Electrochemical behavior of mild steel coated with long alkyl-chain benzothiazole derivatives in acid solution: Effect of aliphatic chain length

Mild steel surfaces were coated with four different benzothiazole derivatives with long alkyl chain, namely 2-(heptyl)-benzothiazole (HEBT), 2-(tridecyl)-benzothiazole (TDBT), 2- (pentadecyl)-benzothiazole (PDBT), and 2-(heptadec-8-en-1-yl)benzothiazole (HDBT) from their respective chloroform solutions. Electrochemical experiments were conducted with coated and uncoated mild steel samples exposed to 1 M aqueous HCl at temperatures between 20 degrees C to 50 degrees C and at different immersion times from 6 h to 48 h. TDBT behaves as the best corrosion inhibitor among the four (more than 99 % efficiency at 40 degrees C) and the order of inhibition efficiency follows the trend: TDBT>HDBT>PDBT>HEBT. This reflects the inhibition efficiency to increase with chain length initially, but decreases after a threshold. HDBT, in-spite of having longest aliphatic chain, exhibits better inhibitory performance over PDBT. This is attributed to the presence of unsaturation in HDBT. TDBT coating maintains high corrosion inhibition efficiency even after the 24 h of exposure (above 98 %). Occurrence of spatial hindrance during adsorption of BT derivatives with long aliphatic chain has been manifested by MD simulation.