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At least 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Pressure‐induced polyamorphism in lanthanide‐solute metallic glasses

The electronic structure inheritance of lanthanide‐solvent atoms in lanthanide‐based metallic glasses has been proposed. Is a polyamorphism possible in lanthanide‐solute metallic glasses? So far, polyamorphic phase transitions in metallic glass containing lanthanide have been observed only in lanthanide‐solvent metallic glasses. Here, a pressure‐induced transition between two distinct amorphous states, accompanied by a 7% volume collapse at ambient pressure, was observed in La 43.4 Pr 18.6 Al 14 Cu 24 metallic glass, with low lanthanide content, by using in situ X‐ray total scattering method. The transformation also indicated by changes in short range and medium range order. Thus, it is proposed that the lanthanide‐solute metallic glasses also inherit 4 f electronic transition from pure lanthanide element in polyamorphic transition. This discovery offers a supplement to research on lanthanide‐based metallic glasses, which further provides a new perspective of the polyamorphic transformation in metallic glasses containing lanthanide element.

Li, Liangliang↗
DOE OSTI2014

NanoSIMS Imaging Alternation Layers of a Leached SON68 Glass Via A FIB-made Wedged Crater

Currently, nuclear wastes are commonly immobilized into glasses because of their long-term durability. Exposure to water for long periods of time, however, will eventually corrode the waste form and is the leading potential avenue for radionuclide release into the environment. Because such slow processes cannot be experimentally tested, the prediction of release requires a thorough understanding the mechanisms governing glass corrosion. In addition, due to the exceptional durability of glass, much of the testing must be performed on high-surface-area powders. A technique that can provide accurate compositional profiles with very precise depth resolution for non-flat samples would be a major benefit to the field. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) depth profiling is an excellent tool that has long been used to examine corrosion layers of glass. The roughness of the buried corrosion layers, however, causes the corresponding SIMS depth profiles to exhibit erroneously wide interfaces. In this study, NanoSIMS was used to image the cross-section of the corrosion layers of a leached SON68 glass sample. A wedged crater was prepared by a focused ion beam (FIB) instrument to obtain a 5× improvement in depth resolution for NanoSIMS measurements. This increase in resolution allowed us to confirm that the breakdown of the silica glass network is further from the pristine glass than a second dissolution front for boron, another glass former. The existence of these two distinct interfaces, separated by only ~20 nm distance in depth, was not apparent by traditional ToF-SIMS depth profiling but has been confirmed also by atom probe tomography. This novel sample geometry will be a major benefit to efficient NanoSIMS sampling of irregular interfaces at the nanometer scale that would otherwise be obscured within ToF-SIMS depth profiles.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2026

Ultrafast Laser Welding and Terahertz Time-domain Spectroscopy of Soda Lime Silicate Glass

Joining and welding techniques of similar and dissimilar materials have reached their limits due to the inflexibility of adapting dielectric materials, e.g., glasses and ceramics, reproducibility for transparent materials, and cycle process time. The ability to join pieces of glasses using laser irradiation allows rapid processing of vacuum insulating glass (VIG) for a widening range of commercial energy-efficient applications. We have used a 1064-nm laser wavelength with 15 picoseconds pulse width and a 155-kHz repetition rate to weld commercial plate glass pieces. The welded samples were characterized via x-ray fluorescence (XRF), time-of-flight secondary ion mass spectrometry (TOF–SIMS), polarimetry, and terahertz time-domain spectroscopy (THz-TDS) to determine the integrity of the weld and chemical changes in the welded areas. Our data shows no significant changes in glass chemistry and structure on average over nano- to micro-scales occurred from the welding process within the limits of the characterization tools. Our results demonstrate successful welding of glass plates without significant changes in the glass chemistry, structure, or properties in the laser-modified region or strains in the bulk glass.

