Physicochemical modeling of interactions in the passive oxide film of an alloy. Thermodynamic model of a regular solution of oxide “molecules”

Alekseev, Yu. V.

doi:10.1007/bf02766734

Cited by 3 publications

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“…For this purpose, a concept of the elementary dissolution act as a transfer of an oxide "molecule" of the alloy component to the alloy can be used. This idea enabled us to construct a model of the passive alloy dissolution [23,24], in which the passivating film is considered as a regular solid solution of the interacting oxide "molecules" of the alloy components. In particular, the model satisfactorily describes the dependence of the summary and partial dissolution rates of a Fe-Cr alloy on the concentrations of its components [25].…”

Section: To the Value And Prospects Of The Kinetic-electrostatic Modelmentioning

confidence: 99%

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Development or Stagnation of the Theory of Metal Passivity

Alekseev

2005

Prot Met

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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...

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Section: To the Value And Prospects Of The Kinetic-electrostatic Modelmentioning

confidence: 99%

“…(22a), and the dissolution current, Eq. (22b), which is equal to it and given in the upper part of scheme (23).…”

Section: The Possible Scheme Of Processes At the Film-solution Interfmentioning

confidence: 99%

Development or Stagnation of the Theory of Metal Passivity

Alekseev

2005

Prot Met

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“…These interactions may most substantially affect the qualitative regularities of the dissolution in passive state [1][2][3].…”

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“…In other words, it is as if M particles ( z i is the charge of the i th alloy component ion) are actually transferred. Bearing in mind this idea, we proposed [1] a thermodynamic model of the interaction between the oxide "molecules," based on the theory of regular solutions, that is, assuming that the interaction between the solution components does not affect its structure ordering, so that the location of component molecules is chaotic as in an ideal solution where interactions between molecules of different kinds are the same or simply absent.…”

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“…These interactions may most substantially affect the qualitative regularities of the dissolution in passive state [1][2][3].The quantitative theoretical description of the dissolution kinetics is based on treating the passivating oxide as a solid solution of "component molecules", an interaction between which should necessarily be taken into account at least in the close-neighbors approximation. Considering thermodynamic "entities" as oxide "molecules" of the alloy components rather than metal cations in the oxide was based in [2] on the concept of the passive metal dissolution [4][5][6][7][8][9] as the transfer of metal cations to the electrolyte together with the stoichiometrically balanced amount of the oxide oxygen atoms.…”

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Thermodynamic Theory of “Irregular” Solutions and Kinetic Model of the Passive Alloy Dissolution

Alekseev

2005

Prot Met

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Developing a productive multivariate theory of corrosion, as well as anticorrosion alloying, is impossible unless the interactions between the alloy components are taken into account. These interactions may most substantially affect the qualitative regularities of the dissolution in passive state [1][2][3].The quantitative theoretical description of the dissolution kinetics is based on treating the passivating oxide as a solid solution of "component molecules", an interaction between which should necessarily be taken into account at least in the close-neighbors approximation. Considering thermodynamic "entities" as oxide "molecules" of the alloy components rather than metal cations in the oxide was based in [2] on the concept of the passive metal dissolution [4][5][6][7][8][9] as the transfer of metal cations to the electrolyte together with the stoichiometrically balanced amount of the oxide oxygen atoms. In other words, it is as if M particles ( z i is the charge of the i th alloy component ion) are actually transferred. Bearing in mind this idea, we proposed [1] a thermodynamic model of the interaction between the oxide "molecules," based on the theory of regular solutions, that is, assuming that the interaction between the solution components does not affect its structure ordering, so that the location of component molecules is chaotic as in an ideal solution where interactions between molecules of different kinds are the same or simply absent.Let us note that in a conventional classification of solutions, people use an ambiguous terminology. It may seem strange that a solution with a chaotic arrangement of molecules is named "regular," while a O Z i /2 partially structured (not chaotic) one is named irregular. However, the term "regular" primarily means customary, which reflects the historically conventional idea that a solution is similar to a gas mixture, in which a "uniformly" chaotic arrangement of molecules is typical, while an "irregular" solution is unusually ordered. ADVANTAGES AND DRAWBACKS OF THE MODEL [2, 3] OF PASSIVE OXIDE FILM AS A REGULAR SOLUTION OF THE ALLOY COMPONENT OXIDE "MOLECULES"In [2], we used a thermodynamic model [1] as a basis in constructing a model of the passive alloy dissolution.For that purpose, we utilized the ideas of the transition state theory [10], which enables one to relate the chemical potential of each solution component to its value in the individual state (that is, oxide "molecules" in the own phase). (For brevity, solution means solid solution, because electrolytes lie beyond the scope of this study.) This made it possible to take into account the change in the dissolution rate of each component due to mixing, i.e., as a result of the appearance of "molecules" of other kinds close to the "molecule" of a particular kind.Model [2] enabled us to estimate partial i i and summary i dissolution rates of the alloy as functions of its composition knowing the dissolution rates of the individual passive metals constituting the alloy. For partial dissolution rates of a binary...

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Statistical approach to simultaneous self-consistent consideration of atomic profile topography and interaction of alloy components at its dissolution

Alekseev

2012

Russ J Electrochem

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Physicochemical modeling of interactions in the passive oxide film of an alloy. Thermodynamic model of a regular solution of oxide “molecules”

Cited by 3 publications

References 0 publications

Development or Stagnation of the Theory of Metal Passivity

Development or Stagnation of the Theory of Metal Passivity

Thermodynamic Theory of “Irregular” Solutions and Kinetic Model of the Passive Alloy Dissolution

Statistical approach to simultaneous self-consistent consideration of atomic profile topography and interaction of alloy components at its dissolution

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