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UNIVERSITI PUTRA MALAYSIA
THAMER H. AHMED
FK 2011 136
SYNTHESIS AND CHARACTERIZATION OF CARBON NANOTUBES IN A VERTICAL FLOATING CATALYST CHEMICAL VAPOUR
DEPOSITION REACTOR
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SYNTHESIS AND CHARACTERIZATION OF CARBON NANOTUBES IN A VERTICAL FLOATING CATALYST CHEMICAL VAPOUR DEPOSITION
REACTOR
By
THAMER H. AHMED
Thesis Submitted to the School of Graduate Studies, University Putra Malaysia, in Fulfillment of the Requirement for the Degree of Master of Science
October 2011
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DEDICATION
This thesis is dedicated to
ALL I LOVE
Specially
MY BELOVED PARENTS
MY WIFE AND MY SONS MY BROTHERS AND SISTERS
My friends
And
MY BLEEDING COUNTRY “IRAQ”
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Abstract of thesis presented to the Senate of Universiti Putra Malaysia in fulfilment of the requirement for the degree of Master of Science
SYNTHESIS AND CHARACTERIZATION OF CARBON NANOTUBES IN A VERTICAL FLOATING CATALYST CHEMICAL VAPOUR DEPOSITION
REACTOR
By
THAMER H. AHMED
October 2011
Chairman: Mohamad Amran Bin Mohd Salleh, PhD
Faculty : Engineering
New approaches to synthesize randomly oriented MWNTs have been achieved in a
vertical floating catalyst reactor. This approach based on the direct injection of the catalyst
into the reactor in powder form by using a new catalyst delivery system. The catalyst was
injected from the top of the reactor and simultaneously vaporized in the reactor, therefore,
eliminating the need to have a traditional preheating of the catalyst.
The ethylene gas as the reactant was used to push the catalyst powder into the reactor. The
new catalyst delivery system consists of three main parts. The first part is a small chamber
used as a temporary container for catalyst powder and having a conical bottom end to
facilitate the flow of the powder (catalyst). The top end of the chamber is a removable
cover equipped with inlet gas probe. Below the chamber, there is a control valve used to
control the flow of catalyst into the reactor. This valve connected to a long thin tube (5
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mm ID, 6 mm OD and L=460 mm) which could be inserted into the reactor at adjustable
length. This arrangement is effective to increase the residence time and provide sufficient
contact between the carbon source gas and the catalyst.
Ferrocene was used as the catalyst precursor and ethylene as the carbon source. The
experiments were performed at atmospheric pressure with process temperatures ranged
between 650 ºC and 850 ºC under argon atmospheres. Argon was flown with flow rate of
650 ml/min through the system before the reaction to purge air from the reactor. Hydrogen
and argon both are entering the reactor from the bottom. Layer of carbon nanotubes was
grown on the reactor walls. The as-grown CNTs were characterized by Field Emission
Scanning Electron Microscopy (FESEM), Transmission Electron Microscopy (TEM),
High Resolution Transmission Electron Microscope (HRTEM) and Thermal Gravimetric
Analysis (TGA).
A parametric study was made to evaluate the influence of the most crucial experimental
conditions on the growth of carbon nanotubes. Reaction temperature, catalyst weight,
ethylene flow rate and reaction time were systematically varied and their influence on
yield, purity, and diameter distribution of carbon nanotubes were evaluated. Although
hydrogen and argon may affect the properties of CNTs, it requires an entirely different
scope of study.
A strong effect of the reaction temperature was found on nanotube growth. Five reaction
temperatures from 650 ºC to 850 ºC were used. Both quality and quantity of CNTs
synthesized were increased with the increase in synthesis temperature from 650 ºC to 750
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ºC. Relatively, the highest purity and yield of CNTs deposit was obtained when reaction
temperature was set at 750 ºC.
Catalyst weight strongly influenced the formation of CNTs, the appropriate catalyst
weight for growing CNTs with best yield and high purity among six weights
(50,100,150,200,250 and 300 mg) used was 250 mg. High catalyst content form large
clusters with low activity.
Ethylene was found to play important roles in the production of CNTs, six different flow
rates from 50 ml/min to 300 ml/min each 50 ml/min were used to investigate effect of
ethylene on the yield, purity, diameter distribution and growth of carbon nanotubes. The
optimal ethylene flow rate was 100 ml/min.
The effect of the reaction time on the purity and yield of carbon nanotubes was studied
from 15 minute to 90 minutes. The maximum yield of carbon nanotubes was achieved at
30 minutes, for reaction duration longer than 30 min the growth rate was continuously
suppressed and gradually the catalyst loses its activity. There was no effect of the reaction
time on the average diameter.
