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At least 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Structural studies of Bi 2 O 3 -Nb 2 O 5 -TeO 2 glasses

Bi 2 O 3 -Nb 2 O 5 -TeO 2 glasses show unusual annealing behavior with appearance of spherulites within the matrix glass structure for the Bi 0.5 Nb 0.5 Te 3 O 8 composition. The textures resemble those found previously among polyamorphic Al 2 O 3 -Y 2 O 3 glasses containing metastably co-existing high- and low-density phases produced during quenching. However the spherulites produced within the Bi 2 O 3 -Nb 2 O 5 -TeO 2 glass are crystalline and can be identified as an “anti-glass” phase related to β-Bi 2 Te 4 O 11 . Here, we used high energy synchrotron X-ray diffraction data to study structures of binary and ternary glasses quenched from liquids within the Bi 2 O 3 -Nb 2 O 5 -TeO 2 system. These reveal a glassy network based on interconnected TeO 4 and TeO 3 units that is related to TeO 2 crystalline materials but with larger Te…Te separations due to the presence of TeO 3 groups and non-bridging oxygens linked to modifier (Bi 3 + , Nb 5 + ) cations. Analysis of the viscosity-temperature relations indicates that the glass-forming liquids are “fragile” and there is no evidence for a LLPT occurring in the supercooled liquid. The glasses obtained by quenching likely correspond to a high-density amorphous (HDA) state. Subsequent annealing above T g shows mainly evidence for direct crystallization of the “anti-glass” tellurite phase. But, some evidence may exist for simultaneous formation of nanoscale amorphous spherulites that could correspond to the LDA polyamorph. The quenching and annealing behavior of Bi 2 O 3 -Nb 2 O 5 -TeO 2 supercooled liquids and glasses is compared with similar materials in the Al 2 O 3 -Y 2 O 3 system.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Redox effects on the structure and properties of Na-Mo-Fe-phosphate glasses

Na-Mo-Fe-phosphate glasses were prepared with reducing and oxidizing raw materials and the effects of the different Fe 2+ /Fe 3+ and Mo 5+ /Mo 6+ ratios on glass structure and properties were determined. Mssbauer spectroscopy confirms significantly greater concentrations of Fe 2+ ions in the reduced glasses and distorted Fe 3+ O 4 sites preferred over the Fe 3+ O 6 sites in the oxidized glasses. Raman spectroscopy reveals the presence of isolated Mo 6+ O 6 sites in the oxidized glasses, and highly distorted Mo 5+ O 5 sites in reduced Mo-rich glasses. The presence of specific Fe- and Mo-polyhedra is correlated with the average phosphate anion length, as characterized by high-pressure liquid chromatography. Generally, for the similar compositions, oxidized glasses have greater molar volumes than the reduced glasses, associated with the formation of isolated Mo 6+ O 6 octahedra and the absence of highly crosslinked Mo 5+ OPO 4 units. Tg increases with increasing Fe 3+ fractions in the Fe-rich glasses, whereas for the Mo-rich glasses, T g increases with greater Mo 5+ fractions.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Structural peculiarities and Raman spectra of TeO{sub 2}/WO{sub 3}-based glasses: A fresh look at the problem

Ideas currently dominating the field of structural studies of TeO{sub 2}-based glasses are critically considered. A new physically and chemically consistent approach to the constitution of binary TeO{sub 2}-WO{sub 3} glasses is proposed, in which the reasoning coming from the Raman spectra reexamination are correlated with the basic principles of thermodynamics. Separation into two phases is suggested in such glasses. One phase is TeO{sub 2}, and another is Te(WO{sub 4}){sub 2} consisting of tetrahedral [WO{sub 4}]{sup 2-} anions and of Te{sup 4+} cations. Supplementary M{sub n}O{sub k} oxides added to the glasses are found incorporated in the former phase, thus producing solid solutions (for M=Ti, Nb) or tellurite compounds (for M=Nd). - Graphical abstract: Raman scattering spectra of TeO{sub 2}-based glasses with the following compositions (mol%): (a) pure TeO{sub 2}, (b) 85TeO{sub 2}-15WO{sub 3}, (c) 80TeO{sub 2}-15WO{sub 3}-5TiO{sub 2} ,(d) 80TeO{sub 2}-10WO{sub 3}-5TiO{sub 2}-5Nb{sub 2}O{sub 5}, (e) 80TeO{sub 2}-12WO{sub 3}-5TiO{sub 2}-3 Nd{sub 2}O{sub 3}, (f) 80TeO{sub 2}-10WO{sub 3}-5TiO{sub 2}-5Nd{sub 2}O{sub 3}. Highlights: Black-Right-Pointing-Pointer Structural studies of TeO{sub 2}-WO{sub 3} glasses are critically considered. Black-Right-Pointing-Pointer The oxide glass formation is analyzed from Raman spectra and thermodynamic principles. Black-Right-Pointing-Pointer Separation into two phases, TeO{sub 2} and Te(WO{sub 4}){sub 2}, is intrinsic in such glasses. Black-Right-Pointing-Pointer TiO{sub 2} or Nb{sub 2}O{sub 5} addition to TeO{sub 2}-WO{sub 3} glasses leads to produce solid solutions. Black-Right-Pointing-Pointer Nd{sub 2}O{sub 3} addition to TeO{sub 2}-WO{sub 3} glasses leads to produce a tellurite compound.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Semiconducting glasses: A new class of thermoelectric materials?

