An extended solid solution of Cu-20wt%Sn with lattice parameter 0.3715 nm, was obtained by mechanical alloying elemental powders in a planetary ball mill under an argon atmosphere. Depending on the milling conditions, solid solutions with crystalline grain sizes ranging from 30 nm to 7 nm were obtained. A DSC trace of mechanically alloyed Cu-20wt%Sn showed an exothermic effect at 643K. X-ray diffraction of the sample after annealing at 643K revealed the crystalline grain growth and the formation of an equilibrium solid solution with a lattice parameter of 0.3654 nm. The modified Kissinger analysis gave an apparent activation energy of 80 kJ/mole, indicated that diffusion is facilitated in nanocrystalline Cu-20wt%Sn alloys. The reaction of Cu-20w%tSn with a Ga-In-Sn alloy was studied at room temperature by measuring peak intensities of CuGa_2 the intermetallic compound formed during the reaction, as a function of time. We observed a strong correlation between the reaction rate and crystalline grain size D of mechanically alloyed powders: the reaction rate increased significantly when D decreased to 7 nm. Nanocrystalline powders are highly reactive and the mechanical alloying process can be used to control the reactivity of nanocrystalline solid solutions, used as components in low temperature solder pastes.
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