Method for visualizing under-coating corrosion utilizing pH indicators before visible damage

Abstract

A new method for under-coating corrosion visualization is developed. The method detects corrosion through local pH gradients which are visualized by pH indicators. pH gradients are induced in a setup similar to the one popularized by Devanathan. On the uncoated back side of the metal, the sample is cathodically polarized, generating hydrogen gas through electrolysis. The hydrogen generated, diffuses through the metal sample and oxidizes on the anodically polarized painted side wherever the coating develops a defect causing a decrease in the local pH. The local pH is then used in imaging the location of defects through the use of a pH indicator, before any visible corrosion damage occurs on the coated metal sample.