The effects of L-cysteine on the inhibition and accelerated dissolution processes of zinc metal
Effect of L-cysteine on the Zn dissolution in 0.5 M NaCl with initial pH of 4–12 was measured in continuously renewed electrolyte and in immersion tests. At short exposures 1 mM L-cysteine inhibited dissolution. The initial inhibition decreased with pH because of pH-enhanced dimerization of L-cysteine, confirmed by UV–vis spectroscopy. In long exposures at pH = 6–8 the inhibition turned into the acceleration. This was not observed at pH = 12. 10 mM L-cysteine accelerated Zn dissolution. The effects were explained by a competition between strong complexation of L-cysteine with Zn-ions and its weak physisorption on the substrate. The hypothesis was confirmed by surface characterizations.