Al-Cu alloy formation by aluminium underpotential deposition from AlCl3 + NaCl melts on copper substrate

Aluminium was incorporated into copper electrode surface by underpotential deposition from equimolar AlCl3 + NaCl melt at 200 degrees C, 250 degrees C and 300 degrees C. The process was studied by linear sweep voltammetry and potentiostatic deposition/galvanostatic stripping. The deposits were characterized by electron probe (EMPA), glancing incidence X-ray diffraction (GIXRD) and Auger electron spectroscopy (AES). The electrochemical measurements showed clear evidence of formation of four intermetallic compounds. This was confirmed by the physical analysis, which showed four layers of successive bulk intermetallic compounds. However, the diffraction patterns of copper samples after two hours of aluminium underpotential deposition at 200 degrees C and 250 degrees C showed the diffraction peaks that we could not attribute to any in the literature cited Al/Cu intermetallic compound. The 2 theta values (degrees) for unattributable diffraction peaks are reported. The constant-potential regions measured during the low-current stripping corresponded to the coexistence of pairs of the four intermetallic phases. The kinetics of growth of the identified compounds is described.