Preparation and luminescent properties of Eu-doped transparent mica glass–ceramics

Eu-doped transparent mica glass–ceramics were prepared, the influence of Eu-doping on the crystallization of the parent glasses was investigated and the luminescent properties of the parent glasses and the glass–ceramics were estimated. A small additive amount of Eu element was very effective in preparing transparent mica glass–ceramics. However, the excess addition led to the coarsening of phase separation in the glass phase and the separation of unidentified crystal phases and β-eucryptite during heating of the parent glasses, which caused white opaque at lower heating temperatures. When mica crystals were separated, Eu ions entered the interlayers of mica crystals. The observed emission and excitation spectra showed that parts of Eu³⁺ ions which were added as Eu₂O₃ were reduced to Eu²⁺ ions during melting of the starting materials and heating the parent glasses in air and the energy transfer from Eu²⁺ to Eu³⁺ ions occurred.     

Structural and magnetic properties of steel slag based glass–ceramics

Crystallisation of magnetite in multicomponent glass melts was investigated. Structural features and magnetic properties were tested using X-ray diffraction, scanning electron microscope techniques, vibrating sample magnetometer and Mössbauer spectroscopy at room temperature. The results show that the magnetite phase was detected in the glass–ceramic samples after heat treatment at higher crystallisation temperature (over 900°C). Fe²⁺ and Fe³⁺ ions contribute to the formation of magnetite crystal. Various crystal morphologies were observed. Isomer shift values suggest that Fe³⁺ and Fe²⁺ are in tetrahedral and octahedral coordination respectively. The saturation magnetisation tends to increase with the crystallisation temperature.     

Effect of MgO addition on the properties of PbO –TiO2–B2O3 glass and glass–ceramics

Glass samples with composition of (50?X) PbO–X MgO–25 TiO₂–25B₂O₃ (where X=0, 5, 10 and 15 mol%) were prepared using conventional quenching technique. The amorphous nature of glass samples were confirmed by XRD. The glass transition temperature, T_g and crystallization temperature T_c were determined from the DTA. It has been observed that the addition of MgO enhances the T_g. The rise in T_g with MgO content may be attributed to the greater field strength of Mg²⁺ cation (as compared to Pb²⁺) which leads to the formation of stronger bonds. These glass samples were converted to glass–ceramics by following a two-stage heat treatment schedule. It was observed that there was good correlation between the density and CTE results of the glass–ceramics. The XRD results revealed the formation of tetragonal lead titanate as a major crystalline phase in the glass–ceramics. The addition of MgO to the glass contributes to the formation of MgB₄O₇. The dielectric constant for all the glass–ceramic samples was observed to be higher than that of corresponding glass samples. Further, with addition of MgO the room temperature dielectric constant for glass–ceramic samples increases up to 10 mol% of MgO and then decreases for 15 mol%. It has been further observed that the variation of dielectric constant of glass–ceramic samples with MgO content is exactly opposite to the variation of crystallite size of PbTiO₃ embedded in the glass ceramic-samples.     

Low temperature production of glass ceramics in the anorthite–diopside system via sintering and crystallization of glass powder compacts

The production of glass ceramics (GCs) with theoretical anorthite–diopside (An–Di) weight ratios of 60/40, 50/50 and 45/55 via sintering and crystallization of glass powder compacts was investigated at different temperatures between 800 and 950 °C. The investigated compositions are located in the cross-section of the ternary fluorapatite–An–Di system close to An–Di binary joint, with constant fluorapatite content of 4.8 wt.%. Two different groups of glass powders, with mean particle size of 2 and 10 μm, were used. The experimental results showed that sintering is almost complete at 800 °C, preceding crystallization, which takes place via surface crystallization mechanism. The properties values of the produced GCs, which are the best for the composition close to An–Di eutectic line, are discussed with respect to the evolution of crystalline phases and the microstructure over increasing firing temperature. Under the technology perspective, the investigated processing route is significantly superior in comparison to the attempts reported in earlier studies.     

