Passivation of Titanium by Molybdate Ion Available to Purchase

The passivating effect of molybdate ion on the corrosion of titanium in deaerated, boiling 1N H₂SO₄ has been explored. In this medium, in the absence of molybdate ion, titanium rapidly corrodes. An immediate passivation process for Ti is observed when Mo⁺⁶ at a concentration as low as 3 mM is added to an H₂SO₄ solution in which Ti is actively corroding. The open circuit potential attained for Ti in molybdate solution is shown to be controlled by redox processes. Through a combination of surface analytical and electrochemical data, it is shown that upon immersion of Ti in acidic molybdate solution, the native TiO₂ oxide is replaced by a salt film containing Mo. This film is adherent when a passivated electrode is transferred to a molybdate-free solution, and it provides a corrosion resistant barrier.