Microstructure Of Glass-ceramics Research Articles

The Effect of Lithium on Crystallization and Microstructure of Glass-Ceramics in Soda-Lime Silicate System

This study investigated the crystallization of soda-lime silicate (NCS) system by re-melting soda-lime silicate glass cullet with Al2O3 CaCO3 and Li2O. The Li2O was added as a nucleating agent. The effect of the nucleating agent on crystallization was investigated in order to study the possibility for use as a parent glass for glass-ceramics. Soda-lime silicate cullet was the main raw material and its chemical composition by weight was 68% SiO2 2% Al2O3 9% Na2O 9% K2O 3.5% CaO 2.5% MgO 1.2% TiO2 3% SrO and 2% ZnO. Glass batches with composition (%wt) of (65-x) Cullet:13Al2O3:22CaCO3:x(Li2O) (x = 0, 1, 2, 4, 6 and 8) were melted at 1500°C for 3 hours and annealed at 600°C. All glasses added with Li2O were clear except x = 8. The crystallization was investigated by Differential Scanning Colorimetry technique (DSC). The results exhibited the exothermic peak of crystallization (TpI and TpII). The glasses with added Li2O exhibited decreasing crystallization temperature with increasing Li content. The glasses were heated at temperatures around the crystallization temperature (700, 750 and 800°C). After heat treatment, the crystalline phase in the glasses was determined by X-ray diffraction technique (XRD). The microstructure was investigated by optical microscope and Scanning Electron Microscope (SEM). The phases of Nepheline (Na,K)AlSiO4 and Wollastonite (CaSiO3) were found. The crystallization depended on the heat treatment temperature. The thermal expansion of the glasses was determined by the dilatometric method to indicate the characteristics of the glass-ceramics. In conclusion, Li2O had a strong effect on the crystallization in soda-lime silicate system. The result could be applied for the production of glass-ceramics from soda-lime cullet.

Effects of heat treatment temperature on microstructure and mechanical properties of lithium disilicate-based glass-ceramics

In this study, the mechanical properties and microstructure of lithium disilicate glass-ceramics in the Li2O-SiO2-P2O5-Al2O3-K2O glass ceramics was investigated for dental applications. The glass-ceramics were prepared from the casting glass melt into warmed mold. After that the samples were heat treatment at 650–850 °C for 2 h. The heat treatment temperatures were determined from the differential thermal analysis (DTA). The microstructure of the glass–ceramics were characterized by X-ray diffraction (XRD) technique and the scanning electron microscopy (SEM). Moreover, the mechanical properties were investigated by Vickers hardness testing. Results indicated that the samples confirmed the occurrence of Li2Si2O5, LiSi2O3 Li3PO4 and LiAlSi2O6 phases in prepared glass ceramics. Moreover, the lithium disilicate glass-ceramic exhibits a high Vickers hardness values in the range of 4.92–5.90 GPa.

The Effects of Co2O3 Addition on Crystallization, Microstructure and Properties of Cordierite-Based Glass-Ceramics

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.

The microstructure and spectroscopic properties of calcium fluoro-aluminosilicate glasses and glass-ceramics by boron substitution

The calcium fluoro-aluminosilicate (4.5SiO2-3Al2O3-1.5P2O5-3CaO-2CaF2) glasses have significant applications in medical and dental fields. However, due to the biological hazard of aluminium element in human body, this study focus on the influence structure and properties of a series of resultant glasses and their correlated glass-ceramics after boron substitution for aluminum at different amounts. The results indicates that by increasing addition amount of boron, the density of the glasses and its glass-ceramics both decrease with the increase amount of bridging oxygens. And the glass transition temperature (Tg) and crystallization temperature (Tp) almost unchange for glasses but for the glass-ceramics, a decrease of both Tg and Tp are observed. Boron atoms only bridges with oxygen in glasses and its glass-ceramics as the form of BO3 and BO4 groups. By reduction of Al in glass, some non-Al containing needle-like calcium phosphate become the main crystalized phase.

