Some New Thiadiazole Derivatives as Corrosion Inhibitors for 1018 Carbon Steel Dissolution in Sodium Chloride Solution

摘要

Three new thiadiazole derivatives (TDADs), namely, (I) N-[4-phenyl-5-(p-tolylimino)-4,5-dihydro- 1,3,4-thiadiazole-2-yl] benzamide, (II) 2-acetyl-4-phenyl-5-(p-tolylimino)-4,5-dihydro-1,3,4-thiadiazole,and (III) Ethyl-4-phenyl-5-(p-tolylimino)-4,5-dihydro-1,3,4-thiadiazole-2-carboxylate, have beensynthesized and used as additives to protect grade 1018 carbon steel from corrosion in naturally aerated0.5 M NaCl solution (~ 3% by wt.). The techniques adopted include open circuit potential (OCP),potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) complemented bysurface examination via scanning electron microscope (SEM). It was found that the quasi-steady stateOCP value shifts positively with increasing TDAD concentration. Polarization technique showed thatTDADs (I揑II) are anodic-type inhibitors, where the corrosion rate decreases with increasing theinhibitor concentration or decreasing temperature. At any given conditions, the protection efficiencyincreases in the order III > II > I as confirmed by SEM observation. Impedance parameters (Rt and Cdl)indicate the formation of protective films via the adsorption of inhibitor molecules on the metal surface.Thermodynamic parameters of the corrosion and adsorption processes indicate generally that adsorptionof these compounds on 1018 carbon steel surface occurs spontaneously through both electrostatic (ionic)and chemisorption (molecular) mechanism following Langmuir adsorption isotherm.