The CNTs diameters increase with increasing these parameters under all experimental
conditions. The optimum reaction have been achieved at the above conditions and the
CNTs produced have yield of 148.4 wt%, purity of 89.4% and diameters from 8-53 nm.
Structure and kinetic of produced carbon nanotubes were studied using HRTEM. The
CNTs display a MWNTs structure of successive graphite sheets with hollow inside.
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Kinetics of MWNTs quantitatively described, the activation energy and frequency factor
are calculated. The equation that fit the growth of carbon nanotubes was presented.
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Abstrak tesis ini dikemukakan kepada Senat Universiti Putra Malaysia sebagai memenuhi keperluan untuk ijazah Master Sains
SINTESIS DAN PENCIRIAN KARBON TIUB NANO DALAM REAKTOR KIMIA PEMANGKIN LAMPUNG TEGAK BERPEMENDAPAN WAP
Oleh
THAMER H. AHMED
Oktober 2011
Pengerusi: Mohamad Amran Bin Mohd Salleh, PhD
Fakulti: Kejuruteraan
Pendekatan baru sintesis secara rawak berorientasikan MWNTs telah dicapai dalam
reaktor keluli tegak dengan menggunakan kaedah pemangkin terapung. Pendekatan ini
berdasarkan suntikan langsung pemangkin ke dalam reaktor dalam bentuk serbuk
dengan menggunakan sistem penyampaian pemangkin baru. Pemangkin disuntik dari
bahagian atas reaktor dan pada masa yang sama dipanaskan oleh tindak balas panas,
oleh itu, menghapuskan keperluan untuk pra-pemanasan pemangkin.
Aliran gas etilena digunakan untuk menolak serbuk pemangkin ke dalam reaktor di
mana kedua-duanya memasuki ke dalam reaktor pada masa yang sama. Sistem
penyampaian pemangkin baru terdiri daripada tiga bahagian utama, semuanya diperbuat
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daripada keluli. Bahagian pertama ialah ruang kecil yang digunakan sebagai bekas
sementara bagi serbuk pemangkin dan mempunyai hujung bawah kon untuk
memudahkan terjerumusnya serbuk (pemangkin). Hujung atas kebuk adalah penutup
boleh tanggal yang dilengkapi dengan prob inlet gas. Di bawah kebuk itu terdapat injap
kawalan yang digunakan untuk menyimpan pemangkin di dalam kebuk sehingga tindak
balas bermula. Injap ini disambungkan kepada tiub yang panjang dan nipis (5 mm ID 6
mm OD dan L = 460 mm,) iaitu sepanjang 360 mm dimasukkan di dalam reaktor sejurus
sebelum bahagian terakhir reaktor. Pengaturan ini adalah berkesan untuk meningkatkan
masa kediaman dan menyediakan kenalan yang mencukupi antara sumber gas karbon
dan pemangkin.
Ferrocene telah digunakan sebagai pelopor pemangkin dan etilena sebagai sumber
karbon. Eksperimen telah dijalankan pada tekanan atmosfera dengan suhu proses yang
berkisar antara 650°C dan 850°C di bawah atmosfera argon. Argon telah dialirkan
dengan kadar aliran 650 ml/min melalui sistem sebelum tindak balas untuk
membersihkan reaktor. Hidrogen dan argon kedua-duanya memasuki reaktor dari
bawah. Lapisan karbon tiub nano berkembang di dinding reaktor. CNTs yang
berkembang dicirikan oleh emisi Field Scanning Electron Microscopy (FESEM),
Transmisi Electron Microscopy (TEM), Mikroskop Elektron Transmisi Resolusi Tinggi
(HRTEM) dan Analisis gravimetrik Terma (TGA).
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Satu kajian parametrik yang dibuat untuk menilai pengaruh syarat-syarat penting
eksperimen pertumbuhan karbon tiub nano. Masa suhu tindak balas, berat badan
pemangkin, kadar aliran etilena dan reaksi secara sistematik diubah dan pengaruh
mereka ke atas pengagihan hasil, ketulenan, dan diameter karbon tiub nano dinilai.
Walaupun hidrogen dan Argon boleh memberi kesan kepada sifat-sifat CNTs, ia
memerlukan skop pengajian yang berbeza.
Kesan yang kuat oleh suhu tindak balas telah ditemui pada pertumbuhan tiub nano. Lima
suhu tindak balas daripada 650ºC ke 850ºC telah digunakan. Kedua-dua kualiti dan
kuantiti CNTs yang disintesis telah meningkat dengan peningkatan dalam suhu sintesis
daripada 650ºC ke 750ºC. Secara relatif, ketulenan tertinggi dan hasil deposit CNTs
telah diperolehi apabila suhu tindak balas telah ditetapkan pada suhu 750ºC.
