1. Field of the Invention
The present invention relates to a diamond and an aggregated carbon fiber. Also, the present invention relates to a producing method of a diamond and a producing method of producing an aggregated carbon fiber.
2. Related Background Art
In 1982, it was reported that a diamond crystal can be synthesized from a vapor phase by means of a chemical vapor deposition method (CVD method). Since then, a large number of synthesis methods and apparatuses have been investigated. Most of them require vacuum devices for decomposing and reacting a mixed gas containing a hydrocarbon gas such as methane and hydrogen under a low pressure by using plasma of microwave discharge, high-frequency discharge, arc discharge or the like, so that the configurations of the entire apparatuses are large (see Japanese Patent Application Laid-Open No. H09-249408). Similarly, the synthesis of a carbon nanotube reported in 1991 employs a method such as arc discharge or irradiation with laser, and hence involves a disadvantage in that a production method and a synthesis condition must be severely adjusted and a disadvantage in that an apparatus is expensive.
Investigations into the application of a diamond in the form of a thin film to high-temperature semiconductor devices, electron emitting materials, devices with environmental resistance, and the like have been made. In addition, carbon nanotubes, carbon nanofibers, and carbon fibers are expected to significantly improve the mechanical characteristics and electrical characteristics of hydrogen storage materials for fuel cells, electron emitting materials, and nano-size electronic devices as well as further composite materials of the carbon nanotubes, the carbon nanofibers, and the carbon fibers are combined with plastics, ceramics, rubber, metal, and the like.
However, according to the above method, a vacuum device is needed, and a gas such as hydrogen and plasma are used. Therefore, it is difficult to simply, inexpensively and safely synthesize a diamond crystal, a carbon nanotube or the like.
Exemplified as a conventional method of producing a diamond is a method of producing a diamond by applying high-density energy under an ultrahigh pressure (Japanese Patent Application Laid-Open No. H09-249408). Such a method involves a disadvantage in that the entire apparatus is large and a disadvantage in that the apparatus is expensive.
In addition, (1) a system for exhausting air by means of a vacuum pump to establish an air-free reaction space (Japanese Patent Application Laid-Open No. 2000-095509) or (2) an apparatus for establishing an air-free reaction space by heating a liquid filled in a reaction vessel from the inside by using three glass vessels (Shizuo Fujiwara, “Chemistry IA Revised Edition”, Sanseido Publishing Co., Ltd., 1998, p. 150) is exemplified as a conventional method of producing a carbon nanotube.
However, the system (1) involves a disadvantage in that the entire apparatus is large and a disadvantage in that the apparatus is expensive. The apparatus (2) involves, for example, a disadvantage in that a substance that can be dissolved into powder or a liquid cannot be used as a substrate. Therefore, further simplification and contrivance of an apparatus and a synthesis method have been demanded to aim for industrial production according to the conventional method.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide methods of producing each of a diamond and a carbon fiber such as a carbon nanotube by performing heat treatment under normal pressure in the saturated vapor of a liquid of a carbon source by using only one glass vessel such as a test tube. That is, an object of the present invention is to provide a simple apparatus configuration using a glass vessel without using a vacuum device, a carrier gas such as hydrogen, and plasma, and a simple production method.
The above object is achieved by the present invention described below. That is, according to one aspect of the present invention, there is provided a methods and apparatuses of a diamond and an aggregated carbon fiber by heating the vapor of a liquid of a carbon source to heat treatment in the absence of air, including the following steps (i) and (iii) of, the following steps (ii) and (iii) of, or the following steps (i), (ii) and (iii) of:
According to another aspect of the present invention, there are provided a diamond produced by means of the above methods.
According to another aspect of the present invention, there are provided an aggregated carbon fiber, including stacked carbon fibers having a concentrically hollow shape, wherein the aggregated carbon fiber is produced by the above methods.
