MgO Al2O3 SiO2 Glass Research Articles

Effect of TiO2 on crystallization and mechanical properties of MgO–Al2O3–SiO2 glasses containing P2O5

MgO–Al2O3–SiO2 glass-ceramics have been widely used in military, industrial, and construction applications. The nucleating agent is one of the most important factors in the production of glass-ceramics as it can control the crystallization temperature or the grain size. In this study, we investigated the effect of replacing P2O5 with different amounts of TiO2 on the crystallization, structure, and mechanical properties of an MgO–Al2O3–SiO2 system. The crystallization and microstructure were investigated by differential scanning calorimetry, Raman spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The mechanical properties were investigated by measuring the Vickers hardness, Young's modulus, and fracture toughness. The results showed that adding TiO2 favored the precipitation of fine grains and significantly increased the Vickers hardness, Young's modulus, and fracture toughness of the glasses. Introducing an appropriate amount of TiO2 can make a glass structure more compact, promote crystallization, and improve the mechanical properties of MgO–Al2O3–SiO2 glass-ceramics.

Mixed alkaline earth effect on the structure and elastic modulus of CaO–MgO–Al2O3–SiO2 glasses: A molecular dynamics simulation

The influence of mixed alkaline earth effect on the atomic structure and elastic modulus of the CaO–MgO–Al2O3–SiO2 glasses were studied by molecular dynamics simulation. The elastic modulus values obtained from the simulation of uniaxial tension and stiffness tensor methods showed the same trend with the change of composition, while the simulated results of the former were closer to the measured data. The variation trend of Qn species obtained by the simulation and Raman spectroscopy was consistent. Ca and Mg cations were more inclined to form non-bridging oxygen when the Ca/Mg ratio exceeded 1, which damaged the tetrahedral connection and further reduced the degree of network polymerization. The ratio of non-bridging oxygen to tetrahedrally coordinated cations (NBO/T) used to characterize the degree of polymerization was found to have a linear relationship with the elastic modulus. In addition, the local cluster of modifier atoms was beneficial to increase the elastic modulus values.

Ultrahigh hardness Li2O–MgO–Al2O3–SiO2 glass–ceramics containing multiphase nanocrystals

AbstractLi2O–Al2O3–SiO2‐based glass–ceramics containing nanocrystals have attracted much attention due to their low expansion coefficient, good mechanical properties, for different applications, such as fire‐safe glass, dental materials, and electronic devices protectors. In current research, ultrahigh hardness Li2O–MgO–Al2O3–SiO2 glass–ceramics were prepared by conventional melt‐quenching and subsequent heat‐treatment method. MgO was introduced via Li2O substitution to change glass crystallization and mechanical properties. The differential scanning calorimetry analysis indicated the glass transition and crystallization temperatures increased with MgO/Li2O ratio increase, for better glass network connectivity from Raman spectra analysis. In addition, the main crystal phase changed from Li2SiO5 and LiAlSi4O10, to the combination of LiAlSi2O6 and MgAl2Si4O12, and finally to MgAl2Si4O12. The Vickers hardness of glass–ceramics was highly dependent on MgO/Li2O ratios in glass components and heat‐treatment temperatures, corresponding with the crystal phases in glass–ceramics. The highest hardness could reach 9.34 GPa, which was much higher than traditional silicate glass–ceramics. The scanning electron microscope images confirmed the crystal diameters that varied from 30 to 100 nm and were determined by MgO content. Transmission electron microscope images and energy‐dispersive spectroscopy mapping also confirmed the precipitation of multiphase nanocrystals in glass matrix. The changes of glass structure, and corresponding crystal combinations in glass–ceramics resulting from MgO introduction, were responsible for the ultrahigh hardness glass.

