(i) Proposed concepts based on either competitive adsorption or surface complex ion formation.
(i) In competitive adsorption mechanism Cl− anions and passivating agents are simultaneously adsorbed. Above a critical potential Cl− adsorption is favored resulting in the breakdown of passivity. (ii) Kolotyrkin suggested that there were critical Cl−/inhibitor concentration ratios, depending on the potential above which pitting would occur.
Occurrence of induction times varying with passive film thickness cannot be explained.
(i) Proposed a theoretical concept based on the potential dependent transpassive dissolution which depends on the electronic properties of the passive film. (ii) The electrochemical stability of a passive film depends strongly on the “electron energy band structure” in the film.
(i) Stated that the critical potential above which potential-dependent dissolution of the film occurs will be less noble at the sites of chloride ion adsorption. (ii) As a result of the increased dissolution rate above the critical potential, local thinning of the passive films occurs until a steady state is reached. (iii) Proposed that the local thinning of the oxide film as a mechanism of pit “initiation”. (iv) Included the effect of dislocations similar to the influences of Cl− ions.
Knowledge of the electronic properties of passive films has not been fully understood. Experimental evidence for this mechanism is lacking.