Patent Application
20120213999
This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2011-033723, filed Feb. 18, 2011, the entire contents of which are incorporated herein by reference.
Embodiments described herein relate generally to a graphite nano-carbon fiber and a method of producing the same.
It is known to use, as a carbon nanostructure material, fibrous nano-carbon produced generally by bringing gas containing carbon into contact with a selected catalyst metal at a temperature of about 500° C. to 1200° C. for a prescribed period of time.
Examples of methods of producing a carbon nanostructure material include an ark discharge method, laser vapor deposition method, and chemical vapor deposition method (CVD method).
In the arc discharge method, arc discharge is made to generate between positive and negative graphite electrodes to thereby vaporize graphite, and a carbon nanotube is generated in a carbon deposit condensed at the tip of the negative electrode.
The laser vapor deposition method involves steps of adding a graphite sample mixed with a metal catalyst in inert gas heated to a high temperature and irradiating the graphite sample with a laser beam to thereby produce a carbon nanostructure material.
Although a carbon nanostructure material having high crystallinity can generally be generated in the arc discharge method and laser vapor deposition method, the amount of carbon to be generated is small and it is therefore said that these methods are scarcely applied to mass-production.
The CVD method is typified by two methods including a vapor deposition substrate method in which a carbon nanostructure material layer is formed on a substrate disposed in a reaction furnace and a fluidized vapor phase method in which a catalyst metal and a carbon source are fluidized together in a high-temperature furnace to synthesize a carbon nanostructure material.
However, the vapor deposition substrate method has a difficulty in attaining mass-production because it is carried out by batch treatment. Also, the direct injection pyrolytic method is inferior in temperature uniformity and is regarded as difficult to produce a carbon nanostructure material having high crystallinity. Moreover, a method modified from the fluidized vapor phase method is known in which a fluidized layer is formed in a high-temperature furnace from a fluidizing material also functioning as a catalyst and carbon raw material is supplied to the furnace to produce a fibrous carbon nanostructure material. This method is, however, inferior in temperature uniformity in the furnace so that it is assumed that this method has a difficulty in generating a carbon nanostructure material having high crystallinity.
The importance of nanostructure materials and particularly, graphite carbon nano-fibers has sharply increased in many industrial applications and studies as to the applications of these nanostructure materials are being made. Examples of these applications include occlusion and absorption/desorption of hydrogen, occlusion and absorption/desorption of lithium, catalytic action, and absorption and occlusion of nitrogen oxides. However, these nanostructure materials still have poor industrial applicability at present. One of the reasons is that structurally uniform graphite carbon nano-fibers cannot be mass-produced.
In light of this, if graphite carbon nano-fibers superior in the high stabilities of, for example, dimension, shape, structure and purity can be mass-produced efficiently at low cost, nano-technological products making use of the characteristics of these graphite carbon nano-fibers can be supplied in a large amount at low cost.
In general, according to one embodiment, there is provided a graphite nano-carbon fiber provided by using an apparatus having a reactor capable of keeping a reducing atmosphere inside thereof, a metal substrate arranged as a catalyst in the reactor, a heater heating the metal substrate, a hydrocarbon source supplying hydrocarbon to the reactor, a scraper scraping carbon fibers produced on the metal substrate, a recovery container recovering the scraped carbon fibers, and an exhaust pump discharging exhaust gas from the reactor. The carbon fibers are linear carbon fibers with a diameter of 80 to 470 nm formed with layers of graphenes stacked in a longitudinal direction.
Hereinafter, apparatuses of producing graphite nano-carbon fibers according to embodiments will be described with reference to the drawings.
An apparatus of producing a graphite nano-carbon fiber according to a first embodiment will be described with reference to
Although ethanol is used as the hydrocarbon in the production apparatus of
The followings describe the action of the production apparatus of
First, the temperature of the reactor 1 is adjusted to 600° C. to 750° C. and preferably 670° C., and ethanol is preheated at 350° C. and injected into the reactor 1. Raw ethanol is thermally decomposed into gas in the reactor 1 and carbon atoms are incorporated into the metal substrate 2. Next, it is considered that when carbon on the metal substrate 2 is saturated, carbon precipitates on the metal substrate 2 and is grown into a crystal form. The matters grown into crystals are the fine carbon fibers 3.
Next, the fine carbon fibers 3 grown on the metal substrate 2 over several tens of minutes are scraped with the scraper 4 and recovered in the recovery container 7 outside of the reactor. In scraping, the fibers are scraped in such a manner that the fibers having a thickness of about 0 to 5 mm are left on the metal substrate 2 and then, the fine carbon fibers 3 grown again are scraped and these operations are repeated. Even if the fine carbon fibers left unscraped exist on the metal substrate 2, the amount of the fine carbon fibers to be generated can be kept constant for a long time because carbon is sufficiently supplied to the metal substrate 2.
