Patent Application
20090214816
The present invention relates to an aligned carbon nanotube bulk structure having portions different in density and a process for producing the same, and to uses thereof. In more detail, the present invention relates to an aligned carbon nanotube bulk structure having portions composed of aligned carbon nanotubes capable of realizing high density, high hardness, high purity, high specific surface area, large scaling and patterning, an aspect of which has not hitherto been achieved, and to a process for producing the same and to use thereof.
Regarding carbon nanotubes (CNT) that are expected for development to functional materials as novel electronic device materials, optical materials, electrically conductive materials, biotechnology related materials and others, energetic investigations of their yield, quality, use, mass productivity and production method are being promoted.
For putting carbon nanotubes into practical use for the above-mentioned functional materials, one method may be taken into consideration, which comprises preparing a bulk aggregate of a large number of carbon nanotubes, large-scaling the size of the bulk aggregate, and improving its properties such as the purity, the specific surface area, the electric conductivity, the density and the hardness to thereby make it patternable in a desired shape. In addition, the mass productivity of carbon nanotubes must be increased greatly.
To solve the above-mentioned problems, the inventors of this application have assiduously studied and, as a result, have found that, in a process of chemical vapor deposition (CVD) where carbon nanotubes are grown in the presence of a metal catalyst, when a very small amount of water vapor is added to the reaction atmosphere, then an aligned carbon nanotube bulk structure having a high purity and having extremely large-scaled as compared with that in conventional methods can be obtained, and have reported it in Non-Patent Document 1, etc.
Non-Patent Document 1: Kenji Hata et al., Water-Assisted Highly Efficient Synthesis of Impurity-Free Single-Walled Carbon Nanotubes, SCIENCE, 2004.11.19, Vol. 306, pp. 1362-1364.
The aligned carbon nanotube bulk aggregate reported in the above-mentioned Non-Patent Document 1 has, for example, a purity before purification of 99.98 mass % and a specific surface area of about 1000 m2/g, and has a height (length) of about 2.5 mm or so, which comprises a large Dumber of single-walled carbon nanotubes growing as aggregated.
However, in order to apply the aligned carbon nanotube bulk structure as a functional material having much better properties, its strength and hardness must be further improved since the density of the structure of the above-mentioned report must is about 0.03 g/cm3 or so and it is mechanically brittle. In addition, there is room for further investigation of the structure in point of the handlability and the workability thereof.
When a patterned aligned carbon nanotube bulk structure is applied to various articles that utilize its electric properties, thermal properties, mechanical properties, gas absorbability, or the like, in some cases, it is preferably used as a bulk structure of which the properties such as the density and the hardness are controlled in sites thereof. In addition, the shape of the aligned carbon nanotube bulk structure is also desired to be readily controllable to a desired shape, while keeping the excellent properties that the carbon nanotubes have. In fact, however, the aligned carbon nanotube bulk structures heretofore proposed could not satisfy the requirements.
With the background described above, therefore, an object of the present application is to provide an aligned carbon nanotube bulk structure of which the properties such as the density and the hardness are controlled in sites thereof, and to provide its production process and its sue.
Another object of the present application is to provide an aligned carbon nanotube bulk structure capable being readily patterned in a desired shape while keeping the excellent properties that the carbon nanotubes have, and to provide its production process and its application.
For the purpose of solving the foregoing problems, this application provides the following inventions.
(1) An aligned carbon nanotube bulk structure having portions different in density, in which plural carbon nanotubes are aligned in a predetermined direction and which has a high-density portion having a density of from 0.2 to 1.5 g/cm3 and a low-density portion having a density of from 0.001 to 0.2 g/cm3.
(2) The aligned carbon nanotube bulk structure having portions different in density according the above (1), which has one or more intermediate density portions falling between the high-density portion and the low-density portion.
(3) The aligned carbon nanotube bulk structure having portions different in density according the above (1), wherein the high-density portion and the low-density portion are disposed regularly.
(4) The aligned carbon nanotube bulk structure having portions different in density according the above (1), wherein the high-density portion and the low-density portion and the intermediate-density portion are disposed regularly.
(5) An aligned carbon nanotube bulk structure having portions different in density, in which plural carbon nanotubes are aligned in a predetermined direction and of which the density continuously or stepwise changes between the highest-density portion having a density of from 0.2 to 1.5 g/cm3 and a lowest-density portion having a density of from 0.001 to 0.2 g/cm3.
