Authored By:
Xiaonan Wang, Bev Christian
BlackBerry, Cambridge, Ontario, Canada
Mark Pritzgker
Department of Chemical Engineer, University of Waterloo
Waterloo, Ontario, Canada
Summary
The corrosion behaviour of pure copper in 16 selected commercial beverages was studied. Experiments were also conducted in the presence of citric and phosphoric acids to investigate their role in the corrosion process in these beverages. Two experimental approaches were used to investigate the corrosion behavior: a chemical method in which the dissolved metal concentration was measured after immersion of a sample in a beverage and an electrochemical method using the Tafel extrapolation technique. The metal surfaces were also examined by SEM/EDX after the immersion tests and electrochemical polarization.
Among the important conclusions from this research are that the order in which the various beverages affect the corrosion rate as evaluated by Tafel extrapolation of the polarization curves did not agree with the order based on measurement of the dissolved metal concentration as determined by the immersion tests.
Second, the ranking of the beverages according to their ability to dissolve copper based on shortterm immersion tests (1 day) did not agree with that based on long-term tests (~5 or 7 days). These discrepancies likely stem from the complicated dynamics of the corrosion of metal and the various physical, chemical and electrochemical processes that take place in these beverages.
No simple correlation was found between the beverage properties and composition and the dissolved copper concentrations after immersion, whether based on shortterm or long-term tests. However, the corrosion rate of copper in the 7 soft drinks as determined by the Tafel extrapolation method was found to depend on the pH, but not in other beverages such as juices, hot drinks, milk and alcohol. SEM examination of copper surfaces showed that they corroded uniformly in all test beverages.
Evidence for the formation of corrosion products containing chlorine was found in both the immersion test and the polarization scan when the applied potential increased to 1.0 V above the open-circuit potential. Of the beverages considered in this study, Gatorade was consistently found to be the most corrosive for copper.
Conclusions
The corrosion behaviour of copper has been studied in 16 commercial beverages by measuring the dissolved metal concentration after immersion for different durations using ICP-OES and by using a number of electrochemical techniques (OCP measurement, Tafel extrapolation methods). Physical properties and chemical composition of 16 commercial beverages were also investigated by a set of efficient methods. The metal surfaces after corrosion were examined and characterized by SEM/EDX analysis. The following conclusions can be drawn from the above experiments:
- The ranking of the beverages according to their ability to dissolve copper based on short-term immersion tests (1 day) did not agree with that based on long-term tests (~5 or 7 days). No correlation was found between the dissolved copper concentrations and beverage properties (e.g. pH, conductivity, etc.) or composition regardless whether shortor long-term immersion tests were conducted.
- The ranking of corrosion rates of Cu estimated from the polarization curves is not in agreement with that based on the measurement of dissolved Cu concentrations after immersion in the various beverages for either short- or longterm.
- The electrochemical measurements indicated that the corrosion rates depend on pH in the 7 soft drinks, but not in other beverages such as juices, hot drinks, milk and alcohol.
- NaCl promotes the corrosion of copper in citric acidcontaining solutions.
5.SEM examination of copper surfaces showed that they corroded uniformly in all test beverages. - The immersion tests show that Gatorade is the most aggressive beverage toward copper. Evidence for the formation of corrosion products containing chlorine was found in both immersion test and the polarization scan.
Initially Published in the SMTA Proceedings
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