Influence of TiO2 content on phase evolution, microstructure and properties of fluorcanasite glass-ceramics prepared through sintering procedure for dental restoration applications

This study aims to highlight the role of TiO2 (titanium dioxide) on concurrent densification-crystallization behavior, microstructure as well as mechanical and chemical properties of fluorcanasite glass-ceramics. According to the obtained results, the addition of TiO2 to the base composition (stoichiometric fluorcanasite) and an increase of its content, decreased crystallinity of the relevant glass-ceramics; but improved their sinterability. Fully densified glass-ceramics were obtained from TiO2 containing compositions after sintering at 900–950 °C. Calcium fluoride and fluorcanasite crystallized in all fabricated glass-ceramics during sintering; while goetzenite crystallized as the dominant crystalline phase in those glass-ceramics contained more than 6 weight ratios of TiO2. On the basis of microstructural observation, the interlocking status between the precipitated crystals was remarkably diminished by an increase of TiO2 content. Measurement of mechanical properties confirmed the rise of Vickers micro-hardness and simultaneous decrease of flexural strength and fracture toughness by enhancing of TiO2 content in the examined glass-ceramics.

Boron Promoted on Crystallization and Microstructure of Strontium Containing Mica Glass-Ceramics

Boron Promoted on Crystallization and Microstructure of Strontium Containing Mica Glass-Ceramics

Enhancement of Dielectric Breakdown Strength and Energy Conversion Efficiency of Niobate Glass-Ceramics by Sc2O3 Doping

Niobate glass-ceramics K2O-SrO-Nb2O5-B2O3-Al2O3-SiO2 (KSN-BAS) doped with different amounts of Sc2O3 have been prepared through a melt quenching/controlled crystallization method, and the influence of the Sc2O3 content on their phase composition, microstructure, dielectric performance, and charge–discharge properties investigated. X-ray powder diffraction results showed that the peak positions of the KSr2Nb5O15 phase shifted to higher angle and the glass-ceramic microstructures were significantly improved by Sc2O3 addition. Based on these results, 0.5 mol.% Sc2O3 doping was found to achieve remarkable enhancement in energy storage density, which reached 9.63 ± 0.39 J/cm3 at dielectric breakdown strength of 1450.38 ± 29.01 kV/cm with high conversion efficiency of ∼ 92.1%. For pulsed power applications, discharge speed of 17 ns and power density of 0.48 MW/cm3 were obtained in the glass-ceramic with 0.5 mol.% Sc2O3. These results could provide a new design strategy for high-performance dielectric capacitors.

Effect of TiO2 content on the crystallization behavior and properties of CaO-Al2O3-SiO2 glass ceramic fillers for high temperature joining application

The effects of TiO2 content on the crystallization behavior, microstructure, microhardness, coefficient of thermal expansion (CTE) and softening temperature of CaO-Al2O3-SiO2 glass ceramic fillers were investigated. The results show that the crystallization activation energy (E) firstly decreases and then increases with the TiO2 addition from 10 wt% to 20 wt%. The microstructure and phase composition of glass ceramics importantly depend on the content of TiO2. Low TiO2 content results in formation of Ti-contained crystals (CaTiSiO5) due to phase separation. In contrast, high TiO2 concentrations lead to precipitation of small titanium oxide crystals that act as nuclei, facilitating the development of CaAl2Si2O8. Furthermore, the formation of crystalline phases is beneficial for improving the microhardness and refractoriness of glass ceramics. The CaO-Al2O3-SiO2 glass with 15 wt% TiO2 addition exhibits the highest crystalline volume fraction possibly due to the lowest activation energy of crystallization. As a result, its microhardness and softening temperature can reach as high as 898.2 HV and 1027 °C, respectively. However, its CTE slightly decreases from 7.44 × 10−6/°C to 6.35 × 10−6/°C after crystallization treatment because of the formation of CaTiSiO5.

