CaO Al2O3 SiO2 Glass Research Articles

Radiation Shielding Properties of Aluminosilicate Glass Systems using Phy-X Software

In this work, we studied the radiation shielding properties of aluminosilicate glasses with constant SiO2 content. By applying Phy-X software, we calculated different radiation attenuation factors for the chosen glasses. The linear attenuation coefficient (LAC) for the chosen CaO–Al2O3–SiO2 glass systems showed an exponential decrease as the energy changes from 0.015 to 15 MeV. For the glass with composition of 35CaO-5Al2O3-60SiO2, the LAC decreases from 29.80 to 1.279 cm-1 between 0.015 and 0.05 MeV. The LAC decreases with the increase in the Al2O3 content. The minimum LAC is found for the glass with the composition of 20CaO-20Al2O3-60SiO2. The effective atomic number (Zeff) was reported, and we found that the highest Zeff is occurred at 0.015 MeV and varied between 14.55 and 16.09. The Zeff decreases when we replaced the CaO by Al2O3. The half value layer was reported and we discussed the impact of the density of the glasses on the HVL values. In the low energy range, the HVL values are small and the different compositions have close HVL. For E>0.08 MeV, the HVL is higher than 1 cm for all glasses, while for E> 0.2 MeV, the HVL becomes higher than 2 cm for all glasses. The glass with composition of 35CaO-5Al2O3-60SiO2 has better attenuation performance than the other glasses in this study.

Microstructure and mechanical properties of SiC joint using anorthite based glass-ceramic and first principles calculation of joint interface

A specialized CaO–Al2O3–SiO2 (CAS) glass-ceramic was innovated to join SiC ceramics. The crystallization kinetics of the CAS glass was studied, revealing distinct anorthite precipitates in the CAS glass-ceramic. The impact of process parameter variations on microstructure and mechanical properties was studied. It revealed that post-joining crystallization heat-treatment could change the size and the content of crystals and significantly improve the shear strength of the joint. It was duly observed that a remarkable shear strength of 86 MPa was achieved when the joint was formed at the temperature of 1450 °C and treated at 1050 °C for crystallization. Notably, this exceptional mechanical endurance remained impressively high, maintaining a value of 85 MPa at 800 °C. Based on density functional theory calculations, it was confirmed that glass/C–SiC (0001) has a stronger interface bond than glass/Si–SiC (0001), resulting in a reliable joining at the glass/C–SiC (0001) interface for CAS glass and SiC.

The Impact of Chemical Composition, Density and Thickness on the Radiation Shielding Properties of CaO–Al2O3–SiO2 Glasses

The Impact of Chemical Composition, Density and Thickness on the Radiation Shielding Properties of CaO–Al2O3–SiO2 Glasses

Effect of Vanadium Oxide on the Crystallization of CaO-Al2O3-SiO2 Glass.

This study investigated the effect of vanadium oxide on the crystallization of CaO-Al2O3-SiO2 (CAS) glass. Specifically, this study subjected CAS glass-ceramics (GCs) with precipitated hexagonal platy particles of metastable CaAl2Si2O8 (CAS GC-H), a layered crystal, that was prepared using metallic molybdenum (Mo) particles as nucleation agents. When the parent glass of CAS GC-H was crystallized with the addition of vanadium oxide in the 0.052-0.21 wt % range, the obtained platy particles of metastable CaAl2Si2O8 displayed an increase in the aspect ratio from 20 to 15 compared with conventional CAS GC-Hs. In addition, no crystallization occurred in the CAS glass with vanadium oxide in the 0.052-0.21 wt % range in the absence of metallic Mo particles. Meanwhile, a CAS glass containing 1.0 wt % vanadium oxide without the addition of metallic Mo particles showed the precipitation of metastable CaAl2Si2O8. Therefore, these results indicated that the aspect ratio of layered crystals in glass was controlled by the addition of a relatively small content of vanadium oxide, and a new nucleation agent for the precipitation of metastable CaAl2Si2O8 in CAS glass using a relatively high content of vanadium oxide was developed.

