Untitled

Self Cite

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...

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

confidence: 83%

Development or Stagnation of the Theory of Metal Passivity

Alekseev

2005

Self Cite

“…The results of the theoretical model of the passive alloy dissolution [2] were compared to the experimental data on the dissolution of Fe-Cr alloys at diverse Cr concentrations ( x 10 ) in the alloy [3,11].…”

Section: Advantages and Drawbacks Of The Model [2 3] Of Passive Oxidmentioning

confidence: 99%

“…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.…”

mentioning

confidence: 99%

See 1 more Smart Citation

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

Alekseev

2005

Self Cite

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...

“…As showed the investigations carried out in Karpov Institute of Physical Chemistry [1][2][3][4][5][6][7][8][9][10], when analyzing the nature and mechanism of the dissolution of metals and their solid solutions, one should take into account the submicrostructure factor relating the reactivity of the crystal surface to its atomic discreteness. The regularities discovered enabled researchers to formulate the following conceptual ideas taking into account both the role of this factor in the active dissolution of a metal and the dependence of its reactivity on the presence of alloying elements.…”

Section: Introductionmentioning

confidence: 99%

To the co-effect of impurity atoms and structure on the dissolution of iron and its low alloys

Plaskeev

2005

Self Cite

With the use of tracers, the separate effect of small nickel additions, as well as phosphorus and manganese impurities (including their combinations with sulfur) on the corrosion electrochemical behavior of active iron is studied. Nickel (2.2%) and phosphorus (only 0.07%), which are substantially more corrosion resistant than iron, are found to noticeably suppress the active dissolution of iron from its alloys, whereas the unstable manganese (0.43%) and its sulfides (in an alloy containing 0.43% Mn and 0.06% S) accelerate the dissolution. An effect similar to that of manganese is produced by a simple increase in the defectiveness of the iron crystalline structure. The largest deceleration is observed at a small surface coverage of the dissolving alloy with nickel or phosphorus, whereas the activating effect of manganese and its sulfides is accompanied by their selective transfer to the solution. With an increase in the potential, both effects decrease in magnitude. Generalizing these and other data on the effects of impurities and structural defects on the active dissolution of iron made us reveal the substantial effect of the metal purity and its surface defectiveness (including that induced by a potential increase) on the steady-state kinetics of the process. All the regularities of the effect theoretically follow from the crystal-chemistry concept of dissolution.