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MM: Fachverband Metall- und Materialphysik

MM 60: Phase Transitions II

MM 60.2: Vortrag

Donnerstag, 25. März 2010, 15:45–16:00, H5

Crystallization in a model system of charged colloidal particles: How do larger particles influence the crystallization process and therefore the resulting microstructure? — •Andreas Engelbrecht and Hans Joachim Schöpe — Johannes Gutenberg-University, 55099 Mainz, Germany

Characteristics of a material often depend on the microstructure of the material (i.e. the grain size in metals,) therefore the control of the crystallization process allows access to new materials of desired properties. Colloidal suspensions of spherical particles are widely used as model system for molecular and atomic systems - especially for metals. Progress understanding the solidification process has been made in recent years studying colloidal suspensions.

The formation of crystals from the melt can be controlled either by the required activation energy or by the rate of particles attaching to the crystal liquid interface. Adding just small amounts (less than 1%) of a larger and higher charged spherical particles to colloidal suspension of charged spheres we observe a drastic variation of the crystallization process and for this reason the resulting microstructure of the solidified material is changing its appearance. Expressed in terms of the classical nucleation theory the observed enormous effect on crystal nucleation is not exclusively induced by a significant change of the nucleation barrier height, but by a modification of the kinetic prefactor. A variation in the transport mechanism of particles form the melt towards the crystals modifies the kinetic prefactor of the classical nucleation theory as well as the crystal growth.