Note: Descriptions are shown in the official language in which they were submitted.
CA 02517965 1991-08-21
- 1 -
NEW FORM OF CARBON
This application is a divisional of co-pending Canadian
Application Serial No. 2,072,117.
This invention relates tQ new forms of carbon
as well as methods for the production and recovery
thereof from carbon sources.
In 1985, Kyoto et al. postulated the existence
of a highly stable molecule composed of 60 carbon atoms
based solely on mass spectroscopic analysis of vaporized
graphite (Ii.W. Kyoto, et al., Nature, Vol. 318, 162, 14
November 1985). More specifically, all that was observed
--was a peak in the mass spectra of said carbon vapor.
Ilowever, Kyoto et al. did not isolate any of said
compound.
A rnodel for this compound was proposed in wr~ich
60 carbon atoms are placed at the vertices of a truncated
2p icosahedron forming a perfect "soccerball" structure.
Subsequent thereto, many publications have strengthened
the evidence for the existence of this molecule. The 60
carbon atom compound (hereinafter C60) was~presumably
produced in situ for the spectroscopic determination
25 reported in these publications. Yet, to date, no one has
been successful in verifying the existence of this
molecule since no one has been successful in isolating
the molecule in measurable amounts. Thus, no processes
for producing recoverable amounts of this new compound
30 have been described to the present time.
Tn the aforesaid publication by Kyoto, et al.,
the authors proposed many uses for the new substance, C60
if it could be produced in quantity such as C60
transition metal compounds, e.g., C60Fe; or halogenated
35 - species like C60F60 which might be a super lubricant;
molecules including oxygen and lanthanum in the C60
interior; C60 would provide a topologically novel
CA 02517965 1991-08-21
-2-
aromatic nucleus for new branches of organic and inorganic chemistry; and Cso
being especially stable and symmetrical provides possible catalyst andlor
intermediate in modelling prebiotic chemistry.
Another form of carbon containing 70 carbon atoms (C~o) has also been
postulated (Kroto, Chemistry in Britain, 40-45 (1990), Kroto, Science, 1139-
1145
(1988)). Like the Cso to date, no one has been successful in verifying the
existence of the C,o. Heretofore, no one has been successful in obtaining the
molecule in any appreciable amounts.
A process has now been developed for the production of recoverable
amounts of Cso and C,o. The present invention relates to a method of producing
Cso and Coo compounds which comprises evaporating graphite in an atmosphere
of an inert quenching gas at effective pressures in an evacuated reactor,
collecting the quenched carbon product produced therefrom and contacting the
quenched carbon product with an extracting non-polar organic solvent under
effective conditions to separate the Cso and C,o compounds therefrom. The
present new process is accomplished by evaporating carbon rods in an
atmosphere of an inert quenching gas maintained at reduced pressure in a
reactor therefor. This process produces a sooty carbon product which is
graphitic
carbon including a few percent of Cso and low levels of Coo which are
recoverable
from the product. However, an increase in the fraction of C,o molecules can be
produced if the pressure is raised to greater than atmospheric pressures.
The recovery process is preferably accomplished by selective extraction of
Cso and C,o with non-polar organic solvents from the sooty graphitic carbon.
Such products can be characterized as being amorphous or crystalline
particulate
matter comprised of Cso or C,o.
In accordance with an embodiment of the present invention there is
provided a method of producing C6o and Coo compounds which comprises
evaporating graphite in an atmosphere of an inert quenching gas at pressures
effective to quench the vaporized carbon in a reactor that had previously been
evacuated, collecting the quenched carbon product produced therefrom and
CA 02517965 1991-08-21
-2a-
contacting the quenched carbon product with an extracting non-polar organic,
solvent under effective conditions to separate the coo and Coo compounds
therefrom.
In accordance with another embodiment of the present invention there is
provided a carbon product, the mass spectrum of which shows a strong peak at
mass 720 amu, the infrared bonds to which have four intense lines at 1424',
1183,
577 and 528 cm'', absorption peaks in the UV at 264 and 339 nm, soluble in non-
polar organic solvents and sublimes at a temperature of from about 300°
to
400°C, present in amounts sufficient to be discerned as a solid.
Another embodiment of the present invention provides a formed or molded
product comprising Cso and C,o.
Yet another embodiment of the present invention provides a free flowing
particulate comprised of Cso and Coo.
A substantially pure Cso and C,o is provided in another embodiment of the
present invention.
