Influence of Substrate Dislocation on Passivation of Pure Iron in pH 8.4 Borate Buffer Solution

Abstract

The influence of substrate dislocations on the passivation behavior of pure iron in a pH 8.4 borate buffer solution was investigated. Cold-rolling was employed to induce dislocation in the annealed substrate. The dislocation density on the cold-rolled substrate depended on the reduction ratio (Red) and was maximum at . The electric charge consumed in the passivation and the passivity-maintaining current increased with an increase in the dislocation density. Electrochemical impedance spectroscopy revealed that the dislocation exposed to the iron surface increased the donor density in the passive film and reduced the charge-transfer resistance for the film aging. It was also demonstrated by radio frequency–glow discharge optical emission spectroscopy that a thick passive film formed on the cold-rolled iron compared with that on annealed iron. These results suggest that substrate dislocations enhance the reactions at the substrate/film interface, resulting in the formation of a highly defective passive film.