SiO2 Glass Ceramics Research Articles

Influence of MgO–Al2O3–SiO2 additive on sintering behavior and microwave dielectric properties of Ba(Mg1/3Nb2/3)O3–MgO ceramics

In this work, MgO–Al2O3–SiO2 (MAS) glass ceramics were used as the liquid sintering aid to promote the sintering process of Ba(Mg1/3Nb2/3)O3–MgO ceramics. The influences of the MAS additions and the cooling rate on the sintering behavior, phase compositions, microstructure, and dielectric properties of the obtained ceramics were studied. The results showed that the addition of MAS significantly improved the sintering process of BMN-MgO ceramics. The sintering temperature of the MAS-added BMN-MgO samples was reduced from 1470 °C to 1300 °C, and the holding time was reduced from 10 h to 30 min. The BMN-MgO ceramics with 5 wt% MAS glass ceramics sintered at 1300 °C for 30 min with a cooling rate of 1 °C/min obtained excellent dielectric properties at 7.5 GHz: εr = 20.61, Q×f = 63,468 GHz, and τf = – 1.72 ppm/°C.

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.

Effect of the substitution of MgO with CaO on the structural and thermal properties of CaO–SrO–B2O3–SiO2 glass and glass-ceramics containing excess TiO2

Borosilicate glass-ceramics are promising materials for sealing applications in solid oxide fuel cells (SOFC). This work synthesized glass and glass-ceramics of the 18CaO–27SrO–10B2O3–45SiO2 composition containing 0, 2, and 4% TiO2 (mol) by conventional melting/quenching and characterized by structural and thermal techniques. The 11B-NMR and 29Si-NMR spectra indicate no significant change in the relative concentration of the tetrahedral (B-IV) and trigonal (B-III) boron populations of all glasses, with the presence of Q2, Q3, and Q4 species. The crystalline phases of CaSiO3, SrB2Si2O8, and Sr2SiO4 precipitated in all the compositions. The thermal expansion coefficients of the glasses and corresponding glass-ceramics are compatible with those of the other stack components, and their glass transition temperatures are below the operating temperature of SOFCs (≈ 800–950 °C), thus can provide a hermetic seal. The sintering temperature of the T2 and T4 glasses is lower than 1000 °C, an essential characteristic for their application. However, the T4 glass exhibited even better sintering characteristics, making it a potential candidate for sealing.

Microstructural control of CaO–Al<sub>2</sub>O<sub>3</sub>–SiO<sub>2</sub> glass-ceramics by the amounts of tungsten oxide and carbon added as nucleation agent sources

Microstructural control of CaO–Al2O3–SiO2 (CAS) glass-ceramics (GCs) bearing metastable CaAl2Si2O8, a layered crystal, from a parent glass having a single composition was achieved by increasing the amounts of WO3 and carbon used as sources of metallic W particle nucleation agents. The average crystal size increased from 9.3 to 49 µm when the amount of WO3 and carbon were increased fivefold in the preparation of CAS GCs. To investigate the effect of WO3 and carbon separately, glass cullet containing WO3 was mixed with glass batches containing carbon and then melted to form glass specimens with different amounts of WO3 and carbon. Upon crystallization of these glass specimens, the average crystal size increased from 9.0 µm to 43 or 49 µm when the amount of WO3 or carbon was increased fivefold, respectively. The results indicate that changing the amounts of WO3 and carbon is necessary to control the CAS GC microstructure.

Some features of the surface modification of MgO–Al2O3–TiO2–SiO2 glass and glass ceramics by Ag diffusion

Diffusion of Ag species into the surface layers of the MgO–Al 2 O 3 –TiO 2 –SiO 2 glass stimulates the crystallization processes therein during subsequent thermal treatment. It was found that the silver doping significantly increases the microhardness of glass and glass ceramics. The effect of the Ag diffusion and the subsequent high-temperature treatment (T > T g ) on the structure and luminescence properties of the MgO–Al 2 O 3 –TiO 2 –SiO 2 glass was studied. The thermal evolution, structure and properties of the glass and glass ceramics were investigated by the DSC method, XRD analysis and luminescence spectroscopy. It was found that the Ag diffusion into the surface layers leads to the formation of numerous different luminescent molecular Ag n clusters. The MgO–Al 2 O 3 –TiO 2 –SiO 2 glass and glass ceramics subjected to the Ag diffusion can operate as effective down-converters of the radiation demonstrating the effective transformation of UV and blue light into the radiation of red and NIR spectral range.

