JP2004189533A - Carbon nanotube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carbon nanotube that is excellent in crystallinity and has a long length. <P>SOLUTION: The carbon nanotube that is excellent in crystallinity and that has a coaxial multi-layer structure and has the long length of more than 10 μm is synthesized by conducting an arc discharging between an anodic electrode and a cathodic electrode using a carbon material. The carbon material of the cathodic electrode of which the electrical resistance is 3,500 μΩ cm or more or the heat conductivity is 52 W/mK or less is used. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００２６】
なお、一般的に炭素材料は、製造時の熱処理温度により、その構造、組織、機械的特性や物性などが大きく異なる。カーボンナノチューブの生成に重要な影響をもたらす因子として、電気抵抗値（固有抵抗）および熱伝導率が考えられ、熱処理温度の比較的低い炭素質の炭素材料では、黒鉛化（結晶化）度が低いため、電気抵抗値（固有抵抗）が高く、熱伝導率の低いものとなる。通常電極用として使用されている炭素電極の電気抵抗値は５００から２０００μΩ・ｃｍ程度の範囲であり、熱伝導率は、５０から２００Ｗ／ｍＫの範囲にある。
【００２７】
さらに、本発明のカーボンナノチューブは、
１０）上述１）、２）、７）〜９）のいずれかにおいて、炭素材料を陰極として陽極電極との間にてアーク放電をおこなうことにより、カーボンナノチューブを合成する際、陰極と陽極の相対位置を移動させながら合成したものであり、
１１）上述１）、２）、６）〜１０）のいずれかにおいて、炭素材料を陰極として陽極電極との間にてアーク放電をおこなうことにより、カーボンナノチューブを合成する際、陰極材料全体もしくは陰極炭素材料のアーク放電部を予熱してから合成したものであり、
１２）上述１）、２）、７）〜１１）のいずれかにおいて、炭素材料を陰極として陽極電極との間にてアーク放電をおこなうことにより、カーボンナノチューブを合成する際、中空の陽極電極の内部から陰極電極に向けて供給されるアルゴンガス等の不活性ガスもしくは不活性ガスを含む混合ガスの流れに沿ってアークを発生させながら合成したものであり、
１３）上述１）、２）、７）〜１２）のいずれかにおいて、アーク放電を大気雰囲気中にて行わせ、合成したものである。
【００２８】
カーボンナノチュブの合成方法において、アークが集中した中心部に高純度のカーボンナノチューブから成る生成物が得られるが、常に同一場所にて放電を行うと、徐々に単位時間当りのカーボンナノチューブの合成量が低下してくると共に、カーボンナノチューブの長さも短いものとなってくる。これは、合成されたカーボンナノチューブが長時間アークに曝されるため、カーボンナノチューブの合成過程と分解過程が同時に進行してくるためであると考えられる。
そこで、上記１０）に係る本発明のカーボンナノチューブは、両電極の相対位置を連続的に移動させ、アークの陰極点を陰極材料上で連続的に移動させることにより、適正な移動速度においては常に単位時間当りのカーボンナノチューブの合成量を最大にすることが出来るとともに、より長いカーボンナノチューブを合成することができた。
【００２９】
本発明者は、先に示したように、陰極に用いる炭素材質によって、合成されるカーボンナノチューブの量および性状が大きく影響されることを確認した。さらに、アーク放電時の陰極材質の温度がある温度以上に保つことが、合成量の多い、かつ長さの長いカーボンナノチューブを生成する上で重要であることを確認した。
そこで、上記１１）に係る本発明のカーボンナノチューブは、陰極電極全体、もしくはアークの陰極点またはアーク前方の陰極電極上を部分的に加熱しながらアーク放電を行うことにより、合成量の多い、かつ長さの長いカーボンナノチューブを合成できた。
【００３０】
一般にアーク放電では、その陰極点は電子放出能の高い個所に選択的に発生する。しかし陰極点がしばらく発生するとその個所の電子放出能が弱まるため、より電子放出能の高い別の個所に陰極点が移動する。このように従来のアーク放電では、陰極点が激しく不規則に移動しながらアーク放電が行われる。さらに、場合によっては、陰極点が陽極対向位置から大きくずれ、電源の負荷電圧容量を上回り、アークが消弧してしまうこともある。このように、陰極点が激しく移動するアーク放電では、陰極のある一点を見た場合、その温度および炭素蒸気密度などの化学的因子が時間的に大きく変動することになる。このため、ある期間はカーボンナノチューブが合成されやすい条件となるが、別の期間ではカーボンナノチューブが合成されにくい条件となるか、カーボンナノチューブが分解されやすい条件となり、結果としてカーボンナノチューブの合成量が少なく、不純物を多く含むカーボンナノチューブが陰極点発生位置全体に合成されることになる。
【００３１】
また、アーク放電法では１０μｍを超えるような長いカーボンナノチューブは合成できなかった。このため、従来技術では、アークの安定とカーボンナノチューブの合成量を増加させるために、密閉容器内の雰囲気ガス種および圧力を適正に選定・制御する手法が採られていた。
しかしながら、密閉容器内の雰囲気ガス種および圧力の調整のみでは、アークの陰極点を完全に固定することは難しく、多くの不純物とカーボンナノチューブの混合体としての陰極堆積物しか回収することはできなかった。また、１０μｍを超えるような長いカーボンナノチューブは合成できなかった。
【００３２】
そこで、上記１２）に係る本発明のカーボンナノチューブでは、陽極電極に中空電極（Ｈｏｌｌｏｗ ｅｌｅｃｔｒｏｄｅ）を用い、中空電極の内部から陰極電極に向けてアルゴンガス等の不活性ガスもしくは不活性ガスを含む混合ガスを吹付けることにより、ガスの電離度が高くなってガス噴出経路にアークが発生しやすい条件を形成させ、また、不活性ガスもしくは不活性ガスを含む混合ガと接している中空電極内部表面に安定した陽極点を形成せしめることができた。このため、アーク発生経路が拘束され、陰極電極上のアーク陰極点の不規則な移動が防止され、その結果、この固定された陰極点の発生位置（アークの中心部）でカーボンナノチューブを効率的に合成することができ、この固定された陰極点の発生位置（アークの中心部）で合成量の多い、かつ長さの長いカーボンナノチューブを合成物することができた。
【００３３】
また、一般に、アーク放電を起こすためには、電極間空間を電離する必要がある。原子の電離には、種々の過程があるが、アーク放電においては、電子との衝突による電離過程が支配的である。また、原子番号の小さいＨｅ、Ｎｅは除き、Ａｒ、Ｋｒ、Ｘｅなどの不活性ガスは、電子との衝突による電離能率が高く、アークを発生しやすい空間を提供する。
