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UNIVERSITI PUTRA MALAYSIA
EFFECT OF HYDROGEN FLOW RATE ON THE QUALITY OF CARBON NANOTUBES PRODUCED USING THE FLOATING CATALYST
CHEMICAL VAPOR DEPOSITION METHOD
RAJA NOR IZAWATI RAJA OTHMAN
FK 2007 10
EFFECT OF HYDROGEN FLOW RATE ON THE QUALITY OF CARBON NANOTUBES PRODUCED USING THE FLOATING CATALYST CHEMICAL
VAPOR DEPOSITION METHOD
By
RAJA NOR IZAWATI RAJA OTHMAN
Thesis submitted to the School of Graduate Studies, Universiti Putra Malaysia, in Fulfilment of the Requirement for the Degree of Master of Science
February 2007
DEDICATED TO
MOHD HANY SUAIB
WAN AHMAD NABIL MOHD HANY
WAN NURIN DAMIA MOHD HANY
2
Abstract of thesis presented to the Senate of Universiti Putra Malysia in fulfillment of the requirement for the degree of Masters of Science
EFFECT OF HYDROGEN FLOW RATE ON THE QUALITY OF CARBON
NANOTUBES PRODUCED USING THE FLOATING CATALYST CHEMICAL VAPOR DEPOSITION METHOD
By
RAJA NOR IZAWATI RAJA OTHMAN
February 2007
Chairman: Associate Professor Fakhru’l-Razi Ahmadun, PhD Faculty : Engineering
Well aligned multi walled carbon nanotubes (MWNTs) was successfully synthesized by
floating catalyst chemical vapor deposition method (CVD) involving the catalytic
decomposition of benzene upon the surface of iron particle. Two sources of hydrogen
were employed and varied; H2* that carried benzene vapor and H2** that supplied fresh
hydrogen into the electrical furnace to analyze the effects they had on quantity as well as
the morphology and structure of the produced CNTs. Total hydrogen flow rate was kept
constant to allow constant residence time. Reaction time was also varied to study the
growth rate of the products. The remaining parameters such as reaction temperature
(850°C), ferrocene sublimation temperature (120°C), and mass of ferrocene (200 mg)
were kept constant throughout the reaction. Argon (300 ml/min flow rate) was flown into
the system before reaction to provide an inert atmosphere in the furnace. It was also
flown after reaction to prevent product oxidation. The quantity of CNTs produced was
highest (0.08g) when the reaction time and supply of benzene were maximized (t = 50
min, H2*=350 ml/min, and H2**= 0 ml/min).
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The structure of the selected CNT samples was then further characterized via the means
of Electron Microscopy (SEM, TEM, and HRTEM) as well as X Ray Diffractometer. By
using TEM, measurement of 50 tubes per sample revealed CNTs of outer diameter (OD)
from 5 to 55 nm and inner diameter (ID) from 5 nm to 25 nm for all conditions studied.
At H2* = 150 ml/min, H2** = 250 ml/min, and t = 50 min, mean OD and ID of 18.64 nm
and 4.85 nm with standard deviation of 18.64 nm and 4.85 nm, respectively were
obtained.
XRD results revealed formation of sharp and narrow peaks at around 26° position (2θ),
which confirms the presence of highly crystallized CNTs for all samples. The values of
the intershell spacing of the wall (d002) are between 0.338 nm to 0.342 nm. The values of
full width at half maximum (FWHM) of the peaks of 0.7144, 0.2273, and 0.0200 was
obtained when H2*=350 ml/min, H2*=250 ml/min and H2*=150 ml/min, respectively at
50 min reaction time. The reduction in the FWHM value indicated the CNTs exhibit more
crystalline graphite as more H2** was supplied.
