JP5649186B2 - Onion-like carbon and method for producing the same - Google Patents

Description

  The present invention relates to onion-like carbon and a method for producing the same.

  Onion-like carbon is also called carbon onion, carbon onion, nano-sized spherical graphite, onion graphite, onion fullerene, and the like, and is a synonym of fullerene and carbon nanotube, and is a material attracting attention as a new carbon material. Its shape is a concentric spherical carbon structure, and spherical carbon structures are nested and overlapped like an onion.

  Onion-like carbon is lightweight and stable, and has excellent resistance to radiation and resistance at high temperatures. In addition, high elasticity is expected from its shape, and application as a solid lubricant that can be used in a vacuum or non-lubricated environment is considered. Applications for hydrogen storage carbon materials for pharmaceuticals, cosmetics, and fuel cells are also considered.

  However, onion-like carbon has a big problem in productivity, and various production methods have been proposed so far. However, all methods still have problems to be put into practical use.

  That is, (1) as a method for synthesizing onion-like carbon, a method is shown in which a molded body made of glassy carbon is subjected to heat treatment at 1000 to 3000 atmospheres at 2000 to 3000 ° C. by hot isostatic pressing. (See Patent Document 1).

  Further, (2) a method of heating diamond fine powder at 1600 to 1800 ° C. in an inert gas atmosphere (see Patent Document 2), and (3) 1700 ° C. using an infrared lamp in an inert gas. The heating method has been disclosed above (see Patent Document 3).

  Also, (4) a method for producing onion-like carbon by irradiating polyyne with light, an electron beam or an ion beam, or by subjecting it to a heat treatment is described (see Patent Document 4). Furthermore, (5) a method of irradiating polytetrafluoroethylene, polyvinylidene chloride or polyvinylidene fluoride with light, an electron beam or an ion beam (see Patent Document 5), (6) electron beam, gamma ray, X-ray on rod-like carbon A method of converting to onion-like carbon by irradiating a high energy beam such as an ion beam is disclosed (see Patent Document 6).

  (7) A method for producing onion-like carbon containing hollow or metal by irradiating a carbon material having a double bond or triple bond with one or more of X-rays, microwaves and ultrasonic waves (patent) Reference 7). (8) A method for producing onion-like carbon by irradiating a material having a double bond or a triple bond with light, an electron beam or an ion beam is also shown (see Patent Document 8).

  (9) A method for producing an onion-like carbon film by an unbalanced magnetron sputtering method is shown (see Patent Document 9).

  (10) A method of generating a compression molded body of SiC powder and Cu powder by applying a compressive impact of 350,000 atmospheres or more and 2700 ° C. or more of ultrahigh pressure / ultra high temperature is disclosed (see Patent Document 10).

  Further, as a method using the discharge phenomenon, (11) a method of producing onion-like carbon by generating arc discharge between carbon electrodes in water (see Non-Patent Document 1) is shown.

Japanese Patent Laid-Open No. 5-208805 JP-A-11-157818 JP 2002-80212 A Japanese Patent Laid-Open No. 11-310406 JP 11-349307 A JP 2001-48508 A JP 2000-109310 A JP 2000-16806 A JP 2002-105623 A JP 2003-137518 A

Materials Research Bulletin 44 (2009) 324-327. Material Research Bulletin 44, 2009, 324-327

The method (1) requires an expensive apparatus corresponding to high-pressure synthesis of diamond, and the production cost is considered to be comparable to that of synthetic diamond, and is not versatile.
In the methods (2 and 3), since the raw material powder is expensive, there is a problem that onion graphite is more expensive than the raw material powder.
In the methods (4, 5, 6, 7, 8), all of these methods have a limited amount of energy input to the target raw material, and there is a limit to mass production.
In the method (9), because of the thin film method, there is a limit to the production of onion-like carbon powder, the production rate is low, and the quantity is limited.
In the method (10), it is necessary to create an extreme environment of high temperature and high pressure, and it is difficult to cope with the apparatus, and there is also a problem in separation and purification after synthesis.
The method (11) has a problem that the selectivity of the reaction is low, a large amount of amorphous carbon is produced, and separation is difficult.

  Accordingly, an object of the present invention is to provide a method capable of producing onion-like carbon stably on an industrial scale.