Microstructure and spectroscopic investigations of calcium zinc bismuth phosphate glass ceramics doped with manganese ions

Multi-component 10CaF2–20ZnO–(15 − x)Bi2O3–55P2O5:xMnO (0 ≤ x ≤ 2.5) glass ceramics were synthesised by melt quenching technique and heat treatment. The prepared glass ceramics were characterised by XRD, DTA, EDS and SEM. Spectroscopic studies such as optical absorption, EPR, FTIR and Raman were also carried out on these glass ceramics. The XRD and SEM studies have indicated that ceramic samples contain well defined and randomly distributed grains of different crystalline phases. The observed increase of enthalpy from DTA patterns up to 1 mol% of MnO indicates that the crystallisation starts initially from the surface of the material then gradually it is extended to the volume of the material and this influence is meagre at higher concentrations of MnO. The absorption spectra of manganese doped glass ceramics have exhibited two types of conventional bands; one due to Mn2+ ions and other due to Mn3+ ions. The EPR spectra of MnO doped glass ceramics showed a resonance signal around g2 = 2.023 with a six line hyperfine structure and another signal at about g1 = 4.314. The relative intensity and half-width of these two signals are observed to increase with the increase in the concentration of manganese ions up to 1 mol% beyond this concentration it is found to decrease. Such observation indicates the conversion of part of Mn2+ ions into Mn3+ ions in the glass ceramic matrix. The observed increase in the intensity of symmetrical structural units at the expense of asymmetrical structural units from the FTIR and Raman spectra at higher concentration of MnO indicating that Mn2+ ions occupy the network forming positions in the glass ceramic structure.

Strontium-releasing fluorapatite glass-ceramics: Crystallization behavior, microstructure, and solubility.

The purpose of this work was to investigate the effect of strontium partial replacement for calcium on the crystallization behavior, microstructure and solubility of fluorapatite glass-ceramics. Four glass compositions were prepared with increasing amounts of strontium partially replacing calcium. The crystallization behavior was analyzed by differential scanning calorimetry and X-ray diffraction (XRD). The microstructure was investigated by scanning electron microscopy. The chemical solubility was quantified according to ISO standard 10993-14. The amount of strontium released in solution after incubation in TRIS-HCl or citric acid buffer was measured by atomic absorption spectroscopy. XRD analyses revealed that partially substituted strontium-fluorapatite and strontium-åkermanite crystallized after strontium additions. The lattice cell volume of both phases increased linearly with the amount of strontium in the composition. Strontium additions led to a reduction in crystal size and an increase in crystal number density. The chemical solubility and amount of strontium released in solution increased linearly with the amount of strontium present in the composition in both TRIS-HCl and citric acid buffers. Total amounts of strontium released reached a maximum of 547 ± 80 ppm in TRIS-HCl and 1252 ± 290 ppm in citric acid buffer for the glass composition with the highest amount of strontium. For all strontium-containing compositions, the amount released in TRIS-HCl continued to increase between 70 and 120 h, indicating sustained release rather than burst release. © 2017 Wiley Periodicals, Inc. J Biomater Res Part B: 106B: 1421-1430, 2018.

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

Abstract Melt-quenching method was employed for obtaining a glass-ceramic with the following composition 42P 2 O 5 ·40CaO·5SrO·10Na 2 O·3TiO 2 (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-Ca 3 (PO 4 ) 2 and β-Ca 2 P 2 O 7 phases was successfully prepared. It was determined that during crystallization the primary phase in the precipitate was β-Ca(PO 3 ) 2. Other phases appearing in the resulting glass-ceramic were: α-Ca 2 P 2 O 7 , γ-Ca 2 P 2 O 7 , Ca 4 P 6 O 19 and CaHPO 4 (H 2 O) 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).

Microstructural development and electrical behavior during crystalization of iron-rich glass-ceramics obtained from mill scale

Abstract Mill scale is one of the most hazardous waste generated from the steelmaking industry. In 2014, around 16.4–32.8 million t of mill scale was generated all over the world. In this paper, we present recent results about the effect of the structure and microstructure of iron-rich glass-ceramics obtained from mill scale on their electrical behavior. Five iron-rich glass compositions were investigated. The crystalline phases of the crystallized (glass-ceramic) materials were identified by X-ray diffractometry, and phase content quantifications were performed by the Rietveld method. The crystallinity and porosity were also related to the electrical behavior of the glass-ceramics, which was determined by impedance spectroscopy, and the hardness, measured by the Vickers indentation method. Albite, andradite, anorthite, clinopyroxene, franklinite, nepheline, and spinel were shown to be the main crystalline phases present in the investigated compositions. The conductivity showed an increasing trend with the degree of crystallinity. This behavior was attributed to a decrease in porosity, an increase in the concentration of charge carriers in the glass phase (iron, Li+, and Na+), and an increase in the number of conduction paths through the glassy phase/crystalline phase interfaces. The relationship between hardness and crystallinity could not be verified due to the structural complexity of the glass-ceramics studied. However, a nearly linear relationship was found between the effect of porosity and hardness. The G2Z composition exhibited a hardness of 6.1 ± 0.5 GPa at 850 °C, which is a value in very good agreement with other iron-rich glass-ceramics studied.

