JP2006240932A - Carbon nanotube - Google Patents
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本発明は、広くはナノサイズの炭素繊維であるカーボンナノチューブに関し、特に分散性に優れたカーボンナノチューブに関するものである。 The present invention relates generally to carbon nanotubes, which are nano-sized carbon fibers, and more particularly to carbon nanotubes with excellent dispersibility.
カーボンナノチューブは、炭素原子の六員環ネット（グラフェン）が円筒状に閉じた直径がナノメートルスケールのチューブである。チューブの壁を構成するグラフェン筒の枚数により、単層と多層の２種類がある。グラフェンの筒が一重のものが単層カーボンナノチューブ（ＳＷＣＮＴ）で、その直径は約１〜数ｎｍである。また、グラフェンの筒が同心状に何重も重なっているものが多層カーボンナノチューブ（ＭＷＣＮＴ）で、その直径は数ｎｍ〜数十ｎｍである。いずれのカーボンナノチューブもアーク放電法、レーザ蒸着法あるいは炭素含有ガスの化学気相成長法（ＣＶＤ法）にて合成することが可能であるが、多層カーボンナノチューブの場合には必ずしも触媒を必要とせず、炭素の蒸発（または分解）・凝縮によって得られるのに対し、単層カーボンナノチューブの場合は金属などの触媒微粒子が必要不可欠である。
以下、代表的な各々の合成方法についてその詳細を説明する。
A carbon nanotube is a tube with a diameter of nanometer scale in which a six-membered net of carbon atoms (graphene) is closed in a cylindrical shape. There are two types, single layer and multilayer, depending on the number of graphene cylinders that make up the wall of the tube. A single-layer graphene tube is a single-walled carbon nanotube (SWCNT), and its diameter is about 1 to several nm. In addition, multi-walled carbon nanotubes (MWCNTs) in which graphene tubes are concentrically overlapped with each other have a diameter of several nanometers to several tens of nanometers. Any of the carbon nanotubes can be synthesized by an arc discharge method, a laser vapor deposition method, or a chemical vapor deposition method (CVD method) of a carbon-containing gas. However, in the case of multi-walled carbon nanotubes, a catalyst is not necessarily required. In the case of single-walled carbon nanotubes, fine particles of catalyst such as metal are indispensable, whereas they are obtained by evaporation (or decomposition) / condensation of carbon.
Details of each typical synthesis method will be described below.
［アーク放電法］
２つの炭素材料の間にてアーク放電を行い、アークの熱で炭素を蒸発させることによりカーボンナノチューブを合成する方法で、一般的には密閉容器（チャンバー）を用い、ヘリウムガスや水素ガスを用いた減圧雰囲気内で放電を行う方法である。直流放電を行った場合、陰極の炭素電極に堆積するカーボン凝縮物（陰極堆積物）の中に多層カーボンナノチューブが合成される。単層カーボンナノチューブを合成する場合は、陽極の炭素材料に単層カーボンナノチューブの成長を促す金属などの触媒を含んだ電極を用いる。単層カーボンナノチューブは気相で生成した煤の中に含まれるため、放電後、電極やチャンバー内面に付着した煤を回収することによって得ることができる。触媒の有無や種類、反応条件などを変えることによって、カーボンナノチューブだけでなく、カーボンナノホーンなど、 種々のナノカーボン材料を合成することもできる。
[Arc discharge method]
A method of synthesizing carbon nanotubes by performing arc discharge between two carbon materials and evaporating carbon with the heat of the arc. Generally, a closed vessel (chamber) is used and helium gas or hydrogen gas is used. This is a method of discharging in a reduced pressure atmosphere. When direct current discharge is performed, multi-walled carbon nanotubes are synthesized in a carbon condensate (cathode deposit) deposited on the carbon electrode of the cathode. When synthesizing single-walled carbon nanotubes, an electrode containing a catalyst such as a metal that promotes the growth of single-walled carbon nanotubes as the carbon material for the anode is used. Since the single-walled carbon nanotube is contained in the soot generated in the gas phase, it can be obtained by collecting the soot attached to the electrode or the inner surface of the chamber after the discharge. Not only carbon nanotubes but also various nanocarbon materials such as carbon nanohorns can be synthesized by changing the presence / absence and type of catalyst and reaction conditions.
