Effect of Halogenation on Yellow Metal Corrosion: Inhibition by Triazoles

The adsorption isotherm and the corrosion rate profile for tolyltriazole (TT) and butylbenzotriazole (BBT) were presented as functions of immersion time in triazole solution. Formation of a triazole film on a yellow metal surface was shown to play a major role in corrosion inhibition. In the absence of triazole in bulk solution, halogenation was detrimental to TT and BBT surface films. The disruption mechanism was attributable to chemical decomposition of the adsorbed triazole by halogen. However, adding TT (> 0.2 mg/L) to the halogen-based biocide solution improved stability of the protective TT film significantly. The improvement in stability was evident from the nearly unchanged surface coverage and lower corrosion rate. Based on this result, an enhanced TT-intermittent-feed method was developed. The metal surface was passivated initially with TT. Addition of halogen-based biocide was accompanied by a concurrent addition of TT (0.5 mg/L to 2 mg/L). Results demonstrated that the enhanced TT-intermittent-feed method performed better than the initial slug feeding of TT and BBT in inhibiting yellow metal corrosion.