Crystallisation and characterisation of dielectric glass ceramics in Li2O–Al2O3–SiO2 system

Abstract

Glass ceramics in the Li₂O–Al₂O₃–SiO₂ system have been synthesised to produce bulk materials grown in a glass phase via quenching followed by controlled crystallisation. The crystallisation and microstructure of Li₂O–Al₂O₃–SiO₂ (LAS) glass–ceramic with nucleating agents (B₂O₃ and/or P₂O₅) are investigated by differential thermal analysis, X-ray diffraction and scanning electron microscopy and the effects of B₂O₃ and P₂O₅ on the crystallisation of LAS glass are also analysed. The introduction of both B₂O₃ and P₂O₅ promotes the crystallisation of LAS glass by decreasing the crystallisation temperature and adjusting the crystallisation kinetic parameters, allows a direct formation of β spodumene phase and as a result, increases the crystallinity of the LAS glass ceramic. Microstructural observations show that the randomly oriented, nanometre sized crystalline is found with residual glass concentrated at crystallite boundaries. Furthermore, it is interesting that codoping of B₂O₃ and P₂O₅ creates not much effect on the crystallisation temperature. The dielectric properties of the glass–ceramics formed through controlled crystallisation have a strong dependence on the phases that are developed during heat treatment. The dielectric constant is continuously increased and the dielectric loss is decreased with addition of additives where mobile alkali metal ions (e.g. Li⁺) are incorporated in a crystal phase and minimise the residual glass phase.     

Optimisation of sintered glass–ceramics from an industrial waste glass

Industrial plasma melting of municipal solid waste (MSW) incinerator fly ashes leads to a glass that may be easily crystallised to gehlenite glass–ceramics, by the sintering of fine glass powders. However, since the glass composition is not optimised for glass–ceramic manufacturing, the viscous flow is much hindered by a very significant surface crystallisation and dense glass–ceramics are feasible only by sintering above 1000 °C. This paper reports a new strategy for obtaining dense and strong glass–ceramics at 950 °C, with a holding time of only 30 min, consisting of the mixing of waste glass with a secondary recycled glass, such as soda-lime–silica glass or borosilicate glass. For an optimum balance between the two types of glass also the addition of kaolin clay, in order to favour the shaping, was found to be feasible. The approach had a positive effect, besides on the mechanical properties (e.g. bending strength exceeding 100 MPa), on the chemical stability.     

Physical properties and electrochemical performance of molybdenum–lead-germanate glasses and glass ceramics

Glasses and glass ceramics of the xMoO₃(100?x)[7GeO₂·3PbO] system where x=0–30 mol% MoO₃ were synthesized and characterized in order to obtain information about the structural correlations and the relationship between structure and physical properties in these materials. Changes of the FTIR, UV–vis and EPR data are discussed in view of the glass network structural changes determined by the evolution of molybdenum ions state, glass composition and MoO₃ concentration.The spectroscopic studies indicate that with increasing of MoO₃ content a fraction of the Mo⁶⁺ ions convert Mo³⁺ and Mo⁵⁺ ions. Accordingly, these modifications cause the depolymerization of the host network, the increase of the structural disorder and formation of GeO₂ and PbMoO₄ crystalline phases. The shape of EPR spectra is modified by the increase of the MoO₃ concentration indicating that molybdenum ions exists in glass and glass ceramics in more than one valence state. The EPR spectra contain a broad line located at g～5.2 and, for the samples with a MoO₃ content up to x≥15 mol%, the presence of the hyperfine structure characteristic for the Mo⁵⁺ ions can be observed, too.The electrochemical performances of the glass and glass ceramics samples with x=10 and 30 mol% MoO₃ were demonstrated by cyclic voltammetry.     

Modification of glass network and crystallization of CaO–Al2O3–MgO–SiO2 based glass ceramics with addition of iron oxide

Modification of glass network and crystallization process of a CaO–Al₂O₃–MgO–SiO₂ (CAMS) based glass ceramic to form diopside through addition of iron oxide were investigated using differential thermal analysis (DTA), Raman spectrum, X-ray diffraction, SEM and EBSD techniques. The experimental results showed that addition of Fe₂O₃ led to remarkable reductions in both the glass transition temperature (Tg) and crystallization temperature (Tp) of the CAMS glass ceramic. At addition level below 5 wt%, the Tg and Tp temperatures were 651°C and 903°C, respectively, and the crystallization only occurred on the surface of the glass ceramic samples. Increasing the addition level to 10 wt% and 15 wt%, not only led to reduction in the Tg and Tp temperatures to 643-641°C and 892-876°C, respectively, but also promoted the formation of crystalline diopside throughout the CAMS samples. Based on the results of Raman spectrums, it was confirmed that Fe₂O₃ addition reduced the strength of glass connection as a result of chemical reactions between the isolated Si–O tetrahedron and Fe³⁺ ion, forming Fe³⁺O₄–SiO₄, which can be regarded as Q₂ unit. And this is the first experimental evidence that proving the approach of Fe³⁺ mending glass network. Microstructural examination also identified the formation of large numbers of spherical Fe-enriched regions within the CAMS glass matrix as a result of the amorphous phase separation due to the Fe₂O₃ addition. The interfaces between the Fe-enriched regions and the glass matrix acted as preferred nucleation sites for the diopside, facilitating the crystallization. Crystallographic analysis using EBSD technique determined the <001> as the most favorite growth direction for the diopside crystals in the CAMS based glass ceramic.     

