5-AMINO-INDOLE AND 5-CHLORO-INDOLE AS MILD-STEEL CORROSION-INHIBITORSIN 1N SULFURIC-ACID

5-aminoindole (AI) and 5-chloroindole (CI) were tested as corrosion in hibitors of mild steel in 1N deaerated sulphuric acid. Their behaviour was compared with that of indole (IN) in the temperature range of 25 to 55 degrees C. The inhibiting effect of AI and CI is more pronounced on the anodic rather than cathodic process with the exception of CI a t highest concentrations. AI and CI generally did not affect the corro sion reaction mechanism. Corrosion rates decreased as inhibitor concen tration increased, but as temperature increased higher corrosion rates resulted. At 25, 35, 45 and 55 degrees C both the adsorption of AI an d CI followed Frumkin's isotherm. The best inhibiting effect was obtai ned at the highest concentrations (0.005-0.0075 M) of CI up to 35 degr ees C. This is probably due to the fact that this molecule, as IN, can form oligomers on the electrode surface. The Contact Electric Resista nce (CER) technique, described below, was used the first time to study the interaction of organic inhibitors with a metal surface. Copyright (C) 1996 Elsevier Science Ltd.