ABSTRACT
Benzotriazole and its derivatives, tolyltriazole and butylbenzotriazole, have proven themselves as excellent corrosion inhibitors for copper and copper alloys under a wide variety of conditions. Chlorine, a popular oxidizing biocide in the industrial water treatment industry, has been reported to affect the protective triazole inhibitor layer (film) formed on copper. In an attempt to expand further on the interaction between chlorine and the triazole inhibitor layer, surface analyses were employed on tolyl triazole and butyl benzotri azole and the results compared to previously reported electrochemical findings.
The impact of chlorine on triazole inhibitor layers should be divided into two steps. The first step is a penetration of the inhibitor film. The triazole film on copper is too thin to be a static barrier between the metal and aqueous environment. Instead the layer is the result of a dynamic equilibrium between the inhibitor film formation and the corrosion reaction of the underlying metal. Therefore, it can be penetrated by water and chlorine molecules, as well as protons, chloride and metallic ions.
This penetration results in copper corrosion and is immediately detected via electrochemistry. The second step is a degradation of the inhibitor film, which takes some time, and can best be observed via surface analyses. Once film degradation has started, penetration is enhanced, and both processes lead to excessive copper corrosion rates. This is particularly the case in the absence of residual inhibitor, available in the bulk water, to repassivate areas of the film affected by chlorine. The current triazole inhibitors react differently to both steps of the chlorine interaction.
An evaluation of the two isomers found in commercially available tolyltriazole - 4-methylbenzotriazole and 5-methylbenzotri azole - indicated only small differences in adsorption and stability between them.
