Pitting corrosion evaluation of titanium in NaBr solutions by electrochemical methods and Raman spectroscopy

The behavior of passive titanium grade 2 (Ti-2) alloy in sodium bromide solutions of different concentrations, following induction of an electric field, was characterized by cyclic potentio-dynamic polarization and electrochemical impedance spectroscopy. The outcome of this exposure was assessed by morphologic characterization via scanning electron microscopy and by depth layer element analysis with X-ray photoelectron spectroscopy. In relatively diluted solutions, the Ti-2 had shown sensitivity to pitting corrosion and breakdown of the passivation layer, while in saturated solution no pitting was encountered, indicating an anomalous behavior for the latter. This was confirmed by measurement of the Raman spectra of the different solutions, which showed that the amount of free water molecules is negligible in saturated solutions and in fact the ultimate majority of water molecules are bounded to the dissolved ions. The implications of these factors on Ti-2 corrosion will be discussed.