# The Use of Some Natural Extracts as Environmentally Friendly Carbon Steel Corrosion Inhibitors
## 1 Introduction
Compared to inorganic inhibitors, organic inhibitors generally exhibit lower toxicity, can be applied in smaller amounts, and possess better film-forming properties. Organic compounds that contain a high quantity of nitrogen, oxygen, sulfur atoms, and \(\pi\) electrons are known to be very effective corrosion inhibitors in aggressive environments like acidic or alkaline conditions. They adhere to the metal surface, providing excellent protection against corrosion and significantly reducing the corrosion rate of the metal [11]. The use of inhibitors has proven to be a cost-effective and easily applicable option, particularly in cases where the modification of aggressive media does not affect the industrial uses of the metallic substrate or the process that employs the liquid to which the inhibitor is added [2; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22]. It is, therefore, of paramount importance to select appropriate and efficient inhibitors. In recent years, the use of green inhibitors has gained increased interest, as they are a less toxic and more environmentally friendly alternative. The use of several natural extracts (garlic peel, _Citrus aurantium_ leaf, apricot, _Lemon verbena_ leaves, lemon balm extracts, Ginko leaf, _Cyclotrichium niveum_, _Cinchona Ila_, chamomile flower, coconut coir) as inhibitors of steel corrosion was investigated. The current studies focus on investigating the inhibition of the corrosion process by these extracts mainly in acidic media, for both short and long periods. Higher efficiencies were observed in longer periods (24 h) for most extracts, with values up to 95% for _Lemon verbena_ extracts. For a garlic peel extract, high efficiency was observed in acidic media with a short immersion time and in basic media with longer immersion periods. In the case of natural inhibitors, the active biomolecules that enable the inhibition effects are difficult to be determined, as these extracts have a complex composition and include various similar compounds from the same class. For instance, for the inhibitors extracted from plants from the _Citrus_ species, substances such as alpha terpineol, linalool, linalyl acetate, and monoter hydrocarbons were indicated as the main corrosion inhibitors. The reduction in the corrosion rate is dependent on the concentration of the plant extract, with higher efficiencies being achieved at higher concentrations [2; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22]. Determining the effectiveness of various inhibitor compounds in reducing the corrosion of carbon steel is one of the topics of a number of published research studies. A number of factors, such as availability, affordability, nontoxicity, and higher performance when compared to their counterparts produced from unnatural sources, make natural and organic extracted materials an intriguing topic of study [6; 9]. _The purpose of this work was to investigate the effect of several environmentally friendly extracts obtained from natural compounds, such as Levisticum officinal and waste from Citrus x clementine--more precisely, the peel of these fruits--on the corrosion of carbon steel in a 3.5% NaCl aggressive medium._