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1.
Transparent glass-ceramics containing eucryptite and nepheline crystalline phases were prepared from alkali (Li, Na) aluminosilicate glasses with various mole substitutions of Al 2O 3 for SiO 2. The relationships between glass network structure and crystallization behavior of Li 2O–Na 2O–Al 2O 3–SiO 2 (LNAS) glasses were investigated. It was found that the crystallization of the eucryptite and nepheline in LNAS glasses significantly depended on the concentration of Al 2O 3. LNAS glasses with the addition of Al 2O 3 from 16 to 18 mol% exhibited increasing Q 4 (mAl) structural units confirmed by NMR and Raman spectroscopy, which promoted the formation of eucryptite and nepheline crystalline phases. With the Al 2O 3 content increasing to 19–20 mol%, the formation of highly disordered (Li, Na) 3PO 4 phase which can serve as nucleation sites was inhibited and the crystallization mechanism of glass became surface crystallization. Glass-ceramics containing 18 mol% Al 2O 3 showed high transparency ~84% at 550 nm. Moreover, the microhardness, elastic modulus and fracture toughness are 8.56 GPa, 95.7 GPa and 0.78 MPa m 1/2 respectively. The transparent glass-ceramics with good mechanical properties show high potential in the applications of protective cover of displays. 相似文献
2.
Nanocrystals doped transparent glasses or glass ceramics have shown promising tunable magnetic and magneto-optical performance. In this study, the Al 2O 3-induced in-situ crystallization of Gd 3Al 2Ga 3O 12 in tellurite glass was reported. 10–20 nm-cubic Gd 3Al 2Ga 3O 12 ( Ia3d space group) nanocrystals formed in tellurite glass with Al 2O 3 content ≤ 0.75 mol% by 400 °C-heat treatment. When Al 2O 3 content in glass was higher than 0.75 mol%, excessive Al 2O 3 triggered the crystallization of orthorhombic GdAlO 3 ( Pnma) in which the Gd and Al ions existed as octahedral GdO 8 and AlO 6 units at a temperature higher than 398 °C. The in-situ crystallization influenced the glass network structure, broke the linkage of tetrahedral TeO 4, and BO 4, and formed trigonal pyramids TeO 3 and BO 3 instead. At the same time, nuclear magnetic resonance spectra revealed the conversion of AlO 4→ AlO 6, GaO 4→ GaO 6, and the changes from bridging oxygen to non-bridging oxygen as well. From energy-dispersive X-Ray analysis, Gd 3+ clusters were observed, leading to the ferromagnetism of glass. Electron paramagnetic resonance spectra witnessed an enhancement of the Zeeman effect which is the reason for the improvement of Faraday rotation. Tellurite glass with 0.75 mol% Al 2O 3 after 400 °C-annealing (A75) showed a giant Verdet constant of 93 rad/T.m at 633 nm which is superior to most of the values from the literature. 相似文献
3.
Glass and in-situ nanocrystalline glass-ceramics of compositions 45SiO 2-25CaO-10Na 2O-5P 2O 5- xFe 2O 3-(15- x) MnO 2 are investigated for their magnetic and in-vitro bioactive properties. The ferrimagnetic character is observed in the high Fe 2O 3 containing in-situ nanocrystalline glass-ceramics. Saturation magnetization and coercivity increases with Fe 2O 3. After soaking in the simulated body fluid (SBF), the powdered as well as the bulk glasses and glass-ceramics are investigated using various characterization techniques. The presence of MnO 2 increases the leaching of Na + ions from the glasses and also attracts the Ca 2+ cations from the SBF as compared to Fe 2O 3 containing nano-crystalline glass-ceramics. It also increases the tendency to form hydroxyl apatite (HAp) layer. Microwave Plasma Atomic Emission Spectroscopy (MP-AES), Fourier Transform Infrared (FTIR) spectra, X-ray diffraction and Scanning electron micrographs (SEM) after soaking in the SBF confirm the HAp formation on the surface of all the glasses and glass-ceramics. Urbach energy also indicates the structural modifications on the surfaces of the glass and glass-ceramics after soaking in the SBF. 相似文献
4.
