SYNTHESIS AND CHARACTERIZATION OF HYBRID NANOFLUIDS FROM MAGNETITE AND GOLD
NANOPARTICLES
BY
HAIZA BINTI HAROON
A thesis submitted in fulfilment of the requirement for the degree of Doctor of Philosophy (Engineering)
Kulliyyah of Engineering
International Islamic University Malaysia
DECEMBER 2019
ii
ABSTRACT
Nanofluids is a good candidate for heat transfer applications due to their anomalous thermal conductivity enhancement. Mixed nanofluids (MNs) also known as hybrid nanofluids based on mixture of magnetite, Fe3O4 and gold, Au nanoparticles were successfully developed in this work. Magnetite, Fe3O4 nanoparticles produced via Massart’s procedure (a simple co-precipitation technique) were used to prepare water based magnetite ferrofluids without addition of any stabilizing agent or surfactant.
Magnetic properties measured by vibrating sample magnetometer (VSM) at room temperature showed that magnetite nanoparticles are almost superparamagnetic with coercivity (Hc) value of 40.164 G. The saturation magnetization (Ms) of the magnetite nanoparticles was 61.864 emu/g which is lower than the bulk value of 92-100 emu/g.
Five water based ferrofluids were prepared using different volume fractions of magnetite suspension 0.1, 0.05, 0.02, 0.01 and 0.005, respectively. Colloidal gold (Au) nanoparticles were synthesized using electro-dissolution-reduction method that consists of a simple two-electrode cells connected to a DC power supply. Throughout the process, bulk gold at the anode was oxidized into gold cations which then reacted with the chloride ions to form aurochloride complex. The complex ions were then reduced by the citrate ion to form colloidal gold nanoparticles. The parameters investigated are effects of terminal voltage and citrate concentration. The effects of these parameters on the particle size, shape and distribution were studied. For the effect of terminal voltage, the mean particle sizes obtained were 28.22 nm, 28.12 nm and 25.04 nm for 32 V, 36 V and 40 V, respectively from transmission electron microscope (TEM) analysis.
For the effect of citrate concentration, the mean sizes of gold nanoparticles were 28.12 nm, 28.33 nm, 29.14 nm and 29.68 nm for 0.05 M, 0.10 M, 0.15 M and 0.20 M, respectively from TEM analysis. TEM micrograph showed that the shape of gold nanoparticles obtained was almost spherical with fairly good uniformity for effects of terminal voltage and citrate concentration. The thermal conductivity and suspension stability of ferrofluids, gold nanofluids and hybrid nanofluids were investigated in order to evaluate their potential application as heat transfer fluid. Thermal conductivity was measured at five different temperature, 25°C, 30°C, 40°C, 50°C and 60°C using KD2 Pro thermal property analyzer. Thermal conductivity increased as the temperature increases and reached its maximum at 60°C for all nanofluids samples. Ferrofluid prepared using 0.01 volume fraction of magnetite suspension demonstrated highest thermal conductivity enhancement of 49.4% with respect to water at temperature 60°C.
Gold nanofluid prepared using 36 V terminal voltage exhibited highest thermal conductivity enhancement of 202.4% compared to water at temperature 60°C. Thus, this nanofluid suspension was selected and introduced to suspended magnetite nanoparticles to increase the thermal conductivity of hybrid nanofluids system. Hybrid nanofluids (HNF1) prepared using highest concentration of gold nanoparticles demonstrated substantial increase in thermal conductivity compared to other hybrid nanofluids that is 1.0794 Wm-1K-1 at 60°C. Overall, all hybrid nanofluids samples demonstrated excellent dispersion up to one week and relatively stable up to 2 weeks.
iii
ثحبلا ةصلاخ
ا تاقيبطت يف ديج لصومك هحرتقم تابكرم ةيونانلا عئاوملا ربتعت لا
لع ةيلاعلا اهتردق ببسب يرارحلا لاقتن ى
ةدايز
هيونانلا عئاوملا طلخ .مظتنم ريغلا يرارحلا ليصوتلا (MNs)
عئاوملا مسأب اضيا فرعي ةيونانلا
نيجهلا ىلع ًءانبة
ديدحلا ديسكوا عم يسيطانغملا جيزملا O4
Fe3
ثحبلا اذه يف حاجنب ةيونانلا تائيزجلا ريوطت مت ،بهذلاو .
ثيح
ةيونانلا تائيزجلا مادختسا مت O4
Fe3
ءارجإ قيرط نع اهجاتنإ متي يتلا (
ريطقتلا ةينقت ا يف )ةطيسبلا
ملا دادع عئاو
رارقتسا لماع يأ ةفاضإ نود ءاملا مادختساب ةطنغمملا .يحطسلا دشلاب ليلقتلا وأ
ترهظأ دقو صئاصخلا
ةيسيطانغملا ةيسيطانغملا سايقم ةطساوب اهسايق دعب
(VSM) تنغملا تائيزج نأ ةفرغلا ةرارح ةجرد يف
ا تي
ابيرقت يه ةيونانلا ةمواقملا ةوق عم ةيزاوتملا ةيسطانغملل ةميق ىلعأ
c) ةغلابلا (H G 40.164 امأ .
