Nanocalorimetric Characterization of the Heterogeneous Nucleation of Rapidly Solidified Bismuth Droplets Embedded in a Zinc Matrix

In this paper, Zn-10Bi (wt.%) alloy with Bi droplets in size from micro- to nanometers embedded in the Zn matrix was prepared. Nanocalorimetry was used to investigate the melting and solidification behavior of the embedded Bi droplets. In the heating process, two endothermic peaks were observed attributing to the high sensitivity of the nanocalorimeter. One is close to the eutectic temperature of Zn-Bi alloy (527 K), while the other is close to the melting point of bulk Bi (544 K). In the cooling process, the Bi droplets solidify in a wide temperature range. The results demonstrate that the Bi droplets melt at the higher temperature but their solidification demand a larger undercooling. In addition, the nucleation kinetics of rapidly solidified nano-sized Bi droplets was studied based on the hemispherical cap model of heterogeneous nucleation, and the calculated results reveal the validity of classical heterogeneous nucleation theory in nano-scale at relative high cooling rates. In a word, due to the high sensitivity and large controllable cooling rate, nanocalorimetry will be a promising technique to investigate the rapid solidification behavior of embedded nano-sized droplets.