System BaO Research Articles

Radio-transparent celsian ceramics modified with glass in a pseudoternary system BaO–Al2O3–SiO2: synthesis, microstructure, thermal and physical properties

The article presents the results of the study of radio-transparent celsian ceramics, in which part of the components were introduced using eutectic glass of the pseudoternary BaO–Al2O3–SiO2 system. The bonding of the components of the experimental glass into the celsian phase was realized according to the principle of reactive structure formation by adding the missing components (crystalline fillers). In this case, the obtained dense sintered water-resistant ceramic, the only crystalline phase in the composition of which is the monoclinic form of celsian, which forms a microhomogeneous structural matrix of the material. Celsian is represented by distinct prismatic crystals of tetragonal and hexagonal shape. The size of celsian crystals increases from 3–5 m to 7–10 m with increasing the content of eutectic glass. The developed celsian ceramic has a set of enhanced physical and thermal properties: zero water absorption and open porosity, mechanical compressive strength (up to 157 MPa), refractory index is 1540–15800C. Celsian ceramic is characterized by a coefficient of linear thermal expansion of 3410–7 0C–1, which provides a sufficiently high thermal shock resistance of 7000C. In terms of the level of relative dielectric permittivity (5.5) and dielectric losses (0.0005) at a frequency of 1010 Hz, the developed ceramic meets the requirements for ultra-high-frequency radio-transparent materials for aviation and rocket technology, which operate under conditions of high-speed high-temperature heating.

Phase equilibria in the system BaO–TiO2

AbstractThe system BaO–TiO2 is technically important because it contains multiple dielectric and ferroelectric phases, including the important BaTiO3, which is one of the most widely studied dielectric perovskites owing to its dual piezoelectric and ferroelectric properties. The present work revises the subsolidus phase equilibria data by synthesizing previous phase equilibria data and new experimental results using high‐temperature (600°–1300°C) and long‐term (≤336 h) equilibration, coupled with analytical work based principally on room‐temperature X‐ray diffraction. The resultant phase diagram is given in both mole and weight percents, extending from the liquidus surface (not investigated) to absolute zero temperature (for inclusion of the previously excluded crystallographic and ferroelectric phase transformations). The major features include (1) correction of four eutectoid and three peritectoid reactions and corresponding temperatures, (2) indication of inferred partial solid solubilities, (3) clarification of the BaTiO3 solid solubility homogeneity regions, and (4) specification of some invariant point compositions on the liquidus surface.

Structure and properties of gallate and germanate langasite infrared optical glass materials

Glasses in the system BaO – La2O3 – Ga2O3 – GeO2 and Langasite crystalline phases with the same stoichiometry have been studied considering the possible use of these glasses for laser-induced space-selective growth of crystalline architectures in the glass compositions. For better understanding of mechanisms involved in such controlled crystallization process, crystalline and glass compounds with same stoichiometry and different La/Ba ratios have been synthesized to compare their local structure. Solid-state Nuclear Magnetic Resonance evidence 4- and 5-coordinated gallium units in the glass matrix, denying unambiguously the formation of 6-coordinated gallium sites observed in crystalline phases. Moreover vibrational spectroscopies suggest a link between a 3D network formed by 4- and 5-coordinated gallium, connected to each other and to 4- coordinated Q4 and Q3 germanium units in the glass and their congruent crystallization. The transition from 4- and 5-coordinated gallium to 6-coordinated gallium sites observed in Langasite crystalline phases remains not still elucidated.

An experimental and theoretical study to evaluate Al2O3–PbO–B2O3–SiO2–BaO radiation shielding properties

This study's objective is to evaluate an Al2O3–PbO–B2O3–SiO2–BaO glass system's radiation shielding characteristics. The composition of the glasses is 15Al2O3–25PbO–(60-x)B2O3–10SiO2–xBaO, with x in the 5–20 mol% range. Experimental results were used to determine the samples' linear attenuation coefficients (LAC), which were then confirmed by Phy-X program. Utilizing narrow beam transmission geometry, the experimental LAC values were determined. According to the results there was high agreement when comparing the theoretical and experimental values. The LAC values were used to calculate the prepared glasses' mass attenuation coefficients (MAC) and other relevant properties. The mean free path (MFP) values of the sample with 5 mol% BaO were 0.079, 2.549, 3.944 and 4.273 cm at 0.0595, 0.662, 1.173, and 1.332 MeV, thus demonstrating that raising the glass system's BaO enhances the prepared glasses' shielding capacity. According to radiation protection efficiency (RPE), the glasses' capacity to shield the photon is enhanced when their BaO content rises.

