EXPERIMENTAL AND COMPUTATIONAL STUDIES ON THE CORROSION INHIBITON OF MILD STEEL BY HYDRAZONES IN 2M HCl.

The title compounds N-benzyl piperidine -4- one phenyl hydrazone (BPPH) and N-benzyl piperidine -4-one hydrazone (BPH) were used to control mild steel corrosion in 2M HCl solutions at different temperatures (303K-333K). The corrosion inhibitory effect of the compounds has been investigated by weight loss study, electrochemical methods, SEM and quantum chemical studies. The weight loss studies were conducted at four different temperatures such as 303K, 313K, 323K and 333K for various concentrations of (0, 25,50, 100, 200 and 300 ppm) for 1h and 2h duration. The study showed that inhibition efficiency increases with increase of BPPH and BPH concentration and decreases with increase of temperature. It was found that inhibition was due to adsorption of BPPH and BPH on the MS surface obeying Temkin’s adsorption isotherm. Electrochemical data for corrosion processes such as corrosion potential(Ecorr), corrosion current(icorr) and Tafel slopes (ba and bc) were determined using Tafel plot, which showed that increase in concentration of BPPH and BPH 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 BPPH and BPH in acid medium. Quantum chemical studies illustrated that the corrosion inhibition efficiency of BPPH and BPH is due to lone pair of electrons of two nitrogen in the hydrazone moiety ? electron of phenyl ring and ring nitrogen