Diopside Glass Research Articles

Influence of the pressure of compacted glass powders on the final structure of sintered glass-ceramics

In reported investigation we studied sintered glass-ceramics from a model diopside glass with moderate crystallization ability by in-situ optical dilatometeric experiments. The initial glass was ground and sieved below 75 μm. Then thus prepared powders were pressed with different pressures between 50 and 250 MPa. In this way were obtained samples out of pressed powders with different initial porosities determined with gas pycnometry. Then the samples were heat treated in a contactless horizontal optical dilatometer and their porosities were measured one more time. Both pressed green samples and synthesized glass-ceramics were analyzed further with X-Ray micro tomography.We observed that the densification of all samples completes in the same moment which corresponds to the formation of a critical percentage crystal phase. Notwithstanding the continuation of the crystallization process, we obtain materials with different percentage of residual porosity. Then no volume variation of the system is observed. This approach is well demonstrated by the first derivative of the shrinkage curves with time.After the end of the shrinkage of the system, the crystallization leads to the formation of crystallization induced porosity (called by us CIPs) observed here.

The Effect of the Chemical Composition on Mechanical Properties of CMAS Diopside Glass Ceramics

Molecular dynamics simulations were performed on CaO-MgO-Al2O3-SiO2 (CMAS) diopside glass ceramics (GCs) to study the effect of nanocrystal on glass and the effect of chemical composition on mechanical properties. Under tensile loading, the GCs demonstrated that the strength lay between its glass and ceramic counterparts and maintained considerable ductility. Moreover, high Mg/Ca ion ratios are conductive to both the strength and ductility of GCs. In addition, Al ions should be avoided as far as possible since they would promote fracture. After analyzing the shear strain and displacement vector map for ion structures, we found that the presence of nanocrystal in glass changes the original deformation pattern and led to the deformation concentration surrounding the nanocrystal. A high Mg/Ca ion ratio would make the deformation more homogeneous, while a high Ca/Mg ion ratio would aggregate the deformation in the glass region near the nanocrystal. The existence of Al ions near the interface between glass and crystal would promote the formation of voids.

Effect of Cr2O3 on Crystallization of Diopside Glass–Ceramics

CaO–MgO–Al2O3–SiO2–Cr2O3 diopside glass–ceramics were prepared from blast furnace slag, low-carbon ferrochromium alloy slag, and quartz sand by the melting method. The prepared glass–ceramics were characterized by differential thermal analysis (DTA), X-ray diffraction (XRD),scanning electron microscopy (SEM), energy-dispersive spectrometer (EDS), and X-ray photoelectron spectroscopy (XPS). The effect of Cr2O3, a nucleating agent, in the crystallization process of diopside glass–ceramics was studied. The results show that chromium is present in glass–ceramics as Cr3+ and Cr6+, and Cr3+ accounts for more than 80% of the chromium contents. When the mass percentage of Cr2O3 in glass–ceramics is less than 1.60%, a small amount of diopside phase is precipitated during heat treatment, and Cr3+ is dispersed in the diopside phase. When the mass percentage of Cr2O3 reaches or exceeds 1.60%, Cr3+ preferentially forms the magnesia chrome spinel phase, which further induces the in situ growth of diopside. The leaching concentration of chromium meets the Chinese national standard, indicating that diopside glass–ceramics can effectively solidify the heavy metal chromium, and this fact makes the application of glass–ceramics feasible.

Novel Functional Glass-Ceramic Coatings on Titanium Substrates from Glass Powders and Reactive Silicone Binders.

‘Silica-defective glasses’, combined with a silicone binder, have been already shown as a promising solution for the manufacturing of glass–ceramics with complex geometries. A fundamental advantage is the fact that, after holding glass powders together from room temperature up to the firing temperature, the binder does not completely disappear. More precisely, it converts into silica when heat-treated in air. A specified ‘target’ glass–ceramic formulation results from the interaction between glass powders and the binder-derived silica. The present paper is dedicated to the extension of the approach to the coating of titanium substrates (to be used for dental and orthopedic applications), with a bioactive wollastonite–diopside glass–ceramic layer, by the simple airbrushing of suspensions of glass powders in alcoholic silicone solutions. The interaction between glass and silica from the decomposition of the binder led to crack-free glass–ceramic coatings, upon firing in air; in argon, the glass/silicone mixtures yielded novel composite coatings, embedding pyrolytic carbon. The latter phase enabled the absorption of infrared radiation from the coating, which is useful for disinfection purposes.

