Indole and its derivatives as corrosion inhibitors for C-steel during pickling

The corrosion of three types of C-steel in 10% hydrochloric acid solution h as been investigated in the absence and the presence of the inhibitors, ind ole (A), indole acetic acid (B), indole butyric acid (C), and 3-acetyl indo le (D), by weight-loss measurements at different temperatures (30 similar t o 70 degrees C). The results showed that inhibiting efficiency depended upo n the presence of the substituted groups in the pyrrole ring. The inhibitin g efficiency of the inhibitors increased in the order: Inh. C<lnh. B<lnh. A <lnh. D. Linear Arrhenius plots were obtained in the absence and the presen ce of inhibitors. Results elucidated the effect of temperatures and molecul ar structure on the inhibition efficiency. The activation energy, E-a, of t he three alloys was calculated and it was found that it depended on the typ e of steel and inhibitor.