Browsing by Author "Borchardt, Günter"

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    Behaviour of rf sputter deposited SiO2 and AI2O3 diffusion barriers on float glass at 300 °C in air
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1993) Chaissac, Martine; Claus, Jürgen; Borchardt, Günter; Slowik, Jacek; Frischat, Günther Heinz; Scherrer, Stanislas; Weber, Sylvain
    In order to study the resistance of high-frequency sputtered thin SiO2 and AI2O3 coatings on float glass to sodium diffusion, coated glasses were submitted to heat treatments in air. The element distribution in the coatings and in the substrates was measured with neutral primary beam-secondary ion mass spectrometry.
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    Initial stages of glass corrosion in water
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1990) Richter, Thomas; Frischat, Günther Heinz; Borchardt, Günter; Scherrer, Stanislas
    Soda-lime-silica glass samples with fresh fracture surfaces were treated in H2O, D2O, H2-18O, and D2-18O for 15, 30, 60, and 120 min at 60 and 85 °C. The leached layers were analyzed by NPB-SIMS, a technique which avoids surface charging by using neutral primary particles. A distinct isotopic effect occurred neither with respect to the hydrogen isotopes nor with respect to the oxygen isotopes. From these and Corbach's results it is concluded that in the initial stage, every alkali ion exchanges with exactly one hydronium ion, but with increasing time, a growing number of unhydrated protons may participate in the exchange process. The reaction of calcium strongly depends on temperature. At 85 °C calcium ions were found to be leached from the outer region of the hydrated layer and to be enriched in a certain depth beneath the surface. On the other hand, at 60 °C calcium does not react in a measurable degree. When the glass is subjected to irreversible deformation occurring in the "plastic zone" around the crack tip, a surface layer with a modified structure is created. The influence of this deformed layer on the leaching kinetics was taken into account by a simple mathematical model.
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    Kinetic model of silicate melts - Equilibrium case
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1989) Kieffer, John; Borchardt, Günter
    Basing on the experimental evidence that in silicate melts silicon is always tetrahedrally coordinated by oxygen and that these structural units principally are able to form polyanionic structures by sharing oxygen atoms between two tetrahedra a kinetic model for the description of silicate melts is developed. As basic kinetic events in such systems the diffusive motion of individual poly anions and the interchange of structural units between different poly anions by condensation and splitting reactions are taken into account. The balance relations formulated for each polyanionic species separately lead to a system of differential equations which are coupled through the reaction terms. The calculation of polyanion distributions corresponding to a dynamical equilibrium is possible and allows principally the estimation of the degree of branching and intramolecular condensation in the melt.