Analysis and information content of quadrupolar NMR in glasses: 25Mg NMR in vitreous MgSiO3 and CaMgSi2O6

The static wideline and high-resolution magic angle spinning (MAS) 25Mg NMR lineshapes measured for isotopically enriched enstatite and diopside glasses indicate a wide distribution of the electric-field gradient (EFG) components at the 25Mg position caused by disorder. The correct characterization of this distribution requires simulations with special attention paid to the experimental parameters. Here, both the static spectra obtained by wideband excitation and the MAS-NMR spectra obtained via rotor-synchronized Hahn spin echo acquisition were successfully simulated with the Czjzek distribution model, using one consistent set of parameters. Average nuclear electric quadrupole coupling constants near 8 MHz and a distribution width around 4 MHz were obtained for both materials, which suggests that earlier results on these glasses need to be re-examined. The results of this study outline a general strategy for characterizing the local environments of strongly coupled quadrupolar nuclei in amorphous and glassy materials. Despite the discrepancies between the interaction parameters extracted from our data and those published in earlier NMR work, the best fit to the data indicate an average isotropic chemical shift near 13 ppm (vs. aqueous MgCl2 solution) for both the enstatite and diopside glasses. Assuming the applicability of the current database relating the 25Mg chemical shifts with coordination numbers in crystalline compounds, this value suggests that the Mg2+ ions are six-coordinated. This conclusion, however, is based on the simplifying assumption that the 25Mg spectrum comprises a Czjzek distribution centered at a single isotropic chemical shift value and stands in contrast to the results of recent isotope-selective neutron diffraction studies which give an average Mg-O coordination number of 4.4–4.5 for both glasses. However, reasonable fits to the MAS-NMR spectra can also be obtained when constraining the average isotropic chemical shift to 50 ppm, a value typical of four-coordinated Mg. We conclude that multiple Mg sites with different coordination numbers may well be present and that, in the present glasses, 25Mg NMR at typically used spinning rates and magnetic field strengths (20 kHz, 14.1 T) is not capable of resolving them due to excessive broadening by quadrupolar interactions.

Oriented surface nucleation in diopside glass

Oriented surface crystallization on polished diopside glass surfaces has been studied with scanning electron microscopy, electron backscatter diffraction, transmission electron microscopy and laser scanning microscopy. An orientation preference of [001] parallel to the glass surface was detected for separately growing diopside crystals even as small as 700 nm in size. This finding shows that crystal orientation occurs in the outermost surface layer without crystal-crystal interaction and indicates that the crystal orientation is a result of oriented nucleation. Depending on surface preparation, monomodal crystal orientation distributions with [100] perpendicular to the surface or bimodal distributions with [100] and [010] perpendicular to the glass surface were detected. It was also shown that the degree of crystal orientation increases with decreasing surface roughness. The observed orientation of diopside crystals could be explained in terms of the interfacial energies of different crystal faces.

Single‐run DSC method for determining surface crystal growth rate in glasses generalized for samples of different shapes

AbstractWe propose a new generalized method for the determination of surface crystallization growth rates in a wide temperature range using a single Differential Scanning Calorimetry (DSC) experiment. It can be applied to different sample geometries—we have tested the method for powdered and millimetric cubic samples. The crystal growth rate is calculated from the DSC crystallization peak profile and the average particle size. The method was successfully tested using diopside (MgO·CaO·SiO2) glass powders and a sodium disilicate glass (Na2O·2SiO2) millimetric cube, which undergoes exclusive stoichiometric surface crystallization. The resulting crystal growth rates spanned ranges of approximately 60 K for diopside glass and 170 K for sodium disilicate. The method is very convenient, requiring a single DSC run and simple sample preparation. The crystal growth rates, , proved to be accurate when compared to literature optical microscopy measurements, with a root mean square deviation of 0.22 in for diopside glass.