The deeper understanding of the factors that affect the dimensionless figure of merit, ZT, and the use of new synthetic methods has recently led to the development of novel systems with improved thermoelectric performances. Albeit up to now with ZT values lower than the conventional bulk materials, semiconducting glasses have also emerged as a new family of potential thermoelectric materials. This paper reviews the latest advances on semiconducting glasses for thermoelectric applications. Key examples of tellurium-based glasses, with high Seebeck coefficients, very low thermal conductivities and tunable electrical conductivities, are presented. ZT values as high as 0.2 were obtained at room temperature for several tellurium-based glasses with high copper concentrations, confirming chalcogenide semiconducting glasses as good candidates for high-performance thermoelectric materials. However, the temperature stability and electrical conductivity of the reported glasses are still not good enough for practical applications and further studies are still needed to enhance them. - Graphical abstract: Power factor as a function of the temperature for the Cu{sub 27.5}Ge{sub 2.5}Te{sub 70} and Cu{sub 30}As{sub 15}Te{sub 55} seniconducting glasses. Highlights: Black-Right-Pointing-Pointer A review of semiconducting glasses for thermoelectrics applications is presented. Black-Right-Pointing-Pointer The studied semiconducting glasses present very low thermal conductivities. Black-Right-Pointing-Pointer Composition can tune electrical conductivity and Seebeck coefficient. Black-Right-Pointing-Pointer ZT=0.2 is obtained at 300 K for different semiconducting glasses.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

The effect of ZnO ↔ Ta{sub 2}O{sub 5} substitution on the structural and thermal properties of SiO{sub 2}-ZnO-SrO-CaO-P{sub 2}O{sub 5} glasses

A series of glasses based on the system 48SiO{sub 2}-(36-X) ZnO-6CaO-8SrO-2P{sub 2}O{sub 5}-XTa{sub 2}O{sub 5} with X varying from 0 mol% (Ta0) to 8 mol% (Ta4) were fabricated. The structural features as a function of Ta{sub 2}O{sub 5} content were investigated by network connectivity (NC) calculations, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The thermal properties of the glasses were obtained by performing simultaneous thermal analysis (STA). XRD showed that all compositions were predominantly amorphous, however the incorporation of tantalum pentoxide (Ta{sub 2}O{sub 5}) resulted in a small degree of crystallinity within the sample. Replacing ZnO with Ta{sub 2}O{sub 5} increases the glass transition, crystallization and melting temperatures. Further, Ta{sub 2}O{sub 5} incorporation results in higher thermal stability suggesting a greater glass forming tendency and the insertion of Ta in the glass network. XPS and FTIR spectroscopy revealed that Ta behaves as a glass former and that Zn has an intermediary role in the vitreous network. - Highlights: • ZnO substitution for Ta{sub 2}O{sub 5} in the glass system SiO{sub 2}-ZnO-CaO-SrO-P{sub 2}O{sub 5} is presented. • ZnO substitution results in greater glass forming tendency. • Ta{sub 2}O{sub 5} addition results in the formation of Si−O−Ta and Ta−O−Ta linkages. • Ta{sub 2}O{sub 5} addition increases the glass thermal stability. • ZnO behaves as an intermediate in this glass system.