Eu3+-Tb3+-Tm3+ co-doped oxyfluoride glass with high quantum yield for a robust white LED color converter

BaF2–Al2O3–B2O3–SiO2 glasses and glass-ceramics doped with Eu3+-Tb3+ were fabricated as an inorganic color converter for white LEDs. The BaF2–Al2O3–B2O3 glass composition was modified by adding SiO2, and thermal and mechanical stability improved with increasing SiO2 content while maintaining a quantum yield (QY) as high as 91%. To realize white color coordinates, Tm3+ was additionally introduced at varying contents, and Eu3+ content was also controlled. Excellent chromatic properties, such as a pure white color coordinates (x = 0.33, y = 0.33) with a co-related color temperature of 5772K, and a color rendering index (CRI) of 91 under 370 nm excitation, were successfully achieved. After the glass was heat-treated at 600 °C to fabricate a glass ceramic, the glass-ceramics were mounted on top of a 370 nm UV-LED, successfully demonstrating a white LED with nearly pure white color coordinates and a high CRI of 86. The increased emission intensity in the glass-ceramic was attributed to the formation of BaF2 crystals which were investigated by X-ray diffractometer (XRD) and a transmission electron microscope with energy dispersive spectroscopy (TEM-EDS).

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.

Microstructural and residual stress effects on toughening of stoichiometric BaO.2SiO2 glass-ceramics

Barium disilicate (BaO.2SiO2=BS2) glass is one of the few stoichiometric glasses that nucleates internally, homogeneously via thermal treatment. This system has been scarcely assessed in microstructure-property studies. Here we address fracture strength and toughness (KIC) variation as a function of crystallized volume fraction and crystal size, as well as the possible effect of residual stresses (RS) in BS2 glass-ceramics (GCs) by independently varying these two microstructural parameters. KIC increased with spherulite size and crystallized volume fraction. KIC variation with crystallized volume fraction was similar for GCs with different crystal sizes. Combination of the current findings on BaO.2SiO2 (crystals under tensile RS) with previous studies of Li2O.2SiO2 GCs (compressive RS) indicates that crystallization of a tougher phase – not type of residual stress in the crystals – is the crucial parameter controlling fracture toughness and strength. These findings are quite useful to design novel strong and tough GCs.

Refinement of ZnAl2O4 crystal in ZnO–Al2O3–SiO2 glass-ceramics by application of thermoelectric coupling field

Transparent glass-ceramics based on ZnO–Al2O3–SiO2 (ZAS) glass system exhibit excellent optical and mechanical properties that are dependent on crystal grains. Gahnite (ZnAl2O4) was the main phase that crystallized in ZAS glass-ceramics via thermoelectric coupling treatment. The morphology and size of ZnAl2O4 crystal were controlled by the electric field strength. Introduction of thermoelectric coupling field led to the refinement and dispersion of large and agglomerated ZnAl2O4 crystal grains, which improved the transmission and Vickers’ hardness of the ZAS-based glass-ceramics. Theoretical calculations revealed that crystal phase is the area of low electric field strength, which resulted in the migration of Zn ions (Zn2+) from glass phase to the ZnAl2O4 crystal regions under the effect of thermoelectric coupling field. The decrease in the amount of Zn2+ in glass phase further limited its grain growth, and refinement of ZnAl2O4 grains was achieved. This research shows an efficient and rapid approach to refine grains in ZAS glass-ceramics by application of thermoelectric coupling treatment.

Physical and structural characteristics of sol–gel derived CaO–B2O3–SiO2 glass-ceramics and their dielectric properties in the 5G millimeter-wave bands

In this study, sol–gel derived CaO–B2O3–SiO2 glass-ceramics with a set B2O3 content of 22.2 mol% and CaO/SiO2 ratios ranging between 0.15 and 0.27 were used for low-temperature cofired ceramic applications in the 5G millimeter-wave bands. X-ray diffraction analysis, scanning electron microscopy, Fourier-transform infrared spectroscopy, and Raman spectroscopy data indicated that, unlike the typical CaO–B2O3–SiO2 glass-ceramics prepared via melting resulted in the presence of calcium silicates, the CaO–B2O3–SiO2 glass-ceramics in this study comprised only an amorphous phase containing different amounts of CaB2O4 crystallites depending on the CaO/SiO2 ratio. Among the formulations evaluated, the 14.5CaO‒22.2B2O3‒63.3SiO2 glass-ceramic sintered at 950 °C exhibited a dielectric constant of 4.33 and a dielectric loss of 0.0012 at 60 GHz, which conferred its low signal propagation delay and low signal attenuation in applications. In addition, the electrical resistivity, breakdown strength, thermal conductivity, and coefficient of thermal expansion of the 14.5CaO‒22.2B2O3‒63.3SiO2 glass-ceramic were 1.72 × 1012 Ω cm, 15.49 kV/mm, 1.70 W/mK, and 4.1 ppm/°C, respectively. The 14.5CaO‒22.2B2O3‒63.3SiO2 glass-ceramic exhibited excellent insulating properties, facilitating its use as substrate material; moreover, its thermal properties matched those of Si and GaAs.

