Glass Structure Research Articles

Lava – substrate interaction: Constraints on flow emplacement and basal sintering, Lebuj rhyolitic flow, Tokaj Mountains, Carpathian-Pannonian region

The surface extrusion of rhyolite lava is linked with a complex edifice morphology and texturally diverse internal structure. The rarely exposed basal flow/dome zones provide a textural record of the mechanical and thermal stress between the overlying lava and existing topography. The Lebuj flow (Tokaj Mountains, Hungary) developed in a Miocene caldera setting, where the erosion exposed its basal zone, including various textures due to the lava substrate interaction. The flow margin is contacted with underlying volcaniclastics along a steeply inclined (50–75°) plane. The lithology describes a complex ductile-brittle transition in the flow and lithification process in the substrate. The relict obsidian grains (marekanite, 0.1% H2O) in the perlite (2–3% H2O) are proof of an incomplete hydration process below the glass transition temperature. The dynamic loading of the lava caused irregular fragmentation developing a brittle basal shear zone with lens-like glass deformation. The substrate has suffered syn-emplacement lithification and the primary glass structure is completely re-crystallized. FTIR and Raman measurements identified low-temperature phyllosilicate minerals and SiO2 polymorphs, which caused additional porosity loss and densification. Using cooling time-temperature-porosity information given by this reconstruction, we suggest parallel-acting processes at elevated (groundmass crystallization-devitrification) and lower temperature (hydration-secondary mineralization) range. These define a relative timescale for the textural development in the lithologically heterogeneous contact zone.

Insights from molecular dynamics into the chemistry-structure relationships of calcium aluminosilicate glasses

Calcium aluminosilicate (CAS) glasses are ubiquitous in nature and play an important role in diverse technological applications ranging from structural glasses to sustainable cementitious materials. Understanding the relationship between the chemical composition and the structure of CAS glasses is an essential step towards optimizing their properties for different uses in the future. Here, we use extensive molecular dynamics (MD) simulations to characterize the multiscale structure of CAS glasses over the full compositional range. Analysis of the short and medium range order of the glasses reveals that Lowenstein's rule is widely violated, that silica is more susceptible than alumina to the depolymerizing effects of calcium, and that high-silica glasses favor calcium in lower oxygen coordination states, while the opposite is true for high-alumina ones. We also find the presence of highly coordinated aluminum and tricluster oxygens in high-alumina glasses, which form as a charge compensation mechanism. We find that current theoretical models used to predict oxygen species, oxygen bridge types, or tetrahedral coordination, while overall qualitatively reasonable, simplify the complex interplay between the different oxides which results in inaccurate predictions, particularly for glasses in intermediate compositional regions. Our analysis of the cluster, chain, and ring topological structures in the aluminosilicate network reveals a sharp transition from a connected to a disconnected graph which depends not only on the calcium content of the glass, but also on the ratio of silica to alumina. Glasses in the compositional region corresponding to such transition display the largest ring and longest chain structures of any glass studied.

Comparing the effects of Ga2O3 and Al2O3 on the structure and mechanical properties of sodium borate glasses

The role of Ga2O3 in oxide glasses remains poorly understood compared to other network forming oxides. To address this, we here study the structure and mechanical properties of sodium gallioborate glasses and compare our findings to those of sodium aluminoborate glasses. The substitutions of both Ga2O3 for B2O3 and Al2O3 for B2O3 increase the fraction of tetrahedral Ga or Al units and decrease the fraction of tetrahedral B. However, unlike in the case of aluminoborate glasses, higher-coordinated polyhedra (i.e., GaV and GaVI) are not observed even in the pergallic region. In both glass series, most mechanical properties exhibit a change in their trend at the peralkaline-to-pergallic transition. The substitution of Ga2O3 for B2O3 decreases the crack initiation resistance, while the substitution of Al2O3 for B2O3 results in an increase in resistance. In the sodium gallioborate glasses, the fracture toughness increases in the peralkaline region and decreases in the pergallic region.

Combined experiments and atomistic simulations for understanding the effect of ZnO on the sodium silicate and sodium borosilicate glass network

Combined experiments and molecular dynamics (MD) simulations were performed over wide range of glass compositions to understand the improved durability of borosilicate glass with ZnO addition. A significant change in glass structure was monitored from short range and intermediate range order parameters. The MD results were found to be in good agreement with the experimental data for Young's Modulus, glass transition temperature, and leaching. Both experiments and MD simulations report the enhanced chemical durability of glass with ZnO addition. Low R (Na2O/B2O3) and high K (SiO2/B2O3) of ZnO doped sodium borosilicate (Zn–NBS) glass surface compared to bare NBS represents the more stable structure of glass surface for Zn–NBS than NBS. The enhanced chemical resistivity of Zn–NBS was established from the increasing activation energy for diffusion of Na ions. The combined experiments and MD simulations disclose many interesting microstructure and dynamics due to the presence of ZnO in the glass.

