JP2002053313A - Thin-filmy particle having skeleton consisting of carbon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydrogen storage technique using carbon fibers having new structural characteristics. SOLUTION: The thin-filmy particles having an independent form with 0.4 to 10 nm thickness and >=20 nm stretch in the plane direction and dispersible in a liquid having >=15 relative dielectric constant are obtained by accelerating separation of layers in the oxidation treatment of graphite. Further, the particles are reduced to obtain thin film graphite particles.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an extremely thin film-like particle having a carbon skeleton.

[0002]

2. Description of the Related Art In recent years, search for substances having high anisotropy in shape and their application have been rapidly progressing. When a large number of such substances are made into a complex with another substance, various properties such as high strength are expected to be exhibited by adding a low fraction.
In addition, if the shape is an extremely thin line (one-dimensional) or an extremely thin plane (two-dimensional) and is an electrically semiconductor or a good conductor, a single or a small number of aggregates may cause a quantum phenomena in electronic properties. Is expected to exhibit a positive effect.

As an anisotropic substance having a carbon atom as a skeleton, a one-dimensional graphite fiber or a carbon nanotube having a particularly fine shape is known, and a two-dimensional graphite fiber, graphite fluoride, graphite oxide or the like is known. It has been known. Of these,
Graphite, fluorinated graphite, and graphite oxide are all multi-layered structures in which two-dimensional basic layers are stacked, and the number of layers is generally very large. The basic layer of graphite consists of sp ² bonded carbon,
It has a structure with a thickness of one carbon atom. Base layer of the fluorinated graphite, the carbon skeleton of the sp ³ bonds for one piece or two pieces of thick carbon atoms counted in columns of carbon in diamond-like zigzag, fluorine bonded to both surfaces of its backbone It has a structured structure. The base layer of graphite oxide is also slightly s thick, one or two carbon atoms, counted in a zig-zag carbon row.
It is considered to have a structure in which a carbon skeleton mainly composed of sp ³ bonds having a tendency of p ² bonds and an acidic hydroxyl group or the like bonded to both sides of the skeleton (for example, “graphite intercalation compound”,
Chapter 5, edited by The Society of Carbon Materials, Realize (1990);
T. Nakajima et al. , Carbon,
26, 357 (1988); Mermouxet
al. , Carbon, 29,469 (1991)).

[0004] As an example in which such a multilayer structure having a carbon skeleton is separated into a large number of basic layers, an example in which isoprene or the like is polymerized between graphite layers (H. Shioyama,
Carbon, 35, 1664 (1997)), which allows polyethylene oxide to penetrate between layers of graphite oxide (Y. Matsuo et al., Carbon, 3).
4,672 (1996)) and those in which aniline or the like is polymerized between layers (JP-A-11-263613).

[0005]

However, in these examples of the separation of the multilayer structure, the base layer or an extremely thin layer close to the base layer exists only as a component inside the composite, and is taken out stably alone. Did not. That is,
Very thin film-like particles having a highly crystalline carbon skeleton and capable of existing as independent particles have not been found. An object of the present invention is to provide such a thin film particle.

[0006]

Means for Solving the Problems In order to achieve the above object, the present inventors have selected graphite oxide, which is considered to be relatively easy to separate layers, from among the above three types of multilayer structures. Synthesis (oxidation and purification) was carried out so as to promote separation of the layers, and the desired thin film-shaped particles were obtained. The structure of the thin film-like particles is almost equal to the structure of graphite oxide known so far, but has an extremely thin shape that has not been known so far, that is, the thickness thereof is larger than the thickness in the plane direction. It has a very small shape. When expressed in terms of the number of layers inside the particle, it is less than 20 layers of the basic layer. As a result, it was possible for these thin film-shaped particles to deform supplely despite having a dense carbon skeleton.

Further, it is desirable that the thin film particles are handled by dispersing them in a liquid. However, not only water, which is a dispersion medium immediately after synthesis, but also exchange with another dispersion medium is examined. Application development to compounding of particle-like particles with other substances has been facilitated. Further, as is known for ordinary graphite oxide, it was possible to reduce the thin film particles into thin graphite particles having an extremely thin and substantially graphite structure or aggregates thereof.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The raw materials for the thin film particles of the present invention include:
Highly crystalline graphite with a developed layer structure is desirable. In such graphite, since each basic layer is large and the frequency of occurrence of sigma bonds connecting two adjacent basic layers is extremely low, the graphite is easily separated into thin film-like particles after the oxidation reaction. Conversely, in the case of graphite having an undeveloped layer structure and low crystallinity, oxidation occurs, but the separation of layers is extremely poor. More specifically, graphite having a single multilayer structure in which the diameter of the widest base layer inside the particle is approximately equal to the diameter of the particle and the entire particle is desirable.
Such graphite includes natural graphite (especially high quality),
Kish graphite (particularly made at high temperatures) and highly oriented pyrolytic graphite are known. Each basic layer of natural graphite and quiche graphite is a single crystal having a substantially single orientation, and each basic layer of highly oriented pyrolytic graphite is an aggregate of many small crystals having different orientations. In the present invention, these graphites,
Expanded graphite in which the layers between these graphite layers are expanded in advance is used as a raw material.

