Journal of Non-Crystalline Solids: X最新文献

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.

The viscoelastic behavior of supercooled Se-deficient liquids in the series As_xSe_100-x (40 ≤ x ≤ 60) and P_xAs_4–xSe₃ (0 ≤ x ≤ 2.8) are studied using parallel plate rheometry. The compositional variations in the viscosity and fragility of these liquids are shown to be consistent with the corresponding structural evolution. While the shear relaxation of As_xSe_100-x liquids with 40 ≤ x ≤ 50 is associated with the dynamics of AsSe bond scission/renewal, the As-rich liquids with x ≥ 55 are found to display an additional low-frequency process, which is related to a cooperative interconversion between molecular and network structural moieties. A similar behavior is also exhibited by the As-rich liquids in the P_xAs_4–xSe₃ series. In contrast, the P-rich liquids characterized by high molecule content display a power-law relaxation behavior resulting from a rather broad distribution of relaxation timescales associated with various dynamical modes of single molecules and molecular clusters.

Low melting Li₂O-PbO-B₂O₃, Me₂O-ZnO-B₂O₃, Me = Li, Na, K, Rb and CaO-ZnO-B₂O₃ glasses were studied with Raman and infrared spectroscopies to advance the structural understanding of zinc borate glasses as potential candidates for substitution of lead containing glasses.

Although the effect of type of alkali ions on the number (N₄) of fourfold coordinated boron (B₄) in the glasses is small, the alkali ions direct the type of borate groups, i.e., pentaborate in lithium, sodium, and calcium zinc borate glasses, as well as diborate in potassium and rubidium containing ones. Both groups were simultaneously found in Li₂O-PbO-B₂O₃. Alkali ions are mainly responsible for the formation of B₄-units and metaborate. Zinc ions favorably compensate non-bridging oxygen and partially form ZnO₄.

With decreasing N₄ and field strength of the alkali ions the atomic packing density, glass transition temperature and Young's Modulus also decrease. The coefficient of thermal expansion increases with decreasing N₄.