Mechanical, thermal, and structural investigations of chemically strengthened Na2O–CaO–Al2O3–SiO2 glasses

For a series of conventional soda-lime-silicate glasses with increasing Al2O3content, we investigated the thermal, mechanical, and structural properties before and after K+-for-Na+ion-exchange strengthening by exposure to molten KNO3. The Al-for-Si replacement resulted in increased glass network polymerization and lowered compactness. The glass transition temperature (Tg), hardness (H) and reduced elastic modulus (Er), of the pristine glasses enhanced monotonically for increasing Al2O3content.HandErincreased linearly up to a glass composition with roughly equal stoichiometric amounts of Na2O and Al2O3where a nonlinear dependence on Al2O3was observed, whereasHandErof the chemically strengthened (CS) glasses revealed a strictly linear dependence.Tg, on the other hand, showed linear increase with Al-for-Si for pristine glasses while for the CS glasses a linear to nonlinear trend was observed. Solid-state27Al nuclear magnetic resonance (NMR) revealed the sole presence of AlO4groups in both the pristine and CS glasses.23Na NMR and wet-chemical analysis manifested that all Al-bearing glasses had a lower and near-constant K+-for-Na+ion exchange ratio than the soda-lime-silicate glass. Differential thermal analysis of CS glasses revealed a “blurred” glass transition temperature (Tg) and an exothermic step belowTg; the latter stems from the relaxation of residual compressive stresses. The nanoindentation-derived hardness at low loads and <5 mol% Al2O3showed evidence of stress relaxation for prolonged ion exchange treatment. The crack resistance is maximized for molar ratiosn(M(2)O)/n(Al2O3)≈1for the CS glasses, which is attributed to an increased elastic energy recovery that is linked to the glass compactness.

Assessment of the Crystallization Process of CaO-Al2O3-SiO2 Glass Probed with Tb3+ Luminescence.

The ratio of the intensity of Tb3+ fluorescence at 543 nm because of an electric dipole transition (5D4–7F5) relative to that at 437 nm due to a magnetic dipole transition (5D3–7F4) was determined to be proportional to the amount of metastable CaAl2Si2O8 crystals precipitated in CaO–Al2O3–SiO2 glass. The present results indicate that Tb3+ luminescence can be used as a probe to evaluate the crystallization of glass.

Low-temperature hot-press sintering of AlN ceramics with MgO–CaO–Al2O3–SiO2 glass additives for ceramic heater applications

Aluminum nitride (AlN) is used a ceramic heater material for the semiconductor industry. Because extremely high temperatures are required to achieve dense AlN components, sintering aids such as Y2O3 are typically added to reduce the sintering temperature and time. To further reduce the sintering temperature, in this study, a low-melting-temperature glass (MgO–CaO–Al2O3–SiO2; MCAS) was used as a sintering additive for AlN. With MCAS addition, fully dense AlN was obtained by hot-press sintering at 1500 °C for 3 h at 30 MPa. The mechanical properties, thermal conductivity, and volume resistance of the sintered AlN–MCAS sample were evaluated and compared with those of a reference sample (AlN prepared with 5 wt% Y2O3 sintering aid sintered at 1750 °C for 8 h at 10 MPa). The thermal conductivity of AlN prepared with 0.5 wt% MCAS was 91.2 W/m∙K, which was 84.8 W/m∙K lower than that of the reference sample at 25 °C; however, the difference in thermal conductivity between the samples was only 14.2 W/m∙K at the ceramic-heater operating temperature of 500 °C. The flexural strength of AlN–MCAS was 550 MPa, which was higher than that of the reference sample (425 MPa); this was attributed to the smaller grain size achieved by low-temperature sintering. The volume resistance of AlN–MCAS was lower than that of the reference sample in the range of 200–400 °C. However, the resistivity of the proposed AlN–MCAS sample was higher than that of the reference sample (500 °C) owing to grain-boundary scattering of phonons. In summary, the proposed sintering strategy produces AlN materials for heater applications with low production cost, while achieving the properties required by the semiconductor industry.

Microstructure, mechanical and optical properties of MgAl2O4/MgAl2O4 joints bonded using CaO-Al2O3-SiO2 glass filler

Transparent MgAl2O4 ceramics were bonded by using CaO-Al2O3-SiO2 (CAS) glass filler. The CAS glass filler exhibited the same thermal expansion behavior as MgAl2O4 ceramic and excellent wetting ability on the surface of MgAl2O4 ceramic. When the cooling rate of 15 °C/min was used, no interfacial reaction was observed and the amorphous brazing seam could be obtained. However, low joining temperature (1250 °C) led to the formation of pores and high joining temperature (1400 °C) resulted in the formation of cracks. Furthermore, the slow cooling rate of 5–10 °C/min induced the crystallization of CaAl2Si2O8 and Mg2Al4Si5O18 due to the dissolution of MgAl2O4 substrate. The optimal flexural strength of 181–189 MPa was obtained when the joining temperature and cooling rate were 1300–1350 °C and 15 °C/min respectively. Moreover, the in-line transmittance of the joint at 1000 nm was 82.1%, which was slightly lower than that of MgAl2O4 ceramic (85.6%).

