Structure of the BaO – Al2O3 – SiO2 System (A Review)

The results of theoretical calculations and experimental studies of the ternary system BaO – Al₂O₃ – SiO₂ in the subsolidus range at temperatures of 1200 – 1400°C are considered. Complete splitting of this system into elementary polytypes is performed, a topological graph of the relationship between these polytypes is shown, and geometrical characteristics of the binary and ternary compounds comprising this system are supplied.     

Properties of RO-Y2O3-Al2O3-SiO2 glasses

The coefficient of linear expansion, glass-transition temperature, temperature at the orset of deformation (strain point), density. Young modulus, microhardness, crystallizability, and contact angle are studied as a function of the composition in RO–Y₂O₃–Al₂O₃–SiO₂ (R=Ca and/or Mg) glass systems. The composition ranges for glasses (with strain point >900°C and coefficient of linear expansion of (32–45)×10^–7°C^–1) that can be used for soldering silicon-nitride ceramics were established.Translated from Steklo i Keramika, No. 12, pp. 5–7, December, 1996     

Phase diagram of the Al2O3-HfO2-Y2O3 system

The phase diagram of the Al₂O₃-HfO₂-Y₂O₃ system was first constructed in the temperature range 1200-2800 °C. The phase transformations in the system are completed in eutectic reactions. No ternary compounds or regions of appreciable solid solution were found in the components or binaries in this system. Four new ternary and three new quasibinary eutectics were found. The minimum melting temperature is 1755 °C and it corresponds to the ternary eutectic Al₂O₃ + HfO₂ + Y₃Al₅O₁₂. The solidus surface projection, the schematic of the alloy crystallization path and the vertical sections present the complete phase diagram of the Al₂O₃-HfO₂-Y₂O₃ system.     

On the Phase Separation and Crystallization of Glasses in the MgO–Al2O3–SiO2–TiO2 System

The changes in the structure and phase composition of glasses in the MgO–Al₂O₃–SiO₂–TiO₂ system (at different TiO₂ contents and ratios MgO : Al₂O₃) upon their heat treatment in the temperature range 700–960°C are investigated by small-angle X-ray scattering (SAXS) technique and X-ray powder diffraction analysis. The influence of gallium oxide additives on the phase separation and crystallization is analyzed. It is demonstrated that the heat treatment results in the phase separation, which occurs through the spinodal decomposition mechanism. A regular structure formed upon phase separation is retained after the completion of crystallization in inhomogeneity regions. The interference effects due to the regularity in the distribution of nanocrystals in the vitreous matrix bring about a decrease in the light scattering intensity and provide transparency of glass-ceramic materials.     

Sintering of Corundum Mixtures Modified by a Vitreous Phase of a Eutectoid Composition

The effect of a vitreous phase of a eutectoid composition on sintering of corundum mixtures is considered. It is established that the additive corresponding to a eutectic composition of the CaO – Al₂O₃ system melting at a temperature of 1395°C improves the service properties of corundum concrete through activating its sintering.     

Specific Features of the Subsolidus Structure of the BaO – Al2O3 – Fe2O3 – SiO2 System. Part 1. Subsolidus Structure of the BaO – Al2O3 – Fe2O3 – SiO2 System at Temperatures Above 1381 K

Results of a thermodynamic and geometric-topological analysis of the subsolidus structure of the BaO – Al₂O₃ – Fe₂O₃ – SiO₂ system at temperatures above 1381 K are reported. Tetrahedratization of the system, with due regard for the existing high-temperature phases, is carried out. Data for solid-state reactions in the system obtained by thermodynamic and geometric-topological calculations are presented. Technological implications in the synthesis a new class of barium-containing cements with allowance for the specific subsolidus structure (associated with reversible solid-state reactions in ternary subsystems and the quaternary BaO – Al₂O₃ – Fe₂O₃ – SiO₂ system proper) are discussed.     

Synthesis of Glass-Ceramic Materials in the BaO–PbO–B2O3–Al2O3–TiO2 System

The influence of PbO, B₂O₃, and Al₂O₃ additives on the glass formation and crystallization of glasses with a high total content of BaO and TiO₂ (65–75 wt % or 76–86 mol %) is investigated. It is shown that glasses of the compositions (wt %) 31–35 BaO, 12–17 PbO, 34–42 TiO₂, 10–13 Al₂O₃, and 2–3 B₂O₃ are promising materials for use in preparing glass-ceramic ferroelectrics based on the melting–molding–crystallization technology. These compounds are characterized by a relatively low melting temperature (1450°C), the absence of spontaneous crystallization during molding, and the possibility of controlling the phase composition of the material through the appropriate choice of the crystallization temperature.     

