Crystallization,microstructure and mechanical behavior of titanium doped barium fluormica glass-ceramics

Crystallization, microstructure and mechanical behavior of TiO₂ doped barium fluorphlogopite glass-ceramics were systematically studied. TiO₂ was used as a doper nucleant in the BaO·4MgO·Al₂O₃·6SiO₂·2MgF₂ glass system. Melting technique was adopted to prepare the glass samples which were analyzed by differential thermal analysis (DTA), X-ray diffraction, scanning electron microscopy, and micro hardness indenter. The DTA study demonstrated that the crystallization exotherm of fluorphlogopite mica appeared in the temperature window of 886-903°C. In this investigation, four glass samples were prepared using 2 (MA1), 4 (MA2), 6 (MA3), and 8 (MA4) wt% of TiO_2. Glass transition (T_g) and peak crystallization (T_p) temperatures escalated with an increase in the TiO₂ content from 2 (MA1) to 4 wt% (MA2). However, beyond this value, T_g and T_p decreased with a surge in TiO₂ content from 6 (MA3) to 8 wt% (MA4). Nevertheless, with a gradual rise in the TiO₂ content, the crystals of the glass-ceramics became enlarged and subsequently exhibited mechanical properties, such as hardness, fracture toughness, and machinability. Therefore, in solid oxide fuel cell applications, TiO₂ is a promising nucleating agent to generate fluorphlogopite mica-based glass-ceramics.     

Influence of nucleating agents on crystallization and electrical properties of SiO2–MgO–MgF2–K2O mica glass-ceramics

The effects of adding ZrO₂ and TiO₂ at the expense of MgF₂ on the crystallization, microstructure, mechanical properties, thermal properties and electrical properties of mica glass-ceramics based on the SiO₂–MgO–MgF₂–K₂O system were investigated by the differential scanning calorimetry (DSC), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), microhardness tester and resistivity tester. The electrical properties were discussed emphatically. The results showed that the additions of ZrO₂ and/or TiO₂ at the expense of MgF₂ effectively increase the viscosity, the glass transition temperatures (T_g) and the crystallization temperatures (T_p) of the glasses. The crystallization activation energy (E_c) of the amorphous glasses varied with the nucleating agents was discussed in depth. It was discovered that the nucleating agents had no effect on the crystal phase type but had a certain effect on the crystallinity and microstructure. Tetrasilicic fluoromica and enstatite were precipitated at different crystallization temperatures. Due to the non-stoichiometric ratio of tetrasilicic fluoromica crystal, the prepared glass-ceramics had high dielectric constant (24.4–34.3) and volume resistivity (>2 × 10¹¹ Ω cm) at 25 ^°C, and the dielectric loss was almost zero.     

Influence of heat treatment temperature on the properties of the lithium disilicate-fluorcanasite glass-ceramics

This study aims to investigate the influence of heat treatment temperatures on the mechanical properties and chemical solubility (CS) of lithium disilicate-fluorcanasite glass-ceramics and to develop new dental materials. The glasses and glass-ceramics were prepared using CaF₂-SiO₂-CaO-K₂O-Na₂O-Li₂O-Al₂O₃-P₂O₅-based glass system using a conventional melt quenching method followed by a two-stage crystallization process. This two-stage method involves two heating temperature steps: first at a constant temperature (T_S1) of 600°C and second step at varying temperatures (T_S2) of 650, 700, 750, and 800°C. The crystallization behavior, phase formation, microstructure, translucency characteristic, density, hardness, fracture strength, and CS were investigated. It was found that the lithium disilicate crystal acted as the main crystalline phase, and the crystalline phase of fluorcanasite occurred at the heat treatment temperatures of 750 and 800°C. In addition, it was found that density, hardness, fracture strength, and CS increased while the translucency values decreased with increasing heat treatment temperatures. Furthermore, the CS increased dramatically when the fluorcanasite phases occurred in the glass-ceramic samples. The maximum density values, Vickers hardness, fracture toughness, and flexural strength are 2.56 g/cm³, 6.73 GPa, 3.38 MPa.m^1/2, and 259 MPa, respectively. These results may offer a possibility to design a new material for dental applications based on lithium disilicate-fluorcanasite glass-ceramics.     

