Green inhibitor from Thaumatococcus daniellii Benn for corrosion mitigation of mild steel in 1M HCl

Abstract

Mild steel is widely used for automobile and structural applications, however, mild steel greatly rusts in acidic environment. Applications of corrosion inhibitors and protective coatings as well as cathodic protection are some of the techniques by which corrosion of mild steel is controlled and minimised. Hence, corrosion inhibitory ability of the acetone extract of Thaumatococcus daniellii Benn on mild steel was investigated in acid-induced (1.0 ​M HCl) medium using electrochemical and gravimetric techniques. Surface characteristics of the extract and mild steel were evaluated using Scanning Electron Microscopy (SEM) and Fourier Transform Infrared (FTIR) spectroscopy. The acetone extract sufficiently inhibited the acid-induced corrosion of mild steel. The T. daniellii extract gave inhibition efficiencies of 82% and 50% by potentiodynamic polarisation and weight loss measurements, respectively, at 298 ​K, 3 ​h and 10 ​× ​103 ​ppm of the inhibitor. The inhibition efficiencies obtained from weight loss method increased to 68% at 323 ​K (3 ​h) and 89% at 96 ​h (298 ​K). The inhibitive effects were verified by four adsorption isotherm models (Langmuir, Freundlich, Temkin and El-Awady) and the Freundlich model was the best isotherm model. The SEM micrographs clearly showed the coverage of the metal surface by the extract, thereby reducing corrosion of the metal in acidic medium. The FTIR spectra showed important functional groups present in the corrosion inhibitor. The adsorption of the green inhibitor to the metal surface was found to be physical in nature and the green inhibitor was effective in minimising corrosion of mild steel in 1.0 ​M HCl.