［レーザ蒸着法］
１２００℃程度に加熱した電気炉の中に挿入した石英管の内部に炭素材料のターゲットを置き、石英管にアルゴンガスを流しながら、ガスの流れの上流側から炭素材料にレーザを照射して炭素を蒸発させ、合成する方法である。電気炉の出口付近の冷えた石英管の内壁や水冷鍋のトラップにカーボンナノチューブを含む煤が付着する。アーク放電法と同様に、触媒の有無や種類、反応条件などを変えることによって、単層および多層のカーボンナノチューブを作り分けることができ、また、カーボンナノホーンなど、種々のナノカーボン材料を合成することもできる。
[Laser deposition method]
A carbon material target is placed inside a quartz tube inserted in an electric furnace heated to about 1200 ° C., and argon gas is allowed to flow through the quartz tube while irradiating the carbon material with a laser from the upstream side of the gas flow. Is a method of evaporating and synthesizing. A soot containing carbon nanotubes adheres to the inner wall of the cooled quartz tube near the outlet of the electric furnace and the trap of the water-cooled pan. Similar to the arc discharge method, single-walled and multi-walled carbon nanotubes can be created by changing the presence / absence, type, and reaction conditions of the catalyst, and various nanocarbon materials such as carbon nanohorns can be synthesized. You can also.
［ＣＶＤ法］
数１００℃〜１２００℃程度に加熱した電気炉に炭化水素ガスをアルゴンガスや水素ガスなどのキャリアーガスとともに供給して合成する方法である。多層カーボンナノチューブの場合は、炉内に設置した基板上に堆積して成長する。単層カーボンナノチューブの場合は、炭化水素ガスとともに触媒材料を供給して合成する。
この方法は、カーボンナノチューブ合成のための材料を大気圧側より簡単に供給できるため、連続運転が可能で生産性が高いが、欠陥の多いカーボンナノチューブができやすく、結晶性を上げるためには合成後に数千度の高温熱処理を行い精製することが必要となる場合がある。
[CVD method]
In this method, a hydrocarbon gas is supplied together with a carrier gas such as argon gas or hydrogen gas to an electric furnace heated to about several hundreds of degrees Celsius to 1200 ° C. for synthesis. In the case of multi-walled carbon nanotubes, they are deposited and grown on a substrate placed in a furnace. In the case of single-walled carbon nanotubes, synthesis is performed by supplying a catalyst material together with a hydrocarbon gas.
This method allows easy supply of materials for carbon nanotube synthesis from the atmospheric pressure side, so continuous operation is possible and high productivity, but carbon nanotubes with many defects are easily formed, and synthesis is required to increase crystallinity. In some cases, it may be necessary to purify by heat treatment at several thousand degrees later.
カーボンナノチューブを構成する主成分は炭素であることは言うまでもないが、炭素以外に種々の元素を含むカーボンナノチューブについて幾つか検討されている。末端あるいは欠陥部位に炭素原子がリンまたはホウ素の化学修飾基と結合する方法が提案されている（例えば、特許文献１参照）。 It goes without saying that the main component constituting the carbon nanotube is carbon, but some carbon nanotubes containing various elements other than carbon have been studied. There has been proposed a method in which a carbon atom is bonded to a chemical modification group of phosphorus or boron at a terminal or a defect site (see, for example, Patent Document 1).
また、黒鉛およびピッチ等の炭素材料については、結晶性を高めるためにホウ素を添加して熱処理する方法も検討されている（例えば、特許文献２〜特許文献４参照）。
For carbon materials such as graphite and pitch, a method of adding boron and heat-treating in order to enhance crystallinity has been studied (for example, see
さらに、直径が５μｍ以下の微細な炭素繊維に対しては、ホウ素を添加して特性を改善する方法も提案されている（例えば、特許文献５参照）。 Furthermore, for fine carbon fibers having a diameter of 5 μm or less, a method for improving the properties by adding boron has also been proposed (see, for example, Patent Document 5).