The size of the graphite basic layer and the minute portions inside the basic layer can be estimated by peak shape in X-ray diffraction, observation of an electron channeling contrast image by a scanning electron microscope, observation by a polarizing microscope, and the like. As another index, for example, it is also a guide that the electric resistance is about 10 ⁻⁶ Ωm or less. However, since these indexes only indicate the possibility of layer separation, it is actually desirable to perform oxidation and purification using the target graphite raw material to confirm the separation of the multilayer structure.

It is desirable that impurities such as metal elements in graphite have been removed to about 0.5% or less in advance. If there are many impurities, separation of the multilayer structure may be hindered.

Since the particle size of graphite is reflected in the size of the thin film particles to be formed in the plane direction, it may be selected according to the size of the thin film particles to be synthesized. Shaped particles can also be synthesized in nature. However, as the particle diameter increases, the time required for oxidation increases. When it is desired to define the shape of the thin film-like particles to be formed in the plane direction as, for example, a square, the particles may be cut into a square beforehand at the stage of the graphite raw material. However, when cutting, it is necessary to recognize the crystal orientation.

In the oxidation of graphite in the present invention, known B
rodie method (using nitric acid and potassium chlorate), Sta
Udenmaier method (using nitric acid, sulfuric acid, and potassium chlorate), Hummers-Offman method (using sulfuric acid, sodium nitrate, and potassium permanganate) can be used. Among these, Hu is particularly oxidized.
mmers-Offeman method (WS Hummer)
s et al. , J .; Am. Chem. Soc. , 8
0,1339 (1958); U.S. Pat. 27988
78 (1957)), and this oxidation method is particularly recommended in the present invention.

In these methods of oxidizing graphite, first, ions of an oxidizing agent penetrate between layers of graphite to generate an intercalation compound. After that, by adding water, the interlayer compound is hydrolyzed to form graphite oxide. Among these reactions, formation of an intercalation compound requires a particularly long time and depends on the particle size of graphite. Therefore, it is desirable to change the time for coexistence with the oxidizing agent according to the particle size of the graphite so that ions of the oxidizing agent enter the graphite particles as much as possible. The present inventors have investigated and found that in the case of the Hummers-Offman method, the intrusion of ions of about 10 μm or more per hour was observed at around 20 ° C.
It is desirable to oxidize graphite for an oxidation time of at least 30 minutes or more, preferably 3 hours or more per 0 μm.

In the above-described method for oxidizing graphite, it is necessary to purify by removing the oxidizing agent remaining in the reaction solution or the ions or components derived from the decomposition of the oxidizing agent. In a known oxidation method, this purification is performed by washing with water, alcohol, or the like. In the present invention, in the purification step, components remaining in the reaction solution or between the layers and possibly hindering the separation of the layers are more positively removed, and the separation into thin film particles is promoted. That is, by removing as much as possible low molecules and small ions other than the dispersion medium coexisting in the liquid, the ionic dissociation degree of the acidic hydroxyl group present in each layer of the graphite oxide is increased, and each layer of the layer which can be regarded as large ionic particles is increased. By strengthening the electrostatic repulsion between them, the separation of the multilayer structure is promoted.

The present inventors have examined that, for example, when the concentration of graphite oxide is about 1 wt% or less, the concentration of sulfuric acid is about 0.1 wt%.
When the content became 05 wt% or less, the separation of the multilayer structure proceeded rapidly. When the calculation is made with the ion dissociation of sulfuric acid up to one stage, the concentration of small ions other than those derived from graphite oxide (including hydrogen ions generated by ion dissociation of graphite oxide) in the reaction solution is about 10 mol / m ³ or less. Therefore, it is desirable to purify the product so as to have a concentration of not more than this concentration. Specifically, after adding water, water is removed together with small ions. The water used is desirably of high purity.

On the other hand, in order to promote separation of each layer, which is large ionic particles, it is also important to lower the concentration of graphite oxide particles in the liquid at the time of purification and increase the degree of ion dissociation in each layer. Therefore, the concentration of graphite oxide at the stage where water is added to uniformly disperse the particles is set to about 5% by weight or less, more preferably 1% by weight or less.