Crystallization kinetics of diopside glass ceramics

The glass ceramics were prepared by a reaction crystallization and sintering method using waste glass powder and a crystallizing promoter with a main crystal phase of the enstatite. X-ray diffraction(XRD), Scanning electron microscope(SEM), Differential scanning calorimetry(DSC), etc. were used to characterize its phase composition, morphology, and thermal decomposition process. The results show that the main crystal phase of the prepared glass ceramics was diopside and the secondary crystal phase was albite. The precipitated crystals were rod-shaped with a maximum length of about 7 μm and a diameter of about 0.6 μm. Diopside glass ceramics were measured with different heating rates, and it was found that the peak temperature increased with the heating rate. The Kissinger method was used to calculate the crystallization kinetics of diopside glass ceramics, and the crystallization activation energy was 872.4 kJ⋅mol−1.

Iron reduction and diopside-based glass ceramic preparation based on mineral carbonation of steel slag.

In this article, a new process for treating steel slag and CO2 simultaneously and preparing calcium carbonate, metallic iron, and glass ceramics without wastewater or gas production is proposed. The reduction of iron and preparation of diopside glass ceramics are studied in this paper, and the results show that the carbon thermal reduction product of the original slag does not reach its melting point, and the slag and iron are well separated in the samples containing the leached steel slag and added silica. Part of the parent glass is converted into a glass ceramic after heat treatment, and the crystalline phases of samples are melilite, diopside, and partial melilite, and diopside and anorthite, respectively. The crystallization activation energy of the best sample in this article is E = 660.664kJ/mol. The Avrami indices calculated at different heating rates are all less than 3, which indicates that the crystallization mode of the glass involves surface crystallization. This finding is consistent with the results for the prepared glass ceramics.

Tunable pore size in diopside glass-ceramics with silver nanoparticles

Volume crystallization was achieved in diopside glasses by the introduction of silver into the glassy network.

Simulation and experimental study of the particle size distribution and pore effect on the crystallization of glass powders

Surface nucleation is a frequent phenomenon and plays an essential role in the crystallization of most glasses, especially glass powders used in sintered glass-ceramics, for example. A technique often employed to study the crystallization kinetics of glassy powders is Differential Scanning Calorimetry (DSC). However, the shape of the crystallization peak profile is usually very complex. For instance, in certain cases of surface nucleation, the crystal growth dimensionality may change during crystallization after crystal impingement, and a large density difference between the parent glass and the resulting crystalline phases may produce cavitation pores in the particle volume. Finally, crushed glass particles are not regularly shaped, as assumed in most models. Hence, to evaluate the crystallization kinetics of glass powders by DSC experiments, in this work, we modified and tested a particle crystallization model using the DSC crystallization peaks of jagged powders of a non-stoichiometric (0.95CaO·0.73MgO·2SiO2) diopside glass having different granulometries and a large crystal/glass density difference. The Reis-Zanotto model was adapted to include two complex variables: particle size distribution and crystallization-induced porosity. As predicted by the modified model, we confirmed the radical change of the DSC peak shape for some particle sizes as a result of crystal impingement and pore formation. This combined experimental-simulation study demonstrates that the adapted model can describe this type of complex and yet frequent crystallization case.

Effects of CeO2 and nano-ZrO2 agents on the crystallization behavior and mechanism of CaO–Al2O3–MgO–SiO2-based glass ceramics**Project supported by the National Natural Sciences Foundation of China (Grant No. 51590881), the National Key Research Program of China (Grant No. 2016YFB0700903), the Inner Mongolia Science and Technology Major Project of China 2016, and the Fujian Institute of Innovation, Chinese Academy of Sciences (Grant

The crystallization behavior and mechanism of CaO–Al2O3–MgO–SiO2 (CAMS)-based diopside glass ceramics with nano-ZrO2 nucleators and CeO2 agents have been investigated. The use of nanoscale ZrO2 as nucleators is favorable to the crystallization of glass ceramic at a relatively lower temperature due to the reduction of the activation energy, while the activation energy is increased after adding the CeO2 agent. The microstructure and orientation have been analyzed by scanning electron microscopy and electron backscatter diffraction. Two discernible layers are observed, featured in glass and crystalline phases, respectively. Remarkably textured polycrystalline diopsides are verified for the samples (A and B) free of CeO2 agents, with c-axes perpendicular to the interface of the two layers. Comparatively, the c-axes of diopside grains of the sample (C) with CeO2 agents are proved to be parallel to the interface. Nanocrystals are detected in the vicinity of the interface for sample C.