ا لا عابش
يسيطانغملا
s) تائيزجلل(M يسيطانغملا
ة ةيونانلا ف تناك 61.864 emu/g
نم لقأ يهو ا
ةيمجحلا ةميقل emu/g
100-92 دقل .
تابكرم نم ةسمخ ريضحت مت عئاوملا
لا ةطنغمم مادختساب ةيئاملا وذ خورش
ةفلتخم ماجحأ ملل
تياتنغ
يه و ، 0.1
،0.05 ،0.02 و0.01 0.005 هذلا تائيزج عينصت مت .يلاوتلا ىلع ، ةيورغلا ب
مادختساب(Au)
خ نم نوكتت يتلا يئابرهكلا نابوذلا نم دحلا ةقيرط لا
خ .ةقاطلا ردصمب ةلصتم بطقلا ةيئانث اي للا
معلا مت ،ةيل
يف بهذلا ةدسكأ بجوملا بطقلا
بكرم ليكشتل ديرولكلا تانويأ عم كلذ دعب تلعافت يتلاو ةيبهذ تانويتاك ىلإ
رولكوروأ ا
كلذ دعب .دي مت
ا ضيفخت لا رتس نويأ ةطساوب ةدقعملا تانوي ي
غلا بهذلا نم ةيونان تاميسج ليكشتل ت .ةيور
مت يتلا لماوعلا اهتسارد
ا تاريثأت يه يئابرهكلا دهجل
يفرطلا رتسلا زيكرتو ي
.ت ت ثيح ع لماوعلا هذه رثؤ مجح ىل
.اهعيزوتو اهلكشو تاميسجلا ةبسنلاب امأ
ل تأ ريث يفرطلا يئابرهكلا دهجلا أ طسوتم ناك ،
تلا تاميسجلا ماجح مت ي
اهيلع لوصحلا يه
( 28.22
، 28.12 و 25.04 رتمونان ) مادختساب ،تلوف32
و تلوف36 ،يلاوتلا ىلع ،تلوف40
ا رهجملا ليلحت نم للإ
ينورتك لاسرلإ . (TEM) امأ
رتيسلا زيكرت ريثأت ي
بهذلا تائيزج ماجحأ طسوتم غلب ، ت
ةيونانلا 28.12 ، رتمونان 28.33
، رتمونان 29.14
و رتمونان 29.68
ل رتمونان ، م0.05
، م0.10 و م0.15
ليلحت نم يلاوتلا ىلع ، م0.20 (TEM)
. ليلحتل ةيرهجملا روصلا ترهظأ يتلا بهذلا تائيزج لكش نأTEM
ناك اهيلع لوصحلا مت ت
لا ريثأتل ام دح ىلإ ديج عيزوت عم ةيورك ابيرقت يئابرهكلا دهج
زيكرتو رتسلا تي . سايق مت
دنع يرارحلا ليصوتلا ةيلباق سمخ
ةفلتخم ةرارح تاجرد (
، 25
،30
،40 50 و 60 ةيوئم ةجرد )
للحم مادختساب
صئاصخلا ةيرارحلا
(KD2 Pro) ةسارد لجأ نم
ةيلباق يرارحلا ليصوتلا ةيرارقتساو
لل قيلعتلا م ئاو ع مملا ،ةطنغ
لو م تاميسج و
و ةيونانلا بهذلا عئا ل
أ نم ةنيجهلا ةيونانلا عئاومل ن عئامك اهقيبطت ةيلامتحا مييقت لج
ا لق لل .ةرارح
ةيلباق نأ جئاتنلا ترهظأ يرارحلا ليصوتلا
تداز صقأ ىلإ تلصوو ةرارحلا ةجرد عافترا عم ا
دنع اه ةجرد60
لا تانيع عيمجل ةيوئم م
لئاو ريضحت مت دقو .ةيونانلا مادختساب طنغمملا عئاملا
يواسي مجح 0.01
مجح نم ءزج
تنغملا ا تي ذلاو رهظا ي يرارحلا ليصوتلل ةدايز ىلعأ ىلا تلصو
٪49.4 ةبسنلاب ىلإ ةرارح ةجرد دنع ءاملا 60
.ةيوئم ةجرد أ ًاضيأ
مادختساب هرضحملا بهذلا عئام تائيزج ترهظ تلوف36
يفرطلا دهجلا نم ةيلباقل ةدايز ىلعأ
ةبسنب يرارحلا ليصوتلا 202.4
٪ ةرارح ةجرد دنع ءاملاب ةنراقم م ةجرد60
،يلاتلابو .ةيوئ دقف
رايتخا مت اذه
يونانلا عئاملا ةيونانلا عئاوملا ماظنل يرارحلا ليصوتلا ةدايزل ةقلعملا ةيسيطانغملا ونانلا تائيزج ىلإ هميدقتو
.هنيجهلا دقو نيجهلا يونانلا لئاسلا رهظا (HNF1)
ةيبهذلا ةيونانلا تائيزجلا نم زيكرت ىلعأ مادختساب رضحملا
iv
ف ةريبك ةدايز ا ةنيجهلا ةيونانلا لئاوسلاب ةنراقم يرارحلا ليصوتلا ةيلباق ي
أل غلبت يتلا ىرخ 1.0794
1
K - 1
Wm-
دنع ةنيجهلا ةيونانلا لئاوسلا تانيع عيمج ترهظأ ،ماع لكشب .ةيوئم ةجرد60 ًاتتشت
بسأ ىلإ لصت ةدمل ا ًزاتمم عو
.نيعوبسأ ىلإ لصت اًيبسن ةرقتسمو دحاو .