(6) The aligned carbon nanotube bulk structure having portions different in density according to any one of the above (1) to (5), wherein the carbon nanotubes are single-walled carbon nanotubes.
(7) The aligned carbon nanotube bulk structure having portions different in density according to any one of the above (1) to (5), wherein the carbon nanotubes are double-walled carbon nanotubes.
(8) The aligned carbon nanotube bulk structure having portions different in density according to any one of the above (1) to (5), wherein the carbon nanotubes are a mixture of single-walled carbon nanotubes and double-walled or more multi-walled carbon nanotubes.
(9) The aligned carbon nanotube bulk structure having portions different in density according to any one of the above (1) to (8), which has a purity of at least 98 mass %.
(10) The aligned carbon nanotube bulk structure having portions different in density according to any one of the above (1) to (9), the high-density portion of which has a specific surface area of from 600 to 2600 m2/g.
(11) The aligned carbon nanotube bulk structure having portions different in density according to any one of the above (1) to (9), the high-density portion of which is unopened and which has a specific surface area of from 600 to 1300 m2/g.
(12) The aligned carbon nanotube bulk structure having portions different in density according to any one of the above (1) to (9), the high-density portion of which is opened and which has a specific surface area of from 1300 to 2600 m2/g.
(13) The aligned carbon nanotube bulk structure having portions different in density according to any one of the above (1) to (12), the high-density portion of which is a mesoporous material having a packing ratio of from 5 to 50%.
(14) The aligned carbon nanotube bulk structure having portions different in density according to any one of the above (1) to (13), the high-density portion of which has a mesopore diameter of from 1.0 go 5.0 nm.
(15) The aligned carbon nanotube bulk structure having portions different in density according to any one of the above (1) to (14), the high-density portion of which has a Vickers hardness of from 5 to 100 RV.
(16) The aligned carbon nanotube bulk structure having portions different in density according to any one of the above (1) to (15), the high-density portion of which is vertically aligned or horizontally aligned on a substrate.
(17) The aligned carbon nanotube bulk structure having portions different in density according to any one of the above (1) to (15), the high-density portion of which is aligned on a substrate in the direction oblique to the substrate surface.
(18) The aligned carbon nanotube bulk structure having portions different in density according to any one of the above (1) to (17), the high-density portion of which has anisotropy between the alignment direction and the direction vertical thereto, in at least any of optical properties, electric properties, mechanical properties and thermal properties.
(19) The aligned carbon nanotube bulk structure having portions different in density according to any one of the above (1) to (18), wherein the degree of anisotropy of the high-density portion between the alignment direction and the direction vertical thereto is at most ⅕ in terms of the ratio of the small value to the large value.
(20) The aligned carbon nanotube bulk structure having portions different in density according to any one of the above (1) to (19), wherein the intensity ratio of any of the (100), (110) and (002) peaks of the high-density portion in the alignment direction and in the direction vertical thereto in X-ray diffraction is from ½ to 1/100 in terms of the ratio of the small value to the large value.
(21) The aligned carbon nanotube bulk structure having portions different in density according to any one of the above (1) to (20), wherein the shape of the high density portion is a thin film.
(22) The aligned carbon nanotube bulk structure having portions different in density according to any one of the above (1) to (20), wherein the shape of the high-density portion is a columnar one having a circular, oval or n-angled cross section (n is an integer of at least 3).
(23) The aligned carbon nanotube bulk structure having portions different in density according to any one of the above (1) to (20), wherein the shape of the high-density portion is a block.
(24) The aligned carbon nanotube bulk structure having portions different in density according to any one of the above (1) to (20), wherein the shape of the high-density portion is a needle-like one.
(25) A process for producing an aligned carbon nanotube bulk structure having portions different in density according to any one of the above (1) to (24) through chemical vapor deposition (CVD) of carbon nanotubes in the presence of a metal catalyst, wherein plural carbon nanotubes are grown, as aligned, then a part of the resulting plural carbon nanotubes are exposed to liquid and thereafter dried, thereby producing an aligned carbon nanotube bulk structure having a high-density portion having a density of from 0.2 to 1.5 g/cm3 and a low-density portion having a density of from 0.001 to 0.2 g/cm3.
