Dianils: New and Effective Corrosion Inhibitors for Oil-Well Steel (N-80) and Mild Steel in Boiling Hydrochloric Acid

Selected condensation products of aromatic aldehydes and p-phenylenediamine have been synthesized and evaluated as corrosion inhibitors for mild steel (MS) and oil-well steel (N-80) in 15% hydrochloric acid (HCl) at 105°C ± 2°C by the weight loss method. All the condensation products showed excellent performance. 2,4-dicinnamyledene aminophenylene (DCAP) was found to be the best corrosion inhibitor. It exhibited 99.75% inhibition efficiency (IE) for MS and 99.12% for N-80 steel at 5,000 ppm of inhibitor concentration. The potentiodynamic polarization studies carried out at room temperature on MS in 15% HCl containing 500 ppm of condensation products showed that all the investigated compounds were mixed type inhibitors, whereas 500 ppm DCAP on N-80 steel behaved predominantly as anodic inhibitors. The adsorption of all the condensation products was found to obey Temkin’s adsorption isotherm.