v
APPROVAL PAGE
The thesis of Haiza Binti Haroon has been approved by the following:
_____________________________
Iskandar Idris Bin Yaacob Supervisor
_____________________________
Ahmad Zahirani Bin Ahmad Azhar Co-Supervisor
_____________________________
Mohammed Saedi Jami Internal Examiner
_____________________________
Ezzat Chan B. Abdullah External Examiner
_____________________________
Che Mohd Ruzaidi Bin Ghazali External Examiner
_____________________________
Roslina Bin Othman Chairman
vi
DECLARATION
I hereby declare that this thesis is the result of my own investigations, except where otherwise stated. I also declare that it has not been previously or concurrently submitted as a whole for any other degrees at IIUM or other institutions.
Haiza Binti Haroon
Signature ... Date ...
vii
INTERNATIONAL ISLAMIC UNIVERSITY MALAYSIA
DECLARATION OF COPYRIGHT AND AFFIRMATION OF FAIR USE OF UNPUBLISHED RESEARCH
SYNTHESIS AND CHARACTERIZATION OF HYBRID NANOFLUIDS FROM MAGNETITE AND GOLD
NANOPARTICLES
I declare that the copyright holders of this thesis are jointly owned by the student and IIUM.
Copyright © 2019 Haiza Binti Haroon and International Islamic University Malaysia. All rights reserved.
No part of this unpublished research may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise without prior written permission of the copyright holder except as provided below
1. Any material contained in or derived from this unpublished research may be used by others in their writing with due acknowledgement.
2. IIUM or its library will have the right to make and transmit copies (print or electronic) for institutional and academic purposes.
3. The IIUM library will have the right to make, store in a retrieved system and supply copies of this unpublished research if requested by other universities and research libraries.
By signing this form, I acknowledged that I have read and understand the IIUM Intellectual Property Right and Commercialization policy.
Affirmed by Haiza Binti Haroon
……..……….. ………..
Signature Date
viii
ACKNOWLEDGEMENTS
Alhamdulillah, praise to Allah S.W.T the Almighty for all the blessings and opportunities He gave on me especially for the good health in every single day of being alive. Peace and blessings be upon the Prophet Muhammad S.A.W. I would like to extend my gratitude to all the individuals that involved directly or indirectly throughout the research work until the completion of this thesis. They had made a significant impact in order to make this research work possible especially during the lab work. Their encouragement and support as well as their assistance had made this work interesting and most memorable experience which I will cherish forever.
I would like to express my deepest appreciation to my supervisor Prof. Iskandar Idris Bin Yaacob for his patience, encouragement, advice, support and guidance throughout the research and writing process. I would also like to thank my co-supervisor Dr. Ahmad Zahirani Bin Ahmad Azhar for his assistance, advice and encouragement during this research work. My sincerely thanks goes to all staffs in Kulliyyah of Engineering including staffs in Manufacturing and Materials Engineering Department for their cooperation towards the completion of this study. Not to forget Dr. Nurin Wahidah Binti Mohd Zulkifli from Department Of Mechanical Engineering, University Malaya for allowing me to use their KD2 Pro Thermal Properties equipment.
