Calorimetric measurements of undercooling in single micron sized SnAgCu particles in a wide range of cooling rates

A fast scanning chip-based calorimeter was applied for the measurement of single micron sized particles. The cooling rate dependence of undercooling was studied for Sn-3.0Ag-0.5Cu (wt.%) alloy particles. Combining DSC and fast scanning chip calorimetry, the cooling rate covers six orders of magnitude. For the single particles under investigation average undercooling ranges from about 30 K at 0.025 K/s to 120 K at 10(4) K/s. After several hundred heating-cooling cycles the single particles remain spherical and do not wet the sensor surface. The data points at one rate are highly scattered due to the stochastic nature of the nucleation event. The newly developed fast scanning calorimeter opens up a possibility to study not only cooling rate but also size dependency of undercooling of single micron and sub-micron sized particles. In future, this technique will allow a comparison between theoretical estimates and experimental data. In this paper we demonstrate the possibility of single particle measurements in a wide range of cooling rates. We focus on the experimental challenges of such experiments like calibration, heat transfer limitations, and sample placement on the sensor Furthermore we discuss problems arising from the significantly enlarged heat exchanging area, when adding a 50 mu m spherical particle to the calorimeter membrane. (C) 2008 Elsevier B.V. All rights reserved.