Still another embodiment of the present invention provides an isolated
carbon product, the mass spectrum of which shows a molecular ion at 840 amu, a
broad
peak in the ultraviolet at 276 nm, and soluble in non-polar organic solvents.
Other embodiments of the present invention provide isolated Coo or
isolated C,o as well as the vapor of Coo and C,o.
In accordance with yet another embodiment of the present invention there
is provided a method of extracting Cso and Coo from a carbon source containing
same which comprises contacting the carbon source with a non-polar organic
solvent.
A still further embodiment of the present invention provides a process for
preparing C6o comprising: (a) vaporizing a carbon source in the presence of an
inert quenching gas under conditions effective to form a sooty carbon product
comprising Cso molecules, the Cso molecules being present in the sooty carbon
product in amounts capable of extracting and recovering predominantly
therefrom
the Cso as a visible solid form; and (b) recovering Cso from the sooty carbon
product.
CA 02517965 1991-08-21
-2b-
An embodiment of the present invention provides a process for preparing
Cso comprising: (a) vaporizing a carbon source in the presence of an inert
quenching gas under conditions effective to form a sooty carbon product
comprising C~ molecules, said Cso molecules being present in said sooty carbon
product in amounts sufficient to be capable of providing a visibly
coloredrsolution
when extracted with sufficient amounts of benzene; and (b) recovering Cso from
said sooty carbon product.
Another embodiment of the present invention provides a process for
preparing C fio comprising: (a) vaporizing a carbon source in the presence of
an
inert quenching gas under conditions effective to form a sooty carbon product
comprising Cso molecules, the Cso molecules being present in said sooty carbon
product in macroscopic amounts; and (b) recovering macroscopic amounts of the
Cso from said sooty carbon product.
In accordance with one embodimenf of the present invention there is
provided a process for preparing fullerenes~comprising: (a) vaporizing a
carbon
source in the presence of an inert quenching gas under conditions effective to
form a sooty carbon product comprising fullerene molecules, the fullerene
molecules being present in the sooty carbon product in macroscopic amounts;
and (b) recovering macroscopic amounts of fullerene from the sooty carbon
product.
In accordance with another embodiment of the present invention there is
provided a process for preparing a carbon allotrope comprising caged molecules
consisting solely of carbon atoms which are soluble in non-polar organic
solvents,
the process comprising: (a) vaporizing a carbon source in the present of an
inert
gas to produce a carbon vapor; (b) quenching the vapor of carbon in the inert
gas
under conditions effective to nucleate. and condense the carbon allotrope, the
allotrope being present in the sooty carbon~product in amounts sufficient to
be
capable of extracting and revering therefrom the allotrope in solid form; and
(c)
recovering the carbon allotrope form the sooty carbon product.
In accordance with a further embodiment of the present invention there is
CA 02517965 2006-O1-20
-2c-
provided a method of extracting Cso from a carbon source containing same which
comprises contacting the carbon source with a non-polar organic solvent.
fn accordance with a still further embodiment of the present invention there
is provided a carbon product comprising Coo, Coo or a mixture of Cso and Coo.
Various other embodiments of the present invention provide far solid Cso,
solid Coo, crystalline Cso, crystalline Coo, substantially pure solid Coo,
substantially
pure solid C,o, substantially pure crystalline Cso, substantially pure
crystalline C,o.
Also provided by embodiments of the present invention are Cso in amounts
sufficient to isolate as a visible solid, Clo in amounts sufficient to isolate
as a
visible solid, macroscopic amounts of Cso, macroscopic amounts of C,o,
substantially pure Coo in amounts sufficient to isolate as a visible solid,
substantially pure Coo in amounts sufficient to isolate as a visible solid.
A still further embodiment of the present invention provides a solution of a
carbon allotrope selected from the group consisting of Cso and C,o being
dissolved in an organic non-polar solvent, the allotrope being present therein
in
amounts sufficient to be capable of recovering it as a solid when the solvent
is
evaporated.
In other preferred embodiments, there are provided a fullerene present in
an amount sufficient to isolate as a solid and a macroscopic amount of
fullerene.
In accordance with a further embodiment of the present invention there is
provided a solid that consists essentially ~of a fullerene, the fullerene
being
isolated from a sooty carbon product formed from vaporizing a carbon source in
the presence of an inert quenching gas, wherein the fulferene is recovered
therefrom in macroscopic amounts.
