Effect of Azadirachta Indica Oil Extracts of on the Corrosion Inhibition and Passivation of Low Carbon Steel in 2.5 M C6H8O7 Acid Solution

Abstract

The inhibition effect of azadirachta indica (AZI) oil extracts on low carbon steel corrosion and passivation in 2.5 M citric acid (C6H8O7) solution was studied with potentiodynamic polarization technique, coupon measurement, open circuit potential measurement, optical microscopy, macro image analysis and ATF-FTIR spectroscopy. Results showed AZI performed effectively from the lowest to highest concentration with optimal inhibition efficiency 99.55% and 88.88% from potentiodynamic polarization and coupon measurement. However, AZI delayed the subsequent passivation of the carbon steel following metastable pitting activity. The inhibition performance of AZI was determined to independent of time and concentration to large degree with anodic type inhibiting properties. AZI induces thermodynamic stability on the corrosion potential of the carbon steel at lower potentials compared to the control sample with significant potential transients at higher potential values. ATF-FTIR spectroscopy confirmed physisorption and physiochemical interaction of the inhibitor molecules on the steel between wavelengths of 500 cm−1 and 3750 cm−1. At 2850 cm−1 and 2900 cm−1 the spectra peaks from C6H8O7/AZI solution completely disappeared due to strong intermolecular interaction. Macro surface analysis showed severe morphological deterioration of the carbon steel with enlarged macro-pits compared to AZI inhibited surface.