- Email: [email protected]
Conversion of carbon nanotubes to carbon nanofibers by sonication
Letters to the editor / Carbon 40 (2002) 1369 – 1383
gases would have partially mixed, and carbon would have been deposited in both halves of the reactor. Instead, there was a clear boundary at the exit, with carbon deposited in the ethane part of the reactor and the argon portion remaining clean. We conclude that convection was not significant. In their final paragraph, HH suggest that a mass balance be obtained between the reduction in the yield of liquid products and the increase in the yield of carbon, at residence times between 6 and 17 s. This is a useful suggestion, which we intend to explore experimentally. We do not wish to base such a comparison on an estimate. As HH have shown elsewhere [9], the deposition rate is not simply proportional to the surface area. The mechanism of formation of carbon from light hydrocarbons is complicated. The Karlsruhe group and others are making efforts to understand this mechanism. Acetylene or radicals formed from acetylene can form carbon directly, or can form benzene and other aromatics [3,7,10]. Benzene or its radicals can also form carbon or larger aromatics directly [11]. Large aromatics can condense to droplets and deposit on reactor surfaces [8]. Polyynes might also be involved [12]. Metals can catalyse the formation of carbon [13]. Different pathways are likely to dominate under different conditions. Determining the detailed nature of these pathways will provide ample scope for interesting future experiments.
1373
Acknowledgements The authors wish to thank Imperial Oil Limited for a University Research Grant, D. Slim for valuable discussions and C. Cawood for illustrations.
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
Hu Z, Huttinger KJ. Carbon 2002;40: in press. Glasier GF, Filfil R, Pacey PD. Carbon 2001;39:497. Glasier GF, Pacey PD. Carbon 2001;39:15. Hoffmann R, Minkin VI, Carpenter BK. Bull Soc Chim Fr 1996;133:117. Laidler KJ. In: Chemical kinetics, 3rd ed., New York: Harper and Row, 1987, p. 276. Espenson JH. In: Chemical kinetics and reaction mechanisms, New York: McGraw-Hill, 1981, pp. 90–4. Xu X, Pacey PD. Carbon 2001;39:1835. Glasier GF, Pacey PD. Nano Letters 2001;1:527. Hu Z, Huttinger KJ. Carbon 2001;39:433. Becker A, Huttinger KJ. Carbon 1998;36:177. Becker A, Huttinger KJ. Carbon 1998;36:201. Krestinin AV. In: 27th International Symposium on Combustion, 1998, p. 1557. Nemes T, Chambers A, Baker RTK. J Phys Chem B 1998;102:6323.
Conversion of carbon nanotubes to carbon nanofibers by sonication Kingsuk Mukhopadhyay*, Chandra Dhar Dwivedi, Gyanesh Narayan Mathur Defence Materials & Stores Research & Development Establishment ( DMSRDE), DMSRDE Post Office G.T. Road, Kanpur 208013, State UP, India Received 24 July 2001; accepted 14 February 2002 Keywords: A. Carbon nanotubes; Carbon fibers; B. Graphitization; C. Transmission electron microscopy; Ultrasonic measurements
The unusual morphology of tubular derivatives of fullerenes, known as carbon nanotubes (CNTs), has been the subject of much experimental and theoretical research since their discovery [1,2]. However, out of various synthetic procedures for large scale production reported, only the catalytic chemical vapour deposition (CCVD) method is effective for use for CNTs as a practical *Corresponding author. Fax: 191-512-450-404. E-mail address: [email protected] (K. Mukhopadhyay).