Investigation of microscale fracture mechanisms in glass–ceramics using peridynamics simulations

Glass–ceramics (GCs), obtained by controlled crystallization of a specially formulated precursor glass, are interesting materials that show great promise in obtaining superior properties compared to those of the precursor glass. Controlled crystallization enables creation of a microstructure with multiple phases which impacts macroscale properties in interesting ways. The present work develops microstructure-scale computational models using the theory of peridynamics to investigate the increase in fracture toughness of GCs compared to traditional glass. Computational modeling is a promising tool to probe microstructural mechanics, but such studies in the literature are scarce. In this work, the theory of peridynamics, a non-local theory of continuum mechanics, is applied to simulate crack propagation through microstructural realizations of a model lithium-disilicate glass–ceramic. The crystalline and glassy phases within the microstructure are explicitly considered, with the size and shape of crystals inspired by experimental data. Multiple toughening mechanisms are revealed, which are functions of crystallinity and morphology, and the impact on fracture toughness is demonstrated. Crack path tortuosity is studied, and it is found that an optimum level of crack path tortuosity can be obtained in the range of 0.6–0.8 crystallinity. Numerical results are shown to agree well with previously published experimental and modeling results.     

Crystallization in a soda–lime-silicate glass after high pressure

This work explored the permanent changes a high pressure (HP) processing could cause on nucleation, Raman vibrational modes, thermal, and mechanical properties of the Na₂O • 2CaO • 3SiO₂ (N₁C₂S₃) glass. It was shown that, with higher pressure values, the number of nuclei per unit of volume, N_V, has decreased. Raman spectra showed no significant changes in the vibrational modes; however, the differential thermal analysis performed indicated that the glass transition temperatures, T_g, were higher than the pristine glass sample and that HP caused the glass to be less stable. The Vickers indentation radial cracks remained constant; however, the lateral cracks increased in size, indicating that the glass is more stressed after HP, and therefore, the relaxation time for nucleation will be higher, lowering N_V further, as observed.     

Bioactivity investigation of glass and glass ceramics in Li2O–SiO2–CaO–P2O5–CaF2 system

Abstract

Glass samples in Li₂O–SiO₂–CaO–P₂O₅–CaF₂ system with different contents of P₂O₅, CaO and CaF₂ in relative ratios responded to fluoroapatite (FA) composition (referred to P₂O₅ addition) have been prepared and heat treated at 550 and 750°C to obtain glass ceramics. Bioactivity of all samples has been proved in vitro by the presence of new layer of apatite-like phases formed after soaking in simulated body fluid (SBF). The development and the apatitic character of created layers have been demonstrated by Fourier transform infrared analysis. Scanning electron microscopy and electron probe microanalysis have demonstrated that the density and the thickness of new layer depend on P₂O₅ content, crystallisation temperature and immersion time. The bioactivity has been enhanced by P₂O₅ addition as well in the case of the base glasses as in the case of glass ceramics. The additional heat treatment appeared to inhibit the bioactive behaviour, though the longer SBF acting leads to the additional formation of apatite-like layer. The mechanical properties, expressed as Vicker hardness, have been found higher and increasing with P₂O₅ in glass ceramics treated at 750°C comparatively with base glass samples and the highest value of 7˙37 GPa has been achieved by 14 wt-%P₂O₅ addition. The same content of P₂O₅ in glass ceramics heat treated at 550°C resulted in a decrease in hardness to a minimum value from all samples. The increase and decrease in hardness responded to development and suppression of crystallisation respectively. The inhibition of crystallisation has been affected by the presence of 'amorphous' FA according to X-ray diffraction and differential thermal analysis results.     

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

Diffusion of Ag species into the surface layers of the MgO–Al₂O₃–TiO₂–SiO₂ glass stimulates the crystallization processes therein during subsequent thermal treatment. It was found that the silver doping significantly increases the microhardness of glass and glass ceramics. The effect of the Ag diffusion and the subsequent high-temperature treatment (T > T_g) on the structure and luminescence properties of the MgO–Al₂O₃–TiO₂–SiO₂ glass was studied. The thermal evolution, structure and properties of the glass and glass ceramics were investigated by the DSC method, XRD analysis and luminescence spectroscopy. It was found that the Ag diffusion into the surface layers leads to the formation of numerous different luminescent molecular Ag_n clusters. The MgO–Al₂O₃–TiO₂–SiO₂ glass and glass ceramics subjected to the Ag diffusion can operate as effective down-converters of the radiation demonstrating the effective transformation of UV and blue light into the radiation of red and NIR spectral range.     

