231 research outputs found

    The Atomic-Scale Structure of Amorphous Hydrogenated Carbon

    Get PDF
    The structure of a common batch of amorphous hydrogenated carbon samples (a-C:H) has been studied in detail using time of flight neutron diffraction, inelastic neutron scattering, NMR and molecular dynamics (MD) simulation. Supplementary work has included differential scanning calorimetry (DSC), infrared (1R) spectroscopy and combustion analysis. A summary of the results is presented as evidence for a new structural model for a-C:H

    An atomic scale comparison of the reaction of Bioglass® in two types of simulated body fluid

    Get PDF
    A class of melt quenched silicate glasses, containing calcium, phosphorus and alkali metals, and having the ability to promote bone regeneration and to fuse to living bone, is produced commercially as Bioglass. The changes in structure associated with reacting the bioglass with a body fluid simulant (a buffered Tris(hydroxymethyl)aminomethane growth medium solution or a blood plasma-like salt simulated body fluid) at 37°C have been studied using both high energy and grazing incidence x-ray diffraction. This has corroborated the generic conclusions of earlier studies based on the use of calcia–silica sol-gel glasses whilst highlighting the important differences associated with glass composition; the results also reveal the more subtle effects on reaction rates of the choice of body fluid simulant. The results also indicate the presence of tricalcium phosphate crystallites deposited onto the surface of the glass as a precursor to the growth of hydroxyapatite, and indicates that there is some preferred orientation to their growth

    Probing vibrational modes in silica glass using inelastic neutron scattering with mass contrast

    Get PDF
    The effective vibrational density of states (VDOS) has been derived from inelastic neutron-scattering data, for isotopically substituted Si O 18 2 and Si O 16 2 glasses, to gain information about the relative contribution to the Si and O partial VDOS. This is a necessary point of comparison for vibrational mode analyses of molecular-dynamics models. The mass contrast has led to a measurable shift between vibrational mode frequencies in the effective VDOS of Si O 18 2 and Si O 16 2, which is well reproduced in an ab initio simulation. The vibrational band centered at 100.2 meV is confirmed to have significantly lower contribution from the oxygen partial VDOS, than the higher (150.3 and 135.8 meV) and lower energy bands (53.3 meV)

    An EXAFS study of rare-earth phosphate glasses in the vicinity of the metaphosphate composition

    Get PDF
    A study of rare-earth phosphate glasses, in the vicinity of the metaphosphate composition, has been undertaken at different temperatures using the extended X-ray absorption fine structure (EXAFS) facility at the Synchrotron Radiation Source, Daresbury Laboratory, UK. The metaphosphate-like glasses examined contained the rare-earth elements La, Sm. Eu and Gd as R3+ ions. The experiments were carried out at room temperature, 145 and 79 K. The data show that the first shell surrounding rare-earth ions contains only oxygen atoms at a mean distance of similar to 2.2-2.4 Angstrom. The 'Iantfianide contraction' is clearly observed, i.e., the R-O distance decreases with increasing atomic number. The observed R(-O) coordination numbers are in the range 5-7. A second correlation shell was found associated with phosphorus atoms around the central rare-earth atom (similar to 3.5 Angstrom), and another rare-earth:oxygen correlation was also identified (similar to 4 Angstrom). Static disorder dominates the Debye-Waller term, but thermal disorder is not negligible. Within the accuracy of the EXAFS data, no significant structural variations were observed over the temperature range studied. We conclude that the anomalous bulk properties are associated with either subtle structural features or primarily due to rare-earth ion Interactions

    Effect of silver content on the structure and antibacterial activity of silver-doped phosphate-based glasses

