminum loss and FeO content in the slag increased with increasing Ca(OH)2 content.

A Study on Electrical Resistivity of BaO–CaO–SiO<sub>2</sub>–Al<sub>2</sub>O<sub>3</sub> Seal Glass Used in Solid Oxide Electrolytic Cell (SOEC)

The electrical resistivty (R) of BaO–CaO–SiO2–Al2O3 (BCSA) based glass, which was used in SOEC, was measured by impedance analyzer from room temperature to sealing temperature, and it was founded that electrical resistivity of all seal glass decreases with temperature. When temperature is lower than the soften temperature of glass, the electrical resistivity of all seal glass was no less than 107Ω∙cm. At 850°C, the resistivity of the 16BaO–16CaO–42SiO2–8Al2O3 glass (G1) reached 4.40×106Ω∙cm, and even at the sealing temperature, their resistivity was still above 105-106Ω∙cm. With the decrease of ratio of Si/B from 3 to 1, the electrical resistivity of glass decreased from 4.40×106Ω∙cm to 8.96×104Ω∙cm. The electrical resistivity of glass in BCSA system could be significantly affected by B2O3 and alkaline earth oxides. The results show that the electrical resistivity of glass was improved with the increasing of non-bridging oxygen and the average field strength. All glasses can be used as sealants at high temperature with no electrical shunting in SOEC.

Development and characterization of glass-ceramic sealants in the (CaO–Al2O3–SiO2–B2O3) system for Solid Oxide Electrolyzer Cells

The efficiency of glass-ceramic sealants plays a crucial role in Solid Oxide Electrolyzer Cell performance and durability. In order to develop suitable sealants, operating around 800 °C, two parent glass compositions, CAS1B and CAS2B, from the CaO–Al2O3–SiO2–B2O3 system were prepared and explored. The thermal and physicochemical properties of the glass ceramics and their crystallization behavior were investigated by HSM, DTA and XRD analyses. The microstructure and chemical compositions of the crystalline phases were investigated by microprobe analysis. Bonding characteristic as well as chemical interactions of the parent glass with yttria-stabilized zirconia (YSZ) electrolyte and ferritic steel-based interconnect (Crofer®) were also investigated. The preliminary results revealed the superiority of CAS2B glass for sealing application in SOECs. The effect of minor additions of V2O5, K2O and TiO2 on the thermal properties was also studied and again demonstrated the advantages of the CAS2B glass composition. Examining the influence of heat treatment on the seal behavior showed that the choice of the heating rate is a compromise between delaying the crystallization process and delaying the viscosity drop. The thermal Expansion Coefficients (TEC) obtained for the selected glass ceramic are within the desired range after the heat treatment of crystallization. The crystallization kinetic parameters of the selected glass composition were also determined under non-isothermal conditions by means of differential thermal analysis (DTA) and using the formal theory of transformations for heterogeneous nucleation.

Structure and high temperature physical properties of glass seal materials in solid oxide electrolysis cell

Three series of BaO–CaO–SiO2–Al2O3, SrO–SiO2–Al2O3, and SrO–CaO–SiO2–Al2O3 glasses are prepared. Their basic physical properties are measured using dilatometry and differential scanning calorimetry from room temperature to the softening temperature. Their structures are characterized with infrared spectroscopy. The wetting characteristics of all glasses are examined by monitoring the change in shape of a cube specimen on crofer22 substrates from room temperature to flow temperature with a high temperature shape microscope. Five main absorption bands can be distinguished in the infrared absorption spectra of the three systems. The optimum ranges of sealing temperature of the glasses are determined. The 24SrO–16CaO–25SiO2–8Al2O3 glass is found to be the best sealant for the solid oxide electrolyzer/fuel cells under low loading without leakage. SrO improves the wetting ability of the glass by decreasing the contact angle between the glass and crofer22 substrates. The thermal properties of all the glasses fulfill the requirements for sealing solid oxide electrolysis/fuel cells. In terms of air tightness, the SrO-containing glass shows the best wetting ability among other glasses, and is the most suitable sealant for planar solid oxide electrolyzers/fuel cells.