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Jonathan F Stebbins - One of the best experts on this subject based on the ideXlab platform.

  • nature of silicon boron mixing in sodium Borosilicate glasses a high resolution 11b and 17o nmr study
    Journal of Physical Chemistry B, 2003
    Co-Authors: Jonathan F Stebbins
    Abstract:

    In several series of sodium Borosilicate glasses, we have applied triple-quantum magic-angle spinning (3QMAS) 11B and 17O NMR to obtain high-resolution information about short-range structure and the connections among various network structural units and their variations with composition. Oxygen-17 3QMAS spectra reveal changes in connectivities between silicate and BO3 ([3]B) and BO4 ([4]B) units, by quantifying populations of bridging oxygens such as Si−O−Si, Si−O−[3]B, Si−O−[4]B, [3]B−O−[3]B, and [4]B−O−[3]B and of nonbridging oxygens. Boron-11 MAS and 3QMAS at a magnetic field of 14.1 T allow proportions of several borate units to be determined, including [3]B in boroxol ring and nonring sites and [4]B with two, three, and four Si neighbors. By combining the 11B and 17O NMR results, detailed information on Si/B mixing in sodium Borosilicates can be derived. Our results shows that [4]B is strongly associated with silicate units, nonring [3]B undergoes random mixing and ring [3]B tends to connect to bora...

  • solid state nmr study of metastable immiscibility in alkali Borosilicate glasses
    Journal of Non-crystalline Solids, 2003
    Co-Authors: Jonathan F Stebbins
    Abstract:

    In several series of lithium, sodium, and potassium Borosilicate glasses whose compositions traverse known regions of liquid–liquid phase separation, we have applied triple-quantum magic-angle spinning (3QMAS) 11B and 17O NMR to obtain high-resolution information about short-range structure and connections among various network structural units, and their variation with composition and thermal history. Oxygen-17 3QMAS spectra reveal changes in connectivities between silicate and BO3 ([3]B) and BO4 ([4]B) units, by quantifying populations of bridging oxygens such as B–O–B, Si–O–B and Si–O–Si, and of non-bridging oxygens. [3]B–O–Si and [4]B–O–Si as well as [3]B–O–[3]B and [4]B–O–[3]B linkages can be distinguished. 11B MAS and 3QMAS at a magnetic field of 14.1 T allow proportions of several borate units to be determined, including [3]B in boroxol ring and non-ring sites and [4]B with 3 versus 4 Si neighbors. By combining the 11B and 17O NMR results, detailed information on Si/B mixing in sodium Borosilicates can be derived, showing, for example, that [4]B and non-ring [3]B tend to mix with silicate units, while ring [3]B is mainly connected to borate groups. In a preliminary study of the effects of varying alkali cation, potassium-containing glasses are similar to those in the sodium Borosilicate system, but a lithium Borosilicate seems to exhibit considerably greater chemical heterogeneity. In annealing experiments that converted an optically clear to obviously phase-separated glasses, the ratio of [3]B to [4]B does not change significantly, but part of the non-ring [3]B converts to ring [3]B as the degree of unmixing increases.

  • Topological Disorder and Reactivity of Borosilicate Glasses: Quantum Chemical Calculations and 17O and 11B NMR Study
    Journal of Physical Chemistry B, 2001
    Co-Authors: Charles B. Musgrave, And Peidong Zhao, Jonathan F Stebbins
    Abstract:

    We present 17O and 11B NMR and quantum chemical calculations based on Hartree−Fock (HF) and density functional theory to investigate the site connectivity, the degree of chemical short-range order (CSRO), and the topological short-range order in binary Borosilicate glasses, which can serve as a simple model system for more complex Borosilicates and other covalent oxide glasses and melts. We also calculate the enthalpy of hydrolysis for each oxygen cluster in such glasses. The stability of [4]Si−O−[3]B was evaluated from the relative energy differences among the bridging oxygen clusters ([4]Si−O−[4]Si, [4]Si−O−[3]B, and [3]B−O−[3]B) calculated at the B3LYP/6-311+G(2d,p)//HF/3-21G and B3LYP/6-311+G(2d,p) levels of theory as well as data from 17O 3QMAS NMR. The fraction of [4]Si−O−[3]B at a boron mole fraction of 0.57 is about 37% (±1), suggesting a significant inter-dispersion of [3]B and [4]Si, where a random distribution of [4]Si and [3]B and complete phase separation lead to 50 and 0% of [4]Si−O−[3]B, re...

  • non bridging oxygens in borate glasses characterization by 11b and 17o mas and 3qmas nmr
    Solid State Nuclear Magnetic Resonance, 2000
    Co-Authors: Jonathan F Stebbins, Peidong Zhao, Scott Kroeker
    Abstract:

    Abstract The concentrations of non-bridging oxygens (NBO) in oxide glasses has major effects on their properties and on those of their precursor glass melts. In borate and Borosilicate glasses, the presence of NBO bonded to boron has generally been inferred from 11B NMR spectra and mass balance considerations. Here we report the direct observation of such NBO using 17O MAS and 3QMAS techniques, and compare estimates of their populations with those derived from high-resolution 11B MAS spectra. For the latter, two independent methods are used, based on the ratios of trigonal to tetrahedral boron and on the concentrations of trigonal boron sites with large quadrupolar asymmetry parameters. We include data on crystalline sodium pyroborate (Na4B2O5) and sodium metaborate (NaBO2), and several sodium and barium borate glasses. 17O chemical shifts and quadrupolar coupling constants for NBO bonded to boron vary considerably depending on their coordination environment. In Borosilicates, peaks for this species may be hidden by overlap with B–O–Si or Si–O–Si resonances.

