Institute of Physics Publishing doi:10.1088/1742-6596/26/1/032
Journal of Physics: Conference Series 26 (2006) 135–138 EMAG–NANO 05: Imaging, Analysis and Fabrication on the Nanoscale
Synthesis of carbon nanotubes on alumina-based supports with different gas flow rates by CCVD method R Aghababazadeh 1, A R Mirhabibi1, 2, H Ghanbari2, K Chizari1, R M Brydson3 and A P Brown3 1
Iran Colour Research Centre, No.32, Afshari Street, Hemmat Highway Junction, Tehran, Iran 2
Materials and Metallurgy Department, Iran University of Science and Technology, Hengam Street, Narmak, Tehran, Iran 3
Institute for Materials Research, University of Leeds, Leeds, LS2 9JT,UK
Email:
[email protected] Abstract. Several methods for the synthesis of carbon nanotubes have been developed in the last decade. The CVD process and their associated parameters affect the structure of the resulting nanotubes. In this work CNT growth has been studied on different supported catalysts with different rates of gas flow as one of the critical points. Different supports were prepared by mixing nanosized alumina with tetraethyl orthosilicate (TEOS) by a chemical method at low temperature and iron as the metal catalyst was impregnated by 5%, 10% and 20% weight of the supports. Methane was used as a carbon source for the synthesis of CNTs at 800°C-1000°C. Aluminium-based support, supported catalysts and CNT samples have been characterised by TEM, SEM, BET and XRD.
1. Introduction Carbon nanotubes (CNTs) are a new class of materials, containing of small tubules formed by rolling graphitic sheets discovered by Iijima in 1991 [1, 2]. These novel materials have been extensively investigated in the past few years because of their unique structure, excellent mechanical properties and promising electronic characteristics and so are predicted to have great future potential in science and industrial applications [3]. Production of nanotubes has been experienced by various methods. The Catalytic Chemical Vapor Deposition (CCVD) technique appears to be a promising method for utilization on the industrial scale since it leads to large yields of carbon nanotubes at low cost of production compared to other synthesis methods such as Arc-Discharge and Laser Vaporisation [4,5,6]. SWNT growth by the CCVD method is affected by the catalyst (composition, type of support and nature of the metal), and carbon source [6]. 2. Experimental 2.1. Support Preparation For preparing S1 supports, nanoparticles of Alumina (γ-δ from Degussa) was suspended in ethanol. Then TEOS (Tetraethyl Orthosilicate, C8H20O4Si, Merck ) was added to the suspension and stirred for © 2006 IOP Publishing Ltd
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15 min. After hydrolysing the TEOS with DI water, HNO3 was introduced to the mixture. After stirring the mixture it was heated under 90˚C, dried and ground in mortar agate and passed through a 400 mesh sieve to remove coarse aggregates. The molar ratios of the compounds TEOS: Al2O3: HNO3: H2O: Ethanol =1: 1: 1.38: 27.76: 85.74. 2.2. Catalyst Preparation Catalysts were made by introducing Fe2SO4.5H2O (Aldrich, 97%) with 5%, 10% and 20% weight of S1 to the support. For impregnating the supports with iron, Fe2SO4.5H2O was added to the S1 which had been suspended in water. The mixture was stirred for 15 min and heated at 90˚C for 2h. The dried powder was ground in an agate mortar and passed through a 400 mesh sieve to remove coarse aggregates. The molar ratios were Fe: Al2O3:SiO2 = 1:16:16. 2.3. CNT Production Production of CNTs was carried out in a horizontal flow furnace at 900˚C in nitrogen atmosphere (99.999% purity) by the catalytic reaction of methane (99.99% purity) on an as-prepared catalyst in a fixed bed reactor. After passing nitrogen, methane was passed over the catalyst bed for 30 min with a flow rate of 4, 6 and 8 l/min and again nitrogen was passed over the reacted catalysts in the considered flow rate until cooling of the furnace to room temperature. 2.4. Characterisation The supports, supported catalysts and grown CNTs were investigated by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and X-Ray Diffraction (XRD). Also the surface area and densities of the samples were measured. 3. Results and Discussion 3.1. Support characterisation An XRD pattern of the support showed that a hybrid of Alumina and silica was formed by this method. The study of the pore structure of the support (S1:Al2O3-SiO2) by the BET method with N2 shows a mixture of type I and IV of characteristic adsorption isotherms (Figure 1). The knee shape of the graph at low p/p˚ indicates small amount of micropores and the hysteresis indicates the existence of mesopores [9]. The surface area of the support by the BET method was determined to be about 2 351.6 m /g. Average pore diameter is 52.8Å. The support density and surface area are shown in Table 1. These results are rather complicated to be judged by the BET data, therefore it seems further studies need to be followed for clarification of these results. Table 1. Densities and surface areas of supports, catalysts and nanotubes S1
S1C5
S1C10
S1C20
S1C10NTF6
S1C10NTF8
3
Density (g/cm )
2.44 2.50 2.50 2.51 – – 351.6 – 21.7 – 57.9 63.3 F stand for flow rate and the subscript shows the rate in l/min. C stand for concentration of the catalyst and the corresponding subscript shows the weight%. NT stand for the prepared nano tube. 2
Surface area (m /g)
3.2. Supported catalyst characterisation An XRD pattern of the supported catalyst shows the presence of Fe2O3 besides the alumina and silica. 2 The surface area of the sample with 10% weight of iron (S1C10) was 21.7 (m /g). The densities of the catalysts are shown in Table 1.
