Microstructural development of copper sulfide on copper exposed to humid H2 S

Pure copper samples were exposed in an environmental chamber for 2, 4, 7, 15, and 30 days at 90% relative humidity, 40°C, and 4 ppm hydrogen sulfide (H2 S). Samples were subsequently subjected to microscopy and microanalysis using different techniques: scanning electron microscopy, energy analysis dispersive X-ray spectroscopy, X-ray diffraction, focused ion beam (FIB), and secondary ion mass spectroscopy. The corrosion samples were cross sectioned and the different corrosion layers were imaged using FIB. After 30 days exposure the predominant corrosion products were copper sulfide (Cu2 S) and cuprite (Cu2 O). Once the Cu2 S reached a minimum thickness, the rate of growth of the layer became parabolic due to the limiting Cu+ diffusion through a thickening film. As the layers reach a critical thickness (∼1000 nm) internal stresses and defects in the corrosion layer allow virtually free access of H2 S and O to the underlying layers, consequently accelerating the film growth.