The chemical formula is benzotriazole (C6H5N3). Benzotriazole is also known by other synonymous names: BTA, 1,2-aminoisophenylene, azimidobenzene, benzene azimide, benzisotriazide, 1,2,3,benzotriazole, cobratec #99, which is a crystalline, yellow, almost odorless substance. Is. This material plays an important role in controlling copper corrosion.
BTA has a molecular weight of 119.13 g/mol, a melting point between 94-97°C and a boiling point of 203-205°C. Its solubility in water at 20 degrees Celsius is 20 grams per liter, and it is also soluble in some organic solvents such as alcohol and acetone.
This material has a pH of 5-6 at 20 degrees Celsius. At temperatures above 160 degrees Celsius, there is a risk of explosion during distillation. Benzotriazole represents an industry standard against which the performance of other inhibitors can be compared.
Benzotriazole has been known to enhance the corrosion resistance of copper and copper alloys for some time. Nearly neutral benzotriazole solutions with rich salts yield yellow to green precipitates, benzotriazole-copper complexes. These complexes are almost insoluble in water and many organic solvents.
These complexes are also thermally stable up to about 250 degrees Celsius. These properties are probably associated with the triazole ring. In these interactions, the N-H group forms insoluble complexes with copper compounds.
A film of the complex formed on the surface is very thin and amorphous. The stoichiometry of benzotriazole with copper is 1:1. In the figure below, the polymer chains of the benzotriazole complex with copper are shown:
Copper is connected to the amine nitrogen on one side of the molecule, and on the other side, it is connected to the unsaturated nitrogen ring with a pair of electrons. Metal copper reacts faster with azole than oxidized copper surfaces. The conclusion is that the reaction order is Cu(0) > Cu2O > CuO. The nitrogen-copper bond is formed on the surface of oxidized and non-oxidized copper.
The benzotriazole polymer film on oxidized copper creates a better barrier for copper ions and prevents them from being transferred to the solution. This is an advantage in the preservation of archaeological artefacts and copper alloy.
The thickness of the film varies between 5-40 Å in the range of pH 3 to 12. It was found that at pH 2 the thickness can reach up to 250 Å. The benzotriazole film reacts primarily as an inhibitor for copper dissolution and secondarily as a coating to prevent oxygen reduction at the metal surface.
If the copper surface is composed of Cu2O and reacts with an aqueous solution of benzotriazole, it forms copper I-benzotriazole and copper II-benzotriazole complexes. The figure below shows copper II-benzotriazole polymer
No comment