material. This is because, apart from the large yield, it produces aligned CNT bundles at much lower temperature, lowering the cost of production [3–12]. To use CNTs as electronic materials their chirality is also important, although it is extremely difficult to control the chirality during the synthesis process [13]. Depending on the chirality, one obtains metallic, semiconducting or even insulating nanotubes. Here we report a systematic study of the effect of sonication time on the structural features of carbon
0008-6223 / 02 / $ – see front matter 2002 Elsevier Science Ltd. All rights reserved. PII: S0008-6223( 02 )00074-X
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Letters to the editor / Carbon 40 (2002) 1369 – 1383
nanotubes. The graphene layers in the nanotubes are destroyed after prolonged sonication and the nanotubes are converted into amorphous carbon nanofibers. During that process semiconductor–insulator junctions might be created in the nanotubes which could be useful for electronic applications. The carbon nanotubes used in this study were prepared by the CCVD method over Fe and Co (each 2.5 wt.%) incorporated in a zeolite support as discussed elsewhere [5,6]. About 1.0 mg of as-prepared carbon nanotube samples were suspended in 10 ml of ethanol and ultrasonicated for 4 h, 8 h and 24 h using an ultrasonicator with a ca. 2 W power delivery. All samples were examined by HREM, solid state UV-Vis spectrometry and solid state FTIR using a KBr pellet. Fig. 1 is a low resolution TEM image of as-synthesized products. It is clearly visible that the tubes are thin and quasi-aligned, having an inner diameter |3–5 nm and external diameter of 12–14 nm. It should be noted that during TEM, as well as electron dispersive X-ray (EDAX) analyses of the tubes, no metal particles have been found either at the base or at the tip of the tubes. Fig. 2 is a series of HREM images showing the
Fig. 1. Low resolution TEM image of as-prepared carbon nanotube bundles. The image shows the quasi-parallel alignment of the nanotubes and illustrates the purity and homogeneity of the sample.
disintegration of the graphene layers as a function of ultrasonication time. Fig. 2a shows the as-prepared sample before sonication. It has 11 concentric graphitic layers with a regular circular shaped inner pore. After 4 h sonication the sample appears as in Fig. 2b, where damage to the regular graphene sheets in Fig. 2a has started and almost one half have been converted into amorphous carbon layers. After 8 h (Fig. 2c) almost all the regular graphene sheets of nanotubes have been converted into amorphous carbon layers, and after 24 h (Fig. 2d) the conversion to an amorphous structure is complete. While the sequence of photographs in Fig. 2 does not follow the same nanotube, the images are representative of the changes taking place. From SEM / TEM observations reported elsewhere [5,6], and also from Fig. 1, it is clear that as-prepared samples contain a very small amount of amorphous carbon, nanoparticles etc. (,5%). Taking advantage of this we have measured the variation of conductivity / resistivity with temperature in both pellet and thin film forms. Preliminary results clearly show the semiconducting nature of the sample. Since amorphous carbon is known to be insulating, after 4 h sonication one could imagine there being a chance for the formation of semiconductor–insulator junctions in the nanotubes. However, detailed studies of resistivity vs. temperature, junction formation characterization and correlation with the morphological features of the nanotubes are currently underway in our group and will be communicated soon. It is known that nanotubes can collapse and be converted to diamond nanocrystals under shock waves [14]. It has also been reported that under high pressure and high temperature (HPHT) treatment both fullerenes and carbon nanotubes can be converted to a diamond-like superhard material [15,16]. A Y-junction in nanotubes has also been reported recently [17]. To our knowledge this is the first report of the progressive conversion of a carbon nanotube to a nanofiber and shows that the creation of semiconducting–insulating junctions by controlled sonication cannot be ruled out in the near future. Solid state UV-Vis and FTIR spectra of all of the samples (unsonicated as well as sonicated) have been measured. In both cases the intensities of the peaks gradually decrease with the increasing sonication time, and hence indicate the conversion of graphitic layers of nanotubes into amorphous carbon layers. For the 24-h sonicated sample almost all the peaks, both UV-Vis and FTIR, have vanished indicating the complete conversion of graphitic layers into amorphous carbon and hence the formation of a carbon nanofiber. Since a greater than 4-h sonication destroys most of the graphitic layers it is now our aim to study sonication between 0 and 4 h in an attempt to control the degree of conversion, and hence possibly control formation of junctions (if any) in the tubes. This work is underway and will be reported in subsequent publications.
