Corrosion inhibitive properties of some new isatin derivatives on corrosion of N80 steel in 15% HCl

Background: The inhibition effect of two synthesized isatin compounds, namely 1- morpholinomethyl-3 (1-N-dithiooxamide)iminoisatin [MMTOI] and 1-diphenylaminomethyl-3(1-N-dithiooxamide)iminoisatin [PAMTOI], on the corrosion inhibition of N80 steel in 15% HCl solution was studied by polarization, alternating current impedance (electrochemical impedance spectroscopy), and weight loss measurements. The surface examination was carried out by scanning electron microscopy and Fourier transform infrared spectroscopy. Results: The compounds [PAMTOI] and [MMTOI] show the maximum of 91.2% and 84.3% inhibition efficiency, respectively, at 200-ppm concentration. Polarization curves revealed that the used inhibitors represent mixed-type inhibitors. Adsorption of used inhibitors led to a reduction in the double-layer capacitance and an increase in the charge transfer resistance. Conclusions: Results show that both inhibitors were effective inhibitors and their inhibition efficiency was significantly increased with increasing concentration. Adsorption of both compounds obeys the Langmuir adsorption isotherm.