The present invention has the features and effects (1) to (5): (1) a reaction is performed under normal pressure without using a carrier gas; (2) a liquid containing at least carbon, oxygen, and hydrogen such as an alcohol is used as a carbon raw material; and thereby (3) a method of easily synthesizing a granular diamond crystal, a diamond film, or a hollow carbon fiber having an amorphous structure and an extremely active surface with high efficiency is obtained; (4) a simple structure, inexpensive and highly safe apparatus of producing them can be assembled because the apparatus can be basically constituted by using only one glass vessel; and (5) an utilizable substrate that can be used can be selected from a significantly expanded range of materials including plate-shaped, granular, fine powdery and pasty solids.
The foregoing is the explanation and illustration of the principle of the present invention, and industrial production is not limited to the foregoing. That is, for example, the glass vessel may be exchanged to a metal vessel equipped with an explosion proof apparatus from the viewpoint of safety, and a vessel volume may be appropriately changed as an example.
The diamond produced by means of the above methods is expected to find applications in electronic emitter materials, high-temperature semiconductor device materials, blue light-emitting device materials, radiation resistant device materials, gas sensor materials, heat sink materials, and electrochemical devices. In addition, a hollow carbon fiber having an extremely large specific surface area and an extremely active surface can find use in a wide variety of applications including electron emitter materials, nano-size transistor materials, molecular wires, secondary battery and capacitor materials, hydrogen storage materials for fuel cells, catalyst materials, biosensor materials, and novel structural materials.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.
Preferred embodiments of the present invention will now be described in detail in accordance with the accompanying drawings.
Hereinafter, the present invention will be described in more detail by way of preferred embodiments.
The outlines of the method and apparatus for producing a diamond or a carbon fiber according to the present invention will be described with reference to
Examples of the liquid 2 containing carbon, oxygen and hydrogen as components include organic compounds such as an alcohol, an ether, a ketone, an ester, an aldehyde, and a carboxylic acid. A compound having an abundance ratio between the number of carbon atoms and the number of oxygen atoms in the range of 1:2 to 6:1 is suitable, and in particular, a compound having such a ratio in the range of 1:1 to 4:1 is preferable. When the ratio of the number of carbon atoms to the number of oxygen atoms is greater than 6:1, a diamond or carbon fiber is hardly obtained, and an amount of soot to be produced increases. Specific examples of a liquid containing carbon, oxygen and hydrogen as components include methanol, ethanol, propanol, butanol, dimethyl ether, methylethyl ether, formaldehyde, acetaldehyde, acetone, formic acid, acetic acid, and ethyl acetate. However, the present invention is not limited to them.
In such a state of the apparatus, the bottom of the glass vessel 1 is heated with a fire 9 of a burner 8 (such as an alcohol lamp or a Bunsen burner) from an outside. There are many methods of heating the bottom of the glass vessel 1 from an outside other than heating with the fire 9.
The conventional method involves several problems in terms of creation of the air-free space 10. In contrast, the present invention employs a method involving: heating from the outside and evaporating a small amount (5 to 8 ml) of the liquid 2 of a carbon source placed in the glass vessel 1 in order to exhaust the air in the glass vessel 1; and exhausting the evaporated vapor together with the air in the glass vessel 1 to the outside through the exhaust pipe 4, and hence has a feature that an apparatus configuration, experimental method, and procedure become extremely easy.
In another examples of the method of exhausting the air in the glass vessel 1, gases such as nitrogen are introduced from the outside into the glass vessel 1 and the air is forcedly exhausted together with these gases. This method is shown in
Since the space 10 contains only the saturated vapor of the liquid 2 of a carbon source and is free of air, the W filament 6 can be heated with safety. Then, the W filament 6 is heated to 1,500 to 2,200° C., and at the same time, the fire 9 heating the bottom of the glass vessel 1 is extinguished. In actuality, the burner 8 is removed. The vapor of the liquid 2 as a carbon source, which is heated to 1,500 to 2,200° C., turns into a gas from the vapor to be vigorously released from the exhaust pipe 4. The air from the outside cannot flow into the glass vessel 1 because the pressure of exhausting gas is high. Therefore, the safety of the apparatus is maintained because no inflammation to the liquid 2 as a carbon source occurs and there is no possibility of explosion. The substrate 5 is heated to 300 to 900° C. by heat radiation from the W filament 6. The substrate 5 is made of Si, the substrate temperature is kept at 700 to 900° C., and a reaction is continued for 1 hour or longer, whereby a diamond crystal grows on the Si substrate 5. In addition, the substrate 5 is made of Ni, the substrate temperature is kept at 300 to 700° C., and a reaction is continued for 10 minutes or longer, whereby the aggregated carbon fiber such as a carbon nanotube deposits on the Ni substrate 5.