Last but not least, I would like to thank my husband, parents and family for their endless love, suppport and continuous encouragement throughout my years of study. To my employer Universiti Malaysia Perlis (UniMAP) and scholar Malaysian High Ministry of Education, thank you for giving me the golden opportunity to pursue my study and financially supported my Ph.D.
ix
TABLE OF CONTENTS
Abstract ………. ii
Abstract in Arabic ………. iii
Approval Page ………... v
Declaration……..………... vi
Copyright…….……….. vii
Acknowledgements ………... viii
Table of Contents ……….. List of Tables ……… ix xii List of Figures ………... xiv
List of Abbreviations ……… xix
List of Symbols ……… xx
CHAPTER ONE: INTRODUCTION ……….….. 1
1.1 Background of the Study ………. 1
1.2 Problem Statement and Its Significance ……….. 5
1.3 Research Philosophy……… 7
1.4 Research Objectives ………... 14
1.5 Scope of Research....………... 14
CHAPTER TWO: LITERATURE REVIEW ……….. 16
2.1 Introduction of Nanoscience and Nanotechnology………... 16
2.2 Nanomaterials ………..……… 18
2.2.1 Nanoparticles ……….……… 19
2.3 Iron Oxide Nanoparticles……….. 21
2.3.1 Synthesis of Magnetite (Fe3O4) Nanoparticles……….. 23
2.3.1.1 Co-precipitation………... 24
2.3.2 Special Features of Magnetite Nanoparticles………. 26
2.3.2.1 Finite–Size and Surface Effects……….……… 26
2.3.2.2 Magnetic Properties of Bulk and Nano-sized Magnetite Nanoparticles………... 27
2.4 Colloidal Gold (Au) Nanoparticles………... 27
2.4.1 Synthesis of Colloidal Gold Nanoparticles……… 29
2.4.1.1 Chemical Reduction……… 33
2.4.1.2 Electrochemical Method……….. 34
2.5 Nanofluids………. 39
2.5.1 Preparation Method………...………. 41
2.5.1.1 One-step Method………..………... 42
2.5.1.2 Two-step Method………..………... 42
2.5.2 Thermal Conductivity of Nanofluids………...……….. 43
2.5.3 Stability of Nanofluids….…...………... 44
2.5.4 Theoretical Model of Nanofluids………..………. 47
2.5.5 Applications of Nanofluids……….………... 53
2.6 Ferrofluids……….…… 54
x
2.6.1 Theoretical Model of Ferrofluids……….……….. 57
2.6.2 Tailoring the Thermal Conductivity Enhancement of Heat Transfer………... 58
2.6.2.1 Influence of Temperature………...………. 59
2.6.2.2 Influence of Volume Fraction……….. 60
2.6.2.3 Influence of Particles Morphology…………...………... 60
2.6.3 Stability of Ferrofluids………...……… 61
2.7 Gold (Au) Nanofluids………... 63
2.7.1 Tailoring the Thermal Conductivity Enhancement of Heat Transfer Gold Nanofluids………... 65
2.7.2 Stability of Gold Nanofluids……….………. 67
2.7.3 Applications of Gold Nanofluids………... 68
2.8 Hybrid Nanofluids……… 69
2.8.1 Thermal Properties of Hybrid Nanofluids……….. 71
2.8.2 Preparation Techniques…………..……… 74
2.8.3 Stability of Hybrid Nanofluids………... 75
2.8.4 Applications of Hybrid Nanofluids……… 76
CHAPTER THREE: RESEARCH METHODOLOGY……….. 77
3.1 Introduction ……….. 77
3.2 Raw Materials ……….………. 79
3.3 Synthesis of Magnetite Nanoparticles: Co-precipitation……….. 80
3.3.1 Experimental.……… …... 82
3.4 Synthesis Colloidal Gold Nanoparticles: Electro-Dissolution Reduction Method………... 83
3.4.1 Experimental……….. 86
3.5 Preparation of Ferrofluids………. 88
3.6 Preparation of Gold Nanofluids………... 90
3.7 Preparation of Hybrid Nanofluids……… 91
3.8 Characterization Methods………. 92
3.8.1 Structural and Morphological………... 92
3.8.1.1 Transmission Electron Microscopy (TEM)………. 92
3.8.1.2 Field-Emission Scanning Electron Microscopy (FESEM)…….…… ……… 93
3.8.2 Phase Analysis……….……….. 94
3.8.2.1 X-ray Diffraction (XRD)………... 94
3.8.3 Suspension Stability………..…………. 95
3.8.3.1 Zeta Potential Analyzer……….….. 95
3.8.4 Thermal Properties……….…… 96
3.8.5 Magnetic Properties……….….. 96
3.8.6 Other Supporting Characterization Techniques of Gold Nanoparticles………...……… 97
CHAPTER FOUR: RESULTS AND DISCUSSION……….... 98
4.1 Introduction ……….. 98
4.2 Magnetite (Fe3O4) Nanoparticles……… 100
4.2.1 Magnetic Properties………..……. 106
4.3 Gold (Au) Nanoparticles………..………. 108
4.3.1 Effects of Terminal Voltage………... 109
xi
4.3.2 Effects of Citrate Concentration………. 125
4.3.3 Stability of Colloidal Gold (Au) Nanoparticles………. 141
4.4 Ferrofluids……….………...……….…… 145
4.4.1 Ferrofluids Thermal Conductivity ………. 144
4.4.2 Ferrofluids Stability………... 147
4.5 Gold Nanofluids………..……….. 151
4.5.1 Gold Nanofluids Thermal Conductivity………... 153
