Finally, An Alternative to Azoles

Benzotriazole and its derivatives have been the dominant yellow metal corrosion inhibitors used in industrial cooling water for the last thirty years. By far, the most popular of these derivatives has been 4-5 methyl benzotriazole, or tolyltriazole. Despite the triazoles dominance, however, they do have weaknesses. Previous studies have shown that the thin tolyltriazole film can be easily penetrated by oxidizing biocides, such as chlorine. These tests found that, while the tolyltriazole film can be very resistant to breakdown in aqueous environments, the thinness of the film does not result in a forgiving barrier when breakdown occurs. The user must assure that there is residual azole inhibitor present to repair the damage. More recent tests have demonstrated that this need to maintain a residual amount of azole may be much more critical than previously suggested. These tests found that both benzotriazole's and tolyltriazole's films are surprisingly weak, even when not in the presence of oxidizing biocides. Their formed films break down immediately when no residual inhibitor is present. These findings demonstrated that the success of the azoles' corrosion protection relies solely on the immediate repair of damaged film by free inhibitor in the water, not in the formation of a tenacious, hydrophobic film.