# The Use of Some Natural Extracts as Environmentally Friendly Carbon Steel Corrosion Inhibitors
## 1 Introduction  
Because of their superior physicochemical, process, and service qualities, metallic materials form the foundation of contemporary industry and are used extensively in the transportation, petrochemical, maritime, and construction sectors. Carbon steel is one of the most significant and versatile metallic materials used in modern manufacturing. High mechanical strength, good workability, weldability, and affordability, together with useful chemical properties, are just a few of the many advantages of carbon steel [1, 2, 3, 4, 5, 6]. Carbon steels play an essential role in various industries such as the oil, gas, marine, and automotive ones [6, 7]. Although it has advantages in terms of mechanical properties [6], carbon steel is an active chemical that is prone to corrosion when its surface is exposed to various aggressive environments such as acids, alkalis, salts, water, and air, due to its propensity to be penetrated by liquid contaminants that react with the metal [5, 7]. Protecting the surfaces of metals, particularly carbon steel, from corrosion has become increasingly crucial in material science and requires the use of anti-corrosion protection methods, which further increases the costs of using steel-based substrates. Among the techniques employed for the protection of metals against corrosion, one can mention cathodic protection, the application of coatings, and the use of organic or inorganic inhibitors [1, 2, 3, 4, 7]. The application of anti-corrosion coatings has emerged as one of the most effective strategies for shielding carbon steels from corrosive conditions. Surface modification methods are crucial for developing protective layers that efficiently safeguard metal surfacesfrom corrosion. However, after a brief period of protection, the coatings gradually deteriorate due to their direct exposure to the corrosive medium, which ultimately leads to the corrosion of steel. Thus, conventional coatings need to be reapplied on a regular basis; moreover, another drawback of using coatings derives from the fact that some of the coatings may pose environmental hazards. To enhance the durability of these coatings and offer carbon steels extended protection, researchers are consistently investigating ways to minimize both the area and the duration of contact between corrosive substances and coatings [7; 8]. Carbon steel is corroded and destroyed when solutions are used in contact with steel substrates, which also accelerates the deterioration of metallic components, machinery, and structures, ultimately resulting in increased production costs, as well as potential safety hazards and negative environmental impacts. Another very popular method for shielding a metal from corrosive attacks is the use of inhibitor compounds that guard against corrosion by adhering to the surface of the metal. The addition of inhibitors, which can be either natural or synthetic compounds, in low concentrations to certain environments can slow corrosion and ensure an effective protection at a low expense. These inhibitors improve anodic or cathodic polarization, enhance the electrical resistance of metal surfaces, and reduce the movement or diffusion of ions towards these surfaces. Among the various corrosion inhibitors, organic substances such as Schiff bases, ionic liquids, and imidazole compounds are frequently employed for corrosion prevention. However, their significant toxicity and persistent degradation contribute to environmental pollution. To address these challenges, innovative, eco-friendly, and water-soluble corrosion inhibitors have been introduced [6; 9; 10]. Corrosion inhibitors can be classified based on their composition into two main types: inorganic inhibitors, which include sulfate, chromate, phosphate, molybdate, and rare-earth metal salts, and organic inhibitors, such as amide inhibitors, imidazoline inhibitors, thiourea inhibitors, amino acid inhibitors, and triazole inhibitors.