4.5.1.1 Gold Nanofluids Prepared Using Different Terminal Voltage………... 154
4.5.1.2 Gold Nanofluids Prepared Using Different Citrate Concentration………... 159
4.5.2 Gold Nanofluids Stability……….. 164
4.6 Hybrid Nanofluids……… 166
4.6.1 Hybrid Nanofluids Thermal Conductivity………. 166
4.6.1.1 Effects of Magnetite Nanoparticles Concentration……. 168
4.6.1.2 Effects of Gold Nanoparticles Concentration…... 172
4.6.2 Hybrid Nanofluids Stability………... 175
4.6.2.1 Effects of Magnetite Nanoparticles Concentration……. 176
4.6.2.2 Effects of Gold Nanoparticles Concentration…... 179
CHAPTER FIVE: CONCLUSION AND RECOMMENDATION…………. 184
5.1 Conclusion ………..………. 184
5.2 Recommendations for Future Work………. 191
REFERENCES………. 193
APPENDIX A………... 200
APPENDIX B………... 202
xii
LIST OF TABLES
Table 2.1:
Several Previous Experimental Investigation on the Thermal Conductivity of Water-Based Nanofluids 40 Table 2.2: Thermal Conductivity Models for Nanofluids 49 Table 3.1: Raw Materials for Synthesis of Magnetite (Fe3O4) Nanoparticles 79 Table 3.2: Raw Materials for Synthesis of Colloidal Gold (Au)
Nanoparticles
80
Table 3.3: Various Volume Fractions of Water Based Ferrofluids 90 Table 3.4: Zeta Potential and Associated Suspension Stability 95 Table 4.1: Terminal Voltage Values Used to Study the Effect on Particle
Size of Colloidal Gold Nanoparticles 109
Table 4.2: EDX Analysis of Gold for 32 V Terminal Voltage 121 Table 4.3: EDX Analysis of Gold for 36 V Terminal Voltage 121 Table 4.4: EDX Analysis of Gold for 40 V Terminal Voltage 122 Table 4.5: The Gold Nanoparticles Concentration of Each Colloidal Gold
Nanoparticles Prepared Using Different Terminal Voltage 124 Table 4.6: Concentration of Citrate Used to Study the Effect on Particle
Size of Colloidal Gold Nanoparticles 126
Table 4.7: Gold Nanoparticles Concentration of Each Colloidal Gold Nanoparticles Prepared Using Different Citrate Concentration 140 Table 4.8: Wavelength and Absorption of Colloidal Gold Nanoparticles
After Synthesis and 12 Months Later 142
Table 4.9: Various Parameters Employed to Study the Effect of Magnetite Nanoparticles Concentration on the Thermal Conductivity Enhancement Compared to Water at Different Temperature 145 Table 4.10: Various Parameters Employed to Study the Thermal
Conductivity of Each Gold (Au) Nanofluids Prepared 151
xiii
Table 4.11: Thermal Conductivity of Gold Nanofluids Prepared Using Different Terminal Voltage, Thermal Conductivity of Water and Thermal Conductivity Enhancement of Each Gold (Au) Nanofluids with Respect to Water at Different Temperature 155 Table 4.12: Thermal Conductivity of Gold Nanofluids Prepared Using
Different Citrate Concentration, Thermal Conductivity of Water and Thermal Conductivity Enhancement of Each Gold (Au) Nanofluids with Respect to Water at Different Temperature 160 Table 4.13: Zeta Potential Value of Gold (Au) Nanofluid Suspensions
Measured by Zeta Potential Analyzer 165
Table 4.14: Parameters Employed to Study the Effect of Magnetite Nanoparticles Suspension on the Thermal Conductivity of Hybrid Nanofluids Measured at Different Temperature 167 Table 4.15: Parameters Employed to Study the Effect of Gold Nanoparticles
on the Thermal Conductivity of Hybrid Nanofluids Measured at
Different Temperature 168
Table 4.16: Thermal Conductivity of Hybrid Nanofluids Measured at
Different Temperature 169
Table 4.17: Thermal Conductivity of Hybrid Nanofluids Measured at
Different Temperature 173
xiv
LIST OF FIGURES
Figure 2.1:
Formation Mechanism of Gold (Au) Nanoparticles with Various Sizes and Shapes by Chemical Reduction Method 34 Figure 2.2: Formation of Electrochemically Produced Tetraalkylammonium-
Stabilized Metal Clusters 35
Figure 2.3: A Schematic Diagram of the Apparatus for the Synthesis of Gold Nanostructures via an Electrochemical Method 37 Figure 2.4: Electrochemical Formation of Silver Nanoparticles in Distilled
Water
38
Figure 2.5: Schematic Representation of Some of the Applications of Nanofluids in (a) Heat Transfer (b) Defect Sensors (c) Anti Infection Therapy (d) Energy Harvesting System (e) Hyperthermia and (f) Cosmetics
54