Effect of Gd3+/Nd3+- dual doped borate glasses on the physical and spectroscopic properties for the NIR emission at 1.069 µm

Near-infrared luminescence properties of dual doped Gd3+/Nd3+-incorporated glasses were manufactured using the melt-quenching technique and characterized by several techniques. The modification in glass structure may be seen in the differences in density, molar volume, and refractive index that occur when the amount of lanthanide oxide in the glass increases. The spectroscopic properties of Nd3+ in these glasses are quite well understood, and the observed optical characteristics may be used to process and eventually determine laser properties. According to the results of XANES, the Nd oxidation state remains the predominant peak for Nd3+ in all of the samples. The transition from 4I9/2 to 4G5/2 +2G7/2 is important for the strongest band in the absorption spectra, which can be seen at 584 nm. The luminescence spectra show peaks caused by 4F3/2→4IJ (J=11/2, 13/2) at three excitation wavelengths of 526, 574 and 805 nm. After the processing, we created glass samples for the study of photoluminescence with various amounts of Nd2O3 incorporated into the best host, 25Li2O-5Al2O3-2.5Gd2O3-(67.5-X)B2O3-XNd2O3. Based on luminescence intensity, it is determined that 1.0 mol% of Nd2O3 is the concentration quenching in the studied glasses. The 4F3/2 →4I11/2 transition at 1069 nm, excited by 526, 578 and 803 nm, has the highest emission intensity. The combined findings of the glasses demonstrate that near-infrared luminescence may be successfully used with them. All of the analysis shows that the dual doped Gd3+/Nd3+ borate glass would be a potential solid-state laser candidate.

Cobalt-containing borate bioactive glass fibers for treatment of diabetic wound

Impaired angiogenesis is one of the predominant reasons for non-healing diabetic wounds. Cobalt is well known for its capacity to induce angiogenesis by stabilizing hypoxia-inducible factor-1α (HIF-1α) and subsequently inducing the production of vascular endothelial growth factor (VEGF). In this study, Co-containing borate bioactive glasses and their derived fibers were fabricated by partially replacing CaO in 1393B3 borate glass with CoO. Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) analyses were performed to characterize the effect of Co incorporation on the glass structure, and the results showed that the substitution promoted the transformation of [BO3] into [BO4] units, which endow the glass with higher chemical durability and lower reaction rate with the simulated body fluid (SBF), thereby achieving sustained and controlled Co2+ ion release. In vitro biological assays were performed to assess the angiogenic potential of the Co-containing borate glass fibers. It was found that the released Co2+ ion significantly enhanced the proliferation, migration and tube formation of the Human Umbilical Vein Endothelial Cells (HUVECs) by upregulating the expression of angiogenesis-related proteins such as HIF-1α and VEGF. Finally. In vivo results demonstrated that the Co-containing fibers accelerated full-thickness skin wound healing in streptozotocin (STZ)-induced diabetic rat model by promoting angiogenesis and re-epithelialization.Graphical

Effect of CaO doping on the properties and crystallization behavior of Y2O3–Al2O3–SiO2 glass

Nowadays, Y2O3–Al2O3–SiO2 (YAS) glass joining is considered to be a promising scheme for nuclear-grade continuous silicon carbide (SiC) fiber reinforced SiC matrix composites (SiC/SiC). CaO has great potential for nuclear applications since it has low reactivity and low decay rate under nuclear irradiation. In this paper, the effect of CaO doping on the structure, thermophysical properties, and crystallization behavior of YAS glass was systematically studied. As the CaO doping content increased, the number of bridge oxygens and the viscosity at high temperatures reduced gradually. After heat treatment at 1400 °C, the main phases in YAS glass were β-Y2Si2O7, mullite, and SiO2 (coexistence of crystalline and glass phases), while that with 3.0% CaO doping turned into a single glassy phase under the same treatment conditions. Moreover, a structural model and the modification mechanism were proposed, which provided a theoretical basis for the subsequent component design and optimization.

