Abstract

The corrision of steel in 2.5 N H 2SO 4 in water-dimethyl formamide (DMF) solutions with various compositions (from 0.0 to 70 vol.% DMF) was studied. The rate of dissolution of steel was measured chemically using gasometry and mass-loss technique and electrochemically using d.c. polarization and a.c. impedance techniques. The results obtained showed that the acid corrosion of steel was inhibited by dimethyl formamide in the medium. Capacitance measurements indicated that the dimethyl formamide molecules were specifically adsorbed at the steel-solution interface. The effect of variation in the composition of the water-dimethyl formamide solution on the protection efficiency of 4-amino-3-H-5-mercapto-1,2,4-triazoline was also studied. The results showed that the protection efficiency of this inhibitor generally decreased as the concentration of DMF in the medium increased. It is suggested that there is competitive adsorption between the dimethyl formamide and the inhibitor molecules. An increase in the concentration of DMF in the solution leads to the displacement of adsorbed inhibitor molecules from the double layer at the steel-solution interface.

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