Synthesis, characterization and in vitro bioactivity of magnesium-doped sol-gel glass and glass-ceramics

Bioactive glass and glass-ceramics in the system CaO-MgO-SiO₂-P₂O₅ have been prepared by the sol-gel and high temperature sintering techniques. The obtained samples were characterized by thermogravimetric and differential thermal analysis (TG/DTA), N₂-adsorption measurement, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). In vitro bioactivity tests were also conducted in simulated body fluid (SBF). The studies of crystallization kinetics under non-isothermal conditions showed the activation energy for crystallization to be 381 kJ/mol and the crystallization mechanism gradually changed from three-dimension growth to two-dimension crystallization with the increase of heating rate. Sintering temperature had great influence on the samples texture and structure. In addition, the apatite-formation on glass and glass-ceramics was confirmed by in vitro tests, and crystallization decreased the samples bioactivity.     

The effect of lithium fluoride on the thermal stability and thermoluminescence properties of borosilicate glass and glass-ceramics

The oxyfluoride glass and glass-ceramics from the LiF-B₂O₃-SiO₂ system are developed. The stable glass can be produced in the range of 20–40 mol% LiF. The effect of LiF admixture on the thermal stability of the glass as well as the thermoluminescence (TL) properties such as glow curves shape is studied. The results show that the increase of lithium fluoride content in the borosilicate glass causes efficiency enhancement of the thermoluminescence signal. We have clearly stated that the process of controlled crystallization of the oxyfluoride glasses can lead again to increased intensity of the TL process. The glass-ceramics with 40 mol% LiF reveals similar level of TL signal to commercially used doped LiF material and can be considered as active material for alpha and beta radiation detectors.     

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.     

Structural and Textural Modifications of Ternary Phosphate Glasses by Thermal Treatment

Phosphate-based glasses of composition xNa₂O−(45+(10−x))CaO−45P₂O₅ with different Na₂O, CaO (x = 1, 5, 10, 15, and 20 mol%), and invariable P₂O₅ (45 mol%) contents were prepared using the rapid melt quench technique. The obtained thermal data from differential thermal analysis revealed a decline in glass transition (T_g) and crystallization (T_c) temperatures of glasses against the compositional changes. The inclusion of Na₂O at the cost of CaO in the glass network led to a reduction in its thermal stability. The thermal treatment carried out on glasses helped to derive their glass-ceramic counterparts. The amorphous and crystalline features of samples were characterized using X-ray diffraction patterns. The crystalline species that emerged out of the calcium phosphate phases confirmed the dominance of Q¹ and Q² structural distributions in the investigated glass-ceramics. The obtained scanning electron micrographs and atomic force microscopic images confirmed the surface crystallization and textural modification of the samples after thermal treatment. The N₂-adsorption–desorption studies explored the reduction of porous structures due to thermal treatment on the melt-driven glass surface. The measured elastic moduli and Vicker's hardness values of the glasses showed an increase after thermal treatment, which were reduced against the inclusion of alkali content in both glass and glass-ceramics.     

Sintering behaviour and properties of YAlSiO and YAlSiON glass-ceramics

Four different YAlSiO and YAlSiON compositions that produced either glass or glass-ceramic materials were designed. Densities, glass transition temperatures, coefficients of thermal expansion and hardness data were established for each material. The sintering behavior was determined from the hot stage microscopy (HSM) runs. For the YAlSiO glass compositions, the viscosity-temperature curves were estimated from five characteristic HSM points using Scholze's method. The YAlSiON glass-ceramics with higher Y content showed YAlO₃ and SiAl₆O₂N₆ crystals and the poorer Y composition had crystalline precipitates of Si₃N₄, Si₄Al₂O₂N₆ and Y₂SiAlO₅N. The effects of the Al/Si and Y/Si ratios, and the nitrogen content on the properties have been discussed. These glass-ceramics showed relatively high thermal expansion coefficient and hardness and, therefore, its application as protective coatings for metallic components against high temperatures and/or corrosive environments is envisaged.     

