Papers by Keyword: Vacancy Clustering

Abstract: The formation process of oxide nanotube via metal oxidation reaction was studied by transmission electron microscopy for Cu, Fe, and Ni nanowires. Cu2O and Fe3O4 nanotubes were formed after the oxidation of Cu and Fe nanowires with a diameter of 55 nm in air at 423 and 573 K for 3.6 ks, respectively. Both Cu2O and Fe3O4 nanotubes had a cylindrical interior pore with uniform diameter. On the other hand, Ni nanowires became bamboo-like structures of NiO with separate interior pores after oxidation at 673 K for 7.2 ks. The formation of the interior pores in Cu2O and Fe3O4 nanotubes and NiO bamboo-like structures can be explained by the rapid outward diffusion of metal ions through the oxide layers and the clustering of excess vacancies.

Abstract: Changes in morphology during the oxidation of iron nanoparticles and nanowires at 473~ 873 K have been studied by transmission electron microscopy. Iron nanoparticles and wires become hollow nanoparticles and nanotubes of Fe3O4 at temperatures below 673 K as a result of vacancy aggregation in the oxidation process. On the other hand, the hollow magnetite transforms into duplex porous structures with an interior nanopore and additional nanovoids at higher temperatures above 673 K, where the shrinkage of hollow nanoparticles and nanotubes starts and the phase transformation from Fe3O4 to -Fe2O3 occurs. Transition in porous structure seems to be related to the outward diffusion of vacancies from interior pore and the phase transformation in the shrinkage process.