In accordance with a still further embodiment of the present invention there
is provided a cage carbon molecule consisting solely of carbon atoms that is
isolated from a sooty carbon product formed from the vaporization of a carbon
source in the presence of an inert quenching gas, the cage carbon molecule
being recovered therefrom in amounts sufficient to be isolated as a visible
solid.
In another embodiment of the present invention there is provided a cage
CA 02517965 2006-O1-20
-2d-
carbon molecule product consisting solely of carbon atoms which is prepared by
(a) vaporizing a carbon source in the presence of an inert quenching gas under
conditions effective to produce a sooty carbon containing the caged carbon
molecule product the inert gas providing a non-reactive atmosphere; (b)
collecting the sooty carbon product; (c) separating the product from the sooty
carbon product, the separated product being free of any sooty carbon product
and consisting solely of carbon atoms, the product being present in amounts
sufficient for the product to be perceived as a visible solid in solid form.
In accordance with a further embodiment of the present invention, there is
provided fullerenes in an amount at least as large as that amount which is
sufficient to see under an optical microscope.
In accordance with a further embodiment of the present invention, there is
provided a process for preparing cage molecules consisting solely of carbon
atoms comprising vaporizing elemental carbon in the presence of an inert
quenching gas under conditions effective to form a sooty carbon product
containing the cage molecules of carbon, the cage molecules being present in
the sooty carbon product in sufficient amounts to be capable of extracting and
recovering therefrom the cage molecules as a solid; and extracting the cage
molecule of carbon from the sooty carbon product.
In accordance with a further embodiment of the present invention, there is
provided a process for preparing cage molecules consisting solely of carbon
atoms comprising vaporizing elemental carbon in the presence of an inert
quenching gas under conditions effective to provide a sooty carbon product
comprising the cage molecules of carbon, the cage molecules being present in
the sooty carbon product in amounts sufficient to be capable of extracting and
recovering therefrom the cage molecules in solid form; depositing the sooty
carbon product on a collecting surface; removing the sooty product from the
collecting surface; and extracting a product which comprises cage molecules
consisting solely of carbon atoms from the sooty carbon product.
CA 02517965 2006-O1-20
-2e-
In accordance with a further embodiment of the present invention, there is
provided a process for preparing caged molecules consisting solely of carbon
atoms comprising vaporizing elemental carbon in the presence of an inert
quenching gas under conditions effective to form a sooty carbon product
comprising the cage molecules, the cage molecule being present in the sooty
carbon product in amounts sufficient to provide a visibly colored solution
when
extracted with effective amounts of benzene; and extracting the cage molecule
from the sooty carbon product.
In accordance with a further embodiment of the present invention, there is
provided a process for preparing a carbon allotrope comprising vaporizing
elemental carbon in the presence of an inert quenching gas under conditions
effective to provide a sooty carbon product comprising the carbon allotrope,
the
carbon allotrope being present in the sooty carbon product in amounts
sufficient
to be capable of providing a visibly colored solution when dissolved in
sufficient
amounts of benzene depositing the sooty carbon product on a collecting
surface;
removing the sooty carbon product from the collecting surface; and extracting
a
product which comprises the carbon allotrope.
In accordance with a further embodiment of the present invention, there is
provided a process for preparing a carbon allotrope comprising vaporizing
elemental carbon in the presence of an inert quenching gas under conditions
effective to form a sooty carbon product comprising the carbon allotrope, the
carbon allotrope being capable of being dissolved in a non-polar organic
solvent
and the carbon allotrope being present in the sooty carbon product in
sufficient
quantities to be capable of extracting and recovering therefrom the allotrope
in
solid form; and extracting the allotrope from the sooty carbon product.
CA 02517965 2006-O1-20
-2f-
In accordance with a further embodiment of the present invention, there is
provided a process for preparing a carbon allotrope consisting solely of
carbon
atoms which is soluble in non-polar organic solvent comprising vaporizing
elemental carbon in the presence of an inert quenching gas under a pressure
ranging from less than 1 atmosphere up to 10 atmospheres under conditions
effective to form a sooty carbon product comprising the carbon allotrope, the
product being present in the sooty carbon product in quantities sufficient to
be
recovered as a visible solid; and separating the carbon allotrope from the
sooty
carbon product.
30
CA 02517965 1991-08-21
- 3 -
In the accompanying figures, Fig. 1 is a micrograph
of typical crystals of the 98 % Coo, 2 % Coo material showing thin
platelets, rods and stars of hexagonal symmetry.
