Pitting Corrosion Behaviour of Aluminium in Water Desalination Plants

The pitting corrosion of aluminium in water containing pitting corrosion agents and metal cations at moderately high temperatures has been investigated by electrochemical and surface analysis methods. Heat pretreatment ameliorated the resistance to pitting corrosion and overcame the aggressive effect of Cl −. This is attributed to the thickening of the protective film and change of its composition into more stable oxides as shown by Auger depth profiling and X-ray diffraction, respectively. Such modifications would shield the points susceptible to pitting initiation and/or suppress the kinetics of the partial cathodic reaction. The severe pitting corrosion suffered by aluminium in presence of Cu 2+ decreased by heat treatment. The induced film modification hinders the deposition of metallic copper by displacement on aluminium surface and, therefore, inhibits the galvanic coupling. In Cd 2+ solutions, where the mixed oxide CdO·6Al 2O 3 was detected on aluminium surface, film modification was not obtained.