Studies on alkyl esters of carboxybenzotriazole as inhibitors for copper corrosion

Abstract

A series of alkyl esters (methyl, butyl, hexyl, octyl) derived from carboxybenzotriazole (CBTAH) have been studied as inhibitors for copper. Coupon tests established that the inhibition efficiency (IE) is concentration, time and pH dependent. At pH∼0 the IEs of the octyl and hexyl esters are considerably higher than that for benzotriazole under similar conditions. As pH increases up to approximately 8 the IE of each ester is decreased, but is still sufficient for practical use. For the butyl and methyl esters an opposite trend was observed; IE increased with increased pH. In acidic sulphate solution (pH∼0) the IE was in the order: octyl>hexyl>butyl>methyl, whilst in the near-neutral solution (pH∼8) this order is reversed. It is proposed that the protonated species (CBTAH 2 +-R) is chemisorbed on the copper through an azole nitrogen and at low pH IE is determined by van der Waals' forces of attraction between adjacent alkyl chains oriented away from the copper surface, which are increased with the length of the alkyl chain. On the contrary it is proposed that at high pH a polymeric complex is formed and steric hindrance acts to make the film less protective. Polarisation, EIS and SERS studies confirm these hypotheses.