Synthesis and Characterisation of Multiwalled Carbon Nanotubes Composite

based on Mill Scale and Boron Trioxide via Chemical Vapor Deposition

By

LEE SHIAN BOON

Thesis Submitted to the Department of Physics, Universiti Putra Malaysia, in

partial Fulfilment of the Requirements for the Degree of Bachelor of Science

(Hons.) Materials Science

MAY 2018

All material contained within the thesis, including without limitation text, logos, icons,

photographs and all other artwork, is copyright material of Universiti Putra Malaysia

unless otherwise stated. Use may be made of any material contained within the thesis

for non-commercial purposes from the copyright holder. Commercial use of material

may only be made with the express, prior, written permission of Universiti Putra

Malaysia.

Copyright © Universiti Putra Malaysia

I

DEDICATION

I dedicate this research to Almighty God who helps us in accomplishing this thesis and

for giving us wisdom. I also dedicate this to my parents who give financial support and to

my friends for giving us moral support.

II

ABSTRACT

Synthesis and Characterisation of Multiwalled Carbon Nanotubes Composite based on

Mill Scale and Boron Trioxide via Chemical Vapor Deposition

by

Lee Shian Boon

178654

MAY 2018

Supervisor: Dr. Raba’ah Syahidah binti Azis

Faculty: Faculty of Science

In this work, multiwalled carbon nanotubes (MWNT) composite has been synthesized by

chemical vapor deposition (CVD) technique. Mill scales and boron trioxide were used as

catalytic substrate. The CVD product was characterized by x-ray diffraction (XRD),

thermogravimetry analysis (TGA), transmission electron microscopy (TEM) and

electromagnetic absorption analysis using vector network analyser (VNA). Typical XRD

peak of (002) phase of MNNTs and distinct nanotube structures revealed by TEM

confirms MWNT presence. For microwave properties, it was observed from 8 GHz to 12

GHz and at 3 mm thickness, composite MWNT/mill scale has the maximum reflection

loss (RL = -28.26 dB) at 9.20 GHz.

III

ABSTRAK

Sintesis dan Pencirian Komposit Nanotiub Karbon Berbilang Dinding berdasarkan Sisik

Besi dan Boron Trioxide melalui Kaedah Pemendapan Wap Kimia

Oleh

Lee Shian Boon

178654

MEI 2018

Penyelia: Dr. Raba’ah Syahidah binti Azis

Fakulti: Fakulti Sains

Dalam kajian ini, pelbagai komposit nanotiub karbon berbilang dinding (MWNT) telah

disintesis melalui kaedah pemendapan wap kimia. Sisik besi dan boron trioksida

digunakan sebagai substrat pemangkin. Produck CVD ini dicirikan menggunakan difraksi

sinar-X (XRD), mikroskop transmisi electron (TEM), analisis termogravimetrik (TGA)

dan analisis penyerapan electromagnet (VNA). Puncak XRD (002) fasa MNNTs yang

biasa dijumpai dan struktur nanotube yang ditunjukkan oleh TEM mengesahkan

kehadiran MWNT. Bagi ciri-ciri gelombang mikro, ia diperhatikan dari 8 GHz hingga 12

GHz dan ketebalan pada 3 mm, komposit sisik besi/MWNT mempunyai kehilangan

pantulan maksimum (RL = -28.26 dB) pada 9.20 GHz.

IV

ACKNOWLEDGEMENT

The researcher would like to thank the following people who helped to make this research

possible. To his supervisor, Dr. Raba’ah Syahidah binti Azis and co-supervisor, Dr.

Ismayadi bin Ismail who patiently taught him everything he needs to know. Thank you I

appreciate from the bottom of my heart. Also, to Dr. Muhammad Syazwan Mustaffa for

always making sure that all questions or requests answered. The researcher appreciates

everything you have done. And now the researcher would like to thank all the people who

supported throughout this research, their families, friends, and classmates.

V

APPROVAL

This thesis entitled “Synthesis and Characterisation of Multiwalled Carbon Nanotubes

(MWNT) Composite based on Mill Scale and Boron Trioxide via Chemical Vapor

Deposition (CVD)” by Lee Shian Boon (Matric No.: 178654), was submitted to the

Department of Physics, Faculty of Science, Universiti Putra Malaysia and has been

accepted as partial fulfilment of the requirement for the degree of Bachelor of Science

(Hons.) Major in Materials Science.

Approved by,

Date: ………………………………

Dr. Raba’ah Syahidah binti Azis

Project Supervisor

Department of Physics

Faculty of Science

Universiti Putra Malaysia

Date: …………………………………

Assoc. Prof. Dr. Chen Soo Kien

Course Coordinator

Department of Physics

Faculty of Science

Universiti Putra Malaysia

Date: …………………………………….

Assoc. Prof. Dr. Zulkifly Abbas

Head of Department

Department of Physics

Faculty of Science

Universiti Putra Malaysia

VI

DECLARATION

Declaration by student

I hereby confirm that:

• this thesis is my original work;

• quotations, illustrations and citations have been duly referenced;

• this thesis has not been submitted previously or concurrently for any other degree at any

other institutions;

• intellectual property from the thesis and copyright of thesis are fully-owned by Universiti

Putra Malaysia, as according to the Universiti Putra Malaysia (Research) Rules 2012;

• written permission must be obtained from supervisor and the office of Deputy Vice-

Chancellor (Research and Innovation) before thesis is published (in the form of written,

printed or in electronic form) including books, journals, modules, proceedings, popular

writings, seminar papers, manuscripts, posters, reports, lecture notes, learning modules or

any other materials as stated in the Universiti Putra Malaysia (Research) Rules 2012;

• there is no plagiarism or data falsification/fabrication in the thesis, and scholarly integrity

is upheld as according to the Universiti Putra Malaysia (Research) Rules 2012.

