Abstract
In order to investigate the role of chloride ion in the corrosion film formation of copper and its evolution over time, the initial corrosion behavior of copper in neutral 3.5% (wt.) NaCl solution was characterized by in-situ Raman spectroscopy along with electrochemical tests. The results demonstrated that the cuprous chloride complexes, such as CuCl and were produced through electrode processes, while the cuprite, seemed to be formed via the chemical precipitation reaction instead of a direct electrochemical transformation from the metal matrix or CuCl and it occurred rather slowly. At the open circuit potential, the chlorides were generated first in the initial 2 h and then they transformed to the oxides with the content in the interface increasing. The in-situ Raman characterization directly evidenced the previously reported mechanism of growth of oxide layers on copper surfaces in neutral media and clearly showed the formation of a corrosion product film and its evolution over time. The electrochemical tests corresponded to the results of in-situ Raman characterization well.
Highlights
Copper has found broad application in industrial fields such as nuclear waste processing [1,2,3,4], printed circuit boards [5,6,7] and it is one of the more stable metals due to its high overpotential for hydrogen evolution and the absence of surface oxides in acidic solutions
The corrosion of copper in Cl− media has been widely studied and the results have indicated that Cl− has a marked impact on the copper corrosion mechanism [9,10,11,12]
The in-situ Raman characterization was performed in a special cell with an aforementioned prepared copper electrode facing up as working electrode, a platinum ring around the copper electrode as the auxiliary electrode and a saturated Ag/AgCl electrode being the reference electrode, which has a potential of 40 mV vs. saturated calomel electrode (SCE)
Summary
Copper has found broad application in industrial fields such as nuclear waste processing [1,2,3,4], printed circuit boards [5,6,7] and it is one of the more stable metals due to its high overpotential for hydrogen evolution and the absence of surface oxides in acidic solutions. The authors proposed that Cl− reacts with a copper atom at the kink site forming a cuprous chloride species as in reaction (4) and it dissolves from the edge to form a CuCl−. The effects of Cl− on the initial stage of anodic dissolution of copper get much more complicated because of the involvement of OH− and the formation of oxide layers as a result. As reported by by Suggs and Bard [15], in a neutral KCl solution (10 mM, pH 6.5) STM images revealed the same Cl− adlattice structure on Cu (111) as that observed in 10 mM hydrochloric acid. In this work, the initial corrosion behavior of copper in neutral 3.5% (wt.) NaCl solution was characterized by in-situ Raman spectroscopy along with electrochemical tests and the formation of the corrosion product film and its evolution over time were demonstrated clearly
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