Abstract
The inhibition efficiency of polar organic inhibitors is correlated with the hard and soft acids and bases principle. It has been reported that an inhibitor acting as a soft base was readily chemisorbed on various transition and non-transition metals, resulting in a high efficiency of corrosion inhibition. Effect of the polar organic compounds was studied on anodic polarization curves of Ni electrode in a 3M HClO4 solution. The compounds used as the inhibitors were those of which polar atoms belong to elements of 4B, 5B, 6B, and 7B groups in the periodic table. Similar relationship between the inhibition efficiency and the HSAB principle, as shown in the previous papers, was also obtained from the results in the active region of polarization curves. The passivation potential shifted toward a noble potential and the critical current density increased with the concentration of the inhibitor and with its softness as the base. The passive current density was enhanced by the addition of the inhibitors of which polar atoms were of the 6B and 7B groups, while lowered by the addition of those of the 5B group. From the discussion of the relationship between the chemical adsorption and the HASB principle, it was concluded that the inhibitors of the 7B and 6B group elements were adsorbed on the metallic Ni surface. However, the inhibitors of the 5B group elements were adsorbed on the passive film of the Ni electrode and reinforced the passive film. No significant difference was observed in the curves of the transpassive region for the electrodes uninhibited and inhibited with the inhibitors.
