Comparison of inhibition efficiency of some azoles on corrosion of type 304 stainless steel in acidic solutions

Inhibition efficiencies have been investigated for two types of azole, namely 2-mercaptobenzoazole (CBA) and 2-methylbenzoazole (MBA), containing nitrogen, sulphur, oxygen, or selenium atoms, on the corrosion of type 304 stainless steel in 2M sulphuric acid (H₂SO₄) and 3M hydrochloric acid (HCl). The study was conducted using weight loss, gasometry, and polarisation methods. It was shown that some of the compounds tested provide 90% inhibition efficiency at a concentration of 5 × 10^-4M and that the efficiency depends on the heteroatom and decreases in the order Se > S > N > O. These inhibitors were more efficient in H₂SO₄ than in HCl whereas the opposite is true for inhibitors with nitrogen alone. Adsorption isotherms were fitted to the experimental findings and some thermodynamics functions were obtained.