4-Amino-4H-1,2,4-triazole-3,5-dithiol influence on the free surface energy and corrosion behavior of low-carbon steel in hydrochloric acid media

• M.D. Plotnikova, M.G. Shcherban and A.B. Shein

Perm State National Research University, Perm, Bukireva str. 15, 614068 Russia

Abstract: The effects of 4-amino-4H-1,2,4-triazole-3,5-dithiol on the corrosion of mild steel in 1 M and 5 M hydrochloric acid solutions were studied. 4-Amino-4H-1,2,4-triazole-3,5-dithiol was synthesized by boiling thiocarbohydrazide with carbon disulfide in pyridine. Several equilibrium tautomer forms of the molecule were determined over a wide pH range using quantum chemical modeling: protonated, zwitter-ionized and uncharged. Weight loss results showed that 4-amino-4H-1,2,4-triazole-3,5-dithiol was an effective corrosion inhibitor in both 1 M and 5 M hydrochloric acid solutions, reducing the corrosion rate from 2.65 to 0.34 g/(m²·h) and from 19.9 to 0.34 g/(²·h), respectively. In 5 M solution, the studied compounds were more effective in slowing down the corrosion process (96% protection) due to the positively charged amino groups. When present in the zwitterionic form, the protective effect does not exceed 87%. The presence of different forms of 4-amino-4H-1,2,4-triazole-3,5-dithiol molecules may lead to the formation of protective layers with different charge values, which is reflected in the energy state of the steel surface. The surface energy state was estimated using the Good-van Oss-Chaudery method (GvOC), determining the acid, base and dispersion components of the surface free energy (SFE). In the initial stage of protective layer formation, when the inhibitor concentration in the solution is low, there are significant differences in the values of the SFE component. With the increase of the inhibitor concentration in the two solutions, the difference in the values of the SFE component is not significant, because at high coverage levels, the film composition is similar.

Keywords: corrosion, inhibitor, surface free energy, contact angle

Int. J. Corros. Scale Inhib., 2025, 14, no. 4, 2279-2286
doi: 10.17675/2305-6894-2025-14-4-29

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