###### Abstract  
A corrosion inhibitor was widely used to improve corrosion resistance of steel bar in reinforcement concrete structure. A kind of multi-component corrosion inhibitor, which is composed of organic and inorganic substances, was developed in this research. This corrosion inhibitor was comparatively studied with various other inhibitors by using open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) methods. The results show that the OCP values and charge transfer resistance (calculated by EIS curves) of the multi-component corrosion inhibitor remain, respectively, as high as \(-0.45\) V and \(932.19\) k\(\Omega\)-cm\({}^{-2}\) after 60 days immersion, which are significantly better than other groups. Wide passivation interval and various peaks in cyclic voltammograms (CV) were applied to analyze the mechanism of adsorption (organic substance) and oxidation-reduction reactions (inorganic substance). The functional groups -OH in triethanolamine (TEA) and tri-isopropanolamine (TIPA) bond to the steel bar surface quickly, behaving as an adsorbent of organic substance in early age. An additional protective precipitate related to the reactions of Fe\({}^{3+}\) was formed by inorganic substances (Fe\({}_{2}\)(MoO\({}_{4}\))\({}_{3}\) and FePO\({}_{4}\)), which is consistent with the EIS results and equivalent electrochemical circuits. As an eco-friendly substitute, multi-component corrosion inhibitors possess similar or even better protecting effects on steel bars in comparison to calcium nitrite. In addition, the concept of a \"multi-functional protective film\" was proposed, providing a new insight to achieve modified anti-corrosion capacity of inhibitors. corrosion resistance; corrosion inhibitor; chloride; cyclic voltammetry +
Footnote †: journal: Applied Sciences  
Nitrites can be hydrolyzed into NO\({}^{2-}\), which then adhere to passive film, promoting the formation process of passive film [13]. Yet, the dissolved NO\({}^{2-}\) exhibits potential toxicity and environmental issues, thus delaying the utilization of nitrites [12]. Searching for a safe and environmentally friendly corrosion inhibitor is necessary for corrosion inhibition [10]. Organic inhibitors, such as amino-based and imidazoline substance inhibitors, are utilized to mitigate steel bar corrosion in simulated concrete pore solutions [14], based on their great adsorption abilities. In the case of amines, such as TEA and TIPA, adsorption occurs in the form of covalent bonds. It is evident in the functional group (Figure 1), where the polar functional group -OH shares its lone pair of electrons with Fe\({}^{2+}\) to form the covalent bond. The formation velocity and the long-term stability of the protective film are among the most important indicators to evaluate the efficiency of inhibitors. However, organic substances can disintegrate the form of the steel bar surface due to the desorption effect, leading to a lack of long-term stability [16; 17]. On the other hand, the inorganic inhibitors become non-effective in high alkaline conditions because the formation velocity of inorganic inhibitors on steel bars is lower than the corrosion reaction introduced by chloride. In addition, the microstructure of passive film can be changed, owing to the pH change or chloride attack [18]. Consequently, even though corrosion inhibitors were equipped, pitting corrosion can still occur in high chloride contamination [19]. The facts proved that using organic or inorganic inhibitors alone on steel bars is not sufficient for mitigating corrosion. A reasonable choice of experimental method is a significant factor for exploring the reaction mechanism of inhibitors on a passive film. Studies for corrosion inhibitors subjected to chloride attack have been typically summarized by means of various electrochemical methods, e.g., electrochemical impedance spectroscopy (EIS) and polarization curve or cyclic voltammetry (CV) [20].