(26) The process for producing an aligned carbon nanotube bulk structure having portions different in density according to the above (25), wherein the starting point to be exposed to liquid is changed to thereby produce an aligned carbon nanotube bulk structure having a different shape.
(27) The process for producing an aligned carbon nanotube bulk structure having portions different in density according to the above (25) or (26), wherein in exposing plural carbon nanotubes to liquid and drying them, pressure of a different level is given thereto in different directions.
(28) The process for producing an aligned carbon nanotube bulk structure having portions different in density according to any one of the above (25) to (27), wherein the shape of the aligned carbon nanotube bulk structure is controlled by a shaping mold.
(29) A functional product comprising an aligned carbon nanotube bulk structure having portions different in density, in which plural carbon nanotubes are aligned in a predetermined direction and which has a high-density portion having a density of from 0.2 to 1.5 g/cm3 and a low-density portion having a density of from 0.001 to 0.2 g/cm3.
(30) The functional product according to the above (29), which is a brush for cleaning and in which the high-density portion is formed as an axis, and from its one end, the low-density portion expands like plural hairs.
(31) The functional product according to the above (29), which is a motor brush.
(32) The functional product according to the above (29), which is a motor commutator.
(33) The functional product according to the above (29), which is an electric contact of motor.
(34) The functional product according to the above (29), which constitutes a slide member.
(35) The functional product according to the above (29), which is an optical member.
The aligned carbon nanotube bulk structure of the present invention is an unprecedented high-strength aligned carbon nanotube bulk structure having a high-density portion and a low-density portion. The density of the high-density portion is at least about 20 times that of the aligned carbon nanotube bulk structure that the inventors of this application proposed in Non-Patent Document 1, and is extremely high (at least 0.2 g/cm3). The hardness of the high-density portion is at least about 100 times that of the previous one and is extremely large; and this is not a material having a soft feeling but is a novel material that exhibits a phase of so-called “solid”.
The high-density portion of the aligned carbon nanotube bulk structure of the present invention is a highly purified one and its contamination with catalyst and side product is inhibited. Its specific surface area is from 600 to 2600 m2/g or so, and is on the same level as that of typical porous materials, activated carbon and SBA-15. Though ordinary porous materials are insulators, the aligned carbon nanotube bulk structure of the present invention has high electric conductivity and, when formed into a sheet, it is flexible. When the aligned carbon nanotube bulk aggregate produced in Non-Patent Document 1 is formed into an aligned carbon nanotube bulk structure, then a material having a carbon purity of at least 99.98% could be produced.
The aligned carbon nanotube bulk structure of the present invention has excellent characteristics in purity, density, hardness, specific surface area, and workability, and can be large-scaled. Accordingly, the present invention is expected to be applicable to various uses such as a commutator, brush and contact of a micro-motor, a fine cleaning kit (brush-like member) for removing fine dust generated in the industrial process, and the like.
Further, according to the process for producing an aligned carbon nanotube bulk structure of the present invention, an aligned carbon nanotube bulk structure, which has excellent properties as above and which is expected to be acceptable in various applications, can be produced with good producibility according to a simple method of chemical vapor deposition (CVD).
The present invention has the above-mentioned characteristics, and its embodiments will be described hereinunder.
The aligned carbon nanotube bulk structure of the present invention is one produced by patterning an aligned carbon nanotube bulk aggregate where plural carbon nanotubes are aligned in a predetermined direction, and is characterized by comprising a high-density portion and a low-density portion.
Typical embodiments of the aligned carbon nanotube bulk structure are the following:
<1> It comprises a high-density portion and a low-density portion, in which the lowermost limit of the density of the high-density portion is 0.2 g/cm3, more preferably 0.3 g/cm3, even more preferably 0.4 g/cm3, the uppermost limit thereof is 1.0 g/cm3, more preferably 1.2 g/cm3, even more preferably 1.5 g/Cm3; and the lowermost limit of the density of the low-density portion is 0.001 g/cm3, more preferably 0.005 g/cm3, even more preferably 0.01 g/cm3, the uppermost limit thereof is 0.05 g/cm3, more preferably 0.1 g/cm3, even more preferably 0.2 g/cm3.