The effect of ZnO/K 2O (Z/K) ratio on the crystallization sequence and microstructure of lithium disilicate (Li 2Si 2O 5: LS2) glass-ceramics was carefully investigated for the SiO 2-Li 2O-K 2O-ZnO-P 2O 5 system. The Z/K ratios of precursor glasses were varied from 0 to 3.5 while the nucleating agent of P 2O 5 and glass modifiers of ZnO plus K 2O were fixed to have 1.5 and 4.5 mol% relative to LS2, respectively. For the samples prepared by two-stage heat treatments of 500 °C for 1 h and 800 °C for 2 h in air, the LS2 nucleation rate was increased with increasing the Z/K ratio due to the variation in crystallization sequence from type II (Li 2SiO 3: LS) to type I (LS + LS2) in addition to an amorphous phase separation in base glass. Consequently, with increasing the Z/K ratio, the LS2 crystalline phase within the glass matrix continuously changed from larger acicular ones to smaller equiaxed ones. 相似文献
5.
The sintering behavior of a Pb-free Bi 2O 3–B 2O 3–SiO 2 glass system was examined as a function of Bi 2O 3 content. The glass transition temperature and the crystallization temperature of the glasses decreased with different decreasing gradients as the Bi 2O 3 content increased. The change in temperature affected the sintering behaviors of the glasses. In the case of the 40 mol% Bi 2O 3 addition, large pore accompanied over-firing phenomenon was observed when the sample was sintered over the optimum sintering temperature. However, over-firing was not observed in the sample with 45 mol% of Bi 2O 3 because of the crystallized phases during sintering. When the Bi 2O 3 content was 50–55 mol%, the crystallization temperature became lower than the glass transition temperature, which resulted in the crystallization of glass and it hindered densification. 相似文献
6.
x ZnO- (100- x) B 2O 3 ( x = 45–64 mol%) glass-ceramics for ULTCC applications were prepared via the solid-state reaction method, and their crystallization behavior, sintering mechanism, microstructure and microwave dielectric properties were investigated. In this work, the zinc boron binary glasses can be formed in the range of 45–73 mol% ZnO content, and the glass with 55 mol% ZnO content has the highest glass-forming ability. The Zn 4B 6O 13 crystal is formed in binary ZnO-B 2O 3 glass at 640 °C, which is much lower than that in ceramics. The glass-ceramics exhibit large grains with 5 ~ 10 µm consisting of fine and uniform secondary structures. The precipitation of Zn 4B 6O 13 crystal and the refinement secondary structure improves the microwave dielectric properties. The 55 ZnO - 45 B 2O 3 glass-ceramic sintered at 640 °C for 5 h exhibits the optimum microwave dielectric properties of εr = 6.09, Q×f = 20,389 GHz, τf = 14 ppm/°C, and also high Vickers hardness of 625 kgf/mm 2 and good chemical compatibility with Ag or Al electrode, which is a good candidate for ULTCC substrate materials. 相似文献
7.
Glass components fabricated by the sintering route have wide-ranging applications. However, one issue is that the crystallization tendency of glass powders often leads to residual pore-glass interfaces and crystal-glass interfaces, thereby causing strong light scattering and rendering the sintered glass opaque. This issue is particularly pronounced in glasses with a low glass transition temperature ( Tg) due to their weak bonding and thus high crystallization tendency. In the present study, a Bi 2O 3-ZnO-B 2O 3 glass with a low Tg of 364°C was fabricated using the conventional sintering method to explore whether transparent glass materials can be obtained. The temperature range of crystallization of the glass powders was analyzed using differential scanning calorimetry. X-ray diffraction was employed to analyze the crystalline phases formed in the sintered glasses. The microstructure of the sintered glasses was examined using scanning electron microscopy. The optical transmittance of the sintered glasses was measured using ultraviolet-visible spectroscopy. The results show that transparent sintered glasses with the highest transmittance of 54% at the wavelength of 650 nm can be obtained by using a coarser initial particle size, lower forming pressure, and an appropriate sintering temperature/time (430°C/30 min). It is suggested that this combination of processing parameters can suppress glass crystallization while maintaining a low glass viscosity during sintering. 相似文献
8.