In the Hummers-Offeman method,
Usually, hydrogen peroxide is added after hydrolysis to decompose permanganate ions into manganese (IV) ions and then washed with water to remove them together with other sulfate ions and potassium ions (WS Hummers et al.). al., JA
m. Chem. Soc. , 80, 1339 (195
8)). However, when it becomes neutral, the solubility of manganese ions decreases, and there is a possibility that the manganese ions become hydroxides of manganese and remain between the layers. Therefore, it is desirable to sufficiently wash with a sulfuric acid aqueous solution or a mixed aqueous solution of sulfuric acid and hydrogen peroxide before washing with water.

For specific purification operations by washing, known means such as decantation, filtration, centrifugation, dialysis, and ion exchange may be used. Here, as the particle diameter of the raw graphite decreases, and as the separation of layers progresses and the number of thin film particles increases, and as the removal of small ions and the like progresses, the charge per unit volume of the thin film particles increases. . As a result, the repulsion between the particles becomes stronger, and the degree to which the dispersion medium is retained (water is hydrated) becomes higher, so that any purification operation becomes difficult. In this case, operations with relatively high purification efficiency are centrifugation, dialysis, and ion exchange, and operations that can be purified in a relatively short time are centrifugation. On the other hand, decantation and filtration become more difficult as the diameter of the thin film particles decreases, due to slow sedimentation and blockage by the thin film particles. In order to temporarily reduce the repulsion between particles, use of another solvent having a low dielectric constant, salting out, or the like may be appropriately combined.

During purification, separation of the multilayer structure occurs spontaneously. In addition to this, when water is removed together with the small ions and then water is added again to form a uniform dispersion, a stirring operation such as shaking is added, so that the separation is further promoted. Ultrasonic irradiation can also be used, but since the basic structure of each layer tends to be destroyed and become smaller as the layers are separated, it is desirable to use the method particularly when it is desired to produce thin film-like particles having a small diameter.

By the purification as described above, the separation of the layers proceeds in many particles, but the separation of the multilayer structure is insufficient.
Some particles that are not in the form of a thin film also remain. These are impurities in the raw materials (e.g., graphite and other inorganic substances that are difficult to separate) and foreign substances mixed during oxidation and purification. Since these generally precipitate easily, they can be removed by decantation or extremely gentle centrifugation during purification.

By the above operation, the separation of the layers progresses in many particles. On the other hand, the possibility of separation increases even between parts that have not been separated, but because of large particles, many hydrogen bonds and the like exist between layers inside the particles, making it difficult to separate in a short time. May have become. Therefore, as a method for further promoting the separation of the layers, it is conceivable to further enhance the molecular motion of the dispersion medium and the motion of the thin film particles after diluting the purified dispersion. In particular,
Examples include ultrasonic irradiation and heating of the dispersion. However, with ultrasonic irradiation, the basic structure of each layer tends to be destroyed and become smaller as the layers are separated as described above. Heating can also be expected to increase the degree of ion dissociation, but it is desirable not to raise the temperature too high, especially at high temperatures, as particles may be partially reduced. Specifically, 5
0 to 150 ° C.

In order to selectively obtain particles in which the layers have further separated, the particles may be separated based on the difference in dispersibility. For example,
Decantation or relatively gentle centrifugation may be performed, and the non-settling portion may be used.

Through the above operations, a dispersion liquid in which extremely thin thin film-like particles, which can be called a nanofilm, are dispersed in water is completed.

When the dispersion liquid of the thin film-like particles is dried at a high concentration, like a general graphite oxide, many particles are aggregated, and it is difficult to re-disperse the particles. Much work on the structure of graphite oxide has been directed to this agglomerated solid, and no thin film particles as in the present invention were known). Therefore, when the thin film particles are used for a specific purpose, they should be handled as a dispersion liquid as much as possible, including preservation of the particles, and aggregation, such as drying from a very low concentration dispersion, spray drying, and freeze drying. It is desirable to obtain a small number of thin film-like particles, to use the dispersion as it is, and to mix it with another substance.

When used as a dispersion, a dispersion medium other than water may be desirable depending on the application. In that case, use another dispersion medium during the purification, or after purification, reduce the water by concentrating the dispersion by centrifugation or the like,
The dispersion medium may be exchanged by repeatedly adding another solvent, mixing and then concentrating by centrifugation or the like. Here, since the thin film particles have high polarity, they have a high affinity for a dispersion medium having a high dielectric constant and a high polarity, and the use of such a dispersion medium causes less aggregation of the thin film particles. Specifically, a dispersion medium having a relative dielectric constant of about 15 or more is desirable. In addition, when the compatibility of the two types of dispersion media is not good when exchanging the dispersion media, the exchange is performed via a third dispersion medium having good compatibility with both of the two types of dispersion media. You may.