Influence of barium oxide on the crystallization, microstructure and mechanical properties of potassium fluorophlogopite glass-ceramics

The influence of barium oxide, heat treatment time and temperature on the crystallization, microstructure and mechanical behavior of the system Ba_x·K_1−2x·Mg₃·Al·Si₃O₁₀·F₂ (where x = 0.0, 0.3 and 0.5) was investigated in order to develop novel, high strength and machinable glass-ceramics. Three glasses were prepared and characterized by differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscope (SEM) techniques and some mechanical testing methods.The crystallization kinetics of glass-ceramics was also studied. Activation energy and Avrami exponent calculated for the crystallization peak temperature (T_p) of three different glass batches. The Vickers hardness decreased slightly on formation of the potassium fluorophlogopite and barium fluorophlogopite phases, but decreased significantly on formation of an interconnected ‘house of cards’ microstructure.     

SiO2–Al2O3–CaO glass-ceramics: Effects of CaF2 on crystallization,microstructure and properties

The effects of fluorine content on the nucleation and crystallization behavior of SiO₂–Al₂O₃–CaO glass ceramics system have been investigated. The crystalline phases were determined by X-ray diffraction (XRD). The crystallization kinetics was determined by differential thermal analysis (DTA). The microstructures were examined by using scanning electron microscope (SEM). Fourier transformed infrared spectra (FTIR) analysis was used to study the glass structure. The results showed that by increasing the fluorine content, both the crystallization peak temperature (T_p) and activation energy (E) decreased. Wollastonite, anorthite and gehlenite are the main crystalline phases that exist in the glass ceramics system. The study shows that fluorine promoted initial crystallization of glass and can be used as an effective nucleating agent in the SiO₂–Al₂O₃–CaO system.     

The influence of TiO2 content on the properties of glass ceramics: Crystallization,microstructure and hardness

The effects of compositional variation, crystallization behavior, crystalline phases and microstructure formed in the SiO₂3Al₂O₃3CaO (SAC) glass system using various amounts of TiO₂ as nucleating agent were investigated by Differential Thermal Analysis (DTA), X-ray powder diffraction (XRD), Scanning Electron Microscope (SEM), Energy-dispersive X-ray spectroscopy (EDAX) and Fourier transform infrared spectroscopy (FTIR) techniques. The crystallization kinetics and mechanical properties of SAC glass ceramics were studied using crystallization peak temperature (T_p) of three different glasses as obtained from DTA, the activation energy (E) and Avrami exponent (n) were also determined. The crystallization peak temperature (T_p) and activation energy (E) were found to increase with the increase in TiO₂ content. The major crystalline phases were anorthite and wollastonite along with gehlenite and titanite as the minor crystalline phases present in the glass ceramic system. The studies showed that the three dimensional crystalline structure and the microhardness increased with the increase of TiO₂ content in the glass ceramics system.     

Synthesis of glass-ceramics in the Na2O/K2O-CaO-MgO-SiO2-P2O5-CaF2 system as candidate materials for dental applications

This study reports on the sintering behavior, crystallization process, and mechanical properties of novel glass-ceramics (CGs) produced by the glass powder compact consolidation method. Substitution of K₂O for Na₂O and MgO for CaO was attempted in the parent glasses belonging to Na₂O-CaO-MgO-SiO₂-P₂O₅-CaF₂ system. Glass powder compacts were heat treated at various temperatures between 700°C and 900°C, taking under consideration the glass transition (T_g) and the crystallization peak (T_p) temperatures, which were experimentally determined for each investigated glass by thermal analysis (dilatometry and differential scanning calorimetry). The experimental results showed that sintering always preceded crystallization, regardless of the type of substitution. In the case of MgO substitution for CaO, crystallization was advanced in the range of 800°C-850°C, resulting in the formation of an assembly of crystalline phases, such as diopside, fluorapatite, and wollastonite. The substitution of K₂O for Na₂O increased the activation energy for crystallization, shifting crystallization process to a high temperature region, with the formation of alpha-potassium magnesium silicate, instead of wollastonite. The GCs produced had values of 22-31 GPa regarding the modulus of elasticity, 5.0-6.1 GPa concerning the microhardness, and 1.4-1.9 MPa⋅m^0.5 as regard the fracture toughness, which are similar to those of the human jawbone.     