The feasibility of preparing low-cost glass-ceramics from Zn-containing dust and secondary molten slag generated during the carbothermal reduction of copper slag was investigated. Analytical-grade agents, such as ZnO, Fe 2O 3, SiO 2, CaO, and Al 2O 3, were used to simulate the dust and secondary slag. The effect of ZnO content on the crystallization behavior, structure, and mechanical properties of the glass-ceramics was investigated through X-ray diffraction analysis, scanning electron microscopy-energy dispersive spectrometry, differential scanning calorimetry, Fourier transform infrared spectroscopy, and Raman spectroscopy. The results showed that with increased ZnO content from 0 to 6 wt%, the crystallization activation energy of base glass increased from 386.05 to 425.89 kJ/mol. Meanwhile, the average value of the crystal growth index increased from 1.91 to 4.10, and the highest crystallization rate of the glass-ceramics increased from about 1.44 to 23.11 mm 3/min. The increased ZnO in glass-ceramics promoted the precipitation of gehlenite, but inhibit the crystallization of anorthite. When the ZnO content was 6 wt%, the comprehensive properties of the glass-ceramics were better; the flexural strength, microhardness, volume density, water absorption rate, and open porosity were 58.67 MPa, 738.35 HV, 2.92 g/cm 3, 0.44% and 1.27%, respectively. 相似文献
9.
Transparent YAG-based glass-ceramics were prepared by a novel method called amorphous sintering followed by controlled crystallization (ASCC) from the compositions of 62.5Al 2O 3–(37.5 ? x)Y 2O 3– xLa 2O 3 (in molar ratio, x = 5, 7, 10 and 20). The stability of the YAG glass was improved by the incorporation of La 2O 3, which increased the activation energy for crystallization. With 10 mol% La 2O 3, bulk YAG glass was prepared by hot-pressing and showed an infrared transmittance of 66%. The YAG glass was converted into glass-ceramics by post annealing at 875 °C for 5 h for controlled crystallization. The obtained glass-ceramic sample showed a crystallite size of 20–50 nm and an infrared transmittance of 60%. With increasing annealing time, the crystallites grew up quickly, resulting in a significant decrease in transparency. In the hot-pressed glass, nano-sized YAG nuclei (~5 nm) were found, which were probably responsible for the crystallization behavior observed at temperatures (e.g. 875 °C) below the onset crystallization temperature. 相似文献
10.
In a MgO/Al 2O 3/SiO 2/ZrO 2 glass-ceramic MgO was substituted by equimolar ZnO concentrations. The effect of this substitution on the crystallization behavior, the microstructure and the mechanical properties of the glass-ceramics was studied. The crystal phases and the microstructure were analysed by X-ray diffraction and scanning electron microscopy. Tetragonal ZrO 2, a high-/low-quartz solid solution (high-/low-QSS) and spinel/gahnite were observed in the entire bulk of the glass-ceramics. Additionally, indialite or cristobalite are detected at the surface of some glass-ceramics. The substitution of small ZnO concentrations induces an increasing low-QSS concentration and hence higher microhardness and Young’s modulus. By contrast, higher ZnO concentrations lead to a liquid/liquid phase separation in the glass. Moreover, spinel/gahnite is the main crystal phase and the concentration of the low-QSS is smaller in theses glass-ceramics which also do not show as good mechanical properties. However, the biaxial flexural strength of the glass-ceramics is not notably affected by the ZnO concentration. 相似文献
11.
