## 1 Introduction  
During the recent years, steel has become one of the most widely used alloys in the sectors of railways and road constructions, as well as in buildings and infrastructures. Steel skeletons are employed for the fabrication of several structures such as bridges, skyscrapers, stadiums and airports [1]. In addition, iron alloys are commonly used in medical, military and aerospace applications because they exhibit enhanced mechanical and tensile strength together with their improved conductivity and ductility properties [2]. Among iron alloys, carbon steel is employed as a construction material for pipeline transport production and processing related industries [2; 3; 4]. The reason is that carbon steel exhibits enhanced mechanical strength and low cost. Steel is assumed to be carbon steel when carbon is the major constituent apart from iron and the carbon content is below wt.% 2.40 [5]. Based on the amount of carbon, three major types of carbon steel exist: low (mild) carbon steel (wt.% 0.04-0.30), medium carbon steel (wt.% 0.31-0.60) and high carbon steel (wt.% 0.61-2.40). The increase in carbon percentage results in an increase in hardness and a decrease in ductility [6]. The difference between carbon steel and black steel is that black steel is fabricated from nongalvanized steel, whereas carbon steel needs galvanization because of its susceptibility to corrosion. Black steel is important in applications where there is no need for galvanized steel. Black steel pipes are seamless, uncoated and widely used for transporting either gas or water for commercial or residential buildings because these pipes are better fire retardants than galvanized pipes and due to the high strength of the steel [4]. Despite the fact that the aforementioned forms of steel have several applications, these types of steel exhibit poor performance in aggressive corrosive environments [7; 8]; their exposure to these types of environments give rise to corrosion processes [9]. Therefore, the identification and development of new groups of protective compounds able to attenuate this problem are required. Several methods have been employed for the metal corrosion protection such as application of coatings [4; 10; 11] and the use of corrosion inhibitors [8; 12; 13]; one of the most widespread methods against corrosion is the use of organic compounds. Organic inhibitors are very efficient for mild steel, due to the fact that they contain atoms such as sulfur, oxygen and nitrogen that result in the enhanced adsorption onto a metal surface [14]. Furthermore, the presence of aromatic and aliphatic functional groups with double and triple bonds also plays a crucial role in their improved metal surface adsorption [15]. Thus, the organic molecule adsorption onto the steel surface results in the isolation of the metal alloy from the aggressive environment improving the metal corrosion resistance. The motivation for this work is the assessment of the corrosion behavior of mild steel in the presence of potential corrosion inhibitor 5-amino-1,3,4-thiadiazole-2-thiol (ATT) loaded into hybrid material. Taking into account our previous studies based on mild steel [16] together with the additional experiments that were conducted on the protection of mild steel related to the corrosion protection effectiveness of potential inhibitor ATT loaded in cerium-titanium oxide (Ce\({}_{x}\)Ti\({}_{y}\)O\({}_{z}\)) nanocontainers, the main aim of this study is to present the role of corrosion inhibitors either in free form or loaded into containers and their potential effect to the corrosion protection mechanisms of steel. In the literature, studies have been conducted on the evaluation of ATT as a corrosion inhibitor on several metal alloys. According to the work of [PERSON] et al. [17], the interaction of ATT with silver panels results in the formation of ATT monolayers onto the silver surface. The type of monolayer depends on the pH of the electrolytic solution. The group of [PERSON] al.