Mechanism of Electrochemical Corrosion of Metals Under Insulating Coatings. (2)

Tomashov, N. D.; Mikhailovskii, Yu. N.; Leonov, V. V.

doi:10.3323/jcorr1954.14.4_172

Cited by 1 publication

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“…dc techniques cannot be applied to impermeable organic films and low conductivity media, but they are the simplest to use in cases where the film is permeable and the medium is conducting, as in the present work. Potentiodynamic polarization and linear polarization are among the widely used dc techniques for studying the corrosion protection ability of coatings (Bacon et al, 1948;Wormwell and Brasher 1949;Clay, 1969;Tomashov et al, 1964;Boxall and Fraunhofer, 1973;Rajagopalan et al, 1975;Devay et al, 1979;Snoeyink and Kuch, 1985;Fontana, 1986). Useful parameters measured by these techniques are the anodic (b a ) and cathodic (b c ) Tafel coefficients, their harmonic mean (µ b ), and the polarization resistance (R p ), given respectively by where R is the symmetry factor, z the ion valence, F the Faraday constant, and i corr the corrosion current.…”

Section: Introductionmentioning

confidence: 99%

Corrosion Protection of Mild Steel by a Calcite Layer

Keysar

Hasson

Semiat

et al. 1997

Ind. Eng. Chem. Res.

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Artificial calcite lining represents a novel technique for the rehabilitation of water mains. Calcite linings, similar to the commonly used cement-mortar linings, are of porous nature. The corrosion protection mechanisms of calcite linings were investigated by polarization techniques, complemented by scanning electron microscopy observations and energy dispersive spectrometry analyses. The effect of time on lining durability was examined by exposure of coated mild steel (1020) coupons in a controlled flowing water system. Iron ion distributions in calcite sections, before and after exposure to water flow, indicate that the calcite corrosion protection mechanism is based mainly on accumulation of corrosion products inside the lining. At the calcite−metal interface, a protective film is formed. At the calcite−water interface, the calcite structure, being alkaline with respect to the water, promotes precipitation of the iron ions and blockage of the pores near that interface. The formation of this protective oxide film was evident from the polarization data which showed that both the anodic Tafel constant and the polarization resistance increase with time. This paper also examines the applicability of potentiodynamic and linear polarization techniques for the characterization of the corrosion protection of a porous lining, such as calcite. It is shown that these convenient electrochemical techniques provide reliable and meaningful corrosion protection information.

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Section: Introductionmentioning

confidence: 99%