Aromatic Azoles

These materials have gained more widespread use in recent years, either used alone or blended with non-polluting treatments containing inorganic phosphate, molybdate, phosphonates or zinc. They are recognized as specific corrosion inhibitors for copper. It has been hypothesized that azoles can act synergistically with other materials to lower mild steel corrosion rates as well.

Mercaptobenzothlazole (MBT) forms a chemisorbed film on metal surfaces. It can provide good corrosion control at minimal dosages of two to five ppm. However, MBT can be attacked by chlorine and loses its corrosion control properties.

Benzotriazole and tolyltriazole, shown in the figure below, have been found to be superior to MBT as copper corrosion inhibitors. A copper ion displaces one hydrogen ion to form a covalent bond. A coordinate covalent bond is formed between the copper and the pair of electrons on the adjacent nitrogen atom. The insoluble complex forms a thin film that reinforces normal cuprous and cupric oxide films

In contrary to their better performances in inhibiting copper corrosion, Benzotriazole and Tolyltriazole are making thinner and harder protection film.

Especially MBT forms 500 times thicker film than Tolyoltriazole. So, in closed cooling water systems, performs better against mechanical erosion.

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