Preparation and characterization of some ferromagnetic glass–ceramics contains high quantity of magnetite

Ferrimagnetic glass–ceramics are promising candidates for magnetic induction hyperthermia, which is one form of inducing deep-regional hyperthermia, by using a magnetic field. The aim of this work was to study the effect of increasing the amount of crystallized magnetite on the magnetic properties of glass–ceramic samples. Two different ferrimagnetic glass–ceramics with the composition based on wollastonite or hardystonite with high quantity (∼60%) of magnetite were prepared by melting the starting materials at 1450 °C for 2 h. The influences of chemical composition, amount of crystallized magnetite and microstructure of ferrimagnetic glass–ceramics on magnetic properties of ferromagnetic glass–ceramics were investigated using differential thermal analysis (DTA), X-ray diffraction (XRD), transmission electron microscope (TEM) and scanning electron microscope (SEM). The X-ray diffraction patterns show the presence of nanometric magnetite crystals in a glassy matrix after cooling from melting temperature. The amount of crystallized magnetite varies as a function of the chemical composition and heat treatment schedule. The presence of ZnO in the glass–ceramics was found to decrease the viscosity and so cases higher degree of mobility of ions leading to higher degree of crystallinity. The higher heat treatment parameters and so the lower viscosity of the glass containing ZnO are assumed to allow the magnetite to grow to larger crystallite size. Glass transition temperature and thermal stability were found to be functions of chemical composition. Magnetic hysteresis cycles were analyzed using a vibrating sample magnetometer (VSM) with a maximum applied field of 15 kOe at room temperature in quasi-static conditions. From the obtained hysteresis loops, the saturation magnetization (Ms), remanance magnetization (Mr) and coercivity (Hc) were determined. The results showed that these materials are expected to be useful in the localised treatment of cancer.     

Preparation,structural and thermo-mechanical properties of lithium aluminum silicate glass–ceramics

Lithium aluminum silicate glasses of composition (wt%) 12.6Li₂O–71.7SiO₂–5.1Al₂O₃–4.9K₂O–3.2B₂O₃–2.5P₂O₅ were prepared by the melt quench technique. These glasses were converted to glass–ceramics based on DTA data. X-ray diffraction (XRD) and Fourier transform infra-red spectroscopy (FTIR) were used to discern the phases evolved in the glass–ceramics. Phase morphology was studied using scanning electron microscopy (SEM). Thermal expansion coefficient (TEC) and glass transition temperature (T_g) of all samples were measured using thermo-mechanical analyzer (TMA). It was found that 3 h dwell time at crystallization temperature yielded samples with good crystallinity with a TEC of 9.461 × 10⁻⁶ °C⁻¹. Glass–ceramic-to-metal compressive seal with SS-304 was fabricated using LAS glass–ceramic. The presence of metal housing and compressive stresses at the glass–ceramic-to-metal interface reduced average grain size and changed the overall microstructure.     

Ultra-fast charge-discharge and high energy storage density realized in NaNbO3–La(Mn0.5Ni0.5)O3 ceramics

Lead-free antiferroelectric (AFE) NaNbO₃ (NN) is one of promising materials for dielectric capacitors, but the recoverable energy-storage density and efficiency get restrained owing to huge remanent polarization and limited dielectric breakdown field strength. In this work, a variety of NN based lead-free bulk (1-x)NaNbO₃-xLa(Mn_0.5Ni_0.5)O₃ (abbreviated as (1-x)NN-xLMN, x = 0, 0.05, 0.10, 0.15, 0.20) ceramics were designed using a solid-state synthesis method. Remarkably, an ultra-fast charge-discharge speed 47 ns and an acceptable recoverable energy-storage density W_rec ~1.77 J/cm³ with a high efficiency η = 77% were obtained under the E_b of 200 kV/cm at x = 0.05. The superior energy storage performance is attributed to the regulation of domain size and voltage resistance by special ions substitution of A and B sites. This work not only proposes an efficient strategy to realize high recoverable energy-storage density and efficiency, but also provide an candidate material for application of advanced pulsed power capacitors.     