Effect of MgF2 addition on sinterability and mechanical properties of fluorapatite ceramic composites fabricated by wollastonite and phosphate glass

In this paper, we successfully report the design and synthesis of fluorapatite ceramic composites using phosphate glass and wollastonite as raw materials via a simple sintering method. The effects of MgF₂ additives in phase composition, microstructure, densification, and mechanical properties are investigated at various temperatures from 600 °C to 900 °C, and characterized by SEM/EDS, XRD, FTIR, linear shrinkage and water absorption, flexural strength analysis. It shows that the densification and mechanical behavior of composites increase with both the sintering temperature and MgF₂ content. Especially, the sample SCPF-7 exhibits the highest densification and optimal mechanical properties at 900 °C. At these conditions, the water absorption of fluorapatite ceramic composite is less than 0.20%, and the flexural strength is over 70 MPa. For the microstructure analysis, the formation of fluorapatite with a rod-like microstructure is enhanced with the increase of MgF₂ content. The amelioration of these properties is due to the formation of a new phase which helps to the formation of compact microstructure. The findings in this work provide a feasible strategy for the preparation of fluorapatite ceramic composites from available phosphate glass and wollastonite at a lower temperature.     

Bioactive glass-ceramics prepared by powder sintering and crystallization of polyphosphate glass containing strontium

Melt-quenching method was employed for obtaining a glass-ceramic with the following composition 42P₂O₅·40CaO·5SrO·10Na₂O·3TiO₂ (mol%) glass. The crystallization and sintering behavior of glass have been studied by using DTA, HSM, XRD, FTIR and SEM methods. It was determined that the surface and volume crystallization mechanisms act simultaneously in bulk glass samples. The comparison of DTA and HSM data revealed that the sintering and crystallization processes are independent. The sintered calcium phosphate glass-ceramic which contained bioactive β-Ca₃(PO₄)₂ and β-Ca₂P₂O₇ phases was successfully prepared. It was determined that during crystallization the primary phase in the precipitate was β-Ca(PO₃)_2. Other phases appearing in the resulting glass-ceramic were: α-Ca₂P₂O₇, γ-Ca₂P₂O₇, Ca₄P₆O₁₉ and CaHPO₄(H₂O)₂. Crystalline phases containing Sr and Ti were not detected. SEM analysis of the glass-ceramic microstructure revealed surface crystallization of glass particles and plate-like morphology of crystal growth. The result of the in vitro bioactivity showed that no apatite layer was formed on the surface of the as-prepared glass-ceramic samples after immersion in the simulated body fluid (SBF).     

Compositional effects on the crosslink density of Ca–(Mg)–(Y)–Si–Al–oxyfluoronitride glasses

The effects of fluorine and nitrogen substitution for oxygen in aluminosilicate glasses, effectively oxyfluoronitride (OFN) glasses, modified by calcium, calcium–yttrium or calcium–magnesium on thermal and physical/mechanical properties have been compared. Thus, 42 glasses in the Ca–(Mg)–(Y)–Si–Al–O–(N)–(F) system have been prepared and characterized with respect to density (ρ), molar volume (MV), compactness (C), free volume (FV), glass transition temperatures measured by DTA (T_g,DTA) and dilatometry (T_g,dil), dilatometric softening point (T_DS), microhardness (μHv) and Young's modulus (E). Gradients of property variation with nitrogen or fluorine substitutions for oxygen are similar for all three different oxyfluoronitride glass systems and are comparable with those reported for other OFN glasses, again indicating independent and additive effects of nitrogen and fluorine. In attempting to further understand how fluorine affects the cross‐link density (CLD) in OFN glasses, it becomes apparent that it is necessary to allow for a greater contribution by aluminum in a modifier role as fluorine content is increased. This modified calculation of CLD values results in good linear fits between T_g and CLD values. This analysis clearly demonstrates and endorses the concepts that thermal properties are related to CLD while physical/mechanical properties are dependent on glass compactness.     