Signature: _______________________ Date: __________________

Name and Matric No.: _________________________________________

VII

TABLE OF CONTENT

Page

ABSTRACT II

ABSTRAK III

ACKNOWLEDGEMENTS IV

APPROVAL V

DECLARATION VI

LIST OF FIGURES IX

LIST OF TABLES X

LIST OF ABBREVIATIONS XI

CHAPTER 1 INTRODUCTION

1.1 Radar Absorbing Materials 1

1.2 Historical Overview 1

1.3 Problem Statement 3

1.4 Research Overview 4

1.5 Objectives 5

CHAPTER 2 LITERATURE REVIEW

2.1 Multi-wall Carbon Nanotube (MWNT) 6

2.2 Mill Scale 7

2.3 Chemical Vapor Deposition 8

2.4 Boron Oxide 10

2.5 Electromagnetic Absorption 11

CHAPTER 3 METHODOLOGY

3.1 Overview 12

3.2 Preparation of Sample 14

3.2.1 Mill Scale 14

3.2.2 Boron Trioxide 15

3.2.3 MWNT 15

3.2.4 Composite Samples 17

3.3 Characterizations 20

3.3.1 X-ray Diffraction 20

3.3.2 TEM 21

3.3.3 TGA 23

3.3.4 VNA 24

CHAPTER 4 RESULTS AND DISCUSSIONS

4.1 Physical Analysis 28

4.1.1 X-ray Diffraction 28

4.1.2 TEM 31

4.1.3 TGA 35

4.2 Absorption Analysis 38

VIII

CHAPTER 5 CONCLUSIONS

5.1 Conclusions 42

5.2 Suggestions 43

BIBLIOGRAPHY 44

VITAE 48

IX

LIST OF FIGURES

Figure Description Page

2.1 Typical TEM images of MWNT sample (Purohit et al. 2014) 7

2.2 X-ray diffraction patterns for reduced mill scale by coke (Lo et al.,

2012)

8

2.3 Crystal structure of boron trioxide (G. E. Gurr, 1968) 10

3.1 Methodology flowchart 13

3.2 SPEX SamplePrep 8000D Dual Mixer/Mill 15

3.3 Ethanol liquid contained in a boiling flask channeled to the

furnace.

16

3.4 CVD product. 17

3.5 Aluminum mold specialized for VNA measurement. 18

3.6 X-ray Diffractometry 20

3.7 Sonicated MWNT dispersion in acetone. 22

3.8 JEM-2100F field emission electron microscope. 23

3.9 Flowchart of forming composite. 25

3.10 Vector Network Analyser. 26

4.1 XRD diagram of (a) mill scale, (b) sample A, (c) sample B and (d)

boron trioxide.

30

4.2 TEM images of sample A. 33

4.3 TEM images of sample B. 35

4.4 TGA and DTG curves of (a) mill scale, (b) boron trioxide and (c)

sample A.

37

4.5 Reflection loss versus frequency graph for (a) sample A, J and K;

(b) sample B, C and H.

41

X

LIST OF TABLES

Table Description Page

3.1 Parameters of HEBM. 14

3.2 Powder substrate weight ratio (B2O3 : Mill scale). 17

3.3 Weight ratio of sample to be incorporated into mold. 19

3.4 Composite weight ratio (resin : hardener : filler). 24

4.1 Weight change of CVD products. 27

4.2 Summary for composite mold composition. 38

4.3 Conversion of reflection loss. 39

XI

LIST OF ABBREVIATIONS

CNT Carbon nanotubes

CVD Chemical vapor deposition

MWNT Multi walled carbon nanotubes

RCS Radar cross section

RL Reflection loss

SEA Shielding effectiveness

SWNT Single walled carbon nanotubes

TEM Transmission electron microscopy

TGA Thermogravimetric analysis

VNA Vector Network Analyzer

XRD X-ray powder diffraction

1

CHAPTER 1

INTRODUCTION

1.1 Radar Absorbing Materials

Radar absorbing materials (RAM), in stealth technology or low observable technology,

are a part of electronic countermeasure. RAM absorb radar in various amounts depending

on atmospheric conditions and different frequencies. They are applied on outer surfaces

of military hardware like aircrafts, ships and missiles to deceive enemy’s radar. Together

with proper craft’s shaping design which, RAM makes military hardware less detectable

by reducing the radar cross section (RCS) and hence radar signature of a craft or a missile.

(Saville, 2005)

On the other hand, RAM is integral in measurements of electromagnetic compatibility

(EMC) and antenna radiation patterns. Test setup in such measurements unavoidably emit

unwanted signals which could cause measurement errors and ambiguities. Hence, arrays

of RAM made from lossy material will cover all internal surfaces of the anechoic chamber

to absorb incident RF radiation. Commonly, RAM in this setting comprise rubberized

foam material impregnated with controlled mixtures of carbon and iron oxide. (Gaylor,

1989)

1.2 Historical Overview

RADAR is an acronym for radio detection and ranging. It uses electromagnetic waves at

sub-optical (400 THz) frequencies to detect position or velocity of an object. Transmitted

2

from an antenna, these electromagnetic waves travelled radially outwards. Eventually,

they reflect off some distant object and return an echo to the sender, where they are

received, amplified, and processed electronically to yield an image showing the object’s

location. Object’s travelling velocity is determined by the shifted frequency due to

Doppler’s effect. (Bole et al., 2014)

RADAR started with the theoretical work of James Clerk Maxwell, followed by Heinrich

Hertz, who did all the experimental work to understand the nature of electromagnetic

waves. (Rohling, 2010). Initially developed as a mean to detect proximity object and

prevent ship collision due to poor visibility, RADAR had found itself a significant role as

navigation and tracking devices. Its application in navigation and tracking of craft at sea

and in the air, has seen rapid advancement since the World War II. It was developed

independently by researchers in the United Kingdom, France, Germany, Italy, Japan, the

Netherlands, the Soviet Union, and the United States. (Wolters et al., 2002)

In 1943, Allied RADAR was deemed to pose imminent threat to U-boats by the

Oberkommando der Marine (Nazi Germany’s Naval High Command) and a conference

was called in Berlin. The secret project to come up with a successful countermeasure was

named Schornsteinfeger (Chimney Sweep). Schornsteinfeger was an adsorbent coating

made from ferrites that, when applied to a submarine’s hull and snorkel mast, insulated

the steel and greatly reduced the reflected electronic signal in the 20-cm radar band the

Allies used. (Primus et al., 1991)