Liu Qing - One of the best experts on this subject based on the ideXlab platform.

  • Effect of Tin Penetration on Surface Crystallization of Borosilicate Glass
    Journal of Wuhan University of Technology, 2010
    Co-Authors: Liu Qing
    Abstract:

    Tin ions may penetrate into Borosilicate glass surface layer when they were produced by float technics.Surface properties were changed by these tin ions.In this article,the effect of tin penetration on surface crystallization of Borosilicate glass was researched using optical microscopes and XRD etc.instruments.The difference of crystallization between two surfaces,the surface contacting with tin and the surface no-contacting with tin,were compared.The results indicate there were cristobalites on surface of glass after heat treatment at 750 ℃.The amount of cristobalite on the surface contacting with tin were more than another surface.As a result,tin penetration do not aggravate the surface crystallization of Borosilicate glass.

  • Study on Tin Penetration into Bottom Surface of Float Borosilicate Glass
    Glass & Enamel, 2007
    Co-Authors: Liu Qing
    Abstract:

    Using a special mini-graphite tin bath to simulate the float process of float Borosilicate glass,the tin penetration profiles in different temperature area from 1 250 ℃ to 650 ℃ were studied by EPMA/EDS.It was found out that tin diffused into the Borosilicate glass with a total depth of 40μm.Tin ion diffused towards the deeper layer in the Borosilicate glass under the higher temperature and only entered the superficial layer under the lower temperature.In the whole float processes,the tin penetration profiles showed a tin hump,but the tin hump disappeared at the temperature at outlet of tin bath.

Marcel Potuzak - One of the best experts on this subject based on the ideXlab platform.

  • topological principles of Borosilicate glass chemistry
    Journal of Physical Chemistry B, 2011
    Co-Authors: Morten Mattrup Smedskjaer, John C Mauro, Randall E Youngman, Carrie L Hogue, Marcel Potuzak
    Abstract:

    Borosilicate glasses display a rich complexity of chemical behavior depending on the details of their composition and thermal history. Noted for their high chemical durability and thermal shock resistance, Borosilicate glasses have found a variety of important uses from common household and laboratory glassware to high-tech applications such as liquid crystal displays. In this paper, we investigate the topological principles of Borosilicate glass chemistry covering the extremes from pure borate to pure silicate end members. Based on NMR measurements, we present a two-state statistical mechanical model of boron speciation in which addition of network modifiers leads to a competition between the formation of nonbridging oxygen and the conversion of boron from trigonal to tetrahedral configuration. Using this model, we derive a detailed topological representation of alkali–alkaline earth–Borosilicate glasses that enables the accurate prediction of properties such as glass transition temperature, liquid fragi...

Richard Kerner - One of the best experts on this subject based on the ideXlab platform.

  • structure and function of window glass and pyrex
    Journal of Chemical Physics, 2008
    Co-Authors: J C Phillips, Richard Kerner
    Abstract:

    Window glass is a ternary mixture, while Pyrex (after window glass, the most common form of commercial glass) is a quaternary. Here, we investigate the chemical, physical, and mathematical factors that determine the compositions of these optimized glasses. Previously, we succeeded in deriving exactly the composition of window glass (sodium calcium silicate) without adjustable parameters. Borosilicates are a much more challenging problem, and Pyrex (sodium aluminum Borosilicate) requires a different approach. Our analysis shows that mean-field (or global) models (networks without significant clustering) are sufficient for window glass and probably most other commercial silicate glasses. However, it appears that the most important property of pyrex, its ability to resist mechanical shocks, requires a cluster model (large medium range order). We propose such a model, and argue that it also follows from hierarchical principles. Our model is strongly supported by specific experiments, and we suggest further experiments to test the principles underlying commercial glasses.

Prabhakar Singh - One of the best experts on this subject based on the ideXlab platform.

  • a review of the structures of oxide glasses by raman spectroscopy
    RSC Advances, 2015
    Co-Authors: Avadhesh Kumar Yadav, Prabhakar Singh
    Abstract:

    The family of oxide glasses is very wide and it is continuously developing. The rapid development of advanced and innovative glasses is under progress. Oxide glasses have a variety of applications in articles for daily use as well as in advanced technological fields such as X-ray protection, fibre glasses, optical instruments and lab glassware. Oxide glasses basically consist of network formers, such as borate, silicate, phosphate, Borosilicate, borophosphate, and network modifiers such as alkali, alkaline earth and transition metals. In the present review article, Raman spectroscopy results for the structures of borate, silicate, phosphate, Borosilicate, borophosphate, aluminosilicate, phosphosilicate, alumino-Borosilicate and tellurite glasses are summarized.