Browsing by Author "Gattef E."

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    An X-ray and neutron scattering study of the structure of zinc vanadate glasses
    (2001-01-01) Hoppe U.; Kranold R.; Gattef E.; Neuefeind J.; Keen D.A.
    The short-range order of vitreous V2O5 and of three (ZnO)x(V2O5)1-x glasses with x = 0.2, 0.4, and 0.5 is studied by X-ray and neutron diffraction experiments where the change of the contrast allows to resolve the V-O and Zn-O correlations. The V-O and the Zn-O first-neighbor peaks are approximated by several Gaussian functions. In case of vitreous V2O5 two obvious V-O distances exist which are related with VO4 and VO5 units. With ZnO additions the V-O coordination number decreases from 4.4 in vitreous V2O5 to 4.0 in the metavanadate glass where the strongest decrease of the fraction of VO5 units is found for glasses of x < 0.2. Dominantly, the VO5 groups are linked with the neighboring units by corners. The Zn-O coordination numbers of the modified glasses are about five with closest distances of ≅ 0.200 nm.
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    Structure, crystallization and electrochemical corrosion behaviour of amorphous Cu66Ti34 alloy
    (1998-01-01) Zaprianova V.; Raicheff R.; Gattef E.
    The effect of thermally induced structural changes to electrochemical corrosion behaviour of amorphous Cu66Ti34 alloy is studied using electrochemical potentiodynamic polarization technique in conjunction with XRD, TEM and DTA. The heat treatment has been carried out at two temperatures: 300 °C - where the procedd of structural relaxation is only possible and 500 °C - where metallization of the alloy occurs. An model corrosive media IN H2SO4 and 1N HNO3 solutions are used. The short range order of the amorphous samples is studied with the total pair correlation function. Some changes of the interatomic distances and a tendency to increasing of the density of the amorphous structure after low temperature heating are established. The crystallization leads to formation of Cu3Ti2, β-Cu3Ti and Cu2Ti crystalline phases. It has been found that structural relaxation may have a beneficial effect on the susceptibility of the amorphous alloy to passivation, while crystallization lowers considerably its corrosion resistance.