ELECTROCHEMICAL-BEHAVIOR OF A COPPER-ALUMINUM ALLOY IN CONCENTRATED ALKALINE-SOLUTIONS

The electrochemical behaviour of a low-aluminium copper alloy (Alfa al uminium-bronze) in concentrated (1-8 N) NaOH is characteristically pas sive over broad potential regions, exhibiting passive currents that in crease with alkali concentration. This passive behaviour is attributed to a duplex film, with an inner compact part composed of Cu2O and Al2 O3 . 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 interf ace while it is continuously forming at the alloy-film interface. The film thickness is shown to increase with potential such that the poten tial gradient in the film is constant. The alloy undergoes selective d issolution with the de-aluminification factor depending on the potenti al and alkali concentration. X-ray diffraction analysis of the polariz ed alloy surface revealed the presence of Cu(OH)(2) and the selective dissolution of the grains oriented in the 111 direction with enrichmen t in the grains oriented in the 220 direction. Copyright (C) 1996 Else vier Science Ltd