Electrochemical Factor

Factors Influencing the Stability of Crystal Structures 5.1. Electrochemical Factor 

The effect of a strong electrochemical factor in an alloy system depends on the electron concentration, as Hume-Rothery has pointed out. When the electron concentration is high it leads to the forma- 

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All organic coatings show varying degrees of solubility and permeability for components of the corrosive medium, which can be described as permeation and ionic conductivity (see Sections 5.2.1 and 5.2.2). An absolute separation of protected object and medium is not possible because of these properties. Certain requirements have to be met for corrosion protection, which must also take account of electrochemical factors [1] (see Section 5.2). 

The metallic or semi-metallic character of many common sulfides implies the significance of electrochemical factors in the study of their oxidation, which is relevant to environmental, energy, and metallurgical issues, e.g., in connection with the direct electrochemical conversion of sulfide ores to metals, the pressure leaching of ore materials, or flotation processes. 

Though accelerating effect of redox mediators is proved, differences in electrochemical factors between mediator and azo dye is a limiting factor for this application. It was reported that redox mediator applied for biological azo dye reduction must have redox potential between the half reactions of the azo dye and the primary electron donor [37], The standard redox potentials for different azo dyes are screened generally between -430 and -180 mV [47],... 

He did not think of it then, and when he did, he showed that apparently the formation of a metal-carbon bond was unlikely on thermochemical grounds [68] in other words, he was taken in by his own propaganda but in a Note added in Proof in that same work he indicated that electrochemical factors (solvation and Coulombic energies) could make this initiation exo-energetic. However, at that time, 1960-1970, such a suggestion would have been no more plausible than when it was made by others. It was only the painstaking and detailed exploration of the nature of the solutions of A1X3 in alkyl halides [104, 112] that provided the basis of fact which was required to make the theory plausible. 

When one component in a binary alloy is very electropositive relative to the other, there is a strong tendency to form compounds of high stability in which valence rules are satisfied (Pearson 1972). Such alloys are considered to show a strong electrochemical factor. 

Attempts have been performed to analyse (in terms of rate constants) the steric-to-electrochemical factors which can influence the interaction of ferrocenium derivatives with reduced GOD, or the ability of ferrocenes to act as mediators in the enzymatic oxidation of glucose as a function of cyclopentadienyl substituents.63... 

The reduction in overall efficiency on scale-up deserves further design and performance consideration. The net power output was lower than expected from the summed performance of the individual units and the optical, solid state or electrochemical factors which contribute to this reduction in performance need to be classified. 

It appears in this discussion that electrochemical parameters and not substrate properties are the main deciding factors in determining the texture of deposits. This is indeed so when the deposit s thickness is 1 gm or more. In case of thinner deposits, the substrate plays an important role as well (see text above). Another non-electrochemical factor may be the codeposition of particulate matter with some metal deposits. To summarize, we note that texture is influenced mostly by deposition current density, as it is itself a function of bath pH, potential, and other parameters. Not surprising, then, is the fact that in the case of physical vapor deposition (PVD) the deposition rate is the determining factor in setting the texture of the coating. 

The aqueous corrosion of ceramics may involve a charge-transfer or electrochemical dissolution process. However, in many cases, dissolution or corrosion may take place with no charge transfer yet may be determined by one or more electrochemical factors such as absorbed surface charge or electronic band bending at the surface of narrow-band-gap semiconducting ceramics. The aqueous corrosion of ceramics is important in a number of areas. One of the most important is the stability of passive oxide films on metals. The stability of ceramics is a critical aspect in some aqueous photoelectrochemical applications (12), an example being the photoelectrolytic decomposition of water. Structural, nonoxide ceramics such as SiC or Si3N4 are unstable in both aqueous acid and alkaline environments the latter is virtually unstudied, however. 

Another electrochemical factor of great importance is the molar conductivity A, which is a ratio of electric conductivity and mass quantity in 1 m (concentration c) ... 

Comparing the effects of concentrations of the reacting ions and the supporting electrolyte on the shape of the polarization curves, it can conclude that an increase in the concentration of the supporting electrolyte relative to the concentration of the reacting ion reduces the importance of the ohmic potential drop and enhances the importance of the overpotential as the electrochemical factor that makes the current density distribution more uniform. 

Thus, calculation of the electrode potentials on the basis of ion concentration, the determination of polarization characteristics, and other electrochemical operations are not as simple in atmospheric corrosion as they are in liquid immersion corrosion. However, all of the electrochemical factors which are significant in corrosion processes do operate in the atmosphere. 

The following are the electrochemical factors which contribute to corrosion fatigue Mark YES or NO)... 

In general, the way to deal with this type of phenomena consists of inhibiting at least one of the factors that participate in these processes or both. The mechanical factors can be inhibited by the development of new materials or alloys of better mechanical properties or higher resistance to wear. The electrochemical factors can be inhibited by incorporating substances into the corrosive enviromnent that reduce the rate of electrochemical activity (Liu et al, 2003). 

Various materials of construction for refinery and petrochemical plant service may exhibit accelerated metal loss under unusual fluid-flow conditions. Attack is caused by a combination of flow velocity (mechanical factors) and corrosion (electrochemical factors) known as erosion-corrosion. 

Salvarezza, R.C. and Videla, H.A (1978). Biological and electrochemical factors involved in microbial corrosion of alumimim. Anales Asoc. 

As seen from this review of the published data, stereospecificity in electrode reactions is still a little-investigated subject. In some cases the effect of purely electrochemical factors can be clearly traced, in other cases a much greater part is evidently played by factors which also arise in normal homogeneous reactions. Detailed investigation of the effect of electrode potential on the stereochemistry of oxidation and reduction products is of undoubted interest and may lead to methods for controlling the course of many of these reactions. 

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