Berlin 2012 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 17: Poster Session

MM 17.4: Poster

Montag, 26. März 2012, 17:00–19:00, Poster B

Measurement of nucleation rates using fast scanning calorimetry on samples prepared by the Droplet Emulsion Technique (DET) — •Christian Simon, Joachim Bokeloh, and Gerhard Wilde — Westfälische Wilhelms-Universität Münster, Institut für Materialphysik, Wilhelm-Klemm-Str. 10, 48149 Münster

The most difficult part in heterogenous nucleation experiments is the control of the heterogenous nucleant. On one hand, parasitic nucleants like the container wall and impurities must be removed, and on the other hand the target nucleant phase must be kept at a constant potency. The DET is uniquely suited to accomplish this task. With the DET microsized droplets of a material are prepared by heating it above the melting temperature in a special organic solution and then dispersing it to a fine emulsion of droplets by violent stirring. While the fine dispersion reduces the influence of impurities, the organic solution forms a non-catalytic surface layer and thus reduces the nucleation potency of the surface.

The nucleation rate is evaluated by a statistical analyses that treats nucleation as a non-homogenous Poisson process. A DSC measurement is used to analyse the undercooling of an ensemble of droplets. A fast scanning nano-calorimeter (10 K/s - 100000 K/s) is used to analyse the undercooling and nucleation rate over a large number of repeated heating-cooling-cycles on single droplets, allowing for an heretofore unprecedented accuracy in the nucleation rate measurement.