<2> In the above <1>, the structure has one or more intermediate-density portions falling between the high-density portion and the low-density portion.
<3> The density continuously changes between the highest-density portion where the lowermost limit of the density is 0.2 g/cm3, more preferably 0.3 g/cm3, even more preferably 0.4 g/Cm3 and the uppermost limit thereof is 1.0 g/cm3, more preferably 1.2 g/cm3, even more preferably 1.5 g/cm3, and the lowest-density portion where the lowermost limit of the density is 0.001 g/cm3, more preferably 0.005 g/cm3, even more preferably 0.01 g/cm3 and the uppermost limit thereof is 0.05 g/cm3, more preferably 0.1 g/cm3, even more preferably 0.2 g/cm3.
<4> The density stepwise changes between the highest-density portion where the lowermost limit of the density is 0.2 g/cm3, more preferably 0.3 g/Cm3, even more preferably 0.4 g/cm3 and the uppermost limit thereof is 1.0 g/Cm3, more preferably 1.2 g/cm3, even more preferably 1.5 g/cm3, and the lowest-density portion where the lowermost limit of the density is 0.001 g/cm3, more preferably 0.005 g/Cm3, even more preferably 0.01 g/cm3 and the uppermost limit thereof is 0.05 g/cm3, more preferably 0.1 g/cm3, even more preferably 0.2 g/cm3.
The aligned carbon nanotube bulk structure of the present invention is expected to be applicable to various fields such as optical field, electric and electronic field, machinery field and energy storage field capable of utilizing the characteristics of the high-density portion of carbon nanotubes and those of the low-density portion thereof.
The density range of the high-density portion of the aligned carbon nanotube bulk structure of the present invention is a range necessary for making the structure have a sufficient mechanical strength; and the high-density portion of the aligned carbon nanotube bulk structure having such a density is not a soft-feeling material but exhibits a phase of so-called “solid”. The density of the high-density portion is extremely larger than the density of heretofore-proposed aligned carbon nanotube bulk structures.
The density range of the low-density portion of the aligned carbon nanotube bulk structure of the present invention is a range that makes it possible to utilize properties different from those of the high-density portion.
The carbon nanotubes that constitute the high-density portion of the aligned carbon nanotube bulk structure of the present invention may be single-walled carbon nanotubes or double-walled carbon nanotubes, or may also be in the form of a mixture of single-walled carbon nanotubes and double-walled or more multi-walled carbon nanotubes in a suitable ratio.
Regarding the production process for the aligned carbon nanotube bulk structure of the present invention, the structure may be produced according to the process of the invention of above-mentioned [25] to [28], and its details are described hereinunder. In case where the aligned carbon nanotube bulk structure obtained according to the process is used in an application in which the purity thereof is taken into consideration, its purity can be preferably at least 98 mass %, more preferably at least 99 mass %, even more preferably at least 99.9 mass %. When the production process that the inventors of this application proposed in Non-Patent Document 1 is utilized, then an aligned carbon nanotube bulk structure having a high purity as above can be obtained even though it is not processed for purification. The aligned carbon nanotube bulk structure having such a high purity contains few impurities, and therefore it may exhibit the properties intrinsic to carbon nanotubes.
The purity as referred to in this description is represented by mass % of carbon nanotubes in a product. The impurity may be obtained from the data of elementary analysis with fluorescent X rays.
A preferred range of the height (length: dimension of carbon nanotubes in the lengthwise direction) of the aligned carbon nanotube bulk structure of the present invention varies, depending on the application thereof. In case where it is used as a large-scaled one, the lowermost limit of the range is preferably 5 μm, more preferably 10 μm, even more preferably 20 μm; and the uppermost limit thereof is preferably 2.5 mm, more preferably 1 cm, even more preferably 10 cm.
The high-density portion of the aligned carbon nanotube bulk structure of the present invention has an extremely large specific surface area, and its preferred value varies depending on the use of the structure. For applications that require a large specific surface area, the specific surface area is preferably from 600 to 2600 m2/g, more preferably from 800 to 2600 m2/g, even more preferably from 1000 to 2600 m2/g. The high-density portion of the carbon nanotube bulk structure of the present invention that is unopened preferably has a specific surface area of from 600 to 1300 m2/g, more preferably from 800 to 1300 m2/g, even more preferably from 1000 to 1300 m2/g. The high-density portion of the aligned carbon nanotube bulk structure of the present invention that is opened preferably has a specific surface area of from 1300 to 2600 m2/g, more preferably from 1500 to 2600 m2/g, even more preferably from 1700 to 2600 m2/g.
