Researchers used a variety of tools to characterize copper corrosion on their copper samples. Typical tools included the scanning electron microscope (SEM) [1,2,3] and focused ion beam (FIB), [1] but they also used energy analysis dispersive X-ray spectroscopy (EDS), [1,3] X-ray diffraction (XRD), [1] secondary ion mass spectroscopy (SIMS), [1] X-ray photoelectron spectroscopy (XPS), [2,3] cathodic reduction, [3] and coulometric reduction. [2] Tools like the SEM and FIB were used to image the corrosion surfaces, not characterize corrosion compounds. XRD, cathodic reduction, and coulometric reduction were used to actually characterize the corrosion compounds. XRD analysis seemed to be the most effective in this analysis as cathodic reduction was reported to damage corrosion surfaces. [3]

Among all of the articles that were reviewed none of them discuss specific procedures to their electron microscope imaging processes. The most detailed procedure was found in Reid et al., which described a "crater" boring process into the sample that was then tilted at 45˚ to image the cross-section of corrosion. [1] Demirkan et al. mentioned the use of an epoxy to mount the sample in their procedure. [3] It is evident that reaching out to the authors of these articles and metal reduction reaction experts on Northeastern University's campus is necessary to gather a detailed electron microscope analysis procedure.

The two most cited corrosion products expected should be copper sulfide (Cu2S) and cuprite (Cu2O). [1,2,3] Other corrosion products expected include Posnjakite [Cu4SO4( OH)6*H2O], brochantite [Cu4SO4(OH)6], and antlerite [Cu3SO4(OH)4]. [1] These ones are not expected to be found on our samples though.

Only Demirkan et al. reported the use of an epoxy to mount the copper samples before imaging under the electron microscope. They did not detail the exact brand of the epoxy though. An article discussing proper scanning electron microscope specimen preparation for cement samples explains why epoxies are used for this process though. [4] They claim:

"Epoxy impregnation of the pore system serves two purposes: A) it fills the voids and, upon curing, supports the microstructure serving to restrain it against shrinkage cracking, and B) it enhances contrast between the pores, hydration products, and cementitious material."

They go on to explain that the low-permeable cements require ultra-low viscous epoxies, which they recommend L.R. White, hard grade for ultra-low viscous. It may be advantageous to see how this may be applied to the corrosion analysis of the copper rods.

References

1) Reid M, Punch J, Ryan C, et al. Microstructural development of copper sulfide on copper exposed to humid H2S. J. Electrochem. Soc. 2007; 154(4): C209-C214. doi: 10.1149/1.2436612

2) Tran TTM, Fiaud C, Sutter EEM, and Villanova A. The atmospheric corrosion of copper by hydrogen sulphide in underground conditions. Corros. Sci. 2003; 45: 2787-2802. doi: 10.1016/S0010-938X(03)00112-4

3) Demirkan K, Derkits Jr. GE, Fleming DA, et al. Corrosion of Cu under highly corrosive environments. J. Electrochem. Soc. 2010; 157(1): C30-C35. doi: 10.1149/1.3258288

4) Strutzman P and Clifton J. Specimen Preparation for Scanning Electron Microscope. National Institute of Standards and Technology. Published April 1999.