また、多層カーボンナノチューブを酸素などの気相酸化剤を用いて表面酸化することにより、無機および有機系の溶媒中で容易に分散する機能があることも提案されている（例えば、特許文献６参照）。 It has also been proposed that multi-walled carbon nanotubes have a function of being easily dispersed in inorganic and organic solvents by surface oxidation using a gas phase oxidant such as oxygen (see, for example, Patent Document 6). ).
このように、炭素以外に種々の元素を含むカーボンナノチューブについては既に知られている。しかながら、炭素、ホウ素、および酸素を主成分とするカーボンナノチューブに関しては、合成された報告はない。 Thus, carbon nanotubes containing various elements other than carbon are already known. However, there has been no report on carbon nanotubes mainly composed of carbon, boron, and oxygen.
上記のように従来の技術では、ホウ素を添加することにより結晶性の良好なカーボンナノチューブを合成することは可能であったが、分散性が悪く、溶媒中に分散させた際に短時間で凝集もしくは沈降するという問題があった。さらに、表面酸化されたカーボンナノチューブは無機および有機系の溶媒中で容易に分散するものの、その状態を長時間維持することができず再凝集もしくは沈降するという問題があった。
本発明は、無機および有機系の溶媒中において均一に分散し、しかもその状態を長時間保持することが可能であり、かつ結晶性が高いカーボンナノチューブを提供することを目的としている。
As described above, with the conventional technology, it was possible to synthesize carbon nanotubes with good crystallinity by adding boron, but the dispersibility was poor, and aggregation occurred in a short time when dispersed in a solvent. Or there was a problem of sedimentation. Furthermore, although the surface-oxidized carbon nanotubes are easily dispersed in inorganic and organic solvents, there is a problem that the state cannot be maintained for a long time and reaggregation or sedimentation occurs.
An object of the present invention is to provide a carbon nanotube that is uniformly dispersed in inorganic and organic solvents and that can maintain the state for a long time and that has high crystallinity.
本発明者らは、上記の課題を解決すべく鋭意研究を行った結果、カーボンナノチューブにホウ素と酸素を含有させることによって、無機および有機系の溶媒中において均一に分散し、しかもその状態を長時間保持することが可能であり、かつ結晶性が高いカーボンナノチューブが得られることを見出し、この知見に基いて本発明を完成するに至った。 As a result of intensive studies to solve the above-mentioned problems, the present inventors have made boron and oxygen contained in carbon nanotubes so that they can be uniformly dispersed in inorganic and organic solvents, and the state has been prolonged. The inventors have found that carbon nanotubes that can be held for a long time and have high crystallinity are obtained, and the present invention has been completed based on this finding.
すなわち、本発明は以下のようなカーボンナノチューブを提供するものである。
炭素、ホウ素および酸素を主成分とするカーボンナノチューブであって炭素の含有量が８０〜９９．９８重量％、ホウ素の含有量が０．０１〜１０重量％および酸素の含有量が０．０１〜１０重量％であることを特徴とするカーボンナノチューブ
That is, the present invention provides the following carbon nanotubes.
A carbon nanotube mainly composed of carbon, boron and oxygen, having a carbon content of 80 to 99.98% by weight, a boron content of 0.01 to 10% by weight, and an oxygen content of 0.01 to Carbon nanotube characterized by being 10% by weight
本発明によれば、炭素、ホウ素および酸素を主成分とするカーボンナノチューブは、無機および有機系の溶媒中において均一に分散し、しかもその状態を長時間保持することが可能であるという効果が得られる。 According to the present invention, carbon nanotubes mainly composed of carbon, boron and oxygen are uniformly dispersed in inorganic and organic solvents, and it is possible to maintain the state for a long time. It is done.