STRUCTURAL DESIGN OF Eu<sup>2+</sup>-CONTAINING GLASS AND GLASS-CERAMICS BASED ON THE SYSTEM BaO–ZrO<sub>2</sub>–SiO<sub>2</sub>–MgF<sub>2</sub> FOR LED APPLICATION

For the first time, an approach to designing the structure of Eu2+ containing silicate glass-ceramics materials has been experimentally implemented, which consists in the fact that rare earth activator is introduced into various crystals formed during glass crystallization. Transparent Eu-containing glass and glass ceramics based on the system BaO–ZrO2–SiO2–MgF2 were prepared by the traditional glass melting method at 1450°C. The crystal structure and properties of materials were characterized by XRD analysis and photoluminescence spectroscopy during different stages of glass crystallization. It is shown that the simultaneous incorporation of Eu into different silicate crystals (Ba2SiO4, BaMgSiO4, and BaSiO3) formed during the glass crystallization leads to the formation of a material with a wide luminescence band in the visible part of the spectrum. The study of photoluminescence and luminescence excitation spectra of the glass suggests the possibility of energy transfer from Eu2+ to Eu3+ ions. The structures of Eu2+ luminescent centers are similar in the glass and glass-ceramics that is related to some phase separation in the glass before crystallization. The study of luminescence properties of prepared materials showed that these materials can be promising for the application in LEDs techniques.

STUDY OF THE INFLUENCE OF INTENSIFYING ADDITIVES ON LOW-TEMPERATURE SYNTHESIS OF SLAVSONITE AND CELZIAN IN THE CREATION OF RADIOTRANSPARENT CERAMIC MATERIALS

The studies carried out concern the development of structural radiotransparent ceramic materials based on the four-component system BaO–SrO–Al2O3–SiO2. Due to the widespread use of radar equipment at modern aviation facilities, the development of radiotransparent fairings for them is a rather important and urgent task.The purpose of the fairings is to protect the antenna devices of radar stations from environmental influences during flight. Based on this, the fairings must meet a complex set of requirements for aerodynamic, thermal, radio engineering and mechanical properties. These requirements at supersonic flight speeds of modern objects increase significantly, since the improvement of the aerodynamic shape, the increase in the mechanical strength and thermal stability of the fairings contradicts the interests of radio engineering, leading to a significant deterioration in their radiotransparency and to distortions of antenna directional patterns. The consequence is a decrease in the range of radar stations and serious deterioration in their accuracy characteristics.The aim of the research was to obtain, on the basis of the BaO–SrO–Al2O3–SiO2 system, crystalline phases of slavsonit and celsian at low temperatures and times of synthesis, by introducing sintering intensifiers with fluxing and modifying action.The influence of a number of additives on the intensification of the low-temperature synthesis of slavsonit and celsian is investigated. The positive effect of the eutectic additive of the SnO2–Li2O system on the preparation of a densely sintered ceramic material based on solid solutions of slavsonit and monoclinic celsian is shown. It has been established that, according to its dielectric properties, the obtained ceramic material can be classified as structural radio-transparent materials.

Features of formation of the celsian phase during firing of heat-resistant ceramics in the system BaO–Al2O3–SiO2

