The atmospheric corrosion of iron and steel

Most characteristic for the atmospheric corrosion is the alternating wetting and drying of the corroding metal surface. By this, the atmospheric corrosion is distinctly different from the corrosion of immersed electrodes. It has been shown that the beneficial effect of alloying elements like Cu is restricted to such changing corrosion conditions (1m3) and therefore it is quite important to analyze the corrosion behaviour of an atmospherically corroding metal surface as a function of time during several dry-wet-dry transitions. As the electrolyte layer may be very thin during these transitions, non-electrochemical techniques have to be used to measure corrosion rates and corrosion potentials as a function of time. The rate of the anodic metal dissolution has been measured by a magnetic technique (3,4), the rate of the O 2 -reduction gasvolumetrically (3,4), and the corrosion potential using a Kelvin probe (5,6). The latter allows to measure corrosion potentials without touching the surface under investigation. All techniques have been described in detail elsewhere (3m6).