本発明におけるカーボンナノチューブは、単層カーボンナノチューブ、多層カーボンナノチューブのいずれであってもよい。各成分の含有量は、炭素が８０〜９９．９８重量％、ホウ素が０．０１〜１０重量％、および酸素が０．０１〜１０重量％であるが、好ましくは、ホウ素が０．１〜７重量％、より好ましくは０．５〜５重量％、そして酸素が０．１〜７重量％、より好ましくは０．５〜５重量％、従って、炭素が８６〜９９．８重量％、より好ましくは９０〜９９重量％のものである。 The carbon nanotube in the present invention may be either a single-walled carbon nanotube or a multi-walled carbon nanotube. The content of each component is 80 to 99.98% by weight of carbon, 0.01 to 10% by weight of boron, and 0.01 to 10% by weight of oxygen. 7% by weight, more preferably 0.5-5% by weight, and oxygen 0.1-7% by weight, more preferably 0.5-5% by weight, therefore carbon 86-99.8% by weight, more Preferably, it is 90 to 99% by weight.
このような本発明のカーボンナノチューブは、アーク放電法、レーザ蒸着法、化学気相成長法（ＣＶＤ法）のいずれの方法により合成された単層カーボンナノチューブもしくは多層カーボンナノチューブを出発原料として、ホウ素化処理と酸化処理とを組み合わせることにより合成することができる。
しかしながら、ＣＶＤ法により合成されたカーボンナノチューブには不純物として触媒金属を含有している場合が多く、塩酸、硫酸等の酸性溶液を用いて酸溶解処理を行うことにより触媒金属を予め除去しておくことが好ましい。
以下、カーボンナノチューブを出発原料として、ホウ素化処理または酸化処理を行う方法について説明する。
Such carbon nanotubes of the present invention are boronated using single-wall carbon nanotubes or multi-wall carbon nanotubes synthesized by any of the arc discharge method, laser vapor deposition method, and chemical vapor deposition method (CVD method) as a starting material. It can synthesize | combine by combining a process and an oxidation process.
However, carbon nanotubes synthesized by the CVD method often contain a catalytic metal as an impurity, and the catalytic metal is previously removed by performing an acid dissolution treatment using an acidic solution such as hydrochloric acid or sulfuric acid. It is preferable.
Hereinafter, a method for performing a boronation treatment or an oxidation treatment using a carbon nanotube as a starting material will be described.
［ホウ素化処理］
ホウ素化処理は、カーボンナノチューブにホウ素化号物を混合し、不活性ガス雰囲気中で高温に加熱することにより行うことができる。
ホウ素化合物として、酸化ホウ素（Ｂ2Ｏ3）のほか、例えば、ホウ酸（Ｈ3ＢＯ3）またはメラニンボレート等の有機ホウ酸化合物を用いることができる。ホウ素化号物の量は、カーボンナノチューブに対するホウ素の重量比で０．０１〜７０倍程度、好ましくは０．１〜１０倍程度が適当である。ホウ素の比率を高くすると得られたカーボンナノチューブのホウ素の含有量が多くなる。
[Boronization treatment]
Boronation treatment can be performed by mixing a boronated compound with carbon nanotubes and heating to high temperature in an inert gas atmosphere.
In addition to boron oxide (B 2 O 3 ), for example, an organic boric acid compound such as boric acid (H 3 BO 3 ) or melanin borate can be used as the boron compound. The amount of the boronated compound is about 0.01 to 70 times, preferably about 0.1 to 10 times, as the weight ratio of boron to carbon nanotubes. Increasing the boron ratio increases the boron content of the carbon nanotubes obtained.
不活性ガス雰囲気に使用されるガスは、窒素、ヘリウム、アルゴン等である。
加熱温度は、酸化ホウ素の場合１５００℃以上、好ましくは１８００℃以上、ホウ酸の場合は１０００℃以上がよい。加熱温度の上限は２５００℃程度である。加熱時間は、加熱温度にもよるが１〜１０時間程度である。一般に、加熱温度を高くしあるいは加熱時間を長くすると得られるカーボンナノチューブのホウ素の含有量が多くなる。
The gas used for the inert gas atmosphere is nitrogen, helium, argon or the like.