Letters to the editor / Carbon 40 (2002) 1369 – 1383
1375
Fig. 2. HREM images of carbon nanotubes: (a) unsonicated showing 11 graphene layers on each side; (b) after 4 h sonication with almost half the graphene layers converted into amorphous carbon layers, hence forming possible semiconductor–insulator junctions; (c) after 8 h sonication with almost complete conversion of graphene layers into amorphous layers; (d) after 24 h sonication, conversion into a carbon nanofiber.
Letters to the editor / Carbon 40 (2002) 1369 – 1383
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Acknowledgements KM is grateful to Prof. Hisanori Shinohara of Nagoya University, Japan for his kind help and cooperation. We are thankful to Mr. K.K. Gupta for doing UV-Vis and to Mrs. Reema Mehrotra and Mr. A.K. Saxena for doing FTIR of the samples.
References [1] Iijima S. Helical microtubules of graphitic carbon. Nature (Lond) 1991;354:56–8. [2] Kukovitsskii EF, Chernozatonkii LA, Lvov SG, Melnik NN. Carbon nanotubes of polyethylene. Chem Phys Lett 1997;266:323–8. [3] Journet C, Maser WK, Bernier P, Loiseau A, Chapelle ML, Lefrant S et al. Large-scale production of single-walled carbon nanotubes by the electric arc technique. Nature (Lond) 1997;388:756–8. [4] Thess A, Lee R, Nikolaev P, Dai P, Petit P, Robert J et al. Crystalline ropes of metallic carbon nanotubes. Science 1996;273:483–7. [5] Mukhopadhyay K, Koshio A, Tanaka N, Shinohara H. A simple and novel way to synthesize aligned nanotube bundles at low temperature. Jpn J Appl Phys 1998;37:L1257– 1259. [6] Mukhopadhyay K, Koshio A, Sugai T, Tanaka N, Shinohara H, Konya Z et al. Bulk production of quasi-aligned carbon nanotube bundles by the catalytic chemical vapour deposition (CCVD) method. Chem Phys Lett 1999;303:117–24.
[7] Terrones M, Grobert N, Olivares J, Zhang JP, Terrones H, Kordatos K et al. Controlled production of aligned-nanotube bundles. Nature (Lond) 1997;388:52–5. [8] Li WZ, Xie SS, Qian LX, Chang BH, Zou BS, Zhou WY et al. Large-scale synthesis of aligned carbon nanotubes. Science 1996;274:1701–3. [9] Rao CNR, Sen R, Satishkumar BC, Govindaraj A. Large aligned-nanotube bundles from ferrocene pyrolysis. J Chem Soc Chem Commun 1998;:1525–6. [10] Ren ZF, Huang ZP, Xu JW, Wang JH, Bush P, Siegal MP et al. Synthesis of large arrays of well-aligned carbon nanotubes on glass. Science 1998;282:1105–7. [11] Nath M, Satishkumar BC, Govindaraj A, Vinod CP, Rao CNR. Production of bundles of aligned carbon and carbon– nitrogen nanotubes by the pyrolysis of precursors on silicasupported iron and cobalt catalysts. Chem Phys Lett 2000;322:333–40. [12] Sen R, Govindaraj A, Rao CNR. Carbon nanotubes by metallocene route. Chem Phys Lett 1997;267:276–80. [13] Mirsky S. Tantalizing tubes. Scientific American 2000;:40– 2. [14] Li Q, Fan S, Han W, Sun C, Liang W. Coating of carbon nanotube with nickel by electroless plating method. Jpn J Appl Phys 1997;36:L501–503. [15] Chow L, Wang H, Kleckley S, Daly TK, Buseck PR. Fullerene formation during production of chemical vapour deposited diamond. Appl Phys Lett 1995;66:430–2. [16] Han W, Fan S, Li Q, Zhang CL. Conversion of nickel coated carbon nanotubes to diamond under high pressure and high temperature. Jpn J Appl Phys 1998;37:L1085–1086. [17] Satishkumar BC, Thomas PJ, Govindaraj A, Rao CNR. Y-junction carbon nanotubes. Appl Phys Lett 2000;77:2530– 2.
