Corrosion inhibition of extracts from the expired traditional Chinese patent medicines for Q235 carbon steel in hydrochloric acid

Abstract

During the COVID-19 epidemic, traditional Chinese patent medicine played a significant role in treatment and prevention. However, excessive production of medicines will face serious disposal problems once they are expired, and how to achieve safe and efficient utilization of resources becomes another challenge. In this study, the diverse organic components of traditional Chinese patent medicine-YanReQing Granules (YGE) have been extracted and enriched using a low-temperature extraction method, and the main compositions have been analyzed by liquid chromatography-mass spectrometry (LC-MS). The inhibition performance of YGE for Q235 steel in 0.1 mol L−1 HCl solution was evaluated by various methods. The results indicated that the corrosion rate of metal decreased significantly with the addition of YGE, and the corrosion potential shifted positively as the increase of cathodic and anodic Tafel slopes, indicating that the YGE belongs to a mixed type of corrosion inhibitor with the simultaneously inhibition on cathode and anode. The inhibition efficiency of YGE increased gradually with the more additive amounts, and exceeded 99% calculated by the fitting current density in polarization curves. The active ingredients in YGE are mainly composed of hydroxyl and carbon-based aromatic hydrocarbons, which are easily protonated in hydrochloric acid solution and carry a positive charge, and then adsorb at the metal interface electrostatically to form a shielding layer. Moreover, the theoretical calculations have confirmed that the chemical adsorption can be achieved between the polar atoms and metal to enhance the protective layer ultimately.