Berat pemangkin mempengaruhi pembentukan CNTs. Berat pemangkin yang sesuai
untuk perkembangan CNTs dengan hasil yang terbaik dan ketulenan yang tinggi di
kalangan enam berat (50,100,150,200,250 dan 300 mg) yang digunakan adalah 250 mg.
Kandungan pemangkin yang tinggi membentuk kelompok besar dengan aktiviti yang
rendah.
Etilena dikenalpasti memainkan peranan yang penting dalam pengeluaran CNTs. Enam
kadar aliran yang berbeza dari 50 ml/min ke 300 ml/min setiap min 50 ml/telah
digunakan untuk menyiasat kesan etilena pada hasil, ketulenan, pengedaran diameter
dan pertumbuhan karbon tiub nano. Kadar aliran etilena yang optimum ialah 100
ml/min.
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Kesan jangkamasa tindak balas kepada ketulenan dan hasil nanotube karbon telah dikaji
dari 15 minit hingga 90 minit. Hasil maksimum karbon tiub nano telah dicapai dalam 30
minit, untuk tempoh tindak balas yang lebih lama daripada 30 min kadar pertumbuhan
terus ditindas dan secara beransur-ansur pemangkin kehilangan aktivitinya. Tidak ada
kesan jangkamasa tindak balas pada purata diameter.
Garis pusat yang dihasilkan meningkat dengan menambah parameter ini di bawah semua
keadaan uji kaji. Keadaan tindak balas yang optimum telah dicapai dan CNTs yang
dihasilkan mempunyai hasil 148,4% berat, ketulenan 89,4% dan diameter 8-53 nm.
Struktur dan kinetik karbon tiub nano yang dihasilkan telah dikaji menggunakan
HRTEM. CNTs memaparkan struktur MWNTs kepingan grafit berturutan dengan
dalaman berongga. Kinetik MWNTs secara kuantitatif diterangkan, tenaga pengaktifan
dan faktor frekuensi dikira. Persamaan yang sesuai dengan pertumbuhan karbon tiub
nano telah dibentangkan.
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ACKNOWLEDGEMENTS
I am deeply grateful to Allah S.W.T for giving me the power and strength with patience to
finish this work successfully.
This work would not been accomplished without the help of so many people. In the
following lines is a brief account of some but not all who deserve my thanks.
First, I would like to thank and appreciate Dr. Mohamad Amran bin Mohd Salleh for
taking the burden of supervising this research and his valuable comments and suggestions
that have been indispensable in the preparation of this thesis. He helped, reviewed and
motivated this research.
My deepest gratitude and appreciation goes to Dr. Abd. Rahim for providing valuable
comments and suggestions that enabled me improve and complete my master study
smoothly.
My warmest gratitude goes to my parents, my wife, my children (Zahra Zain Alabedeen
and Talib), my brothers, my sisters and all other relative and friends who always
encourage and helped me through the study duration.
I am also want to thank all of my second family members in Malaysia, including both the
colleges’ student and the staff, for providing me with great experience in my academic and
social life.
Finally, special thanks from me to MALAYSIA and to Malaysian people in general for
their perfect hospitality in their green land during my study period.
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I certify that a Thesis Examination Committee has met on 21 October 2011 to conduct the final examination of Thamer H. Ahmed on his thesis entitled "Synthesis and Characterization of Carbon Nanotubes In A Vertical Floating Catalyst Chemical Vapour Deposition Reactor" in accordance with the Universities and University Colleges Act 1971 and Universiti Pertanian Malaysia [P.U.(A) 106] 15 March 1998. The Committee recommends that the student be awarded the Master of Science. Members of the Examination Committee were as follows: Robiah Binti Yunus, PhD Professor Faculty of Engineering University Putra Malaysia (Chairman) Suraya Binti Abdul Rashid, PhD Associate Professor Faculty of Engineering University Putra Malaysia (Internal Examiner) Luqman Chuah Abdullah, PhD Professor Faculty of Engineering University Putra Malaysia (Internal Examiner) Abdul Rahman Mohamed, PhD Professor School of Chemical Engineering Universiti Sains Malaysia (External Examiner)
SEOW HENG FONG, PhD Professor and Deputy Dean School of Graduate Studies Universiti Putra Malaysia
Date: 20 December 2011
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This thesis was 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 were as follows:
Mohamad Amran Mohd. Salleh, PhD Lecturer Faculty of Engineering Universiti Putra Malaysia (Chairman)
Abdul Rahim Abu Talib, PhD Associate Professor Faculty of Engineering Universiti Putra Malaysia (Member)
BUJANG BIN KIM HUAT, PhD Professor and Deputy Dean School of Graduate Studies Universiti Putra Malaysia Date:
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DECLARATION
I declare that the thesis is my original work except for quotations and citations which have been duly acknowledged. I also declare that it has not been previously, and is not concurrently, submitted for any other degree at Universiti Putra Malaysia or other institutions.