Structural and dynamic properties of MgO–Al2O3–SiO2 glasses from molecular dynamics simulations and NMR

Magnesium aluminosilicate glasses have a wide range of applications in composite fiber reinforcements, aircraft windshields, due to their excellent chemical stability and mechanical properties. In this work, molecular dynamics simulations were used to obtain the short- and medium-range structural evolution of MgO/Al2O3 in MgO–Al2O3–SiO2 glass. The structural information was verified using a combination of combining Raman and Nuclear Magnetic Resonance (NMR) spectroscopy. The composition-structure-property relationship of the MgO–Al2O3–SiO2 glasses was constructed, using high-temperature viscosity results calculated by the Einstein-Stoke equation. The results showed that with the increase of MgO/Al2O3 ratio, Mg2+ changed from charge compensator to network modifier, which led to the gradual depolymerization of the glass network. Moreover, with the gradual replacement of Si by Al in the glass network, the disorder of the glass system increases, evidenced by the high-frequency Raman bands and the average chemical shifts of [AlOn] (n = 4, 5) shift linearly. In addition, we found that the de-polymerization led to a decrease in viscosity and an increase in fragility. The viscosity is negatively correlated with both the fragility and the atomic diffusion coefficient. It provides a theoretical basis for improving the preparation process of MgO–Al2O3–SiO2 glass and optimizing the glass properties.

Effects of BaO on crystallization, structure and dielectric properties of MgO–Al2O3–SiO2 glass–ceramics for LTCC applications

Cordierite-based glass–ceramics for LTCC applications were prepared by traditional sintering method. And the effects of BaO addition on the crystallization, structure and dielectric properties were investigated by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), X-ray diffractometer (XRD), dilatometer and impedance instrument. The DSC curves displayed that the glass transition temperature (Tg) slowly decreased with the BaO content increasing from 0 to 4 mol%. However, the onset of crystallization temperature (Tx) and crystallization peak temperature (Tc) showed the opposite trend. XRD analysis revealed that μ-cordierite was the major crystal phase for all the glass–ceramic samples, while α-cordierite precipitated as the minor crystal phase with BaO addition. As more BaO was added, the bulk density gradually increased, while the porosity decreased, indicating that BaO improved the sinterability of the glass samples. The dielectric constant showed minimum value with the addition of 2 mol% BaO, and the dielectric loss reached the minimum value when the content of BaO was 3 mol%. Wherein, after heated at 950 °C, glass–ceramics doped with 2 mol% BaO showed a dense structure, a relatively low dielectric constant (4.53), a low dielectric loss (2 × 10−3) at 1 MHz, and a proper CTE value (3.74 × 10–6/°C), which can be used to prepare LTCC materials.

Crystallization behavior and structure of CaO–MgO–Al2O3–SiO2 glass ceramics prepared from Cr-bearing slag

Glass ceramics were successfully prepared from Cr-bearing slag and the effect of the slag content (40–70 wt%) on the crystallization behavior and morphology of the glass ceramics was investigated. The values of the crystallization activation energy and crystallization index for crystal growth calculated using various methods were consistent. The crystallization activation energies of the samples exhibited in the range of 165–252 kJ/mol, and it tended to decrease with increasing Cr-bearing slag content. The crystallization index results indicated that the crystallization mechanism of the samples is bulk crystallization. Additionally, the principal phase composition of the glass ceramics with Cr-bearing slag contents of 40, 50, and 60 wt% was diopside; however, anorthite precipitated as a second phase when the slag content was 65% or 70%. Furthermore, the results suggesting that the CMAS glass ceramics could also be synthesized from Cr-bearing slag without using an additional nucleating agent.

Crystallization of CaO–MgO–Al2O3–SiO2 glass ceramic derived from blast furnace slag via one-step method

CaO–MgO–Al2O3–SiO2 glass ceramic was successfully prepared from blast furnace slag (BFS), which was the raw material, by the one-step thermal treatment. The comprehensive crystallization characteristic, phase transition, kinetic parameters of crystallization, microstructural evolution, and orientation relations between diopside and spinel were investigated using differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, and electron backscatter diffraction. Experimental results revealed that the beginning of crystallization and the end of nucleation overlapped. A thermal nucleation treatment applied in the special temperature region (791–840 °C) confirmed the coexistence of spinel and diopside by modern analytical methods, providing direct evidence of achieving bulk crystallization via the one-step method. Traditional spinel, which typically includes Fe, induces the formation of diopside. However, the spinel phase in this study did not contain sufficient Fe because the Fe content in the BFS was small. This suggests that the Mn-containing spinel phase served as the nucleation agent. The epitaxial growth mechanism was confirmed to be diopside {200}//spinel {111}, diopside [001]//spinel [112]. Moreover, glass ceramic crystallized at 980 °C has better corrosion resistance and has an acid and alkaline resistance of 96.64% and 99.41%, respectively. The one-step preparation of glass ceramic has profound significance in terms of energy saving and waste utilization. Furthermore, the results of this study have a guiding significance for the industrialization of the glass ceramic prepared by the one-step method.

