Synthesis and properties of ferrimagnetic glass-ceramics and glass fibers derived from pyrite slag

Ferrimagnetic nano-crystal glass-ceramics and glass fibers were prepared based on the ferrosilicate glass system of SiO₂–Fe₂O₃–B₂O₃–Al₂O₃ using large amount of pyrite slag (PS) and small quantities of pure chemicals. Two different fabrication methods were employed, eg, annealing and fiber-drawing method, without performing any nucleation and crystallization heat treatments. The influence of PS content on the magnetite spontaneous crystallization is investigated by the X-ray diffraction, FTIR, SEM, and TEM. The X-ray diffraction patterns show the presence of nanometric magnetite crystals in glass matrix. The ferrimagnetic glass fibers with a diameter of about 20 μm were one-step drawn. The magnetic hysteresis loops of the glass-ceramic and glass fiber samples were analyzed using a vibrating sample magnetometer (VSM). Electromagnetic parameters of samples were also examined.     

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).     

Improving the sealing performance of glass-ceramics for SOFCs applications by a unique ‘composite’ approach: A study on Na2O-SiO2 glass-ceramic system

The rigid nature of sealing glass-ceramics restricts the thermal cycling stability of Solid Oxide Fuel Cells (SOFCs), which thus evokes an interest in designing a sealing glass without crystallization under the operational condition of SOFCs. In this paper, we report that the sealing performance of 30Na₂O-70SiO₂ (in mole%) glass-ceramic can be significantly improved by Fe₂O₃ dopant through a composite approach. In particular, the crystallization in glass can be suppressed by appropriate Fe₂O₃ dopant amount (8?mol%), which results in the improved sealing property of glass. In addition, the glass modified with Fe₂O₃ shows good chemical compatibility with 8?mol% yttria-stabilized zirconia (8YSZ) electrolyte and metallic interconnect (430 stainless steel) in dual atmospheres. The possible mechanism for the improved sealing performance of 30Na₂O-70SiO₂ glass-ceramic by this unique composite approach is also discussed.     

Effect of MgO/Al2O3 ratio on the crystallization behaviour of Li2O–MgO–Al2O3–SiO2 glass-ceramic and its wettability on Si3N4 ceramic

The composition governs the crystallization ability, the type and content of crystal phases of glass-ceramics. Glass-ceramic joining materials have generated more research interest in recent years. Here, we prepared a novel Li₂O–MgO–Al₂O₃–SiO₂ glass-ceramic for the application of joining Si₃N₄ ceramics. We investigated the influence of the MgO/Al₂O₃ composition ratio on microstructure and crystallization behaviour. The crystallization kinetics demonstrated that the glasses had excellent crystallization ability and high crystallinity. β-LiAlSi₂O₆ and Mg₂SiO₄ were precipitated from the glass-ceramics, and the increase of MgO concentration was conducive to the precipitation of Mg₂SiO₄. Among the glass-ceramic samples, the thermal expansion coefficient of LMAS2 glass-ceramic was 3.1 × 10^?6/°C, which was very close to that of Si₃N₄ ceramics. The wetting test showed that the final contact angle of the glass droplet on the Si₃N₄ ceramic surface was 32° and the interface was well bonded.     

Preparation of glass-ceramic by low-pressure hot-pressing sintering of CaO-MgO-Al2O3-SiO2(-CaCl2) glass powder

CaCl₂ can dissolve in the silicate glasses, and thus, using the CaCl₂-bearing glass for the preparation of glass-ceramic could be a potential method for treating CaCl₂-bearing wastes. In this work, two kinds of glass powders, CaO-MgO-Al₂O₃-SiO₂ and CaO-MgO-Al₂O₃-SiO₂-CaCl₂, were sintered at 825–850 ℃ to prepare the glass-ceramic. Besides, a low-pressure (19.1kPa) hot-pressing sintering technology was applied to reduce the porosity and pore size of the glass-ceramic. The addition of CaCl₂ (5 wt%) reduced the polymerization degree, glass transition temperature, crystallization peak temperature, and crystallization activation energy of the glass. Augite was the main crystalline phase of the glass-ceramic, and the addition of CaCl₂ promoted the precipitation of anorthite. The glass-ceramic prepared from the Cl-containing glass always exhibited a higher bending strength than that obtained from the Cl-free glass. When sintered at 825 ℃ for 8 h, the glass-ceramic showed the highest bending strength of 171 MPa.     

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.     

