expanded to other applications, such as power plants, the foodindustry,petrochemicalplants,refineries,heatexchangers,marinestructuresandmedicalprostheses(4,5). Commercially available titanium is classified depending on its purity and elemental composition. The main classification for titanium is provided by the American Society forTestingandMaterials(ASTM).Thefirst4ASTMgradesof titanium are referred to as "commercially pure" and are not alloyed but only present differences in terms of contents of impurities, especially oxygen (6): grade 1 contains a maxi-mumof0.18% oxygen whilegrade4hasamaximumof0.40%.

The corrosion behavior of commercially pure titanium (UNS R50400) was investigated in presence of aggressive, bromides containing, species; reported to cause severer localized corrosion compared to chlorides. To enhance localized corrosion resistance of the metal, several surface treatments were performed. Samples anodized at potentials between 10 V and 200 V were characterized in term of oxide thickness and morphology and tested with potentiodynamic analyses in NH 4 Br. This treatment was found to greatly enhance corrosion resistance of titanium but it suffers localized removal of the oxide due to wrong handling of the part before their installation. For this reason, another treatment, suitable for in-situ surface recovering was developed through chemical oxidation in NaOH 10 M.

Titanium is well known as one of the most corrosion-resistant metals. However, it can suffer corrosion attacks in some specific aggressive conditions. To further increase its corrosion resistance, it is possible either to modify its surface, tuning either thickness, composition, morphology or structure of the oxide that spontaneously forms on the metal, or to modify its bulk composition. Part 2 of this review is dedicated to the corrosion of titanium and focuses on possible titanium treatments that can increase corrosion resistance. Both surface treatments, such as anodization or thermal or chemical oxidation, and bulk treatments, such as alloying, are considered, highlighting the advantages of each technique.

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Background: Titanium has outstanding corrosion resistance due to the thin protective oxide layer that is formed on its surface. Nevertheless, in harsh and severe environments, pure titanium may suffer localized corrosion. In those conditions, costly titanium alloys containing palladium, nickel and molybdenum are used. This purpose investigated how it is possible to control corrosion, at lower cost, by electrochemical surface treatment on pure titanium, increasing the thickness of the natural oxide layer. Methods: Anodic oxidation was performed on titanium by immersion in H 2 SO 4 solution and applying voltages ranging from 10 to 80 V. Different anodic current densities were considered. Potentiodynamic tests in chlorideand fluoride-containing solutions were carried out on anodized titanium to determine the pitting potential. Results: All tested anodizing treatments increased corrosion resistance of pure titanium, but never reached the performance of titanium alloys. The best corrosion behavior was obtained on titanium anodized at voltages lower than 40 V at 20 mA/cm 2. Conclusions: Titanium samples anodized at low cell voltage were seen to give high corrosion resistance in chloride-and fluoride-containing solutions. Electrolyte bath and anodic current density have little effect on the corrosion behavior.