Abstract
The potential‐dependent breakdown of the native oxide film (∼20 Å thick) on titanium has been investigated in aqueous 
solutions and in solutions that contain a mixture of 
and anions that inhibit oxide breakdown (i.e., 
, 
, 
, 
, and 
. The oxide film is unstable in neutral pH solutions containing only 
, resulting in the formation of stable corrosion pits at relatively low potentials (∼1.4 V vs. Ag/AgCl). The pitting potential, 
, is strongly dependent upon the concentration of 
, and can be modeled using a Langmuir isotherm to describe the adsorption of 
at the oxide film/electrolyte interface. Addition of a second anion inhibits oxide film breakdown, as indicated by a large positive shift in 
and a decrease in the number of stable corrosion pits. The dependence of 
on the relative concentrations of 
and the inhibitor anion is consistent with competitive adsorption of the anions. Equilibrium adsorption coefficients for 
, 
, and 
are estimated from the dependence of 
on anion concentration. The results are used to establish a physical basis for the anomalously low pitting potential for titanium in aqueous 
solutions. © 2000 The Electrochemical Society. All rights reserved.