Fig. 2 is an x-ray diffraction of a microcrystalline
powder of the 98% C6o, 2% Coo solid material. Tnset at upper
left is a single crystal electron diffraction pattern indexed
with Miller indices compatible with the x-ray pattern, taken
on a thin platelet as in Figure 1 with the electron beam
perpendicular to the flat face.
Fig. 3 is an infrared absorption spectrum of an
approximately 2 micrometer thick coating of the 98~ Cso, 2% C
material on a silicon substrate, referenced to a clean silicon
substrate. Absorption is given as optical density=logo (1/T),
where T is transmission. Apparent negative absorptions are due
to the coating acting in part as a non-reflecting layer.
Fig. 4 is a visible-ultraviolet absorption spectrum
of an approximately 0.1 micrometer thick coating of the 98%
C6o, 2 % C-,o material on quartz. Shown. at the bottom are
positions and relative oscillator strengths for allowed
transitions calculated for the C6Q molecule by Larsson, et al.
The first step in the production of C6o and C-,o
molecules is vaporizing carbon from any source containing
carbon in its various forms, e.g. graphite, amorphous and
glassy carbon. It is preferred that this vaporization takes
place in an evacuated reactor (e. g., a bell jar). The carbon
is vaporized by heating in the presence of an inert quenching
gas. The carbon vapor is nucleated in the presence of the
inert quenching gas to form smoke particles.
CA 02517965 1991-08-21
l In the production of C60 and C~~, and procedure
Lor vapori::in9 carbon can be used, although the preferred
method relics on the use of a high intensity electrical
current with graphite rods as electrodes. These rods are
constructed to permit vaporization of.carbon at tire tip
of the rod to produce a high density vapor of carbon.
For best results, the end of one of the rods is reduced
in diameter so that the vaporization occurs at the
reduced tip. The rods can be prepared using any of the
various forms of carbon, such as graphite, amorphous and
glassy carbon.
The inert quenching gas can be any of the usual
inert gases such as the noble gas. Argon and helium are
preferred, the latter being most preferred. Other inert
gases commonly employed to provide a non-reactive
atmosphere can also be used as quenching gas.
The amount of C60 and C~0 produced from this
carbon source is dependent upon the pressure of the
quenching gas. At lower pressures relatively pure.C60
molecules can be produced~in high yield with uinor
concentrations of CEO. For the production of
predominantly C~0 molecules, the pressure at which the
quenching gas is maintained should be subatmospheric and
preferably about 50-400 torr. Especially preferred is a
pressure of approximately 100 torr. The use of any lower
pressure may result in reduced yield of C60'
However, as the pressure is raised, the ratio
of C-,o:C~o is also increased.
. If the pressure is increased to at least two
atmospheres, the greatest percentage of C.,o product is
formed. Theoretically, the pressure can be raised to any
level just below the point where the reactor would
CA 02517965 1991-08-21
-5-
1 explode from tie increased pressure. Iiowever, at the
higher pressures, the yield of the overall product (C6o
and C-,o) is reduced even though the ratio of C~~,:C~o is
also increased. Therefore, as a practical consideration,
the pressure of the quenching gas should not be greater
than 10 atmospheres. The preferred pressure for
maximizing the amount of C-,o produced is 2-3 atmospheres.
The produced quenched vapor of carbon, i.e.,
the smoked particles coats the internal surface of the
reactor and of collecting substrates as black soot.
These collecting surfaces are inert to the vaporized
carbon. They can be transparent and/or coated with an
inert metal. Examples include glass, or gold coated
glass surfaces and the like. These collecting surfaces
are located in the reactor in the
. path of the carbon
smoke. The black coating can be removed by any suitable
means, e.g., by scraping the solids from the coated
surfaces. The C60 and C~0 molecules can be removed from
this collected quenched product by contacting sold
quenched product with an extracting solvent. In other
words, the black soot is placed in a container containing
the extracting solvent, or the extracting solvent is
poured onto the black soot placed in a container. In
either case, the C60 and C~0 molcules become dissolved in
the solvent, while the remainder of the black soot
remains insoluble. The insoluble material is separated
from the solution containing the C60 and C~0 molecules,
e.g., by decanting, or by filtration, and the like.
Suitable solvents include non-polar organic
solvents, such as the alkanes containing S-10 carbon
atoms (e. g. pentanes, hexanes, heptanes, octaves),
benzene and alkyl-benzenes (e. g. toluene, xylene), carbon
disulfide, carbon tetrachloride, naphtha,l,l,l-
CA 02517965 1991-08-21
-6-
1 trichloroethane, and the like. Simple solubility
determinations using classical laboratory methods will
permit selection of other suitable solvents. The.
preferred solvents are carbon disulfide, benzene, carbon
tetrachloride and toluene. Especially preferred are
benzene, carbon tetrachloride and carbon disulfide.
