Electrochemistry of nanocrystalline copper

Nanocrystalline copper (Cu-nc), prepared by inert gas condensation, pulsed electrodeposition and by ball-milling, was characterized by XRD (mean grain diameter D; mean micro strain epsilon). Under fetal exclusion of O-2, the electrode potentials E-nc of these materials as well as E-mc of microclystalline copper could be measured in acid solutions of CuSO4. The differences Delta E-ex = E-nc-E-mc which range up to 16.8 mV for the sample with the lowest diameter, D = 8 nm, are inversely proportional to D according to a modified Gibbs-Thomson equation, when the deformation energy is taken into account. Thus, if can be concluded that Cu,,forms a metastable equilibrium with Cu ions and that the electrode potentials of Cu-nc are quasi reversible, within the time of observation. The intrinsic grain growth of Cu-nc (outside the solution) is much slower than the apparent growth in solution. Corrosion on Cu-nc could best be defected by electrochemical impedance spectrocopy: Channels and pores in the surface give rise to an unusual diffusion type. (C) 1999 Acta Metallurgica Inc.