The specific surface area may be determined through computation of adsorption/desorption isothermal curves. One example is described with reference to 50 mg of a high-density portion of an aligned carbon nanotube bulk structure of the present invention. Using Nippon Bell's BELSORP-MINI, liquid nitrogen adsorption/desorption isothermal curves were drawn at 77 K (see
When the high-density portion of the aligned carbon nanotube bulk structure of the present invention is processed for opening, then the top end of the carbon nanotube is opened to thereby increase the specific surface area thereof. In
For the opening treatment, employable is a dry process of treatment with oxygen, carbon dioxide or water vapor. In case where a wet process is employable for it, it may comprise treatment with an acid, concretely refluxing treatment with hydrogen peroxide or cutting treatment with high-temperature hydrochloric acid.
The aligned carbon nanotube bulk structure having such a large specific surface area exhibits great advantages in various applications. When the specific surface area is too small and when the structure having such a small specific surface area is used in the above-mentioned applications, then the devices could not have desired properties. The uppermost limit of the specific surface area is preferably as high as possible, but is theoretically limited.
The high-density portion of the aligned carbon nanotube bulk structure of the present invention may be in the form of a mesoporous material having a packing ratio of from 5 to 50%, more preferably from 10 to 40%, even more preferably from 10 to 30%. In this case, the material preferably contains those having a mesopore diameter of from 1.0 to 5.0 nm. The mesopores in this case are defined by the size thereof in the aligned carbon nanotube bulk structure. When the carbon nanotubes in the aligned carbon nanotube bulk structure are opened through oxidation treatment or the like, and when liquid nitrogen adsorption/desorption isothermal curves of the structure are prepared and SF plots are obtained from the adsorption curves, then the mesopores corresponding to the size of the carbon nanotubes may be computed. On the contrary, from the above-mentioned experimental facts, it is known that the opened high-density portion of the aligned carbon nanotube bulk structure can function as a mesopore material. The packing ratio in the mesopores may be defined by the coating ratio of the carbon nanotubes. When the packing ratio or the mesopore size distribution falls within the above range, then the aligned carbon nanotube bulk structure is favorably used in applications of a mesoporous material and may have a desired strength.
An ordinary mesoporous material is an insulator, but the high-density portion of the aligned carbon nanotube bulk structure of the present invention has high electric conductivity and, when formed into a sheet, it is flexible.
The Vickers hardness of the high-density portion of the aligned carbon nanotube bulk structure of the present invention is preferably from 5 to 100 HV. The Vickers hardness falling within the range is a sufficient mechanical strength comparable to that of typical mesoporous materials, active carbon and SBA-15, and exhibits great advantages in various applications that require mechanical strength.
The aligned carbon nanotube bulk structure of the present invention may be provided on a substrate, or may not be thereon. In case where it is provided on a substrate, it may be aligned vertically to the surface of the substrate, or horizontally or obliquely thereto.
Further, the aligned carbon nanotube bulk structure of the present invention preferably shows anisotropy between the alignment direction and the direction vertical thereto, in at least any of optical properties, electric properties, mechanical properties and thermal properties. The degree of anisotropy of the aligned carbon nanotube bulk structure between the alignment direction and the direction vertical thereto is preferably at most ⅓, more preferably at most ⅕, even more preferably at most 1/10. The lowermost limit may be about 1/100 Also preferably, the intensity ratio of the (100), (110) and (002) peaks in the alignment direction and in the direction vertical thereto in X-ray diffraction is from ½ to 1/100 in terms of the ratio of the small value to the large value.
The quality of the carbon nanotubes (filaments) in the high-density portion of the aligned carbon nanotube bulk structure can be evaluated through Raman spectrometry. One example of Raman spectrometry is shown in
Further, the aligned carbon nanotube bulk structure of the present invention may be patterned in a predetermined shape. The shape includes, for example, thin films, as well as any desired blocks such as columns having a circular, oval or n-angled cross section (n is an integer of at least 3), or cubic or rectangular solids, and needle-like solids (including sharp, thin and long cones). The patterning method is described hereinunder.
