Journal of Non-Crystalline Solids: X最新文献

The process related to the formation of a multicomponent amorphous material during the reduction of α-Fe₂O₃ with the products of thermodestruction of WAS is studied using x-ray powder diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). Because WAS contains sand and clay along with its bio-components, the thermal treatment of WAS is accompanied by the formation of amorphous carbon, SiO₂, Al₂O₃, and multicomponent alloys. At T = 1000 °C, under oxygen-deficient conditions, iron oxide was reduced according to the scheme: α-Fe₂O₃ → (amorphous phase)_{main part} + (Fe + Fe_0.94O)(crystalline)_{little part}. The main product of the Fe₂O₃ reduction is amorphous iron with a lamellar structure. Newly formed amorphous alloys form interlayers between the iron plates and 3D inclusions. Inclusions of C, SiO₂, and Al₂O₃ agglomerates are observed between the lamellar packs. This macrostructure of the material allows slow cooling of the 3D-samples while preserving the amorphous state of iron.

Glass structure remains puzzling to scientists, especially due to the challenges in characterizing their structural order beyond the first coordination shell, i.e., the so-called medium-range order. Structural method development is therefore needed to advance our understanding of, e.g., structure-property relations in these disordered materials. To this end, we here review the fundamentals, applications and perspectives of an interesting new approach, namely persistent homology, which is a type of topological data analysis. This method allows for the analysis of both ring- and void-type structures in materials without making any assumptions of the network structure. As discussed herein, it has recently been used to analyze atomic position data (as obtained from atomistic simulations or reverse Monte Carlo) of glasses, especially regarding their medium-range order structure. We also discuss the opportunities in coupling persistent homology analyses with machine learning calculations as well as the open questions and challenges that require further investigations.

We studied the short-range order and the atomic dynamics of stable and undercooled binary Zr₂Co alloy melts as well as their density and viscosity. The containerless processing technique of electrostatic levitation was used to achieve deep undercooling and to avoid contaminations. Static structure factors are determined by combining this technique with neutron and high energy X-ray diffraction. Co self-diffusion coefficients are measured by quasielastic neutron scattering. Our results reveal that the short-range order of the Zr₂Co melts closely resembles that previously observed for Zr₆₄Ni₃₆. We consider this as the origin of the very similar melt dynamics of these two alloys at same temperatures. On the other hand, the difference in the structure and dynamics when compared with those of Zr₂Cu and Zr₂Pd shows clearly that not only the atomic sizes, but also electronic properties or chemical bonding have an important influence on the melt properties of Zr-based glass forming melts.

PACS number(s): 61.20.−p, 61.25.Mv, 66.30.Fq, 61.05.F-, 61.05.cp

Silver quantum clusters (Ag QCs), with broadband molecular luminescence, are stabilized in the borosilicate glasses with the [SiO₄]/[BO₄]⁻/[BO₃] blended networks. The introduction of SiO₂ in the B₂O₃-Ag₂O-BaO glasses induces the transformation of [BO₃] to [BO₄]⁻ to prevent over-growth of Ag QCs → Ag NPs and uniformly disperse Ag QCs in glass matrix. Due to the uniformly distribution of Ag QCs, the photoluminescence (PL) quenching due to cross relaxation (CR) between Ag QCs is highly suppressed, achieving PL quantum yields (QYs) as high as 67.38%. The Ag QCs activated glass based WLEDs exhibit not only excellent chemical durability but also superior luminance performances with a color coordinate of (0.32, 0.37), a correlated color temperature (CCT) of 6030 K and a color rendering index (CRI) of 89.7. Thus, the Ag QCs activated borosilicate glasses can be considered as a new type of efficient luminescent materials for various photonic application.

Applications of Li₂O-Al₂O₃-SiO₂ glass-ceramics (LAS GC) have been extended to electronic and optical devices and production process equipment in addition to their conventional use in cookware. For further expansion and application to new markets, we demonstrate three topics of our research on the material and production processes from viewpoint of glass phases. The first topic is spherical LAS GC powder for a filler application. It has been developed successfully, which can be prepared in a single heat treatment where spheroidizing by viscous flow and crystallization are achieved simultaneously by considering the kinetics of the two phenomena. Second, high transparent LAS GC was obtained by the composition design of the glass-matrix phase, Ti-free, or increasing Al content based on the coloration mechanism. Third, the fan shape of the feeder in our forming process has accomplished to prevent devitrification and form the largest sheet of 2200 × 2500 × 5 mm.