The heating temperature is 1500 ° C. or higher for boron oxide, preferably 1800 ° C. or higher, and 1000 ° C. or higher for boric acid. The upper limit of the heating temperature is about 2500 ° C. The heating time is about 1 to 10 hours depending on the heating temperature. Generally, when the heating temperature is increased or the heating time is lengthened, the boron content of the carbon nanotube obtained increases.
加熱中に、ホウ素化合物は気化または表面拡散によりカーボンナノチューブに到達し、化学反応を起こし、カーボンナノチューブ中にホウ素が一部固溶してホウ素を含有したカーボンナノチューブを生成する。ホウ素の含有量の調節は、ホウ素化合物の量、加熱温度と加熱時間を操作することによって行うことができる。このホウ素化処理には、公知の方法を適用できる。 During heating, the boron compound reaches the carbon nanotubes by vaporization or surface diffusion and causes a chemical reaction, and boron partially dissolves in the carbon nanotubes to generate carbon nanotubes containing boron. The boron content can be adjusted by manipulating the amount of the boron compound, the heating temperature and the heating time. A known method can be applied to the boron treatment.
［酸化処理］
酸化処理は、硫酸、硝酸、硫酸と硝酸の混合液、クロロ硫酸、もしくは過マンガン酸カリウム水溶液中に多層もしくは単層カーボンナノチューブを加えて加熱することによって行うことができる。
[Oxidation treatment]
The oxidation treatment can be performed by adding multi-walled or single-walled carbon nanotubes to sulfuric acid, nitric acid, a mixed solution of sulfuric acid and nitric acid, chlorosulfuric acid, or an aqueous potassium permanganate solution and heating.
加熱は、大気雰囲気中で、１２０〜１８０℃程度で１〜１０時間程度煮沸還流することによって行うことができ、加熱温度を高くしあるいは加熱時間を長くすると、得られるカーボンナノチューブの酸素の含有量が多くなる。 Heating can be performed by boiling and refluxing at about 120 to 180 ° C. for about 1 to 10 hours in an air atmosphere. When the heating temperature is increased or the heating time is lengthened, the oxygen content of the carbon nanotubes obtained Will increase.
酸素の含有量の調節は、加熱温度と加熱時間を操作することによって行うことができる。この酸化処理も公知の方法を適用できる。 The oxygen content can be adjusted by manipulating the heating temperature and the heating time. A known method can be applied to this oxidation treatment.
酸化処理後は、ろ過等により液からカーボンナノチューブを分離し、純水等で洗浄して付着物等を除去すればよい。
上記のホウ素化処理あるいは酸化処理において導入されたホウ素または酸素の含有量は、Ｘ線光電子分光（ＸＰＳ）法を用いて測定することができる。
After the oxidation treatment, the carbon nanotubes may be separated from the liquid by filtration or the like and washed with pure water or the like to remove deposits and the like.
The boron or oxygen content introduced in the above boronation treatment or oxidation treatment can be measured using an X-ray photoelectron spectroscopy (XPS) method.
以下、実施例を示して、本発明におけるカーボンナノチューブに関してさらに詳しく説明する。 Hereinafter, the carbon nanotube in the present invention will be described in more detail with reference to examples.
実施例１
アーク放電法により合成した多層カーボンナノチューブを出発原料として用いた。図１に、出発原料の多層カーボンナノチューブの走査型電子顕微鏡（ＳＥＭ）写真を示す。まず、酸化ホウ素（Ｂ2Ｏ3）４．０ｇと多層カーボンナノチューブ１５０ｍｇとを混合して、アルゴン雰囲気中にて約２０００℃で１時間加熱して、ホウ素含有多層カーボンナノチューブを合成した。
Example 1
Multi-walled carbon nanotubes synthesized by arc discharge method were used as starting materials. FIG. 1 shows a scanning electron microscope (SEM) photograph of the starting multi-walled carbon nanotube. First, 4.0 g of boron oxide (B 2 O 3 ) and 150 mg of multi-walled carbon nanotubes were mixed and heated in an argon atmosphere at about 2000 ° C. for 1 hour to synthesize boron-containing multi-walled carbon nanotubes.
