Corrosion Evaluated by Using Speckle Decorrelation with Potentiodynamic Test of the Corrosion Rate

Abstract

Abstract There are corrosion experiments that require an investigated surface larger than the normal surface permitted by the apparatus specializing in such measurements. There are also corrosive environments in which the classic electrodes used are in danger of damage. Thus, in this article, a test in which the surface is investigated using speckle and the electrodes are all made from graphite, a material that is more resistant to chemical attacks, was imagined. The optical method used to investigate the surface alteration was speckle decorrelation, which has proved to be a sensitive indicator of corrosion. Because the decorrelation speed is obviously influenced by the corrosion rate, the main objective was to find out if there is a relationship between these two quantities in the frame of the speckle measurements. Using the electrochemical procedure of chronopotentiometry, it was found that the speckle decorrelation is sensitive not only to surface alteration due to corrosion but also to some reversible processes that occur in the electrolyte near the sample surface. In the first phase of the tests a solution of NaCl was used in order to have a reference environment known for the results obtained, followed in the next stage by more corrosive solutions that change the environment.