Next described is a process for producing the aligned carbon nanotube bulk structure of the present invention.
The process for producing the aligned carbon nanotube bulk structure of the present invention is a process for producing an aligned carbon nanotube bulk structure having portions different in density through chemical vapor deposition (CVD) of carbon nanotubes in the presence of a metal catalyst, wherein plural carbon nanotubes are grown, as aligned, then a part of the resulting plural carbon nanotubes are exposed to liquid and thereafter dried, thereby producing an aligned carbon nanotube bulk structure having a high-density portion having a density of from 0.2 to 1.5 g/cm3 and a low-density portion having a density of from 0.001 to 0.2 g/cm3.
First described is the method of aligned growth of plural carbon nanotubes through CVD.
As the carbon compound for the starting carbon source in CVD, usable are hydrocarbons like before, and preferred are lower hydrocarbons such as methane, ethane, propane, ethylene, propylene, acetylene. One or more of these may be used, and use of lower alcohols such as methanol or ethanol, acetone, and low-carbon oxygen-containing compounds such as carbon monoxide may also be taken into consideration within an acceptable range for the reaction condition.
The atmospheric gas for reaction may be any one that does not react with carbon nanotubes and is inert at the growing temperature. Its examples include helium, argon, hydrogen, nitrogen, neon, krypton, carbon dioxide, chloride, and their mixed gases; and especially preferred are helium, argon, hydrogen and their mixed gases.
The atmospheric pressure in reaction may be any one falling within a pressure range within which carbon nanotubes can be produced, and is preferably from 102 Pa to 107 Pa (100 atmospheres), more preferably from 104 Pa to 3×105 Pa (3 atmospheres), even more preferably from 5×10 Pa to 9×10 Pa.
As so mentioned in the above, a metal catalyst is made to exist in the reaction system, and the catalyst may be any suitable one heretofore used in production of carbon nanotubes. For example, it includes thin film of iron chloride, thin film of iron formed by sputtering, thin film of iron-molybdenum, thin film of alumina-iron, thin film of alumina-cobalt, thin film of alumna-iron-molybdenum, etc.
The amount of the catalyst may fall within any range heretofore employed in production of carbon nanotubes. For example, when an iron metal catalyst is used, then its thickness is preferably from 0.1 nm to 100 nm, more preferably from 0.5 nm to 5 nm, even more preferably from 1 nm to 2 nm.
Regarding the catalyst positioning, employable is any method of positioning the metal catalyst having a thickness as above, suitable for sputtering deposition.
The temperature in the growth reaction in CVD may be suitably determined in consideration of the reaction pressure, the metal catalyst, the carbon source material, etc.
According to the process of the present invention, a catalyst may be disposed on a substrate, and plural carbon nanotubes may be grown, as aligned vertically to the substrate surface. In this case, any substrate heretofore used in production of carbon nanotubes is employable, for example, including the following:
(1) Metals and semiconductors such as iron, nickel, chromium, molybdenum, tungsten, titanium, aluminium, manganese, cobalt, copper, silver, gold, platinum, niobium, tantalum, lead, zinc, gallium, germanium, indium, gallium, germanium, arsenic, indium, phosphorus, antimony; their alloys; and oxides of those metals and alloys.
(2) Thin films, sheets, plates, powders and porous materials of the above-mentioned metals, alloys and oxides.
(3) Non-metals and ceramics such as silicon, quartz, glass, mica, graphite, diamond; their wafers and thin films.
For the method of patterning the catalyst, employable is any suitable method capable of directly or indirectly patterning the catalyst metal. It may be a wet process or a dry process; and for example, herein employable are patterning with mask, patterning by nano-imprinting, patterning through soft lithography, patterning by printing, patterning by plating, patterning by screen printing, patterning through lithography, as well as a method of patterning some other material capable of selectively adsorbing a catalyst on a substrate and then making the other material selectively adsorb a catalyst thereby forming a pattern. Preferred methods are patterning through lithography, metal deposition photolithography with mask, electron beam lithography, catalyst metal patterning through electron beam deposition with mask, and catalyst metal patterning through sputtering with mask.
