Effect of BaO on thermal and mechanical properties of alkaline earth borosilicate glasses with and without Al2O3 (original) (raw)
Related papers
Optical and structural properties of BCBS glass system with and without alumina
Physica B: Condensed Matter, 2018
BaO-CaO-Al 2 O 3-SiO 2 (BCAS) glass and their derivatives have gained extreme importance for their high endurance to elevated temperatures and being suitable for various electrochemical applications. Two glass systems, one being 50mol% [SiO 2-B 2 O 3 ]-xBaO-(45x)CaO-5Al 2 O 3 called as BCBSA and another without Al 2 O 3 termed as BCBS were synthesized using melt quenching technique in the present work. Addition of ZnO and MgO as flux helped in melting them at 1300 ᴼC which is much lower than the usual melting temperature of these glasses [1-4]. Density of the quenched glasses was measured by Archimedes method and structural bond vibrations were confirmed through FTIR. UV Visible spectroscopy was used to determine band gap energy and confirm the insulating nature of the synthesized glasses. The samples were isothermally heated at 700 ᴼC, 800 ᴼC for 50 hours and at 900 ᴼC for 50 and 100 hours duration in air to allow the devitrification process to take place. The heat treated samples were analyzed by X-ray diffraction to identify the developed phases. Five Al 2 O 3 free samples synthesized at 1300 ᴼC by regular melt quenching technique were found to be devoid of the monocelsian phase. This is a detrimental phase for high temperature sealant applications as it has a very low coefficient of thermal expansion (CTE). Al 2 O 3 free BCBS glasses, properties of which are being reported for the first time and glasses with low BaO concentrations are found to meet the requirements for high temperature applications as sealants in Solid Oxide Fuel Cell (SOFC).
Alkaline Earth Based Borosilicate Glasses as Sealants in Solid Oxide Fuel Cell Applications
Silicon, 2019
Alkaline earth based glasses of composition 35AO-50B 2 O 3-15SiO 2 (A = Ba, Ca, Sr) was prepared by conventional melt quenching technique. Density of the glasses was measured using Archimede's method. X-ray diffraction patterns confirmed the amorphous nature of the glasses. This result was supported by scanning electron microscope (SEM) image. The structure of the glasses was investigated by FT-IR spectroscopy. FT-IR spectrum revealed the characteristic bands due to various borate and silicate structural units. FT-Raman spectroscopy was used to investigate the characteristic bands of these glasses and its changes due to the presence of various alkaline earth metals. The microhardness of the glass samples was measured by indentation technique. Microhardness of all glasses were high (6.9-7.1) GPa, reflecting higher bond strength. The coefficient of thermal expansion (CTE) were measured and lie within the range (8-10) × 10-6o C −1 , which was in good agreement with that of the other SOFC components.
Effect of Calcination Temperature and Time on Synthesis of BaO-CaO-Al 2 O 3 -SiO 2 Glass
Materials Today: Proceedings, 2018
Alkaline-borosilicate glass of a particular composition was prepared. 30mol%BaO-15CaO-05Al 2 O 3-40SiO 2-10B 2 O 3 glass system mix was calcined at different temperatures, from 300 °C to 400 °C for varying number of hours from 0 to 7 hrs. X Ray Diffraction (XRD) and Thermo Gravimetric Analysis (TGA) studies were conducted on non calcined and calcined powders. Conversion of H 3 BO 3 to B 2 O 3 was observed from XRD studies and increase in thermal stability was confirmed from thermal analysis study.
2002
The viscosity and thermal expansion of binary alkali borate glasses containing lithium, sodium and potassium oxides obtained by different glass melting conditions were studied. Glasses of the following compositions were chosen as objects for this study (mol%): 5·5R2O.94·5B2O3, 15R2O.85B2O3, where R =Li, Na, K and 25Na2O.75B2O3. By varying times of melting from 1 up to 4 h and by using remelting under vacuum the glasses of the same composition with different water contents were obtained. Hydroxyl concentrations in studied glasses were estimated by an absorption spectroscopy in near infrared region. Thermal dependencies of viscosity were determined by the beam bending method in the range of viscosity from 10 10 up to 10 13 dP s. Thermal expansion coefficients in the range of temperatures below and above glass transition and glass transition temperatures at cooling were determined by using the hysteresis dilatometer curves of studied glasses. It was found that the glasses investigated ...