Crystallization mechanism and kinetics of a Fe-diopside (25CaO·25MgO·50SiO2) glass–ceramic

Diopside-based ceramics and glass–ceramics have been studied because of their applications in electronics and biomedicine. However, since diopside glass presents poor internal nucleation ability, sintering combined with surface crystallization of powdered glasses has been reported to obtain diopside glass–ceramics. On the other hand, in this work, we explore the effect of an efficient nucleating agent (Fe2O3) to induce copious internal nucleation in this glass, which enabled the production of single-phase diopside glass–ceramics by the traditional route. The crystallization kinetics of a diopside glass (25CaO·25MgO·50SiO2) containing 8.26 mol% of Fe2O3 was investigated under isothermal conditions by differential thermal analysis (DTA) and was modeled by the Johnson-Mehl-Avrami-Kolmogorov-Erofeev (JMAKE) equation. The crystals formed were iron-diopside—the X-ray diffraction pattern was indexed to the ferric-diopside card (Ca0.991(Mg0.641Fe0.342)(Si1.6Fe0.417)O6). Through a systematic DTA study, we successfully determined the mechanism and kinetics of crystallization of this material, which provided relevant information to guide the development of this novel type of internally crystallized glass–ceramic.

Preparation and Properties of Blast Furnace Slag Glass Ceramics Containing Cr2O3

AbstractIn this study, the blast furnace slag of the Baotou Steel and Iron Company was used as the main raw material to prepare glass ceramics with diopside as the main crystal phase. The composition of the parent glass was designed by thermodynamic calculations with FactSage software. Small amounts of the nucleation agent Cr2O3were then added to the parent glass to induce crystallization. Differential thermal analysis was used to determine the nucleation and crystallization temperatures of the glasses, and scanning electron microscopy and X-ray diffraction were adopted to determine the microstructures and phase compositions of the glasses after heat treatment, respectively. The results showed that glass ceramics of the diopside phase can be prepared with up to 73 wt% blast furnace slag when 1.44–1.91 wt% Cr2O3is added, and the ceramics have uniform compact grains and a high bending strength of about 84.6–101.7 MPa. In addition, the mechanical properties are better than those of natural marble and granite. These results provide basic information and a scientific basis for industrial production of diopside glass ceramics using molten blast furnace slag as the main raw material.

Sintering and rounding kinetics of irregular glass particles

AbstractCompacts of irregular glass particles sinter up to five times faster than spherical‐particle compacts of the same composition. This effect has been attributed to the sharp edges of irregular particles. In this article, we propose and test a phenomenological model for the sintering kinetics of jagged glass particles considering their rounding during sintering. We assume that the small radii of curvature of the particle edges increase as the particles round off and control the sintering rate. We tested the model by measuring the sintering shrinkage of spherical and irregular particle compacts of a diopside (MgO·CaO·2SiO2) glass and using literature sintering data for particles of different shapes of a soda‐lime‐silica glass. The sintering rate of irregular‐particle compacts is initially much higher but tends to reach that of their spherical counterparts as they round off. Our model describes the experimental shrinkage of both glasses and explains the shrinkage anisotropy of irregular‐particle compacts in the initial stages of sintering, providing a significant step toward the understanding and description of the sintering kinetics of jagged glass particles.

Simple model for particle phase transformation kinetics

We propose a new model for the kinetics of phase transformation of particles starting from surface and internal nucleation sites. The model's analytical equation is very simple, allowing for easy usage and interpretation. We tested the model against the crystallization of glass particles using differential scanning calorimetry, DSC. We used diopside (CaO·MgO·2SiO2) glass particles having different number densities of surface nucleation sites, NS, and also lithium disilicate glass particles, which show simultaneous surface and internal crystallization, having different number densities of internal nuclei, NV. Simulations of DSC traces provided accurate predictions of the transformation kinetics. We compared our model results to those of rigorous (more complex) models in terms of three non-dimensional parameters: the number of surface nuclei, the number of internal nuclei and a non-dimensional time. Our model, with a simpler equation, provided similar results. We believe it may also provide a more realistic approximation for particles that sinter during phase transformation, such as glass particles that simultaneously crystallize during sintering, and for transformations starting from the grain boundaries in polycrystalline materials.

