Adsorption and protective properties of alkylmalonic acids’ derivatives on zinc in a neutral chloride solution

• M.O. Agafonkina¹, Yu.I. Kuznetsov¹, N.P. Andreeva¹, Kh.S. Shikhaliev² and Yu.A. Kovygin²

¹ A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninskii pr. 31, 119071 Moscow, Russian Federation
² Voronezh State University, 1 Universitetskaya pl., 394018 Voronezh, Russian Federation

Abstract: The adsorption of sodium malonate and its alkyl-substituted derivatives on zinc in a borate buffer solution with pH 7.4 and their protective effect on the oxidized surface of this metal in an aqueous solution of sodium chloride with a concentration of С_NaCl=0.01 mol/L were studied. It was shown that their adsorption on zinc at E=0.2 V is adequately described by the complete Temkin isotherm equation. Sodium nonylmalonate anions have the highest standard free energy of adsorption (–ΔG⁰_ads=76.7 kJ/mol), which is almost 2 times higher than for the malonate anions itself (38.7 kJ/mol). Such high values of (–ΔG⁰_ads) indicate the chemisorption interaction of these organic anions with the oxidized surface of zinc. Corrosion tests of zinc plates in a chloride solution with addition of a three-component mixture containing sodium malonate+C₂-malonate with 2-mercaptobenzimidazole showed high results: at C_in=0.004 mol/L, complete protection of zinc for 7 days can be achieved under natural aeration conditions of 0.01 M NaCl aqueous solution.

Keywords: zinc, passivity, inhibition, carboxylates, adsorption, alkylmalonic acid, local depassivation potential, degree of protection, Temkin isotherm, ellipsometry

Int. J. Corros. Scale Inhib., 2024, 13, no. 4, 2438-2453
doi: 10.17675/2305-6894-2024-13-4-30

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