Structure and magnetic properties of Bi-doped calcium aluminosilicate glass microspheres

Abstract Bi-doped CaO–Al2O3–SiO2 glass microspheres with Ca2Al2SiO7 (gehlenite) composition were prepared by combination of solid-state reaction and flame synthesis. The concentration of Bi was 0.0, 0.5, 1 and 3 mol%. The chemical composition of prepared glass microspheres was determined by X-ray fluorescence (XRF). The structural and magnetic properties of prepared glass microspheres and their polycrystalline analogues were studied by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Raman spectroscopy and SQUID magnetometry. The closer inspection of glass microspheres surface by SEM confirmed smooth surface and revealed no features indicating presence of crystalline phases. All Bi-doped microspheres are X-ray amorphous, however in case of undoped microspheres XRD detected traces of crystalline gehlenite. XRD analysis of samples crystallized at 1273 K for 10 h revealed the presence of gehlenite as the main crystalline phase. The presence of gehlenite in crystallized samples were also confirmed by Raman spectroscopy. All samples (glass microspheres and their crystalline analogues) showed diamagnetic or weak ferromagnetic behavior at room temperature, whereas paramagnetic or weak ferromagnetic behavior was observed at 2 K.

Plasma-resistant characteristics according to sintering conditions of CaO–Al2O3–SiO2 glass coating layer

Plasma-resistant characteristics according to sintering conditions of CaO–Al2O3–SiO2 glass coating layer

Predicting CaO-(MgO)-Al2O3-SiO2 glass reactivity in alkaline environments from force field molecular dynamics simulations

In this investigation, force field-based molecular dynamics (MD) simulations have been employed to generate detailed structural representations for a range of amorphous quaternary CaO-MgO-Al2O3-SiO2 (CMAS) and ternary CaO-Al2O3-SiO2 (CAS) glasses. Comparison of the simulation results with select experimental X-ray and neutron total scattering and literature data reveals that the MD-generated structures have captured the key structural features of these CMAS and CAS glasses. Based on the MD-generated structural representations, we have developed two structural descriptors, specifically (i) average metal oxide dissociation energy (AMODE) and (ii) average self-diffusion coefficient (ASDC) of all the atoms at melting. Both structural descriptors are seen to more accurately predict the relative glass reactivity than the commonly used degree of depolymerization parameter, especially for the eight synthetic CAS glasses that span a wide compositional range. Hence these descriptors hold great promise for predicting CMAS and CAS glass reactivity in alkaline environments from compositional information.

Effect of CaF2 on fluorocarbon plasma resistance and thermal properties of CaO-Al2O3-SiO2 glasses

ABSTRACT The effect of CaF2 addition on plasma resistance and thermal properties of CaO-Al2O3-SiO2 (CAS) glasses was investigated. The amount of SiO2 and Al2O3 was fixed to 42.9 and 9.1 (in mol%), respectively, while total amount of CaO and CaF2 was 48 mol% and the ratios of CaO:CaF2 were changed from 10:0 to 8:2. As the amount of CaF2 of CAS glass increased, CF4/O2/Ar plasma etch rate of glass decreased proportionally. In case of sample with CaO:CaF2 = 8:2, its etch rate had 5.04 ± 0.14 ㎚/min, which was about 20 times lower than that of quartz glass and was improved by more than 25% compared to the glass without CaF2. All glass samples maintained the initial surface and roughness even after plasma etching. In addition, the glass transition (Tg), crystallization (Tc), and the first melting temperature (Tf1) temperatures decreased with the amount of increased CaF2. F− ion in CAS glasses not only enhances the plasma resistance but also facilitates glass melting and forming operations.