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Abstrak tesis yang dikemukakan kepada Senat Universiti Putra Malaysia sebagai memenuhi keperluan untuk ijazah Master Sains
KESAN ALIRAN GAS HIDROGEN KE ATAS KUALITI NANOTIUB KARBON MELALUI KAEDAH PEMANGKIN TERAPUNG-PENGURAIAN WAP KIMIA
Oleh
RAJA NOR IZAWATI RAJA OTHMAN
Febuari 2007 Pengerusi: Profesor Madya Fakhru’l-Razi Ahmadun, PhD Fakulti: Kejuruteraan
Nanotiub karbon menjajar pelbagai dinding (MWNTs) telah berjaya disintesis dengan
menggunakan kaedah pemangkin terapung-penguraian wap kimia, (floating catalyst
chemical vapor deposition (CVD)) yang melibatkan penguraian bermangkin benzena di
atas permukaan zarah ferum. Dua sumber gas hidrogen telah digunakan dan
dipelbagaikan, H2* yang membawa wap benzene dan H2** yang membekalkan hidrogen
segar ke dalam sistem untuk menganalisa kesan kadar aliran tersebut terhadap kuantiti,
morfologi, dan struktur nanotiub karbon yang terhasil. Masa tindakbalas juga
dipelbagaikan untuk mengkaji kadar pertumbuhan produk. Nilai parameter yang
selebihnya seperti suhu tindakbalas (850°C), suhu pemejalwapan ferosin (120°C), dan
jisim ferosin (200 mg) dikekalkan sepanjang tindakbalas. Gas argon (kadar aliran
sebanyak 300 ml/min) digunakan sebagai gas lengai semasa tempoh pemanasan relau
sebelum tindakbalas dan semasa tempoh penyejukan relau selepas tindakbalas untuk
mengelakkan pengoksidaan produk. Kuantiti maksimum nanotiub karbon (0.08g)
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diperolehi apabila masa tindakbalas dan pembekalan benzena adalah pada tahap
maksimum (t = 50 min, H2*=350 ml/min, dan H2**= 0 ml/min).
Struktur CNT yang terpilih kemudiannya dicirikan dengan menggunakan mikroskopi
electron (SEM, TEM, and HRTEM) dan X Ray Diffractometer. Dengan menggunakan
TEM, pengiraan 50 tiub untuk setiap sampel menunjukkan garis pusat luar (OD) CNT
diperolehi adalah dari 5 ke 55 nm dan garis pusat dalam (ID) CNT dari 5 ke 25 nm untuk
semua keadaan yang dikaji. Pada H2* = 150 ml/min, H2** = 250 ml/min, dan t = 50 min,
purata OD dan ID diperolehi adalah 18.64 nm and 4.85 nm dengan nilai piawai deviation
masing-masing sebanyak 18.64 nm and 4.85 nm.
Keputusan XRD menunjukkan penghasilan puncak yang tajam dan sempit pada posisi
26°, iaitu 2θ. Nilai jarak di antara dinding dalaman (d002) adalah di antara 0.338 nm dan
0.342 nm. Nilai full width at half maximum (FWHM) puncak diperolehi adalah 0.7144,
0.2273, dan 0.0200 apabila H2*=350 ml/min, H2*=250 ml/min dan H2*=150 ml/min,
masing-masing pada masa tindakbalas tertinggi iaitu 50 minit. Pengurangan di dalam
nilai FWHM menunjukkan CNT mempunyai lebih tahap kekristalan grafit apabila lebih
H2** dibekalkan.
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ACKNOWLEDGEMENTS
I am deeply grateful to Allah S.W.T. for giving me the strength and patience that enables
me to complete this study.
I would like to extend my gratitude and appreciation to the supervisory committee;
Chairman, Associate Professor Dr. Fakhru’l-Razi Ahmadun; Committee Members, Dr
Salmiaton Ali and Dr Suraya Abdul Rashid for providing invaluable advice, untiring
assistance, encouragement, motivation, and support that enabled me to complete the
Masters program smoothly and efficiently.
I also wish to thank Universiti Putra Malaysia for financial support.