In the synthesis of heat-resistant ceramics in the system BaO–Al2O3–SiO2 (BAS), it is important to find ways of intensifying the process of transition of hexagonal celsian to monoclinic celsian without an increase in sintering temperature. Monoclinic form of celsian is characterized by higher thermal, electro-insulating, and mechanical properties. This paper deals with the features of formation of the phase composition of celsian ceramics when using BAS glass of eutectic composition and glass in the system Li2O–Al2O3–B2O3–SiO2 (LABS) of spodumene composition as modifying components. It is shown that monoclinic celsian is the final crystalline phase formed in ceramics synthesized on the basis of barium carbonate and kaolin. Monoclinic celsian is formed stepwise; and the hexagonal celsian appears first. The complete transition hexagonal celsianmonoclinic celsian occurs only in the process of high temperature firing at 12500C. Notably, the degree of ceramic sintering remains low (water absorption is 11.0%). Introduction of BAS glass contributes to the complete transition of hexagonal celsian to monoclinic celsian at a reduced temperature of 11000C. Maximum effect in the formation of monoclinic celsian is achieved by the introduction of LABS glass. As a result, the temperature of formation of this modification maximally decreases to 8000C. In this case, complete sintering of celsian ceramics is achieved at the temperature of 12500С.

Chemical approach to the glass structure and properties

AbstractThis paper continues the series of works by the present authors on the modeling of glass structure and properties. Calculations are performed using the concept of the chemical structure based on the rigorous thermodynamic model of associated solutions. The aim of the present contribution is to demonstrate the applicability of the concept to a wider range of systems than that considered before. For this reason, glasses in the systems with different chemical natures determined by the acidity and basicity of the constituent oxides are considered. The glass structure is calculated at the level of the short‐range order in the systems BaO‒SiO2 and M2O(MO)‒P2O5 (M = Li, Na, and Zn) and the intermediate‐range order in the systems Rb2O‒B2O3 and Cs2O‒B2O3. The structure‐property relationship is quantitatively established by the example of the molar volume of BaO‒SiO2 glasses. All calculations are performed without the use of adjustable parameters and the results obtained are compared with the experimental data available in the literature.

Properties of glasses in the system BaO–B2O3–SiO2–xAl2O3 (x=0; 5; 10 mol.%)

This article shows the prospect of the system BaO–Al2O3–B2O3–SiO2 as the basis of vitreous and glass ceramic materials, which are widely used in rocket production for high-temperature protection of heat resistant alloys, in the power industry for sealing solid oxide fuel cells, and in the production of heat resistant glass ceramic materials. We examined the conditions of glass formation and properties of glasses with the following content of components (mol.%): BaO 30–70, B2O3 10–50, SiO2 20–60, and Al2O3 0–10. We established experimentally that the physical and chemical properties of glass, depending on its chemical composition, vary within the following limits: coefficient of linear thermal expansion of (71–122)10–7 К–1; glass transition temperature of 500–6500С; dilatometric softening point of 540–6700С; and density of 3.20–4.21 g cm–3. The volume resistivity of the studied glasses is within 1011–1013 Ohmcm at the temperature of 1500С. Generalization of the dependences of glass properties on their chemical composition was carried out with the use of the additive equations, for which the partial contributions of oxides to the values of the corresponding properties were determined by experimental and statistical methods. The established patterns of influence of components and conditions of glass formation on the physical and chemical characteristics of glasses allows implementing the process of designing of a wide range of glass compositions with the complex of specified properties in order to solve the tasks of their practical use.

STUDY OF THE INFLUENCE OF INTENSIFYING ADDITIVES ON LOW-TEMPERATURE SYNTHESIS OF SLAVSONITE AND CELZIAN IN THE CREATION OF RADIOTRANSPARENT CERAMIC MATERIALS

The studies carried out concern the development of structural radiotransparent ceramic materials based on the four-component system BaO–SrO–Al2O3–SiO2. Due to the widespread use of radar equipment at modern aviation facilities, the development of radiotransparent fairings for them is a rather important and urgent task.The purpose of the fairings is to protect the antenna devices of radar stations from environmental influences during flight. Based on this, the fairings must meet a complex set of requirements for aerodynamic, thermal, radio engineering and mechanical properties. These requirements at supersonic flight speeds of modern objects increase significantly, since the improvement of the aerodynamic shape, the increase in the mechanical strength and thermal stability of the fairings contradicts the interests of radio engineering, leading to a significant deterioration in their radiotransparency and to distortions of antenna directional patterns. The consequence is a decrease in the range of radar stations and serious deterioration in their accuracy characteristics.The aim of the research was to obtain, on the basis of the BaO–SrO–Al2O3–SiO2 system, crystalline phases of slavsonit and celsian at low temperatures and times of synthesis, by introducing sintering intensifiers with fluxing and modifying action.The influence of a number of additives on the intensification of the low-temperature synthesis of slavsonit and celsian is investigated. The positive effect of the eutectic additive of the SnO2–Li2O system on the preparation of a densely sintered ceramic material based on solid solutions of slavsonit and monoclinic celsian is shown. It has been established that, according to its dielectric properties, the obtained ceramic material can be classified as structural radio-transparent materials.

