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MM: Fachverband Metall- und Materialphysik

MM 35: Topical Session Heterogeneous Nucleation I

MM 35.7: Vortrag

Donnerstag, 17. März 2011, 12:45–13:00, IFW D

Experimental determination of nucleation rates — •Joachim Bokeloh and Gerhard Wilde — Institut für Materialphysik, WWU Münster

Upon cooling a metallic melt, the nucleation rate changes from practically zero to virtually infinite in the small range of accessible crystallization temperatures, thus leaving only a narrow temperature window for experimental as well as for computational investigations. Both, the system size and the time scale of computational studies differ from those within reach of experimental studies by several orders of magnitude. Thus, for a meaningful comparison of computational and experimental works, the nucleation rates have to be extrapolated over several orders of magnitude. For this procedure, an accurate coverage of the nucleation rate over the complete accessible range is imperative. We present here data on the liquid undercooling behavior of Nickel obtained by repeated melting and crystallization in a DTA. This method allows acquiring a statistically meaningful data set under clean and reproducible conditions, from which nucleation rates can be determined. Supported by a variation of the sample mass from 10µg to 60 mg and classical isothermal nucleation rate measurements, the nucleation rate of pure Nickel was determined experimentally over a range of eight orders of magnitude and a temperature window of 70 K, thus allowing a true quantitative testing of the classical nucleation theory. Nickel was chosen as a model system because it shows high levels of undercooling and a well refined embedded atom potential is available for concurrent simulations.