上記１３）に係る本発明のカーボンナノチューブは、酸素、窒素等に比べ電離能率が高いＡｒ、Ｋｒ、Ｘｅなどの不活性ガス、もしくは不活性ガスを含む混合ガスを、大気雰囲気中にて陽極電極から陰極電極に向けて供給しながらアーク放電を行うことによって、アークをガス流路に沿って集中して発生させることができ、陰極点を安定化させることができる。この結果、合成量の多い、かつ長さの長いカーボンナノチューブを合成することができた。
【００３４】
【発明の実施の形態】
［実施の形態１］
図１（ａ）、（ｂ）は、本実施の形態１における、合成された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。 図１（ａ）は陰極堆積物の中心部のＳＥＭ写真、図１（ｂ）はカーボンナノチューブの拡大ＳＥＭ写真である。
本実施の形態において、陽極電極として、外径３６ｍｍ、内径１０ｍｍの中空電極を用い、大気圧下、大気雰囲気中で電流５００Ａ、電圧３５Ｖ（アーク長約５ｍｍ）にて１分間アーク放電を行った。電極間の相対移動は行わず、１分間のアーク放電を行ったところ、陰極電極に数１０ｍｇのカーボンナノチューブが得られた。中空電極内から送給したガスは３％の水素を含むアルゴンガスで、流量は１０リットル／分である。
【００３５】
図１（ｂ）に見られるように、合成されたカーボンナノチューブは長く、ほとんどのカーボンナノチューブが、１０μｍ越えの長さを有している。さらに、別途実施した詳細なＳＥＭ観察の結果、半数以上のものが２５μｍ越えの長さを有し、５０μｍ越えのものも多数観察された。
中空電極内部から送給するガスは、純アルゴンもしくは２０％程度の水素ガスやヘリウムガスを混入した混合ガスを用いたがアーク形態に大きな変化は見られなかった。適正ガス流量は、電極穴の断面積に影響され、穴の断面積１ｍｍ² 当り１０〜４００ｍｌ／分が適正であった。
【００３６】
［実施の形態２］
図２は本実施の形態２における、カーボンナノチューブの合成方法を示す説明図である。図２における２Ａは陰極電極、１１は陽極電極、３はアーク、３１Ａはカーボンナノチューブが複雑に絡み合って形成された膜状物質である高純度ＣＮＴテープを示す。
図２において、陽極電極１１としては外径１０ｍｍ、内径４ｍｍの中空炭素電極を用い、陰極電極２Ａとして直径３５ｍｍの円柱状炭素電極を用いた。陰極電極２Ａを回転させるとともに、陽極電極（中空電極）１１を陰極電極２Ａの軸方向に直線的に移動させて、陰極電極２Ａ上に螺旋を描く形で陰極点を移動させた。陰極電極２Ａの回転速度は１．５回転／分であり、陽極電極（中空電極）１１の移動速度は、３５ｍｍ／分である。また、アーク放電は、大気圧下、大気雰囲気中で行い、中空電極内から送給したガスには純アルゴンガスを用い、流量は１リットル／分とした。放電条件は、電流１００Ａ、電圧２０Ｖ（アーク長約１ｍｍ）である。陰極電極２Ａに用いた炭素材料は、電気抵抗率が４２００μΩ・ｃｍの炭素質炭素材料である。
【００３７】
アーク放電後、陰極電極２Ａ上で陰極点が移動した螺旋状の位置に、幅２〜３ｍｍ程度、厚さ１０〜１００μｍ程度のテープ状の物質、高純度ＣＮＴテープ３１Ａが合成され、一部に自然剥離する現象が観察された。
【００３８】
本実施の形態における、合成されたカーボンナノチューブは、直径に比し、長さが極めて長く、かつ、丸まったりして複雑に絡み合って陰極堆積物を構成しているので、その長さを定量的に評価することは困難である場合が多い。そこで、陰極堆積物に外力を与えて引きちぎり、その破断部における、引き伸ばされたカーボンナノチューブの長さを、走査型電子顕微鏡（ＳＥＭ）にて観察した。
図３は、引きちぎられて引き伸ばされた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。
端部のカーボンナノチューブは、外力によりほぼ直線状に引き伸ばされ、切断されたものと考えられる。切断されたカーボンナノチューブの長さは、１本のカーボンナノチューブと同定できる部分だけでも５０μｍを越える長さのものも有り、かつ、破断部の両方の端部に同様なものが観察されるので、実際の長さは、５０μｍの倍以上、つまり１００μｍ以上に及ぶものも存在すると考えられる。
本実施の形態２においては、螺旋状に連続合成された高純度ＣＮＴテープ３１Ａは、上述のように陰極電極２Ａの表面から自然剥離ないし容易に剥離することができ、カーボンナノチューブ繊維の連続性を期待することができる。実質、本実施の形態２においては、高純度ＣＮＴテープ３１Ａは、陰極電極２Ａの円周長さ約１／２乃至３周分切断なしで連続生成することができた。従って、本実施の形態２において合成されたカーボンナノチューブの長さと直径の比（以下、アスペクト比という）と、前記実施の形態１におけるカーボンナノチューブのアスペクト比約３０００〜２００００に対する割合Ｋは、生成可能な連続長さの割合と仮定すれば約１０〜１００倍程度になる可能性が認めらる。
また、本実施の形態におけるアスペクト比は、その合成条件を適宜選択することにより大幅に増加向上させることが可能であり、また、前記の相対移動に対し集中アーク角度を移動方向に所定角度傾け合成することによって、より好ましい増加向上を図ることができる。
さらにまた、上記剥離性の特徴と相俟って相対移動を、平面を対象するものとすることも容易に行い得る。
【００３９】
［実施の形態３］
図４は、本実施の形態３における、カーボンナノチューブの合成方法を示す説明図であり、図中前述の実施の形態２の図２と同じ部分には同一の符号を付してあり、説明を省略する。
図４において、陰極電極２Ａに交流電流５を通電し、陰極電極２Ａを５００℃〜２０００℃に予熱した。その他の合成条件は前記実施の形態２におけるものと同じである。本実施の形態により合成の結果、テープ状カーボンの合成量を大幅に増加させることができた。
【００４０】
図５は、本実施の形態３において合成されたテープ状物質の外観写真を示す。図５から分かるように、合成されたテープ状物質は、ミリメートルサイズの広がりを持った膜状で、しなやかに撓む可撓性と、取扱い上十分な強度を有している。
【００４１】
図６は、本実施の形態３において合成された陰極堆積物のＳＥＭ写真を示す。図６において、合成された陰極堆積物は、ほとんど全て長いカーボンナノチューブにより構成されており、その長さは、先に示した実施の形態１における静止アークの場合に比し、ほとんどのものが１０μｍ越えの長さを有しており、５０μｍ越えのものも多く、前記生成物の剥離性の特徴と相俟って、生成条件により前記実施の形態１におけるアスペクト比に対するアスペクト比の割合Ｋが２０〜３００倍にも及ぶ可能性があることが予想される。
【００４２】
図７は、本実施の形態３において合成されたテープ状物質の構成物であるカーボンナノチューブのＴＥＭ写真を示す。
図７から分かるように、合成されたカーボンナノチューブは、ほぼ完全なグラフェン筒による同軸多重構造を示している。また、詳細な調査の結果その直径は４〜３０ｎｍであり、４〜１５ｎｍのものが全体のほぼ９０％を占めていた。
また、図８（ａ）、（ｂ）は、図７のカーボンナノチューブ先端構造および中実構造の説明図である。
図８（ａ）は、カーボンナノチューブ先端のグラフェン筒が完全に開いたもの、図８（ｂ）はカーボンナノチューブ先端の外周部のグラフェン筒が開いており、かつ内部までグラフェン筒の詰まった構造のものであり、これらが混在しているのが観察された。
【００４３】
上述のごとく、本発明においては、結晶性が優れ、かつ１０μｍ越えの長さを有する長いカーボンナノチューブが大量に密集して合成されているために、図４に示されるような可撓性を有する薄い膜状の長いテープ物質が形成し得たものと考えられる。
【００４４】
従来、カーボンナノチューブのみの集合体は、粉末状または塊状もしくは海綿状で得られるが、不純物やバインダーなどを用いずに、または、基板上に合成するなどの方法を用いずに、純度の高いカーボンナノチューブを薄く、かつミリメートルサイズの広がりを持った膜状物質単体として、かつ利用上十分な強度を持って形成することはできなかった。