Effects of Li2O replacing Na2O on glass forming, structure and properties of Na2O–MgO–Al2O3–SiO2 glass and glass-ceramics

Glasses and glass-ceramics in the xLi2O-(5-x)Na2O–20MgO–20Al2O3–54SiO2 system have been prepared by using a conventional melt quenching technology and subsequently a two-step heat-treating method. The effects of Li2O replacing Na2O on crystallization, structural and electrochemical properties of Na2O–MgO–Al2O3–SiO2 glasses and glass-ceramics are studied. The results reveal that the glass forming ability, the bending strength, micro-hardness and ionic conductivity of parent glasses firstly decrease and then increase as Li2O gradually replacing Na2O from 0 mol.% to 5 mol.% due to the disconnection of Si–O–Si network, the suppression of the mobile species and the electrodynamic interaction between the Na–O- and Li–O- oscillating electric dipoles. The main crystalline phase of glass-ceramics is cordierite and the ionic conductivity is three orders of magnitude higher than that glasses. The ionic conductivity of MgO–Al2O3–SiO2 glass-ceramics with 5.0 mol.% Li2O replacing Na2O reaches the highest ionic conductivity (3.4 × 10−6 S/cm), which provides a potential application for glass-ceramics as solid electrolytes in the future.

Evolution of crystal growth in MgO–Al2O3–SiO2 glass ceramics

A new explanation for crystal growth limitation in MgO–Al2O3–SiO2 glass ceramics is proposed using TEM and molecular dynamics simulation.

Structure and properties of CaO–MgO–Al2O3–SiO2 glasses obtained by vitrification of granite wastes

Structure and properties of CaO–MgO–Al2O3–SiO2 glasses obtained by vitrification of granite wastes

Crystallization of CaO–MgO–Al2O3–SiO2 glass prepared by float process

CaO–MgO–Al2O3–SiO2 (CMAS) glass was prepared by float process. The effects of TiO2 and heat-treatment on properties and crystallization behaviors of float glasses were investigated by atomic force microscope, differential scanning calorimeter, X-ray diffraction, electron probe microanalyzer, field emission scanning electron microscope and viscosity test. The results showed that CMAS parent glasses produced by float process had a high surface flatness (Ra is less than 80.1 ± 0.1 nm) and low tin penetration (14 μm). When the concentration of TiO2 increased from 3.51 to 5.01 wt %, the glass transition temperature was decreased, and the crystallization temperature was shifted from 913 to 887°C using differential scanning calorimeter. Field emission scanning electron microscope images showed that phase separation was discovered in CMAS parent glass (containing 3.51 wt % TiO2) treated at 670°C. Diopside as a major crystalline phase was precipitated in CMAS glass-ceramics nucleated at 700°C for 30 min and followed by crystallization at 910°C for 30 min.

Effect of the ZrO2 concentration on the crystallization behavior and the mechanical properties of high-strength MgO–Al2O3–SiO2 glass–ceramics

High-strength, colorless glass–ceramics in the MgO/Al2O3/SiO2 system with high concentrations of ZrO2 and a great potential for technical application, e.g., as high-performance hard disc substrates, are investigated. ZrO2 concentrations from 6 to 9 mol% are added to a stoichiometric cordierite glass to investigate the influence of the concentration of the nucleating agent on the crystallization behavior and the mechanical properties. The phase formation and the microstructure of the glass–ceramics are studied using X-ray diffraction and scanning electron microscopy including electron backscatter diffraction. It is shown that the volume crystallization of ZrO2, a low-/high-quartz solid solution (low-/high-QSS), and spinel is accompanied by the surface crystallization of indialite. This phase offers a much smaller coefficient of thermal expansion than the other crystal phases, which may induce high compressive stresses in the surface layer of the glass–ceramics after cooling and seems to result in excellent mechanical properties of the material. Biaxial flexural strengths of up to 1 GPa were measured. Higher ZrO2 concentrations reduce the surface crystallization of indialite and decrease the mean size of the crystals resulting in a higher translucency. The volume-crystallizing phases and the mechanical properties of the glass–ceramics do not seem to be significantly affected by the analyzed ZrO2 concentrations.

