| WEN Jiaxin.Corrosion Inhibition Effect of Imidazol-4-methylimine Thiourea for Carbon Steel in Sulfuric Acid Medium[J],53(6):123-132 |
| Corrosion Inhibition Effect of Imidazol-4-methylimine Thiourea for Carbon Steel in Sulfuric Acid Medium |
| Received:March 01, 2023 Revised:June 14, 2023 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2024.06.011 |
| KeyWord:corrosion inhibition effect sulfuric acid medium imidazol-4-methylimine thiourea carbon steel electrochemical test theoretical calculation |
| Author | Institution |
| WEN Jiaxin |
Chongqing Industry Polytechnic College, Chongqing , China |
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| Abstract: |
| Carbon steel is widely used in industrial and agricultural production by virtue of its superior performance. However, carbon steel is prone to be corroded in the acidic medium, which may cause huge economic loss or even accidents. The addition of corrosion inhibitors is considered as a straightforward and effective way to address this problem. In this work, a Schiff base compound of imidazol-4-methylimine thiourea (MIT) was successfully synthesized with thiosemicarbazide and imidazole-4-carbaldehyde as the raw materials through a simple one-step reaction with the yield of 79%, and its chemical structure was characterized by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy (NMR) and electron impact mass spectrometry (EI-MS). The MIT compound was explored as an effective corrosion inhibitor for carbon steel in the H2SO4 medium. The inhibition performance of MIT in 0.5 mol/L H2SO4 solution was evaluated by gravimetric measurements, electrochemical tests, and corrosion morphology analyses. The adsorption behavior of MIT molecules on the carbon steel surface was examined by the adsorption model and X-ray photoelectron spectroscopy (XPS) analyses, and the theoretical calculation study was conducted using density functional theory (DFT) and molecular dynamics (MD) methods. The test results showed that the inhibition efficiency of MIT for carbon steel in H2SO4 solution increased with enhancing inhibitor concentration and decreased with rising temperature. The inhibition efficiencyvalue of MIT could reach 95.4% at an ideal concentration of 240 mg/L at 293 K. MIT acted as a mixed-type corrosion inhibitor that could block both anodic and cathodic corrosion reactions. The electrochemical inhibition mechanism could be explained with "geometric blocking effect". With the addition of MIT, the double capacitance at the carbon steel/solution interface dropped, while the charge transfer resistance increased significantly. The metallographic image on the inhibited carbon steel surface indicated that the corrosion degree dropped apparently. The physical-chemical mixed adsorption of MIT molecules existed on the carbon steel surface, which obeyed the Langmuir adsorption isotherm, was a thermodynamic spontaneous adsorption process ( = −31.62 kJ/mol, 293 K). The heteroatoms of N, S and other unsaturated groups in the MIT molecule contained large number of lone pairs that could be ligated with the unoccupied d orbitals of Fe atom, thus producing the chemical adsorption of MIT molecules on the carbon steel surface, which was demonstrated by XPS analyses. The results of the theoretical calculations highlighted that the MIT compound could be strongly adsorbed on the carbon steel surface. The low ΔEgap and Eads values between Fe (110) surface and MIT molecules were calculated to be 400.70 and −1 415.92 kJ/mol, respectively, further implying that MIT had a strong capability to build a barrier against the carbon steel corrosion. MIT can effectively suppress the corrosion process of carbon steel in H2SO4 solution, which originates from two aspects. First, MIT molecules can be adsorbed on carbon steel to form a strong protective film that suppresses the active sites on the carbon steel surface. Otherwise, the addition of MIT decreases the aggressive ions of the solution and thus retards the corrosion process. The synthesis of MIT inhibitor not only offers a valid way to inhibit the corrosion of carbon steel in H2SO4 solution, but also opens a new avenue in exploring the corrosion inhibitor for carbon steel in other acidic media. |
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