The Mechanism of Sulphide Film Growth on Copper in Anaerobic Sulphide Solutions Under Natural Corrosion Conditions

Abstract

Background and Method: The growth mechanism of sulphide films formed on copper in anaerobic 0.1 M NaCl + 5 x 10 -4 M Na2S solution has been investigated under natural corrosion conditions for exposure periods up to 1691 hours using scanning electron microscopy, focused ion beam cross-sectioning, and a Au marker procedure. Results and Conclusions:The film formed by a chemical deposition process via an outward growth mechanism. This process was controlled by cuprous ion transport in the film combined with sulphide diffusion in solution.

The effects of chloride and sulphate on the growth of sulphide films on copper in anoxic sulphide solutions

“…However, in SO 4 2− ‐containing solution, R P values continued to increase. Since our previous study demonstrated that the film growth was proceeding under diffusion control in Cl − ‐containing solutions, [ 14 ] and that film deposition occurred at the Cu 2 S/electrolyte interface, [ 23 ] the dependence of film growth rate on SH − supply is consistent with a porous film which does not act as a significant corrosion barrier as it thickens.…”

“…with R P −1 proportional to the film growth rate (which can be considered as directly proportional to the corrosion rate). The change of the polarisation resistance is plotted as a function of exposure period for both SO previous study demonstrated that the film growth was proceeding under diffusion control in Cl − -containing solutions, [14] and that film deposition occurred at the Cu 2 S/electrolyte interface, [23] the dependence of film growth rate on SH − supply is consistent with a porous film which does not act as a significant corrosion barrier as it thickens.…”

“…Previous studies [ 12–27 ] showed that Cu would corrode rapidly in the presence of SH − , leading to the deposition of chalcocite (Cu 2 S [ 13 ] ) on the Cu surface. The structure and properties of the Cu 2 S film were shown to depend on the [SH − ], the transport flux of SH − to the corroding Cu surface, and the influence of other groundwater species (i.e., Cl − , SO 4 2− and HCO 3 − /CO 3 2− ), which interfered with sulphide film formation by competition with SH − for surface sites on the Cu surface.…”

“…[5] Once anaerobic conditions are established at the Cu container surface, [8,9] the long-term threat to container durability and integrity will be the degradation by reaction with sulphide (SH − ), remotely produced by the activities of sulphate-reducing bacteria. [10][11][12] Previous studies [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] showed that Cu would corrode rapidly in the presence of SH − , leading to the deposition of chalcocite (Cu 2 S [13] ) on the Cu surface. The structure and properties of the Cu 2 S film were shown to depend on the [SH − ], the transport flux of SH − to the corroding Cu surface, and the influence of other groundwater species (i.e., Cl − , SO 4 2− and HCO 3 − /CO 3 2− ), which interfered with sulphide film formation by competition with SH − for surface sites on the Cu surface.…”

“…It was suggested that this could be attributed to the strong co-adsorption of SO 4 2− and H 2 O on the Cu surface. [26] Long-term studies [13][14][15]17,18,[20][21][22][23] have demonstrated that, under corrosion conditions, the structure and properties of the Cu 2 S film vary greatly with the exposure conditions. When the bulk [SH -] (i.e., 5 × 10 -5 M), the SHflux and the [Cl − ] (i.e., 0.1 M) were low, leading to even lower [SH − ] at the Cu surface, the Cu 2 S film was very porous and nonprotective, and its growth was controlled by the flux of SH − to the Cu 2 S film/electrolyte interface.…”