Browsing by Author "Reinsch, Stefan"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Nucleation at cordierite glass surfaces: Kinetic aspects
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1996) Müller, Ralf; Reinsch, Stefan; Pannhorst, Wolfgang
    The surface nucleation of high-quartz sohd Solution crystals at fractured surfaces of glasses of the stoichiometric cordierite composition (2MgO · 2AI₂O₃ · 5SiO₂) was studied by optical microscopy. Particular attention was focused on the nucleation kinetics. A constant nucleation density, Ν ≈ 10⁻⁴ μm⁻², was found not to be significantly influenced by the time and the temperature of nucleation treatment. Even a very fast heating of samples employing heating rates u p to 1200 K/min does not lower Ν substantially. However, for small average crystal diameters ( < 2 0 μm) a distribution of crystal size in the same order of magnitude is detectable indicating a simultaneous appearance of b o t h measurable nucleation rates and growth velocities. It can be concluded that the surface nucleation of µ-cordierite occurs during the thermal treatment from a limited number of preferred nucleation sites; these sites are "used Up" rapidly enough to cause a strong Saturation effect of nucleation, but slow enough to cause a crystal size distribution at the same time. The surface nucleation rate, Is , was calculated from the observed distribution of crystal sizes. Is progressively increases with rising temperature similar to the crystal growth velocity indicating a broad temperature ränge of essential nucleation activity. The latter must be regarded as t he main obstacle to measure or to control surface nucleation density by means of two-step nucleation and growth treatments and must therefore be claimed to be mainly responsible for the observed constancy of N.
  • Thumbnail Image
    Item
    Viscous flow and surface crystallization caused by Vickers indentation
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2004) Chládek, Jiri; Müller, Ralf; Weh, Lothar; Reinsch, Stefan
    Healing and nucleation activity of crack patterns caused by Vickers micro-indentations on the surface of diopside glass (MgO - CaO - 2 SiO2 ) were studied by optical and surface interference microscopy. Minimizing the glass surface during thermal treatments and healing of cracks result in funnel-like depressions symmetrically arranged around the Vickers indentation. Diopside surface crystals predominantly grow from previous crack edges. Thus, double chains of crystals reveal completely healed radial cracks white long range viscous flow at the formation of funnel-like depressions spreads off former double chains to form circular crystal chains.