Organic Corrosion Inhibitors. Группа авторов

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Figure 4.1 A basic classification of the corrosion inhibitors.

      4.2.1.1 Azoles

Azoles are a class of five‐membered aromatic heterocyclic compounds containing at least one nitrogen atom and have an aromatic structure. They are named according to the number of nitrogen atoms in the aromatic ring and their position. In addition, there are other heteroatom‐containing azo compounds [11–13] such as O and S in their structure, and the main structures are shown in the Figure 4.2. The aromatic structures of azo compounds and the heteroatoms they contain cause an increase in polarity of these compounds due to electron delocalization in compounds, which make these compounds very useful materials for inhibition of corrosion. Srivastava et al. [14] have recently reported the efficiency of a benzo[d]imidazole derivative green corrosion inhibitor has a very good inhibition capability (>98%) on the carbon steel at optimum dosage conditions and continued the strong inhibition adsorption (>95%) even at 333 K. The inhibition ability of pyridine thiazole compound on copper corrosion in acidic medium has been investigated by a series of experiments techniques (EIS, SEM, AFM), and shown by the EIS technique that the maximum inhibition capacity is reached at 94% at 1 mM concentration [15]. Recently, the inhibition capabilities of a series of imidazole derivatives on the corrosion of mild steel in acidic conditions have been investigated by electrochemical, thermodynamic, and also computational techniques; one of the most important results of this investigation is that the imidazole derivatives provide the anodic protection of mild steel and promote cathodic hydrogen reactions as well [16]. Besides, phenanthroimidazole derivatives [17] and bis‐benzothiazoles derivatives [18] have a very high inhibitory potency for mild steel and showed a mixed type inhibitor capacity by TAFEL diagrams, but the priority for the cathode.

Figure 4.2 The chemical structures of the main azole compounds.

      4.2.1.2 Azepines

Azepines with seven‐membered as a subgroup of heterocyclic organic compounds and their effects are generally well known in medicinal fields [19] (Figure 4.3). Potential use of waste drugs as corrosion inhibitors has received increasing attention in recent years. In 2009, Arslan et al. suggested that drug molecules with quantum chemical methods can show inhibitory properties for mild steel in an acidic environment [20]. It has also been reported that different groups of heterocyclic compounds used in many medical fields are promising as environmentally friendly corrosion inhibitors [21]. For a series of triazoloazepine derivatives, the corrosion and protection constants on steel 45 with a concentration of 1 M have been evaluated and suggested that Cl atom substitutions make the main structure more potent against corrosion among all substituents (H, F, Cl, I, CH₃O, and CH₃ on different position of the molecule) [22]. In addition, the inhibitory characteristics of acetonitrile and secondary amines containing triazoloazepine ring for carbon steel corrosion in HCl and hydrogen sulfate have been investigated and reported that the reciprocal effects of triazoloazepine and p‐tolyl groups in the secondary amines provide a maximum synergetic effect during inhibition of steel corrosion in the HCl [23]. In the past, the corrosion inhibition properties of the carbamazepine unused drug on steel in different solvent environments have been examined, and the inhibition efficiency of the carbamazepine has been determined as 85% [24]. Besides, carbamazepine has effective role in both anodic processes and cathodic hydrogen evaluation, and thus the amount of carbamazepine does not affect the corrosion potency [24].

Figure 4.3 The chemical structures of the main azepine compounds.

      4.2.1.3 Pyridine and Azines

Pyridine is a heterocyclic organic compound shown by the simple structural formula C₅H₅N and is widely used in many production areas due to its aromatic structure [25] (Figure 4.4). The lone pair of the nitrogen atom in the structure has sp² hybridization but does not contribute to the aromaticity of the compound as it lies outside the plane of the ring like sigma bonds and facilitates bond formation with an external system through an electrophilic attack. On the other hand, Azines are an organic compound group with the functional group RR′C = N‐N = CRR′, obtained by the condensation of hydrazine with ketones and aldehydes [26]. In the past, many papers have been reported on pyridine and its derivatives and suggested that they have sufficient potency for inhibition of iron, aluminum, carbon steel, N80 steel, mild steel, and zinc in different acidic media СКАЧАТЬ