When glass absorbs high energy from ultrashort-pulsed lasers, a very rapid melting-cooling event occurs. Images taken by a Scanning Electron Microscope (SEM) reveal a surface feature which elucidates the glass is heated to above 2000 °C. A series of voids along the laser path is also observed and analyzed by SEM and High-angle Annular Dark-filed Scanning Transmission Electron Microscopy (HAADF-STEM). Molecular Dynamic simulation predicting observable voids in fused silica glass requires the temperature to be above 10,000 Kelvin. This suggests that the thermal effect from nonlinear absorption along cannot explain the void generation. Thermal stress analysis based on three different types of glasses revealed that stress generated by laser heating is highly correlated to thermal expansion coefficient. Such thermal stress may be a key factor for laser cutting.

Borate and boron oxide containing bioactive glasses have drawn attention because of their unique properties and potential biomedical applications. In this paper, we review recent advances in understanding of boron oxide addition on the structures and properties of bioactive glasses from both experimental and simulation studies. After reviewing the synthesis, characterization and applications of these novel bioactive glasses, recent developments of simulation methodologies including the interatomic potentials to model boron oxide containing bioactive glasses are reviewed. Effect of boron oxide to silica substitution on a range of properties such as density, glass transition temperature, coefficient of thermal expansion, diffusion and mechanical properties, as well as crystallization behavior, both from our own studies and those from literature, are summarized. Furthermore, influence of boron oxide on in vitro bioactivity in several bioactive glass series are reviewed and discussed, emphasizing the importance of in vitro testing conditions on the bioactivity evaluation. Lastly, an outlook of future directions of the field has been provided.

Prediction of brittle fracture of amorphous oxide glasses continues to be a challenge due to the existence of multiple fracture mechanisms that vary with loading conditions. To address this challenge, we present a model for all three regimes of crack growth in glasses. Regimes I and III are controlled by Arrhenius processes while regime II is transport controlled along with a simple Arrhenius model for viscoelastic stress relaxation. Through dimensional arguments and physical reasoning, we propose a single mechanism which underlies both regime III subcritical crack growth and near-crack-tip viscoelastic relaxation. By combining the subcritical crack growth and viscoelastic models we obtain a prediction for a threshold stress intensity, $K_{\mathrm{th}}$, below which stresses around the crack relax faster than it propagates. For stress intensity $K_I<K_{\mathrm{th}}$, no subcritical crack growth is predicted to occur, allowing for the design of stable glass systems. The prediction is compared to measured subcritical fracture threshold data for soda-lime silica glasses.

In recent years, molecular dynamics (MD) simulation has been used to study the deformation behaviors of glass under nanoindentation, mainly using ideal geometries like a spherical indenter or a 2.5-D sample geometry to simplify post-analysis and save computational costs. To generate stress/strain fields that can be directly compared with experiments, we developed a 3-D nanoindentation protocol in this work to study the deformation behaviors of a model metallic glass under sharp contact loading in MD. Our studies show that the indenter sharpness controls the shear band formation, and the interaction between shear bands dictates the crack initiation in the model metallic glass. Shear bands and residual stress fields in the model metallic glass from our simulated nanoindentation tests are consistent with observations in soda-lime silicate (SLS) glass from the instrumented indentation in experiments, as both of them favor shear deformation under sharp contact loading.

Mixed modifier effect refers to the nonlinear variations of glass properties when mixing different types of modifier ions. The effect plays an important role since it can be applied to design glasses with controlled properties and it is also related to the raw materials selection. In this review, we will summarize the recent important progress on the mixed modifier effect in oxide glasses. The effect has been found in various properties, but we mainly focus on glass transition temperature (T_g), hardness (H), elastic modulus (E), and coefficient of thermal expansion (α) since these properties are critical in glass manufacture and products performance. Different properties exhibit unique features and many theories are proposed to account for the effect. The compositional dependence of these properties is reviewed and the theories proposed to explain this effect are discussed. Moreover, we suggest some future directions for the further work on the mixed modifier effect.