36 MATERIALS SCIENCE↗
DOE OSTI2012

The structural influence of aluminium ions on emission characteristics of Sm{sup 3+} ions in lead aluminium silicate glass system

Graphical abstract: The optical absorption and photoluminescence spectra of Sm ions in PbO-Al{sub 2}O{sub 3}-SiO{sub 2} glasses mixed with different concentrations of Al{sub 2}O{sub 3} have been investigated. From these spectra, the emission probabilities and also fluorescence lifetime principal transition viz., {sup 4}G{sub 5/2} {yields} {sup 6}H{sub 7/2} of Sm{sup 3+} ions of has been evaluated. The analysis of results of these studies has indicated that there is a less radiative trapping and enhanced fluorescence lifetime and high quantum efficiency in the glasses mixed with 8.0 mol% of Al{sub 2}O{sub 3}. Highlights: Black-Right-Pointing-Pointer Glasses of the composition (40 - x)PbO-(5 + x)Al{sub 2}O{sub 3}-54SiO{sub 2}:1.0Sm{sub 2}O{sub 3} with x = 5-10 mol% were prepared. Black-Right-Pointing-Pointer Spectroscopic properties (OA, PL and IR) were investigated. Black-Right-Pointing-Pointer Emission probability, lifetime, branching ratio of {sup 4}G{sub 5/2} {yields} {sup 6}H{sub 7/2} transition of Sm{sup 3+} have been evaluated. Black-Right-Pointing-Pointer Analysis of the results indicated that glass mixed with 8.0 mol% exhibits high luminescence efficiency. -- Abstract: Optical absorption and photoluminescence characteristics of Sm{sup 3+} ions in lead silicate glasses mixed with different concentrations of Al{sub 2}O{sub 3} (5-10 mol%) have been investigated. From these studies, the radiative properties viz., spontaneous emission probability A, the total emission probability, the radiative lifetime {tau}{sub R}, the fluorescent branching ratio {beta} of emission transition of {sup 4}G{sub 5/2} {yields} {sup 6}H{sub 7/2} along with other transitions for Sm{sup 3+} have been evaluated and found to be the highest for the glass mixed with 8.0 mol% of Al{sub 2}O{sub 3}.The IR spectral studies have indicated that Al{sup 3+} ions do participate in the glass network with AlO{sub 4} and AlO{sub 6} structural units and further revealed that the concentration of octahedral aluminium ions induce bonding defects in the glass network. Such bonding defects are assumed to be responsible for low phonon losses in these glasses and lead to higher values of radiative parameters for the glass mixed with 8.0 mol% of Al{sub 2}O{sub 3}.

36 MATERIALS SCIENCE↗
DOE OSTI2012

The effects of CeO{sub 2} addition on crystallization behavior and pore size in microporous calcium titanium phosphate glass ceramics

Highlights: ► We prepare a phosphate glass ceramic in the system of CaO–TiO{sub 2}–P{sub 2}O{sub 5} and add 2 to 6 mol% CeO{sub 2} to it. We determine the optimum percentage of CeO{sub 2} addition. ► We study phase separation, suitable time and temperature for crystallization in the microporous Calcium Titanium Phosphate Glass Ceramics utilizing DTA, SEM and XRD. ► We investigate on pore size utilizing BET and SEM techniques before and after CeO{sub 2} addition. ► CeO{sub 2} increases the pore size in the Calcium Titanium Phosphate Glass Ceramics. -- Abstract: In this research the effect of the addition of CeO{sub 2} to microporous Calcium Titanium Phosphate glass ceramics was studied. Different molar percentages of CeO{sub 2} were added to three samples of a base glass whose composition was P{sub 2}O{sub 5} 30, CaO 45, TiO{sub 2} 25 (mol%). The first sample had 2 mol% CeO{sub 2}, the second sample had 4 mol% CeO{sub 2}, and the third sample had 6 mol% CeO{sub 2}. The fourth sample did not contain any CeO{sub 2}. The glass samples were melted and crystallized to bulk glass ceramics by a conventional method. Differential Thermal Analysis (DTA) was utilized to determine the appropriate nucleation and crystallization temperatures. Among the samples, the DTA curve of the sample which had 2 mol% CeO{sub 2} had the sharpest crystallization peak. Therefore, this sample was chosen to prepare the glass ceramics. Using X-ray Diffraction (XRD) it was found that in all samples β-Ca{sub 3}(PO{sub 4}){sub 2} and CaTi{sub 4}(PO{sub 4}){sub 6} were the major phases. The β-Ca{sub 3}(PO{sub 4}){sub 2} phase was dissolved away by soaking the glass ceramics in HCl, leaving a porous skeleton of CaTi{sub 4}(PO{sub 4}){sub 6}. CeO{sub 2} addition increased the glass transition temperature and decreased the crystallization time and temperature. It was shown that CeO{sub 2} addition resulted in an increase in the mean pore diameter while the specific surface area decreased. The median pore diameter and specific surface area were determined as 27 nm and 14 m{sup 2}/g, respectively, for the sample containing 2 mol% CeO{sub 2}.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Preparation and nonlinear optical properties of indium nanocrystals in sodium borosilicate glass by the sol–gel route