The structure of barium phosphate glasses and its influence on their thermodynamic stability and viscous flow

The Shakhmatkin and Vedishcheva thermodynamic (SVTD) model of associated solutions has been developed in glasses of the system BaO–P2O5, with the aim of deriving their short range structure and predicting the volume properties. The applicability of the model was examined by comparing the structure obtained from thermodynamic modelling and by Nuclear Magnetic Resonance spectroscopy. The evaluation of the molar volume of the investigated glasses was carried out through comparison of the experimental values calculated by two approaches: i) with the glass molar volume obtained through a linear combination of the product of the molar fractions of system components and their respective crystalline volume; and ii) with the molar volumes calculated by a multilinear regression analysis of the experimental molar volume of each composition. Furthermore, the viscosity curves were determined at low and high temperature ranges by beam-bending and rotation methods from which the fragility and activation energy of the viscous flow have been calculated and correlated with the thermodynamic chemical structure of the glasses.

Crystal growth, structural characteristics and electronic structure of Ba1-xPbxFe12O19 (x = 0.23–0.80) hexaferrites

The formation of (Ba,Pb)Fe12O19 crystals in the ternary system BaO–PbO–Fe2O3 and electronic structure of the crystals at high lead content are considered in the present study. The phase equilibria in the BaO–PbO–Fe2O3 system and related thermophysical parameters were defined. The analysis suggests that the use of lead oxide as a solvent reduces the minimum temperature for the hexaferrite crystal growth in the PbO–BaFe12O19 section to about 960 °C and, at the same time, gives an appropriate temperature range of about Δ500 °C (from 960 to 1465 °C). High-quality single crystals Ba1–xPbxFe12O19 with x = 0.23(2), 0.44(2) and 0.80(3) were grown by the flux technique and the structural properties were studied. The electronic structure of Ba0·2Pb0·8Fe12O19 hexaferrite was evaluated in parallel by X-ray photoelectron spectroscopy and density functional theory calculations to assess the effects of Pb2+ incorporation into the BaFe12O19 lattice. It is obtained by X-ray photoelectron spectroscopy measurements that the electronic parameters of Ba2+, Fe3+ and O2− ions are nearly the same in Ba0·2Pb0·8Fe12O19 and BaFe12O19 hexaferrites, and it indicates that the ionicities of Ba–O and Fe–O bonds are not affected by the presence of Pb2+ ions in the crystal lattice. On the base of density functional theory calculations, it is found that both the top of valence bands (from −10 eV to 0 eV) and bottom of the conduction bands (3 eV–8 eV) are dominantly occupied by Pb 6s 6p, Fe 3d and O 2p orbitals, indicating that the physicochemical properties of Ba0·2Pb0·8Fe12O19 related to the electron transitions across the forbidden bands are determined by Pb2+ cations, FeO4 and FeO6 groups. In particular, the incorporated Pb2+ cations have a more prominent contribution to the electronic states near the Fermi level than Ba2+ ions.

Determination of the crystallization mechanism of glasses in the system BaO/SrO/ZnO/SiO2 with differential scanning calorimetry

In order to identify suitable volume nucleation agents in glasses, heat treatments and subsequent traditional microscopic investigations are necessary. Those analyses are laborious and time-consuming. Therefore, often DSC methods are used to get information about the preferred crystallization mechanism or adequate nucleation and growth temperatures. In principle, these non-isothermal methods are much faster. In this study, different glasses from the system BaO–SrO–ZnO–SiO2 were prepared. The pairs show only slight compositional variations but a clearly different crystallization behavior. Each pair consists of one glass, which shows volume crystallization and another one, which crystallizes solely at the surface. The DSC results are correlated with the microstructures of the glass ceramics obtained from microscopic studies. It is shown that conventional DSC methods cannot give a distinct answer which crystallization mechanism really exists. One method was identified to securely determine the crystallization mechanism.