Fabrication, sintering and characterization of cordierite glass–ceramics for low temperature co-fired ceramic substrates from kaolin

Non-stoichiometric α-cordierite glass ceramic doped with H3BO3 and NH4H2PO4 as additives has been fabricated successfully from sandy kaolin as low temperature co-fired ceramics (LTCC) substrate materials. The sintering and crystallization behaviors of the glass–ceramics were investigated by the differential scanning calorimetry, X-ray diffraction, and field emission scanning electron microscope. In addition, various physical properties were characterized, such as dielectric properties, thermal expansion and flexural strength. The results indicated that there was only onefold α-cordierite formed from MgO–Al2O3–SiO2 glasses in the temperature range from 875 to 925 °C. The glass–ceramics could been highly densified at any experimental temperature and they showed excellent properties: low dielectric constants in the range of 5.5–7.5, low dielectric losses in the range of 0.015–0.025, low coefficients of thermal expansion between 1.22–4.32 × 10−6 K−1 and applicable flexural strength at the level from 110 to 145 MPa. All of the performance qualified cordierite glass ceramic to be used as potential LTCC substrate.

Microstructural design of phlogopite glass-ceramics

Fluorophlogopite glass-ceramics in the MgO–Al2O3–SiO2 glass systems were crystallized by two stages thermal treatments. Obtained glass-ceramics were characterized by DTA, X-ray diffraction and scanning electron microscopy. The heat treated samples at 705°C/3 h + 1000°C/15 min showed 2570.32 ± 98 MPa microhardness. The effect of heat treatment and preparation methods on microhardness and microstructure were studied. The microstructure of samples showed phlogopite and forsterite phases and solved or soft edge in the semi-rod like crystals was recorded which can explain the small value of microhardness. The various microhardness were determined in the range between 1591.61 to 9610 ± 147 MPa.

Microstructure and photoluminescent properties of MgO–Al2O3–SiO2 silicate glass-ceramics doped with Eu3+ and Dy3+

The Eu3+/Dy3+-activated 5MgO–5Al2O3–90SiO2 (5MA–90S)/10MgO–10Al2O3–80SiO2 (10MA–80S) glass and glass-ceramics were prepared by the sol–gel method. The prepared 5MA–90S:Eu3+/Dy3+/10MA–80S:Eu3+/Dy3+ samples were characterized by the X-ray diffraction, high-resolution transmission electron microscopy, and photoluminescent spectra. After annealing at temperatures ≤900 °C, amorphous glass state was obtained. The higher the heating temperature (≥900 °C), the MgAl2O4 nanocrystals were formed. The luminescent behaviors of 5MA–90S:Eu3+/Dy3+/10MA–80S:Eu3+/Dy3+ glass and glass-ceramics with different heat treatment temperatures under λ ex = 351, 395 nm are studied. It is important and interesting that the color can be tuned through altering the composition and the heat temperature. The Eu3+/Dy3+-activated MgO–Al2O3–SiO2 glass and glass-ceramics were prepared by the sol–gel method. The prepared 5MgO–5Al2O3–90SiO2/10MgO–10Al2O3–80SiO2 glass and glass-ceramics were characterized by the X-ray diffraction, high-resolution transmission electron microscopy, and photoluminescent spectra. The luminescent behaviors of Eu3+-doped, Dy3+-doped, and Eu3+/Dy3+-co-doped 5MgO–5Al2O3–90SiO2/10MgO–10Al2O3–80SiO2 with different heat treatment temperatures and composition under λ ex = 351, 395 nm are studied.

Effect of molybdenum and tungsten oxides on nucleation and crystallization behaviors of MgO–Al2O3–SiO2 glasses

To investigate the effect of novel nucleating agents, this study investigates the crystallization behavior of a MgO–Al2O3–SiO2 glass with molybdenum or tungsten oxide addition. Under a reducing condition, crystals formed in the bulk of the supercooled liquids, whereas melting in air yielded only surface crystallization. The first crystalline phase precipitated inside the glass was enstatite and Mg–petalite in glasses doped with molybdenum and tungsten oxides, respectively, whereas the surface precipitate was cordierite. Molybdenum oxide yielded a finer microstructure of the glass-ceramic than tungsten oxide. Some fractions of the nucleating agents were considered to be reduced to metallic states and dispersed through the glasses, providing heterogeneous nucleating sites for enstatite and Mg–petalite.

