Adsorption and passivation properties of S-containing heterocyclic compounds on copper

The adsorption of sulfur-containing heterocyclic compounds on Cu and their passivating ability with respect to copper in neutral chloride solutions was studied. Sulfur-containing aminotriazoles, despite their hydrophilicity, have a better passivating effect on copper in a neutral aqueous solution than MBT or BTA. Adsorption of triazoles on the oxidized copper surface at E= 0.0 V is polymolecular. The first monolayer is adequately described in the region of average surface coverage by the logarithmic Temkin isotherm with values of the standard free energy of adsorption (-Delta G(a)(0)) = 69-89 kJ/mol, which is evidence in favor of the assumption of chemisorption on copper. Corrosion under harsh conditions of 100% relative air humidity and daily moisture condensation on copper samples showed the high efficiency of the studied sulfur-containing compounds. The longest duration of copper passivity is provided by an adsorption, probably polymolecular film formed in a dilute solution (2 mmol/L) of 5-C5H11S-3-AT, which is significantly superior in this respect to a similar film formed by MBT or BTA. In neutral aqueous solutions, an increase in the hydrophobicity of S-containing 5-substituted 3-ATs may not only fail to increase their adsorption and protective properties but also weaken them, possibly due to steric hindrance to the adsorption of the inhibitor. When protecting copper from atmospheric corrosion under harsh conditions of periodic moisture condensation on the copper surface, the positive role of increasing hydrophobicity is more pronounced.