Traud

Fig. 1.29 Wagner-Traud method of representing (a) a single reversible reaction and (b) a corrosion reaction (note that E orr the potential when = 4)...

Pourbaix has shown by means of E-i diagrams (Wagner and Traud type) that the differential principle is applicable only at certain pH values, and the situation when the pH is the same in both the aerated and non-aerated zones is as follows ... 

The main system chosen by Wagner and Traud themselves was the corrosion of zinc amalgam in aqueous HCl. They measured the current-potential curves of... 

Although the original additivity principle of Wagner and Traud has been an immensely useful concept with applications in numerous fields, carefully designed studies in receiit years have revealed a number of exceptions. These have been described above and are summarized in... 

Thus, the first chapter touches on an aspect of electrochemistry for which the author has become justly well known application of the Wagner and Traud theorem of 1938 according to which electrochemical systems may function on a single electrode. In the next chapter, the article by Koczorowski treats a seldom-visited but truly fundamental area, that of voltaic measurements at liquid interfaces. 

Figure 8. Wagner-Traud (Evans) diagram for aluminum in aqueous solution, in the absence of dissolved oxygen.

Jennifer L. Clancy, Marco Nousch, David T. Humphreys, Belinda J. Westman, Traude H. Beilharz, and Thomas Preiss... 

Further, these anodic and cathodic reactions can occur spatially at adjacent locations on the stuface of a metal electrode rather than on two separated metal electrodes as shown in Fig. 11-1, where the anodic dissolution of iron and the cathodic reduction of hydrogen ions proceed simultaneously on an iron electrode in aqueous solution. The electrons produced in the anodic dissolution of iron are the same electrons involved in the cathodic reduction of hydrogen ions hence, the anodic reaction cannot proceed more rapidly than that the electrons can be accepted by the cathodic reaction and vice versa. Such an electrode at which a pair of anodic and cathodic reactions proceeds is called the mixed electrode . For the mixed electrodes, the anode (current entrance) and the cathode (current exit) coexist on the same electrode interface. The concept of the mixed electrode was first introduced in the field of corrosion science of metals [Evans, 1946 Wagner-Traud, 1938]. 

Zhou, Z., Traud, R., Yadav, R., Fedkiw, P. and DeSimone, J. M. 2007. Curable, 100% solids Liquid precursors to patterned PEMs. In Advances in materials for proton exchange membrane fuel cell systems, Pacific Grove, CA, Feb. 18-21. 

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... 

Figure 8.2. Wagner-Traud diagram for the total (/total) rid component current potential curves (/, / ) for the overall reaction of electroless deposition.

Figure 8.5. Wagner-Traud diagram for electroless Ni(B) deposition E = — 840 mV versus SCE. Electrode area 0.68 cm. (From Ref. 43, with permission from the American Electroplaters and Surface Finishers Society.)...

The corrosion behavior of semiconductors can, in principle, be described within the framework of the same concepts as for metals (see, for example, Wagner and Traud, 1938), but with due account for specific features in the electrochemical behavior of a solid caused by its semiconducting nature (Gerischer, 1970). One of the main features is photosensitivity related to a change in the free-carrier concentration under illumination. Photosensitivity underlies the phenomenon of photocorrosion. 

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... 

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. 

The basic mechanism for the instability of ultrapure metals was suggested by Wagner and Traud in a classic paper in 1938.1 The essence of their view is that for corrosion to occur, there need not exist spatially separated electron-sink and -source areas on the corroding metal. Hence, impurities or other heterogeneities on the surface are not essential for the occurrence of corrosion. The necessary and sufficient condition for corrosion is that the metal dissolution reaction and some electronation reaction proceed simultaneously at the metal/environment interface. For these two processes to take place simultaneously, it is necessary and sufficient that the corrosion potential be more positive than the equilibrium potential of the M, + + ne M reaction and more negative than the equilibrium potential of the electronation (cathodic) reaction A + ne — D involving electron acceptors contained in the electrolyte (Fig. 12.8). 

Consider a system consisting of a metal corroding in an electrolyte. The corrosion process involves a metal-dissolution deelectronation (anodic) reaction at electron-sink areas on the metal and an electronation (cathodic) reaction at electron-source areas. (This picture is applicable to a metal s corroding by a Wagner-Traud mechanism provided one imagines the sink and source areas shrunk to atomic-sized dimensions and considers the situation at one instant of time.)... 

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