My heartfelt and sincere appreciation goes to my children; Wan Ahmad Nabil and Wan
Nurin Damia, my parents (Raja Othman Raja Abdul Hamid, Fatimatul Rahni Chik, Suaib
Haron, and Khadijah Abdul Rahman), Ayunda Sanusi, other relatives and friends who
always encouraged and supported me during the study period. Last but not least, my
special thanks to my husband, Mohd Hany Suaib, for his love, constant encouragement,
sacrifices, patience, and understanding that enable me to finish the study successfully.
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I certify that an Examination Committee has met on 14 February 2007 to conduct the final examination of Raja Nor Izawati Raja Othman on her Master of Science thesis entitled “Effect of Hydrogen Flow Rate on the Quality of Carbon Nanotubes Produced Using the Floating Catalyst Chemical Vapor Deposition Method” in accordance with Universiti Pertanian Malaysia (Higher Degree) Act 1980 and Universiti Pertanian Malaysia (Higher Degree) Regulations 1981. The Committee recommends that the candidate be awarded the relevant degree. Members of the Examination Committee are as follows: Robiah Yunus, PhD Associate Professor Faculty of Engineering Universiti Putra Malaysia (Chairman) Thomas Choong Shean Yaw, PhD Associate Professor Faculty of Engineering Universiti Putra Malaysia (Internal Examiner) Tinia Idaty Mohd. Ghazi, PhD Lecturer Faculty of Engineering Universiti Putra Malaysia (Internal Examiner) Subhash Bhatia, PhD Professor Faculty of Engineering Universiti Sains Malaysia (External Examiner)
_________________________________ HASANAH MOHD. GHAZALI, PhD Professor/Deputy Dean School of Graduate Studies Universiti Putra Malaysia Date:
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This thesis submitted to the Senate of Universiti Putra Malaysia and has been accepted as fulfilment of the requirement for the degree of Master of Science. The members of the Supervisory Committee are as follows: Fakhru’l-Razi Ahmadun, PhD Associate Professor Faculty of Engineering Universiti Putra Malaysia (Chairman) Salmiaton Ali, PhD Lecturer Faculty of Engineering Universiti Putra Malaysia (Member) Suraya Abdul Rashid, PhD Lecturer Faculty of Engineering Universiti Putra Malaysia (Member)
______________________ AINI IDERIS, PhD Professor/Dean School of Graduate Studies Universiti Putra Malaysia
Date:
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DECLARATION I hereby declare that the thesis is based on my original work except for quotations and citation, which has been duly acknowledged. I also declare that it has not been previously or concurrently submitted for any other degree at UPM or other institutions.
___________________________________
RAJA NOR IZAWATI RAJA OTHMAN
Date:
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TABLE OF CONTENTS
Page
DEDICATION 2 ABSTRACT 3 ABSTRAK 5 ACKNOWLEDGEMENTS 7 APPROVAL 8 DECLARATION 10 LIST OF TABLES 13 LIST OF FIGURES 14 LIST OF ABBREVIATIONS/NOTATIONS/GLOSSARY OF TERMS 16 CHAPTER
1 INTRODUCTION 17 1.1 Background 17 1.2 Objectives and Scopes of Work 21 1.3 Thesis Outline 22
2 LITERATURE REVIEW 23 2.1 Introduction 23 2.2 History: Fullerenes and Carbon Nanotubes 24 2.3 Carbon Nanotube Properties and Application 27 2.3.1 Mechanical properties 28 2.3.2 Electronic Properties 29 2.3.3 Other physical properties 30 2.3.4 Application of carbon nanotubes 31 2.4 Major Carbon Nanotube Synthesis Methods and
comparison 33 2.4.1 Arc discharge 33 2.4.2 Laser vaporization 35 2.4.3 Chemical Vapor Deposition 37 2.4.4 Comparison of the Nanotube Synthesis Method 48
