Effects of inlet gas-flow rates on synthesis of CuO nanowires during thermal oxidation

Ω-shaped copper specimens were oxidized in a tube furnace with wet air at 1 atm. and inlet gas-flow rates from 0.01 to 1.4 l/min at 500 °C for 4 hours. Scanning electronic microscope (SEM) results show that the density of nanowires formed on the surface of specimens during oxidation is significantly related to inlet gas-flow rate and the positions of a Ω-shaped specimen. A 3-dimensional (3D) flow simulation using a CFD solver (Fluent) was used to express local gas flow field near the surface of the specimen. The relation among oxide morphology, including, no-wire, whisker and nanowire, shear stress of flowing gas near the surface of the specimen and inlet gas-flow rate is given in this paper. When the inlet gas-flow rate reaches the critical value of 0.15 l/min, whiskers or nanowires can be formed on the positions of Ω-shaped specimens with low shear stress of flowing gas near the surface of the specimen. The experimental results are explained by oxygen resident time on specimen surface and amount of oxygen through the local surface of a specimen.