Matthies, Kathleen [ORNL] (ORCID:0009000213135441)↗
DOE OSTI2016

The Controversial Role of Inter-diffusion in Glass Alteration

Current kinetic models for nuclear waste glasses (e.g. GM2001, GRAAL) are based on a set of mechanisms that have been generally agreed upon within the international waste glass community. These mechanisms are: hydration of the glass, ion exchange reactions (the two processes are referred as inter-diffusion), hydrolysis of the silicate network, and condensation/precipitation of partly or completely hydrolyzed species that produces a porous and amorphous layer and crystalline phases on surface of the altered glass. Recently, a new idea with origins in the mineral dissolution community has been proposed that excludes inter-diffusion process as a potential rate-limiting mechanism. To understand how the so-called interfacial dissolution/precipitation model can change the current understanding of glass behavior, a key experiment used to account for this model was replicated to further revisit the interpretation. This experiment was performed at 50°C, with SON68 glass, in static mode, deionized water and S/V ratio of 10 m-1 for 6 months. It turn out that glass alters in an intermediate kinetic regime between the forward and the residual rate. According to previous and new solid characterizations, it is concluded that neither a simple inter-diffusion model nor the interfacial dissolution precipitation model can account for the observed elemental profiles within the alteration layer. More generally, far and close-to-saturation conditions must be distinguished and literature provides evidences that inter-diffusion takes place in slightly acidic conditions and far from saturation. However, closer to saturation, when a sufficiently dense layer is formed, a new approach is proposed requiring a full description of chemical reactions taking place within the alteration layer and involving water molecules as it is thought that water accessibility to the pristine glass is the rate-limiting process.

Gin, Stephane↗
DOE OSTI2026

Effects of Composition and Oxidation States on the Structures of Chromium-Containing Sodium Silicate Glasses: Molecular Dynamics Simulations using Machine Learning Interatomic Potentials

Chromium represents a significant challenge for the vitrification of high-level nuclear waste into silicate and borosilicate glasses due to its low solubility and variable oxidation states, which can limit the waste loading due to promotion of crystallization or phase separation during processing. In this study, we modeled chromium containing silicate glasses using molecular dynamics simulations with three machine learning interatomic potentials (MLIPs), MACE, CHGNet, and PFP were employed, to gain insights on glass composition and oxidation states on the structures of these glasses. One of the goals is to evaluate their ability of these MLIPs to accurately represent the general structure of silicate glasses and chromium local environments as a function of chromium oxidation states. Density Functional Theory (DFT) based calculations and experimental data such as neutron structure factors were used to validate the structural models. It was found that the foundation models of all three MLIPs are able to reproduce general structural features of the sodium silicate glass structure consistent with experimental and DFT data, but only CHGNet and PFP can accurately capture the oxidation states and local environment of chromium: tetrahedral for Cr6+ and octahedral for Cr3+. Furthermore, we studied the effect of varying Cr3+/ Cr6+ (Cr3+/Crtotal) ratio and total chromium content using PFP. Our results show that Cr6+ enhances network polymerization by reducing non-bridging oxygens through Na? charge compensation required due to the formation of chromate (CrO42-) species, while Cr³? acts as a network modifier that disrupts connectivity. System size effects on the structural characteristics and chromium environments were also tested using the PFP potential. This work highlights the importance of careful validation on the precision, transferability, and potential of MLIPs for modeling glasses containing transition metal elements that can exist in multiple oxidation states. It is also encouraging to see the foundational models are all three MLFFs are able to reproduce the basic sodium silicate glass structures, while suggesting additional training or refining is needed to improve the description of more complex systems containing transition metals.

Puga, Christina L.↗
DOE OSTI2015

Probing Toluene and Ethylbenzene Stable Glass Formation using Inert Gas Permeation

Inert gas permeation is used to investigate the formation of stable glasses of toluene and ethylbenzene. The effect of deposition temperature (Tdep) on the kinetic stability of the vapor deposited glasses is determined using Kr desorption spectra from within sandwich layers of either toluene or ethylbenzene. The results for toluene show that the most stable glass is formed at Tdep = 0.92 Tg, although glasses with a kinetic stability within 50% of the most stable glass were found with deposition temperatures from 0.85 to 0.95 Tg. Similar results were found for ethylbenzene, which formed its most stable glass at 0.91 Tg and formed stable glasses from 0.81 to 0.96 Tg. These results are consistent with recent calorimetric studies and demonstrate that the inert gas permeation technique provides a direct method to observe the onset of molecular translation motion that accompanies the glass to supercooled liquid transition.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2025

Ab Initio Simulation of Medium-Range Ordering in Ionic Glass Electrolytes LiSiPON and LiNaSiPON

