Microstructural Development of Copper Sulfide on Copper Exposed to Humid H[sub 2]S

Abstract

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 ͑H 2 S͒. 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 ͑FIB͒, 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 ͑Cu 2 S͒ and cuprite ͑Cu 2 O͒. Once the Cu 2 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 ͑ϳ1000 nm͒ internal stresses and defects in the corrosion layer allow virtually free access of H 2 S and O to the underlying layers, consequently accelerating the film growth.

Characterization of the patina formed on a low tin bronze exposed to aqueous hydrogen sulfide

“…There is general agreement that Cu 2 S (chalcocite) is formed on copper exposed to H 2 S(g) . The growth of Cu 2 S on copper exposed to moist air containing H 2 S has been observed previously and competes with formation of Cu 2 O and CuO depending on temperature and relative humidity . The results reported here indicate dominance of Cu 2 S and an absence of CuO, not surprising in the O 2 ‐purged solutions used, but the electrochemical formation mechanism could be similar and occur without the need to invoke O 2 : …”

Study of Mixed Flowing Gas Exposure of Copper

“…During the first 7 days of exposure, the thickness of the corrosion film increased linearly, followed by a slowdown, suggesting a transition from activation control ͑where the determining step is the reaction of the corrosive species with the Cu͒ to diffusion control ͑where the diffusion of the species through the corrosive layer is more important͒. 12,13 After the slowdown behavior, an additional slower rate of linear growth ͑slower than the first week͒ was observed, possibly indicating a combination of activation and diffusion control. Figure 3 shows a typical cathodic reduction curve for one Cu coupon exposed for 2 days.…”

Characterisation of corrosion products formed on copper exposed at indoor and outdoor sites with high H2S concentrations

“…The coexistence of cuprite and chalcocite suggests that the 7 Glow discharge optical emission spectroscopy depth profiles of copper, sulphur and oxygen for copper plate exposed indoors 8 Glow discharge optical emission spectroscopy depth profiles of copper, sulphur and oxygen for copper plate exposed outdoors a low magnification image (100 times); b high magnification image (500 times); c EDX spectra for point marked in b 6 Images (SEM) and EDX spectra for copper plates exposed outdoors formation of both phases occurred simultaneously during exposure. Reid et al studied copper sulphidation at 40uC and 90%RH with 4 ppm H 2 S. 38 Depth profiling analysis of the corrosion layers by secondary ion mass spectrometry showed that chalcocite was the main component of the corrosion layer. Secondary ion mass spectrometry depth profiling showed that there was a thin cuprite layer at the interface between the corrosion layer and copper substrate.…”