Cooling rate dependence of undercooling of pure Sn single drop by fast scanning calorimetry

Non-adiabatic fast scanning calorimetry has been developed to in-situ measure the response of single metallic drops to temperature changes in a large range of cooling rate spanning four orders of magnitude. In particular, the effect of cooling rate on the degree of undercooling of one 10 mu m Sn-drop is studied. The experimental results show that the undercooling could be increased first significantly with increasing cooling rate going over to a stage of slow increase for high cooling rates, which indicates a shelf-like dependence of undercooling level on cooling rate before and after a crossover at a cooling rate of about 1000 K/s where two different heterogeneous mechanisms act simultaneously. First theoretical estimates are developed on the specific feature of the heterogeneous nucleation process of the effect analyzed and possible directions of further research are anticipated.