Chloride-induced corrosion layers

Concrete exposed to deicer salts, or to a marine environment is subjected to chloride and sodium loading. The ability of concrete to resist the penetration of chlorides and sodium is a primary design consideration in marine or cold environments. The ingress of chlorides into concrete is a major problem due to chloride-induced corrosion of the reinforcing steel and deicer salt scaling [a process by which a thin layer (< 1 mm) of concrete deteriorates from the surface of the concrete]. The penetration of sodium from sea water or deicer salts is generally... 

Carbonation is manifested as a reduction in the pH of the pore solution in the outer layers of the concrete and often appears as a well-defined front parallel to the external surface. This front can conveniently be made visible by applying a phenolphthalein indicator solution to freshly exposed concrete surfaces. Behind the front, where all the calcium hydroxide has been depleted, the pH is around 8, whereas ahead of the front, the pH remains in excess of 12.5. The passivating ability of the pore solution diminishes with the decrease in pH. Carbonation-induced corrosion tends to proceed in a more uniform manner over the rebar surface than chloride-induced corrosion damage. 

Schematic of the three situations that are used for the assessment of metal chloride evaporation, (a) Vapor pressure of the gaseous metal chloride above solid or liquid metal chloride in a closed system (value used in Equation 13.23 and for determining T ). (b) Equilibrium partial pressure of pMe Cl in a closed system containing O2 and CI2 as gas phase and Me, Me Oj, and Me,.Cly as solid or liquid phases (value used for the establishment of the "static" quasi-stability diagram), (c) Mej.Cly transport rate in the gas boundary layer (metal consumption rate) as criterion for the amount of chlorine-induced corrosion in an open system with gas flow across the surface (value used for the establishment of the "dynamic" quasi-stability diagram).

Bauer et ah, 1986). It is also a significant corrosion product of Fe alloy phases on Antarctic meteorites where its formation is induced by the chloride ions coming from airborne seaspray and/or volcanic activity (Buchwald and Clarke, 1989). In these meteorites, akaganeite is located adjacent to the corroding surface and beneath a layer of goethite/spinel into which it eventually transforms. 

FIGURE 3.1 Scanning electron microscopy (SEM) image of an ITO layer immersed in a 0.1-M HCl solution after a potential scan from 0.3 to 1.2 V (SCE). (Reprinted from Anodic corrosion of indium tin oxide films induced by the electrochemical oxidation of chlorides, 301, Eolcher, G. et al.. Thin Solid Films, 242-248, Copyright 1997, with permission from Elsevier.)... 

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