Abstract
Corrosion inhibition by 2-mercaptobenzothiazole (MBT) at the surface termination of various types of grain boundaries (GBs) was studied at the nanometer scale on microcrystalline copper in HCl acid solution using in situ electrochemical scanning tunneling microscopy (ECSTM). Macroscopic electrochemical analysis by cyclic voltammetry showed highly effective inhibition of Cu(I) active dissolution blocked by MBT pre-adsorption in a potential range of 0.15–0.2 V. ECSTM analysis of the initial stages of intergranular corrosion confirmed the mitigation of net intergranular dissolution by the pre-adsorbed MBT surface layer but also revealed the local accumulation of reaction products in the GB regions. For Coincidence Site Lattice boundaries other than coherent twins, intergranular dissolution, mitigated by the pre-adsorbed MBT layer, and protection by intergranular formation of a film of reaction products were observed. For random GBs, protection by reaction products was dominant, in agreement with their more reactive intrinsic character, generating more Cu(I) ions under anodic polarization and thus promoting the formation of a protective film of reaction products. Coherent twins did not show preferential intergranular reactivity compared to adjacent grains, indicating equally strong efficiency than on grains. These results bring new insight on how inhibition operates locally at various types of GBs.
Highlights
To cite this version: Sagar Sharma, Vincent Maurice, Lorena Klein, Philippe Marcus
No stable copper oxide is formed at pH 2 and the Cu(I) ions formed in HCl medium.[57,58,59,60]
Half of them (25, 27, 29, 31 and 33) show an increase of the grain boundary (GB) depth after 4 cyclic voltammograms (CVs) to a value higher that the initial value measured before cycling, indicating a pronounced alteration of the transient protection against anodic dissolution brought by the initial growth of the surface film of reaction products
Summary
We report on the nanoscale local characterization using electrochemical scanning tunneling microscopy (ECSTM) of the inhibition of early intergranular corrosion of copper by MBT in HCl acid solution in which no stable copper oxide is formed. I.e. a nearly random texture, was obtained[23] and 66% of the GB length corresponded to ∑3 CSL boundaries, the other 34% being random boundaries for the most part.[22,23] Samples were mechanically polished with diamond spray down to a final grade of 0.25 μm for surface preparation, which was followed by electrochemical polishing in 66% orthophosphoric acid at 3 V vs a copper counter electrode for 15 s in order to remove the cold work layer. Two cycles were enough to fully reduce the native oxide formed after electropolishing After this pre-treatment, ECSTM images of the microcrystalline copper surface in the metallic state were taken at −0.45 V/SHE for localization of grain boundaries of interest. Ten different measurements were performed for each selected site and the reported error bar is the standard deviation for these ten measurements
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