THE CORROSION OF NICKEL-ALUMINUM BRONZES IN SEAWATER .2. THE CORROSION MECHANISM IN THE PRESENCE OF SULFIDE POLLUTION

Electrochemical corrosion rates of a nickel-aluminium bronze were meas ured in synthetic seawater with and without sulphide pollution. The in crease of the corrosion rate of the passive alloy due to the deteriora tion of the protective layer and the change in reaction kinetics due t o sulphide contamination were studied using a rotating disc electrode. The structure of corrosion layers was investigated by X-ray diffracti on, Auger electron spectroscopy and X-ray photo-electron spectroscopy. Loss of passivity in sulphide-containing seawater is caused by the fo rmation of copper sulphide in the corrosion layer which markedly accel erates the charge transfer kinetic of the oxygen reduction. As a conse quence, the overall corrosion process is entirely cathodically control led. The high corrosion rates resulting from sulphide exposure were st rongly dependent on the velocity of flow. The increase of the corrosio n current show a direct correlation to the copper sulphide content of the corrosion layers.