Figure 3.1: Flow Chart of Synthesis Process of Magnetite Nanoparticles by
Co-Precipitation Method 81
Figure 3.2: Flow Chart of Synthesis Process of Gold Nanoparticles Using Electro-Dissolution-Reduction Method and the Characterization Techniques
84
Figure 3.3: A Schematic Diagram of the Apparatus for the Synthesis of Gold Nanoparticles via Electro-Dissolution-Reduction Method 87 Figure 3.4: (a) - (f) Illustrate a Typical Color Changes of the Solution Starting
From Colorless to Red-Wine Throughout the Synthesis Process of
Colloidal Gold Nanoparticles 88
Figure 3.5: Flow Chart of the Preparation of Heat Transfer Ferrofluids 89 Figure 3.6: Flow Chart of the Preparation of Heat Transfer Hybrid Nanofluids 91 Figure 4.1: TEM Micrographs of Magnetite, Fe3O4 Nanoparticles at (a), (b)
Low and (c) High Magnification 102
Figure 4.2: Particle Size Distributions of Magnetite Nanoparticles Synthesized Using Co-Precipitation Technique 103 Figure 4.3: SEM Micrographs of Magnetite, Fe3O4 Nanoparticles at
Magnification 100 KX 104
xv
Figure 4.4: XRD Pattern for Magnetite Nanoparticles Produced by Co-
Precipitation Technique 106
Figure 4.5: Hysteresis Loop of Magnetite, Fe3O4 Nanoparticles at Room
Temperature 108
Figure 4.6: TEM Micrograph of Colloidal Gold Nanoparticles at (a), (b) Low and (c) High Magnification for Terminal Voltage 32 V (Sample
Au9V32C0.05) 110
Figure 4.7: TEM Micrograph of Colloidal Gold Nanoparticles at (a), (b) Low and (c) High Magnification for Terminal Voltage 36 V (Sample
Au10V36C0.05) 111
Figure 4.8: TEM Micrograph of Colloidal Gold Nanoparticles at (a), (b) Low and (c) High Magnification for Terminal Voltage 40 V (Sample
Au13V32C0.05) 112
Figure 4.9: Particle Size Distribution of Colloidal Gold Nanoparticles
Produced Using 32 V Terminal Voltage 114
Figure 4.10: Particle Size Distribution of Colloidal Gold Nanoparticles
Produced Using 36 V Terminal Voltage 115
Figure 4.11: Particle Size Distribution of Colloidal Gold Nanoparticles
Produced Using 40 V Terminal Voltage 115
Figure 4.12: SEM Micrograph of Gold Nanoparticles Produced Using 32 V Terminal Voltage (a) at Magnification 50 KX (b) at Magnification
150 KX 117
Figure 4.13: SEM Micrograph of Gold Nanoparticles Produced Using 36 V Terminal Voltage (a) at Magnification 50 KX (b) at Magnification
150 KX 118
Figure 4.14: SEM Micrograph of Gold Nanoparticles Produced Using 40 V Terminal Voltage (a) at Magnification 50 KX (b) at Magnification
150 KX 119
Figure 4.15: Elemental Analysis of Gold Nanoparticles for 32 V Terminal Voltage
121
Figure 4.16: Elemental Analysis of Gold Nanoparticles for 36 V Terminal Voltage
121
Figure 4.17: Elemental Analysis of Gold Nanoparticles for 40 V Terminal Voltage
122
xvi
Figure 4.18: UV-Vis Spectra of Colloidal Gold Nanoparticles Synthesized by Electro-Dissolution-Reduction Method at Different Terminal Voltage (a) 32 V, (b) 36 V and (c) 40 V 123 Figure 4.19: A Plot of Gold Nanoparticles Concentration Against Terminal
Voltage Applied for Electro-Dissolution-Reduction Method 124 Figure 4.20: TEM Micrograph of Colloidal Gold Nanoparticles at (a), (b), (c)
Low and (d) High Magnification for Citrate Concentration 0.05 M
(Sample Au59V36C0.05) 128
Figure 4.21: TEM Micrograph of Colloidal Gold Nanoparticles at (a), (b), (c) Low and (d) High Magnification for Citrate Concentration 0.10 M
(Sample Au62V36C0.10) 129
Figure 4.22: TEM Micrograph of Colloidal Gold Nanoparticles at (a), (b), (c) Low and (d) High Magnification for Citrate Concentration 0.15 M
(Sample Au63V36C0.15) 130
Figure 4.23: TEM Micrograph of Colloidal Gold Nanoparticles at (a), (b), (c) Low and (d) High Magnification for Citrate Concentration 0.20 M
(Sample Au64V36C0.20) 131
Figure 4.24: Particle Size Distribution of Colloidal Gold Nanoparticles Produced Using 0.05 M Citrate Concentration 132 Figure 4.25: Particle Size Distribution of Colloidal Gold Nanoparticles
Produced Using 0.10 M Citrate Concentration 133 Figure 4.26: Particle Size Distribution of Colloidal Gold Nanoparticles
Produced Using 0.15 M Citrate Concentration 133 Figure 4.27: Particle Size Distribution of Colloidal Gold Nanoparticles
