Investigation of calcareous deposits formation on 5052 aluminium alloy under cathodic polarisation in natural and artificial sea water

Abstract

The required current densities for cathodic protection of aluminium alloys are generally small, e.g. roughly 10 times less than the current densities required for carbon steels in sea water. Nowadays, cathodic polarisation is applied not only to prevent corrosion, but it is specifically directed toward coating growth as well. In the present work, calcareous deposits were formed on 5052 aluminium alloy at various cathodic potentials from −1·1 to −1·3 V/SCE (where SCE stands for saturated calomel electrode) and under static and rotational conditions in natural and artificial sea water. Chronoamperometry technique was used to investigate the scaling process, whereas scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction were employed to evaluate the calcareous deposits morphology. At potentials less than −1·2 V/SCE in both environments, no considerable calcareous deposits were observed under static and rotational conditions. At potentials more negative than −1·2 V/SCE aragonite was the predominant compound in artificial sea water, while brucite was the main compound in natural sea water. It seems that the applied cathodic polarisation and the rotation speed are two possible major factors for calcareous deposits formation during cathodic protection of aluminium alloys and they complement each other.