An approach to monitor the real-time deformation during heat treatment of 3D-printed glass

This study suggests a tool for a better control on the sintering/crystallization of 3D-printed bioactive glass-ceramics bodies. A small cantilever in form of a bar with square cross section attached to a base and inclined 34° with the horizon, was used to monitor the viscous flow and sintering/crystallization headway of a glass-ceramic systems. 3D printing and sintering of bioactive glass-ceramics is of great interest for medical care applications. Viscous flow ensures sufficient densification of the typically low density printed green bodies, while crystallization prevents the structure from collapsing under the gravitational load. As a model system, a bioactive glass called BP1 (48.4 SiO₂, 1 B₂O₃, 2 P₂O₅, 36.6 CaO, 6.6 K₂O, 5.6 Na₂O (mol%)), which has a chemical composition based on that of ICIE16, was employed in this work. In addition, ICIE16 was used as a reference glass. The results show that the suggested design is a very promising tool to track the real-time deformation of 3D printed glass-ceramic specimens and gives a good indication for the onset of crystallization as well.     

Investigation on low-temperature reactive viscous flow sintering behavior of lanthanum-borate glass-ceramic with BaTi4O9 ceramic filler

In this paper, the sintering behavior of the lanthanum-borate (B₂O₃-La₂O₃-MgO-TiO₂,BLMT) glass-ceramic with BaTi₄O₉ filler composite was investigated in terms of the wetting behavior, interfacial reaction, sinter-shrinkage process, sintering activation energy, as well as phase and microstructure evolution with change in filler contents and sintering temperature. Our research suggested that the glass is unable to wet the filler material within a temperature up to 1000 °C, indicating that the densification process of composites is dominated by viscous flow of glass matrix. The increase in filler content that performs as a rigid particle in composite causes the rise in the sinter-shrinkage-onset and -end temperature, thereby proving that the viscous-flow densification of the composites with x≤ 30 wt% filler content is accomplished before the crystallization of BLMT glass, whereas the composites with x≥ 40 wt% cannot. After densification, a chemical reaction that almost synchronizes with the glass crystallization occurred between glass and ceramic, which not only imposes significant influence on the crystallization behavior, but eradicates the closed pore formed by the viscous flow and the induced crystallization porosity. The densification process of the BaTi₄O₉ filler-BLMT glass composite was referred to as two-stage reactive assisted viscous flow sintering process which consists of viscous flow of glass, of the crystallization process of glass, and/or of the chemical reaction between glass and filler.     

Composite materials based on sitall glass and technical aluminum and titanium oxides

The possibility of fabrication of glass-ceramic composite materials based on sitall glass of the SiO₂-TiO₂-Al2O₃-CaO-BaO-B₂O₃ nonalkaline system and fillers-powdered industrial oxides with low sintering and crystallization temperatures and high wear resistance — was investigated. Industrial aluminum and titanium oxides were used as the fillers.     

The direct experimental observation and solidification mechanism of heavy metals in blast furnace slag glass-ceramics

Glass-ceramics with high performance and high crystallinity was produced using rare earth blast furnace slag (REBFS) as the primary raw material, along with composite nucleating agents Fe₂O₃ and Cr₂O₃. The migration pattern, distribution characteristics, and solidification properties of heavy metals in glass-ceramics were investigated by the controlled heat treatment. The findings indicated that the heat treatment temperature has a significant effect on the distribution and color of heavy metals in glass-ceramic. In the crystallized glass-ceramic, spinel acts as the crystal core for heavy metal solidification, Cr, Cu, and Mn can exist stably in the spinel by the solid solution. The glass-ceramic was expected to be used as a decorative building material.     

Effect of soluble Cr2O3 on the silicate network,crystallization kinetics,mineral phase,microstructure of CaO-MgO-SiO2-(Na2O) glass ceramics with different CaO/MgO ratio

Cr₂O₃ is often used as a glass additive to prepare glass ceramics. Chromium element exists mainly in two parts in the glass ceramics: chromium-containing spinel and soluble chromium in glass matrix. Herein, effect of soluble chromium on the CaO-MgO-SiO₂-(Na₂O) glass system is researched. Glass and glass ceramics were characterized by Raman spectrum, X-ray diffraction, scanning electron microscopy, energy dispersive spectrometry. It is found that the addition of Cr₂O₃ increased the Q²si structure unit in glass networks, especially in glass systems with high MgO content. The crystallization temperatures of the systems were increased with the addition of Cr₂O₃. Soluble chromium reduced the crystallization activation energy of the glass system slightly, but did not alter its crystallization behavior (surface crystallization). With the increase of MgO content, the mineral phases of the glass ceramics gradually changed from wollastonite to diopside. Cr₂O₃ reduced the lattice parameters of the mineral phases. The addition of Cr₂O₃ has a significant effect on grain refinement and structural compactness of the glass ceramics system with high MgO content.     

