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

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 СNaCl=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 (–ΔG0ads=76.7 kJ/mol), which is almost 2 times higher than for the malonate anions itself (38.7 kJ/mol). Such high values of (–ΔG0ads) 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 Cin=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.