Cathodes depolarization

The only above reaction in which bacteria plays a direct role is Reaction 6.4, the cathodic depolarization process. 

Crevices, deposits on metal surface or any geometrical configuration which results in differences in the concentration of oxygen or other cathodic depolarizers (e.g., Cu ). Metal in contact with the lower concentration—this follows from considerations of an equivalent reversible cell, although the situation is more complex in practice. 

Environment Differences in aeration or concentration of cathodic depolarizers. Metal in contact with lower concentration. 

Oxygen dissolved in aqueous solutions, even in very low concentrations, is a leading cause of corrosion problems (i.e., pitting) in drilling. Its presence also accelerates the corrosion rate of other corrodents such as hydrogen sulfide and carbon dioxide. Oxygen plays a dual role both as a cathodic depolarizer and an anodic polarizer or passivator. Within a certain range of concentration the... 

Chlorides, in particular, can present a problem because they are cathodic depolarizing agents (depolarizers) and thus negate the effectiveness of cathodic polarization techniques. 

Small cathodes promote a high current density, which tends to retard cathodic depolarization mechanisms. 

Chloride is both a cathodic depolarizing agent (depolarizer) and a depassivating agent, and the presence of high chlorides in steam-water circuits significantly increases the risk of stress corrosion cracking of austenitic steels (type 300 stainless). 

Therefore, one main drawback of the PEMFC configuration with a standard proton exchange membrane (such as Nafion) and a standard platinum gas diffusion cathode is the cathode depolarization caused by a mixed potential resulting from the methanol crossover through the mem-... 

Stainless steel microelectrodes were prepared by sheathing 100-pm diameter stainless steel wire in glass. Tips were polished on a precision diamond wheel. Electrode response to variation in cathodic depolarizer concentration was confirmed by exposure to solution containing up to 6 mM HjOj. The increase in for the electrode was comparable to the change observed for sample coupons exposed to the same H2O2 concentrations. The electrode was conditioned by exposure to the influent reactor solution for several hours before measuring E, within the biofouling deposits. 

Porous carbon electrodes were used in the field of electrolyte-soluble (p-nitraniline) [34] and electrolyte -insoluble (nitrobenzene) [35] organic cathodic depolarizers. 

To prevent the cathode potential from becoming so negative that unintended ions are reduced, a cathodic depolarizer such as NO can be added to the solution. The cathodic depolarizer is more easily reduced than H30+ ... 

A cathodic depolarizer is reduced in preference to solvent. For oxidation reoctions. anodic depolarizers include N2H4 (hydrazine) and NH2OH (hydroxylamine)... 

Desulfovibrio desulfuricans Anaerobic sulfate reducer that causes corrosion and precipitation of iron by sulfide. Corrosion can be serious, developing deep pits under slime it is especially troublesome in paper mills, steel plants, refineries, and other large cooling systems. Corrosion rates are enhanced by the removal of hydrogen from the cathode by sulfate reducers (cathodic depolarization), as follows ... 

Murphy JO, Hitchens GD. Method and apparatus for using gas and liquid phase cathodic depolarizers. United States Patent 5,770,033, 1998. 

The CEFM is based upon the differential aeration hypothesis (DAH) for localized corrosion that was first enunciated by U. R. Evans at Cambridge University in the 1920s. The DAH postulates that there exists a spatial separation between the local anode, which is located in that region of the system that has the least access to the cathodic depolarizer (e.g., O2), and the local cathode, which forms at the location that has the greatest access to the cathodic depolarizer, with the proviso that both regions must be in electronic and electrolytic communication (Fig. 7). This arrangement results in the flow of positive current in the electrolyte phase... 

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