ABSTRACT

The Electrochemical Noise Method (ENM) was used to investigate the protection afforded by coatings to steel and aluminium. This method uses the tiny voltage and current fluctuations emitted naturally by materials in a conducting environment. From these the parameter Resistance Noise (Rn ) is calculated. Rn has been found to relate to general corrosion rates of metal. Previous work on coatings has shown Rn to be approximately equivalent to the low frequency impedance of the coating/metal system. ENM affords a non-intrusive alternative to the more standard d.c. resistance method to assess coating performance. Results for two waterborne coatings on steel and aluminium are presented. The electrochemical noise values were similar to the d.c. resistance values for the higher resistance coating, with differences being attributable to the lower sensitivity of the noise equipment at high resistances. The less protective film gave higher Rn than d.c. values; the former related better to observed protection.

Application of the noise method for evaluating detached coatings was investigated as it allows variation of temperature and external solution to be studied which are established methods for accelerating coating degradation. Results show ENM to be a promising method for continuous monitoring, assisting formulation (screening paints) in the laboratory, for quality control purposes and investigating degradation mechanisms.