According to the process of the present invention, an oxidizing agent such as water vapor may be added to the reaction atmosphere described in Non-Patent Document 1 thereby growing a large quantity of aligned single-walled carbon nanotubes. Needless-to-say, the invention should not be limited to the process, in which, therefore, any other various processes may be employed.
In the manner as above, an aligned carbon nanotube bulk aggregate before exposed to liquid and dried may be obtained.
The method of peeling the aligned carbon nanotube bulk structure from the substrate may be a method of peeling it from the substrate physically, chemically or mechanically. For example, herein employable are a method of peeling it by the action of an electric field, a magnetic field, a centrifugal force or a surface tension; a method of mechanically peeling it directly from the substrate; and a method of peeling it from the substrate under pressure or heat. One simple peeling method comprises picking it up directly from the substrate with tweezers and peeling it. More preferably, it may be cut off from the substrate by the use of a thin cutting tool such as cutter blade. Further, it may be peeled by suction from the substrate, using a vacuum pump or a vacuum cleaner. After peeled, the catalyst may remain on the substrate, and it may be again used in the next step of growing carbon nanotubes. Needless-to-say, the aligned carbon nanotube bulk structure formed on the substrate may be directly processed as it is in the next step.
According to the process of the present application, a part of the plural aligned carbon nanotubes produced in the manner as above are exposed to liquid and then dried to give the intended aligned carbon nanotube bulk structure. The shape of the obtained structure may be controlled to various characteristic shapes, depending on the shape of the aligned carbon nanotube bulk aggregate before exposure to liquid, the starting point for exposure to liquid, the amount of the liquid for exposure thereto and the use of a shaping mold.
The liquid to which plural aligned carbon nanotubes are exposed is preferably one that has an affinity to carbon nanotubes and does not remain in the carbon nanotubes wetted with it and then dried. The liquid of the type usable herein includes, for example, water, alcohols (isopropanol, ethanol, methanol), acetones (acetone), hexane, toluene, cyclohexane, DMF (dimethylformamide), etc.
For exposing plural aligned carbon nanotubes to the above-mentioned liquid, for example, employable are a method comprising dropwise applying the liquid droplets little by little onto the upper surface of the aligned carbon nanotube structure and repeating the operation until the aligned carbon nanotube structure is finally completely enveloped by the liquid droplets; a method comprising wetting the surface of the substrate with the liquid by the use of pipette, then infiltrating the liquid into the aligned carbon nanotube structure from the point at which the structure is kept in contact with the substrate, thereby wetting entirely the aligned carbon nanotube structure; a method comprising vaporizing the liquid and exposed the entire aligned carbon nanotube structure with the vapor in a predetermined direction; a method comprising spraying the liquid onto the aligned carbon nanotube structure so as to wet it with the liquid. For drying the aligned carbon nanotube structure after wetted with the liquid, for example, employable is a method of spontaneous drying at room temperature, vacuum drying, or heating on a hot plate or the like.
When plural aligned carbon nanotubes are exposed to the liquid, their structure may shrink a little and may much shrink when dried, thereby giving an aligned carbon nanotube bulk structure having a high density. In this case, the shrinkage is anisotropic, and one example is shown in
Raman data of the high-density portion of the aligned carbon nanotube bulk structure produced by exposing a part of plural aligned carbon nanotubes to water followed by drying are shown in
Some examples of producing the aligned carbon nanotube bulk structure having a high-density portion and a low-density portion are described below.
As shown in
(a) A catalyst is circularly patterned, then carbon nanotubes are grown, and a pillar-structured aligned carbon nanotube bulk aggregate is produced on a substrate. In this case, it is produced in such a manner that the adhesiveness between the aligned carbon nanotube bulk aggregate and the substrate could be low. The surface of the substrate on which the aligned carbon nanotube bulk aggregate is grown is wetted with a minor amount of liquid so that the aligned carbon nanotube aggregate could be immersed with the liquid from the point at which it is kept in contact with the substrate, whereby the lower part is shrunk and densified to have a high density. In this case, the amount of the liquid to be given is controlled, and the upper part is kept to have a low density after grown. Since the interaction between the substrate and the aligned carbon nanotube bulk aggregate is weak, the aligned carbon nanotube bulk aggregate peels off from the substrate during shrinking, thereby forming a balloon-shaped aligned carbon nanotube bulk aggregate structure.