3

Commonly known types of RAM are iron ball paint, Jaumann absorber, Split-ring

resonator absorber. Research of CNT incorporation in RAM is currently undergoing. Iron

ball paint contains tiny spheres coated with carbonyl iron or ferrite. Radar waves induce

molecular oscillations from the alternating magnetic field in this paint, which leads to

conversion of the radar energy into heat. The heat is then transferred to the aircraft and

dissipated. The iron particles in the paint are obtained by decomposition of iron

pentacarbonyl. Lockheed F-117 Nighthawk utilises iron ball paint. The carbonyl iron ball

paint is most effective when the balls are evenly dispersed, electrically isolated, and

present a gradient of progressively greater density to the incoming radar waves. (Patil,

2008)

A Jaumann absorber or Jaumann layer is a radar-absorbent substance. (Gaylor, 1989)

When first introduced in 1943, the Jaumann layer consisted of two equally spaced

reflective surfaces and a conductive ground plane. One can think of it as a generalized,

multi-layered Salisbury screen, as the principles are similar. Being a resonant absorber, it

uses wave interfering to cancel the reflected wave. Because the wave can resonate at two

frequencies, the Jaumann layer produces two absorption maxima across a band of

wavelengths (if using the two layers configuration). (Primus et al., 1991)

1.3 Problem Statement

Being frequency selective, RAM never gives high absorption across whole RADAR

frequency range and can never be assumed to decrease an aircraft’s RCS values to a

considerable extent. It can absorb a portion of the incident energy, with the rest being

4

reflected. Although fighter-sized stealth aircraft could be detected by low-frequency radar,

missile lock and targeting sensors primarily operate in the X-band.

A solid waste, known as mill scale, is generated by the oxidation of the metal surface

during the continuous casting and rolling steps in an integrated steel plant. (Cristina et al.,

2015) Being produced approximately 35–40 kg per ton of produced steel, mill scale

potentially serves as catalyst in multi walled carbon nanotube (MWNT) production. (Sun

et al., 2013)

In 2018, Kolanowska et al. stated that, in the stealth technology, composites exhibiting

appreciable electrical conductivity and high shielding effectiveness (SEA) are used. While

doped boron provides conduction carriers, it further reduces the resistivity of the MWNT.

(Ishii et al., 2011)

Hence, in this study, samples with different composition of mill scale and boron trioxide

are synthesized and their microwave absorption properties at X-band are studied.

1.4 Research Overview

The electromagnetic absorption performance of MWNT composite filler is greatly

affected by weight ratio of MWNT in MWNT composite. By altering the weight ratio, we

can produce fillers with different reflection loss across the frequency spectrum. Therefore,

investigations on the material with different MWNT samples with altered catalyst

composition will give us a valuable information in achieving low reflection loss, wide

bandwidth RAM.

5

In this research, MWNT is synthesised by CVD. After the CVD process, MWNT’s

physical properties will be studied. Then, composite material samples are prepared, and

their electromagnetic performance is probed.

1.5 Objectives

1. To synthesise MWNT via CVD method using substrate of mill scale and boron

trioxide.

2. To characterise the structural and the physical properties of MWNT samples.

3. To study the electromagnetic performance of MWNT samples.

6

CHAPTER 2

LITERATURE REVIEW

2.1 Multi-wall Carbon Nanotube (MWNT)

Carbon nanotubes are members of the carbon family with significant mechanical and

electrical properties. They can be viewed as a graphene sheet rolled up into a nanoscale

tube form to produce the single walled carbon nanotubes (SWNT). There may be

additional graphene tubes around the core of a SWNT to form multi-walled carbon

nanotubes (MWNTs). These elongated nanotubes usually have a diameter in the range of

a few angstroms to tens of nanometres and a length of several micrometres up to

millimetres with both ends of the tubes normally capped by fullerene-like structures

containing pentagons. (Schrand & Tolle, 2006)

CNT/epoxy composite coatings have been used as high radar transparency or radar

absorbing coatings to disguise or reflect objects from an enemy's night-vision equipment.

Alternatively, SWNT/epoxy mixtures can be used as sprays or sizing agents for other

composite materials to enhance the interphase/interface between reinforcements and the

matrix. (Oh et al., 2004) Composite materials reinforced by multi wall carbon nanotubes

(MWNT) as shown in Figure 2.1 are studied for their interesting microwave absorption

capability. (Micheli et al., 2014)

7

Figure 2.1: Typical TEM images of MWNT sample (Purohit et al., 2014)

2.2 Mill Scale

Mill scale is a waste from the oxidation of steel surfaces in the steelmaking process like

continuous casting and rolling steps. (Cristina et al. 2015) The separation of steel mill

scale is performed using either mechanical or chemical means. Mill scale comprises iron

oxides, such as wustite (FeO), magnetite (Fe3O4), and hematite (Fe2O3), besides traces of

non-ferrous metals, compounds of alkali metals, and oils from the rolling process. On

average, specific production of mill scale is 40 kg per ton of produced steel. (Lo et al.,

2012)

8

Figure 2.2: X-ray diffraction patterns for reduced mill scale by coke (Lo et al.,

2012)

Figure 2.2 shows the X-ray diffraction patterns for reduced mill scale similar to the mill

scale used in this research. The method of X-ray diffraction is effective in monitoring the

crystallinity of CNTs and of metallic nanoparticles. The technique has also been used for

estimating an average size of the nanoparticles and the diameter distribution of nanotubes.

(Lo et al., 2012)

2.3 Chemical Vapour Deposition

There are various techniques used for growth of CNTs. Three popular methods are arc

discharge, laser ablation, & chemical vapor deposition (CVD). The common characteristic

of these techniques is to provide energy to a carbon source for the creation of Carbon

atoms that generate CNTs. (Purohit et al., 2014)

9

In chemical vapour deposition, the decomposition of the carbon precursor and CNT

formation take place on the surface of catalyst particles. CNT size can be controlled by

varying the size of catalyst particles. Commonly used carbon sources are carbon

monoxide, methane, acetylene and ethanol. Carbon source is taken in the gas phase and

resistively heated coil imparts energy to gaseous carbon molecules. (Purohit et al., 2014)

CNT growth in CVD is affected by three main parameters which are the hydrocarbon,

catalyst and growth temperature. The yield of CNT’s synthesized by chemical vapour

deposition is greatly influenced by the growth parameters like catalyst particle size,

catalyst concentration, pressure, growth time, growth temperature and gas flow rate.