Since the thin film particles obtained in the present invention have a functional group such as a hydroxyl group, a reaction with, for example, formaldehyde, carboxylic acids, isocyanates, epoxy compounds and the like can be expected. In such a case, if another molecule to be reacted with the thin film-shaped particles has a plurality of functional groups or a plurality of functional groups capable of forming a bond, the plurality of thin film-shaped particles are crosslinked.

When the thin film particles obtained by the present invention are mixed with another organic or inorganic polymerizable substance and the polymerizable substance is polymerized, a composite containing the thin film particles can be obtained. In this case, when the dispersion liquid of the thin film particles is mixed with another polymerizable substance and polymerized after removing the dispersion medium, aggregation of the thin film particles in the composite can be minimized.

When the thin film particles obtained in the present invention are expected to have electronic properties, it is desirable to reduce the thin film particles to make them into an electronic state mainly composed of sp ² bonds similar to graphite to increase the electric conductivity. . Various known reduction reactions using a reducing agent and an electrode reaction (electrolytic reduction) using a reducing agent can be used for the reduction. In particular, when the reducing agent is used, if the base layer has not been decomposed, the inside of the multilayer particle may be reduced. The complete reduction of is considered difficult. On the other hand, as a general behavior of graphite oxide, it is possible to form a graphite-like structure up to the inside of the multilayer by heating, and if a plurality of particles are heated in an agglomerated state, heating between layers within the multilayer particle or between the plurality of particles. It is known that a pi bond occurs and a macroscopic shape such as a normal graphite film can be provided (J. Maire et al.).
al. , Carbon, 6,555 (1968)).
Since the thin film-shaped particles of the present invention have a particularly thin shape, they are made into a structure similar to graphite by the same heating, so that single thin film-shaped graphite particles can be called carbon nanofilms or graphite nanofilms. Such a single thin-film graphite particle or a larger film-like structure in which a plurality of the thin-film graphite particles are aggregated in a planar shape is expected to exhibit a two-dimensional quantum effect on electronic properties and the like. For specific use, for example, the thin film particles may be placed on a suitable substrate having high heat resistance, reduced by heating, and the obtained thin graphite particles may be processed into a predetermined shape by various etching methods. .

It is also possible to mix the thin-film graphite particles with another polymerizable substance and polymerize the polymerizable substance to form a composite containing the thin-film graphite particles. Can be given.

Further, the thin-film graphite particles may be a precursor of a novel carbon structure such as a thin-film diamond and a thin-film large hydrocarbon.

Since the thin film particles obtained in the present invention are thin structures having a dense carbon skeleton, the thin particles, including the reduced form thereof, may be used alone or when a plurality of particles are aggregated in a plane. When a large film-like structure is formed, there is a possibility that the film material may be a selectively permeable or shielding film material such as elementary particles such as muons and protons, small ions, and low molecules.

[0032]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto.

Example 1 Natural graphite (manufactured by SSC Co., Ltd., SNO-25, purity 99.97 wt% or more, purified product from which impurities were removed by heating at 2900 ° C., average particle size 24 μm, particle size 4.6 μm or less) 10 g of sodium nitrate (purity 99%) and 7.5 g of sodium nitrate (purity 99%) were put in an Erlenmeyer flask, 345 cm ³ of sulfuric acid (purity 96%) was added, and a stirrer was put therein.
The mixture was stirred while being cooled in a water bath containing ice water, and 45 g of potassium permanganate (purity: 99%) was gradually added thereto over about 1 hour. The cooling was completed in 2 hours, and the mixture was left at about 20 ° C. for 5 days with gentle stirring. The obtained high-viscosity liquid was treated with a 5 wt% sulfuric acid aqueous solution (a water having a conductivity of less than 0.1 μS / cm was used for dilution (the same applies hereinafter)) 1
The mixture was added to 000 cm ³ with stirring for about 1 hour, and further stirred for 2 hours. Hydrogen peroxide (30 wt%
(Aqueous solution) was added and stirred for 2 hours.

This solution was centrifuged in a centrifuge bottle (with a capacity of about 400 c
m ³ ) Transfer to ³ tubes and centrifuge (maximum turning radius 17 cm)
(The same applies hereinafter), 1000 rpm, 10 minutes), and the supernatant (a small amount of the sediment is mixed in, the same applies hereinafter) was discarded to obtain only the precipitate. Further, while keeping the precipitate in a centrifuge bottle, 3 wt%
Sulfuric acid / 0.5 wt% hydrogen peroxide mixed aqueous solution (about 6 times to about 4 times the precipitation, magnification decreases as the operation proceeds)
Was added, the bottle was shaken, the bottle was shaken to re-disperse the precipitate, centrifuged (3,000 rpm, 20 minutes), and the supernatant was discarded 15 times. A total of about 13 kg was used as the mixed aqueous solution.