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Figure 1. Isotherm plot of the support(S1)
SEM micrographs of the samples with 10% (S1C10) and 20% weight of iron (S1C20) are shown in figure 2. As can be seen these catalysts are not homogenised catalysts but EDX from different parts of the samples showing the presence of iron element on the support.
(a)
(b)
Figure 2. SEM picture (SE mode) of the supported catalyst by (a) 10 % (b) 20% weight of
iron. 3.3. Nanotube characterisation Figure 3 shows the SEM pictures of the as-synthesised carbon material. SEM pictures of carbon filaments which are grown on the catalysts with 10% weight of iron at flow rates of 4, 6 and 8 l/min (S1C10NTF4) (S1C10NTF6) (S1C10NTF8) and 20% weight of iron at flow rates of 4 and 6 l/min (S1C20NTF4) (S1C20NTF4) are shown in figure 3. It can be seen that the grown nanotubes on the S1C10 catalysts at different gas flow rate are longer than on the S1C20 catalysts. No filaments were seen on the S1C20 at a flow rate of 8 l/min.
(a)
(d)
(b)
(e)
(C) Figure 3. SEM figures of nanotubes on different supports by various flow rates. (a)S1C10NTF4 (b)S1C10NTF6 (c)S1C10NTF8 (d)S1C20NTF4 (e)S1C20NTF6
The TEM images of the supported catalyst with 5% and 10% weight of iron subjected to methane treatment are shown in Fig. 4. These figures revealed that the carbon filaments in SEM images are
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nanotubes. Also amorphous carbon can be detected on the walls of the tubes. Figure 4.c shows the mapping of iron enclosed by nanotubes (white regions). A comparison of the TEM images of the multiwall nanotubes which are grown on impregnated support by 5% and 10% weight of iron with the same flow rate of methane indicated that the nanotubes on the second catalyst (S1C20NT) are thicker than the first group of synthesised nanotubes (S1C10NT). Surface areas of the samples are shown in Table 1. Surface area data revealed that an increase of the rate of gas flow increases the yield of production.
(a)
(b)
(C)
Figure 4. TEM pictures of the Nanotubes in (a) S1C5NTF6, (b) S1C10NTF6 and (c) mapping of iron as a
seed of the nanotubes in S1C10NTF6 4. Conclusions Because of the less time of contact between the gas and catalyst the decrease of nanotube growth can occur due to decreasing of flow rate of methane. By increasing the amounts of iron the number of walls of tubes increases and the length of tubes decreases. 5. References [1] Nagy P, Mikl´osi J, P´oczik P, Papp K, Konya Z, Kiricsi I, P´alinkas G, K´alm´an E., Appl Phys A 2001 [2] Iijima S., Nature 1991; 354-56 [3] Tae Young Lee, Jae-Hee Han, Sun Hong Choi, Ji-Beom Yoo, Chong-Yun Park, Taewon Jung, SeGi Yu, W.K. Yi, I.T. Hanb, Kim J M., Diamond and Related Materials 2003; 12: 851-855 [4] Kong J, Cassell A.M, Dai H., Chemical Physics Letters 1998; 292 (N4-6):567-574 [5] Sinha Anil K, Hwang Dennis W, Hwang Lian-Pin., Chemical Physics Letters 2000; 332:455460 [6] Liu B.C, Lyu S.C, Jung S.I, Kang H.K., Yang C.-W, Park J.W, Park C.Y, Lee C.J., Chemical Physics Letters 2004; 383: 104-108 [7] Young Joon Yoon, Jun Cheol Bae, Hong Koo Baik, Seong Jin Cho, Se-Jong Lee, Kie Moon Song, No Seung Myung., In CVD process Physica B 2002; 323:318–320 [8] Cassell M, Jeffrey A, Raymakers A, Jing Kong, Hongjie Dai., J Phys Chem. B 1999; 103: 64846492 [9] Gregg J S and Sing K S W 1982 Adsorption, Surface Area and Porosity (London:Academic Press Inc) chapter 3 pp111-160
EMAG–NANO 2005: Imaging, Analysis and Fabrication on the Nanoscale - Abstract - Journal of Physics: Conference Series - IOPscience
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Paul D Brown and Richard Palmer 2006 J. Phys.: Conf. Ser. 26doi:10.1088/1742-6596/26/1/E01
EMAG–NANO 2005: Imaging, Analysis and Fabrication on the Nanoscale Paul D Brown and Richard Palmer
