Biological environments, corrosion

Corrosion associated with the action of micro-organisms present in the corrosion system. The biological action of organisms which is responsible for the enliancement of corrosion can be, for instance, to produce aggressive metabolites to render the environment corrosive, or they may be able to participate directly in the electrochemical reactions. In many cases microbial corrosion is closely associated with biofouling, which is caused by the activity of organisms that produce deposits on the metal surface. 

It should be mentioned that in a warm, dry climate the chlorides improve the sulphate attack [280], Presumably, it is the reason, apart from the known effect of temperature on the rate of chemical reactions (Arrhenius mle), that in a warm climate the concrete corrosion occurs more rapidly than for example in the North Sea. The examples of disastrous quick concrete corrosion in the warm seas in the Middle East are known, as well as the excellent durability of drilling platforms situated on the North Sea [278]. The conditions governing in different geographic zones temperature, erosion, biological environment, are highly variable and therefore the mechanisms of concrete deterioration are greatly modified [61]. 

Complex physical, chemical and biological nature, corrosion aggressiveness, and ( namic interactions with the environment... 

Edyvean, R. G. J., Thomas, C. J., Brook, R., and Austen, I. M., "The Use of Biologically Active Environments for Testing Corrosion Fatigue Properties of Offshore Structural Steels, Proceedings, Biologically Induced Corrosion, S. C. Dexter, Ed., NACE-8, National Association of Corrosion Engineers, Houston, TX, 1986, p. 254. 

The basic in vitro tests derived from teehnieal applications are the salt spray test (ASTM B-117) and the submersion test, performed in saline solutions (3.5% NaCl, ASTM G31-72 (2004) Standard Practice for Laboratory Immersion Corrosion Testing of Metals). Both tests are conducted at room temperature. By such tests the mass loss ean be determined according to equation (10.5). The mass loss is calculated after removing the corrosion products with chromic acid, which at the same time removes the corrosion products and inhibits further corrosion (Forking, 1964), which is suitable for technical applications but may raise problems in biological environments. 

Crevice zones may result from fhe design of the component (see Figure 10.1) or from the formation of deposits during service, shutdown, or even fabrication. These deposits may come from suspended solids in the environment, corrosion products, or biological activity. Low-flow areas are prone to the formation of such deposits. 

Biological Corrosion The metabohc activity of microorganisms can either directly or indirectly cause deterioration of a metal by corrosion processes. Such activity can (1) produce a corrosive environment, (2) create electrolytic-concentration cells on the metal surface, (3) alter the resistance of surface films, (4) have an influence on the rate of anodic or cathodic reaction, and (5) alter the environment composition. 

As mentioned earlier, there is an inverse relationship between water volumes and oxygen concentration in soil. As soils dry, conditions become more aerobic and oxygen diffusion rates become higher. The wet-dry or anaerobic-aerobic alternation, either temporal or spatial, leads to higher corrosion rates than would be obtained within a constant environment. Oxygen-concentration-cell formation is enhanced. This same fluctuation in water and air relations also leads to greater variation in biological activity within the soil. 

The interaction in an interface of device/tissue is limited by two factors. There is the corrosive environment, such as biological fluid, which contains salts and proteins among other cellular structures in which the sensor device must survive [47, 48], Second, there is the encapsulation material which may induce a toxic reaction due to poor biocompatibility and hemocompatibility [49, 50], It is crucial to use a biomaterial that can overcome both limiting factors to maintain the lifetime of the sensor device and protect the body [51, 52],... 

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