CORRELATION BETWEEN VOLATILITY OF RARE-EARTH-METALS AND ENCAPSULATION OF THEIR CARBIDES IN CARBON NANOCAPSULES

Encapsulation of metals in multilayered graphitic capsules has been studied for al the rare-earth elements (Sc, Y, and Ln = La, Ce, ..., Lu) excluding Pm by using electric are discharge. Electron microscopy and X-ray diffraction of carbonaceous products revealed that most of rare-earth metals (Sc, Y, La, Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, and Lu) were encapsulated in the form of carbides, but the others, Sm, Eu, and Yb, were not. The metals in the former group that were encapsulated had vapor pressures definitely lower than those in the latter group. In the case of thulium (Tm), whose vapor pressure is intermediate between the two groups, only a trace amount of encapsulated carbide was formed. Correlation of volatility of metals with encapsulation was clearly found, suggesting that the volatility of a metal plays an important role in a process of the metal encapsulation.