Electrochemical behaviour of a copper-aluminium alloy in concentrated alkaline solutions

The electrochemical behaviour of a low-aluminium copper alloy (Alfa aluminium-bronze) in concentrated (1-8 N) NaOH is characteristically passive over broad potential regions, exhibiting passive currents that increase with alkali concentration. This passive behaviour is attributed to a duplex film, with an inner compact part composed of Cu2O and Al2O3 . xH(2)O and an outer porous part composed of Cu(OH)(2) and Al2O3 . xH(2)O. The film undergoes dissolution at the film-electrolyte interface while it is continuously forming at the alloy-film interface. The film thickness is shown to increase with potential such that the potential gradient in the film is constant. The alloy undergoes selective dissolution with the de-aluminification factor depending on the potential and alkali concentration. X-ray diffraction analysis of the polarized alloy surface revealed the presence of Cu(OH)(2) and the selective dissolution of the grains oriented in the 111 direction with enrichment in the grains oriented in the 220 direction. Copyright (C) 1996 Elsevier Science Ltd