Protection of Copper and Its MNZh 5-1 Alloy with Sodium Salts of Malonic and Ethylmalonic Acids in a Neutral Chloride Solution

The adsorption, protective, and passivating effects of sodium salts of malonic and ethylmalonic acids on the oxidized and reduced surface of copper and MNZh 5-1 copper alloy in a neutral chloride solution have been studied. It was shown that sodium ethyl malonate anions, which are less hydrophilic than sodium malonate, have higher adsorption free energies ( - Δ G_a,max^0 ) on copper and MNZh 5-1 alloy at E = 0.0 V. On copper, they are 69.4 and 47.7 kJ/mol, respectively, and they are 78.7 and 74.1 kJ/mol on the MNZh 5-1 alloy. Such values ( - Δ G_a,max^0 ) indicate the chemisorption of anions of both inhibitors on the surface, and their stronger adsorption on the alloy, apparently, is due to its increased adsorption activity of the heterogeneous surface as compared to copper. The thicknesses of conditional monolayers of inhibitors on metal and alloy surfaces have been calculated. At cathode potential E = –0.60 V on the reduced copper surface, the values ( - Δ G_a,max^0 ) are significantly less (for malonate and ethyl malonate, respectively, they are 38.3 and 64.2 kJ/mol). Corrosion testing of copper in water with a chloride content of 10 mmol/L also showed the advantage of ethyl malonate over malonate. At the same time, for C in = 1.5 mmol/L, the degree of protection is 71 and 65