Wagner-Traud mixed-potential theory

Cathodic protection (CP) is defined as the reduction or elimination of corrosion by making the metal a cathode by means of impressed current or sacrificial anode (usually magnesimn, aluminum, or zinc) [11]. This method uses cathodic polarization to control electrode kinetics occurring on the metal-electrolyte interface. The principle of cathodic protection can be explained by the Wagner-Traud mixed potential theory [12]. 

An electrochemical model for the process of electroless metal deposition was suggested by Paunovic (10) and Saito (8) on the basis of the Wagner-Traud (1) mixed-potential theory of corrosion processes. According to the mixed-potential theory of electroless deposition, the overall reaction given by Eq. (8.2) can be decomposed into one reduction reaction, the cathodic partial reaction. 

Wagner-Traud Diagram, According to the mixed-potential theory, the overall reaction of the electroless deposition, [Eq. (8.2)] can be described electrochemically in terms of three current-potential i-E) curves, as shown schematically in Eigure 8.2. First, there are two current-potential curves for the partial reactions (solid curves) (1) ic =f(E), the current-potential curve for the reduction of ions, recorded from the rest potential E eq M the absence of the reducing agent Red (when the activity of is equal to 1, eq,M E m) and (2) = f(E), the current-potential... 

Wagner-Traud Diagram. According to the mixed-potential theory, the overall reaction of the electroless deposition, [Eq. (8.2)] can be described electrochemically in terms of three current-potential (i-E) curves, as shown schematically in Figure 8.2. 

Metals are obtained by the treatment of oxides and sulfide ores found in the earth. However, there is an initial difficulty—the desirable ores are often mixed up with those of little commercial value, and the problem is to obtain the desired ore free from those of lesser worth. For many years now, largely due to the initiative of Australian workers, it has been possible to find organic substances which, when added to a suspension of mixed ores, pick out the desired one, and (when air is bubbled into the system) float it to the surface, from which it can be raked off, i.e., separated and made available for chemical or electrochemical extraction of the metal. It turns out that the basis of this mineral flotation technology involves the Wagner and Traud mixed-potential concept and is thus indirectly related to corrosion theory. 

Polarisation methods involve changing the potential of the WE and monitoring the current which is produced as a function of time or potential. One of the most relevant physical quantities measured by DC polarisation methods is linear polarisation resistance (LPR). Its definition is based on the mixed potential theory proposed by Wagner and Traud [4], that explains the corrosion reactions by assuming that cathodic and anodic partial reactions occur at the metal-electrolyte interface at a certain corrosion (or mixed ) potential,... 

In order to explain the corrosion process of metals, Wagner and Traud [54] developed the mixed potential theory, which assumes that the current-potential relationship is given by... 

The mixed potential theory partly mentioned earlier, is used with advantage to predict the rate of corrosion of metals and alloys in given environment. It was postulated by Wagner and Traud in 1938. It has two basic assumptions ... 

The current-density-polarization relation, or polarization equation, of a corroding metal has been derived by Wagner and Traud, using mixed potential theory ... 

Wagner and Traud [141] developed the theory of mixed potentials in order to explain the corrosion of electrode surfaces. This theory assumes that the measurable current—potential curves for an electrode where more than one electrochemical reaction takes place simultaneously is represented by... 

C. Wagner and W. Traud, Z. Elektrochem. 44 391 (1938). The original formulation of the mixed potential concept and the basic theory of corrosion of a pure metal. 

Equation (41) is identical in form to Eqs. (18 and 24). The curve is centered around Ecorr rather than and the current density at zero overpotential is icorr instead of io- This expression, along with the theory for mixed potentials, was derived by Wagner and Traud, and therefore will be referred to as the Wagner-Traud equation. As described in the Chapter 7.3.1.2 on experimental techniques, the Wagner-Traud equation is used in software analysis packages that accompany modem computer-controlled potentiostats. A nonlinear least squares fit of this equation to the experimental data provides values of corr. corr. ha. and he vvith the assumption that perfect Tafel behavior is observed for both the anodic and cathodic reactions, and that the extrapolations of the Tafel portions of the curves both intersect at the corrosion potential. 

In his own paper, Frumkin also analyzed the effect of the sodium amalgam concentration on the rate of electrolysis of water, and arrived at the conclusirm that even for physically and chemically uniform surfaces, the processes of anodic metal dissolution and cathodic hydrogen evolution could occur simultaneously at the same potential. This same idea was later used by K. Wagner and W. Traud (1938) in their formulation of the theory of the mixed potential, the cornerstone of modem corrosion theory. 

Solid materials, in general, are more or less subject to corrosion in the environments where they stand, and materials corrosion is one of the most troublesome problems we have been frequently confronted with in the current industrialized world. In the past decades, corrosion science has steadily contributed to the understanding of materials corrosion and its prevention. Modem corrosion science of materials is rooted in the local cell model of metallic corrosion proposed by Evans [1] and in the mixed electrode potential concept of metallic corrosion proved by Wagner and Traud [2]. These two magnificent achievements have combined into what we call the electrochemical theory of metallic corrosion. It describes metallic corrosion as a coupled reaction of anodic metal dissolution and cathodic oxidant reduction. The electrochemical theory of corrosion can be applied not only to metals but also to other solid materials. 

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