Corrosion inhibition of copper by new triazole phosphonate derivatives
Introduction
Copper is commonly used in heating and cooling systems due to its excellent thermal conductivity and exciting mechanical workability. Copper is one of the most important nonferrous metals used in industry as well as water distribution networks. It is susceptible to different forms of corrosion such as pitting corrosion induced by different corrosive species like chloride, sulphate and nitrate ions [1], [2].
Heat exchangers require good thermal conductivity, corrosion, stress-corrosion resistance, and strength at modest cost. These requirements vary in importance for each application. Biological fouling decreases thermal efficiency and inherent to localised corrosion attack; hence, resistance to biofouling is sometimes important. Copper and copper alloys offer good combinations of these properties. Fouling and corrosion are the two important operational problems in heat exchangers and associated cooling water system pipelines. The problems include flow blockage of pipes, pipe punctures and unacceptable general corrosion rates of the system components.
The inhibition of copper corrosion in neutral or slightly alkaline oxygen containing solutions is one of the most hectic tasks for cooling water system operations. A study of mechanistic action of corrosion inhibitors has relevance both from the point of view of a search for new inhibitors and also for their effective usage [3]. Many authors have investigated the corrosion control of copper in various media using large numbers of organic and inorganic compounds. Results showed that organic compounds, especially those containing nitrogen [4], [5], [6] or sulphur [7] gave a very good inhibition for copper corrosion in different media. It is well known that triazole types of organic compounds are good corrosion inhibitors for many metals and alloys in various aggressive media [8], [9]. However, in the presence of an organic inhibitor, the properties of the protective layer can be modified.
Phosphonic acids renowned their hydrolytic stability, scale inhibiting property and ability to form complexes with metal cations, has been a choice as candidate for corrosion inhibitors [10], [11]. Hence in the present investigation some triazole derivatives are synthesised that contains phosphonic acid group and their efficiency in the inhibition of copper corrosion in neutral aqueous environment are studied.
Generally, for controlling fouling and corrosion, continuous addition of inhibitors as well as the addition of biocides every week or once in a fortnight is explored. It is not known as to whether interference effect between biocides and inhibitors will lead to any adverse effect. Recently, few researchers have turned their attention to these aspects. However, the knowledge on effect of inhibitors and biocide on corrosion control in cooling water systems are limited.
Hence, it is quite essential to study the interference between inhibitors and biocide for cooling water systems. In the present study synthesised triazole phosphonates was used as inhibitors while the biocide, cetyl trimethyl ammonium bromide (CTAB) is used to study their interference effect on corrosion process of copper.
Section snippets
Synthesis of triazole derivatives
Three grams of 3-amino 1,2,4- triazole at a concentration of 0.05 M was dissolved in 20 ml of concentrated HCl and to this solution 2.5 ml of hypophosporus acid was added. The reaction mixture was put inside the fuming cupboard and to this 4.5 ml aldehyde (R) was added [12], [13], [14]. The reaction mixture was refluxed for 4 h on an oil bath inside the fuming cupboard. The reaction mixture was evaporated and cooled. Addition of water and methanol to this cooled solution resulted in the formation of
Electrochemical study
The cathodic and anodic polarisation of copper in lake water in the presence and absence of various concentrations of triazole derivatives for 3 days were carried out. Each inhibitor was studied at different concentration levels e.g. 2, 3, 4, 5, 6, 8 and 10 ppm. The efficiency was found to increase appreciably with the increase in inhibitors concentrations upto 4 ppm after which it decreases. The optimum concentrations of inhibitors were evaluated based on inhibition efficiency.
Various corrosion
Conclusions
The present study leads to the following conclusion in corrosion control of copper in natural aqueous environment.
- 1.
In various inhibitor systems, system IV has higher efficiencies than system III and elucidates the minimal interference between biocide and inhibitors system.
- 2.
The inhibition efficiencies calculated from ac measurement show the same trend as those observed from dc polarisation results.
- 3.
The dissolution of copper in presence of VATP and AATP with biocide mixture is negligible compared to
Acknowledgements
The authors greatly acknowledge TamilNadu State Council for Science and Technology (TNSCST) for providing financial support for doing this work.
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