Eu3+ doped ferroelectric CaBi2Ta2O9 based glass-ceramic nanocomposites: Crystallization kinetics,optical and dielectric properties

We report Eu³⁺ doped transparent glass-ceramics (GCs) containing bismuth layer-structured ferroelectric (BLSF) CaBi₂Ta₂O₉ (CBT) as the major crystal phase. The CBT crystal phase was generated in a silica rich glass matrix of SiO₂-K₂O-CaO-Bi₂O₃-Ta₂O₅ glass system synthesized by melt quenching technique followed by controlled crystallization through ceramming heat-treatment. Non-isothermal DSC study was conducted to analyze crystallization kinetics of the glass in order to understand the crystallization mechanism. The optimum heat-treatment protocol for ceramization of precursor glass that has been determined through crystallization kinetics analysis was employed to fabricate transparent GCs containing CBT nanocrystals, which was otherwise difficult. Structural analysis of the GCs was carried out using XRD, TEM, FESEM and Raman spectroscopy and results confirmed the existence of CBT nanocrystals. The transmittance and optical band gap energies of the GCs were found to be less when compared to the precursor glass. The refractive indices of the GCs were increased monotonically with increase in heat-treatment time, signaling densification of samples upon heat-treatment. The dielectric constants (ε_r) of the GCs were progressively increased with increase in heat-treatment duration indicating evolution of ferroelectric CBT crystals phase upon heat-treatment.     

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.     

The effects of temperature and Ce-dopant concentration on the synthesis of zirconolite glass-ceramic

Zirconolite based glass-ceramic has been deemed as a promising waste form for high-level waste (HLW). In this study, the zirconolite (nominally CaZrTi₂O₇) glass-ceramic based on a SiO₂-B₂O₃-Na₂O-CaO-ZrO₂-TiO₂-Al₂O₃ system was sought to be synthesized by two-step thermal treatment. The temperature effects such as nucleation temperature and cooling rate were studied. The influence of the Ce-dopant concentration on crystallization behavior was also investigated. For characterization, powder X-ray diffraction (XRD), thermogravimetry-differential scanning calorimeter (TG-DSC) and scanning electron microscopy (SEM) were applied. Our results illustrate that homogeneous zirconolite with the particle size of 1.8?μm can be the target phase when the glass matrix underwent a rapid cooling process and the nucleation temperature was controlled at around 860?°C. Besides, the results also indicate that the distribution of the zirconolite along with its lattice parameters change regularly as the increase of CeO₂ concentration. A larger crystal size of zirconolite phase and some trace amounts of precipitated phases are observed when the CeO₂ concentration exceed 3?wt%. This work emphasizes the synthesis of zirconolite glass-ceramic in a SiO₂-B₂O₃-Na₂O-CaO-ZrO₂-TiO₂-Al₂O₃ system, which is expected to provide basic technical data for underground disposal of HLW.     

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.     

Nucleating role of P2O5 in nepheline-based transparent glass-ceramics

The nepheline-based transparent glass-ceramics are promising candidates for cover glass applications in electronic displays owing to their superior mechanical properties (than glasses) and ability to be chemically strengthened. However, our poor understanding about the kinetic and thermodynamic drivers controlling their crystallization processes usually results in their opacification and development of large internal stresses. The present work focuses on the development of nepheline-based nanocrystalline transparent glass-ceramic designed in the Na₂O–Al₂O₃–SiO₂ ternary system nucleated with P₂O₅. The temporal evolution of the phosphate and nepheline nanocrystal formation has been followed using X-ray diffraction, scanning/transmission electron microscopy, and energy-dispersive spectroscopy. The incorporation of P₂O₅ in the glass structure leads to the phase separation resulting in the crystallization of nanocrystalline Na₃PO₄ as an intermediate phase; thus, acting as a nucleating site for volume crystallization of nepheline. The optimization of nucleation and growth profile in the designed composition results in the formation of a transparent glass-ceramic with high optical transmittance (91.5 ± 0.1%).     

