Development or Stagnation of the Theory of Metal Passivity

Abstract

The main reasons that stimulated the appearance of this paper are as follows:(i) the necessity to reply to the critical comments of Yu.A. Popov and coworkers [7][8][9][10][11][12][13][14][15][16][17][18] concerning the kinetic-electrostatic model proposed in our works with Ya.M. Kolotyrkin [1][2][3][4][5] (which substantially broadens and generalizes the classical concepts developed by Bonhoffer's school [6]) and(ii) the necessity to analyze and compare the adequacy of formalizing the basic physical concepts of Fetter's model [6] and its interpretation and development in [1-5] and [7-18].Having undertaken this investigation, we can state that (i) formalization of the physical concepts was properly carried out in [1][2][3][4][5], while the criticism of [7][8][9][10][11][12][13][14][15][16][17][18] is based on erroneous assumptions originated from the inherent defects of works [7-18] and (ii) the attempts made in [7][8][9][10][11][12][13][14][15][16][17][18] in creating the "bases of the theory of passivity" were unsuccessful, because in all the model variants proposed in [7][8][9][10][11][12][13][14][15][16][17][18], the fundamental laws of nature are violated.The summary of our analysis of the correctness of formalization given in [7][8][9][10][11][12][13][14][15][16][17][18] is illustrated by the logical block-scheme in Fig. 5. It shows the main errors (inadmissible in view of the correctness of formalizing the ideas of [7-18]), which did not allow our opponents to found and improve Fetter's model [6]. On the one hand, the scheme reflects the result of the present analysis of the correctness of passivity models proposed in [7][8][9][10][11][12][13][14][15][16][17][18] and, on the other hand, it may serve as a "guide" in reading both this paper and the original works [7 − 18]. MAIN PROPERTIES OF THE PASSIVE STATE AND THEIR FORMULATION IN FILM MODELS.CRITERIA OF THE MODEL CORRECTNESS 1.1. The Main Properties of Passivity The dispute with our opponents is substantially facilitated by the fact that both models belong to the "film" models and, hence, use almost the same terminology.In these terms, the conventionally accepted basic properties of the passive state are as follows :(1) the stability within a certain potential range of the anodic dissolution of the metal;(2) the formation of the barrier, usually oxide film (with the participation of the solvent, usually water molecules), which exists under the dynamic dissolution conditions;(3) the noticeable (up to several orders of magnitude) drop of the steady-state dissolution rate of the metal upon transition to the passive state and the rate independence of the electrode potential despite the electrochemical nature of the dissolution; and (4) the linear increase in the thickness of the film with an increase in the electrode potential.It seems doubtless (though, unfortunately, it may not be true, see Section 5) that both we and our opponents can find common points if use the conventional concepts of electrochemical kinetics, namely, about the dependence of the reacti...