Biomedical Engineering Reference
In-Depth Information
Since the sorption properties of fullerenes and astralenes
powders are related to their structures, structural investigations
of the samples have been carried out by X-ray diffraction. The X-ray
powder patterns of fullerene and astralene are shown in Fig. 4.1. The
C
fullerene reflections correspond to the face-centered cubic cell
with the parameter 14.166 Å. But such fcc structure is not the only
possible one for fullerenes.
In Ref [24] some fullerene molecules have been removed from
the unit cell by heating C
60
crystals up to 623 K for 15 h. As a result
of defects formation, the crystalline structure of fullerene changed
from face-centered cubic into cubic primitive. This transformation
led to a several fold increase of pores size and of crystalline fullerene
sorption capacity by several fold.
60
Figure 4.1
X-ray powder patterns of crystalline (a) fullerene and (b)
astralene (CuKα).
Fullerene sorption ability can be increased by a factor of about 5
by milling the crystalline fullerene to an amorphous state [35].
Note that changes in fullerene structure from face-centered into
cubic primitive lattice [36, 37] may occur under phase transition
conditions at 260 K, followed by a transition to the amorphous state
at temperatures below 90 K [38].