Effect of ZnO on the structural, physio-mechanical properties and thermal shock resistance of Li2O–Al2O3–SiO2 glass-ceramics

The composition of lithium aluminosilicate (LAS) with different zinc oxide-magnesium oxide (ZnO–MgO) contents that ranged from 0 to 1.45 wt percent (wt%) was investigated to determine the thermal shock resistance properties of the glass-ceramics. The LAS glasses were melted in an alumina crucible at 1550 °C for 5 h, and the green compact samples were then heat-treated at 1100 °C for 3.5 h. The presence of zinc oxide (ZnO) in the compositions did not change the major crystal phase of β-spodumene. However, the addition of ZnO shifted the pronounced peak to a lower angle and increased the percentage of crystallinity from 55% to 59%. Additionally, the function of ZnO in LAS glass-ceramics as the network modifier was confirmed through Fourier Transform Infrared Spectroscopy (FTIR) analysis. The physio-mechanical properties were improved when 1.45 wt% ZnO was added to the LAS glass-ceramics. The results showed increased density (2.42 g/cm3), low porosity (0.85%), high flexural strength (125.23 MPa), and low coefficient of thermal expansion (25–800 °C) (CTE(25–800 °C)) value of 1.73 × 10−6 °C−1. Meanwhile, the thermal shock resistance properties evaluation of the LAS glass-ceramics at different ZnO contents were conducted at different thermal shock temperatures of 200 °C, 500 °C, and 800 °C. The critical temperature of the LAS specimens with 1.45 wt% ZnO demonstrated the ability to withstand a thermal shock at 800 °C while preserving 87% of their initial strength of 108.40 MPa, exemplifying the best LAS glass-ceramics properties for rapid high-temperature change applications.

Rapid preparation of low thermal expansion transparent LAS nanocrystalline glass by one-step thermoelectric treatment

The Li2O–Al2O3–SiO2 (LAS) glass ceramics are prepared by one-step thermoelectric treatment. The influence of thermoelectric treatments on LAS glass-ceramics were studied. The crystal phase composition and microstructure of the LAS glass-ceramics were investigated by DSC, SEM, XRD and FTIR. Moreover, the thermal expansion performance and light transmittance of LAS nanocrystalline glass were characterized. The results show that low-expansion transparent LAS nanocrystalline glass can be produced in a short time by thermoelectric treatment. The free energy of nucleation and the degree of polymerization of the glass network are reduced by the electric field. The key is that the electric field polarizes Ti and Zr ions at the crystallization temperature, so that the crystal nuclei repel the same poles. This allows uniform crystal distribution, promotes crystallization and reduces one-step crystallization of crystal agglomeration. This proves that the rapid preparation of nanocrystalline glass by the one-step method is feasible, and provides a reference for the future one-step processing of glass-ceramics.

The effect of TiO2 and B2O3 on sintering behavior and crystallization behavior of SrO–BaO–B2O3–SiO2 glass-ceramics

To explore the influence of TiO2 and B2O3 contents on the sintering behavior and crystallization of SrO–BaO–B2O3–SiO2 glass-ceramics, the glass-ceramics with different TiO2/B2O3 ratios were prepared by sintering at 800 and 850 °C for 10 min. The results showed that the glass transition temperature and sintering temperature increased with increasing the TiO2/B2O3 ratio. The average bridging oxygen number decreased from 2.44 to 2.07, which revealed that the polymerization degree of the glass-ceramics decreased. With increasing the TiO2/B2O3 ratio, the crystallinity of the glass-ceramics and the homogenization of grains size were improved, and the precipitation of the SrTiO3 phase was promoted. The sample with a TiO2/B2O3 ratio of 0.62, which achieved excellent densification sintered at 850 °C for 10 min, showed a dielectric constant of 18.11, a dielectric loss of 3.93 × 10−3, and a thermal expansion coefficient of 10.04 × 10−6 K−1, indicating that the SrO–BaO–B2O3–SiO2 glass-ceramics have great potential in the application of low-temperature cofired ceramics.