Structural,mechanical, and in vitro characterization of freeze-cast scaffolds prepared using a sol-gel-derived bioactive glass from the SiO2–CaO–Na2O–P2O5–K2O–MgO system

This work deals with the preparation of freeze-cast scaffolds using a bioactive glass from the SiO₂–CaO–Na₂O–P₂O₅–K₂O–MgO system. This material could be sintered at lower temperatures (650 °C) than other variations of bioactive glasses, which is an important advantage in terms of energy and cost savings. This behavior represents a great advantage in terms of energy and cost savings. The freeze-casting step was conducted using water as a solvent and liquid nitrogen as a coolant. The prepared samples were examined according to their pore structure, thermal behavior, mechanical stability, and bioactivity. The glass transition temperature (T_g), crystallization onset temperature (T_x), and maximum crystallization temperature (T_c) evaluated for this bioactive glass were about 660 °C, 690 °C, and 705 °C. Consequently, the freeze-cast scaffolds could be sintered at 650 °C for 2–8 h, which favored viscous flow sintering without crystallization. Bioactivity assays were conducted by soaking the scaffolds in simulated body fluid for up to 21 days, showing that these materials present a bioactive behavior, inducing hydroxyapatite formation. These materials' mechanical properties and biocompatibility make them promising candidates for use in trabecular bone repair.     

High-strength,translucent glass-ceramics in the system MgO-ZnO-Al2O3-SiO2-ZrO2

In a MgO/Al₂O₃/SiO₂/ZrO₂ 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 ZrO₂, 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.     

Preparation and characterization of alkali-free glass substrates with enhanced properties for TFT–LCDs applications

To obtain an alkali-free glass substrate with enhanced properties for thin-film transistor–liquid crystal displays (TFT–LCDs) applications, we chose a base glass composed of 3B₂O₃-15Al₂O₃-58SiO₂-22MgO-0.5SrO-1.5MgF₂ (mol%) for nucleation–crystallization. The results show that when the nucleation–crystallization processes of the base glass are 810 °C/6 h + 880 °C/6–9 h, the prepared GC/6–GC/9 glass-ceramics exhibit enhanced properties because of the precipitation of nano-sized cordierite. The transmittances in the visible range of the GC/6–GC/9 glass-ceramics exceed 85%, the densities are 2.564–2.567 g/cm³, thermal expansion coefficients are 2.934–3.059 × 10^-6/°C (25–300 °C), compressive strengths are 417–589 MPa, bending strengths are 141–259 MPa, Vickers hardnesses are 6.8–7.8 GPa, and strain points are approximately 735 °C. Considering these properties, the prepared GC/6–GC/9 glass-ceramics have good potential as candidate materials for alkali-free glass substrates. Additionally, these results demonstrate that it is feasible to improve the properties of alkali-free glass substrates by nucleation–crystallization.     

Crystallization behavior and mechanical properties of high strength mica-containing glass-ceramics from granite wastes