The product obtained contains a mixture of C60
and C70. As described hereinabove, the amounts of C~0
and C~0 present is dependent upon the pressure used. If
subatmospheric pressures are used, such as 50-400 torr,
the product is predominatly pure C60 with a minor amount
of C~0 present. Thus, when the collected product is
dispersed in the extracting solvent, the product obtained
is a mixture of C60 and CEO. For example, 4rhen the'
pressure is 100 torr, the product formed is about 98o C60
and about Za C.,o. This product can be separated from the
organic solvent solution by standard methods as by
evaporation of the solvent or by dilution of the solvent
solution with a non-solvent for C60. The product can be
crystallized by careful evaporation of the organic
solvent or by sublimation~procedures.
In a preferred embodiment of producing C00 and
O, pure graphite rods are vaporized by passing high
electrical current (either do or ac) through narrowed
tips of graphite rods. Electron beam, laser and RF
heating can be used in lieu of electrical heating. This
is done in a reactor (such as a bell jar) that has been
evacuated, purged and filled with inert gas at or
preferably below atmospheric pressure, e.g., pressures
ranging from about 50 to about X00 torr. and even higher.
The graphite rods are typically 1/4 inch in diameter with
CA 02517965 1991-08-21
_7_
1 about 1 cm length of one rod reduced in diameter to about
nun. The electrical heating vaporizes the constricted
tip of the graphite rod producing a high density vapor of
carbon, which quickly condenses into a smoke consisting
of very fine particles (of the order of 0.1 microns) of
graphitic carbon with an admixture of a few percent of
the desired C60 molecule. At this point in the process
there is a heavy black coating on collecting substrates
and/or on the walls of the chamber which can be easily
' scraped oft for the recovery step.
For recovery, the sooty product is treated with
benzene to provide a brownish-red solution. After
separation of the undissolved graphitic carbon, the
benzene solution is evaporated to obtain microcrystalline
product. Alternatively, the product can be sublimed from
the sooty carbon at 300° to A00'C. and the sublimation
product obtained by condensation on a conventional
substrate.
When the pressure of inert quenching gas is 100
torr, the product formed is 9B% C6o~and 2% C.,o. This
product, as obtained from the solvent extract of the
sooty graphitic carbon, is a dark brown to black
crystalline material. When obtained by sublimination in
vacuum or inert atmosphere, the product is obtained as a
brown to gray coating depending on thickness.
On analysis by mass spectroscopy, the spectrum
clearly shows a strong peak at mass 720 amu (i.e., the
mass of C60) and a clean peak at F3A0 amu (i.e., the mass
of C~0). Significant differences in the spectra occur
only in the abundances in the mass domain lower than 300
amu. Most of these differences seem to originate from
the different ionization techniques in the mass
spectrometer and from the different kinds of sample
desorption. So far, the cleanest mass spectra have been
CA 02517965 1991-08-21
obtained when the material was evaporated and ionized in the
vapor phase by electrons. In such spectra the mass range above
40 amu is dominated by the Cso mass along with its expected
isotope lines. The only other large mass found in any
abundance corresponds to Coo, with a ratio of Coo to C6o of about
.02.
Studies by optical microscopy of the Cso material
which is left after evaporating the benzene solution show a
variety of what appear to be crystals -- mainly rods,
platelets, and star-like flakes. Figure 1 shows a micro-
photograph of such a crystal assemblage. AlI crystals tend to
exhibit six-fold symmetry. In transmitted light they appear
red to brown in color; in reflected Light the larger crystals
have a metallic appearance, whereas the platelets show
interference colors consistent with an index of refraction of
about 2.
The platelets can be rather thin and thus are ideally
suited for electron diffraction studies in an electron
microscope. (See the insert in Figure 2).
In order to determine if the C6o molecules form a
regular lattice, electron and x-ray diffraction studies on the
individual crystals and on the powder were carried out. A
typical X-ray diffraction pattern of the purified C6o powder is
shown in Figure 2. To aid in comparing the electron
diffraction results with the X-ray results the electron
diffraction pattern is inserted into the corner of Figure 2.
