Inhibitive effect of 4- and 5-carboxybenzotriazole on copper corrosion in acidic sulphate and hydrogen sulphide solutions

Commercial carboxybenzotriazole (CBT) usually consists of a mixture of the 4- and 5-substituted isomers and as such has been used to inhibit copper co rrosion. Little work has been done on the inhibiting action of the individu al compounds in different corrodents, and this paper describes their effect on the corrosion of copper in aerated acidic sulphate solution (pH =0 and 4), and in an aqueous sulphidising environment. Gravimetric and potentiodyn amic polarisation methods were employed in the acid corrosion studies, whil st coulometry was used to analyse the surface products formed in the H2S co ntaining solutions. Finally, surface enhanced Raman scattering (SERS) spect roscopy was used to examine the initial interaction of the compounds with t he copper surface in acidic solution. The coupon tests in aerated acidic sulphate showed that the inhibition effi ciency of each isomer was pH, concentration, and time dependent. At lower p H the 5-isomer is by far the better inhibitor, and this behaviour continues at a higher pH where 4-CBT promotes corrosion. The inhibition efficiency o f the 5-isomer increased markedly with exposure time and this was attribute d to the increase in thickness of the underlying oxide layer. SERS revealed the presence of a broad peak at approx. 250 cm(-1) and this has been assig ned to the Cu-N stretching mode, resulting from adsorption of CBT onto the copper surface, and subsequent coordination through a triazole nitrogen. Th e anti-tarnishing tests showed that whilst both isomers exhibited these pro perties, once again 5-CBT was the superior inhibitor. (C) 1999 Elsevier Sci ence Ltd. All rights reserved.