Inhibitive effect of 4- and 5-carboxybenzotriazole oncopper corrosion in acidic sulphate and hydrogen sulphidesolutions

Abstract

Commercial carboxybenzotriazole (CBT) usually consists of a mixture of the 4- and5-substituted isomers and as such has been used to inhibit copper corrosion. Little work has beendone on the inhibiting action of the individual compounds in different corrodents, and this paperdescribes their effect on the corrosion of copper in aerated acidic sulphate solution (pH=0 and 4),and in an aqueous sulphidising environment. Gravimetric and potentiodynamic polarisationmethods were employed in the acid corrosion studies, whilst coulometry was used to analyse thesurface products formed in the H 2S containing solutions. Finally, surface enhancedRaman scattering (SERS) spectroscopy was used to examine the initial interaction of thecompounds with the copper surface in acidic solution. The coupon tests in aerated acidic sulphate showed that the inhibition efficiency of eachisomer was pH, concentration, and time dependent. At lower pH the 5-isomer is by far the betterinhibitor, and this behaviour continues at a higher pH where 4-CBT promotes corrosion. Theinhibition efficiency of the 5-isomer increased markedly with exposure time and this wasattributed to the increase in thickness of the underlying oxide layer. SERS revealed the presenceof a broad peak at approx. 250 cm −1 and this has been assigned to the Cu-Nstretching mode, resulting from adsorption of CBT onto the copper surface, and subsequentcoordination through a triazole nitrogen. The anti-tarnishing tests showed that whilst both isomersexhibited these properties, once again 5-CBT was the superior inhibitor.