Growth mechanisms of nanotube are different for different methods. Researchers have

reported various mechanisms, such as vapor-solid-solid (VSS), vapor-liquid-solid (VLS).

(Purohit et al., 2014)

Chemical vapour deposition (CVD) is a unit equipped with a horizontal tube furnace; a

quartz tube was used as a reactor and installed in the furnace. Using a crucible boat to hold

the metal catalyst, CVD process sources its mixture of hydrocarbon and argon gas from a

duct. Ethanol is heated up to its boiling temperature and its vapor is channeled into the

furnace when furnace temperature is at its pre-set temperature.

After carbon deposition of 20 minutes, reactor is cooled to room temperature under argon

gas. After that, the products can be collected. The morphology, length and diameter of the

10

CNTs produced were determined by transmission electron microscopy (TEM). (Iyuke &

Danna, 2005)

2.4 Boron Oxide

Boron trioxide is an odourless stable white powder. Being in vitreous form usually, boron

trioxide crystallizes under extensive annealing. Kracek et al. in 1938 found B2O3 to form

as a fine powder during dehydration of meta-boric acid under carefully controlled

conditions. Each boron is triangularly surrounded by 3 oxygen atoms with a B-O distance

of 1.37 Å as shown in Figure 2.3. It melts at 450 ⁰C.

Figure 2.3: Crystal structure of boron trioxide (G. E. Gurr, 1968)

11

2.5 Electromagnetic Absorption

Upon leaving a transmitting antenna, a radio wave propagates in a widening beam at the

speed of light (> 186,000 miles per hour or 3 × 108 m/sec). It continues propagating until

it encounters an obstacle, a medium whose characteristic impedance differs from that of

air and vacuum (> 377 Ω), it splits into two parts. One part passes into the obstacle and is

generally absorbed, and the other is reflected. Shape of the obstacle dictates the

propagation direction of reflected wave. Roundish or irregular obstacles tend to scatter

energy through a wide angle, while flat or facet-like surfaces tend to send it off in a single

direction, just as a flat mirror reflects light. If any part of the outgoing wave is reflected at

180° (which is not guaranteed) it will return to the transmitter. This returned or

backscattered signal is usually detected by the same antenna that sent the outgoing pulse;

this antenna alternates rapidly between transmitting pulses and listening for echoes, thus

building a real-time picture of the reflecting targets in range of its beam. Electromagnetic

radiation power is attenuated due to reflection, absorption and/or multiple reflection.

(Patil, 2008)

12

CHAPTER 3

METHODOLOGY

3.1 Overview

This chapter describes the mechanism used to grow MWNT via chemical vapor deposition

(CVD) procedures and the preparation of composite samples. The study will comprise

characterization techniques like X-ray diffraction (XRD), Thermogravimetric analysis

(TGA), transmission electron microscopy (TEM) and PNA Vector Network Analyzer

(VNA).

For CVD process, 5 powder substrates with different weight ratio of boron trioxide to mill

scale are prepared by weighing powders and mixing them accordingly. MWNT synthesis

for each sample runs separately. Before introducing hydrocarbon into the horizontal

furnace, the crucible containing 0.5 g of catalytic substrate is heated gradually to 750 ⁰C

under steady flow of argon gas. Upon furnace temperature reaching the 750 ⁰C mark,

ethanol vapor heated in a boiling flask is channeled into the furnace alongside with argon

gas for 20 minutes. Finally, the ethanol vapor valve is closed, and argon continues flowing

until furnace temperature drops to room temperature. The physical properties and

electromagnetic absorptive ability of samples were examined under several

characterization processes. The methodology flowchart is briefly illustrated in Figure 3.1.

13

Figure 3.1: Methodology flowchart

XRDA

BMill scae

Boron trioxide

TGA

A

Mill scale

Boron trioxide TEM

A B

Resin Composite

(VNA)A

B

C H

J

K

A

B

C

D

E

Weighing

Mill Scale

Boron Trioxide

CVD process

Synthesis process

Characterization

14

3.2 Preparation of Sample

3.2.1 Mill Scale

High energy ball milling (HEBM) prepares mill scale using parameters as stated in Table

3.1. Milling machine is shown in Figure 3.2 and it is used for substrate powder mixing as

well.

Table 3.1: Parameters of HEBM.

Parameter Values

Rotation per minutes 1760

Ball to powder ratio 10:1

Ball milling time (hrs) 7

The average particle size of iron oxide milled at 6 hours obtained is 53.76 nm. High energy

imparted from the collision of milling media to the iron oxide particles causes the size of

iron oxide nanoparticles decreased. (Suhada et al., 2017)

The decomposition of the carbon precursor & CNT formation take place on the surface of

catalyst particles. Hence, manipulation of catalyst particle size affects the morphology of

MWNT. (Purohit et al., 2014)

15

Figure 3.2: SPEX SamplePrep 8000D Dual Mixer/Mill

3.2.2 Boron Trioxide

Boron trioxide in this study passes through a 60-mesh sieve (Alfa Aesar, 97.5%).

3.2.3 Multi-walled Carbon Nanotuubes

Horizontal quartz furnace is cleaned thoroughly and heated up to 900 ⁰C to remove any

moisture as well as carbonaceous particles. Prior to CVD process, catalytic substrate

powder is weighted and distributed evenly on a boat-shaped crucible. The wall edge of

crucible facing the hydrocarbon vapor feed is removed to facilitate the decomposition of

the carbon precursor & CNT formation on substrate. The furnace temperature raises as

resistively heated coil imparts energy to it. It is sealed and argon gas flows steadily through

a stainless steel pipe into the furnace. Argon is an inert gas which acts as carrier gas.

(Adnan et al., 2015) Liquid ethanol is held in a boiling flask and it is boiled to supply

16

carbon source in the gas phase. The setup of apparatus is shown in Figure 3.3. (Purohit et

al., 2014)

Figure 3.3: Ethanol liquid contained in a boiling flask channeled to the furnace.

When furnace reached 750 ⁰C, the carbon source valve is opened, and carbonaceous vapor

is formed in the furnace. At pressures below 10 atm, the decomposition of CH3CH2OH

occurs primarily by the dehydration reaction producing C2H4 + H2O. (Park et al., 2012)

Steady flow of ethanol is maintained for 20 minutes. Finally, the valve is closed, and the

furnace is left to cool down under continuous steady flow of argon gas. The CVD products

are shown in Figure 3.4. Powder substrate weight ratio for respective samples is tabulated

in Table 3.2.