The exhaust pipe 4 of
As described above, the air from the outside atmosphere does not flow into the glass vessel 1 because the exhaust pressure of a gas through the exhaust pipe 4 is high.
The vapor of the liquid 2 as a carbon source is heated by heat of the W filament 6 to be decomposed into carbon-based excited species (such as C, CH, and C2) and carbon-based gases (such as CH4, C2H2, and CO). A part of those excited species and carbon-based gases is expected to deposit as a diamond crystal or a carbon fiber. As the reaction proceeds, the liquid 2 as a raw material is consumed.
Results of crystallographic characterization of the resultant deposit are shown. When a reaction time is 1 hour or shorter, a diamond deposits as a granular crystal. When the reaction time is 1 hour or longer, or if possible, 2 to 3 hours, the diamond deposits as a film-shaped diamond. When the surface morphology is observed with a field emission-type scanning electron microscope (FE-type SEM), a film having a diameter of several microns surrounded by a triangle (111 plane) and a quadrangle (100 plane) is observed. Furthermore, characterization by means of laser Raman spectroscopy identified the resultant film-shaped substance as a diamond because the substance has a sharp peak at 1,333 cm−1 as in a natural cubic diamond.
In addition, when the resultant aggregated carbon fiber is observed with a FE-type SEM, a large number of rope-shaped carbon fibers are observed. The diameter of each of those carbon fibers is in the range from about 10 nm to submicrons. Observation with a transmission electron microscope (TEM) shows that there is a carbon nanotube having a diameter of 75 nm and an internal diameter of 20 nm (hollow nano-size carbon fiber). Further, it is also shown that those carbon fibers have an amorphous structure. The carbon fibers are considerably different from the crystalline carbon fibers conventionally reported in this point. This difference is probably because a temperature for producing them is as low as 300 to 700° C.
A substrate to be used as the substrate 5 suitable for the growth of a diamond preferably contains at least one element selected from Si, Mo, W, Cu, Ta, Ti, Pt, Ir, Zn, and Al. A substrate made of each of the carbides such as SiC, Mo2C, WC, TaC, and TiC is also preferable. On the other hand, a substrate to be used as the substrate 5 suitable for the growth of a carbon fiber preferably contains at least one element selected from Ni, Fe, Co, Pd, Pt, Ru, Rh, Ti, and Cu, and the substance may have various shapes such as plate-like, granular, fine powdery, and pasty shapes. A substrate made of Ni, Fe, or Co is most desirable for the growth of a carbon fiber. A substrate made of the sulfides such as FeS or NiS is also preferable.
Application and use of a metal complex having a Group-X metal such as Ni, Pd, or Pt or having a metal such as Fe or Ru onto a substrate increase the production yield of a carbon fiber. Specific examples of the metal complex include platinum acetylacetonate, nickel acetylacetonate, palladium acetylacetonate, cobalt acetylacetonate, and iron acetylacetonate. However, the present invention is not limited to them.
In addition, the liquid 2 as a carbon source may be mixed with water to be used. The effect of the present invention is confirmed even when the liquid 2 as a carbon source is added with 1 to 50% by volume of water. For the efficacy, the water content is desirably 20% by volume or less for synthesis of a diamond crystal, while the water content is desirably 10% by volume or less for synthesis of a carbon fiber.
The dispersion or dissolution of the metal complex compound into the liquid 2 as a carbon source increases the growth rate of a hollow carbon fiber. The concentration of the compound is 0.0005 to 1.0 g, desirably 0.001 to 0.5 g with respect to 100 ml of the liquid.
