Thermal stability of indium nanoparticles embedded in an aluminum matrix

The thermodynamics of nanoscaled systems have drawn considerable scientific attention due to the strong influence of the particle size and shape. In the present work, nanoparticles of indium embedded in an aluminum matrix were processed by rapid quenching using the melt-spinning technique. The as-processed samples were analyzed using conventional and analytical transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). TEM data revealed isolated and mainly spherical nanoparticles of indium with a size in the range of 20 to 300 nm. Indium particles in aluminum grains are equiaxed, whereas particles at aluminum grain boundaries show elongation. Analytical TEM showed neither a notable concentration of indium in the aluminum matrix nor a concentration gradient at the interfaces of the particles. By DSC experiments using a wide range of different constant heating and cooling rates, broad melting and crystallization peaks were observed. A slight reduction of the melting temperature of the embedded particles in comparison to the bulk indium is detected, whereas the crystallization temperature shifts to remarkable low temperatures. Upon thermal cycling, the melting as well as the crystallization temperatures of the nanoparticles reduces and the peak shape changes clearly.