Produced Using 0.20 M Citrate Concentration 134 Figure 4.28: SEM Micrograph of Gold Nanoparticles Produced Using 0.05 M
Citrate Concentration (a) at Magnification 50 KX (b) at
Magnification 150 KX 135
Figure 4.29: SEM Micrograph of Gold Nanoparticles Produced Using 0.10 M Citrate Concentration (a) at Magnification 50 KX (b) at
Magnification 100 KX 136
Figure 4.30: SEM Micrograph of Gold Nanoparticles Produced Using 0.15 M Citrate Concentration (a) at Magnification 50 KX (b) at
Magnification 100 KX 137
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Figure 4.31: SEM Micrograph of Gold Nanoparticles Produced Using 0.20 M Citrate Concentration (a) at Magnification 50 KX (b) at
Magnification 100 KX 138
Figure 4.32: UV-Vis Spectra of Colloidal Gold (Au) Nanoparticles Synthesized by Electro-Dissolution-Reduction Method Using Different Citrate Concentration (a) 0.05 M (b) 0.10 M (c) 0.15 M and (d) 0.20 M
139
Figure 4.33: A Plot of Synthesized Gold Nanoparticles Concentration Against Citrate Concentration Used in Electro-Dissolution-Reduction Method
141
Figure 4.34: UV-Vis Spectra of Colloidal Gold (Au) Nanoparticles Synthesized by Electro-Dissolution-Reduction Method Using 0.05 M Citrate Concentration (a) After Synthesis (b) 12 Months After Synthesis
143
Figure 4.35: Thermal Conductivity of Water Based Ferrofluids at Different Concentrations as a Function of Temperature 147 Figure 4.36: Dispersion Property of Water Based Magnetite Ferrofluid
Suspensions (a) Day 1, (b) 2 Days, (c) 3 Days, (d) 4 Days, (e) 1 Week and (f) 2 Weeks, Respectively 150 Figure 4.37: Thermal Conductivity Gold Nanofluids Prepared Using Different
Terminal Voltage and Thermal Conductivity of Water as a
Function of Temperature 156
Figure 4.38: Thermal Conductivity Gold Nanofluids Prepared Using Different Citrate Concentrations and Thermal Conductivity of Water as a
Function of Temperature 162
Figure 4.39: Thermal Conductivity of Hybrid Nanofluids Prepared Using Different Magnetite Nanoparticles Concentrations as a Function of Temperature
169
Figure 4.40: Thermal Conductivity of Enhancement of Hybrid Nanofluids (HNF1) Compared to Ferrofluid Suspension (1M99W) Both Consists of Same Concentration of Magnetite Nanoparticles as a
Function of Temperature 171
Figure 4.41: Thermal Conductivity of Gold Nanofluid Suspension (GNF2V36C0.05), Hybrid Nanofluids (HNF1), Ferrofluid Suspension (1M99W) and as a Function of Temperature 172 Figure 4.42: Thermal Conductivity of Hybrid Nanofluids at Different Gold
Nanoparticles Concentrations as a Function of Temperature 174
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Figure 4.43: Photograph of Hybrid Nanofluids (a) Day 1, (b) 2 Days, (c) 3 Days, (d) 4 Days, (e) 1 Week and (f) 2 Weeks, Respectively 178 Figure 4.44: Photograph of Hybrid Nanofluids (a) Day 1, (b) 2 Days,
(c) 3 Days, (d) 4 Days, (e) 1 Week and (f) 2 Weeks, Respectively 182
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LIST OF ABBREVIATIONS
AAS Atomic Absorption Spectroscopy
Au Gold
AuNP Gold Nanoparticles
EDX Energy Dispersive X-ray Spectroscopy
FCC Face Centered Cubic
FESEM Field Emission Scanning Electron Microscope
HNF Hybrid Nanofluids
MNs Mixed Nanofluids
TEM Transmission Electron Microscope
TG/DTA Thermogravimetric/Differential Thermal Analyzer UV-VIS Ultraviolet-visible Spectroscopy
VSM Vibrating Sample Magnetometer XRD X-ray Diffraction
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LIST OF SYMBOLS
ρ Density (g/cm³)
m Mass (g)
d Dimension (mm)
V Volume (cm³)
M Concentration
T Temperature (°C)
AV Voltage (kV)
WD Working Distance (mm)
λ Wavelength (Å)
A Current (mA)
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CHAPTER ONE INTRODUCTION
1.1 BACKGROUND OF THE STUDY
Continuous device miniaturization and increasing thermal loads in high speed devices, microelectronics and high power engines have led to the importance of having a new cooling liquid for a better heat management. Low heat transfer performance namely thermal conductivity is the main drawback for conventional fluids such as water and ethylene glycol to be used in heat transfer applications that involve an enormous amount of heat exchange (Gupta et al., 2018).
