DSC measurements of the thermal properties of gallium particles in the micron and sub-micron sizes, obtained by sonication of molten gallium Vijay Bhooshan Kumar • Ze’ev Porat • Aharon Gedanken Received: 1 September 2014 / Accepted: 4 January 2015 Ó Akade ´miai Kiado ´, Budapest, Hungary 2015 Abstract The thermal behavior of gallium microparti- cles, in comparison with bulk gallium, was examined by differential scanning calorimetry. All the samples showed a single endothermic signal for melting near the known melting point of gallium. Cooling the molten samples showed super-cooling effect, which was more pronounced for the gallium microparticles than for the bulk metal. Keywords Gallium Á Gallium particles Á DSC Á Melting Á Crystallization Á Super-cooling Introduction Gallium metal exhibits unique thermal and structural properties. Among these are the very low melting point (29.8 °C) and high boiling point (2,237 °C) under atmo- spheric pressure, which leave a wide temperature range of the liquid state. This range is even wider when considering the super-cooling effect of liquid gallium [1, 2]. Briggs reported that slow cooling of gallium droplets yielded freezing at -28 °C, which is 58° below the melting point of gallium [3]. In the solid state, the stable phase is Ga I, having a base-centered orthorhombic structure [4]. At elevated pressure, solid gallium transforms to different crystalline phases [4] while liquid gallium can crystallize at room temperature [5]. Reverse Monte Carlo analysis was applied to the super-cooled liquid, confirming that its structure is similar to that of the beta phase [6]. It was reported that the liquid phase of gallium is known to be anomalous [7]. It is known that metals in the form of nanoparticles exhibit lower melting temperatures than those of bulk metals [8]. The melting temperature decrea- ses sharply below a critical diameter of about 50 nm and is especially pronounced for particle sizes below 5 nm [9, 10]. Melting point depression has been reported for several elements, such as Co [10], Se [11], Fe [12], Ag [13], Bi [14], Sn [15], Ga [16–21] and more. This effect was used to determine the pore-size distribution in water- saturated porous materials such as fibers of polyacryloni- trile [22] and silica gels [23, 24] by measuring the lowering of the freezing and melting temperatures of water and ice within the pores. Liu et al. [16] studied the freezing and melting behavior of gallium encapsulated in carbon nano- tubes. In situ observation by transmission electron micro- scope showed that the Ga remained liquid down to -80 °C. Recently, we reported on the formation of gallium micro- and nano-spheres by ultrasonic cavitation of molten gallium in warm water [25, 26]. These particles were characterized by a variety of physical and microscopic methods and were found to be spherical, in the size range Electronic supplementary material The online version of this article (doi:10.1007/s10973-015-4402-x) contains supplementary material, which is available to authorized users. V. B. Kumar Á A. Gedanken (&) Department of Chemistry, Bar Ilan Institute for Nanotechnology and Advanced Materials, Bar Ilan University, 52900 Ramat Gan, Israel e-mail: gedanken@mail.biu.ac.il Z. Porat (&) Division of Chemistry, Nuclear Research Center-Negev, 84190 Beersheba, Israel e-mail: poratze@post.bgu.ac.il Z. Porat Institute of Applied Research, Ben-Gurion University of the Negev, 84105 Beersheba, Israel A. Gedanken Department of Materials Science and Engineering, National Cheng Kung University, Tainan 70101, Taiwan 123 J Therm Anal Calorim DOI 10.1007/s10973-015-4402-x