The solution to be added was replaced with water, and redispersion, centrifugation (7000 rpm, 30 minutes) and discarding of the supernatant were performed in the same manner.
Repeated times. Further, water was added for re-dispersion, and the mixture was allowed to stand for 1 day to precipitate only a small amount of particles (thick particles and the like) which were likely to precipitate. The precipitate was removed, and the liquid that did not precipitate was centrifuged (7000 rpm, 30 minutes), and the supernatant was discarded. Except for the supernatant, the lower part was a hard-to-flow sediment and the upper part was slightly viscous, and the total was about 650 cm ³ .

This hard-to-flow sediment and a slightly high-viscosity liquid are stirred to make a homogeneous liquid, and about そ の of the liquid (the remainder is used in Example 2) is divided into six centrifuge bottles. Water (approximately 5 to 0.4 times, the magnification decreases as the operation proceeds)
And re-dispersion and centrifugation (7000 rpm, 60 minutes)
And the supernatant were discarded a total of 20 times. Thereafter, a small amount of water was added and stirred to obtain 1350 cm ³ of a highly purified aqueous dispersion of thin film particles. From the weight change before and after drying a part of the liquid, the concentration of the thin film particles in the liquid is 0.4%.
It became 5 wt%.

The obtained aqueous dispersion was placed on a glass plate, dried at a temperature of about 20 ° C. and a relative humidity of about 40% for about 10 days, and subjected to X-ray diffraction measurement. A peak corresponding to 0.83 nm was obtained. This corresponds to the generally known interlayer distance of graphite oxide (when water is held between layers).

A small amount of the obtained aqueous dispersion is placed on a glass plate,
Observation with an optical microscope (OM) after drying revealed that the thin film-shaped particles, which had clear contours and had a maximum spread of several tens of μm in the planar direction, and a thin film-shaped particle covering the entire surface of the glass plate (see the electron microscope observation described later) Is particularly likely to be an aggregate of thin particles). Also, the particles transmitted light well, and observation with reflected light was suitable.

The same aqueous dispersion was diluted 100-fold with water, placed on a glass plate and dried to obtain an average value of the thickness of the thin film particles. When the average thickness of the particle aggregates dried and adhered from the liquid is calculated to be about 12 nm (the particle density is set to 2.1 g / cm ³ ), almost three particles are spread over the entire surface where the liquid is spread. It is O that more than degree overlaps
M observation confirmed (particles were very thin, but could be identified because of their higher reflectivity than glass). Thus, the average thickness of the individual thin film particles is less than 4 nm.

The same aqueous dispersion was treated with methanol (purity 99.8).
%), A small amount of finely ground natural graphite was added as a reference substance, and then placed on a copper mesh with a carbon microgrid for electron microscopic observation and dried. This is observed by OM in advance, and the area where the thin film-like particles on the microgrid overlap frequently (the area where the reflected light is large)
Then, after confirming a region with a small overlap (a region with a small amount of reflected light), image observation and electron beam diffraction (ED) measurement were performed with a transmission electron microscope (TEM).

In the low-magnification TEM images, almost no special pattern was observed in a wide range in any of the regions, but a large number of linear patterns were observed in some parts. Also, E
In D, the region with many overlaps is obtained by overlapping a plurality of sets of six-fold symmetric ED images (similar to graphite) that are in a rotational relationship with each other.
A complex ED image was given. This proved that a plurality of thin film-like particles (the inside of each particle had high crystallinity) overlapped. On the other hand, the region with little overlap gave only one set of the same 6-fold symmetric ED image. From this, it was found that the particles were single thin film-shaped particles (the inside of the particles had high crystallinity). The lattice spacing determined from these ED images (the spacing between lattice planes formed by carbon inside each layer, not the spacing between layers) is calculated to be about 0.215 nm with reference to the ED image of natural graphite. Was. This value indicates that the thin film-shaped particles have a dense crystalline carbon skeleton.
In addition, the ED when the mesh is inclined together with the thin film particles
From the vanishing angle of the image, the thickness of the basic layer giving the ED image was about 0.4 nm.