2.5 Growth mechanism of Carbon Nanotube 49 2.6 Effects of hydrogen in CVD 52 2.7 Current product market and future market outlook
for carbon nanotubes 56
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3 RESEARCH METHODOLOGY 60 3.1 Introduction 60 3.2 Materials 60 3.3 Experimental Apparatus 61 3.4 Experimental Procedure 63
3.4.1 Raw Material and Equipment Set Up 63 3.4.2 Reaction and Product Collection 63
3.5 Experimental Parameters 66 3.6 Sample Analysis and Characterization 69
3.6.1 Mass Analysis 69 3.6.2 Structural Analysis 69
4 RESULTS & DISCUSSION 72
4.1 Introduction 72 4.2 Product formation 72
4.2.1 Product collection and observation 73 4.2.2 Discussion on product distribution 76
4.3 Mass Analysis 82 4.3.1 Mass distribution 83
4.3.2 Empirical correlation on the mass of CNTs 87 4.4 Structural Analysis 93
4.4.1 SEM Observations and Discussion 94 4.4.2 TEM Observations and Discussion 99 4.4.3 CNT Characterizations 106 4.4.4 HRTEM and XRD observation and analysis 112
5 CONCLUSION AND RECOMMENDATIONS 117
5.1 Conclusions 117 5.2 Recommendations 119
REFERENCES 121 APPENDICES 135 BIODATA OF THE AUTHOR 175
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LIST OF TABLES
Table Page
2.1 Comparison of arc-discharge, laser ablation, and CVD methods 49
2.2 CNT price list for the year of 2006 57
3.1 Experimental runs and the combination of the varied parameters 68
4.1 Empirical relations between mass of CNT obtained and H2* flow rate at different reaction time 90
4.2 Outer diameter distribution of CNTs produced at different reaction conditions. 107 4.3 Inner diameter distribution of CNTs produced at different reaction conditions. 110 4.4 Numerical analysis on the microstructure of the CNTs synthesized
at t = 50 min 115
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LIST OF FIGURES
Figure Page
2.1 The chiral vector OA or Ch=na1 + ma2 is defined on the honeycomb lattice of carbon atoms by unit vectors a1 and a2 and the chiral angle θ with respect to the zigzag axis. Along the zigzag axis θ = 0°. Also shown are the lattice vector OB = T of the 1D nanotube unit cell and the rotation angle ψ and the translational τ which constitute the basic symmetry operation R = (ψ│τ) for the carbon nanotube. The diagram is constructed for (n,m) = (4,2). (Dresselhaus et al., 1995) 26
2.2 (a) Schematic diagram of the arc-discharge apparatus (Ando et al.,
2004); and (b) HRTEM micrographs of CNTs produced via arc discharge (Iijima, 1991). 34
2.3 (a) Schematic diagram of the laser ablation apparatus (Ando et al., 2004); and (b) HRTEM micrographs of CNTs produced via laser ablation (Thess et al., 1996). 36 2.4 (a) Schematic diagram of the CVD apparatus (Ando et al., 2004); and (b) HRTEM micrographs of CNTs produced via CVD (Lee et al., 2003). 37
3.1 Schematic of CVD apparatus 61
3.2 CVD apparatus showing 1st furnace and benzene in Erlenmenyer
Flask 62
3.3 2nd furnace and tube that directs unreacted gas to fume hood 62
3.4 Outline of the experiments 64
3.5 Inlets to the CVD Apparatus 65 4.1 Images of the boats after reaction (a) Boat 3; (b) Boat 2; (c) Boat 1; (d) Overall view showing product distribution on each Boat 74
4.2 Carbon products from Boat 2 75 4.3 SEM images of the product obtained from (a) Wall, (b) Boat 1 and (c) Boat 2 76
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4.4 Effects of varying H2* and H2** flow rate on mass of the products obtained for different reaction times; (a) 10 min, (b) 20 min, (c) 30 min, (d) 40 min, and (e) 50 min 84
