The Role of pH on the Inhibition of Aqueous Zinc Corrosion by L-tryptophan

A combination of in situ Scanning Vibrating Electrode Technique (SVET), and time lapse photography were used to investigate the influence of the amino acid, L-tryptophan, on the localized corrosion occurring on unpolarized zinc (Zn) samples immersed in a 0.17 mol.L−1 aqueous sodium chloride electrolyte. The addition of 1 × 10−2 mol.L−1 of L-tryptophan was found to have a significant effect on the corrosion rate for all pH values tested. At both pH 2 and pH 7, primary protection was suggested to occur as a result of adsorption due to electrostatic interactions. A secondary mechanism, whereby an insoluble complex is formed between Zn (II) ions and anionic L-tryptophan, was also proposed to occur at areas of localized high pH. At pH 2 the additions resulted in an 88% decrease in mass loss, as measured by gravimetric mass loss results and SVET, demonstrating the effectiveness of L-tryptophan inhibitors for this material