Further, on a TEM image, when a linear pattern contained in the single thin film particle was enlarged and observed, a stripe pattern corresponding to a crystal lattice was found inside the linear pattern.
This indicates that there is a portion perpendicular to the surface of the mesh (parallel to the traveling direction of the electron beam). In other words, this portion has a structure in which a part of the particles that were flat in the dispersion liquid is wrinkled (rises and returns perpendicular to the plane direction, for example) at the stage where the particles are captured on the microgrid while drying, for example. ) Was considered to have become. The interval between the lattice fringes was about 0.3 to 0.6 nm. The upper limit of this value is 0.61 nm (M.sub.M) between the basic layers of graphite oxide (in the case where the thickness of the carbon skeleton is one carbon atom, hydroxyl groups are present on both sides, and the amount of water between the layers is extremely small). .Mermo
ux et al. , Carbon, 29, 469 (1
991)), and the lower limit is 0.34 between the graphite base layers.
close to nm. Therefore, for example, there is a high possibility that the basic layer of graphite oxide or the basic layer of graphite oxide is heated by an electron beam and reduced to graphite, and further, corresponds to an intermediate structure between them. Also, assuming that half of the width of the wrinkles corresponds to the thickness of the thin film-like particles, a large number of wrinkles were observed for a plurality of thin film-like particles. Was measured to be about 7 nm.

As described above, it was found that the obtained thin film-like particles were extremely thin, and that they were deformable while having a dense carbon skeleton because they were thin.

Example 2 About half of the liquid homogenized in Example 1 was reconstituted with a regenerated cellulose tube (cross-sectional area: 5 cm ² , thickness: 30 μm, molecular weight cut off: 12000-14000, density: 1 g / c.
diameter of about 3 is calculated assuming a globular protein of m ^3.
5 μm or smaller), and sealed.
The dialysis was performed using twice the amount of water as an external solution. After the external solution was exchanged about every two days for a total of 10 times, the internal solution was taken out to obtain 450 cm ³ of a highly purified aqueous dispersion of thin film particles. The concentration was 1.5 wt%.

By OM observation and TEM observation, extremely thin particles similar to those in Example 1 were confirmed.

Example 3 A part of the aqueous dispersion of the thin film particles obtained in Example 1 was centrifuged (7000 rpm, 30 minutes), the supernatant was discarded, and the upper part of the slightly viscous liquid was removed from the rest. A small amount was taken out, placed in a glass bottle, and diluted about 100-fold with water. The glass bottle containing this liquid was placed on a hot plate at 150 ° C., and the liquid was heated (boiled) for about 20 minutes.

The obtained liquid was diluted about 10-fold with methanol, placed on a copper mesh with a carbon microgrid, and dried. This was observed in advance by OM, and after confirming a region where the thin film-like particles on the microgrid had a large overlap and a region where the overlap was small, the TEM was observed.

Although wrinkles similar to those in Example 1 were observed in any of the regions, the wrinkles were not as sharp as in Example 1. An attempt was made to observe wrinkles present in a region with little overlap at a high magnification, but the observation was not possible, probably because the wrinkles were eliminated due to the thermal influence of the strong electron beam. On the other hand,
The wrinkles in the areas of high overlap may be observable, though blurred, because the wrinkled particles are reinforced by other non-wrinkled particles. The length was less than about 1 nm. This is smaller than in the first embodiment. Considering the size of functional groups such as hydroxyl groups present on the surface of the basic layer, the thickness of the basic layer is about 0.61 nm (M. Mermoux et al., Ca.
rbon, 29, 469 (1991)), the obtained thickness was close to the thickness of the base layer, and it was considered that the original multilayer structure was almost completely separated.

Example 4 Natural graphite having a large particle size (produced by SSC, purity 9)
9.76 wt% or more, purified product excluding metal elements and the like by heating at 2900 ° C., about 1.4 to 2.0 mm in diameter and 0.1 mm in thickness.
Example 1 except that 1 g of flakes (1 mm or less) was oxidized for 10 days while being stirred very slowly.
In the same manner as in the above, an aqueous dispersion of thin film-like particles was obtained.

According to OM observation, the obtained particles had an average size in the plane direction of about 0.1 mm, but slightly contained particles of about 0.3 mm or more.

Example 5 The aqueous dispersion of the thin film particles obtained in Example 1 was placed in a centrifuge bottle,
Acetone (dielectric constant at 25 ° C. 20.7, purity 9)
9.5%, about 2 to 4 times that of the aqueous dispersion, the magnification increases as the operation proceeds), and redispersion and centrifugation (7000 rpm)
pm, 30 minutes) and the supernatant was discarded three times in total.
The resulting precipitate had a concentration of about 1.7% by weight and was a mass without fluidity.

Further, while keeping this mass in a centrifuge bottle,
2-butanone (dielectric constant at 20 ° C .: 18.5, purity: 99%, about 4 times that of acetone dispersion) was added, and redispersion, centrifugation (7000 rpm, 30 minutes) and discarding of the supernatant were repeated a total of three times. . The obtained precipitate has a concentration of about 2.0 wt.
%, The mass was non-flowable.

As described above, a dispersion system could be formed from the thin film particles even with a liquid other than water. However, since the repulsion between particles became smaller with a decrease in the dielectric constant, a higher concentration precipitate was easily generated. In addition, since the anisotropy of the shape was high, the surrounding dispersion medium was retained even at a low concentration of several%, and the fluidity of the dispersion liquid was significantly reduced.

