Formation of a Nano--pore during Oxidation of Metal Nanoparticles

摘要

Formation of hollow oxides via the oxidation of Cu and Ni nanoparticles has been investigated by transmission electron microscopy. Hollow Cu_2O was formed after the oxidation of Cu nanoparticles with around 40 nm in diameter at around 350 K in air, while hollow NiO was obtained by oxidizing Ni nanopartciles with around 50 nm at 673 K. Since the diffusion coefficients of metal ions are much larger than those of oxygen ions in Cu_2O and NiO, the Kirkendall effect at the metal/oxide interface, where metal diffuses much faster than oxygen, brings about the generation of supersaturated vacancies in the metal side. As a result of vacancy clustering during oxidation reaction, a nano-pore is introduced in the metal oxide particle, In this paper, formation behavior of voids and nano-pores in the oxidation of Cu and Ni nanoparticles will be discussed on the basis of the diffusion properties of metals and their oxides.