Comparison of the Oxidation Behavior of Nanocrystalline and Coarse-Grain Copper

Abstract

The Oxidation of an electro-deposited nanocrystalline Cu (nc Cu) and a conventional coarse-grain Cu (cg Cu) was investigated at 30-800 • C under 1 atm of oxygen. Both Cu samples formed external scales of copper oxide (Cu 2 O+CuO). At the lower temperature (30-300 • C) the very slow oxidation rates of both the nc and cg Cu might be attributed to the formation of a protective Cu 2 O surface layer. However at the higher temperature (300-700 • C), oxidation rates of the nc Cu were obviously faster than those of the cg Cu, which was attributed to faster diffusion of various species along grain boundaries both in the metal and in the scale. In particular, the scale grew faster on the nc Cu by means of not only rapid external oxidation as a result of outward diffusion of Cu-ions but also a significant contribution from inward diffusion of oxygen along the grain boundaries in the scales. Compared with the cg Cu, dissolved O 2 in the nc Cu may have a certain effect on the faster oxidation of the nc Cu. Above 700 • C, the difference seemed to disappear as a result of the ineffectiveness of grain-boundary diffusion.

Short-circuit diffusion growth of long bi-crystal CuO nanowires

“…As Cu is oxidized, the oxide film replicates the grain structure of polycrystalline Cu. Therefore, a finer grain structure in the copper oxide film is obtained when grown from nanocrystalline or SMAT Cu than from coarse grain Cu [29]. The CuO NW growth by oxidizing Cu in air was found to be dominated by grain boundary diffusion at the temperature range of 400-600°C [26].…”

“…Furthermore, NW growth mainly occurs in the temperature range of $400-600°C. In this temperature range, Cu ion and oxygen diffusion is dominated by diffusion along defects and grain boundaries in the oxide scale [27][28][29]. Therefore, a model was proposed in which CuO NWs are formed as a result of the rapid, short-circuit diffusion of the Cu ions across the Cu 2 O layer.…”

Enhanced anodization growth of self-organized ZrO2 nanotubes on nanostructured zirconium

“…Bei et al reported that numerous crystal defects such as grain boundaries and dislocations in the nanostructured material constitute a high stored energy that may facilitate chemical reaction [24]. Han et al also reported that the oxidation rate of the nanocrystalline Cu was obviously faster than that of the coarse-grained Cu, which was attributed to faster outward diffusion of Cu-ions [38]. As aforementioned in the previous work [25][26][27], SMAT of Zr could create a nanostructured surface layer with thickness more than 20 μm, and the nanostructured layer contains a high density of grain boundaries and dislocations; the nanostructured surface layer of the annealed SMATed-Zr contains a high density of grain boundaries but significantly reduced dislocations; the unSMATedZr appears as coarse-grained structure and few of dislocations were observed.…”

Significant improvement of wear properties by creating micro/nano dual-scale structure in Al–Sn alloys

“…Xue et al reported similar results, in that grain size reduction led to the significant improvement of wear resistance in UFG Ti [11] and NC Ni [12]. Lu et al [13][14][15] reported that with NC Cu metal, it was easy to form a mixed surface layer that prevented wear damage because of the presence of an additional oxidation reaction by sliding.…”

“…10(e), the area ratio of the mechanical mixing layer decreased linearly with reduction in the NC/UFG ratio. Obviously, higher ratio of UFG favors the formation of a mechanical mixing layer because the NC/UFG has a high oxidation rate [15]. This phenomenon could be attributed to the presence of more grain boundaries, which act as nucleation sites for the oxides and diffusion paths of oxygen during the mixing process caused by sliding [13,35].…”