Abstract
The corrosion behaviour and mechanism for mild steel in hydrochloric acid solutions was studied by chemical ( hydrogen evolution, HE & mass loss, ML) and electrochemical ( electrochemical impedance spectroscopy & potentiodynamic polarization) methods at 25 degrees C. The chemical results revealed that mild steel corrodes in HCl solutions with a rection constant of 0.56 and the corrosion rate increases with the increase in acid concentration. Microstructural studies for mild steel after immersion in HCl solutions of different concentrations showed general and pitting corrosion and the latter becomes more pronounced at higher level of HCl concentration. Accordingly, it was found that R-ct value decreases while both C-dl and i(corr). values increase with increasing HCl concentration. PDP results revealed that the steel dissolution is anodically controlled. Estimation of the ratio Z/v(s) from PDP data indicated that mild steel dissolution occurs via multistep mechanism. This mechanism involves two steps each of them is characterized by one electron release and one of them is the rate determining step. The rate determining step may involve adsorbed [FeOH](ads) and/or [FeClOH](ads)(-) groups.