4.5 Mass of CNT synthesized as H2* varies at different reaction time. 89 4.6 SEM images of CNTs produced at t = 10 min. 95 4.7 SEM images of CNTs produced at t = 20 min. 96 4.8 SEM images of CNTs produced at t = 30 min. 96
4.9 SEM images of CNTs produced at t = 40 min. 97 4.10 SEM images of CNTs produced at t = 50 min. 97 4.11 TEM images of CNTs produced at t = 10 min. 100 4.12 TEM images of CNTs produced at t = 20 min. 100 4.13 TEM images of CNTs produced at t = 30 min. 101
4.14 TEM images of CNTs produced at t = 40 min. 101 4.15 TEM images of CNTs produced at t = 50 min. 102 4.16 (a) Fe nanoparticles located at the end and middle of the tube;
(b) Fe nanoparticles formed in the middle of the tube; (c) CNT with open end; (d) CNT with bamboo structure. 104
4.17 Mean outer diameter at different H2* flow rate and reaction time. 109 4.18 Mean inner diameter at different H2* flow rate and reaction time. 111 4.19 HRTEM images showing the wall structures of CNTs for (a)
H2*=150 ml/min (b) H2*=250 ml/min and (c) H2*=350 ml/min at 50-min reaction time with their corresponding XRD peak 113
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LIST OF ABBREVIATIONS
Ar Argon
C Carbon
CNT Carbon Nanotube
CVD Chemical Vapor Deposition
d002 Interlayer spacings between walls
Fe Iron
FeCp Ferrocene
H2 Hydrogen
H2* Hydrogen that carries benzene vapor
H2** Hydrogen that is supplied directly to the furnace
HRTEM High resolution transmission electron microscopy
MWNT Multi walled nanotubes
SEM Scanning electron microscopy
SWNT Single walled nanotubes
TEM Transmission electron microscopy
VGCF Vapor grown carbon fibers
XRD X Ray Diffraction
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CHAPTER 1
INTRODUCTION
1.1 Background
Research in finding new materials has attracted the attention of scientists all over the
world due to the growing need of humankind to improve the quality of life. Research on
carbon materials especially has a lot to be explored due to its unique C-C bonding that
enables carbon to assume different structures such as one-dimensional nanotubes, two-
dimensional graphite, three-dimensional diamond, and even zero-dimensional fullerenes.
The discovery of multiwalled carbon nanotubes (1991) and single walled nanotubes
(1993), both by Iijima of NEC laboratories in Japan has stimulated researchers all over
the world to explore their much-anticipated extraordinary properties. As described by
Iijima (1991), multiwalled nanotubes (MWNTs) consist of two to seven concentric
graphene shells. As the name implies, single-walled nanotubes (SWNTs) consist of a
single graphene cylinder. Compared to MWNTs, SWNTs exhibit superior properties that
emerge from the strong one-dimensionality and crystalline perfection of the structure.
These two are often simply called Carbon Nanotubes (CNTs).
Realizing that these structures exhibits remarkable mechanical, electrical, and electronic
properties, the focus of the CNTs research has moved to the engineering aspect of it, i.e.
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the production of CNTs. In order to fully utilize of their special properties, it is important
to come out with a method for synthesis that can be controlled, relatively cheap, and
scaleable, so that the production of high quality of carbon nanotubes can be
commercialized. Arc discharge (Iijima, 1993) and laser vaporization (Thess et al., 1996)
methods have been used to produce CNTs of superior straightness and highly
crystallized. These two methods however suffer a high cost of manufacturing since they
involve with high operating temperature (>2727°C) and size constraint. Hence, these two
are not economical to produce CNTs on a large scale.