Cracking of n-Butane Over Alkaline Earth-Containing HZSM-5 Catalysts

A series of catalysts, NiSO₄/SiO₂–Al₂O₃, for ethylene dimerization were prepared by the impregnation method using aqueous solution of nickel sulfate. Although SiO₂–Al₂O₃ without NiSO₄ was inactive as catalyst for ethylene dimerization, the SiO₂–Al₂O₃ with NiSO₄ exhibited high catalytic activity even at room temperature. The high catalytic activity of NiSO₄/SiO₂–Al₂O₃ was closely correlated with the increase of acidity and acid strength due to the addition of NiSO₄. The sample having 15 wt% of NiSO₄ and calcined at 500 °C for 1.5 h exhibited maxima for catalytic activity and acidity. In view of IR results of CO adsorbed on NiSO₄/SiO₂–Al₂O₃, it is concluded that the active sites responsible for ethylene dimerization consist of a low-valent nickel, Ni⁺, and an acid.     

Kinetics of Sintering of a Low-Cement Corundum Castable Modified by an Eutectoid Phase

The effect of an eutectoid additive on the kinetics of sintering of a low-cement corundum castable is studied. An eutectic in the CaO – Al₂O₃ system produced at 1395°C is shown to accelerate the sintering.     

Evaluation of Crystallization Capacity of Glasses

A temperature-concentration dependence of the linear velocity of crystal growth (LVCG) of diopside for potassium-bearing glasses of the system CaO – MgO(Al₂O₃) – SiO₂ is determined based on adaptation of the Turnbull-Cohen theoretical equation, and a relationship between the LVCG of devitrite and cristobalite and the chemical composition of glasses located in the respective areas on the phase diagram of the Na₂O – CaO – SiO₂ system phase diagram is established.     

Compositions Based on MgAl2O4, Al6Si2O13, AND Al2TiO5

Binary and ternary fused compositions based on alumomagnesian spinel, aluminum titanate, and mullite are studies using various techniques of physicochemical analysis. The minimum incipient melting temperature in the MgAl₂O₄ – Al₆Si₂O₁₃ – Al₂TiO₅ system is [1645 ± 15] °C. Fused materials with tailored phase compositions are obtained under industrial conditions. Technological properties of a fused composite corundum – alumomagnesian spinel – mullite – aluminum titanate are studied.     

Thermomechanical properties of ceramics in the systems Al2O3-TiO2 and Al2O3-TiO2-mullite

Conclusions We studied certain properties of ceramics in the systems Al₂O₃-TiO₂ and Al₂O₃-TiO₂-mullite, obtained by the use of the double-stage synthesis of aluminum titanate.We established the nature of the change in the high-temperature strength in relation to the ratio of Al₂O₃ and aluminum titanate. The maximum high-temperature strength (bending) at 1200°C is possessed by ceramic with a corundum matrix and a volume proportion of aluminum titanate equal to 40–45%.It is established that the addition of CaO + SiO₂ made in amounts of up to 1.0–1.5% contributes to the partial breakdown of the aluminum titanate in the compositions Al₂O₃-TiO₂ and the production of a ceramic with a bending strength of 160–190 N/mm² at 20–200°C, thermal-shock resistance 650–800°C, and thermal conductivity of 1.9–2.1 W/(m·K).We studied the effect of the mullite concentration on the properties of the ceramic in the system Al₂O₃-TiO₂-mullite. The introduction of mullite in amounts of not more than 50%, containing up to 3% of impurities, contributes to an increase in the ceramic's strength in the range 20–1300°C and in the thermal shock resistance.Translated from Ogneupory No. 2, pp. 22–26, February, 1988.     

Effect of solidification path on the microstructure of Al2O3–Y2O3–ZrO2 ternary oxide eutectic ceramic system

The solidification path of the Al₂O₃–Y₂O₃–ZrO₂ ternary oxide eutectic composite ceramic is determined by a high temperature DTA and laser floating zone (LFZ) directional solidification method to investigate the effect of solidification path on the microstructure of the ternary oxide. The DTA and microstructure analyses show that the YAG or Al₂O₃ tends to form as primary phase under the unconstrained solidification conditions, and then the system enters ternary eutectic solidification during cooling from 1950 °C at rate of 20 °C/min. The as-solidified composite ceramic shows a divorced irregular eutectic structure consisting of Al₂O₃, YAG and ZrO₂ phases with a random distribution. The primary phases are however completely restrained at the directional solidification conditions with high temperature gradient, and the ternary composite by LFZ presents well coupled eutectic growth with ultra-fine microstructure and directional array. Furthermore, the eutectic transformation and growth mechanism of the composite ceramic under different solidification conditions are discussed.     

