Study of the corrosion behaviour of Cu-10Sn bronze in aerated Na2SO4 aqueous solution

Investigation of the electrochemical behaviour of Cu-10Sn (wt.%) alloy has been conducted in aerated aqueous sulphate solution and compared to that of pure Cu and Sn. Eoc versus time and cathodic and anodic polarizations have been performed as a function of the initial sulphate concentration, the rotation speed of the electrode and the immersion time. The surface layer have been characterized by scanning electron microscopy (SEM) and analyzed by energy dispersive spectrometry (EDS) and Fourier transform infrared spectroscopy (FTIR). The anodic behaviour evidences a Cu dissolution phenomenon on the corrosion layer limited by migration process rather than diffusion. The corrosion process conducts to preserve the original surface of the electrode and conducts to an internal growth at the layer/alloy interface, from the initial surface towards the unaltered substrate. The interphase behaviour is governed by the layer formed at Eoe under the experimental conditions and its evolution during the time. Hydroxyl-oxy and sulphate Cu and Sn compounds recover the surface and confer to the interface a blocking behaviour mainly due to the presence of the tin compounds in the layer. The global interphase behaviour matches the Type-I model of blocking adherent layer with decuprification phenomenon evidenced on archaeological bronzes. (c) 2005 Elsevier Ltd. All rights reserved.