Chemical Vapor Deposition (CVD) technique has gained popularity as an alternative
production method due to its potential to produce CNTs on a large scale. With this
method, CNTs are produced via catalytic decomposition of hydrocarbons at relatively
lower temperatures, normally between 427°C to 1400°C in a furnace. Although the
technology had been applied to produce vapor grown carbon fibers (VGCFs) back in
1970s, the VGCFs produced are often of low quality, which formed spaghetti-like
structure (Teo et al., 2004). Driven by the need to produce CNTs on a large scale,
substantial and rapid progress was made in the development of CVD to establish it as a
highly controlled technology for the production of CNTs.
Baker et al. (1972), Oberlin et al. (1976) and Dai et al. (1996) each suggested three
different growth models for the formation of carbon filament or CNT. These authors
however agreed that the formation occurred as a consequence of the precipitation of
carbon through or on the catalyst. The growth would occur as long as the catalyst
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remained active, i.e. the catalyst was not covered by amorphous carbon or the formation
of carbide was prevented. Hence, the presence of catalyst deactivation agent would play
an important role in determining the amount of the CNTs formed. It could also prevent
catalyst poisoning that would eventually yield low purity CNTs.
Hydrogen is known to have significant effect in increasing the amount of CNTs formed
during CVD process. Cui et al. (1999) reported that the growth of CNTs flourished as the
percentage of H2 was increased in their CVD system. Bladh et al. (2000) observed that
the formation of SWNT was enhanced upon moderate addition of hydrogen to the
CO/Fe(CO)5 mixture. Both Neumayer et al. (2004) and Qiu et al. (2004) also reported the
presence of H2 in facilitating the growth of CNTs in their CVD system as well.
The presence of hydrogen also could prevent catalyst poisoning. As a result the as
synthesized CNTs would be of high purity with minimal side product formation. Both
Rao et al. (1998) and Satishkumar et al. (1998) observed that the use of H2 in the gas
flow with argon minimized the amorphous carbon coating on the CNT produced by their
CVD. Li et al. (2001) also observed that low flow-rate of methane accompanied by a
hydrogen co-flow could prevent amorphous formation. Venegoni et al. (2002) observed
encapsulated iron particles in all of their samples with a greater occurrence when
hydrogen was not introduced in the gas phase. Dong et al. (2004) reported formation of
nanoparticles on the surface of the CNTs when hydrogen was not introduced in their
CVD system.
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Previous work in synthesizing CNT at UPM involved synthesizing CNT via floating
catalyst CVD method that employed ferrocene as catalyst and benzene as hydrocarbon
precursors (Atieh, 2005). Hydrogen was used to bubble benzene into the reactor to obtain
CNT. Higher flow rate of hydrogen contributed to higher amount of benzene that would
enhance to the formation of amorphous carbon and encapsulated nanoparticles, as
highligted by this author (Atieh, 2005). Hence, the real effects exerted by hydrogen in
minimizing co-formation of amorphous carbon and encapsulated nanoparticles as
mentioned by other researchers (Rao et al., 1998; Satishkumar et al., 1998; Li et al.,
2001; Venegoni et al., 2002 and Dong et al., 2004) was not fully utilized. This study
seeks to improve the previous process based on the earlier findings.
In spite of the well known effects exerted by hydrogen, not much work has been
published on the CNT grown by adding fresh hydrogen to the benzene-ferrocene-
horizontal-floating catalyst CVD system. Ci et al. (2001) added thiophene to the similar
system and obtained mostly carbon nanofiber, not carbon nanotube, at unnecessarily high
operating temperature (>1000°C). The products obtained were of high impurity (presence
of carbonaceous product), which might be due to H2 that didn't effectively react with
excess carbon. This indicated the failure of H2 as purification agent and the inefficiency
of the parameters employed to control the CNTs growth in their system. The presence of
thiophene might explain such observations.
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1.2 Objectives and Scope of Work
The objectives of this research are
1) To determine the operating conditions to synthesize CNTs of no side products as
well as of highest quality at a relatively low temperature.
2) To study the effects of adding fresh hydrogen into the system on the as produced
CNTs in terms of morphology and growth mechanism.
