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.

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