Corrosion inhibition effect and adsorption behaviour of nicotinamide derivatives on mild steel in hydrochloric acid solution

Background: A new class of nicotinamide derivatives viz., N-((1H-pyrrol-2-yl)methylene)nicotinamide, N-((methyl(phenyl)amino)methylene)nicotinamide, N-nicotinoylbenzimidothioic acid and N-(4-(methylthio)benzylidene)nicotinamide have been synthesized and their corrosion inhibition effect on mild steel in 0.5 M HCl was investigated by mass loss, Tafel polarization technique and AC impedance measurements. Results: The inhibition efficiency of the inhibitors on mild steel in 0.5 M HCl has been studied based on concentration, time interval and temperature. Potentiodynamic polarization studies showed that all the examined inhibitors suppress both anodic and cathodic process and behave as mixed type of corrosion inhibitors. Conclusions: The adsorption of all the inhibitors was found to obey Langmuir isotherm model. Electrochemical impedance data revealed that polarization resistance (RP) increases and double layer capacitance (Cdl) decreases as the concentration of the inhibitors increases. FTIR, EDX and SEM analyses were performed to study the film persistency of the inhibitors

Experimental and theoretical studies on the corrosion inhibition performance of molecules containing tert-butyl benzyl group on mild steel in acid media

The inhibition by (4-tert-butyl-phenyl)-acetic acid hydrazide (TPAH), 5-(4-tert-butyl-benzyl)-[1,3,4] oxadiazole-2-thiol (TBOT) and 5-(4-tert-butyl-benzyl)-4H-[1,2,4] triazole-3-thiol (TBTT) of mild steel corrosion in 0.5 M HCl was investigated using gravimetric and electrochemical techniques. These inhibitors acted more effectively at higher concentration and at lower temperature; among these TBTT being the most efficient inhibitor, which showed highest efficiency of 92.6% at 303 K and 4.8 mM concentration. Adsorption of TPAH followed Freundlich isotherm, whereas TBOT and TBTT followed Langmuir isotherm. Energy of activation for corrosion increased after the addition of inhibitors. Free energy of adsorption showed that all the three inhibitors get adsorbed to the mild steel surface by both physical and chemical processes. EIS studies confirmed that all the inhibitors offered higher charge transfer resistance to the corrosion current and this led to decreased double-layer capacitance. Polarization studies showed that all inhibitors emerged as mixed type. Surface studies confirmed that the pits caused by corrosion were decreased by protective film of inhibitors. Corelation of experimental data with quantum chemical parameters like ELUMO, energy gap, dipole moment, hardness and softness confirmed the superior performance of TBTT as compared to TPAH and TBOT