Inhibition of copper corrosion by several Schiff bases in aerated halide solutions

The inhibitive action of three Schiff bases, N,N-'-o-phenylen-bis(3-methoxysalicylidenimine) (V-o-Ph-V), N,N-'-p-phenylen-bis (3-methoxysalicylidenimine) (V-p-Ph-V) and N-[(2-hydroxy-3-methoxyphenyl)methylene]-histidine (V-His), on copper corrosion in aerated 0.5 mol dm(-)3 NaCl and NaBr solutions was investigated using EIS and steady-state polarization techniques. The inhibitor effectiveness depended strongly on the geometric structure of the Schiff bases. Among the three kinds of Schiff base used, the inhibition efficiency of V-o-Ph-V on copper corrosion was the highest, V-p-Ph-V the next and V-His the lowest. The Schiff bases inhibited the cathodic current more significantly than the anodic current. The different influences of V-o-Ph-V or V-p-Ph-V on the anodic and cathodic reactions led to the appearance of a low frequency capacitive loop in the impedance spectra. The inhibition action of the Schiff bases was due to their adsorption on the copper surface followed by complexation with Cu(I) or Cu(II) ions, forming a blocking barrier to copper corrosion.