The high-strength mica-containing glass-ceramics were prepared from granite wastes by bulk crystallization. The influences of SiO₂/Al₂O₃ molar ratio (S/A = 7.72, 9.62, 12.58, 17.82 and 29.67) on the crystallization behavior, microstructure, mechanical properties and machinability of glass-ceramics were investigated. The results demonstrated that the polymerization degree of the glass network decreased with the S/A ratio increasing, which further caused the decrease in glass transition temperature and crystallization temperatures. The increase in the S/A ratio promoted the precipitation of diopside, hectorite, kalsilite and tainiolite in glass-ceramics when the samples were heated at 750 °C, while inhibiting the precipitation of forsterite. For the glass-ceramics crystallized at 800 and 900 °C, the main crystalline phases transformed from diopside, forsterite, and nepheline to diopside, kalsilite, and tainiolite, with the S/A ratio increasing. As the SiO₂ gradually replaced Al₂O₃, the morphology of crystals changed from lamellar to granular, while the mean size of crystals reduced. The Vickers-Hardness values of glass-ceramics crystallized at 800 and 900 °C ascended with S/A ratio rising, and the values were above 6.30 GPa. The bending strength of most glass-ceramics is stable between 90 and 140 MPa, among which the maximum bending strength is 133.28 ± 14.81 MPa. The fracture toughness of the glass-ceramic crystallized at 800 and 900 °C declined, while that at 700 °C increased with a larger S/A ratio. Glass-ceramics after heat-treated at 900 °C with S/A ratio of 9.62 had the largest fracture toughness of 3.28 ± 0.15 MPa m^1/2. In preliminary tests of machinability, glass-ceramic after heat-treated at 900 °C with S/A ratio of 9.62 showed better results.     

Graphite intercalation compound of magnesium fluoride and fluorine

A graphite intercalation compound of C_xF(MgF₂)_y was prepared under a fluorine atmosphere of 1 atm at temperatures of 20–350°C. The 1st stage compound has the identity period of 9.3–9.4Å. ESCA and ¹⁹F NMR spectra indicate that the chemical interaction of intercalated fluorine with carbon is similar to that for graphite fluoride, however, with C_xF(MgF₂)_y having slightly mobile fluorine atoms chemically adsorbed on carbon atoms of graphite layers.     

Effect of metastable phase on the crystallization and mechanical properties of MgO-Al2O3-SiO2 glass-ceramics without nucleating agents

Glass-ceramics without nucleating agents usually undergo surface crystallization, which deteriorates the overall performance of the products. In this paper, we evaluated the effects of the metastable MgAl₂Si₃O₁₀ crystalline phase on the crystallization behavior of a MgO–Al₂O₃–SiO₂ (MAS) glass without nucleating agents and mechanical properties of the glass-ceramics obtained. The results demonstrated that the precipitation of metastable MgAl₂Si₃O₁₀ crystallites promotes the crystallization mechanism transformed from surface crystallization into volume crystallization with two-dimensional crystal growth. Furthermore, the grain size of MgAl₂Si₃O₁₀ near the surface of the prepared glass-ceramics was larger than that of MgAl₂Si₃O₁₀ inside, which helps to generate compressive stress and improves its mechanical properties. The glass-ceramics containing metastable MgAl₂Si₃O₁₀ phase exhibited an enhanced hardness in the range of 7.6 GPa–9.5 GPa for indentation loads ranging from 2.94 N to 98 N, and indentation size effect behavior was observed in Vickers hardness tests of both MAS glass and glass-ceramics. The load-independent hardness values for MAS glass and glass-ceramics were reliably evaluated by the modified proportional specimen resistance (MPSR) model of 7.1 GPa and 7.6 GPa, respectively, with a high correlation coefficient of more than 0.9999. This work reveals the unexploited potential of the metastable phase in improving the crystallization ability and mechanical properties of glass-ceramics.     

Role of MgO in lowering glass transition temperature and increasing hardness of lithium silicate glass and glass-ceramics

The effect of variation of MgO (1.5, 4.5 and 7.5 mol%) content on glass structure, crystallization behavior, microstructure and mechanical properties in a Li₂O–K₂O–Na₂O–CaO–MgO–ZrO₂–Al₂O₃–P₂O₅–SiO₂ glass system has been reported here. Increased amount of MgO enhanced the participation of Al₂O₃ as a glass network former along with [SiO₄] tetrahedra, reducing the amount of non-bridging oxygen (NBO) and increasing bridging oxygen (BO) amount in glass. The increased BO in glass resulted in a polymerized glass structure which suppressed the crystallization and subsequently increased the crystallization temperature, bulk density, nano hardness, elastic modulus in the glasses as well as the corresponding glass-ceramics. MgO addition caused phase separation in higher MgO (7.5 mol%) containing glass system which resulted in larger crystals. The nano hardness (～10 GPa) and elastic modulus (～127 GPa) values were found to be on a much higher side in 7.5 mol% MgO containing glass-ceramics as compared to lower MgO containing glass-ceramics.     