The composition governs the crystallization ability, the type and content of crystal phases of glass-ceramics. Glass-ceramic joining materials have generated more research interest in recent years. Here, we prepared a novel Li 2O–MgO–Al 2O 3–SiO 2 glass-ceramic for the application of joining Si 3N 4 ceramics. We investigated the influence of the MgO/Al 2O 3 composition ratio on microstructure and crystallization behaviour. The crystallization kinetics demonstrated that the glasses had excellent crystallization ability and high crystallinity. β-LiAlSi 2O 6 and Mg 2SiO 4 were precipitated from the glass-ceramics, and the increase of MgO concentration was conducive to the precipitation of Mg 2SiO 4. Among the glass-ceramic samples, the thermal expansion coefficient of LMAS2 glass-ceramic was 3.1 × 10 ?6/°C, which was very close to that of Si 3N 4 ceramics. The wetting test showed that the final contact angle of the glass droplet on the Si 3N 4 ceramic surface was 32° and the interface was well bonded. 相似文献
12.
The influence of BaO content (up to 15?mol%) on the crystallization behaviour, structure, thermal properties and microwave dielectric properties of the BaO-CaO-B 2O 3-SiO 2 glasses and glass-ceramics system was investigated. The glasses were produced by melting at 1400?°C and quenching into water, and the glass-ceramics were produced via heat treatment at temperatures between 750 and 800?°C. The results of X-ray diffraction analysis showed that increasing the BaO content raised the resistance of the glass against crystallization and favoured the transformation of β-CaSiO 3 and α-CaSiO 3 phases, which crystallized in the Ba-free and in low BaO content compositions, into SiO 2 and Ba 4Si 6O 16, which crystallized in compositions with higher concentrations of BaO. The BaO content had little influence on the glass transition temperature ( Tg) and the linear coefficient of thermal expansion (CTE), but strongly reduced the softening point ( Ts). Even the addition of BaO as minor additives resulted in a dramatic reduction of the Ts; for example, the Ts decreased from 902?°C for the Ba-free composition to 682?°C for the BaO-containing one (5%). Low values of the dielectric constant (5.9?≤? εr ≤?6.63) and dielectric loss (1.12?×?10 ?3 ≤?tan δ?≤?3.15?×?10 ?3) were measured. 相似文献
13.
This article reports on the effect of Al 2O 3 and B 2O 3 added as dopants on the preparation of glass‐ceramics (GCs) belonging to the lithium silicate glass system. The GCs are prepared by sintering route using glass powders. The reasons for the crystallization of the metastable crystalline phase lithium metasilicate (LS) are discussed and the impact of the dopants on the thermodynamics and kinetics of crystallization is investigated. The addition of dopants modifies the thermodynamic equilibrium of the system and this change is mainly entropy driven and also slowdown the kinetics of crystallization. Differential thermal analysis and hot‐stage microscopy are employed to investigate the glass‐forming ability, sintering, and crystallization behavior of the studied glasses. The crystalline phase assemblage studied under nonisothermal heating conditions in the temperature range of 800°C–900°C in air. Well sintered and dense glass‐ceramics are obtained after sintering of glass powders at 850°C–900°C for 1 h featuring crystalline phase assemblage dominated by lithium disilicate (LS 2). 相似文献
14.
The Co2O3 doped MgO-Al2O3-SiO2-B2O3 (MASB) glass-ceramics were successfully fabricated by traditional melt quenching method and the following heat treatment. The effect of Co2O3 addition on crystallization behavior, glass networks, microstructure and physical properties was investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD), Fourier transform infrared absorption spectra (FTIR) and scanning electron microscopy (SEM) measurements. The results show that the metastable phase μ-cordierite and α-cordierite precipitated from the parent glass during the thermal treatment process. With the increase of Co2O3 content, the crystallization tendency of the parent glass increased, and the addition Co2O3 favored the transformation from μ-cordierite to α-cordierite. Meanwhile, the grain size of glass-ceramics increased obviously, Simultaneously, the mechanical strength of glass-ceramics increased first and then decreased, while the thermal expansion coefficient decreased. Glass-ceramic with excellent thermal and physical properties were prepared by adding 0.1 mol% Co2O3 content and then crystallizing it at 1020 ∘C for 3 h. 相似文献
15.