17

Figure 3.4: CVD product.

Table 3.2: Powder substrate weight ratio (B2O3 : Mill scale).

Sample Powder substrate weight ratio (B2O3 : Mill scale)

A 0 : 1.0

B 0.5 : 1.0

C 1.0 : 1.0

D 1.5 : 1.0

E 2.0 : 1.0

3.2.4 Composite Samples

As a second phase, the inorganic fillers can also affect cure exotherms, shrinkage, thermal

and electrical conductivity, machinability, hardness, compressive, flexural, and impact

strength. The extent to which the fillers modify polymer properties is closely associated

with the size, shape and dispersion uniformity of the filler as well as the degree of

interaction between the inorganic filler and the organic matrix. An ideal performance is

18

achieved with inorganic fillers consisting of small particles that are uniformly dispersed

throughout the polymer and interact strongly with the organic matrix.

Substrates were made by proportionating samples according to Table 3.3 using weight

balance. Then, the mixed powder samples are dispersed briefly in the resin system using

magnetic stirrer. Epoxy resins are easily moulded using sturdy aluminium mould

exclusively made for X-band VNA measurement as shown in Figure 3.5. Epoxy resins

have moderate strength, and low hardness. Resin system used consist of two parts, a resin

and a hardener, which are mixed and cured at elevated temperatures of 60 ⁰C. They are

QUICKMOUNT 2 Fast Epoxy Resin Model - ERF-3000-32 and Hardener Model - EHF-

3000-08. The ratio of epoxy to hardener is 17:1 while the filler loading level is carefully

maintained at 10 %. The loading level influence the material’s intensive properties such

as permeability and permittivity.

Figure 3.5: Aluminum mold specialized for VNA measurement.

19

Table 3.3: Weight ratio of sample to be incorporated into mold.

Composite Sample Composition

Weight ratio of

powder

Remark

A

As synthesized

CVD product

Mill scale

Comprises

significant amount

of carbon product

B

0.5 B2O3 : 1 Mill

scale

Comprises

moderate amount of

carbon product

C 1 B2O3 : 1 Mill scale

Comprises

insignificant

amount of carbon

product

H Raw mill scale Mill scale

Magnetic dark

brownish metal

oxide without any

carbon product

J Mixing sample A

and raw boron

trioxide

0.5 B2O3 : 1 sample

A

Comprises certain

amount of carbon

product from

sample A K 1 B2O3 : 1 sample A

20

3.3 Characterisations

3.3.1 X-ray Diffraction Analysis

X-ray powder diffraction (XRD) was performed by employing Cu Kα radiation (λ= 1.54

A ˚, 40 kV, 40.0 mA). All samples were scanned in 2θ = 20⁰ to 80⁰ at a rate of 2⁰ per

minute. The bulk chemical compositional analysis of mill scale is normally carried out

using X-ray. The structural and phase analysis of the samples were performed using X-

ray diffractometer (Philips PW 3040/60 X'pert Pro) as shown in Figure 3.6 with CuKα

radiation (wavelength of 1.5405 Å). Phase identification of the samples was performed

using X’Pert Highscore software with the support of ICDD-PDF-2 database.

Figure 3.6: X-ray Diffractometry

Diffraction occurs as waves interact with a regular structure whose repeating distance is

about the same as the wavelength. X-Rays have wavelengths on the order of a few

angstroms, the same as typical interatomic distances in crystalline solids, and can be

diffracted from crystalline solids that have regular repeating atomic structures. When

21

certain geometric conditions like X-Ray constructive interference occurrence are met, X-

rays diffract into beams.

XRD provides effective, fast and non-destructive technique to study the average structural

properties of MWNTs. All possible orientations are hit by the X-ray incident beam when

nanotubes are probed. This leads to powder-like diffraction profiles which give statistical

characterization of MWNTs. Thus, this shows that XRD is not adopted to study isolated

nanotubes.

The XRD pattern of a MWNT exhibits graphite-like peak (002) and a family of smaller

peaks also attributable to graphene crystals ((100), (101), (102), (004), (110), and (112)),

closely resembling that of a well-crystallized graphitic material. However, the XRD

profile is incapable of differentiating the microstructural details in the nanotubes samples.

The presence of impurities such as catalyst particles will be evidenced by additional peaks

that can be assigned to respective planes.

3.3.2 TEM

Transmission electron microscopy (TEM) is a very useful technique for studying in detail

the structure MWNTs, including defects present in nanotubes. TEM provides information

on the structure of internal and external closures, on the nature of defects, and on how the

tubes are stacked. TEM samples are simply dispersed in acetone and a copper grid will be

dipped into the resulting dispersion. The dilute nanotube slurry was subjected to ultrasonic

dispersion for approximately 5 minutes to reduce agglomeration as shown in Figure 3.7.

22

Figure 3.7: Sonicated MWNT dispersion in acetone.

A JEM-2100F field emission electron microscope (Figure 3.8) was operated at 200kV

accelerating voltage. An advantage of this microscope is its potential for low current

density with a highly coherent beam. Low accelerating voltage avoid damage of the

MWNTs. The FE electron gun (FEG) produces highly stable and bright electron probe

that is never achieved with conventional thermionic electron gun. This feature is essential

for ultrahigh resolution in scanning transmission microscopy and in an analysis of a nano-

scaled sample. The diameter of nanotubes can be obtained directly from the electron

microscopy images in real space.

23

Figure 3.8: JEM-2100F field emission electron microscope.

3.3.3 TGA

Thermal properties of CNT are investigated using thermogravimetric analysis (TGA).

TGA was performed to determine CNTs yield. Mettler Toledo TGA/DSC 1 is used.

Thermogravimetric analysis is a thermal analysis technique in which the percent weight

loss of a sample is recorded while the sample is being heated at a uniform rate in an

appropriate environment. The weight loss over specific temperature range reveals

information of the sample composition (including volatiles and inert fillers) and it thermal

stability. Conventionally, TGA for MWNTs is done under air (thermal decomposition).

24

Oxidation temperature is indicated by a peak of the temperature derivative of the weight

𝑑𝑚/𝑑𝑇. During the thermal oxidation of the samples in ambient air, the sample was

heated from 50 to 1000 °C at 10 °C/min in order to determine the weight loss.

