Insight into anti-corrosion mechanism of Dalbergia odorifera leaves extract as a biodegradable inhibitor for X70 steel in sulfuric acid medium

Dalbergia odorifera leaves extract (DOLE) was obtained by soaking, filtering, and freeze-drying with 0.5 M H2SO4 solution as solvent. The corrosion inhibition performance of X70 steel by DOLE was systematically studied by electrochemical research methods, surface morphology test, infrared spectrum test and theoretical calculation. The electrochemical test data show that the addition of DOLE in sulfuric acid medium can vastly reduce the electric double layer capacitance (Cdl) value of the steel/acid interface, improve the charge transfer resistance, and simultaneously retard the cathodic and anodic reactions of X70 steel. The DOLE reaches 400 mg/L, the anti-corrosion efficiency (η) is 96 %. Fourier transform infrared spectroscopy (FTIR) test data show that DOLE contains a large number of hydroxyl groups, carbonyl groups and unsaturated functional groups, and a large number of lone electron pairs can coordinate with the empty d orbital of Fe, which leads to the formation of chemical adsorption of DOLE at X70 steel. The morphology test showed that the corrosion level of X70 steel decreased memorably after adding DOLE. The adsorption model study manifests that the adhere of DOLE at the interface of X70 steel comply with the Langmuir adsorption isotherm. Theoretical calculation demonstrate that DOLE can exhibit high-level inhibition property.