Investigation on crystallization behavior, structure, and properties of Li2O–Al2O3–SiO2 glasses and glass-ceramics with co-doping ZrO2/P2O5

Li2O–Al2O3–SiO2 (LAS) glasses and glass-ceramics with co-doping ZrO2/P2O5 were prepared by the traditional melt quenching method and nucleation-crystallization process in this study. The effect of ZrO2/P2O5 co-doping on crystallization behavior, structure, and properties of the LAS glasses and glass-ceramics was discussed. The results show that the LAS glass ZP/0.5 exhibits better properties as compared to the other LAS glasses. As for the LAS glass-ceramics, ZrO2/P2O5 with mass ratios of 0–1 have little effect on the crystallization behavior. However, with the ZrO2 content increases to 4 wt% (ZrO2/P2O5 with a mass ratio of 2), an effective crystallization promotion behavior is found. Under a crystallization temperature of 950 °C, the LAS glass-ceramic ZP/2 shows improved properties, including lower density (2.526 g/cm3), higher Vickers hardness (7.23 GPa) and bending strength (94 MPa), and excellent acid and alkali-resistance (4.12 and 5.32 × 10−5 g/cm−2 h).

Crystallization, structure, and properties of TiO2-ZrO2 co-doped MgO-B2O3-Al2O3-SiO2 glass-ceramics

TiO2–ZrO2-codoped MgO–B2O3–Al2O3–SiO2 glass-ceramics were prepared using the traditional melting method. The effects of replacing TiO2 with ZrO2 on the glass stability (GS), crystallization behavior, structures, and properties of the obtained samples were studied. Results showed that the addition of ZrO2 increased the GS, which decreased the crystallization ability of the samples. When the heat treatment temperature was increased from 900 °C to 1000 °C, the mullite and quartz phases first precipitated in the glass matrix, and then converted into cordierite. Because of the low solubility of TiO2 and ZrO2 in this glass system, the rutile and zircon phases will precipitate from the parent glasses. Owing to changes in the composition and structure of the samples, the density and Vickers hardness increased, while the coefficient of thermal expansion of the samples first decreased and then increased when TiO2 was replaced with ZrO2.

Scintillation Properties of Non-doped and Pr-doped BaO–B2O3–SiO2 Glasses and Glass-ceramics

Scintillation Properties of Non-doped and Pr-doped BaO–B2O3–SiO2 Glasses and Glass-ceramics

Effect of SiO2/BaO ratio on sintering behavior, crystallization behavior, and properties of SrO–BaO–B2O3–SiO2 glass-ceramics

SrO–BaO–B2O3–SiO2 glass-ceramics with a high dielectric constant and low dielectric loss were prepared. The influence of the SiO2/BaO ratio on the sintering behavior, crystallization behavior, and properties were systematically investigated. The results showed that the increasing amount of liquid phase from increasing the SiO2/BaO ratio promoted sintering, resulting in an initial decrease in the sintering activation energy. However, the viscosity of the liquid phase continued to increase, leading to an increase in the sintering temperature and sintering activation energy when the SiO2/BaO ratio reached 0.90. As the SiO2/BaO ratio increased, the fraction of the primary phase BaSi2Al2O8 increased, and its grains grew; the minor phase SrTiO3 was suppressed, resulting in changes in the properties of the glass-ceramics. The sample with a SiO2/BaO ratio of 0.69, which was sintered at 850 °C for 10 min, showed excellent properties: a coefficient of thermal expansion (CTE) of 10.63 × 10−6 K−1 (25–500 °C), a dielectric constant (ϵr) of 16.24 (1 MHz), a dielectric loss (tanδ) of 3.39 × 10−3 (1 MHz), a flexural strength of 138.80 MPa, and a quality loss of acid corrosion of 1.06 × 10−4 g mm−2. The results indicated that the SrO–BaO–B2O3–SiO2 glass-ceramics used in this study have great potential for low-temperature co-fired ceramics applications.

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.

Studies on the local structure and spin Hamiltonian parameters for V4+ in Na2 O-PbO-Bi2 O3 -SiO2 glass ceramics.

The local structure, d-d transition band, and spin Hamiltonian parameters (SHPs) are theoretically studied for the V4+ probe in Na2 O-PbO-Bi2 O3 -SiO2 (NPBS) glass ceramics containing V2 O5 dopant with various concentration x (0 ≤ x ≤ 5 mol%) by using the perturbation formulas of the SHPs for tetragonally compressed octahedral 3d1 clusters. The first decreasing (or increasing) and then increasing (or decreasing) d-d transition band (= 10 Dq ) and hyperfine structure constants A// and A⊥ (or g factors g// and g⊥ ) with x can be suitably simulated with the similarly varying Fourier type concentration functions of cubic field parameter Dq , covalence factor N, core polarization constant κ, and reduction factor H (or relative tetragonal compression ratio ρ), with the minima (or maxima) at the middle concentration x = 3 mol%, respectively. The above concentration variations of SHPs and the related quantities may originate from the modifications of local crystal field strength, tetragonal compression, and electron cloud distribution near the impurity V4+ with x, corresponding to the highest [V4+ ]/[V5+ ] ratio at 3 mol%. Present studies would be helpful to explore novel sodium lead bismuth silicate glass ceramics by modifying the concentration of V2 O5 dopant.