Inhibitive Behavior Of Pyridine-2-Thiol On Mild Steel In HCI Acidic Media: Influence Of Hydrodynamic Condition

摘要

In the case of corrosion prevention, the word "inhibitor" may be the first expression which passes through one's mind. It is believed that the molecular structure of inhibitors play an important role in determination of their adsorption mechanism on metallic surfaces. Nevertheless, the environmental conditions would surely affect the overall film formation mechanisms. Generally, the inhibitive performance of these types of materials is constituted of two dependent steps; transfer of the inhibitor molecules from bulk aqueous media to double-layer and then their adsorption onto the corroding surface, resulting in creation of a protective layer. Therefore, the hydrodynamic condition can be a vital factor in inhibitor performance by facilitating the molecular transfer process from bulk to surface (positive effect) and inducing a surface shear stress (negative effect). Consequently, the aim of this study is devoted to investigate the influence of various hydrodynamic conditions on inhibitive behavior of pyridine-2-thiol on mild steel in 0.1 M HCI. It should be claimed that almost no similar research has been conducted on mild steels in HCI hydrodynamic solution. In the present work, the electrochemical behavior of CK15 mild steel samples is investigated by using open circuit potential (OCP), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The corrosion attack morphologies of the corroded samples at various environmental conditions were examined by utilizing the optical microscopy. The hydrodynamic state was acquired by employing a rotating disc electrode at fixed rotation speeds of 0,250, 500,750 and 1000 rpm. Considering the calculated Reynolds numbers, it is noticeable that at these speeds, the fluid flow at surface is almost laminar. The OCP results show that by increasing the rotation speed, the corrosion potential (E_(corr)) shifts toward more positive values. Also, in blank solution the potentiodynamic measurements reveals an interesting behavior, the corrosion current density (i_(corr)) decreases as the rotation speed increases while a contrary behavior is observed in presence of inhibitor. In addition, the EIS recordings at E_(corr) exhibit results which are in agreement with potentiodynamic ones. Performing EIS test at +100 mV overpotential with respect to E_(corr) depicts that the total impedance intensely decreases by increasing in rotation speeds, especially in inhibited solution. At -100 mV overpotential, the total impedance has a larger value in comparison with corresponding value in anodic overpotential, considering that the Warburg element is only obvious in inhibited solution at hydrodynamic state. Finally, the corrosion attack morphologies consistently confirm the previous results obtained from the electrochemical techniques.