Corrosion inhibition behavior and theoretical study on carbon steel in H₂SO₄ by Schizochytrium extract

This study utilized Schizochytrium extract (SE) to explore its protective effect on carbon steel in a 0.5 mol/L H2SO4 solution. The main functional groups of SE were investigated by Fourier infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS). The following conclusions were drawn from electrochemical tests: A corrosion inhibition efficiency of 88.7% was achieved when 1000 mg/L SE was added to a 0.5 mol/L H2SO4 solution. The corrosion inhibition efficiency of SE increased with the increase in corrosion inhibitor concentration but decreased with the increase in temperature. From the polarization curves, the primary function of SE is to prevent metal dissolution at the anode. The morphology of the corroded steel surface was investigated using atomic force microscopy (AFM) and scanning electron microscopy (SEM) techniques, and a smoother metal surface was observed when SE was added to the H2SO4 solution. Parameters such as dipole moments, Mullikan charges, equivalent surfaces (ESP) and binding energies of the four constituent molecules present in SE were calculated using quantum chemical calculations (QC) and molecular dynamics simulations (MS). It was found that the functional groups that play the role of adsorption are mainly carboxyl groups. In addition, Langmuir adsorption isotherms showed that the extracts could adhere to the metal surface and form a long-lasting protective film, thus effectively inhibiting corrosion.