The effect of heat treatments applied to superstructure porcelain on the mechanical properties and microstructure of lithium disilicate glass ceramics

The aim of this study was to investigate that heat treatments with different numbers applied to superstructure porcelain whether effects microstructure and mechanical properties of lithium disilicate ceramic (LDC). Eighty disc-shaped specimens were fabricated from IPS e.max Press. Specimens were fired at heating values of porcelain in different numbers and divided four groups (n=5). Initial Vickers hardness were measured and X-ray diffraction (XRD) analysis was performed. Different surface treatment were applied and then Vickers hardness, surface roughness and environmental scanning electron microscopy (ESEM) analysis were performed. Data were analyzed with Varyans analysis and Tukey HSD test (α=0.05). Initial hardness among groups was no significant different (p>0.05), but hardness and surface roughness after surface treatments were significant different (p<0.05). Lithium disilicate (LD) peaks decrease depended on firing numbers. ESEM observations showed that firing number and surface treatments effect microstructure of LDC. Increasing firing numbers and surface treatments effect the microstructure of LDC.

Resorbability of a Bioglass®-based glass-ceramic scaffold produced via a powder metallurgy approach

Abstract Consolidation processes aimed at manufacturing cellular solids from bioglasses often result in a glass-ceramic microstructure, whose response to aqueous environment affects their performance. In this study, we evaluated the microstructure and the effect of crystallization on the dissolution mechanism of a Bioglass®-based glass-ceramic scaffold, produced with a powder metallurgy inspired technology. All the experiments are conducted in a controlled aqueous environment in order to avoid nucleation of different species or unknown chemical interactions between simulated body fluids and bioglass-ceramic material. The presence of a residual silica glass embedding different phases of not fully crystallized particles is highlighted, showing a complex multiscale structure elucidated via Focused Ion Beam (FIB) preparation and Scanning Transmission Electron Microscopy (STEM) observation. Crystalline and amorphous phases dissolved both in water, with different kinetics. The dissolution appears to be a surface phenomenon, which reduces the section of the foam struts without instability of the glass-ceramic material. Amorphization of crystalline phase is observed during immersion of the glass-ceramic material in stirring conditions at room temperature from the ions dissolved in water.

Nature-inspired design of strong, tough glass-ceramics

Abstract

Optically Clear and Resilient Free-Form µ-Optics 3D-Printed via Ultrafast Laser Lithography.

We introduce optically clear and resilient free-form micro-optical components of pure (non-photosensitized) organic-inorganic SZ2080 material made by femtosecond 3D laser lithography (3DLL). This is advantageous for rapid printing of 3D micro-/nano-optics, including their integration directly onto optical fibers. A systematic study of the fabrication peculiarities and quality of resultant structures is performed. Comparison of microlens resiliency to continuous wave (CW) and femtosecond pulsed exposure is determined. Experimental results prove that pure SZ2080 is ∼20 fold more resistant to high irradiance as compared with standard lithographic material (SU8) and can sustain up to 1.91 GW/cm intensity. 3DLL is a promising manufacturing approach for high-intensity micro-optics for emerging fields in astro-photonics and atto-second pulse generation. Additionally, pyrolysis is employed to homogeneously shrink structures up to 40% by removing organic SZ2080 constituents. This opens a promising route towards downscaling photonic lattices and the creation of mechanically robust glass-ceramic microstructures.