Influence of fluorine source and TiO2 on glass ceramics based on red clay and magnesite

Abstract

Within the Fe₂O₃–BaO–Al₂O₃–SiO₂ glass system, the influence of different fluorine source and TiO₂ on the crystallisation behaviour and thermal expansion characteristics has been investigated. These aluminosilicate glasses, with different nucleation catalysts (TiO₂, AlF₃ and NH₄F), were successfully prepared from Saudi Arabia raw materials (red clay and magnesite). Thermal behaviour, crystalline phases, microstructures, and thermal expansion coefficient were studied by DTA, XRD, SEM techniques, as well as a dilatometer. Spinel, hexacelsian, monocelsian, kinoshitalite, and Ba-osumilite were developed in glass ceramic samples. Spinel was the early phase formed in all glasses; however, with increasing temperature, hexacelsian and kinoshitalite were developed in fluorine free glasses and fluorine containing glasses respectively. Ba-osumilite was developed and hexacelsian was converted into monocelsian during lengthy heat treatment at 1150°C. A bulk crystalline microstructure was obtained; however, a microscale structure was observed in fluorine free samples and a homogeneous nanoscale microstructure was developed in fluorine containing samples. The coefficient of thermal expansion (CTE) varied according to the phases and the heat treatment parameters. Development of spinel, hexacelsian and kinoshitalite in glass ceramic samples gave CTE values between 86·44 × 10^?7 and 52·53 × 10^?7°C^?1, whereas crystallisation of Ba-osumilite and monocelsian gave CTE values between 51·29 × 10^?7 and ?7·35 × 10^?7°C^?1.     

Glass forming,crystallization, and physical properties of MgO-Al2O3-SiO2-B2O3 glass-ceramics modified by ZnO replacing MgO

This study focused on the glass forming, crystallization, and physical properties of ZnO doped MgO-Al₂O₃-SiO₂-B₂O₃ glass-ceramics. The results show that the glass forming ability enhances first with ZnO increasing from 0 to 0.5 mol%, and then weakens with further addition of ZnO which acted as network modifier. No nucleating agent was used and the crystallization of studied glasses is controlled by a surface crystallization mechanism. The predominant phase in glass-ceramics changed from α-cordierite to spinel/gahnite as ZnO gradually replaced MgO. The phase type did not change; however, the crystallinity and grain size in glass-ceramics increased when the glasses were treated from 1030 °C to 1100 °C. The introduction of ZnO can improve the thermal, mechanical, and dielectric properties of the glass-ceramics. The results reveal a rational mechanism of glass formation, crystal precipitation, and evolution between structure and performance in the xZnO-(20-x)MgO-20Al₂O₃-57SiO₂-3B₂O₃ (0 ≤ x ≤ 20 mol%) system.     

Synthesis and characterization of clinopyroxene based glasses and glass-ceramics along diopside (CaMgSi2O6)-jadeite (NaAlSi2O6) join

The crystallization behavior and mechanical characterization of glasses based upon the compositions along diopside (CaMgSi₂O₆)-jadeite (NaAlSi₂O₆) join has been investigated. Six glasses were obtained by the melt-quenching technique. Structural and thermal behaviors of these glasses were investigated by density and molar volume, infrared spectroscopy (FTIR) and dilatometry. The crystallization behavior of glasses was investigated by using differential scanning calorimetry (DSC). Sintering and crystallization behavior of the glass-ceramics were investigated under non-isothermal heating conditions up to temperatures of 850 °C. Mechanical characterization of glasses was investigated by using the measurement of Vickers indentation hardness and elastic constants such as Young's modulus (E), shear modulus (G), bulk modulus (K) and Poisson's ratio (ν). These data of the glasses were correlated with the structure of glasses, nature and role played by glass forming cations.