The duplex copper oxide layer formation process in 0.1 M borax solution has been investigated using different potential/time programs. open circuit potential decay, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). The importance of time in the stability attained by the different oxide species was underscored. The diffusional processes involved in the duplex layer formation and oxide thickness values dependent on experimental conditions were characterized and estimated respectively through EIS data. (C) 2008 Elsevier B.V. All rights reserved.