Processing and luminescence of Eu/Dy-doped Sr2MgSi2O7 glass-ceramics

Glass-ceramics based on the Eu/Dy-doped Sr₂MgSi₂O₇ phosphor have been obtained from sintering and crystallization of glass powders. Electric and gas furnaces were employed for glass melting. The doped parent glasses show red emission under excitation of UV light whereas the corresponding glass-ceramics show blue emission.The microstructure of the glass-ceramics and the crystals responsible for the blue emission were observed by scanning electron microscopy-cathodoluminescence. The composition of the crystallised phases and the distribution and incorporation of rare-earth (RE) ions into the crystals and remaining glassy phase were determined by X-ray diffraction and energy dispersive X-ray analysis, respectively.Photoluminescence emission spectra showed a main peak at 484 nm assigned to the typical Eu²⁺ transitions under excitation at 390 nm in the glass-ceramics. The presence of Dy³⁺ improved persistence in the samples melted in the gas furnace. The glass-ceramics are sensitive to temperature, which modifies both the persistence time and red-blue luminescence.     

LZS/Al2O3 nanostructured composites obtained by colloidal processing and spark plasma sintering

Li₂O-SiO₂-ZrO₂ (LZS) glass-ceramics have high mechanical strength, hardness, resistance to abrasion and chemical attack, but also a high coefficient of thermal expansion (CTE), which can be reduced adding alumina nanoparticles. The conventional glass-ceramic production is relatively complex and energy consuming, since it requires the melting of the raw materials to form a glass frit and a two-step milling process to obtain particle sizes adequate for compaction. This study describes the preparation of LZS glass-ceramics through a colloidal processing approach from mixtures of SiO₂ and ZrO₂ nanopowders and a Li precursor (lithium acetate obtained by reaction of the carbonate with acetic acid). Concentrated suspensions were freeze-dried to obtain homogeneous mixtures of powders that were pressed (100 MPa) and sintered conventionally and by spark plasma sintering. The effect of the alumina nanoparticles additions on suspensions rheology, sintering behavior and properties such as thermal expansion, thermal conductivity, hardness and Young’s modulus were evaluated.     

Enhanced upconversion emissions in Er3+ doped perovskite BaTiO3 glass-ceramics via electric-stimulated polarization technique

In this work, Er³⁺ doped ferroelectric glass ceramics containing high-content BaTiO₃ nanoperovskite have been prepared successfully. Optical behaviors with structural dependence indicate that the perturbation of ligand field by tunable thermal condition in glass-ceramics is beneficial to boost upconversion efficiency, that is, the emission intensity possesses multifold improvement in both green band (²H_11/2, ⁴S_3/2 → ⁴I_15/2) and red band (⁴F_9/2 → ⁴I_15/2). And adding voltage to stimulate polarization reversal of ferroelectric domains has been investigated as a physical mode to broaden luminescence emissions in visible range. Compared with the unpolarized glass-ceramics, over 1.5 folds higher luminescence intensity can be obtained by polarizing the samples. The multiple mechanisms to achieve upconversion enhancement in ferroelectric materials will stimulate and expand the use of innovative optoelectronic devices.     

Crystallization mechanisms of cordierite glass-ceramics with “surface-center” crystallization behavior

Cordierite glass-ceramics usually begin to crystallize from the surface. As an efficient nucleating agent, TiO₂ can promote the rapid transformation of glass to bulk crystallization, but it is easy to cause the increase of dielectric constant and light absorption. High crystallinity cordierite glass-ceramics were prepared by optimizing the heat treatment process without or with different nucleating agents in stoichiometric cordierite glasses. The results show that the crystallization mechanisms of glasses without and with ZrO₂+P₂O₅ as nucleation agents are controlled by surface crystallization. While, the glass with TiO₂+ZrO₂+P₂O₅ as nucleation agents have the tendency to be bulk crystallization. The studied glasses are crystallized from surface and have different crystallization orientations with the inner glass. The thickness of crystalline layer increased with the increasing of heating temperatures, but the “surface-center” crystallization process cannot complete by further increasing heating temperatures because of softening deformation of glasses. At 1020 ℃, the glasses complete the “surface-center” crystallization for long durations. The glasses without nucleation agents and with ZrO₂+P₂O₅ require 10 h, but the glass with TiO₂+ZrO₂+P₂O₅ complete for 5 h. Although all the three glasses complete the “surface-center” crystallization, the glasses with nucleation agents show the higher crystallinity upon the same heat treatments. Finally, glass-ceramics with excellent performance were obtained, for example, the Z1# glass-ceramic have the high microhardness ∼7.4 GPa, low thermal expansion coefficient ∼1.4☓10⁻⁶ ℃⁻¹ at 20–300 ℃, and relatively high thermal conductivity ∼2.4 W/mK. It also exhibits low dielectric constant and loss, which was ∼4.5 and ∼1.2☓10⁻³ at 1 MHz, ∼ 4.9 and 2.3☓10⁻³ at 10.5 GHz..     

