Studio sulla delaminazione di ossidi PEO immersi in acido solforico mediante spettroscopia elettrochimica ad impedenza

Among all the mineral reducing acids, sulphuric acid is the most aggressive towards CP titanium. Thanks to the strong complexing ability of sulphates with Ti4+, it acts promoting uniform attacks over the entire exposed surface, generating corrosion rates of about 7.7 mm/y. Plasma electrolytic oxidation (PEO) on titanium allows the formation of a thick crystalline oxide. The layer is able to protect the substrate until the corrosion potential (E-corr) remains nobler than the hydrogen reduction reaction, which could be considered as a reasonable threshold for oxide passivity, below which proton intercalation and cation reduction to Ti3+ can occur. In the following research, impedance measurements (EIS) has been performed at different cathodic potentials, with the aim of providing a scientific interpretation of the oxide delamination in concentrated hot reducing environment. The formation of a hydrogen bubble at the metal-oxide interface is the necessary condition for oxide failure.