Effect of sulfide on de-passivation and re-passivation of copper in borate buffer solution

Effect of Sulfide Addition on the Corrosion Mechanism of Copper in Saline Groundwater Solution

“…At the lower sulfide concentration, the log-log plots of current vs time are quasi-linear with a slope of 0.6-0.8, indicating repassivation via continuous film formation. Formally, a linear portion in Q −1 -log(i) curves can be detected, however, in analogy to our previous paper, 25 the derivative of the logi-Q −1 plot is not constant in the interval of importance, i.e. the high-field mechanism of repassivation is not operative.…”

“…2) in which the corrosion potentials after 24-48 h of exposure in sulfide-free and sulfidecontaining solutions are indicated Two sulfide phases are predicted to be stable-Cu 2 S and CuS-in agreement with what was reported in our previous paper for chloride-free environment. 25 However, in the presence of chloride, the open-circuit potential is at the CuCl 2 − /Cu equilibrium line and there is no evidence of solid product formation. Addition of sulfide moves the corrosion potential at the Cu 2 S/Cu line in equilibrium with a soluble sulfide-containing product (Cu 2 S(HS) 2 2− ).…”

“…Based on this short review of the literature, it can be concluded that a bilayer Cu x S deposit is formed, the inner layer of which did not exhibit passivation abilities at the corrosion potential, and copper is most probably not prone to localized corrosion modes such as pitting in such environments. In a recent study of ours 25 it has been shown that in borate buffer solution with sulfide addition (0.3 to 2.4 mmol dm −3 ), the general corrosion rate is very high, around 1 mm y −1 , and re-passivation rates are much slower than in environments in which copper is known to be susceptible to SCC such as nitrite solutions. 26 A slow enough re-passivation rate will give time for the initiated crack tip to dissolve, thereby reducing the stress-strain field ahead of the crack tip to a low enough level so that further crack advancement becomes impossible.…”

“…The general corrosion and re-passivation rates are estimated using electrochemical techniques already established in previous work, namely voltammetry, current-time transients and electrochemical impedance spectroscopy. 25 The structure and composition of corrosion layers is assessed with electron microscopic examinations of surfaces and cross-sections coupled to electron dispersive spectroscopy. Based on previously proposed deterministic models for the interaction of Cu with borate buffer containing chloride 28 and sulfide, 25 kinetic parameters of individual reaction steps are estimated, and some conclusions on the (im)possibility for SCC initiation are drawn.…”

“…25 The structure and composition of corrosion layers is assessed with electron microscopic examinations of surfaces and cross-sections coupled to electron dispersive spectroscopy. Based on previously proposed deterministic models for the interaction of Cu with borate buffer containing chloride 28 and sulfide, 25 kinetic parameters of individual reaction steps are estimated, and some conclusions on the (im)possibility for SCC initiation are drawn.…”