Corrosion Studies of Mild Steel in Organic Acid/Chloride Media

This study investigated the corrosion behaviour of mild steel immersed in 0.5 M organic acid media and in 90 %/10 % 0.5 M organic acid media/ 3.5 % NaCl by surface observation and weight loss technique. In all the solutions (0.5 M organic acid and the organic acid  containing 3.5 % NaCl), mild steel corroded more in acetic acid compared to other solutions, while NaCl was lowest. The corrosion rate of mild steel immersed in 90 % organic acid contaminated with 10 % of 3.5 % NaCl was lower than that found when the steel samples were immersed in 100 % organic acid. It can be suggested that an increase in pH of organic acid media as NaCl was added to the organic acids increased the passivity of the mild steel in the solutions. Scanning electron microscope (SEM) was used to examine and characterize the mild steel surface before and after its immersion in the respective media. The elemental composition on the corroded surface of mild steel was detected with the SEM coupled with electron dispersive spectroscopy (EDS). The SEM and the physical observation results showed corrosion products, which were confirmed to be oxide films on the surface of mild steel studied in 100 % organic acid solutions. Meanwhile, morphology of the mild steel after corrosion in organic acids containing NaCl showed that corrosion products were the protective oxide films. The oxides of Fe, Mn, Na, and Si were mostly detected on the surface of mild steel after corrosion.