Nanoparticles and filled nanocapsules Original Research Article

Encapsulation of foreign materials within a hollow graphitic cage was carried out for rare-earth and iron-group metals by using an electric arc discharge. The rare-earth metals with low vapor pressures, Sc, Y, La, Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, Tm, and Lu, were encapsulated in the form of carbides, whereas volatile Sm, Eu, and Yb metals were not. For iron-group metals, particles in metallic phases (α-Fe, γ-Fe; hcp-Co, fcc-Co; fcc-Ni) and in a carbide phase (M3C, M = Fe, Co, Ni) were wrapped in graphitic carbon. The excellent protective nature of the outer graphitic cages against oxidation of the inner materials was demonstrated. In addition to the wrapped nanoparticles, exotic carbon materials with hollow structures, such as single-wall nanotubes, bamboo-shaped tubes, and nanochains, were produced by using transition metals as catalysts.