Ionic glasses can exhibit a unique combination of optical transparency, electronic resistivity, ionic conductivity, and mechanical ductility. The origin of the relatively high ionic conductivity and ductility is poorly understood. Recently, these ionic glasses were found to have medium-range ordering (MRO) similar to that of metallic glasses. This MRO significantly impacts the properties of metallic glasses and is also expected to significantly impact the properties of ionic glasses. Here, this work used ab initio molecular dynamics (AIMD) simulations to study the effect of ionic glass composition on the MRO. The AIMD models showed that the degree of MRO increased as the temperature of the LiSiPON ionic glass decreased. The modeling also showed that the MRO is suppressed when 50% of Li is substituted with Na. This work lays the foundation for using AIMD to identify clear structure–property relationships in ionic glasses, allowing their properties to be optimized.

Osetsky, Yuri N. [Oak Ridge National Laboratory (O↗
DOE OSTI2018

Structure of International Simple Glass and properties of passivating layer formed in circumneutral pH conditions

Knowing the structure of a material is necessary to understand its evolution under various influences; here, the alteration by water of a reference glass of nuclear interest, called International Simple Glass (ISG), is studied. The ISG atomic structure has not yet been thoroughly characterized. Short- and medium-range order in this six-oxide glass was investigated by molecular dynamics (MD) methods. Combining the simulated data with experimental observations acquired from both pristine and altered ISG provided new insight into the formation of surface layers and passivation of the underlying glass. In the tested conditions of 90 °C, silica-saturated solution, and pH 90°C 7, the passivating layer partly inherits the structure of the pristine glass network despite the release of mobile elements (Na, B, and some Ca), with a reorganization of the silicate network following B release. The layer appears to minimize its internal energy by relaxing strain accumulated during glass quenching. The resulting passivated glass shows a strong resistance to hydrolysis. The nanopores of this hydrated material, displaying a mean pore size of ~1 nm, are filled with various water species. Water speciation determination inside the nanopores is therefore an achievement for future water dynamic study in the passivated glass.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Effect of decades of corrosion on the microstructure of altered glasses and their radiation stability

Understanding the microstructural evolution of glasses during their interaction with water and radiation is of fundamental importance in addressing the corrosion of nuclear waste forms under geological disposal conditions. Here we report the results of more than 21 years of corrosion of two borosilicate glasses showing the formation of mesoporous C–S–H gels in Ca-bearing glasses and a mainly microporous microstructure in Al-bearing glasses. These porous corroded glasses were then irradiated with heavy ions to simulate the effects of recoil nucleus damage and monitored in real time using transmission electron microscopy with in situ ion irradiation. The ballistic collisions remarkably healed the porous corroded glasses to a pore-free homogeneous microstructure. Besides providing new insights and predictions about how doped glasses and actual waste forms may evolve under corrosion and irradiation, the results highlight the non-universal nature of the existing corrosion models and the important role that the glass composition and radiation damage play in the evolution of the microstructure during corrosion.

36 MATERIALS SCIENCE↗
DOE OSTI2012

New oxyfluoride glass with high fluorine content and laser patterning of nonlinear optical BaAlBO{sub 3}F{sub 2} single crystal line

A new oxyfluoride glass of 50BaF{sub 2}-25Al{sub 2}O{sub 3}-25B{sub 2}O{sub 3} (mol. %) with a large fraction of fluorine, i.e., F/(F + O) = 0.4, was prepared using a conventional melt-quenching method in order to synthesize new glass-ceramics containing nonlinear optical oxyfluoride crystals. The refractive index at 632.8 nm and ultra-violet cutoff wavelength of the glass were 1.564 and {approx}200 nm, respectively. Eu{sup 3+} ions in the glass showed a high quantum yield of 88% in the photoluminescence spectrum in the visible region. BaAlBO{sub 3}F{sub 2} crystals (size: 50-100 nm) showing second harmonic generations were formed through the crystallization of the glass. Lines consisting of BaAlBO{sub 3}F{sub 2} crystals were patterned successfully on the glass surface by laser irradiations (Yb:YVO{sub 4} laser with a wavelength of 1080 nm, laser power of 1.1 W, scanning speed of 8 {mu}m/s). High resolution transmission electron microscope observations combined with a focused ion beam technique indicate that BaAlBO{sub 3}F{sub 2} crystals are highly oriented just like a single crystal. The present study proposes that the new oxyfluoride glass and glass-ceramics prepared have a high potential for optical device applications.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Effect of Li{sub 2}SO{sub 4} addition on structure and ionic conductivity of lithium borosilicotitanate glasses