The high refractive index La 2O 3–TiO 2–Nb 2O 5 glasses were prepared by containerless processing, and the glass‐forming region was determined. The refractive index showed the range from 2.20 to 2.32, and the values were much higher than those of most optical glasses. The completely miscible 30LaO 3/2–(70? x)TiO 2– xNbO 5/2 (0 ≤ x ≤70) system was fabricated to study the compositional dependence of refractive index and optical transmittance. The crucial determinants of the refractive index of oxide glasses, oxygen molar volume, and electronic polarizability of oxygen ions were calculated. The principle of additivity of glass properties was suitable for the calculation of refractive index between glass and compositional oxides. All the glasses were colorless and transparent in the visible to 6.5 μm middle infrared (MIR) region. These results are useful for designing new optical glasses with high refractive index and low wavelength dispersion in wide optical window. 相似文献
16.
Glasses in the 30La 2O 3-40TiO 2-30Nb 2O 5 system are known to have excellent optical properties such as refractive indices over 2.25 and wide transmittance within the visible to mid-infrared (MIR) region. However, titanoniobate glasses also tend to crystallize easily, significantly limiting their applications in optical glasses due to processing challenges. Therefore, the 30La 2O 3-40TiO 2-(30− x) Nb 2O 5- xAl 2O 3 (LTNA) glass system was successfully synthesized using a aerodynamic containerless technique, which improves glass thermal stability and expands the glass-forming region. The effects of Al 2O 3 on the structure, thermal, and optical properties of base composition glasses were investigated by XRD, DSC, NMR, Raman spectroscopy, and optical measurements. DSC results indicated that as the content of Al 2O 3 increased, the thermal stability of the glasses and glass-forming ability increased, as the 30La 2O 3-40TiO 2-25Nb 2O 5-5Al 2O 3 (Nb-Al-5) glass obtained the highest Δ T value (103.5°C). Structural analysis indicates that the proportion of [AlO 4] units increases gradually and participates in the glass network structure to increase connectivity, promoting more oxygen to become bridging oxygen and form [AlO 4] tetrahedral linkages to [TiO 5] and [NbO 6] groups. The refractive index values of amorphous glasses remained above 2.1 upon Al 2O 3 substitution, and a transmittance exceeding 65% in the visible and mid-infrared range. The crystallization activation energies of 30La 2O 3-40TiO 2-30Nb 2O 5 (Nb-Al-0) and Nb-Al-5 glasses were calculated to be 611.7 and 561.4 kJ/mol, and the Avrami parameters are 5.28 and 4.96, respectively. These results are useful to design new optical glass with good thermal stability, high refractive index and low wavelength dispersion for optical applications such as lenses, endoscopes, mini size lasers, and optical couplers. 相似文献
17.
CaO–B 2O 3–SiO 2–Ta 2O 5 (CBST) glass-ceramics, with different Ta 2O 5 content, (up to 6 mol%), have been prepared by using glass melt quenching followed by heat treatment between 800 and 880 °C. The Fourier Transform Infrared (FTIR) results showed that the stronger the attraction of Ta 5+ to the oxygens in the BO 33? and SiO 32? structures, the more easily the B–O and Si–O bonds will be destroyed. The underlying reason is most probably the high field strength of Ta 5+, which results in a weakening of the vibration intensities of the [BO 3] and [SiO 4] units. Moreover, the Differential Scanning Calorimetry (DSC) results showed that the softening point (T g), crystallization starting temperature (T c1), and exothermic crystallization peak temperature (T p1), of the CaSiO 3 phase, shifted to higher values with the addition of Ta 2O 5. Also, the crystallization activation energy (E a) and the glass stability factor (ΔT) of the CaSiO 3 phase increased, which indicated that the CaSiO 3 phase of the glass became inhibited by the addition of Ta 2O 5. It was, thus, obvious that there was a need of glass characterization. The results of the crystallization kinetics showed that the critical cooling rate decreased with the addition of Ta 2O 5, which indicated that the viscosity of the system had increased. The CBST glass-ceramics, containing 1 mol% Ta 2O 5, that were sintered at 875 °C for 15 min showed excellent dielectric properties: ε r = 6.22 and tanδ = 1.19 × 10 ?3 (1 MHz). To sum up, CaO–B 2O 3–SiO 2–Ta 2O 5 glass-ceramics are potential low temperature co-fired ceramic substrate materials. 相似文献
18.
