Effect of Relative Humidity on the Atmospheric Corrosion of Mild Steel Using the Electrochemical Wet/Dry Method

Abstract

In the present work, corrosion rate W and corrosion potential tow were simultaneously measured as a function of relative humidity RH employing the electrochemical wet and dry method as an accelelated atmospheric corrosion method. The W versus (vs.) RH curve is classified into .three regions, namely, the first W plateau region, the second region of the linear relationship between logarithmic W and RH, finally, followed by an abrupt decay region. Based upon the atmospheric corrosion mechanism of mild steel, we introduced another diagram of vs. RH which is divided into three regions. In the first region, the corrosion scales are composed of single lepidocrocite-phase ; in the second region, -phase coexists with magnetite-phase in the scales and finally the oxide scales change into a single Fe304-phase in the third region. The three distinct regions of both representations share almost each other, which is validated by FT-IR (Fourier transform infra-red) analysis and surface observation. Both representations prove to be convenient and complementary for surveying the spectrum of the atmospheric corrosion of mild steel.