Lithium borosilicotitanate glasses containing Li{sub 2}SO{sub 4} were prepared by melt quenching technique. Electrical conductivity, density, molar volume and glass transition temperature T{sub g} for all the glass samples were measured. IR spectroscopy was used for structural studies of these glasses in the range from 400 to 2000 cm{sub −1}. The conductivity of the Li{sub 2}SO{sub 4} containing glasses was found to be half an order higher than the base glass. The electrical conductivity was interpreted from the point of view of glass structure which suggests that an enhancement in conductivity is due to the incorporation of Li{sub 2}SO{sub 4} in the macromolecular network. The molar volume and glass transition temperature T{sub g} results are found to be in good correlation with conductivity results.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Electronic structures and physical properties of Na 2 O doped silicate glass

Ab initio molecular dynamics has been applied to construct seven sodium silicate glass models with Na2O concentration ranging from 0 to 50 mol. %. The structures of the simulated (Na 2 O) x (SiO 2 ) 1-x glasses are critically analyzed and validated by comparing with available experimental data. Because the initial seed model is based on a near-perfect continuous random network model for amorphous SiO 2 with periodic boundaries, the structures of these silicate glasses are highly reliable. The electronic structure, interatomic bonding, and the mechanical and optical properties of seven models are calculated using the first-principles density functional method. In particular, a single quantum mechanical metric, the total bond order density (TBOD), is used to characterize the internal cohesion of sodium silicate glass. This is a significant step beyond the traditional analysis of glasses based purely on the geometric parameters. The TBOD value is found to decrease with increasing Na content, indicating the destruction of silica network connectivity. The calculated mass density and refractive index increase with x are in good agreement with experiment. The elastic coefficients and bulk mechanical properties exhibit a nonlinear variation in the series and depend greatly on the internal bonding and cohesion of the glass. The calculated Poisson's ratio indicates that the glass becomes more ductile with the addition of Na 2 O. Our results indicate that sodium silicate glass tends to be unstable for x greater than 0.4 due to the total destruction of the SiO 2 network.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Mesoscale Phase Field Modeling of Glass Strengthening Under Triaxial Compression

Recent hydraulic bomb and confined sleeve tests on transparent armor glass materials such as borosilicate glass and soda-lime glass showed that the glass strength was a function of confinement pressure. The measured stress-strain relation is not a straight line as most brittle materials behave under little or no confinement. Moreover, borosilicate glass exhibited a stronger compressive strength when compared to soda-lime glass, even though soda-lime has higher bulk and shear moduli as well as apparent yield strength. To better understand these experimental findings, a mesoscale phase field model is developed to simulate the nonlinear stress versus strain behaviors under confinement by considering heterogeneity formation under triaxial compression and the energy barrier of a micro shear banding event (referred to as pseudo-slip hereafter) in the amorphous glass. With calibrated modeling parameters, the simulation results demonstrate that the developed phase field model can quantitatively predict the pressure-dependent strength, and it can also explain the difference between the two types of glasses from the perspective of energy barrier associated with a pseudo-slip event.

Confined Borosilicate↗
DOE OSTI2016

A Discrete Element Model of Armor Glass Fragmentation and Comminution Failure Under Compression

Because of its exceptional compressive resistance and crystal-clear appearance, lightweight glass has been traditionally used in transparent armor applications. However, due to its brittle nature, glass fails differently from ductile materials in the sense that glass fragmentation occurs instantly ahead of the projectile tip upon penetration. The effective residual strength of the armor glass then inevitably relies on the damaged glass strength within such comminuted zones with confinement from the surrounding intact materials. Physical understanding of damaged glass strength therefore becomes highly critical to the further development of armor designs. In the present study, a discrete element based modeling framework has been developed to understand and predict the evolution of compressive damages and residual strength of armor glasses. With the characteristic fragmentation and comminution failures explicitly resolved, their influences on the mechanical degradation of the loaded glass materials have been evaluated. The effects of essential loading conditions and material properties have also been investigated.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Looking through model medieval green glasses: From color to recipe