The shape of diopside glass particles probed by the non-isothermal crystallization kinetics and Differential Scanning Calorimetry

The densification rate of glass powder compacts on heating can be calculated by the Clusters model of sintering, in which the particle shape is considered as a correction factor and obtained by fitting the model itself to experimental data. The crystallization of a diopside glass particle compact was characterized by Differential Scanning Calorimetry (DSC) and the resulting peak compared with the analytically calculated for particles with distinct regular morphologies and constant volume, aiming to access an effective particle shape parameter independently. The crystallization kinetics was calculated for the diopside composition considering heterogeneous surface nucleation and the phase transformation evolving due to a crystallized surface layer, whose thickness grows inward the particles, contracting the residual glass. The crystallization peaks were compared with the experimental DSC peaks for a diopside glass powder with irregular-shaped particles in a narrow size range. The calculated peaks ranged from the same temperature interval of the experimental one, but their overall shape and maximum temperature were greatly influenced by the different particle geometries. The particle shape must thus be taken into account in the analysis of glass powder crystallization by DSC, which is then a promising technique for the characterization of an effective shape factor for glass particles under crystallization.

Effect of Cr2O3 on the crystallization behavior of synthetic diopside and characterization of Cr-doped diopside glass ceramics

Diopside is the main crystalline phase in silicate materials such as ceramics and glass-ceramics. Herein, the effect of Cr2O3 on the microstructure and crystallization behavior of synthetic diopside, as well as the solubility of Cr2O3 in diopside is discussed. Samples were prepared by the melting method and characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectrometry, and confocal laser scanning microscopy. Results show that the maximum achievable solubility of Cr2O3 in diopside is between 1% and 3% by weight, and that the magnesiachrome spinel formed by Cr2O3 can act as a nucleating agent for the diopside phase. Glass ceramics was prepared by synthesis slag which simulates the chromium-containing waste. The activation energy of crystallization is 274 KJ/mol and Avrami parameter is 3.23. The leaching behavior of glass ceramics was studied. Additionally, the effect of Cr2O3 on the mechanisms of phase change were discussed. The study provides a theoretical basis for the preparation of chromium containing waste-based silicate materials with diopside as the main crystalline phase.

Thermoluminescence and optical absorption properties of glass from natural diopside and of synthetic diopside glass

Glasses based on natural mineral diopside and synthetic glasses starting from oxides of magnesium, calcium and silicon, and some of these glasses doped with 0.1, 1.0, 2.0 and 4.0% of Ag, have been produced for the study of their thermoluminescence and optical absorption properties. A marked different behavior is observed in various glasses, including glass with silver nanoparticles.

Effect of water on the high-pressure structural behavior of anorthite-diopside eutectic glass

We employed in situ high pressure Raman spectroscopy to examine structural variations in hydrous versus anhydrous aluminosilicate glasses as a function of pressure. Raman spectra of anhydrous and water-saturated (6.7wt% H2O) eutectic anorthite – diopside (An-Di) glasses were collected at pressures up to 10GPa in a diamond anvil cell (DAC). Both glasses exhibited a distinct change in compression mechanism at about 2.5GPa. From 0 to 2.5GPa each glass depolymerizes. Above 2.5GPa the anhydrous glass becomes less polymerized, whereas the hydrous glass becomes more polymerized as pressure is increased up to 10GPa. These differences are explained in terms of Al-coordination and formation of triclusters. For the dry glass, at pressures below 2.5GPa, depolymerization occurs by means of tricluster (OT3) formation in which bridging oxygens (BO) become triply coordinated to a third network forming cation, preferentially IVAl, thereby increasing the coordination to VAl. At pressures >2.5GPa compression induced coordination to non-bridging oxygens (NBO) causes tetrahedral IVAl to become highly coordinated V,VIAl. Network modifying cations (Ca and Mg) coordinated to NBO at ambient conditions become charge-balancing cations for V,VIAl at elevated pressure, resulting in decreased polymerization. For the wet glass, compression up to 2.5GPa causes protons in H2O to depolymerize Al tetrahedra into Al-OH. At pressures >2.5GPa most of the highly coordinated Al is present as VIAl and network polymerization increases with the formation of M-OH (M=Ca, Mg) groups that enable Si-O-Si bonds (BO). Bulk modulus measurements support increased polymerization with the wet glass (K0=16±2GPa) shown to be more compressible than the dry glass (K0=52±5GPa).