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 measured in synthetic seawater with and without sulphide pollution. The increase of the corrosion rate of the passive alloy due to the deterioration of the protective layer and the change in reaction kinetics due to sulphide contamination were studied using a rotating disc electrode. The structure of corrosion layers was investigated by X-ray diffraction, Auger electron spectroscopy and X-ray photo-electron spectroscopy. Loss of passivity in sulphide-containing seawater is caused by the formation of copper sulphide in the corrosion layer which markedly accelerates the charge transfer kinetic of the oxygen reduction. As a consequence, the overall corrosion process is entirely cathodically controlled. The high corrosion rates resulting from sulphide exposure were strongly dependent on the velocity of flow. The increase of the corrosion current show a direct correlation to the copper sulphide content of the corrosion layers.