Wiadomości Chemiczne

Fullerenes and Carbon Nanotubes, 1998

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  1. Fullerenes. I. Characteristics of Production Techniques
    Andrzej Huczko, Przemysław Byszewski

  2. Fullerenes. II. Characteristics of Formation Mechanisms
    Andrzej Huczko, Przemysław Byszewskii

  3. Carbon Nanotubes. I. Characteristics of Production Techniques
    Andrzej Huczko, Przemysław Byszewski

  4. Carbon Nanotubes. II. Characteristics of Formation Mechanisms
    Andrzej Huczko

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FULLERENES. I. CHARACTERISTICS OF PRODUCTION TECHNIQUES

Andrzej Huczko1, Przemysław Byszewski2

1Pracownia Chemii Plazmy, Wydział Chemii, Uniwersytet Warszawski, ul. Pasteura 1, 02-093 Warszawa
2Instytut Fizyki PAN, al. Lotników 32/46, 02-668 Warszawa
2Instytut Technologii Próżniowej ul. Długa 44/50, 00-241 Warszawa


The discovery in mid eighties of fullerenes (C60, C70,..) [1] -a new third allotropic form of carbon the discoverers of which were awarded with the Nobel Prize in Chemistry in 1996 - initiated the subsequent explosive development of this new field of physics and chemistry of carbon. Various perspective applications of fullerenes make the subject of the efficient synthesis of C60 and its homologues increasingly the important one. In the paper a review of various methods of synthesis of fullerenes is presented with special emphasis on the most popular techniques. Brief discussions of current methods are also included. Synthesis of fullerenes was first accomplished by laser sublimation of graphite in an inert gas atmosphere by Curl, Smalley and Kroto [1, 6] - Fig. 1. However, this technique did not provide for the production of gram quantities of C60. Efforts to scale-up this approach were unsuccessful and other methods were later developed. These included e.g. resistive heating (Fig. 3) or arcing (Fig. 4-6) of graphite [13-15, 23-57], combustion of hydrocarbons in sooting flames [61-71], thermal [73-76, 78-79] and non-thermal [77, 80-85] plasma pyrolysis of coals and hydrocarbons, carbon sublimation in a solar furnace - Fig. 7 [89-92] and thermal decomposition of hydrocarbons [93-97]. Those various techniques which can produce fullerenes are described in detail but the carbon electric arc approach, mastered by Krätschmer and Huffman in 1990 [14, 23], is currently the winner in the competitions for maximum production rate, cost and ease of implementation. Thus it still remains the only commercial method of fullerene production.


Fullerenes and Carbon Nanotubes, 1998, 5.
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FULLERENES. II. CHARACTERISTICS OF FORMATION MECHANISMS

Andrzej Huczko1, Przemysław Byszewski2

1Pracownia Chemii Plazmy, Wydział Chemii, Uniwersytet Warszawski, ul. Pasteura 1, 02-093 Warszawa
2Instytut Fizyki PAN, al. Lotników 32/46, 02-668 Warszawa
2Instytut Technologii Próżniowej ul. Długa 44/50, 00-241 Warszawa


The discovery of fullerenes still presents a mechanistic puzzle to physical and organic chemists: How can such highly ordered compounds form in significant yields in the entropic conditions of graphite sublimation and out of the chaos of condensing carbon vapour? To make the subject more complex the fullerenes can be formed under quite differentiated conditions, e.g. not only in hot carbon vapours but also in the oxidative atmosphere of sooting flames. In this paper several mechanisms for fullerene formation are presented and critically discussed, both on the basis of theoretical considerations - Fig. 1, 4-6 [3-15] and experimental results [22, 45, 48, 54, 60]. The first, "pentagon road" (Fig. 11), was proposed by Smalley [61, 62], who believes that the fullerene molecule is produced by the growth of open sheets of pentagons and hexagons. Heath [64] proposed an alternative "fullerene road" scheme (Fig. 13) in which fullerenes are formed in the size range of 30 - 40 carbon atoms and grow by addition of small carbon radicals. In other mechanisms, fullerene is formed by the six-fold combination of napthalenic C10 units - Fig. 14 or the growth starts with the combination of a C10 radical with a ring C18 [65-71]. There is no evidence ruling out any of the proposed schemes and a clear choice between them does not seem possible with the available information [77, 79]. Thus, a successful approach toward the understanding of the fullerene formation process is still sought.