  The inventors of the present invention have made extensive studies to achieve the above object, and found that onion-like carbon can be obtained by generating pulse plasma between carbon metal electrodes in a solvent in the presence of a catalyst. It came to.

That is, according to the present invention, the following is provided.
[1] A method for producing onion-like carbon, which comprises performing pulsed plasma discharge between carbon electrodes in a liquid.
[2] Onion-like carbon having a graphite interlayer distance of 0.40 nm or more.

  By the production method of the present invention, onion-like carbon can be produced with a relatively low voltage, low current, and low energy such as performing pulse discharge. Moreover, the onion-like carbon of the present invention has a wide graphite interlayer distance and is useful for electrode applications of Li ion secondary batteries.

It is a TEM photograph of the black powder obtained in Example 1 (magnification: 100,000 times). It is a TEM photograph of the black powder obtained in Example 1 (magnification: 500,000 times). It is a TEM photograph of the black powder obtained in Example 2 (magnification: 100,000 times). It is a TEM photograph of the black powder obtained in Example 2 (magnification: 500,000 times). It is a TEM photograph of black powder obtained by a comparative example (magnification: 200,000 times).

  The onion-like carbon of the present invention has a concentric spherical carbon structure, but is characterized by a graphite interlayer distance of 0.40 nm or more, more specifically 0.50 nm or more. Onion-like carbon having such a wide graphite interlayer distance has not been obtained by the prior art method and is novel. Various ions can be accommodated between the graphite layers, and is particularly useful for electrode applications of Li ion secondary batteries.

  The onion-like carbon production method of the present invention is characterized in that pulse plasma discharge is performed between carbon electrodes in a liquid, and any carbon material such as graphite, amorphous carbon, and glassy carbon is used as the carbon electrode. can do.

  The form of the electrode may be any form such as a bar, wire, or plate. Regarding the size of both poles, it may have a shape such that one of the sizes is different. Moreover, both poles may use the same carbon material or a different material, and may use what was shape | molded by the single or several carbon material.

  In the present invention, onion-like carbon is generated in a liquid. The liquid (solvent) that can be used is not particularly limited as long as it does not affect the reaction. The liquid may be a mixture of two or more compounds. Saturated hydrocarbons such as hexane, octane, decane, cyclohexane, cyclooctane, aromatic hydrocarbons such as benzene, toluene, xylene, naphthalene, water, methanol, ethanol, propanol, butanol, ethylene glycol, propylene glycol, 1,4 -Alcohols such as butanediol, esters such as methyl acetate, ethyl acetate, butyl acetate, methyl benzoate and dimethyl phthalate, ethers such as tetrahydrofuran, tetrahydropyran, dipropyl ether, dibutyl ether, diethylene glycol and tetraethylene glycol Can also be used. In consideration of dispersion, flammability, and oxidizability of the produced carbon product, use of water, saturated hydrocarbons, aromatic hydrocarbons and alcohols is preferred, and use of methanol and ethanol is preferred.

  The amount of liquid used is not particularly limited, and both electrodes only need to be in the liquid. More preferably, it is sufficient that the liquid scatters due to the generation of plasma or the diffusibility of the liquid is not lost depending on the product concentration.

  The temperature at which the pulsed plasma discharge is performed is not particularly limited and depends on the type of liquid used. Usually, it is carried out in the range of room temperature to 300 ° C. An excessively high temperature is not preferable because the vapor pressure of the solvent to be used increases and there is a possibility of being ignited by plasma. An excessively low temperature is not preferable because the viscosity of the solvent increases and the diffusibility of the product is impaired.

  In the present invention, onion-like carbon is generated by performing pulsed plasma discharge between carbon electrodes in a liquid. The voltage for generating plasma is not particularly limited, and is preferably in the range of 60V to 400V and in the range of 80V to 300V in consideration of the range of 20V to 500V, safety, and the necessity of special equipment. More preferred.

  It does not restrict | limit especially as an electric current which generate | occur | produces plasma, It is preferable to implement in the range of 0.2-10A in consideration of the range of 0.1-20A and energy efficiency.

  The interval for applying the pulsed plasma is not particularly limited, but is preferably 5 to 100 milliseconds, and more preferably 6 to 50 milliseconds. If the plasma application interval is too short, the generation of carbon radicals is further induced before the disappearance of the carbon radicals generated by the plasma discharge, which leads to the growth of onion-like carbon and the formation of amorphous carbon, which is not preferable. In addition, an excessively long discharge interval is not preferable because much energy used for inducing plasma is required, and the production efficiency of onion-like carbon is reduced.