In this study, a transparent and environmentally friendly Li 2O–Al 2O 3–SiO 2 (LAS) glass-ceramic was prepared by melt-quenching and two-step heat treatment. The influence of the substitution amount of ZrO 2 by SnO 2 on the crystallization, microstructure, transparency, and mechanical properties of LAS glass and glass-ceramics was investigated by means of differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Ultraviolet–visible Spectrophotometer, three-point bending strength test, and microhardness test. The results indicate that the main crystalline phase of LAS glass ceramics was a β-quartz solid solution when heat treated at 780 °C for 2 h and 870 °C for 1.5 h. When the substitution amount of ZrO 2–SnO 2 increased from 0.4 mol% to 2.5 mol%, the grain size and thermal expansion coefficient of LAS glass-ceramics first decreased and then increased, and the crystallinity first increased and then decreased. When the substitution amount of ZrO 2–SnO 2 was 0.8 mol%, the transparency of the LAS glass-ceramics was maximum, the bending strength was 96 MPa, and the Vickers hardness was 10.9 GPa. 相似文献
19.
The effect of SrO substitution for CaO in two sol–gel glasses with different chemical compositions (mol%) A2Sr: (54− x)CaO– xSrO–6P 2O 5–40SiO 2 and S2Sr: (16− x)CaO– xSrO–4P 2O 5–80SiO 2 ( x=0, 1, 3 and 5) stabilized at 700 °C on their structure (XRD, FTIR) and bioactive properties (SBF test) was investigated. Preliminary in vitro tests using human articular chondrocytes of selected A2Sr glass were also conducted. Moreover, the subject of this study was to detect the changes on material properties after heat treatment at 1300 °C. The results show that the effect of strontium substitution on structure, bioactivity and crystallization after treatment at both the above temperatures strongly depends on CaO/SiO 2 molar ratio. The presence of 3–5 mol% of strontium ions creates more expanded glass structure but does not markedly affect crystallization ability after low temperature treatment. Sintering at 1300 °C of A2 type glasses results in crystallization of pseudowollastonite, hydroxyapatite and also Sr-substituted hydroxyapatite for 3–5 mol% of SrO substitution. The increase of strontium concentration in silica-rich materials after sintering leads to appearance of calcium strontium phosphate instead of calcium phosphate. Bioactivity evaluation indicates that substitution of Sr for Ca delays calcium phosphate formation on the materials surface only in the case of silica-rich glasses treated at 700 °C. Calcium-rich glasses, after both temperature treatments, reveals high bioactivity, while crystal size of hydroxyapatite decreases with increasing Sr content. High temperature treatment of high-silica glasses inhibits their bioactivity. Preliminary in vitro tests shows Sr addition to have a positive effects on human articular chondrocytes proliferation and to inhibit cell matrix biomineralization. 相似文献
20.
High performance ultra-low temperature co-fired ceramic (ULTCC) materials were prepared from CuO- MgO- ZnO- Al 2O 3- B 2O 3- Li 2O glass-ceramics. The sintering behaviors, crystalline phase evolution, microstructure and dielectric properties, as well as their compatibility with Ag and Al electrodes, were investigated. With the suitable substitution of MgO for ZnO, the dielectric properties of glass-ceramics were improved. It is mainly associated with the fine microstructure, highly crystallinity, and decrease in tetrahedral distortion in the crystal lattice. All the glasses completed the densification at 575–600 °C, and ZnB 4O 7 is the only crystalline phase precipitated from the glasses. Moreover, the glass-ceramic with 1 wt% MgO sintered at 575 °C for 5 h, exhibited low relative permittivity ~ 7.1 and low dielectric loss ~ 6.40 × 10 ?4. And the glass-ceramic with 4 wt% MgO sintered at 600 °C for 5 h, also displayed low relative permittivity ~ 7.1 and low dielectric loss ~ 5.77 × 10 ?4. Both two glasses have good sintering compatibility with silver and aluminum electrodes, which provided high potential for ULTCC application. 相似文献
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