Characterization of aramid based activated carbon fibres by adsorption and immersion techniques b ´ S. Villar-Rodil a,b , R. Denoyel a , J. Rouquerol a , A. Martınez-Alonso , b, ´ * J.M.D. Tascon a
` MADIREL ( CNRS-Universite´ de Provence), Site CTM, 26 Rue du 141 eme RIA, 13331 Marseille, Cedex 3, France b ´ , CSIC, Apartado 73, 33080 Oviedo, Spain Instituto Nacional del Carbon Received 2 January 2002; accepted 4 April 2002
Keywords: A. Activated carbon; C. Adsorption, Microcalorimetry; D. Immersion enthalpy, Microporosity
In recent years, there have been a number of studies on the textural properties of aramid-based activated carbon fibres (ACFs). Freeman et al. [1,2] first used aramid fibres as feedstock materials expecting to obtain ACFs with *Corresponding author. Tel.: 134-98-511-9090; fax: 134-98529-7662. ´ E-mail address: [email protected] (J.M.D. Tascon).
distinctive adsorbent properties as a result of the high crystallinity of the precursor. Stoeckli et al. [3] examined the pore structure of steam activated carbon fibres coming from Nomex and Kevlar through adsorption of CH 2 Cl 2 and N 2 O vapours and immersion calorimetry into liquids of different molecular sizes. In one of the authors’ laboratories, Kevlar pulp and Nomex have been activated with CO 2 and studied by N 2 and CO 2 adsorption and
0008-6223 / 02 / $ – see front matter 2002 Elsevier Science Ltd. All rights reserved. PII: S0008-6223( 02 )00114-8
gases would have partially mixed, and carbon would have been deposited in both halves of the reactor. Instead, there was a clear boundary at the exit, with carbon deposited in the ethane part of the reactor and the argon portion remaining clean. We conclude that convection was not significant. In their final paragraph, HH suggest that a mass balance be obtained between the reduction in the yield of liquid products and the increase in the yield of carbon, at residence times between 6 and 17 s. This is a useful suggestion, which we intend to explore experimentally. We do not wish to base such a comparison on an estimate. As HH have shown elsewhere [9], the deposition rate is not simply proportional to the surface area. The mechanism of formation of carbon from light hydrocarbons is complicated. The Karlsruhe group and others are making efforts to understand this mechanism. Acetylene or radicals formed from acetylene can form carbon directly, or can form benzene and other aromatics [3,7,10]. Benzene or its radicals can also form carbon or larger aromatics directly [11]. Large aromatics can condense to droplets and deposit on reactor surfaces [8]. Polyynes might also be involved [12]. Metals can catalyse the formation of carbon [13]. Different pathways are likely to dominate under different conditions. Determining the detailed nature of these pathways will provide ample scope for interesting future experiments.
1373
Acknowledgements The authors wish to thank Imperial Oil Limited for a University Research Grant, D. Slim for valuable discussions and C. Cawood for illustrations.
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
Hu Z, Huttinger KJ. Carbon 2002;40: in press. Glasier GF, Filfil R, Pacey PD. Carbon 2001;39:497. Glasier GF, Pacey PD. Carbon 2001;39:15. Hoffmann R, Minkin VI, Carpenter BK. Bull Soc Chim Fr 1996;133:117. Laidler KJ. In: Chemical kinetics, 3rd ed., New York: Harper and Row, 1987, p. 276. Espenson JH. In: Chemical kinetics and reaction mechanisms, New York: McGraw-Hill, 1981, pp. 90–4. Xu X, Pacey PD. Carbon 2001;39:1835. Glasier GF, Pacey PD. Nano Letters 2001;1:527. Hu Z, Huttinger KJ. Carbon 2001;39:433. Becker A, Huttinger KJ. Carbon 1998;36:177. Becker A, Huttinger KJ. Carbon 1998;36:201. Krestinin AV. In: 27th International Symposium on Combustion, 1998, p. 1557. Nemes T, Chambers A, Baker RTK. J Phys Chem B 1998;102:6323.
