Corrosion Inhibitation Action of p-Substituted Anilines for Corrosion of Copper

Abstract

Polarization of copper has been carried out in each of solutions of nitric acid added several p-substituted anilines. The addition of the p-substituted anilines makes the values of the corrosion potential E_corr (V) noble in the following order: +0.01 (aminophenol)>-0.02 (aniline)>-0.06(nitroaniline)=-0.06(choroanilene)>-0.10(aminobenzoic acid)>-0.12 (benzamide)>-0.17(no addition). The E_corr values are heightened by electron-donor substituents and lowered contrary by electron-acceptor substituents. The values of corrosion current density i_corr (A/cm²) are reduced by the addition of the p-substituted anilines and the i_corr values are in the following order: 1.3×10^-5(nitroaniline)<2.5×10^-5(benzamide)< 4.0×10^-5(no addition)=4.0×10^-5(aminobenzoic acid)<4.5×10^-5(chloroaniline)<1.8×10^-4 (aniline). The data show that the electronic-attractive substituent effect is large in the order NO₂CONH₂>COOH>Cl and the order agrees with that of the corrosion inhibition effects of the substituted anilines. The ab initio 3-21G molecular orbital calculations for the p-substituted anilines were carried out. The electronic charges on the atoms of the substituted anilines show that there are a possibility of two adsorption forms for the substituted anilines on the copper atoms. The one of adsorptions is caused by the benzene ring of the substituted anilines and another is by the substituents. The values of E_corr are heightened by the increase of negative electronic charge of the benzene ring. The large negative charges on the substituents result in the smaller values of i_corr.