Glass samples with the molecular formula (mol%): (30+x) SiO2–(10−x)B2O3–5Al2O3–54Na2O–1MnO2 where x=0, 5, 7·5 and 10 mol% were prepared. The density, glass forming ability, fragility, Vickers hardness and magnetic susceptibility were measured and the results were used to investigate the changes caused by the replacement of boron oxide by silicon oxide. It was found that the density, glass forming ability, fragility and Vickers hardness at first increase at 5 mol% B2O3 (35 mol% SiO2) and then decrease at 2·5 mol% B2O3 (37·5 mol% SiO2) and increase again with increasing SiO2. The replacement of B2O3 by SiO2 increases the concentration of nonbridging oxygens and changes the ratio between BO4 and BO3. The higher density, glass forming ability and fragility of the sample containing 5 mol% B2O3 is due to the ratio between B2O3 and Al2O3 which equals 1, causing BO3 to change to BO4. The magnetic susceptibility increases as the silicon oxide content increases up to 37·5 mol% and then decreases.
Sealing performance in solid oxide cell (SOC) stacks and the devitrification process of commercially available alkaline earth boroaluminosilicate glasses containing 48-61 mol% SiO2, 18-28 mol% CaO, 1-7 mol% MgO, 7-10 mol% Al2O3, 1-11 mol% B2O3 plus minor amounts of Na2O, K2O, FeO and TiO2 were investigated and quantified through analysis of phase assemblages as function of heat treatments above the glass transition temperatures using the electron microprobe and powder X-ray diffraction. For two of these glasses devitrification behavior was compared to the devitrification behavior of similar glasses produced in the laboratory. Glasses were characterized after annealing in air at 800 °C and 850 °C for up to 6 weeks. Even though the glasses lie within a relatively narrow compositional range, sealing performance and the resulting microstructures differed significantly. Best thermomechanical properties was developed in one of the laboratory-produced glasses, MCAS, which may be applied in SOC-stacks by allowing for a slow solidification in the range 750-800 oC followed by crystallization at or slightly above 800 oC. The relatively high thermal expansion coefficient (CTE) from RT-800 oC, 11 10-6 K-1, which was developed over ~1000h at 800 oC, depends mainly on the formation of cristobalite and quartz as well as the presence of a residual glass phase. The glass ceramic sealant appears relatively stable over time, except for a slow transition of cristobalite to quartz, and can possibly show self-healing behavior if later brought close to 850 oC. Devitrification led to increases of the thermal expansion coefficients in all other glasses tested, but did not reach levels interesting for SOC-stack sealing. The devitrification process and formation of crystalline phases from commercial alkaline earth boroaluminosilicate glasses containing 48-61 mol% SiO2, 18-28 mol% CaO, 1-7 mol% MgO, 7-10 mol% Al2O3, 1-11 mol% B2O3 plus minor amounts of Na2O, K2O, FeO and TiO2 were quantified through analysis of phase assemblages as function of heat treatments above the glass transition temperatures using the electron microprobe and powder X-ray diffraction. Treatments at 800 °C and 850 °C lasted up to 6 weeks. Results indicate that devitrification was strongly activated through presence of heterogeneous nucleation, and that the growth mechanism gradually changed from three-dimensional growth at the onset of devitrification towards one-dimensional growth in later stages, when heterogeneous nucleation was absent or less dominating. Most glasses developed entangled and fibrous microstructures with little or no residual glass phase, which are adequate for rigid sealants, and only one of the laboratory analogue glasses, MCAS, developed microstructures with both more equiaxed grains and a considerable amount of residual glass phase, which may be adequate for more compliant and self-healing sealants as often required in SOC-applications. Even though the glasses lie within a relatively narrow compositional range, resulting phase assemblages differed significantly. Anorthite (plagioclase) developed as the main crystalline phase in all samples together with pyroxene (or pyroxenoide) and cristobalite. Calcium-magnesium-silicate pyroxene (diopside) was in a large part replaced by the calcium-silicate pyroxenoid (wollastonite) in the samples where the mol-proportion MgO:CaO was 1:5 or lower. In samples with a very low MgO proportion and consequently a high CaO proportion, calcium metaborate and calcium aluminum borosilicate (okayamalite) crystallized among the main phases and these glasses crystallized completely within the period of heat treatment. Although cristobalite is metastable at the annealing temperatures, both α and β forms were rapidly formed in most of the samples, likely due to kinetic reasons. The presence of the latter is explained by the stabilization effect of Al and B substitution for Si compensated by Ca stuffing in the structure. The stuffed cristobalite transformed with time to quartz (at 800 °C) or quartz plus tridymite (at 850 °C). Boron was incorporated in the first crystallizing phases, especially diopside, substituting for Al and Si, but the so established substitution partly disappeared with time during the heat treatment.