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PREFACE The biennial conference of the Electron Microscopy & Analysis Group (EMAG) was this year co-hosted with the Nanoscale Physics and Technology (NPT) Group of the Institute of Physics and held at The University of Leeds from 31 August to 2 September. The conference attracted 151 delegates from 16 countries. As part of the "Einstein" International Year of Physics, the conference focused on the dominant themes of Imaging, Analysis and Fabrication on the Nanoscale. EMAG and NPT co-organised the scientifc programme, allowing three parallel sessions to run along the lines of (1) Microscopy techniques for nanotechnology; (2) Investigating structure-property relationships in advanced materials; and (3) Nanophysics and nanotechnology. Indeed, one of the motivations for running this conference series has been to encourage and develop the next generation of research scientists, to help maintain the UK's international profle in the areas of microscopy, analysis and innovation in micro- and nanotechnology. In this context, EMAG provided bursaries to cover the registration fees for 25 research students to help meet their costs of attending this event. In addition to the 4 plenary lectures, there were 13 invited oral presentations and 77 contributed oral papers that ran in three parallel sessions. Furthermore, 44 posters were presented throughout the three days. These proceedings comprise 90 papers, beginning with a plenary paper, followed by the invited and contributed oral papers ordered chronologically by session as they appeared during the conference. The collated poster papers are then presented. The papers were submitted in advance of the conference, both electronically in Word and .pdf formats, and in hard copy camera ready format. Each paper was reviewed by two referees. We are indebted to the efforts of the many delegates who kindly provided their valuable time to help in this process. Without their efforts it would not have been possible to produce these proceedings so promptly. We hope that readers of these proceedings will see this volume as a valuable snapshot of microscopy, microanalysis and nanoscale physics and technology in the UK at the time of writing.
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In time honoured tradition, an Advanced School preceded the conference, with tutorial lectures on Imaging in the Electron Microscope; Analysis in the Electron Microscope; STM and Nanostructured Surfaces; and Functionality of Nanoscale Solids, to help research students gain a wider appreciation of the keynote scientifc issues and to provide a background to the detailed conference themes. In addition, a Trade Exhibition was fully integrated into the conference site in the University Sports Hall, within close walking distance of the lecture theatres, giving delegates the opportunity to discuss recent developments in analytical instrumentation. In keeping with the previous EMAG 2003 conference at Oxford University, provision was made for commercial workshops for the promotion of products by the manufacturers and 'question and answer' sessions. The companies on show spanned the range of mainstream electron and scanning probe instrument makers, combined with a broad spectrum of smaller companies providing ancillary equipment, from services for sample preparation to vacuum system support. As ever, we are grateful to the exhibitors and sponsors for their valued contribution to this conference series. Finally, we are extremely grateful for the many people who helped with the running of this conference. On behalf of both the EMAG and NPT groups we'd like to take the opportunity to thank the local organising committee of Rik Brydson, Andy Brown, John Harrington and Andy Scott. Our thanks also to Dave McComb and Bruce Hamilton for collating the scientifc programme, to Stephen Donnelly for co-ordinating the award of student bursaries, and to Richard Baker and Bruce Hamilton for guiding the editing of the proceedings. We'd also like to acknowledge the exceptional contribution of Jill Cowlard and Nicola Deedman of the CEM Group for co-ordinating the Trade Exhibition, and Claire Pantlin and Jasmina Bolfek-Radovani of the IoP without whom there'd be no show on the road! A special thanks also to Jane Lowe of the IoP for her sterling work collating these proceedings!
Paul D Brown, University of Nottingham (EMAG Chair) Richard Palmer, University of Birmingham (NPT Chair)
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