Effect of Fe2O3 on non-isothermal crystallization of CaO–MgO–Al2O3–SiO2 glass

The crystallization behavior and kinetics of CaO–MgO–Al2O3–SiO2 (CMAS) glass with the Fe2O3 content ranging from zero to 5% were investigated by differential scanning calorimetry (DSC). The structure and phase analyses were made by Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). The experiment results show that the endothermic peak temperature about 760 °C is associated with transition and the exothermic peak temperature about 1000 °C is associated with crystallization. The crystallization peak temperature decreases with increasing the Fe2O3 content. The crystallization mechanism is changed from two-dimensional crystallization to one-dimensional growth, and the intensity of diopside peaks becomes stronger gradually. There is a saltation for the crystallization temperature with the addition of 0.5% Fe2O3 due to the decomposition of Fe2O3. Si—O—Si, O—Si—O and T—O—T (T=Si, Fe, Al) linkages are observed in Fe2O3–CaO–MgO–Al2O3–SiO2 glass.

Crystallization mechanisms and properties of α-cordierite glass–ceramics from K2O–MgO–Al2O3–SiO2 glasses

Low temperature co-fired cordierite glass–ceramics were fabricated with K2O–MgO–Al2O3–SiO2 glasses. It was confirmed that α-cordierite crystals were precipitated from the glasses directly below 950°C and at the higher temperature additional leucite crystals were formed. The calculation of crystallization activation energy (Eα) for a onefold α-cordierite was 230.77–279.81kJ/mol; and the Eα of the concurrent precipitation of α-cordierite and leucite was 348.85–374.33kJ/mol, by Kissinger and Ozawa methods. Moreover, the Avrami constant (n) was calculated to be about 2 for onefold α-cordierite and to be 2.27–2.91 for the concomitant α-cordierite and leucite by the Augis–Bennett equation. Therefore, a bulk nucleation with one-dimensional crystal growth mechanism for α-cordierite was determined, which was verified by the results of Scanning Electron Microscope (SEM). The mechanisms for the concomitant α-cordierite and leucite changed from one-dimensional crystal growth to two-dimensional crystal growth with the variation of chemical composition. Furthermore, the α-cordierite glass–ceramics from the low-cost natural material exhibited good sintering capability below 950°C, low dielectric constant (6.0–8.0) and loss (below 0.01), matchable thermal expansion (4.40–5.63×10−6K−1) and applicable flexural strength, which were essential for the application as low temperature co-fired ceramic (LTCC) substrates.

Crystallization, densification and dielectric properties of CaO–MgO–Al2O3–SiO2 glass with ZrO2 as nucleating agent

The zirconium oxide effects on the crystallization and dielectric properties of CaO–MgO–Al2O3–SiO2 (CMAS) glass were investigated. The results showed that phyllosiloxide and anorthite crystallites were observed in sequence during sintering. For glass added with 8wt% ZrO2, homogeneously dispersed tetragonal ZrO2 crystallites were observed at 850°C. The as-prepared CMAS glass–ceramics exhibited a dielectric constant of about 6–7 and a dielectric loss below 0.005 at 100MHz. The dielectric properties of CMAS glass with 8wt% ZrO2 sintered at 850°C show a low dielectric constant of 6.65 and a dielectric loss tangent of about 2.5×10−3, which provides a promising candidate for LTCC applications.

Crystallization and microstructure of CaO–MgO–Al2O3–SiO2 glass–ceramics containing complex nucleation agents

The CaO–MgO–Al2O3–SiO2 (CMAS) glass–ceramics containing binary complex nucleation agents were prepared by body crystallization process, and the effects of complex nucleation agents on the crystallization and microstructure of CMAS glass–ceramics were investigated by differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The complex nucleation agents consist of constant fluorine (8.0wt.% CaF2) and different oxides (3.0wt.% TiO2, ZrO2, or P2O5). Compared with the CMAS glass with only CaF2, the respective addition of oxides promotes the crystallization of CMAS glass, especially TiO2 or P2O5. The addition of TiO2 or ZrO2 has no obvious effect on the compositions of main crystalline phases, while P2O5 results in the precipitation of pyroxene phase instead of diopside phase, with the existence of more small crystals. The CMAS glass–ceramic containing CaF2+TiO2 or CaF2+P2O5 achieves full body crystallization with high crystallization ratio, and has high hardness, good chemical resistance and water absorption.