The effect of fluoride ions on the corrosion behavior of pure titanium in 0.05M sulfuric acid

The corrosion behavior of pure titanium was investigated in 0.05 M H2SO4 solution with fluoride ions using various electrochemical techniques, such as open circuit potential (OCP), potentiodynamic polarization, electrochemical impedance measurements (EIS) and surface analyses via X-ray photoelectron spectroscopy (XPS). The results showed that titanium exhibited spontaneous passivation behavior in solutions with 0 M and 0.0005 M fluoride ions, compared with the active-passive behavior with 0.002 M ∼ 0.005 M. A critical value of the fluoride concentration was defined between 0.0005 M and 0.002 M. Multiple corrosion potentials were found under the conditions with fluoride ions higher than 0.002 M. The fluoride ion accelerated the corrosion of titanium via changing the structure of the film formed at OCP and destroying the protectiveness of the film, while it had few effects on cathodic hydrogen evolution reaction and passivation process at OCP. A corrosion mechanism associated with the fluoride ion was proposed. The corrosion behavior was well interpreted using the proposed mechanism and a criteria for the critical value of the fluoride concentration was also proposed.