The inhibition effect of some nitrogen-heterocyclic compounds on corrosion of aluminium and its alloys in HCl solution

The effect of 1,10-phenanthroline (PHEN), bathophenanthroline (BPHEN), bathophenanthroline disulphonic disodium salts hydrate (BPHENS), 2.2'-bipyridyl (BIPY) and 2,4,6-tris(2-pyridyl)-1,3,5-triazine (PYT) and their complexes with Cu2+ and Fe3+ ions on the corrosion of pure aluminium and its alloys in a 1 M HCl solution was studied using electrochemical impedance spectroscopy (EIS), Measurements were carried out at cathodic, open circuit and anodic potentials. The free inhibitors are found to be predominantly anodic type of pure Al and cathodic of its alloys. PYT inhibited the corrosion of Al-alloys in 1 M HCl even at lower concentrations (10(-6) M), and the inhibition efficiency decreases with an increase in the concentration of the free PYT. This behaviour is suggested to be caused by the formation of an insoluble complex at lower concentrations due to iron traces in the alloys, BPHENS accelerates the corrosion of Al and its alloys at cathodic potential and found more effective on Al-alloys. Fitting corrosion of Al-alloys is reduced in the presence of most investigated inhibitors. The adsorption of most inhibitors is also found to obey Langmuir's adsorption isotherm, thereby indicating that the main process of inhibition is by adsorption Addition of most investigated additives as a complex with Cu2+ and Fe3+ ions enhances efficiency of pure Al particularly at cathodic potential and of its alloys at anodic potential. BPHENS-complex with the two investigated metal ions inhibited the corrosion of pure Al and its alloys. This indicates that catalytic effect of SO3- groups attached to BPHEN molecule is blocked in the complex formation.