We have explored the effects of lanthanum oxide (La 2 O 3 ) on the properties of barium-free SrO-CaO-ZnO-B 2 O 3 -SiO 2 glass system varying its content from 0 to 6 mol%. The coefficient of thermal expansion and glass transition temperature of the glasses are found to be in the ranges 10.6-10.8 × 10 −6 /K (50-600°C) and 650-690°C respectively. Differential scanning calorimetric studies revealed an increase in crystallization peak temperature and thermal stability of the glasses up to 4 mol% and then decrease on further addition. A monotonic increase in characteristic shrinkage temperature of glass powder compact is observed on addition of La 2 O 3 as revealed in the heating stage microscopic study. X-ray diffraction studies revealed reduced crystallization peak intensity in La 2 O 3 added glasses. Fourier transformed infrared spectra disclosed that the addition of La 2 O 3 stabilized the glass structure by reducing the number of non-bridging oxygens. Vickers micro hardness of the glasses varied in the range 2.6-5.6 GPa. Scanning electron microscopy revealed the formation of particulate nature of microstructures in parent glass which is not observed in the La 2 O 3 added glasses. Activation energy of crystallization has increased from 331 to 361 kJ/mol determined by Kissinger and Augis-Bennett models. Above properties of these glasses clearly advocate their applicability as solid oxide fuel cell sealants.
2018
Structural integrity and reliability of sealing materials for planar type solid oxide fuel cells (pSOFCs) is key to attaining the required functionality and subsequent commercialisation of such fuel cells. In this thesis a number of different series of alumino-borosilicate glasses containing alkaline earth modifiers, as well as ZnO and La2O3 are studied as potential sealant materials. The glass ceramics derived from these glasses were also studied. Vickers hardness indentation was used to assess the hardness and indentation fracture toughness of these glasses and acoustic measurements were used to determine their moduli. The results reveal a decrease in mechanical properties with modifier additions in all the series except for increasing La2O3 in xSi(20-x)La(Sr) with little variation of mechanical properties in the case of xB(15-x)Zn (10BaO-(15-x)ZnO-15La2O3-5Al2O3-(10+x)B2O3-45SiO2 (X= 2.5, 5, 7.5, 10)) and xSi(20-x)Zn (10BaO-(20-x)ZnO-15La2O3-5Al2O3-10B2O3-(40+x)SiO2 (X=2.5,5,7.5)...
Influence of glass melting conditions on the viscosity and thermal expansion of alkali borate gla
The viscosity and thermal expansion of binary alkali borate glasses containing lithium, sodium and potassium oxides obtained by different glass melting conditions were studied. Glasses of the following compositions were chosen as objects for this study (mol%): 5·5R 2 O.94·5B 2 O 3 , 15R 2 O.85B 2 O 3 , where R =Li, Na, K and 25Na 2 O.75B 2 O 3 . By varying times of melting from 1 up to 4 h and by using remelting under vacuum the glasses of the same composition with different water contents were obtained.