Dithiobiurets: a novel class of acid corrosion inhibitors for mild steel

The corrosion inhibition behaviour of some substituted dithiobiurets, namely, -1,5-diphenyl-2,4-dithiobiuret (DPDTB), 1-tolyl-5-phenyl-2,4-dithiobiuret (TPDTB), 1-anisidyl-5-phenyl-2,4-dithiobiuret (APDTB), 1-chorophenyl-5-diphenyl-2,4-dithiobiuret (CPDTB) were studied in 1 to 5 M HCl on mild steel. The characteristics of these compounds are explained in terms of factors such as inhibitor concentration, acid concentration, temperature, immersion time and molecular structure. Potentiodynamic polarization and a.c. impedance techniques were used to investigate the inhibition mechanism. Among the compounds studied APDTB exhibited the best performance giving more than 98% inhibition efficiency (IE) in HCl solutions. DPDTB and CPDTB were found to reduce hydrogen permeation through mild steel in HCl solutions. The adsorption of APDTB was also confirmed by Auger electron spectroscopy (AES).