Inhibition of the corrosion of metals by additions of bicyclic triazolopyrimidine in neutral chloride solutions. Part 1

• M.O. Agafonkina¹, N.P. Andreeva¹, Yu.I. Kuznetsov¹ and Kh.S. Shikhaliev²

¹ Frumkin Institute of Physical Chemistry and Electrochemistry Russian Academy of Sciences, 31-4, Leninsky prospect, 119071 Moscow, Russia
² Voronezh State University, Universitetskaya pl. 1, Voronezh, 394018, Russia

Abstract: The adsorption, protective and passivating properties of a bicyclic triazolopyrimidine – 2-methyl-5-phenyl-4,5,6,7-tetrahydro-[1,2,4]triazolo[1,5-α]pyrimidin-7-ol (MPTTP) – on copper, zinc and low-carbon steel St3 in a neutral borate buffer solution with pH 7.4 (BBS) have been studied. Adsorption measurements were carried out on the reduced and oxidized surfaces of metals in the BBS. On all metals, the adsorption of MPTTP on the oxidized surface occurs at lower concentrations than on the reduced metal. The obtained adsorption isotherms were calculated using the full Temkin equation and the values of adsorption free energies in all cases indicate the chemisorption interaction of the MPTTP anion with the metal surface. The passivation ability of MPTTP on all metals was studied in the BBS + 0.01 mol/L NaCl. On copper, the effect of MPTTP is manifested only in the passivation of the first peak of active dissolution at 10 μmol/L. On zinc, a spontaneous transition to a passive state is observed at 0.20 mmol/L. On St3, in the absence of cathodic reduction, a shift of Ecor by 0.05 V in the positive direction occurs at 0.10 mmol/L. Corrosion tests of copper and zinc with MPTTP additives in a 1.0 mmol/L sodium chloride solution showed that at 0.40 mmol/L MPTTP, a protection degree of 99.4% (for Cu) and 96.9% (for Zn) can be achieved.

Keywords: inhibition, copper, zinc, low-carbon steel, substituted pyrimidines, protective effect, free energy of adsorption, ellipsometry

Int. J. Corros. Scale Inhib., 2025, 14, no. 4, 1847-1859
doi: 10.17675/2305-6894-2025-14-4-7

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