Corrosion inhibition of MNZh alloy with sodium salts of lower dicarboxylic acids in neutral aqueous solution

• M.O. Agafonkina, I.A. Kuznetsov, Yu.I. Kuznetsov, O.Yu. Grafov and N.P. Andreeva

A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninskii pr. 31, 119071 Moscow, Russian Federation

Abstract: The adsorption, protective and passivating effect of sodium salts of dicarboxylic acids on the oxidized surface of copper-nickel alloy MNZh 5-1 and on its individual components in a neutral chloride solution has been studied. It is shown that sodium adipate has a higher free energy of adsorption (-ΔG⁰_ads) on the MNZh 5-1 alloy at E=0.0 V than sodium malonate and ethylmalonate. The values of -ΔG⁰_ads are 81.8, 74.1, and 78.1 kJ/mol, respectively, which suggests the chemisorption interaction of these organic anions with the oxidized surface of the alloy. The elemental composition of the alloy surface was determined by the XPS method, in a borate buffer at different electrode potentials. It is shown that at the free corrosion potential, the surface of the copper–nickel alloy is enriched with iron, which reduces the resistance of the alloy to the action of chloride ions. Corrosion tests of the alloy in water, containing 10 mmol/L NaCl for 7 days showed that the composition of sodium adipate with 2-mercaptobenzthiazole (9:1) at 3 mmol/L is capable of providing full protection of the alloy. The addition of only adipate itself at the indicated concentration makes it possible to achieve only Z=49%.

Keywords: copper alloy, sodium malonate, dicarboxylic acids, adsorption, neutral chloride solution, ellipsometry, Temkin isotherm, XPS

Int. J. Corros. Scale Inhib., 2021, 10, no. 1, 349-367 PDF (773 K)
doi: 10.17675/2305-6894-2020-10-1-20

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