Microstructure and ion-exchange properties of transparent glass-ceramics containing Zn2TiO4/α-Zn2SiO4 nanocrystals

Transparent glass-ceramics have particular properties compared with their precursor glasses, and have promising potential applications in many fields. Titanium-relative phases are frequently employed as nucleation agents for crystallization of glass-ceramics, and rarely been precipitated as functional nanocrystalline phases in glass-ceramics. In this work, transparent glass-ceramics containing Zn₂TiO₄ and/or α-Zn₂SiO₄ nanocrystals are investigated. It turns out that Vickers hardness of these glass-ceramics increases with the precipitation of Zn₂TiO₄ and α-Zn₂SiO₄ nanocrystals. Despite the blocking effect of nanocrystals precipitated in the glass-ceramics, structural and compositional modification of the residual glass induced by the precipitation of these nanocrystalline phases facilitates the K-Na ion-exchange, leading to the enhanced depth of layer and further improved Vickers hardness of the glass-ceramics.     

Effects of Al2O3 addition on microstructure and luminescence of transparent germanosilicate glass-ceramics with incorporated spinel Ga-oxide nanocrystals

Ga-oxide spinel nanocrystals are wide band gap systems, which can be incorporated in a glass matrix by phase separation mechanisms. In suitable conditions, this kind of processes can give rise to transparent nanostructured glass-ceramics with UV excitation and luminescence properties potentially interesting in several technological areas. Nanophase size dispersion and volume fraction have been demonstrated to be controllable, at some extent, by suitable thermal treatments for nucleation and nano-crystallization in low-alkali gallium germanosilicate system. Here we report the results on the role of Al₂O₃ additions on the microstructure and optical response of the glass-ceramics fabricated in this system. Data of differential scanning calorimetry, X-ray diffraction, transmission electron microscopy, absorption and fluorescence spectroscopy show that Al₂O₃ addition, up to 4.5 mol%, turns out to have a considerable impact on the size and number density of precipitated nanocrystals, which are solid solutions of γ-Ga_2-xAl_xO₃ resulting from the partial incorporation of Al³⁺ ions into the crystalline phase. We show that the use of Al₂O₃ as an additive in the composition of gallium germanosilicates facilitates glass melting and leads to glass-ceramics with significantly modified photoluminescence characteristics such as decay lifetime and integrated intensity of light emission. The possible reasons are discussed.     

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 influence of MgO on the crystallization behaviour and properties of SrO-rich phosphosilicate glasses

A series of glass was produced to investigate the effect of MgO/SrO replacement on the crystallization characteristics and properties of phosphosilicate glasses containing high SrO content. The glass samples were synthesized by conventional melting technique based on 5CaO-(40-X)SrO-X MgO– 43SiO₂–7P₂O₅–5CaF₂ (where; X = 10, 20, 30 and 40 mol%). The influence of MgO/SrO replacement on phase assemblages, microcrystalline structures, thermal expansion, and mechanical properties was examined as a function of basic chemical compositions and crystallization parameters. Predominant strontium meta-silicates together with strontium fluoroapatite phases are crystallized from the base glass free of magnesium. The substitution of strontium by magnesium up to 50% led to formation strontium akermanite phase Sr₂MgSi₂O₇ at the expense of SrSiO₃ phase. Whereas the increase of the MgO/SrO of more than 50%, which led to the crystallization of the clino-enstatite MgSiO₃ as a predominant phase. The results show that the α-values of the glass-ceramics are ranged in 94–125 × 10⁻⁶ K⁻¹ over the temperature range (25–500 °C). On the other hand, MgO/SrO replacements led to enhancing the microhardness of the resultant crystalline materials from 4713 Mpa to 6744 Mpa. As a result of the designed glass compositions, promising crystalline phases were obtained as well as good thermal and mechanical properties for the resultant glass-ceramics. Therefore, the designed glass-ceramics can be strongly used as biomaterials especially for bone reconstruction applications.     