Conversion of carbon nanotubes to carbon nanofibers by sonication Kingsuk Mukhopadhyay*, Chandra Dhar Dwivedi, Gyanesh Narayan Mathur Defence Materials & Stores Research & Development Establishment ( DMSRDE), DMSRDE Post Office G.T. Road, Kanpur 208013, State UP, India Received 24 July 2001; accepted 14 February 2002 Keywords: A. Carbon nanotubes; Carbon fibers; B. Graphitization; C. Transmission electron microscopy; Ultrasonic measurements
The unusual morphology of tubular derivatives of fullerenes, known as carbon nanotubes (CNTs), has been the subject of much experimental and theoretical research since their discovery [1,2]. However, out of various synthetic procedures for large scale production reported, only the catalytic chemical vapour deposition (CCVD) method is effective for use for CNTs as a practical *Corresponding author. Fax: 191-512-450-404. E-mail address: [email protected] (K. Mukhopadhyay).
material. This is because, apart from the large yield, it produces aligned CNT bundles at much lower temperature, lowering the cost of production [3–12]. To use CNTs as electronic materials their chirality is also important, although it is extremely difficult to control the chirality during the synthesis process [13]. Depending on the chirality, one obtains metallic, semiconducting or even insulating nanotubes. Here we report a systematic study of the effect of sonication time on the structural features of carbon
0008-6223 / 02 / $ – see front matter 2002 Elsevier Science Ltd. All rights reserved. PII: S0008-6223( 02 )00074-X
1374
Letters to the editor / Carbon 40 (2002) 1369 – 1383
nanotubes. The graphene layers in the nanotubes are destroyed after prolonged sonication and the nanotubes are converted into amorphous carbon nanofibers. During that process semiconductor–insulator junctions might be created in the nanotubes which could be useful for electronic applications. The carbon nanotubes used in this study were prepared by the CCVD method over Fe and Co (each 2.5 wt.%) incorporated in a zeolite support as discussed elsewhere [5,6]. About 1.0 mg of as-prepared carbon nanotube samples were suspended in 10 ml of ethanol and ultrasonicated for 4 h, 8 h and 24 h using an ultrasonicator with a ca. 2 W power delivery. All samples were examined by HREM, solid state UV-Vis spectrometry and solid state FTIR using a KBr pellet. Fig. 1 is a low resolution TEM image of as-synthesized products. It is clearly visible that the tubes are thin and quasi-aligned, having an inner diameter |3–5 nm and external diameter of 12–14 nm. It should be noted that during TEM, as well as electron dispersive X-ray (EDAX) analyses of the tubes, no metal particles have been found either at the base or at the tip of the tubes. Fig. 2 is a series of HREM images showing the
Fig. 1. Low resolution TEM image of as-prepared carbon nanotube bundles. The image shows the quasi-parallel alignment of the nanotubes and illustrates the purity and homogeneity of the sample.
