Oxide films formation, efficiency

Sometimes the formation of oxide films on the metal surface binders efficient ECM, and leads to poor surface finish. Eor example, the ECM of titanium is rendered difficult in chloride and nitrate electrolytes because the oxide film formed is so passive. Even when higher (eg, ca 50 V) voltage is apphed, to break the oxide film, its dismption is so nonuniform that deep grain boundary attack of the metal surface occurs. 

The mechanism of inhibition by the salts of the long chain fatty acids has been examined . It was concluded that, in the case of the lead salts, metallic lead was first deposited at certain points and that at these points oxygen reduction proceeded more easily, consequently the current density was kept sufficiently high to maintain ferric film formation in addition, any hydrogen peroxide present may assist in keeping the iron ions in the oxide film in the ferric condition, consequently the air-formed film is thickened until it becomes impervious to iron ions. The zinc, calcium and sodium salts are not as efficient inhibitors as the lead salts and recent work has indicated that inhibition is due to the formation of ferric azelate, which repairs weak spots in the air-formed film. This conclusion has been confirmed by the use of C labelled azelaic acid, which was found to be distributed over the surface of the mild steel in a very heterogeneous manner. ... 

Carbon has been removed to very low levels in sodium at 600°C by the use of Type 316 stainless steel". Neither Zr nor Nb is efficient at C removal, since oxide films inhibit carbide formation. ... 

To increase equipment reliability and plant efficiency, corrosion inhibitors are used in boiler and cooling water programs to control fouling and deposition on critical heat-transfer surfaces. In cooling systems, corrosion inhibition is commonly achieved through the use of passivators, which encourage the formation of a protective metal oxide film on the metal surface ( 1). ... 

Photo-oxidation of LCV by the Pyrene-Bonded Film. The surface properties and structure of these systems should be related to the sensitizer efficiency of pyrenyl groups. Pyrene is a good sensitizer for the oxidative color formation of LCV. The singlet excited state of Py acts as an electron acceptor bringing about one electron oxidation of LCV+. The unit processes are considered as... 

The anodic photocurrent of n-Si in aqueous solutions in the absmce of fluoride decays very rapidly due to the formation of an oxide film. It decays less rapidly in the presence of a reducing agent which can compete efficiently for the holes from the valence band and slow down the rate of oxidation. Ferrate ions and iodine ions have been found to compete favorably with the oxidation of the silicon surface. On the other hand, in solutions containing a small amount of fluoride ions insufficient to completely remove the oxide film, the photocurrent exhibits a fast decay. According to Matsumura and Morrison, the rapid decay of the photocurrent in solutions with a small amount of fluoride is due to the catalytic effect of fluoride ions at the Si/SiO interface. 

Anodic passivation of steel surfaces can be efficiently achieved by metal chromates. Chromates of Intermediate solubility (e.g., zinc chromate and strontium chromate) allow a compromise between mobility in the film and leaching from the film to be achieved. Chromates inhibit corrosion in aqueous systems by formation of a passivating oxide film. The effectiveness of chromate inhibitors in aqueous systems depends on the concentration of other ionic species in solution, for example, chloride. Synthetic resin composition can also significantly influence the effectiveness of chromate pigments. The effect appears to be related to the polarity of the resin (20) chromate pigments appear to be less effective in resins of low polarity. 

Cyclic voltammetry shows two different redox processes which correspond to the reduction/oxidation of the polypyrrole backbone and the ferrocene moiety, respectively. It also confirms that the concentration of ferrocene in the film can be controlled by varying the composition of the feed. There is less efficient film formation with a higher relative concentration of P-6-Fc because of parasitic current for the oxidation of ferrocene. 

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