自然冷却後、ホウ素含有多層カーボンナノチューブ９０ｍｇを硫酸（９６％）２０ｍｌおよび硝酸（７０％）２０ｍｌの混合溶液中で３分間超音波分散する。次に、大気雰囲気中にて攪拌しながら、約１５０℃で４時間程度煮沸還流する。反応後、セラミックフィルター（孔径：０．２μｍ）でろ過し、純水で洗浄した後、一晩自然乾燥させて４０ｍｇのホウ素および酸素含有多層カーボンナノチューブを合成した。 After natural cooling, 90 mg of boron-containing multi-walled carbon nanotubes are ultrasonically dispersed in a mixed solution of 20 ml of sulfuric acid (96%) and 20 ml of nitric acid (70%) for 3 minutes. Next, the mixture is boiled and refluxed at about 150 ° C. for about 4 hours with stirring in an air atmosphere. After the reaction, it was filtered through a ceramic filter (pore size: 0.2 μm), washed with pure water, and then naturally dried overnight to synthesize 40 mg of boron and oxygen-containing multi-walled carbon nanotubes.
このようにして合成した多層カーボンナノチューブの走査型電子顕微鏡（ＳＥＭ）写真を、図２に示す。また、得られた多層カーボンナノチューブをＸ線光電子分光（ＸＰＳ）分析した結果、炭素の含有量９０重量％、ホウ素の含有量５重量％および酸素の含有量５重量％であった。 A scanning electron microscope (SEM) photograph of the multi-walled carbon nanotube synthesized in this way is shown in FIG. As a result of X-ray photoelectron spectroscopy (XPS) analysis of the obtained multi-walled carbon nanotube, the carbon content was 90% by weight, the boron content was 5% by weight, and the oxygen content was 5% by weight.
さらに、本実施例において得られた多層カーボンナノチューブ約２０ｍｇをエタノール水溶液入りの試薬瓶に入れ、超音波を１分間照射して懸濁液を作製した。そして、超音波照射終了後から液中で懸濁粒子が凝集もしくは沈降し始めるまでの時間（ｔ0）を測定した結果、３０時間であり、非常に分散性が良好で凝集し難いカーボンナノチューブであった。 Further, about 20 mg of the multi-walled carbon nanotubes obtained in this example were put in a reagent bottle containing an aqueous ethanol solution, and an ultrasonic wave was irradiated for 1 minute to prepare a suspension. As a result of measuring the time (t 0 ) from the end of ultrasonic irradiation until the suspended particles start to aggregate or settle in the liquid, it is 30 hours, and the carbon nanotubes are very dispersible and hardly aggregate. there were.
実施例２
化学気相成長法（ＣＶＤ法）により合成した単層カーボンナノチューブを出発原料として用いた。まず、ホウ酸（Ｈ3ＢＯ3）１．０ｇと単層カーボンナノチューブ１５０ｍｇとを混合して、窒素雰囲気中にて約１０００℃で４時間加熱して、ホウ素含有単層カーボンナノチューブを合成した。
自然冷却後、ホウ素含有単層カーボンナノチューブ１００ｍｇを硫酸（９６％）２０ｍｌおよび硝酸（７０％）２０ｍｌの混合溶液中で３分間超音波分散する。次に、大気雰囲気中にて攪拌しながら、約１５０℃で３時間程度煮沸還流する。反応後、セラミックフィルター（孔径：０．２μｍ）でろ過し、純水で洗浄した後、一晩自然乾燥させて４０ｍｇのホウ素および酸素含有単層カーボンナノチューブを合成した。
このようにして得られたホウ素および酸素含有単層カーボンナノチューブをＸＰＳ分析した結果、炭素の含有量９６重量％、ホウ素の含有量１重量％および酸素の含有量３重量％であった。
さらに、本実施例において得られた単層カーボンナノチューブ約２０ｍｇをエタノール水溶液入りの試薬瓶に入れ、超音波を１分間照射して懸濁液を作製した。
そして、超音波照射終了後から液中で懸濁粒子が凝集もしくは沈降し始めるまでの間（ｔ0）を測定した結果、３４時間であり、実施例１と同様に非常に分散性が良好で凝集し難いカーボンナノチューブであった。
Example 2
Single-walled carbon nanotubes synthesized by chemical vapor deposition (CVD) were used as starting materials. First, 1.0 g of boric acid (H 3 BO 3 ) and 150 mg of single-walled carbon nanotubes were mixed and heated at about 1000 ° C. for 4 hours in a nitrogen atmosphere to synthesize boron-containing single-walled carbon nanotubes.
