Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
2001-08-08
2003-07-22
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C428S403000, C428S404000, C106S472000, C106S474000, C106S478000, C106S438000
Reexamination Certificate
active
06596396
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to thin-film-like particles of a very small thickness having a skeleton constructed by carbons, and monolayer and stacked-layer very thin isolated films composed of the particles.
In recent years, search for a substance highly anisotropic in shape and its applications have progressed rapidly. A composite of such a substance, gathered in a large number, with other substance can be expected to exhibit various properties, such as high strength, when added at a low fraction. If the substance has a very fine linear (one-dimensional) or very thin planar (two-dimensional) shape and is electrically a semiconductor or a conductor, the substance used alone, or a collective matter of a small number of the substances, can be expected to show a quantum effect in electronic properties.
Among substances having carbon atoms as a skeleton and having an anisotropic shape, a graphite fiber and a carbon nanotube, which is a particularly fine form of the graphite fiber, are known as one-dimensional substances, while graphite, graphite fluoride and graphite oxide are known as two-dimensional substances. Of these substances, graphite, graphite fluoride and graphite oxide are all multi-layer structure materials comprising two-dimensional fundamental single layers stacked, and the number of the layers is generally very large. The fundamental layer of graphite (the fundamental layer is called graphene, and composed of carbons alone) comprises carbons of sp
2
bonds, and has a structure of one carbon atom thick (0.34 nm). The fundamental layer of graphite fluoride has a structure comprising a sp
3
-bonded carbon skeleton of one or two carbon atoms thick counted as rows of diamond-like zigzag carbons, and fluorine bonded to both surfaces of the skeleton. The fundamental layer of graphite oxide is assumed to have a structure comprising a carbon skeleton composed mainly of sp
3
bonds with a slight tendency toward sp
2
bonds and similarly one or two carbon atoms thick counted as rows of zigzag carbons, and acidic hydroxyl groups or the like bonded to both sides of the skeleton (the structure is 0.61 nm thick, if the thickness of the carbon skeleton is equal to the dimension of one carbon atom, hydroxyl groups, etc. are present on both sides of the skeleton, and intercalated water is very little) (for example, “Graphite Intercalation Compounds”, Chapter 5, edited by Carbon Materials Association, Realize Co. (1990); T. Nakajima et al., Carbon, 26, 357 (1988); M. Mermoux et al., Carbon, 29, 469(1991)). When the graphite oxide is highly oxidized and thoroughly dried, its oxygen content is about 40 wt. %.
The electronic structure of graphite and that of graphene are theoretically known to differ slightly. Graphene does not occur naturally, and there is an example of its synthesis as a film deposited on the surface of a nickel crystal by CVD (E. Rokuta et al., Surf. Sci., 427-428, 97(1999)). However, there has been no example of graphene actually prepared as an isolated thin film.
Examples in which such multi-layer structure materials having a carbon skeleton are separated into many fundamental layers include a material having isoprene or the like polymerized in interlayer spaces of graphite (H. Shioyama, Carbon, 35, 1664(1997)), a material having polyethylene oxide penetrating interlayer spaces of graphite oxide (Y. Matsuo et al., Carbon, 34, 672(1996)), and a material having aniline or the like polymerized in interlayer spaces (Japanese Unexamined Patent Publication No. 1999-263613).
In these examples involving separation of the multi-layer structure, the fundamental layers or very thin layers close to them are only existent as constituent components inside the composite, and have not been withdrawn separately and stably. That is, very thin-film-like particles, which have a carbon skeleton with high crystallinity and which can exist as independent particles, have not been discovered. An isolated film that is formed by the linkage of the separated thin layers has not been formed.
The object of the present invention is to provide such thin-film-like particles and an isolated films relatively similar to graphene, but different in structure from graphene.
SUMMARY OF THE INVENTION
To attain the above object, the inventors of the present invention selected the graphite oxide, in which separation of the layers can be expected to occur relatively easily, from the aforementioned three multi-layer structure materials, and further performed its synthesis (oxidation and purification) for promoted separation of the layers, thereby obtaining the desired thin-film-like particles. The structure of the thin-film-like particle is practically equal to the structure of graphite oxide so far known, unless it is very thin. However, the thin-film-like particle has a hitherto unknown, very thin shape, namely, a shape with a very small thickness relative to a breadth in its planar direction. When expressed as the number of layers within the particle, the thickness is less than 20 times the thickness of the fundamental layer. Consequently, the thin-film-like particle can even deform flexibly, although it has a dense carbon skeleton.
The thin-film-like particles are desirably handled as a dispersion in a liquid. However, studies were conducted not only of water, a dispersion medium immediately after synthesis, but also of replacement by other dispersion media. Through these studies, the inventors facilitated applications to composing of the thin-film-like particles with other substances. Furthermore, they made it possible to reduce the thin-film-like particles into thin-film-like graphite particles with a very small thickness and having a nearly graphite-like structure, or a collective matter of the thin-film-like graphite particles, as is known with ordinary graphite oxide.
Besides, the particles in the dispersion can be placed, along with the dispersion, on a mesh, and dried, whereby isolated thin films out of contact with the substrate can be obtained by the linkage of thin-film-like particles.
Graphite with a well-developed layer structure and high crystallinity is desirable as a raw material for the thin-film-like particles of the present invention. In such graphite, the respective fundamental layers are large, and the frequency of existence of a bonds tying the adjacent two fundamental layers together is extremely low. Thus, the graphite is liable to separate into thin-film-like particles after an oxidation reaction. With graphite having an undeveloped layer structure and low crystallinity, by contrast, oxidation occurs, but separation of the layers is extremely difficult. More concretely, desirable graphite is one in which the diameter of the widest fundamental layer within the particle is nearly equal to the diameter of the particle, and the entire particle has a single multi-layer structure. Known examples of such graphite are natural graphite (especially, of a high quality), kish graphite (especially, one produced at high temperatures), and highly oriented pyrolytic graphite. The respective fundamental layers of natural graphite and kish graphite are each an single crystal having a nearly single orientation, while the respective fundamental layers of highly oriented pyrolytic graphite are each a collective matter of many small crystals having different orientations. In the present invention, any of these graphites, or exfoliated graphite having the interlayer spaces of these graphites broadened beforehand is used as the starting material.
The size of the fundamental layer of graphite, and the size of a minute part within the fundamental layer can be estimated from the shapes of peaks in X-ray diffraction, by observation of an electron channeling contrast image under a scanning electron microscope, or by observation under a polarization microscope. Other indicators include, for example, an electric resistance of about 10
−6
&OHgr;m or less. However, such indicators only show the possibility for separation of the layers. Actually, therefore, it is desirable to perform o
Hirata Masukazu
Horiuchi Shigeo
Kiliman Leszek
Mitsubishi Gas Chemical Company Inc.
Roylance Abrams Berdo & Goodman L.L.P.
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