Black tea extract as a corrosion inhibitor for X70 steel in chloride media: Experimental and theoretical investigation

The increased emphasis on sustainability and environmental concerns in metal corrosion is paramount, often achieved through the use of inhibitors, especially by utilizing plant extracts, which is a promising approach due to their availability and ease of extraction. Herein, for the first time, the effectiveness of the black tea inhibitor as a sustainable potent corrosion inhibitor for X70 steel under 3.5 wt% NaCl and 1 M HCl aggressive test solutions is explored, from both experimental and theoretical insights. The corrosion morphology was investigated using atomic force microscopy (AFM), which confirmed the presence of a protective adsorbed layer on the X70 steel surface. By aiding polarization examinations, electrochemical impedance spectroscopy (EIS), and electrochemical current noise analyses, the anti-corrosion capability and the mechanism of the proposed inhibitor were evaluated. The polarization analysis results revealed that in the presence of 200 ppm black tea extract inhibitor, the rates of both cathodic and anodic reactions were significantly decreased, resulting in a reduction in corrosion rate from 0.01 to 0.003 mg/s in NaCl solution and from 0.22 to 0.02 mg/s in HCl medium. Regarding the EIS findings, the most significant inhibition efficiency, approximately 66 %, was achieved after introducing just 200 ppm of black tea extract under the explored corrosive media. Additionally, the density functional theory (DFT) was employed to investigate the electronic properties of the molecules responsible for the inhibitory performance of the as-made black tea inhibitor. Furthermore, a Monte Carlo (MC) simulation and the molecular electrostatic potential (MESP) surface were employed to further comprehend the adsorption mechanism of these molecules on Fe(110) surfaces. The acquired outcomes manifested that the black tea extract possesses significant corrosion inhibition potential for the X70 steel plates.