Grain boundary passivation studied by in situ scanning tunneling microscopy on microcrystalline copper

Abstract

Electrochemical scanning tunneling microscopy (ECSTM) was applied to analyze in situ the passivation of grain boundaries on microcrystalline copper in 0.1 M NaOH aqueous solution. Two types of boundaries, assigned to coherent twin and random grain boundaries, were studied in three different states of the copper surface: metallic after cathodic reduction of the air-formed native oxide film, passive after anodic polarization at 0.7 V vs. SHE to form the duplex Cu(I)/Cu(II) oxide film, and metallic after cathodic reduction of the passive film. The depth measured at several sites along the grain boundaries was extracted from statistical line profile analysis and discussed using an original model allowing differentiating metal consumption by dissolution or by passive film formation at grains and grain boundaries. The results highlight different local passivation properties between randomly oriented grains and grain boundaries and also between the two different types of grain boundaries. Both at coherent twin and random grain boundaries, it is found that more copper irreversibly dissolves during passivation and less copper is consumed to grow the passive film, suggesting a more hydroxylated/hydrated composition less dense in copper than on grains. At random grain boundaries, irreversible dissolution is found to be enhanced and the passive film to be thicker

Current developments of nanoscale insight into corrosion protection by passive oxide films

“…In the case of Cu(I)/Cu(II) passivation (Figure 6b) [92,93], the passive film was found thicker at random boundaries than at coherent twin boundaries like for the Cu(I) passive film.…”

Local Effects of Organic Inhibitor Molecules on Passivation of Grain Boundaries Studied In Situ on Copper

“…The experiments were performed with microcrystalline samples obtained by cryogenic rolling after freezing in liquid nitrogen of highpurity cast electrolytic tough pitch copper. [22][23][24][25][26]65,66,[81][82][83] In order to ensure the relatively smaller grain size necessary for the microstructure to be included in the STM field of view, the annealing treatment for full recrystallization of the samples was limited in time and temperature of 1 min and 200°C, respectively. The resulting samples showed no preferential grain orientation, i.e.…”

Effect of the microstructural properties of copper on corrosion performance

“…It has been reported that, in a 0.1 M NaOH solution, the passive film of Cu(I) oxide is thicker at grain boundaries than on the grains, and that no metal is preferentially consumed by transient dissolution at the grain boundaries [25,26]. Martinez-Lombardia et al investigated grain-dependent corrosion on microcrystalline copper in a 10 mM HCl aqueous solution and reported the dependence of grain orientation on corrosion [27].…”