A Study on Aqueous Corrosion of Metals

Abstract

The measurement of polarization in metals in electrolytic solutions is an effective method of determining the corrosion rate and its mechanism because the local action of the cell on the metal surface, which is one of the typical electrochemical phenomena, is considered to be the causative of aqueous corrosion of metals in general. To this general statement, however, there are limitations as follows:(1) That even with perfect polarization of the metal its active sites on the surface remain constant.(2) That the mechanism of the anodic and the cathodic reactions remain as it is for a wide range of polarization.Through experiments of examining iron pieces of different species, for their contamination at 40°C, in aqueous solution of sulfuric acid, as it was or in the same solution with ferrous ion, the parameters of hydrogen electrode reactions on the metal cathode, their Tafel coefficient, and their exchange current density were obtained as well as their static potential and corrosion current density. The hysteresis on the potential vs. current density curve with increasing and decreasing current was observed in all the sample species while the potential vs. log current density curve made a straight line when the surface of the electrode was sufficiently stabilized by electrolysis at high current density in pure solution of the acid.The report of the experiments is concluded with demonstration to prove that the measurement of polarization is still an effective method of corrosion test.