Further, 2-butanone was added to the precipitate of the thin film particles containing 2-butanone, and the mixture was stirred and redispersed to obtain a 2-butanone dispersion containing about 0.5% of the thin film particles. This solution was mixed with an epoxy resin (cresol novolak epoxy type, imidazole as a curing agent, a 60 wt% 2-butanone solution), and the pressure was reduced while heating to 60 ° C.
After removing butanone, the mixture was cured at 160 ° C. for 2 hours to obtain a composite in which about 1.5 wt% of thin film particles were uniformly dispersed.

Example 6 An aqueous dispersion of the thin film particles obtained in Example 1 was placed on a glass plate, and a liquid obtained by diluting the same aqueous dispersion 200 times with methanol was coated on a copper mesh with a carbon microgrid. Each was dried at about 20 ° C. and then heated at 200 ° C. to reduce the thin film particles.

The reduced product on the glass plate (thickness: about 30 μm,
The electric resistance of the electrode was measured at a distance of 1 mm using a normal electric tester for about 2 cm × 2 cm.
mm low orientation graphite sheet was 1.5Ω). When the reduced product was peeled off from the glass plate and heated at 1000 ° C., the value was about 5Ω.

When the shape of the particles placed on the copper mesh was observed by OM, the shape was hardly changed before and after heating at 200 ° C. Also, the particles are slightly colored by heating,
Although the reflectivity increased, it was translucent due to the small thickness on the mesh.

Example 7 The aqueous dispersion containing the thin film particles obtained in Example 4 was diluted with water, placed on a glass plate, dried at about 20 ° C., and then heated at 200 ° C. to remove the thin film particles. Reduced. According to OM observation, particles before reduction on the glass plate could only be partially identified with a small difference in light and darkness, but after reduction, particles that had already been identified became extremely easy to identify. Further, particles that could be distinguished by a small difference in light and darkness were visible on the entire surface of the glass. It is considered that the particles are slightly colored by the reduction and the reflectance is increased, so that even thinner particles can be identified. These particles were also translucent after reduction.

Example 8 An aqueous dispersion containing the thin film particles obtained in Example 1 was washed with water for about 50 hours.
The resultant was diluted twice, added with aluminum powder (purity 99.9%, average particle diameter 3 μm) and hydrochloric acid (35 wt% aqueous solution), and irradiated with ultrasonic waves to try to hydrogenate the thin film particles. At least the surface of the thin film-shaped particles was reduced, turned into hydrophobic and macroscopically black particles, and most of them floated on the liquid surface. The resulting particles were washed with water, collected with a small amount of water without drying, and placed in a container.

The particles were dried and various measurements were made. OM
Observation revealed that the obtained particles were translucent. TE
As a result of M observation, a single or a plurality of aggregates of the thin film-like particles, which were randomly bent and deformed as if the paper were crushed, were confirmed. Further, X-ray diffraction measurement revealed that the peak corresponding to 0.83 nm observed in the original thin film-like particles had completely disappeared, indicating that the orientation was extremely low due to deformation and aggregation.

Since the thin film-shaped particles according to the present invention are extremely thin, they can be deformed inside the particles while having a dense carbon skeleton. It was found that self-aggregation sometimes occurred. Example 9

The aqueous dispersion containing the thin-film particles obtained in Example 1 was placed on two platinum electrodes (the area in contact with the liquid was about 6 cm each).
² , 1cm spacing, direct current (about 0.02 at 19V)
A) was applied. At the positive electrode (based on the power source), a high-viscosity deposit having a color similar to that of the thin-film particles was produced, and at the negative electrode, a black deposit was produced along with the generation of hydrogen.

Each electrode was placed in a separate container of water to separate each deposit from the electrodes. The deposit on the positive electrode is dispersed again in water, and OM
, Particles similar to the original thin film-like particles were observed. this is,
It was considered that the film-like particles were temporarily aggregated due to a slight decrease in hydroxyl groups. Further, the product of the negative electrode precipitated without being dispersed in water, and the same aggregates as in Example 8 were observed in OM. This was considered to be an aggregate formed by reducing the thin film particles before a part of the generated hydrogen became hydrogen molecules.

Comparative Example 1 In place of natural graphite, synthetic graphite (TIMCAL AMER)
ICA INC. Made, TIMREX KS75, purity 9
Oxidation and purification were carried out in the same manner as in Example 1 using 9.9% or more and an average particle size of about 15 μm). A dispersion of particles having high affinity for water was obtained, which was clearly different from the raw material synthetic graphite, but had a lower viscosity than the dispersion in Example 1, and a higher concentration of precipitate was generated even by centrifugation.

