Inhibition of low-carbon steel corrosion by derivatives of 4,5,6,7-tetrahydro-[1,2,4]triazolo[1,5-a]pyrimidin-7-ol

• D.V. Lyapun, D.S. Shevtsov, A.A. Kruzhilin, O.A. Kozaderov, I.V. Avetisyan, D.A. Machnev, I.D. Zartsyn and Kh.S. Shikhaliev

Voronezh State University, Universitetskaya pl. 1, 394018 Voronezh, Russian Federation

Abstract: The ability of four compounds of 4,5,6,7-tetrahydro-[1,2,4]triazolo[1,5-a]pyrimidin-7-ol class with different alkyl radical lengths to reduce the corrosion rate of low-carbon steel in a solution of 24% HCl has been established. Using a complex of electrochemical research methods (potentiodynamic measurements, impedance spectroscopy) and quantum chemical calculations, the inhibitory effect of the compounds under consideration was revealed. Analysis of the polarization curves showed that all the studied compounds decrease both the anodic and cathodic current density, behaving as the inhibitors with a mixed protective effect. The introduction of the additives causes an increase in the radius of the semicircles on the Nyquist diagrams relative to the control experiment without changing the shape of the hodograph. According to the results of potentiodynamic measurements and electrochemical impedance spectroscopy, a proportional increase in the polarization resistance of the electrochemical reaction was observed. The degree of protection is similar for the investigated additives at the same concentration (C_inh), and it practically does not change in the series of substituents from R–H to R–C₃H₇. With an increase of C_inh from 1.0 to 2.0 g·dm^‑3, the inhibition efficiency increases. The results of experimental electrochemical research and quantum chemical studies correlate with each other. According to electrochemical measurements, the highest degree of protection (up to 94%) was obtained for 5-phenyl-4,5,6,7-tetrahydro-[1,2,4]triazolo[1,5-a]pyrimidin-7-ol at C_inh=2.0 g·dm^–3. The proposed corrosion inhibitors can be used at oil and gas production facilities to reduce the rate of corrosion when using acid solutions in the bottom-hole zone of wells and building structures, including those based on reinforced concrete.

Keywords: corrosion, low-carbon steel, inhibitors, derivatives of 4,5,6,7-tetrahydro-[1,2,4]triazolo[1,5-a]pyrimidin-7-ol

Int. J. Corros. Scale Inhib., 2023, 12, no. 4, 2256-2264
doi: 10.17675/2305-6894-2023-12-4-43

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