Adsorption of 2-mercaptobenzthiazol on copper and MNZh-5-1 alloy and their protection from corrosion in aqueous solutions

Abstract

The adsorption, passivation and protective properties of 3-amino-1,2,4-triazole (3-AT) and 2mercaptobenzothiazole (2-MBT) on copper and MNZh 5-1 alloy were studied. The adsorption characteristics of both compounds on reduced and oxidized surfaces of copper and its alloy were calculated. On oxide-free surfaces (Е =-0.60 V) of both metals, physical adsorption of 3-AT and 2-MBT occurs, whereas chemical adsorption occurs on oxidized surfaces (Е = 0.0 V). The free energies of adsorption calculated by two independent methods, ellipsometry and electrochemical impedance spectroscopy, correlate well with each other. The orientation of the studied compounds on the metal surface was revealed by the ellipsometric method. 2-MBT on reduced and oxidized surfaces of the MNZh 5-1 alloy and copper is adsorbed in planar orientation, forming bonds with the surface through sulfur and nitrogen atoms. 3-AT on cathodically reduced surface of the alloy and copper is in planar orientation, whereas at the anodic potential, in a nearly vertical orientation. 2-MBT is adsorbed on oxidized copper better than 3-AT, apparently due to interaction with its oxide. It allows a protective coating to be formed on the surface that protects the metal well even at high chloride concentrations. Corrosion tests of copper and its alloy in 3.5% sodium chloride solution confirmed the high protective properties of 2-MBT. The created inhibitor mixture of 2-MBT with sodium laurate in equimolar ratio at a total concentration of 0.20 and 0.25 mmol/L allows one to achieve almost complete protection of copper and its alloy with Z = 99.1-99.3%, respectively.