これに対し、本発明のカーボンナノチューブは、結晶性が優れ、かつ長さが１０μｍを越えると考えられる長いものを含む、高純度のカーボンナノチューブで構成されていることにより、極めて優れたテープ状物質を初めて実現できたものである。
【００４５】
【発明の効果】
本発明の カーボンナノチューブは次のような効果を有する。
１．結晶性が良く、かつ長さの長いカーボンナノチューブが合成されることにより、不純物やバインダーなどを用いずに、純度の高いカーボンナノチューブを薄く、かつミリメートルサイズの広がりを持った膜状物質として形成できるようになった。この膜状物質は、可撓性と利用上十分な強度を持っているため、取扱いも容易で、電子放出源やセンサーまたは機能性分離膜など広い用途に、容易に使用できるようになる。
２．本発明の結晶性が良く、長いカーボンナノチューブを樹脂や金属などに混合して使用することにより、従来の短いカーボンナノチューブに比べ同量混入したとしても導電性や強度および熱伝導性などに、より優れた特性を示す。
【００４６】
３．本発明の直径が細く、長さが長いカーボンナノチューブであることによる特性により、その具体的利用技術として、以下のものが考えられる。
（イ）本カーボンナノチューブの細束性および結晶性が優れている特性により、電界放出用電子源として、蛍光表示管やフィールドエミッションディスプレイ（ＦＥＤ）などの陰極材料および電子顕微鏡の探針などへの利用、
（ロ）本カーボンナノチューブを電子源として用いることにより、効率の良いイオンやオゾンの発生装置の作成、およびこれらのイオンやオゾンによる脱臭や消臭効果、特にマイナスイオンによる人の心理面、生理面への良好な波及効果、
なお、上記（イ）、（ロ）については、直径が細いことが望ましい。
（ハ）本カーボンナノチューブの優れた結晶性による高強度が、理論的には鉄の１００倍以上の引張強度を有し、かつ、比重はアルミニウムの約半分であるため、樹脂や金属に混入したり、複合化することにより、軽くて強度の高い構造材料の提供。
【００４７】
（ニ）また、本カーボンナノチューブが、形状が比較的均一で細く、長い特徴により、マイクロマシンの構造部材やアクチュエータの構成部品としての利用、
（ホ）本カーボンナノチューブが、導電性が優れていることにより、ＩＣの配線材料としての利用、また、樹脂や繊維に混入することにより、これらの物質に導電性を持たせたり、静電気の帯電防止機能を持たせること、塗料に混入させた導電性塗膜や導電性インクへの利用、
また、これらのものは、導電性を必要とする部材に利用以外の、電磁波の反射損失や誘電損失に基づく電磁波吸収・遮蔽材としても利用、
【００４８】
（ヘ）また、二次電池の負極材料に混入させることにより、負極導電性の経年劣化の防止、
（ト）さらに、グリスに混入させることにより、グリスに導電性を持たせると共に、通電部でのグリスの性能劣化の防止対策、
（チ）ダイヤモンド以上の熱伝導性を有することにより、ＩＣなどの放熱材としての利用、また、放熱材として利用する場合は、単体として、または、樹脂や金属に混入したものとしての適用、
（リ）アルミ板などの表面に塗布もしくは貼り付けることにより放熱特性の大きな部材への適用、
（ヌ）さらに、ナノサイズのきわめて小さな構造体である本カーボンナノチューブは、量子効果を利用したダイオードやトランジスタ、および量子コンピュータの基本素子である量子ドットなどの電子部品の材料としても利用。
【００４９】
４．また、本発明のカーボンナノチューブは、その集合体として下記の利用効果を有する。
（ａ）比較的均一なナノサイズの直径の長さが長い本カーボンナノチューブが複雑に絡み合ったカーボンナノチューブ集合体は、その密集度から決まるある大きさの空間を有しているため、特定の大きさを有する物質を選別するためのフィルターや分離膜としての利用、
（ｂ）また、その単位重量あたりの表面積の大きさは、活性炭をも凌ぐものであり、有害物質の吸着材や、水素やメタンなどのガス貯蔵材としての利用、
（ｃ）特定ガスを検出するガスセンサなど機能材料としての利用、
（ｄ）さらに、触媒の担持材として利用することによって、各種化学反応の効率の向上、
（ｅ）さらには、医療分野等において、薬剤等を吸着・保持させて体内の病巣部へ運搬するキャリヤーとして利用、その他、キャパシターの電極材料としての利用。
【図面の簡単な説明】
【図１】図１（ａ）、（ｂ）は、本実施の形態１において、合成された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。
【図２】実施の形態２における、カーボンナノチューブの合成方法を示す説明図である。
【図３】引きちぎられて引き伸ばされた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。
【図４】実施の形態３における、カーボンナノチューブの合成方法を示す説明図である。
【図５】実施の形態３において合成されたテープ状物質の外観写真を示す。
【図６】実施の形態３においてる合成されたテープ状物質のＳＥＭ写真を示す。
【図７】実施の形態３において合成されたテープ状物質の構成物であるカーボンナノチューブのＴＥＭ写真を示す。
【図８】図８（ａ）、（ｂ）は、図７のカーボンナノチューブ先端構造および中実構造の説明図を示す。
【図９】カーボンナノチューブ側壁部の六角網面の状態を模式的に表したものであり、図９（ａ）は、アーク法によるカーボンナノチューブの状態を、図９（ｂ）は、小さな網面が断続的に連なった状態を、図９（ｃ）は、長さ方向途中での層の欠如を、図９（ｄ）は、層の食い違い状態を示す。
【符号の説明】
２Ａ 陰極電極、３ アーク、３１Ａ 高純度ＣＮＴテープ、１１ 陽極電極、５ 交流電源。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention generally relates to a carbon nanotube that is a nano-sized carbon fiber, and particularly to a carbon nanotube having excellent crystallinity and a long length.
[0002]
[Prior art]
One piece of a mesh surface in which a six-membered ring of carbon atoms extends infinitely is called graphene, and a tube-shaped carbon nanotube obtained by winding this graphene into a seamless cylindrical shape is known. A single carbon nanotube having a single graphene tube is referred to as a single-walled carbon nanotube, and a carbon nanotube having a plurality of graphene tubes stacked concentrically is referred to as a multi-walled carbon nanotube. Carbon nanotubes have attracted attention as new materials because of their unique physical properties.