Graphical abstract: The sodium borosilicate glass doped with indium nanocrystals have been successfully prepared by sol–gel methods. And the indium nanocrystals in tetragonal crystal system have formed uniformly in the glass, and the average diameter of indium nanocrystals is about 30 nm. The third-order optical nonlinear refractive index γ, absorption coefficient β, and susceptibility χ{sup (3)} of the glass are determined to be −4.77 × 10{sup −16} m{sup 2}/W, 2.67 × 10{sup −9} m/W, and 2.81 × 10{sup −10} esu, respectively. Highlights: ► Indium nanocrystals embedded in glass matrix have been prepared by sol–gel route. ► The crystal structure and composition are investigated by XRD and XPS. ► Size and distribution of indium nanocrystals is determined by TEM. ► The third-order optical nonlinearity is investigated by using Z-scan technique. -- Abstract: The sodium borosilicate glass doped with indium nanocrystals have been successfully prepared by sol–gel route. The thermal stability behavior of the stiff gel is investigated by thermogravimetric (TG) and differential thermal (DTA) analysis. The crystal structure of the glass is characterized by X-ray powder diffraction (XRD). Particle composition is determined by X-ray photoelectron spectroscopy (XPS). Size and distribution of the nanocrystals are characterized by transmission electron microscopy (TEM) as well as high-resolution transmission electron microscopy (HRTEM). Results show that the indium nanocrystals in tetragonal crystal structure have formed in glass, and the average diameter is about 30 nm. Further, the glass is measured by Z-scan technique to investigate the nonlinear optical (NLO) properties. The third-order NLO coefficient χ{sup (3)} of the glass is determined to be 2.81 × 10{sup −10} esu. The glass with large third-order NLO coefficient is promising materials for applications in optical devices.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Removal of hydroxyl groups from Er{sup 3+}/Yb{sup 3+} codoped flurotellurite glasses

Highlights: • We propose a simple and safe method for an efficient removal of hydroxyl groups from Er{sup 3+}/Yb{sup 3+} doped fluorotellurite glasses. • We have shown that using a convenient amount of BaF{sub 2} as drying agent helped to remove partially hydroxyl groups. • For an efficient removal of hydroxyl groups, we have subjected the glasses to an additional heat-treatment in two steps. • The obtained results revealed an efficient removal of water from the glasses which manifested itself in a drastic reduction of the concentration of hydroxyl groups and a significant increase of Er{sup 3+} emission. • This study showed that the addition BaF{sub 2} and the heat treatment process might be a veritable alternative for drying tellurite glasses. - Abstract: In this work, we present a safe and relatively simple procedure to eliminate hydroxyl groups from Er{sup 3+} and Yb{sup 3+} codoped new flurotellurite glasses. It was shown that adding a convenient amount of BaF{sub 2} as drying agent reduced the absorption coefficient and the concentration of hydroxyl groups inside the glass samples. However, to remove efficiently water from the glasses, it was necessary to subject the samples to supplementary heat treatment in two steps. A drastic decrease of the density of hydroxyl groups accompanied with a significant enhancement of the erbium emission was observed after the heat-treatment procedure. The obtained results showed that this method might be a veritable alternative to obtain nearly water free tellurite glasses suitable for many optical devices with small sizes or thickness. However, for a good use of this procedure, we tried to elucidate what has happened at the microscopic scale for the glass taking as a guide the available explanations dealing with the removal of water from silica-based glasses.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Energy-efficient modification of reduction-melting for lead recovery from cathode ray tube funnel glass