3.3.4 VNA

The manufacturing of composite material samples enables computing of the relative

permittivity as function of the frequency of the applied EM field. Electromagnetic and

microwave absorbing properties of the prepared samples were performed using N5227A

PNA Network Analyser (Figure 3.10). The Agilent Technologies 85,071 Materials

Measurement software streamlined the process of measuring complex permittivity and

permeability with VNA in the frequency range of 8-12 GHz.

Table 3.4: Composite weight ratio (resin : hardener : filler).

Composite

weight, g

Composite weight ratio

(resin : hardener : filler)

Resin

weight, g

Hardener

weight, g

Filler

weight, g

1.200 17 : 1 : 2 1.0200 0.0600 0.1200

25

Figure 3.9: Flowchart of forming composite.

Two port calibration is done using ECal calibration which uses four impedance states to

compute the VNA’s systematic error terms to reduce calibration errors. Calibration is

essential to make accurate measurements. The reflection loss of electromagnetic wave

comprises frequency, intensity, and bandwidth of absorption peaks. By measuring the

Resin and hardener is mixed

Filler is added to resin system.

Then, they are mixed homogenously.

After that, it is placed into different sample holders.

The mixture is dried in an oven at 70⁰C for 24 hours for the solidification of the

epoxy.

VNA: Line transmission theory

to characterize microwave absorbing properties.

26

reflection coefficient of the composite backed with a metal plate, the data of reflection

loss peak is measured.

Retrieval of the dielectric parameters was obtained by measuring the microwave scattering

parameters Sij (S11, S21, S12, S22) by means of a vector network analyser (AGILENT, PNA-

L N5235) and a coaxial transmission line. The composite specimens for the measurement

of the microwave absorber properties were prepared by mixing according to Table 3.4.

The filler and the epoxy resin were mixed homogenously using magnetic stirrer, and the

mixture were placed into different sample holders. The mixture was dried in an oven at

70oC for 24 h for the solidification of the epoxy. The flowchart is shown in Figure 3.9.

Figure 3.10: Vector Network Analyser.

27

CHAPTER 4

RESULTS AND DISCUSSION

In the CVD process, CNT growth depends on the carbon source, synthesis temperature

and catalyst. In most cases, the catalyst chosen is of iron, cobalt or nickel based. Generally,

low-temperature CVD (600-900 °C) yields MWNTs. (Purohit et al. 2014) Experiments

were carried out at different weight ratio ranging from 0:1 to 2:1. MWNT growth is

monitored by the weight change of the sample after ethanol decomposition expressed by

the equation

𝑤 (%) = [𝑚𝑓 − 𝑚𝑜

𝑚𝑜] ∗ 100,

where 𝑚𝑜 is the initial weight of substrate before introducing the ethanol into the reactor

and 𝑚𝑓 is the weight of final CVD product.

Table 4.1: Weight change of CVD products.

Sample

Powder substrate

weight, 𝑚𝑜 (g)

CVD product

weight, 𝑚𝑓 (g) Weight change, w

(g)

Weight change,

w (%)

A 0.5074 1.7142 1.2068 237.8

B 0.5023 0.5415 0.0392 7.804

C 0.5016 0.3577 -0.1439 -28.69

D 0.4987 0.2321 -0.2666 -53.46

E 0.5089 0.2038 -0.3051 -59.95

For sample A, the powder substrate is basically mill scale, the weight change is 237.8 %.

This indicates good MWNT growth. However, the yield decreases for sample B (7.804

%), in which boron trioxide has been introduced one third in weight of the powder

28

substrate. Subsequent increase of (B2O3 : mill scale) ratio (1.0 : 1.0, 1.5 :1.0 and 2.0 : 1.0)

leads to negative weight growth (-28.69 %, -53.46 % and -59.95 %) as tabulated in Table

4.1.

This might be explained by the low melting temperature of boron trioxide(450°C). At 750

°C, the boron trioxide constituent has certainly melted and might be engulfing other solid

mill scale substrate, inhibiting decomposition of vapor hydrocarbon on the catalyst.

Catalyst acts as the nucleation site for the nanotubes to grow and further introduction of

boron trioxide has overwhelmed any possible MWNT synthesis.

4.1 Physical Analysis

4.1.1 X-ray Diffraction

Figure 4.1 shows the X-ray diffractograms (XRD) for 4 samples (A, B, H and Boron

Trioxide). For raw mill scale Figure 4.1 (a), the major diffraction peaks of magnetite

(Fe3O4), hematite (Fe2O3) and wüstite (FeO) are observed and can be indexed. Peaks at

30.1⁰ and 35.5⁰ can be assigned to (022) and (113) crystalline plane diffraction peaks

respectively which coincides with cubic magnetite. Peaks at 33.2⁰ is assigned to (104)

crystalline plane diffraction peak of hexagonal hematite. Peaks at 36.5⁰, 42.1⁰ and 61.1⁰

can be assigned to (111), (002) and (022) crystalline plane diffraction peaks respectively

which belong to wüstite.

For sample A shown in Figure 4.1 (b), the MWNTs showed a typical peak of (002) phase

of MWNTs or graphite at 26.4⁰. Peaks at 42.8⁰ and 44.6⁰ can be assigned to (100) and

29

(101) crystalline plane diffraction peaks, respectively and show the presence of MWNTs.

XRD studies demonstrated well-crystallized structure of the MWNT composite.

The XRD pattern of sample B is shown in Figure 4.1 (c). However, the graphite-like (002)

peak is somewhat weakened with a downward shift (2θ = 26.2⁰). The peaks at 42.9⁰ and

43.7⁰ can be assigned to (100) and (101) planes of MWNTs.

The XRD spectrum of boron trioxide is shown in Figure 4.1 (d). The two peaks (2θ =

28.0⁰ and 2θ = 40.3⁰) in the spectrum can be indexed as (3 1 0) and (4 2 0) crystal planes

of the cubic structure B2O3 respectively, not only in the peaks’ positions, but also in their

relative intensity. (Yang et al., 2005)

30

Figure 4.1: XRD diagram of (a) mill scale, (b) sample A, (c) sample B and (d)

boron trioxide.

