Scanning electrochemical microscopy to study the effect of crystallographic orientation on the electrochemical activity of pure copper

The local electrochemical reactivity of high purity copper as a function of the grain orientation in the microstructure has been investigated. The different crystal orientations were determined by means of Electron backscatter diffraction (EBSD) followed by in-situ Scanning electrochemical microscopy (SECM) measurements operating in feedback mode across the very same copper surface. With this procedure it is possible to characterize in-situ the reactivity of selected grains in the polycrystalline microstructure of the copper. The study is focused on monitoring differences in the electrochemical response on <001>//ND and <111>//ND oriented grains. The behaviour of these selected orientations was studied under two surface conditions: passive state of copper after the formation of an anodic oxide layer, and corrosion or active state of the copper by immersion in chloride solution. In the case of the passivated copper it was observed that the grain with an orientation closer to <111>//ND shows a lower reactivity compared to the grain where the orientation is nearer to <001>//ND, which confirmed that grain orientation has an influence on the electrochemical reactivity of the passive layer formed on the metal. It was found that for the copper in the active state, the reactivity of a <111>//ND oriented grain is higher when compared to a <001>//ND oriented grain, which is contrary to the expected behaviour. This discrepancy could be explained by possible neighbouring effects between both grains.