Abstract The colors of medieval stained glasses depend on their chemical composition. The redox interactions in glass between iron and copper and their influence on the color were investigated in two soda‐lime silicate model glasses. Both glasses have close iron and copper redox ratios and copper oxidizes iron when the iron content is smaller than the copper content. The redox speciation of iron and copper was determined using combining x‐ray and optical absorption spectroscopies in relation with the resulting color. The molar extinction coefficient of Cu 2+ was estimated from the combined analysis to be 32 mol/L/cm. The glass color change from green to blue‐green color is assigned to the decrease of the total iron content, confirming that ancient glassmakers could control the final color with the glass recipe. These results provide reference data for further spectroscopic investigations of medieval stained glasses. Comparison with ancient copper‐colored green glass compositions suggests that the higher ratio of copper to iron total contents was imposed by the more reducing melting conditions in medieval furnaces.

Hunault, Myrtille O. J. Y.↗
DOE OSTI2021

Derivation of the Structural Integrity of Residual (SIR) glass model for the enhancement of waste loading

A new model based on glass structure to allow for enhanced waste loading in nuclear waste glass while maintaining chemical durability is proposed. The model is derived by splitting the molar concentrations of the targeted starting glass composition into theoretical crystalline phases anticipated to be observed during devitrification and a residual glass. An empirically derived relationship based on maintaining the residual glass structure, determined from a calculated non-bridging oxygen content, was demonstrated to successfully screen glasses for acceptable durability. The proposed model can successfully identify durable glass compositions containing 20–35 wt% Al 2 O 3 , a concentration that would significantly increase the projected waste loading in glasses processed at the Hanford Tank Waste Treatment and Immobilization Plant.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Vibrational spectroscopy analysis of silica and silicate glass networks

Vibrational spectroscopy has been widely used to investigate various structural aspects of the glass network, and there are a plethora of papers reporting subtle but consistent changes in infrared and Raman spectral features of glass upon alterations of glass compositions, thermal histories, mechanical stresses, or surface treatments. However, interpretations of such spectral features are still obscured due to the lack of well-established physical principles accurately describing vibrational modes of the non-crystalline glass network. Due to the non-equilibrium nature of the glass network, three-dimensionally connected without any long-range orders, vibrational spectral features of glass cannot be interpreted using the analogy with those of isolated molecular moieties or crystalline counterparts. Here, this feature article explains why such comparisons are outdated and describes the recent advances made from theoretical calculations of vibrational spectral features of amorphous networks or comparisons of computational results with experimental data. For the interpretation of vibrational spectral features of silica and silicate glasses, the following empirical relationships are suggested: (i) the intensity-weighted peak position of the Si-O-Si stretch mode negatively correlates with the weighted average of the Si-O bond length distribution, and (ii) the broad band of the Si-O-Si bending mode negatively correlates with the Si-O-Si bond angle distribution. Selected examples of vibrational spectroscopic imaging of surface defects are discussed to deliberate the implication of these findings in the structure-property relationship of silica and silicate glass materials. Unanswered questions and continuing research challenges are identified.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2012

Viscous Glass Sealants for SOFC Applications

Two series of silicate glasses that contain gallium as the primary critical component have been identified and optimized for viscous sealing of solid oxide fuel cells operating from 650 to 850°C. Both series of glass sealants crystallize partially upon heat treatment and yield multiphase microstructures that allow viscous flow at temperatures as low as 650°C. A fully amorphous sealant was also developed by isolating, synthesizing and testing a silicate glass of the same composition as the remnant glassy phase in one of the two glass series. Of ~40 glasses tested for longer than 500 hours, a set of 5 glasses has been further tested for up to 1000h in air, wet hydrogen, and against both yttria-stabilized zirconia and aluminized stainless steel. In some cases the testing times reached 2000h. The reactivity testing has provided new insight into the effects of Y, Zr, and Al on bulk and surface crystallization in boro-gallio-silicate glasses, and demonstrated that at least 5 of the newly-developed glasses are viable viscous sealants.

30 DIRECT ENERGY CONVERSION↗