    Get PDF
    Staphylococcus aureus can cause a range of diseases, such as osteomyelitis, as well as colonize implanted medical devices. In most instances the organism forms biofilms that not only are resistant to the body's defense mechanisms but also display decreased susceptibilities to antibiotics. In the present study, we have examined the effect of increasing silver contents in phosphate-based glasses to prevent the formation of S. aureus biofilms. Silver was found to be an effective bactericidal agent against S. aureus biofilms, and the rate of silver ion release (0.42 to 1.22 µg·mm–2·h–1) from phosphate-based glass was found to account for the variation in its bactericidal effect. Analysis of biofilms by confocal microscopy indicated that they consisted of an upper layer of viable bacteria together with a layer (20 µm) of nonviable cells on the glass surface. Our results showed that regardless of the silver contents in these glasses (10, 15, or 20 mol%) the silver exists in its +1 oxidation state, which is known to be a highly effective bactericidal agent compared to that of silver in other oxidation states (+2 or +3). Analysis of the glasses by 31P nuclear magnetic resonance imaging and high-energy X-ray diffraction showed that it is the structural rearrangement of the phosphate network that is responsible for the variation in silver ion release and the associated bactericidal effectiveness. Thus, an understanding of the glass structure is important in interpreting the in vitro data and also has important clinical implications for the potential use of the phosphate-based glasses in orthopedic applications to deliver silver ions to combat S. aureus biofilm infections

    Characterisation of phosphate coacervates for potential biomedical applications

    Get PDF
    In this study, amorphous (Na2O)x(CaO)0.50−x(P2O5)0.50·yH2O (where x = ∼0.15 and y = ∼3) samples were prepared by a coacervate method. Thermal analysis showed that two types of water molecules were present in the coacervate structures: one type loosely bound and the other part of the phosphate structure. Structural studies using Fourier transform infrared spectroscopy (FTIR) and X-ray total diffraction revealed the samples to have very similar structures to melt-quenched glasses of comparable composition. Furthermore, no significant structural differences were observed between samples prepared using calcium nitrate as the calcium source or those prepared from calcium chloride. A sample containing ∼1 mol% Ag2O was prepared to test the hypothesis that calcium phosphate coacervate materials could be used as delivery agents for antibacterial ions. This sample exhibited significant antibacterial activity against the bacterium Psuedomonas aeruginosa. FTIR data revealed the silver-doped sample to be structurally akin to the analogous silver-free sample

    Electron Volt Spectroscopy On The SNS: Initial Facilities and Functional Design

    Get PDF
    A brief description is presented of the instrument which it is anticipated will be available at the beginning of SNS operations for the development and scientific use of electron volt inelastic neutron spectroscopy

    Bioactive sol-gel glasses at the atomic scale: the complementary use of advanced probe and computer modelling methods

    Get PDF
    Sol-gel synthesised bioactive glasses may be formed via a hydrolysis condensation reaction, silica being introduced in the form of tetraethyl orthosilicate (TEOS) and calcium is typically added in the form of calcium nitrate. The synthesis reaction proceeds in an aqueous environment; the resultant gel is dried, before stabilisation by heat treatment. These materials, being amorphous, are complex at the level of their atomic-scale structure, but their bulk properties may only be properly understood on the basis of that structural insight. Thus, a full understanding of their structure : property relationship may only be achieved through the application of a coherent suite of leading-edge experimental probes, coupled with the cogent use of advanced computer simulation methods. Using as an exemplar a calcia-silica sol-gel glass of the kind developed by Larry Hench, to whose memory this paper is dedicated, we illustrate the successful use of high-energy x-ray and neutron scattering (diffraction) methods, magic-angle spinning solid state NMR, and molecular dynamics simulation as components to a powerful methodology for the study of amorphous materials

    Magnetic Differences on GEM - direct observation of closest R...R approach in rare-earth phosphate glasses

    Get PDF
    Rare-earth (R) phosphate glasses have shown great promise in the laser and optoelectronics industry. Their structure plays an important role in their physical characteristics, with the R...R closest approach affecting their optical and magnetic properties. A novel characterisation method for amorphous materials which makes use of magnetic field effects has enabled the first direct experimental evidence of nearest neighbour R...R separation in these materials
    corecore