The influence of pH value on the efficiency of imidazole based corrosion inhibitors of copper

The aim of this work is to establish the correlation between the solution pH and the inhibiting efficiency of two imidazole compounds (4-methyl-1-phenyl imidazole and 4-methyl-1-( p-tolyl) imidazole) in protection of copper from corrosion in chloride media. It was found that the inhibiting efficiency of both studied imidazoles enhances with the increase of the solution pH value, from about 20% in 0.5 M HCl to 92% in 0.5 M NaCl. This improvement was ascribed to stronger adsorption of neutral imidazole molecule, which can be expected at higher pH values, than that of the protonated imidazole cation, which may be expected in acid solutions.