  The duration per pulsed plasma also varies depending on the applied voltage and current, but is usually 1 to 50 microseconds, preferably in the range of 2 to 30 microseconds considering the discharge efficiency. If the plasma generation time is too long, a large amount of carbon radicals generated by plasma discharge are induced, leading to the growth of onion-like carbon and the generation of amorphous carbon, which reduces the selectivity. In addition, when the discharge time is too short, sufficient energy is not supplied, and a lot of energy used for inducing plasma is required, which is not preferable because the production efficiency of onion-like carbon decreases.

  In the present invention, it is also possible to apply vibration to the electrode. By giving vibration, there is no stagnation of the carbon compound deposited between the electrodes, and it is possible not only to suppress the attachment of the reactive biological material on the stagnation, but also to discharge efficiently, which is preferable. A method for applying vibration is not particularly limited, and a method for applying vibration periodically or a method for applying vibration intermittently may be used.

  The atmosphere for carrying out the present invention is not particularly limited, and it can be carried out under reduced pressure, under pressure, or under normal pressure, but usually, in consideration of safety and operability, nitrogen, argon, etc. It can be carried out under an inert gas.

  Since the produced onion-like carbon is deposited in the liquid, it is possible to obtain the onion-like carbon by a general method, for example, filtering and removing the used liquid by an operation such as decompression.

Example 1
Take 200g of toluene in a 300ml beaker, insert 2 columnar graphite electrodes (purity 99% or more) with a diameter of 6mm and a length of 100mm into the toluene, fix the distance between the electrodes to 1mm, and reaction products on the electrode surface Vibrating was applied to prevent the deposition of and to increase the reaction efficiency. Each electrode was connected to an AC power source and subjected to pulse discharge at 200V and 2A. The interval between pulse plasmas was 20 milliseconds, and the duration per pulse plasma was 10 microseconds. Simultaneously with the start of discharge, it was observed that the black powder was dispersed in the liquid and the reaction occurred. The reaction was continued for 30 minutes, the sediment was separated, the black solution was centrifuged, and an appropriate amount of toluene was added for washing and separation. The consumption of the electrode was 380 mg.

  The resulting black powder was heated and dried under vacuum. The obtained black powder is 254.6 mg. A TEM photograph (magnification: 100,000 times) of the obtained black powder is shown in FIG. 1 (scale of FIG. 1 is 20 nm), and a TEM photograph (magnification: 500,000 times). Is shown in FIG. 2 (the scale of FIG. 2 is 10 nm, and the interlayer distance is shown by two arrows in FIG. 2). From the photograph, it can be seen that the obtained black powder is onion-like carbon having an interlayer distance of 0.62 nm. The yield was 67%.

Example 2
In Example 1, it carried out like Example 1 except having used water as a solvent. A TEM photograph (magnification: 100,000 times) of the obtained black powder is shown in FIG. 3 (scale of FIG. 3 is 10 nm), and a TEM photograph (magnification: 500,000 times) is shown in FIG. 4 (scale of FIG. 4 is 5 nm). The consumption of the electrode was 412 mg, the obtained black powder was 271.9 mg, the yield was 66%, and it can be seen from the photograph that it is onion-like carbon having an interlayer distance of 0.55 nm.

Comparative Example The same procedure as in Example 1 was performed except that the electrode was connected to a DC power source and was continuously discharged at 200 V 2A. The obtained black powder is 312 mg, and a TEM photograph (magnification: 200,000 times) of the obtained black powder is shown in FIG. 5 (the scale of FIG. 5 is 5 nm). Concentric spherical onion-like carbon was not observed.

  According to the production method of the present invention, onion-like carbon can be produced at a relatively low voltage and low current, with low energy such as performing pulse discharge, and has great industrial utility.

Claims (2)

A method for producing onion-like carbon, comprising applying a voltage in the range of 20 to 500 V between carbon electrodes in a liquid to cause pulsed plasma discharge. The manufacturing method according to claim 1, wherein the pulse plasma discharge is given at intervals of 5 to 100 milliseconds, and the duration per pulse plasma is 1 to 50 microseconds.