Oxidative corrosion mechanisms

Although structural, electronic, and conductivity properties of polyaniline are well known, oxidative corrosion mechanisms are not completely understood. It is accepted that for corrosion to occur both oxygen and water must come into contact with the surface. Therefore any barrier material will limit corrosion to some degree. To date, aniline-based coatings have been shown to provide a level of protection beyond the simple barrier limit. In these studies, epoxy-based coatings are com-... 

Underdeposit corrosion is not so much a single corrosion mechanism as it is a generic description of wastage beneath deposits. Attack may appear much the same beneath silt, precipitates, metal oxides, and debris. Differential oxygen concentration cell corrosion may appear much the same beneath all kinds of deposits. However, when deposits tend to directly interact with metal surfaces, attack is easier to recognize. 

Apart from the application of XPS in catalysis, the study of corrosion mechanisms and corrosion products is a major area of application. Special attention must be devoted to artifacts arising from X-ray irradiation. For example, reduction of metal oxides (e. g. CuO -> CU2O) can occur, loosely bound water or hydrates can be desorbed in the spectrometer vacuum, and hydroxides can decompose. Thorough investigations are supported by other surface-analytical and/or microscopic techniques, e.g. AFM, which is becoming increasingly important. 

Tantalum is severely attacked at ambient temperatures and up to about 100°C in aqueous atmospheric environments in the presence of fluorine and hydrofluoric acids. Flourine, hydrofluoric acid and fluoride salt solutions represent typical aggressive environments in which tantalum corrodes at ambient temperatures. Under exposure to these environments the protective TajOj oxide film is attacked and the metal is transformed from a passive to an active state. The corrosion mechanism of tantalum in these environments is mainly based on dissolution reactions to give fluoro complexes. The composition depends markedly on the conditions. The existence of oxidizing agents such as sulphur trioxide or peroxides in aqueous fluoride environments enhance the corrosion rate of tantalum owing to rapid formation of oxofluoro complexes. 

For example, for NGZ, the loss of capacity is higher but comparable with the loss of graphite active mass (66.8 and 50.0% 94.7 and 56.5%). Thus, corrosion mechanism (3) is a predominant one for such an unstable to oxidation graphite class. 

On the basis of the EQCM observations, the authors proposed an adsorption/oxidation/desorption mechanism for the severe pitting corrosion of Al in Lilm- and LiTf-based electrolytes, which is schematically shown in Scheme 19 and Figure 27b.According to this mechanism, Al oxidizes to form adsorbed Al(Im)3 that eventually desorbs from the surface because these species are soluble in the electrolyte solvents. It is the desorption of these oxidized products that leaves the otherwise smooth Al surface with pits. The possibility also exists that, before desorption occurs, the adsorbed species undergoes further oxidation however, since the oxidation of Im is insignificant below 4.5 V according to studies carried out on nonactive electrodes similar to Al, oe seems unlikely that further oxidation of the adsorbed Al-(Im)3 would occur. 

Different behaviors and mechanisms were clearly recognized between these resins. Epoxy resin cured with amine showed no degradation during immersion because of its stable crosslinks. Epoxy resin cured with anhydride showed the uniform corrosion with the softening and dissolution of the surface and also behaved similar to the oxidation corrosion of the metal at high temperature obeying linear law. 

Asami, K. Hashimoto, K. Shimodaira, S. (1978) XPS determination of composition of alloy surfaces and surface oxides on mechanically polished iron chromium alloys. Corrosion Sci. 18 713-723... 

Like all other non-oxide ceramics Si3N4 is metastable in air or combustion gases, both at room and at elevated temperatures. Detailed understanding of oxidation and corrosion mechanisms and the influence of the surrounding atmosphere on the lifetime are necessary before Si3N4 ceramics can be applied under oxidising or corrosive conditions [431-437]. 

In the past ten years the number of chemistry-related research problems in the nuclear industry has increased dramatically. Many of these are related to surface or interfacial chemistry. Some applications are reviewed in the areas of waste management, activity transport in coolants, fuel fabrication, component development, reactor safety studies, and fuel reprocessing. Three recent studies in surface analysis are discussed in further detail in this paper. The first concerns the initial corrosion mechanisms of borosilicate glass used in high level waste encapsulation. The second deals with the effects of residual chloride contamination on nuclear reactor contaminants. Finally, some surface studies of the high temperature oxidation of Alloys 600 and 800 are outlined such characterizations are part of the effort to develop more protective surface films for nuclear reactor applications. ... 

The corrosive activity on copper/lead bearings for typical carboxylic acids, such as decanoic, lauric, palmitic, stearic, and oleic acids, as 1 % w/w solutions in a lubricating oil base stock with excess of hard-core RMs, measured by infrared spectroscopy, supports the observation for the corrosive activity of used lubricating oils. An increase in total acidic number (TAN) is generally either an indication of contamination with acidic combustion products or the result of oil oxidation. Corrosion of bearing metals by used lubricating oils requires the presence of both acids and peroxides and probably takes place by a two-step mechanism. In the first step, the peroxide reacts with the metal to form a metal... 

Modeling fretting corrosion. An equation has been used for steel to evaluate the loss of weight W caused by fretting corrosion based on a model that combines the chemical and mechanical effect of the corrosion by fretting. The chemical factor concerns the oxidation that occurs at the time of wear, corresponding to adsorption of oxygen to form the oxide. The mechanical factor concerns the loss of particles, at the asperities on the opposite surface. 

Refs. [i] Strehblow HH (2003) Passivity of metals. In Alkire RC, Kolb DM (eds) Advances in electrochemical science and engineering. Wiley-VCH, Weinheim, pp 271-374 [ii] Vetter KJ, Gorn F (1973) Electrochim Acta 18 321 [Hi] Strehblow HH (2002) Mechanisms of pitting corrosion. In Marcus P (ed) Corrosion mechanisms in theory and practice. Marcel Dekker, New York, pp 243-285 [iv] Strehblow HH (2003) Pitting corrosion. In Bard AJ, Stratmann M, Frankel GS (eds) Corrosion and oxide films. Encyclopedia of electrochemistry, vol. 4. Wiley, Weinheim, 337... 

Since steel is the main structural material for bridges, buildings, and automobiles, controlling its corrosion is extremely important. To do so, we must understand the corrosion mechanism. Instead of being a direct oxidation process, as we might expect, the corrosion of iron is an electrochemical reaction, as illustrated in Fig. 11.17. 

Perchloric acid s corrosive properties and ability to cause tissue oxidation are mechanisms of toxicity. Perchlorate (CIOT) disrupts endocrine homeostasis by competitively inhibiting the transport of iodide (I ) into the thyroid through the sodium iodide symporter. Potential human health risks exist from chronic exposure to perchlorate via drinking water. Such risks may include hypothyroidism, goiter, and mental retardation (if exposure occurs during critical periods in neurodevelopment). 

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