Crystallization-induced stabilization of foam glass aggregates for heat-insulating concrete

Resistance of the porous glass-based aggregates to alkali-silicate reaction (ASR) was the focus of this study. ASR was studied in mixtures of aggregates with water alkali solutions simulating alkali media of row concrete. Granular foam glass with homogeneous glass in the pore walls is ASR-active, which leads to the leaching of glass and to the formation of hydrated Na-silicate gel, Ca-silicate, and aluminosilicate on the aggregate surfaces. Mitigation of ASR-activity in granular foam glass was achieved by thermo-induced crystallization (850-900ºC) of micro- and nanoscale crystals (Na₄CaSi₃O₉ and/or Na₂Ca₃Si₆O₁₆) in the pore walls with the formation of granular glass-ceramic foams. The main characterization methods were scanning electron microscopy, x-ray powder diffraction analysis, x-ray fluorescence, atomic emission spectrometry, and pH analysis.     

Glass transition and crystallization of ZnO-B2O3-SiO2 glass doped with Y2O3

The effect of Y₂O₃ on the glass transition kinetics, crystallization kinetics, phase separation and crystallization behavior of 60ZnO–30B₂O₃–10SiO₂ glass has been investigated by non-isothermal differential thermal analysis, scanning electron microscopy (SEM) and X-ray powder diffraction (XRD). The glass transition activation energies E_g calculated by using both Kissinger and Moynihan model decrease from 668?kJ/mol to 573?kJ/mol for Kissinger model, and 682?kJ/mol to 587?kJ/mol for Moynihan model with the increase of yttrium oxide doping content from 0 to 6?mol%. And the glass crystallization kinetics parameters, crystallization activation energy E_c and Avrami exponent n stands for crystal growth, are also obtained on the basis of several well developed equations. Increase of about 58?kJ/mol in Ec values obtained by different theoretical equations is caused by addition of 6?mol% yttrium oxide into 60ZnO–30B₂O₃–10SiO₂ glass, and the Avrami exponent (n close to 2) suggests that crystal growth in 60ZnO–30B₂O₃–10SiO₂ glass doped with or without yttrium is mainly one-dimensional growth of crystals. The results on the phase separation and crystallization behavior occurred at 893?K and 993?K respectively for base and doped glass, are well consistent with the glass transition and crystallization kinetics results. Hence, addition of yttrium oxide into 60ZnO–30B₂O₃–10SiO₂ glass decrease the glass transition activation energy while increase the crystallization activation energy of glass, thereby the stability of glass structure is improved. Phase separation phenomenon and crystallization behavior occurred at glass surface provide some useful information for preparing glass ceramics with micro- or nano-crystals in surface.     

Sintering of sodium conducting glass ceramics in the Na2O-Y2O3-SiO2-system

A solid electrolyte is a core component for the development of low temperature sodium batteries with metallic Na-anode. The Na₅YSi₄O₁₂ (N5) composition in the Na₂O-Y₂O₃-SiO₂ system shows a high ionic conductivity comparable to NASICON or β-Al₂O₃. Up to date glass ceramic solid electrolytes of this type have been mainly prepared by crystallization of monolithic, molten glass components. We show that this material can be processed via the glass-ceramic powder route starting with a glass powder. A glass with a composition according to the stoichiometry of the Na₅YSi₄O₁₂-phase and tailored by addition of P₂O₅ allows the separation of sintering and crystallization of the glass powder resulting in dense microstructure. Thermophysical properties and phase content have been correlated with ionic conductivity. The densification and crystallization are completed at temperatures below 1100 °C. Grain conductivities up to 0,18 mS cm^?1 at room temperature in sintered glass ceramic microstructures are demonstrated.     

Crystal phase separation and microstructure of a thermally treated vitrified solid waste

The vitrification method was used to stabilize a solid industrial waste residue rich in iron and lead oxides. Upon devitrification of the glass products, the effect of batch composition on the ability to produce glass-ceramic materials was investigated by electron microscopy techniques. The crystallization and microstructural evolution of the vitreous products was explored with respect to the annealing conditions. In the course of vitrification, ferric oxide functioned as a glass network former, contributing to the structural integrity of the vitreous matrix. After thermal treatment of the vitrified products, at temperatures determined by differential thermal analysis, Pb₈Fe₂O₁₁, PbFe₁₂O₁₉ and Fe₂O₃ were the dominant crystal phases detected in the glass-ceramic products, the former characterized as a new structure. The distribution of iron and lead oxides among different crystalline phases was found to be the dominant parameter determining the efficiency of lead captivation into the volume of the devitrified products, whereas in glass products lead is diffused in the amorphous matrix.