The scopes of the work are directed towards assessing the effects of operating parameters
on the quantity and quality of CNTs produced. The parameters considered in the study
are reaction time, amount of benzene, as well as flow rates of fresh hydrogen supplied.
The reaction involves catalytic decomposition of benzene at constant temperature, which
is 850°C in this reactor. Benzene is chosen due to its low boiling point which is 80°C
(Williamson, 1994). Hence, it is easily decomposed upon entering the low-temperature
reaction zone. Ferrocene is used since it does not need to be pretreated, i.e. can be readily
used upon purchase. The reaction is run under atmospheric pressure to eliminate its
dependency on pressure factor. The weighted sample is characterized by using SEM,
TEM, as well as HRTEM. XRD is further used to identity the crystallinity of the carbon
produced.
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1.3 Thesis Outline
The thesis consists of five chapters. Chapter 1 highlights the background of the problem
and the significance of the research work in the field of carbon nanotubes. Chapter 2
covers the literature reviews on the subject, where extensive review, analysis and
synthesis are given to the reported work of various authors. The review provides the basis
for the experimental and analysis section of the thesis. Chapter 3 is on the development of
the analytical methods. Chapter 4 presents the results and the discussions of the obtained
results. The mass of the pure CNTs produced as well as their outer and inner diameters
are reported. The optimized condition for producing high quality CNTs is suggested.
Chapter 5 presents the conclusion of the work and recommendation for future work.
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CHAPTER 2
LITERATURE REVIEW
2.1 Introduction
Carbon is one of the three basic elements (C, H, and O) that form many kinds of
organisms with other elements to constitute life on earth. Among the pure elements in the
periodic table, carbon can assume different structures such as one-dimensional nanotubes,
two-dimensional graphite, three-dimensional diamond, and even zero-dimensional
fullerenes. The tubule morphology of carbon includes carbon fibers, whiskers, and
nanotubes. Other forms of carbon are glassy carbon, carbon blacks, amorphous carbon,
and liquid carbon (Dresselhaus et al., 1997).
Discovered in 1991 by Iijima, CNTs has attracted attention of scientists and researchers
all over the world due to its unique structure and properties. Since then, tremendous work
has been extensively done to study its unique properties. Due to its wide practical
application, massive work on the methods of its preparation/production has also been
studied to improve its yield in terms of quantity and also quality. This literature reviews
previous work on the synthesis of CNTs by different methods in details; special attention
will be given to ‘Chemical Vapor Deposition’ technique using ‘floating catalyst’ type.
Role of hydrogen in growth mechanism will be discussed in details.
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2.2 History: Fullerenes and Carbon Nanotubes
It was the Kroto-Smalley work (Kroto et al., 1985) that pioneered the field of nano-
structured carbon science era and further stimulated the search of finding new carbon
materials. In this experiment, graphite was laser-vaporized and a new structure was
accidentally found. Fullerenes or C60, a dominant structure of the product was detected by
mass spectrometry. They soon realized that it was a closed cluster containing precisely 60
carbon atoms, which would have a structure of unique stability and symmetry.
Iijima was the first to discover CNTs in 1991. This was multiwalled nanotube (MWNT),
which consisted of two to seven concentric graphene shells, and were embedded in the
fullerene by-product soot materials produced by the arc-discharge method. Researchers
and scientists were stimulated by the remarkable one dimensional quantum effects
predicted for their electronic properties (Iijima, 1991). The remarkable structure and
properties of CNTs also were predicted to give rise to some unique applications (Iijima,
1991).
Independently and at about the same time, Iijima (1993) and Bethune et al. (1993) both
synthesized single walled nanotube (SWNT). Iijima’s important contribution to CNTs
was that he connected his nanotube work to the ongoing fullerene studies. It was
observed that fullerene-like caps or hemisphere were formed at the end of nanotube. As
the name implies, single-walled nanotube (SWNT) consists of a single graphene cylinder.
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