Preparation and characterization of crednerite glass–ceramics in the MnO·CuO·SiO2 system

Nanoscale crednerite (CuMnO₂) was prepared in the system MnO·CuO·SiO₂, using glass–ceramics technique for the first time. Based on obtained data from differential thermal analysis (DTA), the prepared samples were heat-treated at 700 and 800 °C for 2 h. The presence of crystalline phases after and before heat treatment was investigated by X-ray diffraction analysis. Crystallization of crednerite (CuMnO₂), manganese silicate (Mn₂SiO₄) and traces of cuprite (Cu₂O) and cristobalite (SiO₂) phases were recognized. Transmission electron microscopy showed nanoscale crystals in the range 5–10 nm. The prepared glass–ceramics showed ferrimagnetic properties with wide range coercivity from 53 to 2217 Hci and magnetization saturation from 0.21708 to 1.2 emu/g. From IR reflection data; the reflection intensity of the light is high in the range of orange–red color and violet–blue colors and low in the range of green color.     

Microstructure and properties of CaO–ZrO2–SiO2 glass–ceramics prepared by sintering

For the development of a new wear resistant and chemically stable glass-ceramic glaze, the CaO–ZrO₂–SiO₂ system was studied. Compositions consisting of CaO, ZrO₂, and SiO₂ were used for frit, which formed a glass-ceramic under a single stage heat treatment in electric furnace. In the sintered glass-ceramic, wollastonite (CaSiO₃) and calcium zirconium silicate (Ca₂ZrSi₄O₁₂) were crystalline phases composed of surface and internal crystals in the microstructure. The internal crystal formed with nuclei having a composition of Ca_1.2Si_4.3Zr_0.2O₈. The CaO–ZrO₂–SiO₂ system showed good properties in wear and chemical resistance because the Ca₂ZrSi₄O₁₂ crystals positively affected physical and mechanical properties.     

Indentation-induced ductile behavior of glass–ceramics involving layered aluminosilicates

Contact damage in materials is critical in engineering applications because it influences mechanical resistance, such as wear, erosion, and impact failure. Indentation tests were performed using a tungsten carbide ball indenter (Hertzian contact) on the surfaces of glass–ceramics containing hexagonal CaAl₂Si₂O₈ or mica crystals (fluorophlogopite), both of which have a layered structure. The stress–strain relation and the permanent deformation on the surface, as well as the observation of the microcrack zone by X-ray computed tomography using synchrotron radiation, revealed that the glass–ceramic with hexagonal CaAl₂Si₂O₈ showed ductility similar to the quasi-plastic behavior previously observed in the mica glass–ceramic. The yield stresses of the glass–ceramics were estimated from the stress deviating from the stress–strain relation assuming complete elastic response between the ball and the sample. The ratio of the yield stress to Young modulus (Y/E) of the glass–ceramic with hexagonal CaAl₂Si₂O₈ was determined to be higher than that of the mica glass–ceramic.     

Rigid-resilient transition in calcium borosilicate sealing glass–ceramics: Effect of preferred orientation

At present, the insufficient thermo-mechanical stability of sealing glass presents a challenge for solid oxide fuel cells (SOFCs). In this work, we report for the first time that a rigid-resilient transition occurs in a calcium borosilicate sealing glass upon heating at 700?°C for different durations. The elastic modulus increases from 28.1–40.0?GPa for 24?h to 92.3–105.1?GPa for 100?h, while the corresponding hardness increases from 2.5–3.1?GPa to 8.1–9.2?GPa. In addition, a possible mechanism for the rigid-resilient transition has been proposed. The reported results provide a new approach to solve the sealing problem of SOFCs.     

Evolving energy-storage performances during temperature-induced antiferroelectric P–R phase transition in NaNbO3-based lead-free ceramics

Temperature-driven antiferroelectric (AFE) P to AFE R phase transition in MnO₂-doped 0.90NaNbO₃-0.10CaTiO₃ ceramics was investigated through polarization-field response, energy-storage and charge-discharge properties as well as ex/in-situ multiscale structure characterization. Both room-temperature AFE P and high-temperature AFE R phases show double polarization-electric field hysteresis loops, indicating a reversible field-driven AFE to ferroelectric (FE) phase transition. An abnormal variation of critical fields for the AFE-FE and FE-AFE phase transition and a faster polarization-field response contribute to the reduced polarization hysteresis for both AFE P and R phases but an obviously expanded linear polarization-field response only for AFE R phase, being responsible for a two-time significant enhancement in energy-storage properties from P phase to P–R phase boundary and then to R phase. The variation of unit cell anisotropy and domain morphology with temperature was found to play crucial roles in the modulated field-driven phase transition behavior and polarization-field response on heating.