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