Experimental Determination and Fitting of Solid–Liquid Equilibria in the Ternary System BaO–P2O5–H2O at 323.2 K

In this work, solubilities and physicochemical properties including pH, density, and refractive index were studied by the isothermal dissolution equilibrium method for the ternary system BaO–P2O5–H...

Development of oxyfluoroborate glass ceramics doped with Er3+ and Yb3+

The preparation of oxyfluoroborate glasses and glass–ceramics doped with Yb3+ and Er3+ with improved luminescent properties is reported. Glasses with compositions (100 − x − y) (MO·2B2O3) + xPbF2 + y(YbF3:ErF3) (% in mol), where M is Sr, Ba, Ca, x = 10–40% and y = 0, 1 or 5% were prepared by the melt/quenching technique. Glass crystallization was studied using thermal analysis and X-ray diffraction techniques. Optical absorption and infrared up-conversion were studied on both glasses and glass–ceramics. The incorporation of a fluoride compound into the borate glass resulted to depend on the ionic radius of the glass modifier: as it increases, glasses become more stable against crystallization. On the other hand, alkali–fluoride compounds such as BaF2 and SrF2 can be crystallized from these systems by selecting an appropriate proportion between their components. Furthermore, the up-conversion response can be tuned by changing the glass modifiers (Sr, Ba and Ca) of the borate matrix, which also influence the type of fluoride crystallized compound. The strontium glass–ceramics have the highest luminescence response due to the crystallization of SrF2 compound in the system SrO–B2O3–PbF2. Meanwhile, the lowest luminescence signal was obtained for samples in the system BaO–B2O3–PbF2 where the Pb1.33Ba2.66B11FO20 phase crystallizes. With this strategy, new materials with improved luminescence properties that can be used as up converters, were obtained.

High-Temperature Flux Growth as a Tool for the Preparation of Mixed-Framework Metal-Y Silicates: A Systematic Evaluation of the Influence of Experimental Parameters

We report new aspects of the application of the flux-growth method for the preparation of single crystals of silicates, in particular, mixed-framework (octahedral–tetrahedral) metal-Y silicates, in air. The detailed investigations involve flux-growth syntheses in the system BaO–K2O–Y2O3–SiO2–MoO3, in which various important run parameters have been varied in a systematic way (heating and cooling rates, Tmax and duration of holding step, continuous or stepwise cooling, total duration of run, amount of MoO3 solvent, Y2O3/SiO2 molar ratio, size and filling volume of platinum crucible). The results demonstrate that the crystallization of various silicate structure types are strongly controlled by the Y2O3/SiO2 molar ratios and the amount of MoO3 solvent in the precursor mixtures. A decrease of the Y2O3/SiO2 ratio, i.e., an increasing amount of SiO2, promotes an increasing structural complexity of the silicates; nesosilicates crystallize at comparatively low SiO2 concentrations, sorosilicates at intermediate o...

Glass‐Ceramics in the System BaO–SrO–ZnO–SiO2 with Adjustable Coefficients of Thermal Expansion

Glasses from the system BaO–SrO–ZnO–SiO2 with different Ba/Sr ratios were characterized regarding crystallization behavior as well as the thermal expansion of almost fully crystallized glasses. Depending on the SrO concentration, different crystalline phases precipitate from the glasses. Those with low SrO concentrations precipitate crystals with the structure of low‐temperature BaZn2Si2O7 as one of the major phases. Higher SrO concentrations cause the formation of Ba1−xSrxZn2Si2O7 solid solutions with the structure of high‐temperature BaZn2Si2O7. Both, the low‐ as well as the high‐temperature phase exhibit very different thermal expansion behaviors ranging from a very high coefficient of thermal expansion in the case of the low‐temperature phase to a very low coefficient of thermal expansion in the case of the high‐temperature phase. The glass‐ceramics with the highest and that with the lowest coefficient of thermal expansion measured between 100°C and 800°C show a difference of 7.9 × 10−6 K−1, which is caused solely by a substitution of BaO with SrO. In contrast, the maximum variation in the thermal expansion of the glasses was only 1.5 × 10−6 K−1. The microstructure of sintered and afterward crystallized glass powders was analyzed via scanning electron microscopy and showed crack‐free samples with low porosity.

