Inhibition of synthesized mannich bases on mild steel corrosion in acid medium

Abstract

Mild steel corrosion is one of the major issues in many chemical industries because of increasing usage of mild steel and inorganic acids in chemical industries. One of the best methods to control mild steel corrosion is using organic compounds as inhibitors. In the present investigation three mannich bases, namely aminocyclohexane-N -methyl urea (ACMU), aminocyclohexane-N -methyl acetamide (ACMAA) and aminocyclohexane-N -methyl acetone (ACMA) were synthesized, characterized using FT-IR, H1NMR and C13NMR spectra and these were tested as corrosion inhibitor for mild steel in 1 N HCl and 1 N H2SO4 solutions using weight loss, potentiodynamic polarization and AC impedance techniques over the temperature range of 303-333K. The inhibition efficiency was increased with increase in concentration of inhibitor and time in both the environments. Adsorption mechanism of these inhibitors was combination of physisorption and chemisorption. Adsorption of these inhibitors follows Langmuir and Temkin adsorption isotherms. Adsorption process is endothermic in 1 N HCl environment and exothermic in 1 N H2SO4 environment. The FT-IR spectral values showed that nitrogen and oxygen atoms present in inhibitors involved in the adsorption process. SEM analysis showed that inhibitors adsorbed on mild steel surface to protect mild steel from corrosion. Among the three mannich bases ACMU exhibited maximum inhibition efficiency for mild steel in 1 N HCl and 1 N H2SO4 environment. Among the two environments, mannich bases exhibited better inhibition efficiency for mild steel in 1 N HCl environment at higher temperature. The order of inhibition efficiency offered by the mannich bases in both environments are found to follow the order ACMU (HCl) gt ACMAA (HCl) gt ACMA (HCl) gt ACMU (H2SO4) gt ACMAA (H2SO4) gt ACMA (H2SO4). The highest inhibition efficiency reported in this thesis was 98 % for the ACMU (leading others by 6 %) in HCl environment. A suitable mechanism of corrosion inhibition is proposed, which corroborates all the above experimental res