Investigation of the Mechanism for Acetic Acid Corrosion of Mild Steel

摘要

Acetic acid is recognized as an important factor in mild steel corrosion. Like carbonic acid, acetic acid is a weak acid, which partially dissociates as a function of pH and the solution temperature. Stronger than carbonic acid (pKa 4.76 vs. 6.35 at 25°C), acetic acid is the main source of hydrogen ions when the concentration of each acid is the same. According to many studies, acetic acid enhances the corrosion rate of mild steel by accelerating the cathodic reaction. The mechanism of acetic acid reduction at the metal surface is still being debated. When the reduction of the adsorbed acetic acid molecule occurs at the metal surface, the mechanism is called "direct reduction". If the role of acetic acid is to dissociate near the metal surface to provide additional hydrogen ions and the only cathodic reduction is reduction of hydrogen ions, this mechanism is referred to as a "buffering effect". In the present study, electrochemical techniques such as potentiodynamic sweeps and electrochemical impedance spectroscopy were used in order to investigate the effect of acetic acid on the cathodic reaction. It was found that acetic acid affects only the limiting cathodic current, but had no effect on the charge transfer current. The charge transfer current is found to respond to a change of pH. It was concluded that the buffering effect was proven correct.