Understanding the inhomogeneous structure of organic coatings: causes and consequences on corrosion protection

A systematic study by Dr. J E O Mayne’s group at Cambridge University in the 1960’s and 70’s revealed intrinsic inhomogeneity in the structure of organic coatings. It was also found that the mechanism of ionic conduction through randomly distributed areas differed from one area of coating to another; there being isolated areas of relatively high permittivity (D type areas) where the ionic conductivity followed that of the ionic strength of the electrolyte. The reverse was true in the remainder of the coating, classified as I type. This had great significance to the corrosion protection afforded by varnish coatings, with corrosion being initiated at D areas. The aim of this work is to review the current knowledge of D areas with the aim to understand how they are formed and how they can be eliminated. Recent study on statistical modelling of D areas in organic coating will also be discussed.