Crystallization behavior and properties of CaO-MgO-Al2O3-SiO2 glass-ceramics synthesized from granite wastes

Granite wastes were used as the raw materials for the preparation of CaO-MgO-Al2O3-SiO2 glass-ceramics. The waste loading was about 50.24–68.34wt% in the batch depending on the chemical compositions of glasses. Effects of SiO2/(CaO+MgO) ratio on the crystallization behavior, microstructure and properties of glass-ceramics were investigated. The results showed that the crystallization activation energy Ec increased from 322.68 to 477.10kJ/mol, and Avrami parameter n decreased from 3.78 to 2.89 as the SiO2/(CaO+MgO) ratio increase from 1.72 to 4.99, while, the crystallinity of diopside decreased gradually, and the main crystalline phase changed into armalcolite with SiO2/(CaO+MgO) ratio increase to 4.99. The increase in SiO2/(CaO+MgO) ratio lead to the decreasing in Vicker's hardness, bending strength and alkali resistance of the glass-ceramics, but improved the acid resistance.

Preparation and characterization of SO3-doped barium borosilicate glass-ceramics containing zirconolite and barite phases

In order to improve the solubility of actinides and sulfate in the glass matrix, barium borosilicate glass-ceramics containing zirconolite and barite crystalline phases were developed. The effects of SO3 addition (0–8wt%) on crystalline phases, microstructure, and chemical durability of glass-ceramics belonging to SiO2-B2O3-Na2O-BaO-CaO-TiO2-ZrO2-Nd2O3-SO3 system were mainly studied. The results show that glass transformation temperature decreases slightly with increasing SO3 content. The main crystalline phase is zirconolite for all of the samples. When the addition SO3 content is higher or equal to 4wt%, rice-shaped barite crystals appear in the bulk of glass-ceramics. Barite phase was formed during the melting stage. X-ray fluorescence analysis indicates that about 1.3wt% of SO3 can be incorporated in the glass-ceramics when the addition content of SO3 is 6wt%. S element mainly distributes in the barite crystals. The decomposition of sulfate mainly occurs during the melting process. Moreover, the addition of a certain content (≤6wt%) of sulfate has no significant influence on the chemical durability of barium borosilicate glass-ceramics.

Effect of Heat Treatment Time on Properties of Mica-Based Glass-Ceramics for Restorative Dental Materials

The objective of this research is to focus improving the properties of machinable mica-based glass-ceramics in order for restorative dental materials. The glass-ceramics derived from the SiO2- Al2O3-MgO-MgF2-SrCO3-CaCO3-CaF2-P2O5 system were produced by a two-stage heat treatment. It was elucidated that the optimum nucleation and the crystallization temperatures were at 643°C and 892°C. The various heat treatment times in the first stage were applied as 3, 6, 12, 24, 48 and 72 h, respectively, on the optimum nucleation temperature to produce mica-based glass-ceramics. XRD results showed that specimens of variety of nucleation time had similar crystalline structures such as calcium-mica, fluorapatite, stishovite, anorthite, strontiumapatite and forsterite phases. The microstructures of glass-ceramics were observed by SEM basically as interlocked plate-like and needle-like microstructures of mica and fluorapatite, respectively, in all specimens. Furthermore, different heat treatment times influenced on the revealed crystal size of the glass-ceramics; the longer heat treatment, the smaller crystals. The resultant glass-ceramics gave the results of biaxial flexural strength (178-224 MPa) and Vickers hardness (295-393 HV) increasing with the formation of the interconnected mica phases which contributed to improve the machinability. The values of the properties were comparable to those of human enamel and suitable for some restorative dental applications.

Effect of MnFe2O4 and the Heat Treatment Temperature on the Bioactive Glass Properties

In this study, the effects of heat treatment temperatures on structural and magnetic properties in MnFe2O4(MF)/SiO2-Na2O-CaO-P2O5 (bioglass) bioactive glass ceramics were investigated. The MF/SiO2-Na2O-CaO-P2O5 bioactive glass ceramics were fabricated under various heat treatment temperatures in a range of 600-1000 °C. X-ray diffraction (XRD) technique, the scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are used to characterize phase and microstructure. The magnetic properties were determined from Vibrating Sample Magnetometer (VSM). The X-ray diffraction peaks presented two major crystalline phases: MnFe2O4 and Na2Ca2Si3O9. It was found that the heat treatment temperatures are the most influential parameter on microstructure and magnetic properties of the bioactive glass ceramics. The highest magnetic properties of studied ceramics were found in the sample heated at 1000 °C with adding 20 wt%. MF. The microstructural properties of the studies samples were investigated and the results were then correlated with the characteristics of heat treatment temperatures as well as the microstructure of the bioactive glass ceramic.