[0003]
The diameter of the carbon nanotube is from about 0.7 nm for a single-walled carbon nanotube to usually about 1 to 3 nm, and about 4 to 50 nm for a multi-walled carbon nanotube. In addition, the tip portions of these carbon nanotubes are often closed by the inclusion of a five-membered ring like fullerene (C60). Apart from these, there are cup-stacked carbon nanotubes with a shape in which several cups that have come off overlap, and bamboo-type carbon nanotubes with nodes in the middle like bamboo. Moreover, some of the carbon nanotubes synthesized by the vapor phase growth method (CVD) have many structural defects in the graphene and the graphene cylinders are not clear one by one.
[0004]
Many studies have been made on carbon nanotubes, and are graphite fibers having a cylindrical structure with an outer diameter of 30 nm or less, such as a cylindrical graphite fiber having a fiber end ending in a conical shape (for example, see Patent Document 1), A fine fibrous tube having a plurality of graphitic layers of 3.5 to 75 nm, a carbon fibril having a length of at least twice the diameter (for example, see Patent Document 2), and a plurality of graphite cylinders concentrically at the center of the cylinder Graphite-based nanofibers that are densely laminated (for example, see Patent Document 3) are known.
[0005]
[Patent Document 1]
JP-A-7-11520 (paragraph 0005, FIGS. 2 and 3)
[Patent Document 2]
JP-T2-503334 (page 4, column 937-40)
[Patent Document 3]
JP-A-2000-327317 (2nd page column, line 248 to 3rd page column, 32 lines, FIGS. 3, 4 and 5)
[0006]
[Problems to be solved by the invention]
However, conventionally, it has been difficult to synthesize a long carbon nanotube having a good structure of a graphene cylinder and in which each graphene cylinder can be clearly recognized. The fact that the structure of the graphene cylinder is good and that each graphene cylinder can be clearly recognized is generally expressed by the term “good crystallinity”. It is generally said that carbon nanotubes having good crystallinity are synthesized by the arc discharge method. However, in the conventional arc discharge method, only long carbon nanotubes of about 1 μm could be synthesized.
[0007]
Although it is said that a long carbon nanotube can be synthesized by the vapor phase growth method (CVD), many long carbon nanotubes have a diameter as large as 50 nm or more and have poor crystallinity. Carbon nanotubes with poor crystallinity can be reformed to have good crystallinity by heat treatment. However, the reforming requires not only a heat treatment at a temperature close to 3000 ° C. (for example, see Patent Document 2). ), It was difficult to prevent a layered defect occurring at a certain probability in the length direction of the carbon nanotube even after heat treatment. Further, in the heat treatment process, the length of the carbon nanotube was shortened, and it was difficult to obtain a carbon nanotube having good crystallinity and a length as long as more than 10 μm.
[0008]
Here, the meaning of the word crystallinity of the carbon nanotube will be described. FIG. 9 schematically shows the state of the hexagonal mesh plane on the side wall of the carbon nanotube. FIG. 9A shows a state of the carbon nanotube by the arc method. The mesh plane is long in parallel with the fiber axis, and the graphene cylinder is clearly formed, and the lamination intervals are also uniform.
[0009]
On the other hand, as shown in FIG. 9B, the structure of the carbon nanotube synthesized by the CVD method is a state in which small mesh planes are intermittently connected, and although they are oriented substantially parallel to the fiber axis, The surface spacing is also variable. Originally, a crystal must have regularity in the arrangement of three-dimensional atoms, and a certain regular relationship also exists in the direction of lamination of the mesh plane. , A so-called turbostratic structure.
[0010]
Therefore, although it is different from graphite crystal in a strict sense, as shown in FIG. 9A, a net plane is long in parallel with the fiber axis and the lamination interval is also equal. It is represented by As described above, the structure in which the mesh plane is connected to the fiber axis in parallel for a long time is a factor showing characteristics excellent in strength, heat conductivity, and conductivity. FIGS. 9 (c) and 9 (d) show layer-like defects which are likely to occur when carbon nanotubes are heat-treated by the CVD method. FIG. 9C shows the absence of a layer in the middle of the length direction, and FIG. 9D shows the difference between the layers.
[0011]
Aggregates of only carbon nanotubes are usually obtained in the form of powder, lump, or sponge.However, without using impurities or binders, high-purity carbon nanotubes are converted into thin, film-like substances with a millimeter-size spread. If formed, it is easy to handle and can be easily used in a wide range of applications such as electron emission sources, sensors or functional separation membranes. In order to form such a film-like substance with sufficient strength for utilization, long carbon nanotubes having good crystallinity are required.
[0012]
Also, when carbon nanotubes are used in a mixture with a resin or metal, the crystallinity is good, and long carbon nanotubes are short in many respects, such as conductivity, strength and thermal conductivity, even if mixed in the same amount. Shows superior properties compared to nanotubes. However, conventionally, because of good crystallinity and no long carbon nanotubes, many carbon nanotubes have to be used in order to obtain predetermined conductivity, strength, thermal conductivity, and the like. In addition, it was not possible to form a film-like substance composed of high-purity carbon nanotubes with sufficient strength for use.
[0013]
The present invention has been made to solve the above problems, and an object of the present invention is to provide a carbon nanotube of a novel substance that can solve the problems of the conventional carbon nanotubes.
[0014]
[Means for Solving the Problems]
The carbon nanotube of the present invention,
1) It has a length exceeding 10 μm synthesized by an arc discharge method,
2) In the above 1), the cylinder made of graphene has a coaxial multilayer structure,
3) The tube made of graphene is a carbon nanotube having a coaxial multilayer structure, the tube is densely stacked to the center thereof, and has a length exceeding 10 μm;
4) A tube made of graphene has a coaxial multilayer structure, a carbon nanotube having an outermost diameter of 4 to 30 nm, and a length exceeding 10 μm,
5) A graphene-made cylinder having a coaxial multilayer structure, a carbon nanotube having an outermost diameter of 4 to 30 nm, a densely stacked cylinder up to the center, and a length exceeding 10 μm. It is.
[0015]
Since the carbon nanotubes of the present invention according to the above 1) and 2) are synthesized by an arc discharge method, the structure of the graphene cylinder is good, and each graphene cylinder can be clearly recognized, that is, so-called crystallinity. Since it is an excellent carbon nanotube and has a length exceeding 10 μm, it exhibits excellent characteristics compared to a short carbon nanotube in many points such as conductivity, strength and thermal conductivity. In addition, a film-like substance composed of high-purity carbon nanotubes can be formed with sufficient strength for use.
[0016]
Furthermore, since the tube made of graphene is a so-called multi-walled carbon nanotube having a coaxial multi-layer structure, it has high thermal, electrical, and mechanical strength and durability. In particular, the graphene tube is densely stacked up to the center. Therefore, when used as an electron source, more current can flow and durability can be improved. This is because the effective cross-sectional area of the carbon nanotube that allows current to flow increases, but it is effective without increasing the diameter of the carbon nanotube by stacking the graphene cylinder densely up to the core without any space in the center. The cross-sectional area can be increased. When the diameter of the carbon nanotube is increased, the field emission characteristics of the carbon nanotube due to its fine bundle property are inferior.