Highlights: • We recovered Pb from cathode ray tube funnel glass using reduction melting process. • We modified the melting process to achieve Pb recovery with low energy consumption. • Pb in the funnel glass is efficiently recovered at 1000 °C by adding Na{sub 2}CO{sub 3}. • Pb remaining in the glass after reduction melting is extracted with 1 M HCl. • 98% of Pb in the funnel glass was recovered by reduction melting and HCl leaching. - Abstract: Lead can be recovered from funnel glass of waste cathode ray tubes via reduction melting. While low-temperature melting is necessary for reduced energy consumption, previously proposed methods required high melting temperatures (1400 °C) for the reduction melting. In this study, the reduction melting of the funnel glass was performed at 900–1000 °C using a lab-scale reactor with varying concentrations of Na{sub 2}CO{sub 3} at different melting temperatures and melting times. The optimum Na{sub 2}CO{sub 3} dosage and melting temperature for efficient lead recovery was 0.5 g per 1 g of the funnel glass and 1000 °C respectively. By the reduction melting with the mentioned conditions, 92% of the lead in the funnel glass was recovered in 60 min. However, further lead recovery was difficult because the rate of the lead recovery decreased as with the recovery of increasing quantity of the lead from the glass. Thus, the lead remaining in the glass after the reduction melting was extracted with 1 M HCl, and the lead recovery improved to 98%.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2021

Estimating Internal Stress of an Alteration Layer Formed on Corroded Boroaluminosilicate Glass through Spectroscopic Ellipsometry Analysis

Aqueous corrosion of glass may result in the formation of an alteration layer in the glass surface of which chemical composition and network structure are different from those of the bulk glass. Since corrosion occurs far below the glass-transition temperature, the alteration layer cannot fully relax to the new structure with the lowest possible energy. Molecular dynamics simulations suggested that such a network will contain highly strained chemical bonds, which can be manifested as a stress in the alteration layer. Common techniques to measure stress in thin films or surface layers were found inadequate for thick monolithic glass samples corroded in water. Here, we explored the use of spectroscopic ellipsometry to test the presence of internal stress in the alteration layer formed by aqueous corrosion of glass. Furthermore, a procedure for analyses of spectroscopic ellipsometry data to determine birefringence in the alteration layer was developed. Findings with the established fitting procedure suggested that a stress builds up in the corroded surface layer of a boroaluminosilicate glass if there is a change in relative humidity, pH, or electrolyte concentration of the environment to which the glass surface is exposed. A similar process may occur in other types of glass, and it may affect the surface properties of corroded glass objects.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2013

Cooling rate and size effects on the medium-range structure of multicomponent oxide glasses simulated by molecular dynamics

A set of molecular dynamics simulations were performed to investigate the effect of cooling rate and system size on the medium-range structure of melt-derived multicomponent silicate glasses, represented by the quaternary 45S5 Bioglass composition. Given the significant impact of the glass degradation on applications of these materials in biomedicine and nuclear waste disposal, bulk structural features which directly affect the glass dissolution process are of particular interest. Connectivity of the silicate matrix, ion clustering and nanosegregation, distribution of ring and chain structural patterns represent critical features in this context, which can be directly extracted from the models. A key issue is represented by the effect of the computational approach on the corresponding glass models, especially in light of recent indications questioning the suitability of conventional MD approaches (that is, involving melt-and-quench of systems containing ∼10{sup 3} atoms at cooling rates of 5-10 K/ps) when applied to model these glasses. The analysis presented here compares MD models obtained with conventional and nonconventional cooling rates and system sizes, highlighting the trend and range of convergence of specific structural features in the medium range. The present results show that time-consuming computational approaches involving much lower cooling rates and/or significantly larger system sizes are in most cases not necessary in order to obtain a reliable description of the medium-range structure of multicomponent glasses. We identify the convergence range for specific properties and use them to discuss models of several glass compositions for which a possible influence of cooling-rate or size effects had been previously hypothesized. The trends highlighted here represent an important reference to obtain reliable models of multicomponent glasses and extract converged medium-range structural features which affect the glass degradation and thus their application in different fields. In addition, as a first application of the present findings, the fully converged structure of the 45S5 glass was further analyzed to shed new light on several dissolution-related features whose interpretation has been rather controversial in the past.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Luminescent properties of Eu{sup 2+}-doped BaGdF{sub 5} glass ceramics a potential blue phosphor for ultra-violet light-emitting diode