Degradation-controlling mechanisms in natural organic acid solutions of CaO–Al2O3–SiO2–B2O3 glass-ceramics by partially substituting Ca2+ with Ba2+ and Sr2+

The degradation of environmentally friendly CaO–Al₂O₃–SiO₂–B₂O₃ (CASB) glass-ceramics, which consist of anorthite and glass phase, was investigated in three natural organic acid solutions. The results indicated that citric acid had the most significant effect on the degradation of CASB glass-ceramics. While the chemical stability of anorthite is relatively poor, the glass phase also contributed significantly to the effective degradation of CASB glass-ceramics. Subsequently, Ba²⁺ or Sr²⁺ was used for full or partial substitution of Ca²⁺ in CASB glass-ceramics, and the degradation-controlling mechanism of the substituted CASB glass-ceramics was further researched. The full substitution of Ca²⁺ in CASB glass-ceramics by the two cations resulted in the occurrence of borate [BO₄] units in the glass phases, and the interlinkage of [BO₄] with broken silicate [SiO₄] network structures caused a complementary network effect. Consequently, the degradation of CASB glass-ceramics by organic acids was reduced due to the improvements in the chemical stability of the modified glass-ceramics. Additionally, degradation control can also be achieved based on a mixed-alkali effect, originating from the partial substitution of Ca²⁺ in CASB glass-ceramics by Ba²⁺ or Sr²⁺. The degradable glass-ceramics have the potential to be applied in low-temperature co-fired ceramic technology because of their good physical properties, which include a dielectric constant of 3–5, a dielectric loss as low as 10⁻³, a coefficient of thermal expansion of 3–9 × 10⁻⁶/°C, and an average bending strength of about 47 MPa. Noticeably, the development of the degradable glass-ceramics is helpful to the low-cost and pollution-free recycling of valuable metal electrodes, which is significant for the sustainable development of electronic packaging technologies.     

Enhancement of glass-ceramic performance by TiO2 doping: In vitro cell viability,proliferation, and differentiation

A new TiO₂-containing bioactive glass and glass-ceramics based on 50SiO₂-(45-X)CaO-(XTiO₂)-5P₂O₅ system was designed using a sol–gel technique (where X = 5, 7.5 and 10 wt %). The roles of the crystallization behavior and physicochemical characteristics of the designed glass and glass-ceramics which were played in the introduction of TiO₂ substitutions were investigated. Moreover, cell proliferation and differentiation were evaluated against human osteosarcoma cells (Saos-2). The TiO₂/CaO replacements led to the formation of a stronger glass structure and thus increased thermal parameters and the chemical stabilization of the designed materials. The FTIR data confirmed the existence of Ti within the glass and glass-ceramics samples, and no remarkable effect on their chemical integrity was observed. The XRD patterns indicated that calcium-containing minerals, including Ca₂SiO₄,Ca₃(PO₄)₂, Ca(Ti,Si)O₅, CaTiSiO₅, and Ca₁₅(PO₄)₂·(SiO₄)₆ phases were developed as a role of structure/texture under the applied heat-treatment. The results of the cytotoxicity test proved that a safe sample dose is 12–50 μg/ml, at which cell viability is ≥ 85%. The cell differentiation determined by ALP test proved the superiority of glass-ceramics compared with their native glasses. Therefore, the obtained materials could be safely used as novel biocompatible materials for the regeneration of bone tissue.     

High toughness transparent glass-ceramics with petalite and β-spodumene solid solution as two major crystal phases

Lithium aluminosilicate glass-ceramics are well known for good transparency, high fracture toughness, low thermal expansion, and good ion exchange ability. In this study, new transparent Li₂O-Al₂O₃-SiO₂ (LAS) glass-ceramics with petalite and β-spodumene solid solution as the major crystalline phases were invented for favorable mechanical properties and potential for application in the hollowware, tableware, container, and plate glass industries. Crystal phases are mainly influenced by the ratio of Al₂O₃ to SiO₂ concentrations. The concentration of SiO₂ required to form specific crystalline phases in the glass-ceramics is higher than that inferred from the ternary phase diagram. Al₂O₃ content is required to be sufficiently high for the formation of crystals, instead of balancing excess amounts of Li₂O in the glass. The average transmittances of 2.0 ± 0.1 mm thickness samples in visible light regions (400–700 nm) can reach more than 80% with crystal sizes of 20–40 nm. Transmittance is significantly decreased for heat treatments around 710°C, due to the high growth rate of β-spodumene solid solution crystals. Vickers hardness, indentation toughness, and crack probabilities of transparent LAS glass-ceramics are significantly improved compared with standard soda lime silicate glass, due to the crack bridging and deflection of crystal grains.     