Development of barium boron aluminosilicate glass sealants using a sol–gel route for solid oxide fuel cell applications

A key problem in the fabrication of planar solid oxide fuel cells is the sealing of the metallic interconnect to the ceramic electrolyte. The sealing material must be gas-tight, stable in different atmospheres at high temperature, chemically compatible with the other cell components and resistant to thermal stresses. Glass–ceramic sealants are good candidates because of their high mechanical properties and the possibility to use a wide range of chemical compositions to control some physical properties like viscosity or coefficient of thermal expansion (CTE). In this work, glass sealants were synthesized using a sol–gel route, which generally allows to obtain both homogeneity at a nanoscale and reduction of the processing temperature. The studied glasses were based on the system BaO–B2O3–Al2O3–SiO2 with varying amounts of CaO and MgO additions. Dilatometry, differential thermal analysis and hot-stage microscopy were the techniques used to determine optimal thermal treatment for sealing operation (880 °C with a dwell time of 10 h). The thermomechanical properties of the sealants were improved after sealing by a thermal treatment transferring the sealant into a favourable partially polycrystalline state. Gas-tightness tests performed after joining and 100 h ageing treatment at 800 °C under air of steel-sealant-steel assemblies highlighted that 4 of the selected glass chemical compositions remained impermeable. Joining degradations, crystalline phases evolution and CTE of these glasses were analysed. Electrical resistivities were larger than 105 Ω cm at 700 °C. On the basis of these results, four glasses were identified as promising candidates for this application.

Interfacial reactions between a crystallizing sealing glass from the system BaO–ZnO–NiO–SiO2 and Crofer 22 APU

A glass from the system BaO–ZnO–NiO–SiO2 was used as a crystallizing glass seal for Crofer 22 APU steel. The glass was characterized with respect to crystallization, thermal expansion, and sealing behavior. In crystallized specimens, different barium silicates as well as a solid solution with the generalized compositions BaZn2−xNixSi2O7 were detected. The coefficient of thermal expansion can be adjusted between 9.3 and 12.5 × 10−6 K−1, depending on the thermal treatment. An increasing crystallization temperature leads to an increase in the coefficient of thermal expansion. Sealing experiments were performed on Crofer 22 APU in inert atmosphere to prevent the joint from forming BaCrO4. Strong interfacial reactions occur which, depending on the processing temperature, lead to the formation of metallic nickel particles near the interface. The mechanism of this reaction is described and discussed. Sealing temperatures between 815 and 965 °C, lying in the range of the working temperature of high-temperature reactors, were applied.

High thermal expansion of crystallized glasses in the system BaO–ZnO–NiO–SiO2

Crystallizing glasses in the system BaO–ZnO–NiO–SiO2 were studied with respect to the glass formation, crystallization and thermal expansion behavior. A maximum NiO concentration of 8.8mol% was reached in the glasses. The high thermal expansion phase BaZn2Si2O7 and the solid solutions BaZn2−xNixSi2O7 derived hereof can be crystallized from the prepared glasses. The incorporation of NiO in the solid solution strongly increases the transition from the low to the high temperature phase. The introduction of NiO into the solid solution was studied, using ultraviolet–visible-near-infrared spectroscopy. Phase transitions were analyzed using in situ high-temperature X-ray diffraction and dilatometry. The introduction of NiO in the as mentioned phases led to a thermal expansion coefficient in the range from 11.1 to 17.2×10−6K−1. In contrast to other crystallized sealing materials, the thermal expansion coefficient is nearly constant over a wide temperature range (25–1000°C). Furthermore, it is shown, that the thermal expansion behavior of the multiphase glass ceramics can be predicted from the thermal expansion of the different ceramic phases. The crystallizing glass may be suitable as sealing material for components with high coefficients of thermal expansion such as ferritic stainless steels or nickel alloys.