Structural and mechanistic inferences in the mechanochemical synthesis of nanostructured Ni-Sn and Co-Sn alloys

We focus on the synthetic path of nanostructured Ni-Sn and Co-Sn systems by mechanical alloying. A similar reaction path seems to characterize the process for both the systems: the formation of intermediate, metastable, Sn rich phases has been evidenced, not provided for by the corresponding equilibrium phase diagrams. Their crystallographic and thermodynamic properties were evaluated through a structural and calorimetric investigation. Further mechanical processing induced structural evolutions by the progressive alloys enrichment in Ni and Co respectively, according to the stoichiometric constraints. Quantitative assessment of relative abundance of crystallographic phases let us investigate the alloying kinetics. By resorting to a previously developed procedure we evaluated collision frequency and impact energy. Then the analytical solution of the kinetic curves allowed us to relate the conversion degree to the effective collisions undergone by each powder particle.