Amines as steel corrosion inhibitors in ethanol-gasoline blends

Several amines with different chemical structures were tested as corrosion inhibitors for carbon steel in ethanolgasoline blends (EGBs) using electrochemical methods. The electrochemical measurements were supplemented by surface analyses (SEM, XPS) and static corrosion tests. The findings established that the inhibition efficiency or passivation of steel in the tested EGBs was significantly influenced by the chemical structure and related physical properties of the amines. This inhibitory efficiency was somewhat dependent on the polarity of the corrosion environment and the formation of a corrosively aggressive aqueous microphase on the steel surface. Among the tested inhibitors, hexamethylenediamine, ethylenediamine, diethylenetriamine, triethylenetetramine, and piperazine exhibited the highest effectiveness. Using these amines, polarization resistances in the order of magnitude of M Omega . cm2 were measured. The electrochemical results highlighted the superior efficiency of these amines, which was higher than 96 % even at concentrations as low as 25 mg/L. At concentrations of 100 mg/L, these amines were able to compensate for 500 mg/L of the acetic acid and 20 mg/L of sodium chloride in the EGBs. The highest polarization resistance and efficiency of 9 M Omega . cm(2) and of 99.9 %, respectively, were measured on mild steel in the presence of hexamethylenediamine. Its high efficiency was also confirmed during the immersion test, where an efficiency of 97.6 % was found after three months of exposure.