Month: September 2020

To study the nature of the residue and possible methods for reduce or eliminate it, is relevant to many topics of the fullerene research. For example, there is a fundamental interest for the interactions between fullerenes and solvents and the stability of possible compounds or adducts. In addition the presence of solvent molecules trapped in the fullerene crystals and of solid phases of C60 wih solvents may affect the measured basic properties of C60.

Here we have evaluated several analytical tools to verify the purity of commercially available C60 samples. Our data clearly show that differential scanning calorimetry is the best candidate to establish a purity
criterion based on the sc-fcc transition of a C60 sample.

Here we have evaluated several analytical tools to verify the purity of commercially available C60 samples. Our data clearly show that differential scanning calorimetry is the best candidate to establish a purity
criterion based on the sc-fcc transition of a C60 sample

Extraction and chromatographic separation of individual
fullerenes are the necessary stages of the fullerene synthesis.1
In both stages, fullerenes are dissolved in a suitable solvent
(usually aromatic) or in a solvent mixture. Fullerite (crystalline
fullerene) is obtained after crystallization from the corresponding
solution. Crystals prepared by such a technique are used as the
starting material for further investigations. The resulting product
is usually washed with nonaromatic solvent (ether, hexane) and
further annealed in a vacuum or purified by sublimation to
remove solvent molecules from fullerite. However, it was shown
that residual solvent remains in solid C60 even after vacuum
treatment of the samples of C60 at elevated temperatures.

Conclusions

The results of the study of the series of C60 samples prepared
by various methods allowed us to draw the following conclusions.
(1) The molecules of solvent are not incorporated into the
crystal lattice of C60, but rather are adsorbed at the interfaces
of microcrystals.
(2) “Sintering” of the microcrystals upon heating is assumed
to be responsible for entrapping some of the solvent molecules
in the sample. This may be the reason solvents cannot be
completely removed by vacuum heating of samples of C60 and
only sublimation makes it possible to obtain virtually solventfree
materials.
(3) Disappearance of the orientational phase transition in DSC
curves of mechanically treated samples was observed as earlier,
with the nature of this effect being explained in terms of the
space defects in the crystals of C60.