(b) A catalyst is circularly patterned, then carbon nanotubes are grown, and a pillar-structured aligned carbon nanotube bulk aggregate is produced on a substrate. In this case, it is produced in such a manner that the adhesiveness between the aligned carbon nanotube bulk aggregate and the substrate could be high. The surface of the substrate on which the aligned carbon nanotube bulk aggregate is grown is wetted with a minor amount of liquid so that the aligned carbon nanotube aggregate could be immersed with the liquid from the point at which it is kept in contact with the substrate, whereby the lower part is shrunk and densified to have a high density. In this case, the amount of the liquid to be given is controlled, and the upper part is kept to have a low density after grown. Since the interaction between the substrate and the aligned carbon nanotube bulk aggregate is strong, the aligned carbon nanotube bulk aggregate is still held on the substrate during shrinking, thereby forming a mortar-shaped aligned carbon nanotube bulk aggregate structure.
(c) The same operation as in (b) is repeated for an angular aligned carbon nanotube bulk aggregate.
(d) The aligned carbon nanotube aggregate is peeled from the substrate, using tweezers, and then cleaved by hand and using tweezers, in such a manner that the alignment direction could be in the lengthwise direction, thereby working it to have a shape of rod; and then the lower part of the rod is picked up with tweezers, the picked part is exposed to an extremely minor amount of water so that only the water-exposed part could be shrunk and densified to have a high density, and thereafter this is put on a hot plate kept at 170° C. and dried thereon.
Application examples of the aligned carbon nanotube bulk structure of the present invention are shown below, to which, needless-to-say, the invention should not be limited.
<1> CNT brush
<2> Contact of commutator
<3> Axis of commutator
The high-density portion of the aligned carbon nanotube bulk structure of the present invention has an extremely large density and a high hardness as compared with conventional aligned carbon nanotube bulk aggregates or structures. Further, in the aligned carbon nanotube bulk structure having the high-density portion and the low-density portion, the high-density portion and the low-density portion have various properties and characteristics such as ultra high purity, ultra heat conductivity, high specific surface area, excellent electronic and electric properties, optical properties, ultra mechanical strength, ultra high density, etc., respectively; and therefore, they can be applied to various technical fields as mentioned below.
Examples are shown below, and described in more detail. Needless-to-say, the present invention should not be limited to the following Examples.
An aligned carbon nanotube aggregate was grown through CVD under the condition mentioned below.
Carbon compound: ethylene, feeding speed 100 sccm
Atmosphere (gas) (Pa): helium/hydrogen mixed gas, feeding speed 1000 sccm, one atmospheric pressure
Water vapor amount added (ppm): 150 ppm
Reaction temperature (° C.): 750° C.
Reaction time (min): 10 min
Metal catalyst (existing amount): thin iron film, thickness 1 nm
Substrate: silicon wafer
A sputtering vapor deposition device was used for disposing the catalyst on the substrate; and an iron metal having a thickness of 1 nm was disposed through vapor deposition.
Next, the aligned carbon nanotube aggregate produced in the above was peeled from the substrate, using tweezers, and then cleaved by hand and using tweezers, in such a manner that the alignment direction could be in the lengthwise direction, thereby working it to have a shape of rod; and then the lower part of the rod was picked up with tweezers. The part picked up with tweezers was exposed to an extremely minor amount of water so that only the water-exposed part could be shrunk and densified to have a high density, and thereafter this was put on a hot plate kept at 170° C. and dried thereon. Accordingly, a CNT brush comprising the aligned carbon nanotube bulk structure of the present invention was produced, as in
The characteristics of the high-density portion (handle) and the low-density portion (brush top) of the thus-obtained aligned carbon nanotube bulk structure (CNT brush) are shown in Table 1, as compared with each other.
The purity of the aligned carbon nanotube bulk aggregate of Example 1 was 99.98%.
Next, the friction property of the CNT brush of Example 1 and that of a silicon nitride ball were investigated, as in the image of
In Example 1, the aligned carbon nanotube bulk aggregate as-grown was cut into strips with the alignment direction being the lengthwise direction thereof, and the center part of the strip was exposed to water and then dried to form a commutator having the shape shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-001905 | Jan 2006 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2007/050049 | 1/5/2007 | WO | 00 | 10/8/2008 |