The Viscosity of Molten Material in Pores and Capillary Channels of the Matrix Phase of High-Alumina Castables Employed in Thermal Power Units of Ferrous Metallurgy. 1. Viscosity Analysis of Melts in the CaO – Al2O3 –FeO – Fe2O3 – SiO2 System

A new approach to the viscosity analysis of high-alumina, low-calcium melts of the CaO – Al₂O₃ – FeO – Fe₂O₃ – SiO₂ system is used. A mathematical formalism for handling experimental viscosity data on the CaO – FeO – Fe₂O₃ – SiO₂ system is proposed that allows viscosity of the system to be evaluated within _av = 0.004 Pa · sec in the temperature range of 1500 – 1700°C at concentrations (mol.%) of CaO = 15.3 – 50.3, Fe_xO_y = 2.3 – 38.5, and SiO₂ = 17.7 – 57.7. An equation describing viscosity as a function of temperature is derived. Using this equation, the viscosity of model melts compositionally analogous to the products of interaction between molten slag and the glassy matrix phase of castables employed in thermal power units of ferrous metallurgy is considered.     

Sintering and some properties of compositions in the Al2O3-Al2TiO5 system with additions of amorphous silica

Conclusions We studied the effect of addtions of amorphous silica in amounts of 6–11% on the properties of compositions in the Al₂O₃-Al₂TiO₅ system.The presence of SiO₂ enables us to obtain, at reduced firing temperatures (1580°C), adequately dense (P_open=3–4%) compositions while preserving the high thermal-shock resistance and compressive strength at 1050°C (360–420 MPa).Translated from Ogneupory, No. 8, pp. 19–20, August, 1986.     

Glass Formation in the ZrF4–LaF3–BaF2–NaF System

The glass formation in the ternary ZrF₄–LaF₃–BaF₂and quaternary ZrF₄–LaF₃–BaF₂–NaF systems at a zirconium fluoride content of 50–60 mol % is investigated. The glass formation region in the ternary system has the shape of a petal and lies along the LaF₃–BaZr₂F₁₀join. The glass formation regions in the quaternary system are either localized or continuous depending on the zirconium fluoride content. The glass transition temperatures T _gfall in the range 180–290°C, and the temperatures of the onset of crystallization lie in the range 250–340°C. Glasses crystallize in one, two, or three stages. The melting temperature varies in the range from 390 to 650°C. The microhardness of glasses is measured. The compositions of the most stable glasses are determined.     

Phase evaluation during high temperature long heat treatments in the Y2O3–Al2O3–SiO2 system

The effect of high temperature long heat treatments on the microstructure of the eutectic glass composition in the Y₂O₃–Al₂O₃–SiO₂ system was examined. The qualitative and quantitative phase analyses were conducted by using scanning electron microscopy combined with energy dispersive analysis and electron microprobe. Simultaneous thermal analyses were carried out to determine the transition temperatures and enthalpies. The crystallization behavior of these glasses was monitored with X-ray powder diffraction. A needle like X-phase was observed in the structure of this eutectic composition after long heat treatment at 1350 °C.     

Effect of flux-forming additives on the sintering temperature and the properties of a corundum-based ceramic

Conclusions The sintering behavior and the structure evolution of the corundum-based ceramics containing various flux-forming additives of eutectic compositions were studied.It was established that the addition of the flux-forming agent belonging to the CaO-B₂O₃-SiO₂-BaO system has the most favorable effect on the sintering process and the properties of the experimental corundum-based ceramic.We obtained a corundum material containing 97% Al₂O₃ and 3% flux-forming additive (consisting of 31.92% CaO, 26.25% SiO₂, 16.67% BaO, and 25.16% B₂O₃) and requiring a low temperature (up to 1500°C) for achieving complete sintering. The material possesses a fine-grained properties.Translated from Ogneupory, No. 8, pp. 31–33, August, 1986.     

Synthesis and long-term test of borosilicate-based sealing glass for solid oxide fuel cells

A series of borosilicate-based glasses, ternary BaO-SiO₂-B₂O₃ and quaternary BaO-SiO₂-B₂O₃-Al₂O₃ systems, are prepared as sealing materials for intermediate temperature solid oxide fuel cells (IT-SOFCs). The thermal expansion, crystalline phases, glass forming ability, and thermo-chemical stabilities of the glasses are characterized. Additionally, the effect of the B₂O₃/SiO₂ ratio and Al₂O₃ and BaO contents on the coefficient of thermal expansion (CTE) are discussed and compared. Test results show that one glass (G6) can fully wet various substrates at the sealing temperature of 1000 °C and match thermal expansion. Possible interfacial reactions between the glass and those cell components aging up to 5000 h are investigated by element mapping, XRD, SEM, and EPMA. Leakage testing was also performed at temperatures up to 650 °C. The results show that the glass (G6) remains amorphous after 5000 h test and is stable under these conditions and compatible with the other fuel cell components.     

The System BaO – Al2O3 – Fe2O3

Results of a study of the subsolidus structure of the BaO – Al₂O₃ – Fe₂O₃ system at 1300°C are presented. Based on thermodynamic and experimental data, the triangulation of the system, previously unreported, is carried out with regard for all phases stable at this temperature. Geometrical and topological characterization of the system is given.