Eu{sup 2+} doped transparent oxyfluoride glass ceramics containing BaGdF{sub 5} nanocrystals were successfully fabricated by melt-quenching technique under a reductive atmosphere. The structure of the glass and glass ceramics were investigated by differential scanning calorimetry, X-ray diffraction (XRD), and transmission electron microscopy (TEM). The luminescent properties were investigated by transmission, excitation, and emission spectra. The decay time of the Gd{sup 3+} ions at 312 nm excited with 275 nm were also investigated. The results of XRD and TEM indicated the existence of BaGdF5 nanocrystals in the transparent glass ceramics. The excitation spectra of Eu{sup 2+} doped glass ceramics showed an excellent overlap with the main emission region of an ultraviolet light-emitting diode (UV-LED). Compared with the as-made glass, the emission of glass ceramics is much stronger by a factor of increasing energy transfer efficiency from Gd{sup 3+} to Eu{sup 2+} ions, the energy transfer efficiency from Gd{sup 3+} to Eu{sup 2+} ions was discussed. In addition, the chromaticity coordinates of glass and glass ceramics specimens were also discussed, which indicated that the Eu{sup 2+} doped BaGdF{sub 5} glass ceramics may be used as a potential blue-emitting phosphor for UV-LED.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Glass formability in medium-sized molecular systems/pharmaceuticals. I. Thermodynamics vs. kinetics

Scrutinizing critical thermodynamic and kinetic factors for glass formation and the glass stability of materials would benefit the screening of the glass formers for the industry of glassy materials. The present work aims at elucidating the factors that contribute to the glass formation by investigating medium-sized molecules of pharmaceuticals. Glass transition related thermodynamics and kinetics are performed on the pharmaceuticals using calorimetric, dielectric, and viscosity measurements. The characteristic thermodynamic and kinetic parameters of glass transition are found to reproduce the relations established for small-molecule glass formers. The systematic comparison of the thermodynamic and kinetic contributions to glass formation reveals that the melting-point viscosity is the crucial quantity for the glass formation. Of more interest is the finding of a rough correlation between the melting-point viscosity and the entropy of fusion normalized by the number of beads of the pharmaceuticals, suggesting the thermodynamics can partly manifest its contribution to glass formation via kinetics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Perspective: Highly stable vapor-deposited glasses

This paper describes recent progress in understanding highly stable glasses prepared by physical vapor deposition and provides perspective on further research directions for the field. For a given molecule, vapor-deposited glasses can have higher density and lower enthalpy than any glass that can be prepared by the more traditional route of cooling a liquid, and such glasses also exhibit greatly enhanced kinetic stability. Because vapor-deposited glasses can approach the bottom of the amorphous part of the potential energy landscape, they provide insights into the properties expected for the “ideal glass”. Connections between vapor-deposited glasses, liquid-cooled glasses, and deeply supercooled liquids are explored. The generality of stable glass formation for organic molecules is discussed along with the prospects for stable glasses of other types of materials.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Influence of Hydrogen Bonding on the Kinetic Stability of Vapor Deposited Glasses of Triazine Derivatives

It has recently been established that physical vapor deposition (PVD) can produce organic glasses with enhanced kinetic stability, high density, and anisotropic packing, with the substrate temperature during deposition (Tsubstrate) as the key control parameter. The influence of hydrogen bonding on the formation of PVD glasses has not been fully explored. Herein, we use a high-throughput preparation method to vapor-deposit three triazine derivatives over a wide range of Tsubstrate, from 0.69 to 1.08Tg, where Tg is the glass transition temperature. These model systems are structural analogues containing a functional group with different H-bonding capability at the 2-position of a triazine ring: (1) 2-methylamino-4,6-bis(3,5-dimethyl-phenylamino)-1,3,5-triazine (NHMe) (H-bond donor), (2) 2-methoxy-4,6-bis(3,5-dimethyl-phenylamino)-1,3,5-triazine (OMe) (H-bond acceptor), and (3) 2-ethyl-4,6-bis(3,5-dimethyl-phenylamino)-1,3,5-triazine (Et) (none). Using spectroscopic ellipsometry, we find that the Et and OMe compounds form PVD glasses with relatively high kinetic stability, with the transformation time (scaled by the α-relaxation time) on the order of 103, comparable to other highly stable glasses formed by PVD. In contrast, PVD glasses of NHMe are only slightly more stable than the corresponding liquid-cooled glass. Using IR spectroscopy, we find that both the supercooled liquid and the PVD glasses of the NHMe derivative show a higher average number of bonded NH per molecule than that in the other two compounds. These results suggest that H-bonds hinder the formation of stable glasses, perhaps by limiting the surface mobility. Interestingly, despite this difference in kinetic stability, all three compounds show properties typically observed in highly stable glasses prepared by PVD, including a higher density and anisotropic molecular packing (as characterized by IR and wide-angle X-ray scattering).

