Inhibition, corrosion benzotriazole

Copper Corrosion Inhibitors. The most effective corrosion inhibitors for copper and its alloys are the aromatic triazoles, such as benzotriazole (BZT) and tolyltriazole (TTA). These compounds bond direcdy with cuprous oxide (CU2O) at the metal surface, forming a "chemisorbed" film. The plane of the triazole Hes parallel to the metal surface, thus each molecule covers a relatively large surface area. The exact mechanism of inhibition is unknown. Various studies indicate anodic inhibition, cathodic inhibition, or a combination of the two. Other studies indicate the formation of an insulating layer between the water surface and the metal surface. A recent study supports the idea of an electronic stabilization mechanism. The protective cuprous oxide layer is prevented from oxidizing to the nonprotective cupric oxide. This is an anodic mechanism. However, the triazole film exhibits some cathodic properties as well. 

Boilers and steam systems Steel steam lines can be inhibited by the use of a volatile amine-based inhibitor such as ammonia, morpholine or cyclohexylamine introduced with the feedwater. It passes through the boiler and into the steam system, where it neutralizes the acidic conditions in pipework. The inhibitor is chemically consumed and lost by physical means. Film-forming inhibitors such as heterocyclic amines and alkyl sulphonates must be present at levels sufficient to cover the entire steel surface, otherwise localized corrosion will occur on the bare steel. Inhibitor selection must take into account the presence of other materials in the system. Some amine products cause corrosion of copper. If copper is present and at risk of corrosion it can be inhibited by the addition of benzotriazole or tolutriazole at a level appropriate to the system (see also Section 53.3.2). 

Dissimilar metals in the same system Because of the specific action of many inhibitors towards particular metals, problems arise in systems containing more than one metal. In the majority of cases these problems can be overcome by the choice of a formulation incorporating inhibitors for the protection of each of the metals involved. With this procedure it is necessary not only to maintain an adequate concentration of each of the inhibitors but also to ensure that they are present in the correct proportion. This is because of two effects firstly, failure to inhibit the corrosion of one metal may intensify the attack on the other metal the best example of this is with aluminium and copper in the same system, and failure to inhibit copper corrosion — usually achieved with sodium mercaptobenzothiazole or benzotriazole—can lead to increased corrosion of the aluminium as a result of deposition of copper from copper ions in solution on to the aluminium surface. Secondly, an inhibitor of the corrosion of one metal may actually intensify the corrosion of another metal. Thus, benzoate is usually used to prevent the corrosion of soldered joints by nitrite inhibitor added to protect cast iron in the same system. A benzoate nitrite ratio of greater than 7 1 is necessary in these cases. 

Inhibitors form a film on the surface that blocks the dissolution of the substrate. Adsorption of an alkyl-thiol to the surface of the CU3AU alloy resulted in an inaeased surface tension of the gold film this is observed as an increase in the value of <., which depresses dissolution of copper. This behavior resembles inhibition of copper corrosion on a pure copper surface where benzotriazole increases the potential to start significant copper dissolution this was demonstrated by Cruickshank et using in situ AFM. However, when the critical potential for benzotriazole film... 

Azole compounds, poly-N-vinylimidazole (PVI-1) and 2-undecylimidazole (UDI), are studied as alternative inhibitors to benzotriazole (BTA) for copper corrosion in aqueous systems using electrochemical techniques. It is shown that UDI, either as a cast film or dissolved in solution at concentrations as low as 7 X inhibits oxygen reduction on... 

Azole compounds such as benzotriazole, benzimidazole, indazole and imidazoles are efficient anti-corrosion agents for copper and copper-base alloys [1-10]. Many experimental techniques [11-15] have been used to study the corrosion inhibition mechanisms, however, the mechanisms are still not well understood. It is believed that the complex formation between copper and nitrogen atoms would inhibit oxygen adsorption on copper surface [16-20]. 

Walsh J, Dhariwal H, Gutierrez A, Finneti P, Mur5m C, Brookes N, Oldman R, Thornton G. Probing molecular orientation in corrosion inhibition via a NEXAFS study of benzotriazole and related molecules on Cu(lOO). Surf Sci 1998 415 423. 

Aramaki K, Kiuchi T, Sumiyoshi T, Nishihara H. Surface enhanced Raman scattering and impedance studies on the inhibition of copper corrosion in sulphate solutions by 5-substituted benzotriazoles. Corr Sci 1991 32(5-6) 593. 

Associated with these above properties of corrosion inhibition is the readiness of triazoles and benzotriazoles to form complexes with different metals. Benzotriazole and its 5-bromo... 

EP 0462666, C 23 F 11/10. Phenylmercapto-tetrazole/tolyltriazole and/or benzotriazole corrosion inhibiting compositions. C.V. Cha and P.P. Vander-pool, 1991. 

U.S. Patent 5874026, C 23 F 11/14. Method of forming corrosion inhibiting films with hydrogenated benzotriazole derivatives. J. P. Pilsits, J.S. Gill and A.M. Cognetti, 1999. 

These findings led to the development of an inhibition concept and in cases where corrosion was extensive, e.g. for copper, inhibition was possible by addition of small amounts of IH-benzotriazole. 

SFG can provide considerable information regarding the buried interface that is of central importance to corrosion inhibition processes. A model system in this respect is the monolayer of benzotriazole (BTA) that forms beneath a thick multilayer of the same molecule on Cu. Two SFG studies have examined this system thus far [125, 126]. In the study by Schultz et al., SFG showed that BTA forms a relatively well-ordered monolayer on Cu(lOO) between -0.7 and -tO.2 V, while on Cu(lll) this order is only present at high potential. Titration with Cl showed that the monolayer was destabilized at lower Cl concentrations than those needed to destabilize the polymeric and somewhat more inaccessible multilayer. Work performed by Romero et al. using 5-methylbenzotriazole on Cu(poly) show that the 5-methylbenzotriazole is stable on the surface with no orientation changes with potential [125]. Similarly to the system studied by Schultz, the degree of preferential ordering of BTA on Cu(lll) seems to be less than that on the Cu(poly) surface. 

The triazole moiety has anticorrosive properties in general. For copper and its alloys, in aqueous medium, benzotriazole is most widely used as a corrosion inhibitor. 5-Aminotriazole is used as such in an anticorrosion lubricating oil composition. The corrosion of metals in acidic solutions is inhibited by adding 0.01-1 wt.% of a pol5mier with a backbone of 1,2,4-triazole. ... 

Matheswaran, P. and Ramasamy, A. K. Influence of benzotriazole on corrosion inhibition of mild steel in citric acid medium. E-Journal of Chemistry,7(3), 1090-1094 (2010). 

Selvi, S. T, Raman, V., and Rajendran, N. Corrosion inhibition of mild steel by benzotriazole derivatives in acidic medium. Journal of Apphed Electrochemistry, 33(12), 1175-1182(2003). 

Some of the types of compounds that function through electrostatic adsorption may also function by chemisorption. Chemisorption is most evident with nitrogen or sulfur heterocyclics. Benzotriazole and polytriazole, both effective inhibitors of copper corrosion, are believed to operate through chemisorption, as does 0. IM butylamine, which is effective in inhibiting the corrosion of iron in concentrated perchloric acid. However, the effectiveness of a given compound depends on the mechanism and operating conditions. 

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