Evaluation of Electrochemical Techniques for Monitoring of Atmospheric Corrosion Phenomena

Abstract

A review is presented of past and present efforts to use electrochemical techniques to evaluate basic phenomena of atmospheric corrosion, measure time of wetness, and perform corrosion-rate measurements in outdoor exposure. This is followed by a summary of recent work carried out in the author's laboratory. Time-of-wetness measurements have been carried out continuously over a three-year period at the same location using copper/steel and copper/zinc sensors. An analysis of the monthly distribution of relative humidity and corrosion rates determined with the same sensors has resulted in correlations between them. Weight-loss measurements under thin layers of electrolytes that are drying out at RH < 100 percent have shown that, in most cases, corrosion rates are much higher under these conditions than in bulk solutions. Electrochemical measurements carried out under identical conditions show the continuous increase of corrosion rates during the drying period. A comparison of corrosion rates determined by weight loss and electrochemical techniques under thin layers of electrolytes indicates that the electrochemical data underestimate the true corrosion rates. The determination of cell factors based on weight-loss data is one approach for using the electrochemical technique in a more quantitative manner.