36 MATERIALS SCIENCE↗
DOE OSTI2024

Different structural behavior of MgSiO 3 and CaSiO 3 glasses at high pressures

Knowledge of the structural behavior of silicate melts and/or glasses at high pressures provides fundamental information for discussing the nature and properties of silicate magmas in the Earth’s interior. The behavior of Si-O structures under high-pressure conditions has been widely studied, while the effect of cation atoms on the high-pressure structural behavior of silicate melts or glasses has not been well investigated. Here, in this study, we investigated the structures of MgSiO 3 and CaSiO 3 glasses up to 5.4 GPa by in situ X-ray pair distribution function measurements to understand the effect of different cations (Mg 2+ and Ca 2+ ) on high-pressure structural behavior of silicate glasses. We found that the structural behavior of MgSiO 3 and CaSiO 3 glasses are different at high pressures. The structure of MgSiO 3 glass changes by shrinking of Si-O-Si angle with increasing pressures, which is consistent with previous studies for SiO 2 and MgSiO 3 glasses. On the other hand, CaSiO 3 glass shows almost no change in Si-Si distance at high pressures, while the intensities of two peaks at ~3.0 and ~3.5 Å change with increasing pressure. The structural change in CaSiO 3 glass at high pressure is interpreted as the change in the fraction of the edge-shared and corner-shared CaO 6 -SiO 4 structures. The different high-pressure structural behavior observed in MgSiO 3 and CaSiO 3 glasses may be the origin of differences in properties, such as viscosity between MgSiO 3 and CaSiO 3 melts at high pressures. This signifies the importance of different structural behaviors due to different cations in investigations of the nature and properties of silicate magmas in Earth’s interior.

36 MATERIALS SCIENCE↗
DOE OSTI2011

COMPUTER MODELING OF HIGH-LEVEL WASTE GLASS TEMPERATURES WITHIN DWPF CANISTERS DURING POURING AND COOL DOWN

This report describes the results of a computer simulation study to predict the temperature of the glass at any location inside a DWPF canister during pouring and subsequent cooling. These simulations are an integral part of a larger research focus aimed at developing methods to predict, evaluate, and ultimately suppress nepheline formation in HLW glasses. That larger research focus is centered on holistically understanding nepheline formation in HLW glass by exploring the fundamental thermal and chemical driving forces for nepheline crystallization with respect to realistic processing conditions. Through experimental work, the goal is to integrate nepheline crystallization potential in HLW glass with processing capability to ultimately optimize waste loading and throughput while maintaining an acceptable product with respect to durability. The results of this study indicated severe temperature gradients and prolonged temperature dwell times exist throughout different locations in the canister and that the time and temperatures that HLW glass is subjected to during processing is a function of pour rate. The simulations indicate that crystallization driving forces are not uniform throughout the glass volume in a DWPF (or DWPF-like) canister and illustrate the importance of considering overall kinetics (chemical and thermal driving forces) of nepheline formation when developing methods to predict and suppress its formation in HLW glasses. The intended path forward is to use the simulation data both as a driver for future experimental work and, as an investigative tool for evaluating the impact of experimental results. Simulation data will be used to develop laboratory experiments to more acutely evaluate nepheline formation in HLW glass by incorporating the simulated temperatures throughout the canister into the laboratory experiments. Concurrently, laboratory experiments will be performed to identify nepheline crystallization potential in HLW glass as a function of time and temperature, the results of which will be fed back into simulations to evaluate the potential impacts. Through an iterative process involving computer simulations and experimental results, the potential for nepheline crystallization in HLW glass can be predicted, evaluated, and suppressed to maximize waste loading and throughput of canisters.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