Origin of medium-range atomic correlation in simple liquids: Density wave theory

The atomic pair-distribution function of simple liquid and glass shows exponentially decaying oscillations beyond the first peak, representing the medium-range order (MRO). The structural coherence length that characterizes the exponential decay increases with decreasing temperature and freezes at the glass transition. Conventionally, the structure of liquid and glass is elucidated by focusing on a center atom and its neighboring atom shell characterized by the short-range order (SRO) and describing the global structure in terms of overlapping local clusters of atoms as building units. However, this local bottom-up approach fails to explain the strong drive to form the MRO, which is different in nature from the SRO. We propose to add an alternative top-down approach based upon the density wave theory. In this approach, one starts with a high-density gas state and seeks to minimize the global potential energy in reciprocal space through density waves using the pseudopotential. The local bottom-up and global top-down driving forces are not mutually compatible, and the competition and compromise between them result in a final structure with the MRO. This even-handed approach provides a more intuitive explanation of the structure of simple liquid and glass.

Thermal and thermo-mechanical analysis of a novel pass-through all-glass evacuated collector tube by combining experiment with numerical simulation

The collector tube could be a significant component of a solar water heater (SWH), that directly determines its performance and application eventualities. Here, a completely unique pass-through all-glass evacuated collector tube (ETC) is projected, which includes an easy structure composed inner and outer layers with each ends amalgamate along and no free ends. In addition, the flow pattern of the working medium in the tube also changes from laminar to turbulent flow, and natural convection changes to forced convection, greatly improving the convective heat transfer efficiency. Such a solar collector tube reaches 50% thermal efficiency at 54 °C in operation temperature and DNI = 1000W/m2, and might reach about 82 °C stagnation temperature at identical condition. Compared to standard Dewar tube, the pass-through ECT includes a higher thermal efficiency thanks to a lower inner layer temperature and better exit temperature. Completely different thermal expansions cause thermal stress within the glass structure, however the utmost stress between the inner and outer tubes was unbroken at intervals 40–120 MPa guaranteeing safe and stable operation at intervals the attainable temperature regime.

Optical Properties of Fluorozirconate Glasses Doped with Chromium Ions

Chromium trifluoride-doped fluoride glasses in the ZrF4–BaF2–LaF3–AlF3–NaF (ZBLAN) system with partial substitution of fluorine for chlorine have been synthesized. The spectral data obtained confirm that chromium ions enter the glass structure and exhibit broadband luminescence caused by the 4T2 → 4A2 transition in the Cr3+ ion. The observed long-wavelength shift of the broadband luminescence band and Cr3+absorption bands in fluoride–chloride glass compared to fluoride glass corresponds to the expected behavior of the Cr3+ luminescence and absorption spectra when fluoride ions are replaced by chloride ions, which should lead to a weakening of the strength of the crystal field acting on Cr3+ ions. At room temperature, the luminescence of Cr3+ ions at 888 and 908 nm is strongly quenched due to the thermally stimulated nonradiative transition from the 4T2 excited state to the 4A2 ground state.

Effect of B/Si molar ratio on the structure and properties of borosilicate bioactive glasses assessed using molecular dynamics simulations

Due to the improvement and innovation of theoretical methods and the increasing enhancement of high performance computing, computer simulations provide a new method and strategy for optimizing complex composition of novel bioactive glass. In this work, molecular dynamics simulations were used to analyze the effect of B/Si molar ratio on the structure of borosilicate bioactive glass (BBG) and to investigate the effect of structural alterations on its ions release and biological effects. Structural descriptor a theoretical structural descriptor that estimates the overall strength of the glass network (F net) was calculated from the simulated data, and the linear relationships of F net with B and Mg releasing rate in deionized water and simulated body fluid were built. In vitro mineralization experiments showed that all three BBGs could generate hydroxyapatite and the release of some network modifier ions such as Mg would be regulated by the B/Si ratio. In vitro cellular experiments revealed that the BBG sample with a composition of 1.25B (6Na2O–8K2O–8MgO–22CaO–22.5B2O3–2P2O5–31.5SiO2) promoted the proliferation and osteogenic differentiation of rat bone marrow mesenchymal stem cells, and significantly enhanced the expression of osteogenesis-related genes such as osteopontin, which might be related to the release of Mg at an early stage.

Depicting Defects in Metallic Glasses by Atomic Vibrational Entropy.

