Protective organic coatings: Membrane properties and performance

A probabilistic model for estimation of ionically permeable inhomogeneities in polymer coatings

“…It was observed that a coating that maintained a resistance of 10 8 Ohm cm 2 provided good corrosion protection while one whose resistance fell below 10 6 Ohm cm 2 did not. Since that time, ionic resistance has been used as a major criterion for determining the corrosion protection afforded by an organic coating [2][3][4][5].…”

“…Since that time, ionic resistance has been used as a major criterion for determining the corrosion protection afforded by an organic coating [2][3][4][5]. Later studies revealed a bimodal mechanism of ionic conduction through polymer films [6][7][8] and determined the presence of highly permeable areas that form a small fraction of the coating. These domains are observed to be significantly more permeable than the bulk of polymer film to ionic species such as chloride [9] and increase in number and permittivity as the coating absorbs water [10].…”

Diffusion of cations beneath organic coatings on steel substrate

“…Figure 3 Figure 4 for m = 1 where the slope of the dimensionless concentration profiles is less at higher values of a/R. In Figure 5 (6,7). One of the possible explanations for the higher diffusion coefficient of Na"^obtained in this study is due the alkaline environment produced by the corrosion process at the coating/steel interface.…”

“…Swelling pressures in the range of several hundred kgcm*^have been reported for polyamidecured epoxy films when they absorb water (7). Since the osmotic pressure gradient is a function of the water activity of the outside environment, the use of distilled water in the outer cylinder in the present study should facilitate the coating to take up maximal water and the film should stretch to its greatest extent.…”

“…The sign and concentrations of these fixed charges alter substantially when the environment in contact with the coatings change from neutral and acidic to basic (7). Since osmotic pressure is directly related to the concentration of fixed charge in the coatings (7) the alkaline environment at the coating/steel interface is expected to increase the swelling pressure in the coating.…”