disintegration of the graphene layers as a function of ultrasonication time. Fig. 2a shows the as-prepared sample before sonication. It has 11 concentric graphitic layers with a regular circular shaped inner pore. After 4 h sonication the sample appears as in Fig. 2b, where damage to the regular graphene sheets in Fig. 2a has started and almost one half have been converted into amorphous carbon layers. After 8 h (Fig. 2c) almost all the regular graphene sheets of nanotubes have been converted into amorphous carbon layers, and after 24 h (Fig. 2d) the conversion to an amorphous structure is complete. While the sequence of photographs in Fig. 2 does not follow the same nanotube, the images are representative of the changes taking place. From SEM / TEM observations reported elsewhere [5,6], and also from Fig. 1, it is clear that as-prepared samples contain a very small amount of amorphous carbon, nanoparticles etc. (,5%). Taking advantage of this we have measured the variation of conductivity / resistivity with temperature in both pellet and thin film forms. Preliminary results clearly show the semiconducting nature of the sample. Since amorphous carbon is known to be insulating, after 4 h sonication one could imagine there being a chance for the formation of semiconductor–insulator junctions in the nanotubes. However, detailed studies of resistivity vs. temperature, junction formation characterization and correlation with the morphological features of the nanotubes are currently underway in our group and will be communicated soon. It is known that nanotubes can collapse and be converted to diamond nanocrystals under shock waves [14]. It has also been reported that under high pressure and high temperature (HPHT) treatment both fullerenes and carbon nanotubes can be converted to a diamond-like superhard material [15,16]. A Y-junction in nanotubes has also been reported recently [17]. To our knowledge this is the first report of the progressive conversion of a carbon nanotube to a nanofiber and shows that the creation of semiconducting–insulating junctions by controlled sonication cannot be ruled out in the near future. Solid state UV-Vis and FTIR spectra of all of the samples (unsonicated as well as sonicated) have been measured. In both cases the intensities of the peaks gradually decrease with the increasing sonication time, and hence indicate the conversion of graphitic layers of nanotubes into amorphous carbon layers. For the 24-h sonicated sample almost all the peaks, both UV-Vis and FTIR, have vanished indicating the complete conversion of graphitic layers into amorphous carbon and hence the formation of a carbon nanofiber. Since a greater than 4-h sonication destroys most of the graphitic layers it is now our aim to study sonication between 0 and 4 h in an attempt to control the degree of conversion, and hence possibly control formation of junctions (if any) in the tubes. This work is underway and will be reported in subsequent publications.
Letters to the editor / Carbon 40 (2002) 1369 – 1383
1375
Fig. 2. HREM images of carbon nanotubes: (a) unsonicated showing 11 graphene layers on each side; (b) after 4 h sonication with almost half the graphene layers converted into amorphous carbon layers, hence forming possible semiconductor–insulator junctions; (c) after 8 h sonication with almost complete conversion of graphene layers into amorphous layers; (d) after 24 h sonication, conversion into a carbon nanofiber.
Letters to the editor / Carbon 40 (2002) 1369 – 1383
1376
Acknowledgements KM is grateful to Prof. Hisanori Shinohara of Nagoya University, Japan for his kind help and cooperation. We are thankful to Mr. K.K. Gupta for doing UV-Vis and to Mrs. Reema Mehrotra and Mr. A.K. Saxena for doing FTIR of the samples.
References [1] Iijima S. Helical microtubules of graphitic carbon. Nature (Lond) 1991;354:56–8. [2] Kukovitsskii EF, Chernozatonkii LA, Lvov SG, Melnik NN. Carbon nanotubes of polyethylene. Chem Phys Lett 1997;266:323–8. [3] Journet C, Maser WK, Bernier P, Loiseau A, Chapelle ML, Lefrant S et al. Large-scale production of single-walled carbon nanotubes by the electric arc technique. Nature (Lond) 1997;388:756–8. [4] Thess A, Lee R, Nikolaev P, Dai P, Petit P, Robert J et al. Crystalline ropes of metallic carbon nanotubes. Science 1996;273:483–7. [5] Mukhopadhyay K, Koshio A, Tanaka N, Shinohara H. A simple and novel way to synthesize aligned nanotube bundles at low temperature. Jpn J Appl Phys 1998;37:L1257– 1259. [6] Mukhopadhyay K, Koshio A, Sugai T, Tanaka N, Shinohara H, Konya Z et al. Bulk production of quasi-aligned carbon nanotube bundles by the catalytic chemical vapour deposition (CCVD) method. Chem Phys Lett 1999;303:117–24.