Due to the chaotic structure of amorphous materials, it is challenging to identify defects in metallic glasses. Here we tackle this problem from a thermodynamic point of view using atomic vibrational entropy, which represents the inhomogeneity of atomic contributions to vibrational modes. We find that the atomic vibrational entropy is correlated to the vibrational mean-square displacement and polyhedral volume of atoms, revealing the critical role of vibrational entropy in bridging dynamics, thermodynamics, and structure. On this method, the local vibrational entropy obtained by coarse-graining the atomic vibrational entropy in space can distinguish more effectively between liquid-like and solid-like atoms in metallic glasses and establish the correlation between the local vibrational entropy and the structure of metallic glasses, offering a route to predict the plastic events from local vibrational entropy. The local vibration entropy is a good indicator of thermally activated and stress-driven plastic events, and its predictive ability is better than that of the structural indicators.

New Swiss technical specification SIA 2057 for glass structures and its post failure limit state concept

Until recently, designing and constructing with glass in Switzerland was not performed on a uniformly regulated basis due to the lack of a national standard for glass. Therefore, foreign regulations and codes were typically applied. However, this practice repeatedly caused problems. In August 2021, the Technical Specification SIA 2057 Glass Structures has been published to close this codification gap and to create a uniform design basis for the Swiss glass industry. A wide range of glass applications is covered, taking into account the latest findings from practice and science, such as use of shear transfer in laminated glass. The SIA 2057 follows the well-proven SIA principles of regulating only where necessary. Thus, a flexible application of the code is made possible, and innovation is encouraged. In addition to simple design methods, engineers are free to pursue alternative and innovative paths in glass design. The present article provides an overview of the SIA 2057 with focus on laminated safety glass design and post fracture limit state verification.

Review of the Main Mechanical Testing Methods for Interlayer Characterization in Laminated Glass

In the last decades, the use of structural glass has increased exponentially. The reliability of brittle structural glass elements is considerably improved if laminated glass elements are chosen because, in this case, a redistribution of internal forces is permitted once a limited breakage occurs. Thus, instead of monolithic glass, composite materials consisting of two or more glass plies bonded together using a polymeric film as an interlayer are used. In the event of glass failure, because of the chemical bond between the different materials, the adhesion to the interlayer prevents glass fragments from scattering. To design structural elements, the definition of the mechanical features of the interlayer is necessary. However, several standards and techniques can be applied, considering the characterization of either the interlayer itself or the laminated glass. The paper reviews the main existing methods and focuses on the standard suggested by the CEN/TS 19100:2021, analyzing in detail the effect of the different parameters involved. A numerical model is presented to account for the effect of the stress level, glass, and interlayer thickness. Although the standard leaves a certain degree of freedom in choosing those parameters, in some cases the results can differ.

Unraveling the relationship between the structural features and solubility properties in Sr-containing bioactive glasses

Understanding the effect of glass network structure on the solubility properties of bioactive glasses is fundamental for designing new compositions with tailored biological functions and applications. This paper bridged the composition-structure-property relationship utilizing experimental measurements and molecular dynamics simulations. The Sr atom reorganized the network structures through a partial transformation of tetrahedral to trigonal boron units and the change of the ratio of bridged oxygen/non-bridged oxygen, which modified the glass structures at longer lengths scales, such as through changing the ring size distribution. Our results demonstrated that the evolution of solubility properties can be linked to the atomic structure change in short- and medium-range ordering. The structure-property relationship can be used to design and tune bioactive glass composition with specific properties.

Improving fatigue property of Zr–Ni–Al metallic glass by tailoring chemical composition with high structure stability

Improving the tolerance to fatigue damage for bulk metallic glass (BMG) is of vital importance for its industrial applications during long-term mechanical service. In this work, the composition dependence of structure stability against thermal and mechanical stimuli are studied with Zr–Ni–Al BMGs from the perspective of atomic topological packing and chemical affinity. Large atomic size disparity and strong interactions between component elements facilitate the stability of glass structure, which impart BMGs with relatively higher glass transition temperature and yield strength. Fatigue failure of BMG initiates from the accumulation of inelastic shear transformation events on the sample surface under cyclic loading. The fatigue endurance limit of Zr–Ni–Al BMG is effectively improved by tailoring the chemical composition with increased structure stability, which is characterized by high mismatch entropy and mixing enthalpy. Aluminum plays a role in enhancing the fatigue tolerance of Zr–Ni–Al BMGs, which presumably arises from the covalent-like bond character of aluminum that promotes the formation of rigid atomic packing motifs with great resistance to shear rearrangement, and consequently mitigates the fatigue crack initiation process.

