Effect of Platinum, Copper and Iron Ions On Corrosion and Passivity of Titanium In 15 Percent Hydrochloric Acid

An investigation has been made of the effect on corrosion rate of titanium in 15 percent hydrochloric acid of introducing cations of more noble metals, particularly Pt⁴⁺, Cu²⁺ and Fe³⁺. It was found that such ions cause a shift in metal potential in the positive direction, enhancing the cathodic process and resulting in anodic passivity of the titanium.

In addition to acting initially as cathodic depolarizers, the noble metals deposit galvanically, forming more effective cathodic areas and further accelerating cathodic depolarization. However, in concentrations lower than those required to attain passivity, the noble metal ions increase rather than decrease the corrosion rate of titanium in 15 percent hydrochloric acid.

In the presence of the fluoride ion, Pt⁴⁺ ions accelerate the corrosion rate of titanium in HCI with increases in their concentration, the opposite of the effect when concentrating Pt⁴⁺ ions before fluoride is introduced.