After natural cooling, 100 mg of boron-containing single-walled carbon nanotubes are ultrasonically dispersed in a mixed solution of 20 ml of sulfuric acid (96%) and 20 ml of nitric acid (70%) for 3 minutes. Next, the mixture is boiled and refluxed at about 150 ° C. for about 3 hours while stirring in an air atmosphere. After the reaction, the mixture was filtered through a ceramic filter (pore diameter: 0.2 μm), washed with pure water, and then naturally dried overnight to synthesize 40 mg of boron- and oxygen-containing single-walled carbon nanotubes.
As a result of XPS analysis of the boron- and oxygen-containing single-walled carbon nanotubes thus obtained, the carbon content was 96% by weight, the boron content was 1% by weight, and the oxygen content was 3% by weight.
Furthermore, about 20 mg of the single-walled carbon nanotubes obtained in this example were placed in a reagent bottle containing an aqueous ethanol solution, and ultrasonic waves were applied for 1 minute to prepare a suspension.
As a result of measuring the time (t 0 ) from the end of ultrasonic irradiation until the suspended particles start to aggregate or settle in the liquid, it is 34 hours, and the dispersibility is very good as in Example 1. The carbon nanotubes hardly aggregated.
実施例１および実施例２と同様の方法にて、ホウ素および酸素含有量の異なる合計２０種類のサンプルを合成し、ｔ0を測定した結果を表１に示す。表１を基に、酸素含有量３重量％（○印）、５重量％（●印）および１２重量％（▲印）において、横軸にホウ素含有量（重量％）、縦軸にｔ0（時間）をプロットしたものを図３に示す。同様に、ホウ素含有量１重量％（○印）、５重量％（●印）および１１重量％（▲印）において、横軸に酸素含有量（重量％）、縦軸にｔ0（時間）をプロットしたものを図４に示す。 Table 1 shows the results obtained by synthesizing 20 types of samples having different boron and oxygen contents and measuring t 0 in the same manner as in Example 1 and Example 2. Based on Table 1, when the oxygen content is 3% by weight (◯ mark), 5% by weight (● mark) and 12% by weight (▲ mark), the horizontal axis represents the boron content (% by weight) and the vertical axis represents t 0. A plot of (time) is shown in FIG. Similarly, the oxygen content (% by weight) on the horizontal axis and t 0 (time) on the vertical axis at boron content of 1% by weight (circle), 5% by weight (●) and 11% by weight (▲) 4 is plotted in FIG.
図３および図４より、ホウ素含有量が０．０１〜１０重量％であり、かつ酸素含有量が０．０１〜１０重量％である範囲のカーボンナノチューブにおいて、ｔ0は約２０時間以上であり非常に分散性に優れていることがわかった。 From FIG. 3 and FIG. 4, in the carbon nanotube in which the boron content is 0.01 to 10 wt% and the oxygen content is 0.01 to 10 wt%, t 0 is about 20 hours or more. It was found that the dispersion was very excellent.
本発明のカーボンナノチューブは、従来のカーボンナノチューブと比較して、分散性に優れているだけではなく、分散状態を長時間保持することが可能であることから、電界放出型電子源のエミッター、熱放出素子、導電性材料、機能性樹脂のフィラー材、化学センサー、バイオセンサー等に広く利用できる。 The carbon nanotubes of the present invention are not only superior in dispersibility compared to conventional carbon nanotubes, but also can maintain a dispersed state for a long time. It can be widely used for emission elements, conductive materials, functional resin filler materials, chemical sensors, biosensors, and the like.
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