The dispersion or dissolution of a sulfur-containing compound such as thiol, thioether, thiocarbonyl, carbon sulfide, hydrogen sulfide, a sulfuric acid compound, or an aromatic thio compound into the liquid 2 as a carbon source also increases the growth rate of a hollow carbon fiber.
The sulfur-containing solution desirably has a composition with an element abundance ratio between carbon and sulfur in the range of preferably 100:1 to 1,000,000:1, particularly preferably 300:1 to 100,000:1.
As described above, the present invention relates to specific methods of producing a diamond and a hollow carbon fiber, and a simple synthesis apparatuses constituted by a glass vessel. In addition, the present invention is, for example, characterized in that: (1) the apparatuses are basically constituted by one glass vessel; (2) no carrier gas is used; (3) no vacuum device is needed because a reaction is performed under normal pressure; (4) the safety operation at experiment increases because the amount of a liquid can be reduced from that of the conventional method by one tenth to one several tenth; and (5) a substrate can be selected from a significantly expanded range including plate-shaped, granular, fine powdery, and pasty solids.
Hereinafter, the present invention will be described more specifically by way of examples.
The capacity of the glass vessel shown in
Observation with a FE-type SEM revealed that each granular crystals each having a diameter in the range from 2 to 5 μm deposited. Furthermore, characterization by means of laser Raman spectroscopy identified the resultant crystal as a diamond because the resultant crystal had a sharp peak at 1,333 cm−1 as in a natural cubic diamond. It was also found that the crystal contained an amorphous carbon component because the crystal had a broad peak nearby 1,550 cm−1. Evaluation of the quality of the crystal by means of an X-ray diffraction method revealed that the crystal was a polycrystalline diamond.
The apparatus shown in Example 1 was used. A reaction was performed under the same conditions as those of Example 1 except that a Si substrate surface polished with a fine diamond powder was used, and a reaction time was changed to 4 hours. As a result, a film-shaped diamond was obtained. A film thickness and a growth rate were measured by means of a scanning electron microscope (SEM). An average film thickness was 10 μm and the growth rate was about 2.5 μm/h. The result confirmed that polishing the Si substrate surface had an increased effect on the growth rate.
The apparatus shown in Example 1 was used, and a film-shaped diamond grew under the same conditions as those of Example 2 except that the Si substrate was changed to a Mo plate, a W plate, a Ta plate, a SiC plate, a Mo2C plate, and a TaC plate, the temperature of the W filament was increased to 2,200° C., and a reaction time was set to 4 hours. As a result, the increase of the heating temperature by 200° C. increased the growth rate to 3 μm/h.
Deposition of a diamond crystal was performed by using the apparatus shown in
Deposition of a diamond crystal was performed by using the apparatus shown in
5 ml of methanol as a carbon source were charged into the bottom of a vessel. The configuration of the apparatus shown in
A raw material for the liquid as a carbon source was methanol added with 12.5% by volume of ethanol. A reaction was performed by adopting the apparatus and experimental procedure shown in Example 1, a reaction time of 4 hours, and a Si substrate with a polished surface. As a result, a film-shaped diamond was obtained. A carbon source concentration increased owing to the mixing of ethanol, whereby the growth rate increased to about 4 μm/h.
The same apparatus as that of Example 1 was used, but the carbon source was changed to ethanol, the substrate was changed to Ni substrate, and a gap between the W filament and the substrate was set to 5 mm. When the filament temperature was set to 2,000° C., the Ni substrate temperature kept on 500° C. A reaction was continued for 15 minutes. As a result, black deposits grew on the Ni substrate. Observation by means of a FE-type SEM revealed that the deposits were carbon fibers of a nano-size to submicron-size. Characterization by means of a TEM was performed in order to observe the inside of each of the fibers. The characterization revealed that the carbon fibers were typically carbon nanotubes (hollow carbon fibers) each having a diameter of 80 nm and an internal diameter of 30 nm. Observation by means of a TEM also revealed that those carbon fibers each had an amorphous structure.