ZCAS-assisting low-temperature hot-press sintering of SiC ceramic for immobilizing simulated radioactive graphite

The safe treatment and disposal of high-level radioactive graphite is an essential challenge in the governance of irradiated graphite. SiC has an insurmountable defect in densification sintering at low temperatures, although it is an ideal host material for immobilizing high-level radioactive graphite. To solve this issue, we employ ZCAS (short for ZnO–CaO–Al2O3–SiO2 glass) as a sintering aid to prepare SiC-ZCAS composite ceramic with the relative density up to 98% by vacuum hot-press sintering. For investigating the optimum formula and technological conditions of (1-x) SiC-x ZCAS composite ceramic, the effects of synthesis and sintering process on preparation (1-x) SiC-x ZCAS (x = 25-40 wt%) composites were investigated in detail. The results show that the SiC-ZCAS composite powder with x = 25-40 wt% can be synthesized at 1350 °C for 2 h when the Si/C mole ratio is 1.05:1. The relative density, Vickers hardness, and thermal conductivity of SiC-ZCAS composites ceramic increase rapidly by increasing sintering temperature and pressure. However, these properties will display different effects from the increase in the content of ZCAS, such as continuous elevation of the relative density and dramatic depression of thermal conductivity. the Vickers hardness starts to decline when the content of ZCAS is 30 wt%. Considering the above mentioned, we can conclude that the 0.7SiC-0.3ZCAS composite ceramic has choiceness comprehensive properties when sintered at 1550 °C and 60 MPa for 1 h, with the relative density, Vickers hardness and thermal conductivity of 95.5%, 1084 (HV 10) and 7.104 W/m·k, respectively.

Corrosion resistance of CaO–Al2O3–SiO2 glasses used for flame spraying on concrete

Concrete components can severely suffer from corrosion during their service lifetime. To achieve higher durability, glass coatings can be applied onto the concrete surface for protection purposes. Current solutions for protection measures are either sticking thin glass panes onto the concrete or applying plastic layers using flame spraying. The aim of this work was to develop an optimised glass composition for protective layers, in order to be suitable for flame spraying on concrete. The main advantage of this process is the deposition of continuous and joint-free glass layers onto complex geometries. Dense glass layers provide a much higher corrosion resistance and lifetime compared to polymer layers. The challenge encountered by these glass coatings resides in the contact with strong acidic fluids on one side and with the alkaline concrete on the other. Therefore, a new glass appropriate for flame spraying has been developed. The composition of this glass is cheaper compared to established reference glass products while providing comparable alkaline resistance. As the acid resistance of this glass is not sufficient, in order to ensure the desired requirements of an adequate corrosion protection, a multilayer glass coating was developed, in which the first layer consists of the alkaline-resistant CaO–Al2O3–SiO2 glass and the second layer of an acid-resistant glass.

Density of MgO–Al2O3–SiO2, MgO–CaO–SiO2 and MgO–CaO–Al2O3–SiO2 glasses and the structural role of MgO

Density and molar volume of MgO–Al2O3–SiO2, MgO–CaO–SiO2 and MgO–CaO–Al2O3–SiO2 glasses have been correlated with the structure by following the change in type and concentration of structural units with composition. It is assumed that for (MgO+CaO)≥Al2O3 all Al atoms form AlO4 tetrahedra. The type of modified units of SiO2 (Q3 and Q2) are determined by the ratio [(MgO+CaO)−Al2O3]/SiO2. In the case of (MgO+CaO)<Al2O3, there is a fraction of Al2O3 that forms units based on the AlO3/2 formula. The entire SiO2 content would be in the form of Q4 units. Any of the structural units has its own constant volume that is independent of the type of glass. The agreement between calculated and experimental density and molar volume strongly suggests that MgO has only a modifier role in the studied glasses. Formation of assumed MgO4, MgO5 and MgO6 polyhedra can be due to change in coordination of oxygen, rather being looked as structural units.

Effect of crystallinity and microstructure on mechanical properties of CaO-Al2O3-SiO2 glass toughened by precipitation of hexagonal CaAl2Si2O8 crystals

In order to identify the most effective level of crystallinity and microstructure to increase the toughness of CaO–Al2O3–SiO2 glass with precipitated hexagonal-CaAl2Si2O8 crystals, we measured the fracture toughness and investigated the microcracking behavior of samples containing different amounts of the crystalline phase. The glass-ceramics were prepared in the range of 10–48 wt% crystallinity by changing the parent glass composition. Five glass compositions, xCaO–yAl2O3–zSiO2 wt% (x= = 25.6–22.7, y= = 18.0–28.1, z= = 56.4–49.2), were examined by Single Edge V-Notched Beam (SEVNB) method for fracture toughness measurement, and Vickers indentation tests for hardness measurement. Although the fracture toughness increased for a crystal content of up to 21 wt%, it remained constant at 21–40 wt%, and then started to decrease at 48 wt%. The Vickers hardness showed a minimum in the range of 21–35 wt% crystallinity. Microcrack formation around indentations was clearly observed in the same range of crystallinity. Also, non-elastic behavior was found at the same levels of crystallinity during bending tests for measurement of fracture toughness, with more fractured surface area. The microstructure of these glass-ceramics was characterized as a “house-of-cards” structure, suggesting that this microstructure was most effective at decreasing the brittleness of the glass by microcrack toughening.