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.     

Low Li2O content study in Li2O-Al2O3-SiO2 glass-ceramics

The price of lithium-containing minerals and other chemical materials continues to increase, resulting in an increase in the production cost of Li₂O-Al₂O₃-SiO₂ (LAS) system glass-ceramics. In the LAS glass-ceramics component, the reduction in the amount of Li₂O used can reduce the cost of the product. It is worthwhile to study whether it is possible to prepare glass-ceramics with low expansion properties under low Li₂O content. The effect of Li₂O content on the glass-ceramics of LAS system was studied. In this paper, spodumene was used as the main raw material, and TiO₂ and ZrO₂ were added as crystal nucleating agents to prepare transparent glass-ceramics with low expansion coefficient. The effects of the change of Li₂O content on the crystal phase and microstructure of glass-ceramics were investigated by XRD, DSC, FTIR and SEM. The results show that the main crystalline phase of the low expansion transparent glass-ceramics is β-quartz solid solution. When Li₂O content is in the range of 2.99 wt% to 4.13 wt%, low expansion glass ceramics can be prepared by an appropriate method. With the increase of Li₂O content, the average coefficient of thermal expansion (CTE) in the temperature range of 30 °C–300 °C shows a decreasing trend. When Li₂O content is in the range of 3.51 wt% to 4.13 wt%, the thermal expansion coefficient of the glass ceramics is extremely small, and even a negative expansion coefficient occurs.     

Structural,optical, and spectroscopic properties of Er3+-doped TeO2–ZnO–ZnF2 glass-ceramics

Transparent fluorotellurite glass-ceramics have been obtained by heat treatment of precursor Er-doped TeO₂–ZnO–ZnF₂ glasses. ErF₃ nanocrystals nucleated in the glass-ceramics have a typical size of 45 ± 10 nm. Based on the Judd-Ofelt theory, the main radiative parameters for the ⁴I_13/2 → ⁴I_15/2 transition have been obtained. The split of the absorption and emission bands and the reduction of the Ω₂ parameter, as compared to the glass, confirm the presence of Er³⁺ ions in a crystalline environment in glass-ceramic samples. The analysis of the ⁴I_13/2 decays suggests that a fraction of Er³⁺ ions remains in a glass environment while the rest forms nanocrystals. For the glass-ceramics, intense red and green upconversion emissions were observed with an enhancement of the ⁴F_9/2 → ⁴I_15/2 red one compared to the glass sample. The temporal evolution of the red emission together with the excitation upconversion spectra suggests that energy transfer processes are responsible for the enhancement of the red emission.     

Migration,transformation and solidification/stabilization mechanisms of heavy metals in glass-ceramics made from MSWI fly ash and pickling sludge

In consideration of recycling solid waste to achieve high value-added products, glass-ceramics have been fabricated from municipal solid waste incineration (MSWI) fly ash, pickling sludge (PS), and waste glass (WG) by melting at 1450 °C firstly to achieve parent glass and then crystallizing at 850 °C. Results demonstrated that heavy metals have been well solidified in the prepared glass-ceramics, and relatively/extremely low leaching concentrations of heavy metals have been detected. The synthetic toxicity index of heavy metals has been greatly reduced from 7-18 to <3.2 after crystallization treatment, and the leaching concentrations of Cr, Ni, Zn, Cu, and Pb are 0.15, 0.05, 0.26, 0.12, 0.19 mg L^-1 respectively. Chemical morphology analysis, principal component analysis, TEM and EPMA were utilized to clarify the migration, transformation, and solidification mechanism of heavy metals from the as-received solid wastes. The major heavy metals, Cr and Ni which is responsible for the most toxicity, mainly exist in form of the oxidation state and residual state in parent glass, while the residual state in the glass-ceramics. The solidification performance was mostly positively correlated with the form of residue state, which the stability of heavy metals in glass-ceramics is improved. The solidification mechanism of heavy metals in glass-ceramics could be explained by the combination of chemical solidification/stabilization and physical coating. The TEM and EPMA confirmed that Cr and Ni mainly exist in the spinel crystalline (NiCr₂O₄, Fe_0.99Ni_0.01Fe_1.97Cr_0.03O₄) by solid solution or chemical substitution, and a small amount of Cr in the diopside phase. Pb, Cu, and Zn are homogenously dispersed in the glass-ceramics, which is considered as physical coating solidification.