Tetrazole derivatives as corrosion inhibitors for copper in chloride solutions.

This paper discusses the results obtained in studying the beahaviour of tetrazole and some of its derivatives, usually at 1mM concentration, as corrosion inhibitors of OFHC Cu cilinders in 0.1M NaCl solutions, at pH values spontaneously assumed by inhibitor addition or shifting pH to 4.0 or 8.0 (extreme limits considered for industrial waters), at temperatures of 40° and 80°C. The prefilming properties of the additives on the Cu surfaces have also been tested. The following compounds have been examined as inhibitors: tetrazole; 5-mercapto-tetrazole; 5-mercapto(Na salt)-1-methyl-tetrazole; 5-mercapto-1-acetic acid Na salt)-tetrazole; 5-mercapto-1-phenyl-tetrazole; 5-phenyl-tetrazole; 5-amino-tetrazole. The inibiting performances of the additives have been evaluated by recording polarisation resistance and polarisation curves, after 60 minutes of immersion of the electrodes in the solutions. Long term (300 hours) inhibition tests have been conducted, determining at the end the amount of dissolved copper ions. In some cases, after immersion of Cu sheets in inhibited chloride solutions, the reflection FTIR spectra have been recorded with the purpose to emphasize the interaction mechanism of the additives onto metal surface. The best results of the series of long term inhibition test (total absence of localized attack and 93% of inhibition efficiency) have been shown in the presence of 5-phenyl-tetrazole. The behaviour of the tetrazole derivatives is discussed by considering their suddivision in two groups: the first, including tetrazole, 5-phenyl-tetrazole and 5-amino-tetrazole, with the hydrogen atom in position 1 of the heterocyclic ring; the second, showing substitution of H atom in position 1, such as 5-mercapto-1-phenil-tetrazole and 5-mercapto-1-methyl-tetrazole