The Early-Stage Corrosion of Copper Materials in Chloride and Sulfide Solutions: Nanoscale Characterization and The Effect of Microstructure

Abstract

The microstructures of copper (Cu) materials were investigated by electron backscatter diffraction, showing that electrodeposited (ED) Cu has a homogenous polycrystalline microstructure, while cold spray (CS) Cu has a heterogeneous microstructure with varying grain size, pores, and interfacial splat regions. The corrosion rate was examined by corrosion potential (ECORR) and polarization resistance (Rp) measurements on Cu specimens in solutions containing 0.1 M NaCl + 1 × 10−3 M Na2S. Although the as sprayed CS-Cu was the least corrosion resistant, the corrosion rate of the heat-treated CS-Cu was similar to that of the ED-Cu and wrought Cu (SKB-Cu). Electrochemical behaviours of Cu materials were investigated by either a potentiodynamic scan or a potentiostatic polarization at a more positive potential (E > ECORR) for various experiment durations up to 4 h, showing that the heat-treated CS-Cu, SKB-Cu and ED-Cu exhibited very similar behaviour while the as sprayed CS-Cu showed erratic behavior consistent with a variable surface reactivity. Nanoscale scanning transmission electron microscopy analysis has been performed at the cross-section of an anodically-oxidized CS-Cu specimen, revealing a two-layer film structure, mostly composed of Cu sulfide, with a minor diffusion of sulfur in the local area of an interfacial splat boundary tip.

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“…Various types of Cu materials in Figure 1 were exposed to 0.1 M NaCl + 1 × 10 −3 M Na 2 S for short time periods (in most cases on the order of minutes) with the aim of studying early stage sulfide formation. [ 36 ] As part of this, a goal was to characterize the sulfide film formed on Cu at the nanoscale to evaluate both the microstructure and morphology of the film. Application of analytical TEM methods to better understand corrosion mechanisms at localized regions (e.g., pits) has become frequent in the past two decades, partly due to the widespread use of FIB‐SEM for site‐specific sample preparation.…”

“…The latter surface preparation details are also reported elsewhere. [ 36 ] Figure 1b shows that the ED Cu has a solid solution, fine grain microstructure (<5 µm), while the P‐doped oxygen‐free SKB Cu, proposed for use in Sweden, in Figure 1d has a large grain microstructure (>100 µm). Figure 1a shows the AS‐CS Cu, which has particle–particle boundaries, decorated by large voids, which are formed during the CS process.…”

“…Scanning electron microscope images of electropolished Cu specimens: (a) secondary electron (SE) image of an AS‐CS Cu sample, (b) SE image of an electrodeposition‐Cu sample, (c) backscattered electron (BSE) image of a heat‐treated CS‐Cu sample, and (d) SE image of the P‐doped oxygen‐free Cu. Reprinted from Guo et al [ 36 ] © The Electrochemical Society. Reproduced by permission of IOP Publishing.…”

“…Electrochemical corrosion tests were carried out as part of a study to examine the early stage corrosion of Cu in sulfide‐containing solutions. [ 36 ] A 700 mL three‐electrode cell was used with a Cu working electrode (WE), Pt counter electrode (CE), and saturated calomel reference electrode (SCE). Electrochemical measurements were recorded using a Gamry Interface 1010E potentiostat (Gamry Instruments Inc.) and processed using Echem Analyst software.…”

“…Generally, experiments were conducted slightly more anodic than the corrosion potential to investigate early sulfide formation (at −0.9 V vs. SCE). However, the sample of interest to this work was an AS‐CS Cu specimen potentiostatically polarized at −0.4 V versus SCE for 3.5 h to promote the growth of a thicker sulfide film for subsequent nanoscale characterization using transmission electron microscopy [ 36 ] (TEM, see Section 2.5). Indentation of the sample was used as a reference to identify the same area before and after exposure.…”