Corrosion Inhibition of Mild Steel in Hydrochloric Acid Medium by 1-Methyl-3-Ethyl-2, 6-Diphenyl Piperidin-4-One Oxime

摘要

The corrosion inhibitory effect of 1-methyl-3-ethyl-2, 6-diphenyl piperidin-4-one oxime (PO) against mild steel (MS) in 1 M hydrochloric acid medium has been investigated by weight loss study, electrochemical methods, SEM, and theoretical studies. The weight loss studies were conducted at four different temperatures such as 30, 40, 50, and 60 °C for various concentrations (0, 25, 50, 100, 150, 200, 250, 300, 400 and 500 ppm) over 2 h duration. The study showed that inhibition efficiency (IE) increases with increase of PO concentration and decreases with increase of temperature. It was found that inhibition was due to adsorption of PO on the MS surface obeying Temkin's adsorption isotherm. The calculated values of free energy of adsorption (△G_(ads)) support physisorption mechanism. Electrochemical data for corrosion processes such as corrosion potential (E_(corr)), corrosion current (i_(corr)), and Tafel slopes (b_a and b_c) were determined using Tafel plot, which showed that increase in concentration of PO decreases corrosion current and behaves as mixed mode inhibitor. AC impedance measurement as determined by Nyquist plot revealed that charge transfer resistance increases with increase of concentration, whereas double layer capacitance decreases with increase of concentration complimenting each other. SEM studies revealed the surface protecting ability of PO in HCl medium. Quantum chemical studies illustrated that the corrosion IE of PO is due to the electrons of phenyl ring.