Observation by OM revealed that most of the non-planar particles were small and that the number of flat particles was small. They are,
Although all were transparent, most were thick enough to be easily identified by transmitted light.

Comparative Example 2 Graphite was oxidized and purified in the same manner as in Example 1 except that the oxidation time was set to 2 hours, and that particles that easily precipitated were not removed.

When observed by OM, the diameter was about 40 μm.
The following particles were mostly transparent and thin planar. On the other hand, larger particles consist of non-planar and planar ones, both thick enough to be easily identified by transmitted light, with the periphery of the particles being transparent but the central part being black and opaque. Was. The central part was not considered oxidized.

Comparative Example 3 In the same manner as in Example 1, graphite was oxidized and 3 wt% sulfuric acid / 0.1%
The dispersion at the stage after washing with a mixed aqueous solution of 5 wt% hydrogen peroxide was observed by OM. Most were planar particles, but most were thick enough to be easily identified by transmitted light. From comparison with Example 1, it was found that layer separation progressed at the stage of removing small ions.

Comparative Example 4 An aqueous dispersion of the thin film-shaped particles obtained in Example 1 was heated to about 50 ° C. on a glass plate placed on a hot plate to remove water, and a lump having a thickness of about 0.1 mm was obtained. Was dried.

The obtained dried product was put in water and stirred for 6 hours. There were aggregates that could be discerned with the naked eye, and complete redispersion was difficult.

[0071]

The thin-film particles of the present invention are much thinner than conventionally known graphite oxide and have a highly anisotropic shape. Therefore, despite having a dense carbon skeleton inside the particles, it is possible to deform flexibly,
When complexed with other substances, various properties such as high strength are expected to be exhibited by adding a low fraction. further,
When this thin film-like particle is reduced to an electronic state similar to graphite, it exhibits electrical conductivity and its shape is extremely thin.
It is expected to exhibit a dimensional quantum effect.

[Brief description of the drawings]

Fig. 1 Optical micrograph of thin film particles (on a glass plate)

FIG. 2 is a transmission electron micrograph of a thin film particle (a flat surface including many wrinkles, a flat portion other than the wrinkles cannot be recognized, and a black and thick portion is a carbon microgrid)

FIG. 3 is a transmission electron micrograph of a thin film particle (enlargement of one wrinkle).

FIG. 4 is a transmission electron micrograph of an aggregate of thin film particles reduced with aluminum and hydrochloric acid.

Claims (12)

[Claims] 2. The method according to claim 1, which is obtained by oxidizing graphite and has a thickness of 0.4 to
Thin film-like particles having a skeleton made of carbon, having a size of 10 nm, a size in a plane direction of 20 nm or more, and being dispersible in a liquid having a relative dielectric constant of 15 or more. 2. A dispersion of thin-film particles, wherein the thin-film particles according to claim 1 are dispersed in a liquid having a relative dielectric constant of 15 or more. 3. A thin-film graphite particle or an aggregate of thin-film graphite particles obtained by reducing the thin-film particle according to claim 1. 4. The thin film according to claim 1, wherein the raw material is graphite having a single multilayer structure in which the diameter of the widest basic layer inside the particle is substantially equal to the diameter of the particle. Method for synthesizing shaped particles. 5. The method for synthesizing thin film particles according to claim 1, wherein graphite from which impurities are removed to 0.5% or less is used as a raw material. 6. The method according to claim 1, wherein the graphite is oxidized for an oxidation time of 30 minutes or more per 10 μm of the particle size of the graphite. 7. The thin film according to claim 1, wherein after the graphite is oxidized, the concentration of small ions other than those derived from the oxidation product in the reaction solution is reduced to 10 mol / m ³ or less to purify the oxidation product. Method for synthesizing shaped particles. 8. The method for synthesizing thin film particles according to claim 1, wherein after the oxidation of the graphite, the concentration of the oxidized product in the reaction solution at the time of dispersion is 5 wt% or less to purify the oxidized product. Method. 9. The method for synthesizing thin-film particles according to claim 1, wherein particles of the multilayer structure having insufficient separation are settled out during purification. 10. A dispersion of the thin film-shaped particles at 50 to 150 ° C.
The method for synthesizing thin-film particles according to claim 1, wherein the heating is performed in the temperature range described above to further promote separation of the multilayer structure inside the thin-film particles. 11. The liquid serving as a dispersion medium is exchanged from water to another liquid having a different relative dielectric constant.
3. The method for producing a dispersion liquid of thin film-like particles according to item 1. 12. Heating the thin film-shaped particles according to claim 1,
The method for synthesizing thin-film graphite particles or an aggregate of thin-film graphite particles according to claim 3, wherein the reduction is performed by a reducing agent or an electrode reaction.