THAMER H. AHMED Date:
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TABLE OF CONTENT
PageDEDICATION ii ABSTRACT iii ABSTRAK vii ACKNOWLEDGEMENTS xi APPROVAL xii DECLARATION xiv LIST OF TABLES xviii LIST OF FIGURES xix LIST OF ABBREVIATIONS xxvii
CHAPTER
1 INTRODUCTION TO SYNTHESIS OF CARBON NANOMATERIALS
1
1.1 Background 1 1.2 Research problem 5 1.3 Objectives of the study 8 1.4 Scope of the study 8
2 LITERATURE REVIEW 10 2.1 Introduction 10 2.2 History of Carbon Nanotubes 13 2.3 Properties of Carbon Nanotubes 14 2.3.1 Electrical Properties 14 2.3.2 Mechanical Properties 16 2.3.3 Thermal properties 18 2.4 Application of Carbon Nanotubes 20 2.5 Basic Methods of Manufacturing Carbon Nanotubes 24 2.5.1 Arc Discharge Method 24 2.5.2 Laser Ablation Method 28 2.5.3 Chemical Vapor Deposition (CVD) Method of
Nanotube Synthesis 31
2.6 Growth Mechanism of Carbon Nanotube 48 2.7 The role of growth parameters 52 2.7.1 Reaction Temperature
2.7.2 Catalyst Precursor 2.7.3 Carbon Precursor 2.7.4 Reaction Time 2.7.5 Hydrogen
52 54 57 61 62
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2.8 Assessment Purity of CNTs 63
3 RESEARCH METHODOLOGY 66 3.1 Introduction 66 3.2 Materials 68 3.3 Experimental Apparatus 68 3.4 Catalyst Delivery System 71 3.5 Experimental Procedures 76 3.6 Sample analysis and characterization 77 3.6.1 Scanning Electron Microscopy (SEM) 77 3.6.2 Transmission Electron Microscopy (TEM) and
High Resolution Transmission Electron Microscopy (HRTEM)
78
3.6.3 Thermogravimetric Analysis (TGA) 79 4 RESULTS AND DISCUSSION 81
4.1 Introduction 81 4.2 Effect of Reaction Temperature on the Growth of
Carbon Nanotubes 82
4.2.1 Effect of Reaction Temperatures on the Yield of Carbon Nanotubes
83
4.2.2 Effect of varying Reaction Temperature on the Purity of Carbon Nanotubes
86
4.2.3 Effect of Reaction Temperatures on the Diameter Distribution of Carbon Nanotubes
91
4.2.4 SEM Observations 96 4.2.5 TEM Observations 99 4.3 Effect of Catalyst content on the Growth of Carbon
Nanotubes 102
4.3.1 Effect of Ferroccne content on the Yield of Carbon Nanotubes
103
4.3.2 Effect of Ferrocene Content on the Purity of Carbon Nanotubes
105
4.3.3 Effect of catalyst content on the diameters distributions of Carbon Nanotubes 4.3.4 SEM Observations 4.3.5 TEM Observations
110
115 119
4.4 Effect of ethylene flow rate on the growth of Carbon Nanotubes
122
4.4.1 Effect of ethylene flow rate on the yield of Carbon Nanotubes
123
4.4.2 Effect of ethylene flow rate on the purity of 125
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Carbon Nanotubes 4.4.3 Effect of ethylene flow rate on the diameters
distribution of Carbon Nanotubes 128
4.4.4 SEM Observation 133 4.4.5 TEM Observation 136 4.5 Effect of Reaction Time on the Growth of Carbon
Nanotubes 138
4.5.1 Effect of Reaction Time on the Yield of Carbon Nanotubes
139
4.5.2 Effect of Reaction Time on the Purity of Carbon Nanotubes
141
4.6 Structure of Carbon Nanotubes 145 4.7 Kinetic of Carbon Nanotubes 147 5 CONCLUSIONS AND RECOMMENDATIONS
5.1 Conclusion 5.2 Recommendations
151
151 153
REFERENCES 155
BIODATA OF THE STUDENT
LIST OF PUBLICATIONS
179
180