Corrosion inhibition of mild steel by amphoteric surfactants

The corrosion inhibition of mild steel, in 3% NaCl solution of pH3, by amphoteric surfactants was evaluated in absence and in presence of 600 and 1200 mg H2S/l and at temperatures of 25, 40 and 65 degrees C. These surfactants have the general formula. [GRAPHICS] R= C10H21 (I), C12H25 (II), C14H29 (III), C16H33 (IV), C18H37 (V) The presence of surfactants in the aqueous solution affected both the cathodic and anodic polarization areas, the corrosion potential. E-corr, shifted to more positive values and i(corr), decreased with the increase of surfactants concentrations. These surfactants have a good ability to form protective layer on the metal surface even in the presence of small concentrations of the surfactant. This was attributed to the amphoteric properties of the surfactants which contain both anionic and cationic moiety in the same molecule and also to the pressure of Cli ions in the aqueous solution. The inhibiting efficiency of the surfactants increased with the increase of the length of alkyl groups (R) in the surfactant. The value of P.I. increased to some extent in synergistic effect.