Uncovering metallic glasses hidden vacancy-like motifs using machine learning

Vacancies are a ubiquitous type of defect in crystalline materials that can affect their properties and behavior, including atomic diffusivity, deformation processes, thermal conductivity, and electrical conductivity. While well-defined in crystals, it is challenging to identify such topological footprints in the amorphous structure of metallic glasses (MGs). Here, we uncover an unforeseen vacancy-like structural motif named Q7, which refers to an atomic Voronoi polyhedron with seven quadrangular faces, by investigating MG local atomic configurations with the help of machine learning. The Q7 motif exhibits characteristics similar to crystalline vacancies and plays a significant role in short-range structural disorder in MGs. The atoms at the center of the Q7 motif display larger local entropy, atomic volume, and local tension. Additionally, its concentration follows an Arrhenius-like relationship with temperature, accurately indicating the glass transition temperature, and is strongly correlated with the yield and failure of MGs during mechanical deformation. The discovery of the Q7 motif provides new insights into understanding the intricate relationship between local disorder and structural relaxation in MGs, offering a remarkable ability to predict their thermal and mechanical behavior. This potentially paves the way for enhancements in the design and manufacturing processes of MGs and other amorphous materials.

The Light-Trapping Character of Pit Arrays on the Surface of Solar Cells

Surfaces with light-trapping structures are widely used in solar cells to enhance light capturing and to transform efficiency. The study of light-trapping character is important for light-trapping structures in solar cells. In the present study, the light-trapping character for the regular hemisphere pit arrays (RHPAs) in solar cells was intensively investigated in terms of reducing light reflection, suppressing light escape, and increasing the length of the optical path. Results show that the RHPAs can decrease surface reflectivity by ~54% compared with the plane structure, and can reflect ~33% of the light that has not been absorbed back into the absorption layer of the solar cell. The total optical path of the cell with the RHPAs structure remarkably increased from 2ω to 4ω. To verify the theoretical research conclusions, we produced the glass structure samples with different aspect ratios by using micro/nanometer-processing technology. The reflection ratios for silicon wafers covered by plane and RHPAs glass samples were tested. The test results were compared with the theoretical calculation results, which showed consistency.

Investigation of Li2O/Na2O effect on the atomic structure and mechanical properties of aluminosilicate glasses using molecular dynamics simulation, Raman and NMR spectroscopy

Aluminosilicate glasses are extensively used in flat panel displays and aircraft windshields because of their superior mechanical characteristics. Understanding the influence of the components on the glass network structure and mechanical properties is essential to designing aluminosilicate glasses with desirable mechanical functions. In this paper, the molecular dynamic simulations were used to obtain atomic structural information of the glasses, and the results were compared with Raman, Nuclear magnetic resonance, X-ray photoelectron spectroscopy, Differential thermal analysis, and Vickers hardness to elucidate the effect of Li2O/Na2O on the atomic structure and mechanical properties of aluminosilicate glasses. We show through experiments and molecular dynamic simulations that an increase in the Li2O/Na2O ratio can increase the mechanical properties of the glass. Li ions reorganized the glass network by partial conversion of [AlO5] to [AlO4] units and changes in the bridging oxygen/non-bridging oxygen ratio, which in turn alters the glass on a longer scale, for example, by sharpening the ring distribution and an increase in the number of loops, leading to structural clustering of the glass network and increased mechanical properties. This composition-structure-property relationship can be used to design aluminosilicate glasses with particular properties.

Achieving strength-ductility synergy in metallic glasses via electric current-enhanced structural fluctuations

Structural applications of metallic glasses are limited by their room-temperature brittleness and strain-softening, associated with the extreme localization of plastic flow in shear bands. Herein, we alleviate this dilemma by the structural fluctuation induced by electric currents, achieving simultaneous improvement of strengths, compression plasticity, and strain hardening capacity. The electric current enhances the structural fluctuations at the atomic scale, introducing more soft zones while densifying their surroundings, which differs from previously reported rejuvenation strategies. This unique structural pattern featuring soft zones surrounded by hard zones leads to extensive sprouts and interactions of shear bands, capturing substantial atoms to participate in the deformation. The plausible mechanism behind the electric current-influenced dynamic evolution of amorphous clusters is proposed. Electric current introduces interatomic electrostatic forces between shell atoms of amorphous clusters through charge transfer. This force decreases the coordination of Zr- and Cu-centered clusters and increases the Al-centered icosahedra in the glassy matrix. Differential evolution of clusters under electric currents enhances atomic structural fluctuations and originates from the cohesion mechanism determined by electron distribution. These findings are suggestive of vanishing room-temperature brittleness and shed atomic-scale light on modulations of the structure and properties of metallic glasses by electric currents.