Study of the Efficiency of the Amino Acid L-Histidine as a Corrosion Inhibitor of 1018 Carbon Steel in Saline Solution Without and with CO2 Saturation

L-histidine was analyzed in this work as a corrosion inhibitor for AISI 1018 carbon steel in chloride solution, without (pH 7) and with carbon dioxide saturation (pH 4). Mass loss methods and electrochemical tests were used. In a medium with pH 4 saturated with CO2, the inhibition efficiency values (IE%) did not reach 34%. For the pH 7 condition, an inhibition efficiency of up to 89% was observed. The values corroborated with the quantum chemistry and Density Functional Theory (DFT) calculations, showing that the histidine molecule is responsible for the excellent inhibition potential. A Fourier transform infrared spectroscopy (FTIR) study and a thermogravimetric study (TGA) of the amino acid were also carried out. The substrate surface was analyzed by scanning electron microscopy and atomic force microscopy.