An apparatus of producing a graphite nano-carbon fiber according to a second embodiment will be described with reference to
A cylindrical metal substrate (catalyst) 12 is disposed inside of a vertical cylindrical reactor 11 which can shut off external air and keep a reducing atmosphere inside thereof, and is arranged coaxially with the reactor 11. In the reactor 11, a scraper that scrapes fine carbon fibers 3 generated on the surface of the metal substrate 12 is arranged. Here, the scraper is constituted by a driving unit 13, a main shaft 14 which is axially supported by the driving unit 13 in such a manner as to be rotatable in the direction of the arrow A, and a spiral scraping blade 15 attached to the main shaft 14. An inert gas source 16 is communicated with the reactor 11 to supply inert gas. A seal member 17 is arranged around the main shaft 14 on the upper part of the reactor 11. It should be noted that the hydrocarbon and metal substrate material used in the production apparatus of
The followings describe the action of the production apparatus of
First, the temperature of the reactor 11 is adjusted to 600° C. to 750° C. and preferably 670° C., and ethanol is preheated at 350° C. and injected into the reactor 11. Raw ethanol is thermally decomposed into gas in the reactor 11 and carbon atoms are incorporated into the metal substrate 12. Next, it is considered that when carbon on the metal substrate 12 is saturated, carbon precipitates on the metal substrate 12 and is grown into a crystal form. The matters grown into crystals are the fine carbon fibers 3.
Next, the fine carbon fibers 3 grown on the metal substrate 2 over several tens of minutes are scraped with the scraper 4 and recovered in the recovery container 7 outside of the reactor. In scraping, the distance between the metal substrate 12 and the tips of rotary blade 15 is adjusted in such a manner that the fibers having a thickness of about 0 to 5 mm are left on the metal substrate 12. Here, the scraping blade 15 having a spiral form is rotated at a rate of 0.01 to 0.05 rpm in the direction of the arrow A by the driving unit 13 to scrape fibers continuously or intermittently at intervals of 20 to 60 min. As a result, the fine carbon fibers 3 are scraped, and then, the fine carbon fibers 3 grown again are scraped again, thereby enabling continuous production. Even if the fine carbon fibers left unscraped exist, the amount of the fine carbon fibers to be generated can be kept constant for a long time because carbon is sufficiently supplied to the metal substrate.
The above descriptions are relating to the apparatus and method of producing fine carbon fibers, and then, the followings describe the dimension, shape, structure and purity of the generated fine carbon fibers.
From the above fact, it was found that the fine carbon fibers produced by the apparatus of the embodiment were linear graphite nano-carbon fibers (GNF) which have a diameter of 100 to 300 nm and in which layers of graphenes were stacked in a longitudinal direction. Further analysis of the fine carbon fibers revealed that the distance between graphenes was 0.3 to 0.4 nm, these layers of graphenes were stacked to constitute a crystallite having an average crystal thickness of 3 to 10 nm and these crystellites are stacked, thereby constituting linear graphite nano-carbon fibers having a diameter of 100 to 300 nm.
The diameter of the fine carbon fiber was measured. Each distribution of the diameter of the measured four samples is shown in Table 1 below. Table 1 shows a diameter distribution with a primary diameter ranging from 100 to 300 nm. Also, Table 1 shows that the average diameter is 151.5 to 198.9 nm with a primary average diameter ranging from about 150 to 200 nm. The diameter including the data of other samples is 80 to 470 nm and preferably 130 to 300 nm.
The following Table 2 shows the results of measurements of specific surface area and bulk density. In the table, four samples are shown as examples. From Table 2, the specific surface area was 92.46 to 128.5 m2/g (gas adsorption BET method), and the specific surface area including the data of other samples is 70 to 130 m2/g and preferably 90 to 130 m2/g. The bulk density including the data of other samples is 0.1 to 0.35 g/cm3 and preferably 0.15 to 0.35 g/cm3.
The results of four samples measured by this method are shown in the following Table 3. Table 3 shows the distribution of the decomposition initiation temperature (heat resistant temperature) ranging from 540° C. to 616° C. Also, the heat resistant temperature including the data of other samples is 530° C. to 630° C. and is preferably 540° C. to 620° C. Moreover, from Table 3, the rate of weight reduction (purity) is about 94% or more. Also, the rate of weight reduction including the data of other samples is 90 to 97% and is preferably 94 to 97%. The residues are components not combusted at 1000° C. and are assumed to be, for example, the catalyst.
In the production apparatus according to the above embodiment, carbon fibers are grown on the substrate and therefore, the catalyst metal is transferred to the carbon fiber to a minimal extent, so that the carbon fibers have very high purity. Also, the production apparatus enables continuous production and can therefore attain mass production, bringing about the possibility of industrial distribution.
Further, the carbon fibers produced in the above embodiment are expected to be dispersed with a smaller graphene shape due to its structure. The carbon fibers may be expected to be used in new applications such as electronic parts utilizing a high level of photoelectron mobility, chemical sensors and hydrogen storage materials utilizing chemical sensitivity and chemical reaction, mechanical sensors utilizing a high level of mechanical strength, laser parts and transparent electrodes utilizing light transmittance and electroconductivity and wiring materials utilizing high-current density resistance.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-033723 | Feb 2011 | JP | national |