Joining of SiC ceramics using CaO-Al2O3-SiO2 (CAS) glass ceramics

CaO-Al2O3-SiO2(CAS) glass ceramics were designed and prepared using a melt-quench approach. The coefficient of the thermal expansion (CTE) of the synthesized CAS (4.12 × 10−6 K−1) matched perfectly with that of the SiC ceramic (4.01 × 10−6 K−1). Thermal analysis of the CAS was conducted. Then the joining of the SiC ceramics by the CAS glass ceramics under various process parameters were conducted. The bonding temperature affects the fluidity of the CAS glass and the oxidation of the SiC substrate. The holding duration decides the infiltration of the CAS glass into the SiC substrate. The optimal bonding parameter is 1400 ℃/10 min and the corresponding highest shear strength of the SiC/CAS/SiC bonded joints in average was 56 MPa. Fracture observation was also conducted to help analyze the relationship between the interfacial microstructure and the joint strength. Finally, the formation mechanism of the SiC/CAS/SiC bonded joints was proposed.

3D microstructure and crack pathways of toughened CaO–Al2O3–SiO2 glass by precipitation of hexagonal CaAl2Si2O8 crystal

AbstractWe investigated CaO–Al2O3–SiO2 glass partially crystallized with molybdenum particles as nucleating agents. Microstructure of the material was characterized as a house‐of‐cards structure composed of plate‐like crystals. Microcracks propagated along the crystal plane parallel to the double layer of SiO4/AlO4 tetrahedrons separated by layers of calcium atoms. To investigate the fracture behavior of the hexagonal CaAl2Si2O8 crystals, molecular dynamics simulations were performed, which demonstrated that a crack can be easily triggered by shear deformation along the calcium layer. Additionally, once a crack was generated in the calcium layer, it propagated rapidly, whereas the crack perpendicular to the calcium layer hardly propagated. This simulated behavior is consistent with the experimentally observed cleavage behavior of the hexagonal CaAl2Si2O8 crystal. The experimental and simulation results effectively explained the non‐elastic fracture behavior of the material.

The effect of composition of plasma resistance of CaO–Al2O3–SiO2 glasses under Fluorocarbon Plasma with Ar+

This study investigated the plasma resistance of CaO–Al2O3–SiO2 (CAS) glass depending on composition. The glass compositions were selected by two methods; (1) glass compositions selected by conventional method around eutectic point and (2) known compositions in previous study (Choi et al., 2019). Also, the plasma resistance of each glass composition was examined by analyzing their surface microstructure and etching rate when the glasses were exposed to CF4/O2/Ar plasma gases.There was no statistical difference in plasma resistance between two compositions groups. The CAS glasses showed 5–10 times superior plasma resistance compared to sintered Al2O3 or sapphire, where the etching rate of the Al2O3 and CAS glasses is 76.06 and 6.77–18.42 nm/min, respectively. Within the selected glassification range of the CAS-based glass, it was determined that the Al2O3 component most significantly affected plasma resistance. Glass compositions using conventional method can be more advantageous for glass fabrication.

Synthesis and crystallisation kinetics study of nano-Al2O3 containing bio-active glass-ceramics

Bio-active glass-ceramics of CaO−Al2O3−SiO2 (CAS) system have been synthesized using nano-alumina and compared with the standard alumina based CAS glass system. The glass-ceramics samples were characterized by DTA, XRD, SEM-EDS, and FTIR. The crystallization behaviour and microstructure was determined for all the glass batches. With addition of nano alumina, the glass transition temperature (Tg) first decreases and then increases while the crystallization peak temperature (Tp) increases and activation energy (E), Avrami parameter (n) are independent. Avrami parameter values for all the glass batches are n≅ 3, it indicates two-dimensional crystal formation. Fluorapatite (FA) was the main crystalline phase as indicated from the XRD analysis.