From the hexagonal array of diffraction spots indexed as shown
in the Figure, a d-spacing of 8.7 A was deduced corresponding
to the (100) reciprocal lattice vector of a hexagonal lattice.
The most obvious correspondence between the two types of
.
diffraction is between- the 5.01 A peak of the X-ray pattern
and the (100) spot of the electron diffraction pattern, which
a
gives a spacing of about 5.0 A. Assuming that the Coo
CA 02517965 1991-08-21
_ g
molecules are behaving approximately as spheres stacked in a
hexagonal close packed lattice with a c/a ratio of 1.633, d-
spacings can be calculated. The results are shown in Table I.
Table I: X-Ray Diffraction Results and Assignments
For a Hexagonal Lattice Using
a o
a = 10.02 A, = 16.36 A
c
1 = 4 (h2 + hk kz) + QZ
-
d2 3 ( a2 ) c2 ,
Measured Measured Calculated Assignment
d-spacing d-spacing (hlcl)
0
ydegreesy (A) (A)
10.2 shoulder 8.7 8.68 (100)
10.81 8.18 8.18 (002)
7.57 (101)
20 17.69 5.01 5.01 (110)
20.73 4.28 4.27 (112)
21.63 4.11 4.09 (004)
28.1 3.18 3.17 (114)
30.8 2.90 2.89 (300)
32.7 2.74 2.73 (006)
The values derived from this interpretation are a =
0 0
20.02 A and c = 16.36 A. The nearest neighbor distance is
0
thus 10.02 A. For such a crystal structure the density is
calculated to be 1.678 g/cm3, which is consistent with a value
of 1.65 +/- .05 determined by suspending crystal samples in
aqueous GaCl3 solutions of
CA 02517965 1991-08-21
-10-
known densities. Although the agreement shown in Table 1
is good, the absence of the characteristically strong
(101) diffraction in hcp and the broad continuum in
certain regions suggest a less than perfect crystalline
order. Furthermore, X-ray diffraction patterns obtained
on carefully grown crystals up to S00 micrometers in size
with well developed faces yielded no clear spot pattern
(in contrast to the electron diffraction pattern on
micron-size crystals). It thus appears that these larger
~ crystals do not exhibit long range periodic order in all
directions.
A likely explanation for the unusual
diffraction lies in the disordered stacking arrangement
of the molecules in planes normal to the c-axis. It is
well known that the position taken by spheres in the
third layer of~stacking determines which of the
close-packed structures occurs, the stacking arrangement
in fcc being ABCABC while that in hop is AHABA~. If the
stacking sequence varies, the X-ray lines due to certain
planes will be, broadened by the disorder while other
lines will remain sharp. Such disordered crystalline
behavior was observed long ago in the close packed
structure of cobalt, where X-ray diffraction lines such
as (101), (102) and (202) were found to be substantially
broadened due to the stacking disorder. Reflections from
planes such as (002 remain sharp since these planes have
identical spacings in both fcc and hcp structures. A
general expression for which peaks are broadened by this
kind of disorder have been given in terms of Miller
indices (h,k,l) as h - k = 3t ~ 1, 1 # 0, where t is an
integer. None of these broadened reflections are
apparent in the X-ray pattern of Figure 2. This may
explain the weakness of the characteristically strong
CA 02517965 1991-08-21
-11-
1 (101) peak. Whether or not this stacking disorder is
related to the presence of the possibly elongated Coo
molecules is yet to be determined.
In.small crystals at least, the C6~ molecules
appear to be assembling themselves into a somewhat
ordered array as though they are effectively spherical,
which is entirely consistent with the soccer ball
hypothesis for their structure: The additional diameter
over the calculated 7.1 ~ value for the carbon cage
'itself must represent the effective van der Waals
diameter set by the repulsion of the pi electron clouds
extending outward from each carbon atom. Scanning
tunnelling spectroscopy of the C6Q molecules clearly
shows the spherical nature of the C6o molecules.
Some scanning tunnelling microscope images of a
carbon sample prepared in accordance with the procedure
described hereinabove at pressures of helium at 100 torr
show a spherical molecule of twice the diameter of the
C6o molecules. This is evidence of the existence of a
caged molecule containing 240 carbon atoms or a C2d4
molecule.
Samples were prepared for spectroscopy by
subliming pure material onto transparent substrates for
transmission measurements. Depending on the pressure of
helium in the sublimination chamber, the nature of the
coatings can range from uniform films (at high vacuum) to
coatings of C60 smoke (i.e., sub-micron microcrystalline
particles of solid C60) with. the particle size depending
to some extent on the pressure.
