Electrode dissolution

In most corrosion processes passivity is desirable because the rate of electrode dissolution is significantly reduced. The rate of aluminum corrosion in fresh water is relatively low because of the adherent oxide film that forms on the metal surface. A thicker film can be formed on the surface by subjecting it to an anodic current in a process known as anodizing. In most electrochemical conversion processes passive films reduce the reaction rate and are, therefore, undesirable. 

Fig. 4.29. The burst of electrode dissolution during the current pulse produces a layer of ions adjacent to the dissolving electrode (negative ions are not shown in the diagram).

Fig. 4.31. Plots of the fraction n/n,o,ai of ions (produced in the pulse of electrode dissolution) against the distance x from the electrode. At t= 0, all the ions are on the x = 0 plane, and at f > 0, they are distributed in the solution as a result of dissolution and diffusion. In the diagram, f3> > > 0, and the distribution curve becomes flatter and flatter.

Fig. 4.32. Schematic of experiment to note the time interval between the pulse of electrode dissolution (at t=0) and the arrival of radioactive ions at the window where they are registered in the Geiger-counter system.

Fig. 4.34. When diffusion occurs from an instantaneous plane source (set up, e.g., by a pulse of electrode dissolution), then 68% of the ions produced in the pulse lie between x = 0 and x = x g, after the time t.

Insonation of an electrosynthetic reaction can produce altered product ratios, greater efficiencies, lessened cell power requirements, and a diminution of detrimental electrode fouling. In electrodeposition, ultrasound alters the properties of the product coating, be it a metal deposited, a semiconductor, a polymer, or some other electrogenerated material. Sonication also affects corrosion and electrode dissolution, and is useful, for example, in systems employing sacrificial electrodes. 

The highest residual traces of Cr(VI) occur in the anodic sections of the experimental cells. Cr(VI) removal from aqueous solutions is enhanced by the presence of ferric iron oxyhydroxide phases, as Cr(VI) adsorbs onto FeOOH (e.g. Aoki and Munemori, 1982 Mesuere and Fish, 1992a,b Mukhopadhyay, Sundquist, and Schmitz, 2007). The amount of released by anodic electrode dissolution primarily depends on the applied current and the duration of the passage of the current through the electrodes (e.g. Mukhopadhyay, Sundquist, and Schmitz, 2007). Differences in the lateral extent of iron mineralization in the three experiments illustrate that the buffering capacity of the soils influenced the spatial extents of the zone of Cr(VI) reduction and complementary alkaline zone. The Warwick soil (experiment A) operated at half the applied voltage to experiments B and C, experienced the furthest advance of iron mineralization from the anode array, quickly developed a sharp pH jump, and attained the most acidic conditions. Collectively, these attributes indicate that the Warwick soil had a comparatively low buffering capacity relative to the other two soils examined. 

Several examples of deposition and electrode dissolution, including electrochemical machining, will be discussed. 

In the case of electrode dissolution, the vectors XN(K) and YN(K) are also constructed and the new electrode profile is interpolated by a cubic natural spline. 

Accordingly at each end the electrodeposition or electrode dissolution algorithm can be applicable. An example is given in fig. 4-. 15. 

An algorithm was developed that keeps the boundary closed in all circumstances of electrodeposition, electrode dissolution, electrochemical machining and levelling. 

Electrodeposition and electrode dissolution in copper electrorefining. Numerical and experimental results... 

Fig. 2 Current-voltage curves of a DBL containing a strong binary electrolyte. Magnitudes Z2, A, I, and /(. are defined with sign subscript 2 denotes the electroinactive species. Negative values of ///(. correspond to electrode dissolution (anodic or cathodic), and positive values to single ion discharge at the electrode.

Electrode dissolution (corrosion, electropolishing, shaping by anodic dissolution [18], often accompanied by formation of supersaturated product films). 

The platinum eleetroehemical dissolution rate in fuel cell operation is a critical durability issue due to loss of catalyst surface area vs. time. The dissolution behavior and solubility of platinum are governed by the chemical state of the platinum surfaee and the equilibrium platinum species in the solution. Temperature, pH, eleetrolyte composition, potential, and particle size are all major factors influencing the solubility and the dissolution rate. Potential cycling of Pt electrodes has been extensively investigated, and the platinum electrode dissolution rates from the literature are summarized in Table 23.5 [9, 33, 70-74], Both Pt(II) and Pt(IV) speeies were detected in sulfuric solution after potential cycling from... 

Tivol WF, Agnew WF, Alvarez RB, Yuen TGH (1987) Characterization of electrode dissolution products on the high voltage electrode microscope. J Neurosci Methods 19 323-337... 

The test is typically conducted by setting a stimulation protocol with a constant pulse width. The current amplitude is then gradually increased as successive measurements are recorded. This sequence is used to avoid the effect of electrode activation. To minimize electrode dissolution, a cathodic pulse measurement of the same magnitude and duration should be made following each anodic pulse measurement. 

In a cataphoretic emulsion, when an electric field is applied (approximately 1 kV m" ), micelles migrate by electrophoresis toward the cathode at the rate of micrometres per second. In addition, all the water-soluble components also migrate with the micelle. The conductivity of the solution permits controlled electrolysis, and water decomposes to raise the pH at the cathode and lower the pH at the anode. The anode is usually made of an inert material, such as stainless steel, since, being the oxidizing electrode, dissolution is possible. 

In cataphoretic deposition no metal ions are incorporated into the coating from electrode dissolution, but the volume of hydrogen produced can cause problems through the formation of resist defects (pinholes) if it is not removed. 

Cell materials under certain conditions may undergo undesirable phase transition that leads to cell capacity fade. Jahn-Teller distortion occurring in IiMn204 at 280 K is an example of this kind of failure mechanism related to the intrinsic stability of the molecular structure. Upon particle fracture, the contact surface area between particles and electrolyte greatly increases, and this may strongly affect electrode dissolution and the stabiUty of the SEI layer. 

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