[7] Terrones M, Grobert N, Olivares J, Zhang JP, Terrones H, Kordatos K et al. Controlled production of aligned-nanotube bundles. Nature (Lond) 1997;388:52–5. [8] Li WZ, Xie SS, Qian LX, Chang BH, Zou BS, Zhou WY et al. Large-scale synthesis of aligned carbon nanotubes. Science 1996;274:1701–3. [9] Rao CNR, Sen R, Satishkumar BC, Govindaraj A. Large aligned-nanotube bundles from ferrocene pyrolysis. J Chem Soc Chem Commun 1998;:1525–6. [10] Ren ZF, Huang ZP, Xu JW, Wang JH, Bush P, Siegal MP et al. Synthesis of large arrays of well-aligned carbon nanotubes on glass. Science 1998;282:1105–7. [11] Nath M, Satishkumar BC, Govindaraj A, Vinod CP, Rao CNR. Production of bundles of aligned carbon and carbon– nitrogen nanotubes by the pyrolysis of precursors on silicasupported iron and cobalt catalysts. Chem Phys Lett 2000;322:333–40. [12] Sen R, Govindaraj A, Rao CNR. Carbon nanotubes by metallocene route. Chem Phys Lett 1997;267:276–80. [13] Mirsky S. Tantalizing tubes. Scientific American 2000;:40– 2. [14] Li Q, Fan S, Han W, Sun C, Liang W. Coating of carbon nanotube with nickel by electroless plating method. Jpn J Appl Phys 1997;36:L501–503. [15] Chow L, Wang H, Kleckley S, Daly TK, Buseck PR. Fullerene formation during production of chemical vapour deposited diamond. Appl Phys Lett 1995;66:430–2. [16] Han W, Fan S, Li Q, Zhang CL. Conversion of nickel coated carbon nanotubes to diamond under high pressure and high temperature. Jpn J Appl Phys 1998;37:L1085–1086. [17] Satishkumar BC, Thomas PJ, Govindaraj A, Rao CNR. Y-junction carbon nanotubes. Appl Phys Lett 2000;77:2530– 2.
Characterization of aramid based activated carbon fibres by adsorption and immersion techniques b ´ S. Villar-Rodil a,b , R. Denoyel a , J. Rouquerol a , A. Martınez-Alonso , b, ´ * J.M.D. Tascon a
` MADIREL ( CNRS-Universite´ de Provence), Site CTM, 26 Rue du 141 eme RIA, 13331 Marseille, Cedex 3, France b ´ , CSIC, Apartado 73, 33080 Oviedo, Spain Instituto Nacional del Carbon Received 2 January 2002; accepted 4 April 2002
Keywords: A. Activated carbon; C. Adsorption, Microcalorimetry; D. Immersion enthalpy, Microporosity
In recent years, there have been a number of studies on the textural properties of aramid-based activated carbon fibres (ACFs). Freeman et al. [1,2] first used aramid fibres as feedstock materials expecting to obtain ACFs with *Corresponding author. Tel.: 134-98-511-9090; fax: 134-98529-7662. ´ E-mail address: [email protected] (J.M.D. Tascon).
distinctive adsorbent properties as a result of the high crystallinity of the precursor. Stoeckli et al. [3] examined the pore structure of steam activated carbon fibres coming from Nomex and Kevlar through adsorption of CH 2 Cl 2 and N 2 O vapours and immersion calorimetry into liquids of different molecular sizes. In one of the authors’ laboratories, Kevlar pulp and Nomex have been activated with CO 2 and studied by N 2 and CO 2 adsorption and
0008-6223 / 02 / $ – see front matter 2002 Elsevier Science Ltd. All rights reserved. PII: S0008-6223( 02 )00114-8