, rigure 3 shows the transmission spectrum of an
approximately 2 micrometer thick C60 coating on a silicon
substrate. The infrared bands show the four tnost intense
lines at 1429, 1183, 577, and 52~ cm 1, with no
CA 02517965 1991-08-21
-12-
1 underlying continuum remaining from the soot. In early
tries at purifying C60 material, the infrared spectrum
showed a strong band in the vicinity of 3.0 micrometers,
which is characteristic of a CI1 stretching mode. After
much effort, this contaminant was successfully removed by
washing the soot with ether and using distilled benzene
in the extraction. The spectrum in Figure 3 was obtained
when the material cleaned in such a manner was sublimed
under vacuum onto the substrate. The spectrum shows very
little indication of CII impurities.
The presence of only four strong bands is what
is expected for the free, truncated icosahedral molecule
with its unusually high symmetry. Also present are a
number of other weak infrared lines which may be due to
other causes, among which may be absorption by the C?0
molecule or symmetry breaking produced, for example, by
isotopes other than C12 in the C60 molecule or by mutual
interaction of the C60 molecules in the solid.
Noteworthy, are weaker features at about 2330 and 2190
cm 1 which are located in the near vicinity of the free
C02 and CO stretching modes. This may imply some
attachment of C02 or CO to a small fraction of the total
number of C60 molecules. Another noteworthy effect can
be observed in the feature at 675 cm 1, which is weak in
the thin film samples but almost as strong as the four
main features in the crystals. This vibrational mode may
be of solid state rather than rnolecular origin.
Figure 4 shows an absorption spectrum taken on
a uniform film coated onto a quartz glass substrate. The
ultraviolet features are no longer obscured by the
graphitic carbon background as in our previous spectra.
Hroad peaks at 216, 264 and 339 nm dominate the spectra.
Weaker structures show up in the visible, including a
CA 02517965 1991-08-21
-13-
1 plateau with ends at about 960 and 500 nm and a very weal:
peak near 625 nm. At the bottom of Figure 4 are snown
pos?tions and relative oscillator strengths taken from
Larsson, et al. CChem. Phys. Lett. 137, 501-504)
calculated for the C60 molecule. This reference also
shows a variety of forbidden bards with the lowest energy
ones in the vicinity of 500 nm. There seems to be a
rough correspondence between the present measurements on
thin films and the allowed transitions predicted for the
molscule. There was no band at 386 nm in our films of
C60, a disclosed by Fieath, et al. (J. Chem. Phys. 87,
4236-4238 (1987)) using a laser depletion spectroscopy
method and attributed to the C60 molecule. Quite similar
spectra to that in Figure 4 have been recorded for
microcrystalline coatings deposited at helium pressures
of 100 tort, for example. The peaks occur at the
5liC;-ttly shifted positions o~ 219, 268, and 345 nm.
The C.,o molecule is larger than the C6o
molecule. The C~o molecule shows a molecular ion peak at
g40 amu. Furthermore, a noticeable peak in the
ultraviolet spectrum of the_C~o molecule taken on a
uniform film coated onto a guartz glass substrate is
exhibited at about 216 nm. This is a broad peak.
Suprisingly, it appears that the C70 molecule is more
stable than C60'
Thus, using the procedures described
hereinabove, at quenching pressures of less than 1
atmospheric pressure and especially at pressures of
50-400 tort, a product is produced which is predominantly
C60 and car~tains minor amounts of C70. The C60 product
can be used or can be further purified.
Further purification and separation of C60 and
C70 can be made by many conventional techniques known to
CA 02517965 1991-08-21
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1 one sl:filled in the art, e.g., fractional crystallization,
column chromatography, capillary electrophoresis, IIPLC,
preparative thin-layer chromatographf, and the lil:e.
Because the molecular figuration of C~0 end C~0
are different, the attractive intermolecular iorces~are
different which allows for the two molecules to be
readily separated.
Furthermore, the solubility of C60 and C~0 in
pure solvents and mixed solvents are also different from
each other, which also makes the two compounds separable
by using conventional techniques known to one spilled in
the art, such as crystallization, extraction, and the
like.
For example, pure C00 and pure C~0 molecules
can be isolated as follows. The black sooty tniy:ture of
C60 and C~0 which is produced according to the procedure
described hereinabove is placed in the extracting
solvent, such as benzene. The insoluble residue is
removed and the resulting benzene solution containing.C60
and C~0 molecules is concentrated. 'fhe C60 and
solution is added to a packed column with an adsorbent,
such as alumina. The column is eluted with an eluent
such as benzene or a mixture of benzene and toluene.