20 25 30 35 40 45 50 55 60 65 70 75 80

Inte

nsi

ty (

a.u

.)

2θ (°)

(d)

(c)

(b)

(a)

(002)

(002)

(100)

(100)

(101)

(101)

(310)

(420)

MWNT

Magnetite (Fe3O4)

Hematite (Fe2O3)

Wüstite (FeO)

Boron trioxide

(022)

(104)

(113)

(111)

(002)

(022)

31

4.1.2 TEM

Figure 4.2 displays representative TEM images of the fabricated MWNTs. Figure 4.2 (a)

contains a micrograph of sample A, showing MWNTs with diameters as small as 55.76

nm and as big as 64.63 nm. Most of MWNTs exhibited bamboo-type morphology and

rough nanotube surfaces. In Figure 4.2 (b), the inner diameter is 9.21 nm and outer

diameter is 55.58 nm. The outer region of multiple essentially continuous layers of ordered

atoms is observed and a distinct inner core is visible, almost coaxial yet tampered with

kinks at several sites. Besides, multiple nanoparticles with different shapes and sizes are

isolated and contained as shown in the circled region. In Figure 4.2 (c), it is clearly seen a

MWNT with an inner diameter of 10.83 nm and an outer diameter of 25.48 nm. The

bamboo morphology is easily observed along the inner core. There is a nanoparticle-sized

lump believed to be mill scale encapsulated along a distinct nanotube below. It is probable

that the different MWNTs morphologies found in samples could be attributed to the

catalytic metallic nanoparticles. The final shape of these nanoparticles could give us

information about the process involved in the growth of different MWNTs observed.

Encapsulated nanoparticles with irregular morphologies distort the MWNTs structure and

form junctions (circled parts).

32

(a)

(b)

33

(c)

Figure 4.2: TEM images of sample A.

In Figure 4.3 (a), the outer tube diameters depicted are 170.36 nm, 211.49 nm and

160.43 nm which are larger than that of sample A. Sample B is synthesized by

substrate comprising mill scale and boron trioxide via CVD method. The lump seen

in Figure 4.3 (b) is excessively larger than 300 nm which might explain the lack of

distinct nanotubes. The catalyst particle size has been found to dictate the nanotube

diameter. Figure 4.3 (c) exhibits twisted nanotubes with multi collapsed sites and

lumps of varied sizes.

34

(a)

(b)

35

(c)

Figure 4.3: TEM images of sample B.

4.1.3 TGA

To analyse the thermal stability and reactivity of samples, thermo gravimetric analysis

(TGA) is carried out under oxygen atmosphere. The samples were analysed using a rate

heating of 10 ⁰C/min. Figure 4.4 shows the degradation curve for each sample, plotted as

loss mass (%) versus temperature.

No observable weight loss for mill scale as depicted in Figure 4.4 (a). Residual mass is

same with initial mass. This is anticipated as mill scale has been sintered at elevated

temperature during powder preparation. Any water or gases has been liberated

beforehand, rendering it stability throughout the thermal analysis.

36

Boron trioxide curve in Figure 4.4 (b) has the maximum value of the first loss mass

derivative 132.23 ⁰C. The degradation temperature is obtained from the maximum value

of the value of the first loss mass derivative. The mass loss halted at 447.63 ⁰C. By the

end of the thermal analysis, 68.08 % of initial sample is left. The residue is amorphous

boron trioxide. The weight liberated is believed to be water and impurities.

For sample A curve in Figure 4.4 (c), the degradation temperature is found to be 872.55

⁰C, where residual mass is 64.42 %. The mass starts to drop at 809.91 ⁰C and continues to

drop beyond 1000 ⁰C. The residual ash content observed at the final degradation

temperature can be attributed to the mill scale. The derivation curve shows a shoulder at

849.42 ⁰C before starting to plummet to the head at -0.00087 s-1 and eventually levelling

to -0.00021 s-1 like that of during at the shoulder earlier.

(a)

37

(b)

(c)

Figure 4.4: TGA and DTG curves of (a) mill scale, (b) boron trioxide and (c)

sample A.

38

4.2 Absorption Analysis

All composite samples are successfully prepared using resin system according to Table

4.2. Electromagnetic and microwave properties of the prepared samples were performed

using Agilent Technologies N5227A PNA Network Analyzer. 85071 Material

Measurement Software E07.02.29 automates complex permittivity and permeability

measurements. Measurements are taken within X-band (8-12 GHz).

Table 4.2: Summary for composite mold composition.

Sample Composition Remark

Weight ratio (B2O3 : Mill scale)

CVD product A 0 : 1.0

B 0.5 : 1.0

C 1.0 : 1.0 Weight ratio (Mill scale)

Raw mill scale without

undergoing CVD H 1.0

Weight ratio (B2O3 : A)

Mixing CVD product A

with unreacted raw B2O3

J 0.5 : 1.0

K 1.0 : 1.0

The log of the ratio of two powers P1 and P0, is measured in Bels:

1 𝐵𝑒𝑙𝑠 = 10 𝑑𝐵

and

𝑟𝑎𝑡𝑖𝑜 (𝑑𝐵) = 10 × 𝑙𝑜𝑔𝑃1

𝑃0= 20 × log Γ

where Γ is the reflection coefficient and

39

Γ = 𝑉𝑜𝑙𝑡𝑎𝑔𝑒1

𝑉𝑜𝑙𝑡𝑎𝑔𝑒0

Radar cross section (RCS) reduction is given by:

RCS = 1 − Γ2

The conversion of several reflection loss value is tabulated in Table 4.3 for convenient

reference.

Table 4.3: Conversion of reflection loss.

