Berlin 2008 – wissenschaftliches Programm
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MM: Fachverband Metall- und Materialphysik
MM 10: SYM Phase Transformations in Metallic Melts IV
MM 10.6: Vortrag
Montag, 25. Februar 2008, 17:45–18:00, H 1058
Structural changes of undercooled melts in charged colloidal model systems — •Patrick Wette1, Ina Klassen1, Dieter M. Herlach1, Dirk Holland- Moritz1, Thomas Palberg2, and Stefan Volkher Roth3 — 1Institut für Materialphysik im Weltraum, Deutsches Zentrum für Luft- und Raumfahrt, 51170 Köln, Germany — 2Institut für Physik, Universität Mainz, Staudinger Weg 7, 55128 Mainz, Germany — 3DESY, HASYLAB, 22603 Hamburg, Germany
Colloidal model systems are often used to describe equilibrium properties of fluid and solid materials. Here we used them to study the short range order and the nucleation process in undercooled melts. We employed charged colloidal silica spheres in aqueous dispersion, which enables the precise adjustment of surface charge density and particle interaction via the controlled addition of sodium hydroxide leading to a rich phase behaviour. This colloidal system is characterized by convenient time scales between seconds and minutes and particle distances up to 500nm and is thus accessible by simple, yet powerful optical techniques. By contrast to metals heterogeneous nucleation can either be efficiently suppressed or, if present, clearly discriminated and separated from data evaluation. Microscopy and light scattering yield complementary information on equilibrium properties and crystallization kinetics from real and reciprocal space. Comprehensive measurements of structural changes of the melt with increased undercooling and the corresponding changes of the solidification were carried out by means of the USAXS- technique at HASYLAB (Hamburg).