Various fractions of set volume e.g., 10 mL, are
collected. The eluent i.e., the solvent is removed from
each fraction such as by evaporation to dryness. The
fractions faith product will contain microcrystals, the
identity of which can be confirmed by spectroscopy, e.g.,
mass spectroscopy.
Thus, the process of the present invention can '
produce a product which is predominantly C60, which, if
desired, can be further purified by the purification and
separation techniques described liereinabove.
CA 02517965 1991-08-21
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Furthermore, the present invention contemplates
two different variations of the procedure described
hereinabove to make C~0 molcules. First, if
subatmospheric pressures of quenching gases are used in
the initial step, small amounts of C70 are produced,
which can be separated from the C60 molecules using the'
purification techniques described hereinabove. However,
if the pressure of the quenching gas is raised to at
least 2 atmospheres, after separation and purification, a
'greater percentage of substantially pure Coo would be
produced from each vaporization of carbon.
The present new products, Cso, Coo, or mixtures
thereof have the similar utilities as graphite. liowever,
they are particularly valuable for forming products of a
higher order of stability than those formed from
graphitic carbon, and can be processed into formed or
molded products such as C60 fibers, C~0 fibers, or
mixtures thereof using standard processing techniques.
In this regard, free-flowing, particulate C60 anc C~0 are
of special value particularly for use in producing molded
products, especially those extended .in at least one
direction. C60, and C~0 are also useful for producing a
low temperature C60 vapor (300°-400°C.) and C70 vapor of
the respective molecules to produce low temperature
atomic and molecular beams of carbon which is not now
possible using graphite as the carbon source. Further,
the synthesis of compounds such as C60~;60 and C60F60 can
be accomplished by introducing hydrogen and fluorine,
respectively, into a reactor containing C60 vapor.
Furthermore, the C60 product and the C~0 product may be
used as an industrial paint pigment or as a lubricant.
Moreover, since the C60 and C~0 molecule are hollow, they
could be used for binding and/or storing molecules e.g.,
toxic material.
CA 02517965 1991-08-21
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1 LXAMPLE 1
C60-containing carbon dust was produced in a
conventional bell-jar carbon evaporator which was first
evacuated to 10 4 tore by either an oil diffusion pump or
a turbo pump, both equipped with liquid nitrogen trap's ,
and then filled with an inert quenching gas, lielium and
argon were used at pressures ranging up to 400 torr.
Then graphite rods (as'previously described herein) were
evaporated using a current of about 100 amps (either AC
or DC) .
The smoke which formed in the vicinity of the
evaporating carbon rods was collected on substrates which
were placed within 5 cm to 10 cm of the evaporating
carbon rods.
The evaporator was opened after a cool down
period of 10-30 min. and the carbon dust samples removed
by scraping substrate surfaces and the internal surfaces
of the bell-jar. After washing with ether, the collected
dust samples were then extracted with benzene to produce
a wine-red to brown solution. On evaporation of the
solution, C60 was obtained,as a microcrystalline residue.
The crystals were sublimed by heating in vacuo
or in a quenching inert gas to 400°C. and collected on a
substrate. The sublimed product was brown to gray in
color.
In powder form, the present new carbon
allotrope is brownish-red.
35
CA 02517965 1991-08-21
-17_
EXAMPLE 2 -
The procedure of Example 1 is repeated except,
in the original step, the graphite rods are evaporated at
2 or more atmospheres of helium pressure in the chamber.
The product obtained from this procedure contains a
greater percentage of C.,o than does the product in
Example 1.
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25
3o
CA 02517965 1991-08-21
-18-
1
wrrnnr c o
Pure C6~ and pure C~~ are obtained as follows:
The C~~ and C.,o mixtures prepared in either examples
1 or 2 are dissolved in benzene and added to an alumina
column. Using benzene as the eluent,~the fractions,.are
collected and each elute traction is evaporated to
. dryness. The presence of Cso or C~o.in the traction can
be determined by taking mass spectroscopy thereof.
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35
CA 02517965 1991-08-21
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1 The above embodiments and examples are given to
illustrate the scope and spirit of the instant invention.
These embodiments and examples are within the
contemplation of the present invention. Therefore, the
present invention should be limited'only by the appended
claims.
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35
