Coalescence in nano-sized metallic systems

During heating, nanoparticles undergo to specific phenomena such as coalescence, which affect their phase stability. This aspect is of great importance for the potential application of nanosized metallic system. The driving force for the coalescence of two nanoparticles is the surface energy reduction due to lower surface area of the new nanoparticle. In fact, the process begins with the contact of nanoparticles and is followed by the alignment of the coalescing planes at the interface and by the subsequent growth of the neck. The study on coalescence includes three topics, i.e. surface diffusion, physical and thermodynamic properties and coalescence mechanisms. The nanoparticles growth at high temperature by coalescence have been analyzed by means of the theoretical predictions; an important parameter for predicting the final particle size is the rate of coalescence. The studies of the coalescence processes involve nanoparticles diffusion, nanoparticles properties relevant to the diffusion, such as melting points, volumes and diffusion coefficients as well as overall coalescence mechanisms. A few examples of coalescence in a "small systems" using the literature data are presented (i.e. Co, Au); in addition, a modeling of the coalescence of pure Sn and Bi nano-sized particles will be done to compare the theoretical results with own experimental data.