[0017]
Further, the carbon nanotubes of the present invention according to the above 3), 4) and 5) are carbon nanotubes having a graphene cylinder having a coaxial multilayer structure and a length exceeding 10 μm, and having an outermost diameter of 4 to 4 μm. A carbon nanotube having excellent field emission characteristics and durability can be obtained by using a 30 nm one and further densely stacking the cylinders to the center thereof in consideration of durability and a current value that can flow. it can. The diameter of the carbon nanotube is preferably 4 to 30 nm, more preferably 4 to 15 nm.
In general, the smaller the diameter and the longer the length of carbon nanotubes, the stronger the characteristics unique to various types of carbon nanotubes. However, from a practical point of view, in single-walled carbon nanotubes with a diameter of 3 nm or less, There is a problem in its durability. For example, when these are used as electron emission sources, they operate at a low threshold voltage, but do not produce a high current density and are reported to have low durability. The present invention has solved this problem.
[0018]
Further, the carbon nanotube of the present invention,
6) One or both ends of the carbon nanotubes open at least a part or the whole of a cylinder made of outermost graphene,
7) The carbon nanotubes described in 3) to 6) above are synthesized by an arc discharge method.
8) In any of the above 1), 2) and 7), when carbon nanotubes are synthesized by performing an arc discharge between a carbon material as a cathode and an anode electrode, the material of the cathode carbon material is It is synthesized using what is mainly carbonaceous,
9) In any of the above 1), 2), 7) and 8), when synthesizing carbon nanotubes by performing arc discharge between the carbon material as a cathode and an anode electrode, the cathode carbon material is And those having an electric resistance of 3500 μΩ / cm or more or a thermal conductivity of 52 W / mK or less.
[0019]
When a carbon nanotube is used as an electron source for field emission, the thinner and longer the diameter, the lower the threshold voltage for electron emission. However, in consideration of durability and a current value that can be passed, as described above, it is preferable that the graphene cylinder is densely stacked to the center, and that the diameter be 4 to 30 nm, more preferably 4 to 15 nm. Another factor that has a large effect on the threshold voltage of electron emission is the shape of the tip of the carbon nanotube.If the tip of the carbon nanotube is closed in a curved surface or conical shape by graphene containing a five-membered ring. As a result, the threshold voltage of electron emission becomes higher than in the case where the end is broken and opened.
Therefore, the carbon nanotube of the present invention according to the above 6) further improves the field emission characteristics by opening at least a part or the whole of the outermost cylinder made of graphene at one or both ends. Can be done.
[0020]
Further, the carbon nanotube of the present invention according to the above 7) is synthesized by an arc discharge method, has a good structure of a graphene cylinder, and can clearly recognize each graphene cylinder, that is, so-called crystallinity. And exhibits excellent properties in many aspects such as conductivity, strength, and thermal conductivity in addition to the above properties.
[0021]
In the carbon nanotube of the present invention according to the above 8), which is a carbon nanotube generated by arc discharge, carbon vapor and carbon ions mainly generated from the anode carbon electrode diffuse to the cathode side, and the surface of the cathode electrode having a lower temperature than the anode To synthesize carbon nanotubes (particularly multi-walled carbon nanotubes). Therefore, it has been said that the lower the temperature of the cathode, the faster the growth rate of the carbon nanotubes, and the cathode material does not need to be a carbon material as long as it is a heat-resistant conductive material. However, the present inventor has confirmed that the properties of the synthesized carbon nanotube are greatly affected by the carbon material used for the cathode, and the carbon nanotube is formed by performing an arc discharge between the anode and the anode using the carbon material as the cathode. When synthesizing, when the material of the cathode carbon material is synthesized using mainly carbonaceous material, compared with the case of using a graphite carbon material for the cathode, the synthesis amount of the carbon nanotube is large, and It was found that the length of the carbon nanotube was significantly increased.
[0022]
In this case, the synthesized carbon nanotubes are long, and most of the carbon nanotubes have a length exceeding 10 μm. In addition, as a result of detailed SEM observation separately performed, more than half of them had a length of more than 25 μm, and many more than 50 μm were observed.
The carbonaceous material referred to here means carbon with a low degree of crystal development, in comparison with graphite material, and the size of crystallites is smaller than that of graphite material, and the degree of arrangement and stacking of layer surfaces are small. It has poor regularity.
[0023]
Further, in the carbon nanotube according to the above 9), by setting the electrical resistivity at room temperature to 3500 μΩ · cm or more and the thermal conductivity to 52 W / mK or less, when a carbon material having these characteristics is used as a cathode, Since the cathode electrode of the arc generating portion has a high current density during arc discharge, the temperature near the cathode point becomes high due to electric resistance heating. Further, since the thermal conductivity is low, a narrow range near the cathode spot is kept at a high temperature for a long time. Therefore, the temperature of the cathode was in a temperature range in which carbon nanotubes were easily generated, and a carbon nanotube with a high synthesis amount and a long length could be generated.
[0024]
Table 1 shows the results of examining the amount of synthesized carbon nanotubes and the length of the synthesized carbon nanotubes when arc discharge was performed using various carbon electrodes as cathodes. The discharge conditions were as follows: a bar-shaped carbon anode having a diameter of 10 mm and a carbon cathode having a diameter of 36 mm were opposed to each other under atmospheric pressure in an air atmosphere, and a direct current arc discharge was performed between the two for a certain period of time. It is a result of examining the synthesis amount and length of carbon nanotubes. Those containing carbon nanotubes having a length exceeding 10 μm were defined as “long”. As can be seen from these results, long carbon nanotubes are synthesized on the cathode carbon electrode having an electric resistivity (specific resistance) of 3500 μΩ · cm or more and a thermal conductivity of 52 W / mK or less. Desirably, by using a carbon material having an electric resistivity (specific resistance) of 4000 μΩ · cm or more and a thermal conductivity of 40 W / mK or less as the cathode electrode, the synthesis amount of carbon nanotubes can be increased. Within the experimental range of Table 1, the larger the electrical resistivity (resistivity) of the cathode carbon electrode and the lower the thermal conductivity, the more carbon nanotubes having a longer length were synthesized. When a carbon material having a thermal conductivity of 50,000 μΩ · cm or more and a thermal conductivity of 10 W / mK or less is used as a cathode electrode, the frequency of arc occurrence failures at the time of arc ignition increases and the stability of the arc deteriorates. The electrical resistivity (specific resistance) of the carbon electrode is desirably 50,000 μΩ · cm or less, and the thermal conductivity is desirably 10 W / mK or more.
[0025]
[Table 1]

[0026]
In general, the structure, structure, mechanical properties, physical properties, and the like of carbon materials vary greatly depending on the heat treatment temperature during production. Factors that have an important influence on the formation of carbon nanotubes are considered to be electric resistance (specific resistance) and thermal conductivity. A carbonaceous carbon material having a relatively low heat treatment temperature has a low degree of graphitization (crystallization). Therefore, the electric resistance (specific resistance) is high and the thermal conductivity is low. The electric resistance of a carbon electrode used for an ordinary electrode is in the range of about 500 to 2000 μΩ · cm, and the thermal conductivity is in the range of 50 to 200 W / mK.