A reaction was performed under the same conditions as those of Example 8 except that the Ni substrate was changed to a substance made of submicron-size Ni fine powder. The Ni fine powder is expected to increase the growth rate because it has an extremely large surface area as compared to a Ni plate. Deposition of carbon fibers was observed even with a reaction time of about 3 to 5 minutes. The resultant carbon fibers were hollow, and the dimensions and structure of the fibers were substantially the same as those of Example 8. The above results showed that the use of a substance with a large surface area increases a growth rate.
By performing RF sputtering of a metal Ni, a nano-size Ni catalyst nucleus was formed on a Si substrate. By using the substrate and the apparatus shown in Example 1, an experiment was performed under the same experimental conditions as those of Example 8. Observation by means of a FE-type SEM and a TEM revealed that very thin carbon fibers deposited as a result of the experiment. The fibers were carbon nanotubes each having an external diameter of 15 nm and an internal diameter of 10 nm as typical numerical values, and a part of the fibers had graphite structures and were crystallized.
5 ml of methanol as a carbon source were charged into the bottom of a vessel. The configuration of the apparatus shown in
A reaction was performed under the same conditions as those of Example 8 except that the temperature of the W filament was 1,700° C. As a result, a small amount of hollow amorphous carbon fibers were obtained.
A reaction was performed under the same conditions as those of Example 8 except that ethanol as a raw material was changed to a methanol solution, and the substrate temperature was changed to 400° C. As a result, the obtained carbon fibers were found to have a hollow shape. Furthermore, observation by means of a FE-type SEM revealed that the surface of each fiber had a large ragged structure.
A reaction was performed under the same conditions as those of Example 8 except that ethanol as a raw material was changed to a mixed liquid of 30 volume % of ethanol and 70 volume % of propanol. Although the amount of soot increased, carbon fibers were obtained. Observation by means of a SEM and a TEM revealed that each of the fibers had a hollow shape.
The Si substrate 5 shown in
A reaction was performed under the same conditions as those of Example 8 except that 85 ml of ethanol and 15 ml of water (the addition amount of water was 15 volume % by volume) were used as raw materials (carbon sources). Observation by means of a SEM and a TEM confirmed that hollow carbon fibers can be synthesized. Addition of water reduced the amount of hollow carbon fibers and reduced the external and internal diameters of each carbon fiber. However, a large amount of soot was observed to be removed. Observation by means of a SEM showed that hollow carbon fibers were synthesized to cover the entire surface of the Ni substrate.
The apparatus shown in
A reaction was performed under the same conditions as those of Example 8 except that ethanol as a raw material was changed to dimethyl ether. As a result, hollow carbon fibers were obtained.
A reaction was performed under the same conditions as those of Example 8 except that ethanol as a carbon source was changed to acetone. As a result, hollow carbon fibers were obtained.
A diamond obtained according to the production method of the present invention can use in applications including semiconductor device materials, electron emitting materials, materials for environmental resistance, and sensor materials when the diamond is formed into a thin film. Possible applications of carbon nanotubes, carbon nanofibers and carbon fibers include conductive fillers for conductive resins and for rubber materials because the carbon nanotubes, the carbon nanofibers, and the carbon fibers have good compatibility with resin materials. Those conductive resins and rubber materials can be used, for example, for electrophotographic functional components such as charging rollers, transferring rollers, transferring belts, and intermediate transfer parts. In addition, the carbon nanotubes, carbon nanofibers and carbon fibers can be used for catalyst carriers for fuel cells, hydrogen storage materials and the like because the surface of each fiber has high activity and low resistance.
The present invention is not limited to the above embodiments and various changes and modifications can be made within the spirit and scope of the present invention. Therefore to apprise the public of the scope of the present invention, the following claims are made.
This application claims priority from Japanese Patent Application No. 2004-089533 filed on Mar. 25, 2004, which is hereby incorporated by reference herein.
Number | Date | Country | Kind |
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2004-089533(PAT.) | Mar 2004 | JP | national |