Chemistry of inorganic compounds – Carbon or compound thereof – Elemental carbon
Reexamination Certificate
2002-02-26
2004-02-17
Wong, Edna (Department: 1753)
Chemistry of inorganic compounds
Carbon or compound thereof
Elemental carbon
C423S44500R, C423SDIG003, C423SDIG004, C204S157440, C204S157470, C204S157600, C204S157630
Reexamination Certificate
active
06692718
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a novel process for preparing a carbonaceous material, and more particularly, to modification of carbon black and to a process for preparing and purifying nano-size particulate graphite, a kind of fullerene.
BACKGROUND ART
A fullerene which has received attention as new carbon is, chemically, a transformation of carbon black. Comparing the former with the latter with respect to a micro structure; the latter is formed by stacking an infinite honeycomb-shaped network plane at uniform intervals in parallel regularly in three-dimensions; contrary to this, in the case of the former a closed minimum unit system corresponding to a molecule can be strictly defined and the individual system is composed of, in principle, polyhedron-type network comprising arbitrary number of hexagon and 12 pentagons. For such a unique structure, the fullerene has been investigated as a new material of the twenty-first century in each field and it has been expected that the fullerene can be applied in a wide variety of fields from a superconductor, semiconductor and nonlinear optical material down to new type fuel and novel pharmaceutical active substances.
Form of the fullerene can be divided into spherical-type and tube-type. And mono layer-type and multi-layer type are known in each type. An active basic research has been developed everywhere in the world on C
60
, C
70
and mono-layer and multi-layer carbon nano-tubes as objects. Papers of 13,000 and above have been printed and published from 1990 and 1991 when these two forms of fullerene carbon has been isolated for the first time up to the present time. Nobel Prize for chemistry was awarded for discovery of C
60
. From such facts as above described, strength of impact given by the appearance of fullerene carbon to a scientific and technological field can be surmised. Examining, however, aspects of the applications of the fullerene, it can be said that there are many technical problems to be solved from the standpoint of industrial aspect, for example the production cost of C
60
and carbon nano-tube are not yet short of ¥1,000,000 per kg at present, respectively.
The fullerene is included in specific soot, that is, fullerene black obtained by subjecting a graphite electrode to arc-discharge or irradiating graphite with laser in an inactive atmosphere such as helium and so on to vaporize carbon, cooling slowly and aggregating. The form of the fullerene is generally as follows: Mono-layer sphere—Fullerene in a narrow sense shown by the general formula C
n
, While C
60
and C
70
are representative for C
n
, the arc many cases where 76≦n<100 is called as “higher fullerene” or 76≦n<100 is called “giant fullerene.” The higher fullerene is soluble in an organic solvent and can be extracted and isolated from the fullerene black. C
60
is a true sphere having a diameter of 0.7, but the remainder is an ellipsoidal sphere or polyhedron. Multi-layer sphere—Concentric multi-layer polyhedron particles having a small cavity therein exist in the fullerene black, which are called as “carbon nano-particle.” Mono-layer tube-type—This takes the form that a mono-layer fullerene is divided into two equal parts and a small wound graphite plate is inserted between them and connected. This can be formed by mixing a certain kind of metal catalyst with graphite by means of arc discharging method to vaporize, which is called as “mono-layer carbon nano-tube.” Multi-layer tube-type—This has the structure that several or tens layers of mono-layer carbon nano-tubes having different thicknesses are stacked concentrically. This can be formed in a residue of cathode by arc-discharge on a graphite electrode without a catalyst. In the multi-layer sphere fullerene of the above-described fullerenes, the true sphere-type having no excess space therein has been discovered other than the above-described polyhedron type having a cavity therein. That is to say, if the fullerene black is irradiated with a concentrated electron beam in an electron microscope, a polyhedron-type carbon nano-particle contained therein changes to a substantial true sphere-type multi-concentric structure having no cavity therein. This product is called as “carbon nano-onion.” Since the carbon nano-onion shows substantially perfect sphere, it has been expected to have more interesting performance than the polyhedron-type carbon nano-particle, and it is called as “ultimate fullerene.”
Each of the concentric polyhedron-type fullerene having a cavity therein, that is “carbon nano-particle” and the concentric true sphere-type fullerene having no cavity can be regarded as a cage transformation of graphite. The latter true sphere-type fullerene is a kind of unstable phase as described below, and it is considered that the latter true sphere-type fullerene changes to a stable polyhedron-type fullerene having no cavity by heat treatment.
However, the studies on nano-size particulate graphite have been undertaken by making use of fullerene black as a raw material. Since it is, however, difficult to separate amorphous carbon or other products contained in the fullerene from the nano-size particulate graphite, the nano-size particulate graphite itself has not been isolated yet. Further, an effective method for preparing the nano-size particulate graphite has not yet developed. It is, therefore, the present condition that the properties of the nano-size particulate graphite have not been clarified yet.
DISCLOSURE OF THE INVENTION
For such reasons as above described, it has been eagerly required to produce nano-size particulate graphite efficiently and in high purity and to clarify its properties.
That is to say, a problem of the present invention is to provide a process for preparing nano-size particulate graphite efficiently and in high purity and to provide high-purified nano-size particulate graphite produced by the process.
The inventor of the present invention has studied devotedly in order to solve the above-described problem. In the process of our studies, soot-like carbon having a grape-like aggregate structure of nano-primary particles formed by stacking irregular concentric spheres in multiple layers was irradiated with high energy beam such as strong electron rays for a short time. As a result, it has been surprisingly observed that the primary particles changes to true sphere-like carbon nano-onion and simultaneously the aggregate is transformed to a state that particles are dispersed.
It has been considered that the carbon black does not take a micro structure having three-dimensional regularity such as graphite, but is not perfect amorphous, and that the carbon black shows broad absorption in the vicinity of low diffraction angle of 20-30° in powder X-ray diffraction and has a partial structure in which nano-size carbon flakes comprising multi-nucleus aromatic skeleton are stacked in multiple layers. For this reason, the carbon black is called as low regularity carbon. When such carbon intact is heat-treated at temperatures of 3000° C. and above, there is a case where it is graphitized such as pitch coke (easily-graphitization carbon). However, it becomes generally a concentric polyhedron-type micro particle having faces formed by minute graphite layers stacked and having a big cavity therein. The latter is not graphitized, even if it is heated at high temperatures (hard-graphitization carbon). When, however, the micro structure of the carbon black or soot before heat-treatment is well observed, it appears that substantial sphere nano-size particles aggregate in a state of grape and the primary particle has a lamellar structure.
It has been believed from X-ray analysis that such a lamellar structure is formed by depositing plane-like graphite crystallites having an average size of 1.7 nm repeatedly in the direction parallel to a spherical surface. It can be, therefore, said that the above-described discovery by the inventors of the present invention is entirely surprising.
The inventors of the present invention have devotedly studied the structure
Futaba Corporation
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Wong Edna
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