[0027]
Further, the carbon nanotubes of the present invention,
10) In any of the above 1), 2), 7) to 9), when a carbon nanotube is synthesized by performing an arc discharge between the anode and the anode using a carbon material as a cathode, the relative distance between the cathode and the anode is increased. It is synthesized while moving the position,
11) In any of the above 1), 2), 6) to 10), when synthesizing carbon nanotubes by performing arc discharge between a carbon material as a cathode and an anode electrode, the entire cathode material or the cathode It is synthesized after preheating the arc discharge part of carbon material,
12) In any of the above 1), 2), 7) to 11), when a carbon nanotube is synthesized by performing an arc discharge between a carbon material as a cathode and an anode electrode, a hollow anode electrode Synthesized while generating an arc along the flow of an inert gas or a mixed gas containing an inert gas such as an argon gas supplied from the inside toward the cathode electrode,
13) In any one of the above 1), 2), 7) to 12), arc discharge is performed in an air atmosphere to synthesize.
[0028]
In the method of synthesizing carbon nanotubes, a product consisting of high-purity carbon nanotubes is obtained in the central part where the arc is concentrated, but if discharge is always performed in the same place, the amount of carbon nanotubes synthesized per unit time gradually increases. And the length of the carbon nanotubes becomes shorter. It is considered that this is because the synthesized carbon nanotube is exposed to the arc for a long time, and the synthesis process and the decomposition process of the carbon nanotube proceed simultaneously.
Therefore, the carbon nanotube of the present invention according to the above 10) is always moved at an appropriate moving speed by continuously moving the relative positions of both electrodes and continuously moving the cathode point of the arc on the cathode material. The synthesis amount of carbon nanotubes per unit time could be maximized, and a longer carbon nanotube could be synthesized.
[0029]
The present inventor has confirmed that, as described above, the amount and properties of the synthesized carbon nanotubes are greatly affected by the carbon material used for the cathode. Furthermore, it has been confirmed that maintaining the temperature of the cathode material during arc discharge at a certain temperature or higher is important for producing carbon nanotubes having a large amount of synthesis and a long length.
Therefore, the carbon nanotube of the present invention according to the above 11) has a large synthesis amount by performing arc discharge while partially heating the entire cathode electrode, the cathode point of the arc or the cathode electrode in front of the arc, and A long carbon nanotube was synthesized.
[0030]
In general, in arc discharge, the cathode spot is selectively generated at a portion having a high electron emission ability. However, when the cathode spot is generated for a while, the electron emission ability at that location is weakened, and the cathode spot moves to another location having a higher electron emission ability. As described above, in the conventional arc discharge, the arc discharge is performed while the cathode spot moves strongly and irregularly. Further, in some cases, the cathode point is greatly displaced from the anode facing position, exceeds the load voltage capacity of the power supply, and the arc is extinguished. As described above, in the arc discharge in which the cathode spot moves violently, when a certain point on the cathode is viewed, chemical factors such as the temperature and the carbon vapor density greatly vary with time. For this reason, it is a condition that carbon nanotubes are easily synthesized during a certain period, but it is a condition that carbon nanotubes are difficult to synthesize or a condition that carbon nanotubes are easily decomposed during another period, and as a result, the synthesis amount of carbon nanotubes is small. Thus, carbon nanotubes containing a large amount of impurities are synthesized over the entire cathode spot generating position.
[0031]
In addition, a long carbon nanotube exceeding 10 μm could not be synthesized by the arc discharge method. For this reason, in the prior art, in order to stabilize the arc and increase the synthesis amount of carbon nanotubes, a method of appropriately selecting and controlling the type of atmospheric gas and the pressure in the closed vessel has been adopted.
However, it is difficult to completely fix the cathode point of the arc only by adjusting the atmosphere gas type and pressure in the closed container, and it is possible to collect only the cathode deposit as a mixture of many impurities and carbon nanotubes. Was. In addition, carbon nanotubes having a length exceeding 10 μm could not be synthesized.
[0032]
Therefore, in the carbon nanotube of the present invention according to the above item 12), a hollow electrode (Hollow electrode) is used as the anode electrode, and an inert gas such as argon gas or a mixture containing an inert gas is directed from the inside of the hollow electrode to the cathode electrode. By spraying the gas, the degree of ionization of the gas is increased and an arc is easily generated in the gas ejection path, and the inner surface of the hollow electrode in contact with the inert gas or the mixed gas containing the inert gas is formed. Thus, a stable anode spot could be formed. For this reason, the arc generation path is restricted, and irregular movement of the arc cathode spot on the cathode electrode is prevented. As a result, carbon nanotubes are efficiently removed at the position where the fixed cathode spot is generated (the center of the arc). A carbon nanotube with a large amount of synthesis and a long length could be synthesized at the position where the fixed cathode spot was generated (the center of the arc).
[0033]
Generally, in order to cause arc discharge, it is necessary to ionize the space between the electrodes. There are various processes in the ionization of atoms, but in arc discharge, the ionization process due to collision with electrons is dominant. In addition, except for He and Ne having small atomic numbers, inert gases such as Ar, Kr, and Xe have a high ionization efficiency due to collision with electrons and provide a space in which an arc is easily generated.
The carbon nanotube of the present invention according to the above 13) is characterized in that an inert gas such as Ar, Kr, Xe or a mixed gas containing an inert gas having a higher ionization efficiency than oxygen, nitrogen, etc. The arc can be generated along the gas flow path by performing the arc discharge while supplying the arc toward the cathode electrode, and the cathode spot can be stabilized. As a result, a carbon nanotube having a large amount of synthesis and a long length could be synthesized.
[0034]
BEST MODE FOR CARRYING OUT THE INVENTION
[Embodiment 1]
FIGS. 1A and 1B show scanning electron microscope (SEM) photographs of the synthesized carbon nanotubes in the first embodiment. FIG. 1A is an SEM photograph of the center of the cathode deposit, and FIG. 1B is an enlarged SEM photograph of the carbon nanotube.
In this embodiment, a hollow electrode having an outer diameter of 36 mm and an inner diameter of 10 mm was used as an anode electrode, and an arc discharge was performed at a current of 500 A and a voltage of 35 V (arc length of about 5 mm) for 1 minute under atmospheric pressure and in an air atmosphere. . When arc discharge was performed for 1 minute without performing relative movement between the electrodes, several tens mg of carbon nanotubes were obtained on the cathode electrode. The gas sent from the inside of the hollow electrode is an argon gas containing 3% of hydrogen, and the flow rate is 10 liter / min.
[0035]
As can be seen in FIG. 1 (b), the synthesized carbon nanotubes are long, and most carbon nanotubes have a length exceeding 10 μm. In addition, as a result of detailed SEM observation separately performed, more than half of them had a length of more than 25 μm, and many more than 50 μm were observed.
As the gas fed from the inside of the hollow electrode, pure argon or a mixed gas containing about 20% of hydrogen gas or helium gas was used, but no significant change was found in the arc form. The appropriate gas flow rate is affected by the cross-sectional area of the electrode hole, and the cross-sectional area of the hole is 1 mm. ^Two 10-400 ml / min per hour was appropriate.