Fullerenes and Carbon Nanotubes, 1998, 23.
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CARBON NANOTUBES. I. CHARACTERISTICS OF PRODUCTION TECHNIQUES

Andrzej Huczko1, Przemysław Byszewski2

1Pracownia Chemii Plazmy, Wydział Chemii, Uniwersytet Warszawski, ul. Pasteura 1, 02-093 Warszawa
2Instytut Fizyki PAN, al. Lotników 32/46, 02-668 Warszawa
2Instytut Technologii Próżniowej ul. Długa 44/50, 00-241 Warszawa


Carbon nanotubes are the novel nanostructures (Fig. 1) discovered in 1991 by Iijima [4] in cathode deposits, formed during the process of electric arc synthesis of fullerenes (Fig. 3-7). Their amazing mechanical and electronic properties [10-24] prompted extensive experimental and theoretical studies with the number of publications rapidly approaching the one for the fullerenes. This is mostly due to the exciting prosperous applications of carbon nanotubes, mostly in material science [10-13] and electronics [15-24]. Nanotubes can be produced now routinely and in this paper the main methods of their synthesis are presented. Two basic approaches - carbon arc plasma synthesis (Fig. 3) [4, 50-57] and catalytic decomposition of hydrocarbons [102-107] - are disscussed with emphasis on both the production of single-wall and multi-wall nanotubes. Some other techniques are also mentioned, e.g. laser sublimation of graphite (Fig. 9) [108, 109], thermal [110] and non-thermal [111, 112] plasma pyrolysis of hydrocarbons, solar furnace [113], low-pressure condensation of carbon vapours [20, 114, 115], thermal decomposition of hydrocarbons [116-119] and electrolysis of molten salts (Fig. 10) [120, 121]. However, the presented methods still exibit their inherent limitations related mostly to the low yield. The produced material is also not homogeneous - nanotubes are not aligned and contain carbon debris. Thus, the efficient technique for the large-scale production of pure single-wall and aligned carbon nanotubes is still sought.


Fullerenes and Carbon Nanotubes, 1998, 45.
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CARBON NANOTUBES. II. CHARACTERISTICS OF FORMATION MECHANISMS

Andrzej Huczko

Pracownia Chemii Plazmy, Wydział Chemii, Uniwersytet Warszawski, ul. Pasteura 1, 02-093 Warszawa


Any prosperous application of carbon nanotubes will be undoubtedly related to the subject of their efficient formation in order to lower their production costs. This, however, won't be achieved unless the formation mechanism of nanotubes is not well understood. In the paper several models of carbon nanotube formation are des-cribed, mostly related to an arc or catalytic techniques applied. Also, the theoretical considerations (Fig. 3) [18-23] are presented. Regarding the electric arc an "open-end" model of growth was postulated (Fig. 4) [24, 25]. Smalley [23, 28-31] put a strong emphasis on the electronic behaviour of the tube's cap - Fig. 5. According to Dravid [34] graphite nanosheets are transformed into nanotubes in an arc zone - Fig. 7. Many other mechanisms were further proposed from the experi-mental observations [35-39], e.g. Gamaly and Ebbesen [40] considered the nano-tube formation as the result of isotropic and anisotropic transport of carbon species within the arc zone. Regarding the catalytic formation of single-wall nanotubes the proposed mechanisms can be applied both to arc plasma and hydrocarbon pyrolysis. The catalyst morphology seems to play a crucial role in the process - Fig. 11 [48-50]. Smalley [52-55] suggested the "scooter mechanism" with the atom of catalyst annealing the dangling bonds at the tube's cap - Fig. 12. According to Setlur [59] poliaromatic compounds may be important in the formation of carbon nanostructures, including nanotubes - Fig. 15. Despite the various approaches we are still far from a full and self-consistent description of the processes leading to both single-wall and multi-wall carbon nanotube formation. It may also well be that the univocal mechanism of their formation simply does not exist at all [8].


Fullerenes and Carbon Nanotubes, 1998, 67.
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