RL dB = 20 log Γ Γ = 𝑉𝑜𝑙𝑡𝑎𝑔𝑒1

𝑉𝑜𝑙𝑡𝑎𝑔𝑒0

𝑃𝑜𝑤𝑒𝑟1

𝑃𝑜𝑤𝑒𝑟0 RCS reduction RCS reduction (%)

-1.0000 0.8913 0.7943 0.2057 20.5672

-2.0000 0.7943 0.6310 0.3690 36.9043

-3.0000 0.7079 0.5012 0.4988 49.8813

-4.0000 0.6310 0.3981 0.6019 60.1893

-5.0000 0.5623 0.3162 0.6838 68.3772

-6.0000 0.5012 0.2512 0.7488 74.8811

-7.0000 0.4467 0.1995 0.8005 80.0474

-8.0000 0.3981 0.1585 0.8415 84.1511

-9.0000 0.3548 0.1259 0.8741 87.4107

-10.0000 0.3162 0.1000 0.9000 90.0000

-15.0000 0.1778 0.0316 0.9684 96.8377

-20.0000 0.1000 0.0100 0.9900 99.0000

-25.0000 0.0562 0.0032 0.9968 99.6838

-30.0000 0.0316 0.0010 0.9990 99.9000

-40.0000 0.0100 0.0001 0.9999 99.9900

Figure 4.5 shows the frequency dependence of reflection loss of six composite samples

which describes the electrical behaviour of linear electrical networks when undergoing

various steady state stimuli by electrical signals. Composite samples backed with metal

plate will exhibits quarter-wavelength cancellation through destructive superposition.

40

With similar composite thickness (t = 3mm), the reflection loss (RL) of each composite is

plotted in Figure 4.5 across the X band frequency (8-12 GHz). The RL value of composite

in Figure 4.5 (a) starts small in the low frequency region. It rapidly increases at the high

frequency region before gradually decreases in magnitude. Composite A has the

maximum reflection loss (RL = -28.26 dB) at 9.20 GHz. This translates to 99.85 % of

radar cross section reduction. The maximum reflection loss of composite J (RL = -13.50

dB) occurs at 9.76 GHz. Whereas the RL of composite K does not cross -5 dB mark before

10.46 GHz and attains its maximum reflection loss (RL = -6.74 dB) at 11.22 GHz.

For Figure 4.5 (b), none of the composites attains RL across the -5 dB mark. Composite

H has three RL peaks (RL = -2.18 dB, -4.14 dB and -3.30 dB) at 8.88 GHz, 11.12 GHz

and 11.80 GHz respectively. It is noted that no RL peak is found in composite B curve

across X-band although showing an increasing trend towards higher frequency. Maximum

reflection loss recorded at 12.00 GHz is -2.64 dB. Composite C has a RL peak (RL = -

0.90 dB) at 8.74 GHz and starts levelling off beneath RL = -1.00 dB border.

41

(a)

(b)

Figure 4.5: Reflection loss versus frequency graph for (a) sample A, J and K;

(b) sample B, C and H.

-30.0

-25.0

-20.0

-15.0

-10.0

-5.0

0.08.00E+09 9.00E+09 1.00E+10 1.10E+10 1.20E+10

Ref

lect

ion

loss

(d

B)

Frequency (Hz)

-5

-4

-3

-2

-1

08.00E+09 9.00E+09 1.00E+10 1.10E+10 1.20E+10

Ref

lect

ion

loss

(d

B)

Frequency (Hz)

H

B

C

A

J

K

42

CHAPTER 5

CONCLUSION

5.1 Conclusions

In this study, MWNT composites are synthesized via chemical vapor deposition method

using mill scale and boron trioxide as catalytic substrate. The variation of powder substrate

weight ratio (B2O3 : Mill scale) sees the introduction of boron trioxide annihilating the

MWNT growth due to its unsuitability as a hydrocarbon deposition catalyst. The

mechanism of growth involves hydrocarbon in gas phase dissociation on metal surfaces,

followed by diffusion to the particle surface of the particle where MWNT is precipitated.

Boron trioxide has a lower melting temperature (T = 450 ⁰C) than the CVD reactor

temperature (T = 750 ⁰C). Nevertheless, only sample A obtains a good yield of 237.8 %

of weight change after CVD process. Thus, they are studied using X-ray diffractometry,

transmission electron microscopy, thermogravimetric analysis and electromagnetic

absorption analysis.

All major XRD peaks is assigned to boron trioxide and raw mill scale powder which

contains magnetite, wüstite and hematite. CVD products, Sample A and Sample B, show

distinct (002) graphitic peak which indicates presence of MWNTs. Despite this, the TEM

images reveal that MWNT present contains multiple defects and some encapsulated

nanoparticles are observed along the nanotubes. Composite A starts to degrade at 872.55

⁰C and continues to lose weight beyond the terminal test temperature. While, mill scale

43

has no weight loss in thermal decomposition that runs up to 1000 ⁰C and boron trioxide

suffer a 32 % final weight loss long after its degradation temperature at 132.23 ⁰C.

From 8 GHz to 12 GHz, the microwave absorption studies reveal that composite A has

the maximum reflection loss (RL = -28.26 dB) at 9.20 GHz. It denotes composite A being

the more promising electromagnetic absorptive composite with the highest RL that

translates to 99.85 % of radar cross section reduction. Composite A is produced from CVD

process using only mill scale as its catalytic substrate and vaporized ethanol as its

hydrocarbon source. With the introduction of boron trioxide in CVD process, composite

B and C have insignificant electromagnetic absorption performance in which both

recorded maximum reflection loss not more than -4.5 dB across X-band.

5.2 Suggestions

Across 8-12 GHz, MWNT presence in sample A has distinctly improves the

electromagnetic absorption ability (RLmax = -28.26 dB) as compared to sample H, a raw

mill scale where RLmax does not cross -5.00 dB. Despite that, the introduction of boron

trioxide into the CVD substrate has retarded MWNT growth. Hence, further study could

be directed towards a binary system comprising both MWNT synthesis catalyst. Further

investigation on the Raman spectroscopy of MWNT synthesized in this project could be

done to better understand carbon nanotubes’ structures.

44

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48

VITAE

Lee Shian Boon

Home Address: 1, Jln Bunga Tanjung Satu, 12300 Butterworth, Penang, Malaysia.

Current address: No 4111, Tingkat 1, Blok 30, Kolej Sultan Alaeddin Suleiman

Shah, Universiti Putra Malaysia, 43400 Serdang.

Email: shianboon@hotmail.com

Phone No.: 012-4411962

Education:

University Putra Malaysia

Bachelor Science of Materials Science

CGPA : 3.75

Graduation Year : June 2018

SMJK (C) Chung Ling Butterworth, Penang

STPM

CGPA : 3.25

Graduation Year : December 2013

Personal Particulars:

Age: 24 Years Old Date of Birth: 28-03-1994

Nationality: Malaysian Marital Status: Bachelor

49