[0036]
[Embodiment 2]
FIG. 2 is an explanatory diagram illustrating a method for synthesizing carbon nanotubes according to the second embodiment. In FIG. 2, 2A indicates a cathode electrode, 11 indicates an anode electrode, 3 indicates an arc, and 31A indicates a high-purity CNT tape which is a film-like substance formed by complexly entangled carbon nanotubes.
In FIG. 2, a hollow carbon electrode having an outer diameter of 10 mm and an inner diameter of 4 mm was used as the anode electrode 11, and a columnar carbon electrode having a diameter of 35 mm was used as the cathode electrode 2A. While rotating the cathode electrode 2A, the anode electrode (hollow electrode) 11 was moved linearly in the axial direction of the cathode electrode 2A, and the cathode spot was moved in a spiral on the cathode electrode 2A. The rotation speed of the cathode electrode 2A is 1.5 rotations / minute, and the movement speed of the anode electrode (hollow electrode) 11 is 35 mm / minute. The arc discharge was performed at atmospheric pressure and in the atmosphere, and pure argon gas was used as the gas fed from inside the hollow electrode, and the flow rate was 1 liter / minute. The discharge conditions were a current of 100 A and a voltage of 20 V (arc length about 1 mm). The carbon material used for the cathode electrode 2A is a carbonaceous carbon material having an electric resistivity of 4200 μΩ · cm.
[0037]
After the arc discharge, a tape-like substance having a width of about 2 to 3 mm and a thickness of about 10 to 100 μm, and a high-purity CNT tape 31A are synthesized at the spiral position where the cathode spot has moved on the cathode electrode 2A, and partially. A phenomenon of spontaneous peeling was observed.
[0038]
In the present embodiment, the synthesized carbon nanotube has an extremely long length, compared to the diameter, and is rounded and intertwined to form a cathode deposit, so that the length is quantitatively determined. It is often difficult to evaluate Then, an external force was applied to the cathode deposit to tear it off, and the length of the stretched carbon nanotube at the broken portion was observed with a scanning electron microscope (SEM).
FIG. 3 shows a scanning electron microscope (SEM) photograph of the torn and stretched carbon nanotubes.
It is considered that the carbon nanotube at the end was stretched almost linearly by an external force and cut. As for the length of the cut carbon nanotube, there is a length exceeding 50 μm even in a portion that can be identified as one carbon nanotube, and a similar thing is observed at both ends of the broken portion, The actual length may be as long as 50 μm or more, that is, 100 μm or more.
In the second embodiment, the high-purity CNT tape 31A continuously synthesized in a spiral shape can be spontaneously or easily separated from the surface of the cathode electrode 2A as described above, and the continuity of the carbon nanotube fibers can be improved. You can expect. Substantially, in the second embodiment, the high-purity CNT tape 31A can be continuously produced without cutting the cathode electrode 2A for about 1/2 to 3 circumferences. Therefore, the ratio between the length and the diameter of the carbon nanotube synthesized in the second embodiment (hereinafter referred to as “aspect ratio”) and the ratio K of the carbon nanotube in the first embodiment to the aspect ratio of about 3000 to 20,000 can be generated. If it is assumed that the ratio of the continuous length is small, it is recognized that there is a possibility that the ratio becomes about 10 to 100 times.
Further, the aspect ratio in the present embodiment can be greatly increased and improved by appropriately selecting the synthesizing conditions. In addition, with respect to the above-described relative movement, the concentrated arc angle is inclined by a predetermined angle in the moving direction and synthesized. By doing so, a more preferable increase can be achieved.
Furthermore, the relative movement can be easily performed on a flat surface in combination with the above-mentioned releasability feature.
[0039]
[Embodiment 3]
FIG. 4 is an explanatory diagram showing a method for synthesizing carbon nanotubes in the third embodiment. In the figure, the same portions as those in FIG. 2 of the second embodiment described above are denoted by the same reference numerals. Omitted.
In FIG. 4, an alternating current 5 was applied to the cathode electrode 2A, and the cathode electrode 2A was preheated to 500 ° C. to 2000 ° C. Other synthesis conditions are the same as those in the second embodiment. As a result of the synthesis according to the present embodiment, the synthesis amount of the tape-shaped carbon could be greatly increased.
[0040]
FIG. 5 shows a photograph of the appearance of the tape-like substance synthesized in the third embodiment. As can be seen from FIG. 5, the synthesized tape-like material is a film-like material having a millimeter-size spread, has flexibility to flex flexibly, and has sufficient strength for handling.
[0041]
FIG. 6 shows an SEM photograph of the cathode deposit synthesized in the third embodiment. In FIG. 6, the synthesized cathode deposit is almost entirely composed of long carbon nanotubes, and the length is almost 10 μm compared to the case of the stationary arc in the first embodiment shown above. In some cases, the length K exceeds 20 μm, and the ratio K of the aspect ratio to the aspect ratio in the first embodiment is 20 depending on the production conditions, in combination with the characteristic of the releasability of the product. It is expected that this could be up to 300 times.
[0042]
FIG. 7 shows a TEM photograph of carbon nanotubes that are constituents of the tape-like substance synthesized in the third embodiment.
As can be seen from FIG. 7, the synthesized carbon nanotube shows a coaxial multiplex structure with a substantially complete graphene cylinder. Further, as a result of detailed investigation, the diameter was 4 to 30 nm, and the diameter of 4 to 15 nm occupied almost 90% of the whole.
FIGS. 8A and 8B are explanatory views of the carbon nanotube tip structure and the solid structure of FIG.
FIG. 8A shows a structure in which the graphene tube at the tip of the carbon nanotube is completely opened, and FIG. 8B shows a structure in which the graphene tube at the outer peripheral portion of the tip of the carbon nanotube is open and the graphene tube is clogged to the inside. It was observed that these were mixed.
[0043]
As described above, in the present invention, since the long carbon nanotubes having excellent crystallinity and having a length exceeding 10 μm are densely synthesized in large quantities, they have the flexibility as shown in FIG. It is believed that a long tape material in the form of a thin film could have formed.
[0044]
Conventionally, aggregates of only carbon nanotubes are obtained in the form of powder, lump, or sponge.However, without using impurities or binders, or without using a method such as synthesis on a substrate, high-purity carbon It has not been possible to form a nanotube as a thin film substance having a thickness of millimeter size and with sufficient strength for use.
On the other hand, the carbon nanotubes of the present invention are excellent in crystallinity and are made of high-purity carbon nanotubes, including long ones that are considered to have a length exceeding 10 μm. Was realized for the first time.
[0045]
【The invention's effect】
The carbon nanotube of the present invention has the following effects.
1. By synthesizing carbon nanotubes with good crystallinity and a long length, high-purity carbon nanotubes can be formed as thin and millimeter-sized film-like materials without using impurities or binders. It became so. Since this film-like substance has flexibility and sufficient strength for use, it is easy to handle and can be easily used for a wide range of uses such as an electron emission source, a sensor or a functional separation membrane.
2. The crystallinity of the present invention is good, and by using a long carbon nanotube mixed with a resin or metal, etc., even if mixed in the same amount as compared with the conventional short carbon nanotube, the conductivity, strength and thermal conductivity, etc. are improved. Shows excellent properties.
[0046]
3. Due to the characteristics of the present invention, which is a carbon nanotube having a small diameter and a long length, the following can be considered as specific utilization techniques.
(A) Due to the properties of the carbon nanotubes, which are excellent in fine bundle and crystallinity, they can be used as a field emission electron source for cathode materials such as a fluorescent display tube and a field emission display (FED) and a probe of an electron microscope. Use,
(B) By using this carbon nanotube as an electron source, an efficient ion and ozone generator can be created, and the deodorizing and deodorizing effects of these ions and ozone, especially the psychological and physiological aspects of humans due to negative ions. Good ripple effect on the
In addition, it is desirable that the diameters of (a) and (b) are small.
(C) The high strength due to the excellent crystallinity of the carbon nanotubes theoretically has a tensile strength 100 times or more higher than that of iron, and the specific gravity is about half that of aluminum. Providing light and high-strength structural materials by combining and compounding.
[0047]
(D) In addition, the present carbon nanotube has a relatively uniform, thin and long shape, and is used as a structural member of a micromachine or a component of an actuator.
(E) Because the carbon nanotubes have excellent conductivity, they can be used as wiring materials for ICs, and when mixed with resins and fibers, these materials can be made conductive or charged with static electricity. To have a prevention function, use for conductive coatings and conductive ink mixed in paint,
In addition, these materials are not only used for members requiring conductivity, but also used as electromagnetic wave absorbing / shielding materials based on electromagnetic wave reflection loss and dielectric loss,
[0048]
(F) In addition, by being mixed with the negative electrode material of the secondary battery, the aging of the negative electrode conductivity can be prevented,
(G) Furthermore, by mixing the grease with the grease, the grease has conductivity, and measures for preventing the performance of the grease from deteriorating at the current-carrying portion are provided.
(H) Having thermal conductivity higher than that of diamond, it can be used as a heat radiating material for ICs and the like.
(I) Applying or pasting to the surface of an aluminum plate or the like to apply it to a member with a large heat radiation property;
(U) The carbon nanotubes, which are extremely small structures of nano size, are also used as materials for electronic components such as diodes and transistors utilizing quantum effects and quantum dots which are basic elements of quantum computers.
[0049]
4. The carbon nanotube of the present invention has the following utilization effects as an aggregate thereof.
(A) A carbon nanotube aggregate in which a relatively uniform nano-sized carbon nanotube having a long diameter and a long length is intricately intertwined has a certain space determined by the density of the carbon nanotube aggregate. Use as a filter or separation membrane to sort out substances with
(B) In addition, the surface area per unit weight exceeds that of activated carbon, and it is used as an adsorbent for harmful substances and a gas storage material for hydrogen and methane.
(C) Use as a functional material such as a gas sensor that detects a specific gas,
(D) Further, by using the catalyst as a support material, the efficiency of various chemical reactions can be improved,
(E) Further, in the medical field and the like, it is used as a carrier for adsorbing and holding a drug or the like and transporting it to a lesion in a body, and as an electrode material of a capacitor.
[Brief description of the drawings]
FIGS. 1 (a) and 1 (b) show scanning electron microscope (SEM) photographs of carbon nanotubes synthesized in the first embodiment.
FIG. 2 is an explanatory diagram illustrating a method for synthesizing carbon nanotubes according to a second embodiment.
FIG. 3 shows a scanning electron microscope (SEM) photograph of a torn and stretched carbon nanotube.
FIG. 4 is an explanatory diagram showing a method for synthesizing carbon nanotubes in a third embodiment.
FIG. 5 shows an appearance photograph of a tape-like substance synthesized in Embodiment 3.
FIG. 6 shows an SEM photograph of a synthesized tape-like substance according to the third embodiment.
FIG. 7 shows a TEM photograph of carbon nanotubes that are constituents of a tape-like substance synthesized in Embodiment 3.
8 (a) and 8 (b) are explanatory diagrams of the carbon nanotube tip structure and the solid structure of FIG. 7;
9 schematically shows a state of a hexagonal mesh plane on the side wall of the carbon nanotube. FIG. 9 (a) shows a state of the carbon nanotube by the arc method, and FIG. 9 (b) shows a small mesh plane. 9C shows a state where the layers are intermittently connected, FIG. 9C shows the absence of a layer in the middle of the length direction, and FIG. 9D shows a state where the layers are staggered.
[Explanation of symbols]
2A cathode electrode, 3 arc, 31A high purity CNT tape, 11 anode electrode, 5 AC power supply.

Claims (13)

A carbon nanotube having a length exceeding 10 μm, which is synthesized by an arc discharge method. The carbon nanotube according to claim 1, wherein the cylinder made of graphene has a coaxial multilayer structure. A carbon nanotube, wherein the tube made of graphene is a carbon nanotube having a coaxial multi-layer structure, the tube is densely stacked up to the center thereof, and has a length exceeding 10 μm. A carbon nanotube, wherein the cylinder made of graphene has a coaxial multi-layer structure, a carbon nanotube having an outermost diameter of 4 to 30 nm, and a length exceeding 10 μm. The tube made of graphene has a coaxial multilayer structure, the outermost diameter is a carbon nanotube with a diameter of 4 to 30 nm, the tube is densely stacked to the center, and has a length exceeding 10 μm. Carbon nanotube. A carbon nanotube characterized in that at least one or both ends of one or both ends of the carbon nanotube are open at least partially or entirely in a cylinder made of graphene. The carbon nanotube according to any one of claims 3 to 6, wherein the carbon nanotube is synthesized by an arc discharge method. By performing an arc discharge between the carbon material and the anode electrode as a cathode, when synthesizing a carbon nanotube, the cathode carbon material is synthesized using a material whose material is mainly carbonaceous. The carbon nanotube according to claim 1. When a carbon nanotube is synthesized by performing arc discharge between a carbon material as a cathode and an anode electrode, the cathode carbon material has an electric resistance of 3500 μΩ / cm or more or a thermal conductivity of 52 W / mK or less. The carbon nanotube according to claim 1, wherein the carbon nanotube is synthesized using a carbon nanotube. 8. The carbon nanotubes are synthesized by shifting the relative positions of the cathode and the anode when synthesizing the carbon nanotubes by performing an arc discharge between the anode and the carbon material as a cathode. 10. The carbon nanotube according to any one of items 1 to 9. When carbon nanotubes are synthesized by performing arc discharge between the anode electrode and the carbon material as a cathode, the entire cathode material or the arc discharge portion of the cathode carbon material is preheated and then synthesized. Item 11. The carbon nanotube according to any one of Items 1, 2, 7 to 10. When a carbon nanotube is synthesized by performing an arc discharge between a carbon material as a cathode and an anode electrode, an inert gas such as an argon gas or an inert gas supplied from the inside of the hollow anode electrode toward the cathode electrode when synthesizing the carbon nanotubes. The carbon nanotube according to claim 1, wherein the carbon nanotubes are synthesized while generating an arc along a flow of a mixed gas containing an active gas. The carbon nanotube according to claim 1, wherein the carbon nanotube is synthesized by causing an arc discharge to be performed in an air atmosphere.

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