Advances in nanotechnology have made it possible to produce new category of heat transfer fluids termed nanofluids. At present, nanofluids are regarded as a good candidate to overcome these issues due to their remarkable thermo-physical properties with no or low penalty in pressure drop, substantial enhancement in heat transfer characteristics and excellent transport properties (Das, 2017).
Nanofluids are stable suspension of nanometer-sized solid particles called nanoparticles in the range of 1-100 nm in a carrier fluids or a base fluids. Based on numerous experimental and theoretical studies, researchers have pointed out that nanofluids generally exhibit greater heat transfer characteristics than the common cooling fluids. Addition of solid particles with higher thermal conductivity than base fluid is one of the key initiative to improve thermophysical properties of conventional fluids. The exceptional properties of nanofluids precisely anomalous enhancement in
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thermal conductivity have opened the door for their possible applications in heat transfer. At present, extensive research studies have been carried out to use this novel medium in solar energy system especially solar collectors (Yazdanifard et al., 2017).
Although, nanofluids have emerged as a potential candidate for tailoring and production of heat transfer fluid, nanofluid is not about simply preparing a liquid-solid mixture. The most important criterion of this engineered colloidal suspension is agglomeration-free stable suspension for long durations without any chemical changes in the carrier fluid. For that reason, dispersion of nanoparticles in the base fluid is one of the critical issues in nanofluids. Nanofluids can offer numerous benefits when the nanoparticles are properly dispersed aside from enhanced thermal conductivity. It can improve heat transfer and stability, microchannel cooling without clogging, the possibility of miniaturizing systems scaling and reduction in pumping power (Haddad et al., 2014).
Hence, proper preparation methods is the key aspect of nanofluids stability that determine their sustainability and efficiency. In many cases, suitable stabilization methods are also required to produce a long term stable nanofluids. Likewise, selection of instruments and characterization method for stability inspection, analytical models and precise measurement techniques of nanofluids are undoubtedly crucial.
Ferrofluids are colloidal suspension of magnetic nanoparticles and may be considered as subclass of nanofluids. This new engineering medium depends on external magnetic fields due to structure formation, such as clusters or chains of the magnetic particles (Krichler & Odenbach, 2013). Recent studies have shown significant
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enhancement in the thermal conductivity of magnetite, Fe3O4 when magnetic field is applied. The main mechanism responsible for such enhancements is believed to be particle alignment in the direction of the applied magnetic field, parallel to the temperature gradient (Azizian et al., 2014).
A number of experimental and theoretical studies have been published on gold nanofluids due to their unique physical and chemical properties such as high thermal conductivity, easy modification and functionalization, bio-compatibility as well as their promising applications. Wu and Liu, 2014 have investigated the use of gold nanofluids as thermal energy system (TES) medium in concentrating solar power (CSP) by adding gold nanoparticles in molten salt. The addition of gold nanoparticles has remarkably improved thermal stability and reduced oxidation of molten salt. They also pointed out that the synthesized TES medium demonstrated thermodynamic property enhancement that can subsequently lead to more safe and effective operation of CSP plants (Wu &
Liu, 2014). However, there are only one or two studies that specifically focused on the thermal conductivity enhancement of gold nanofluids for heat transfer applications.
Developments in the area of nanofluids and demand for stable nanofluids with further improved thermal conductivity have led to the mixed nanofluids (MNs) known as hybrid nanofluids. In real terms, one type of material unable to have all the positive characteristics that are required for a specific purpose. Thus, manmade mixed nanofluids (MNs) combines all physical and chemical properties of different constituent materials with the intention of having exceptional properties that single material cannot possess such as superior thermal conductivity, mechanical resistance and chemical stability (Sarkar et al., 2015).
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Then again, the thermal conductivity of hybrid nanofluids has not been explored in depth by researchers although hybrid nanofluids are predicted to have high thermal conductivity due to the synergistic effect. To date, there are very limited thermophysical properties and heat transfer parameters models developed for hybrid nanofluids compared to single system nanofluids (Kumar & Arasu, 2018).
Predominantly, different base fluid, types of nanoparticles, temperature, stability, types of nanoparticles, solid volume fraction, particle size, shape, pH and types of surfactant are among several factors that influence the thermophysical properties of hybrid nanofluids. Analogous to single type of nanofluids, conflicting results were reported in the literature. These parameters clearly have an effect on the thermophysical properties of the hybrid nanofluids (Gupta et al., 2018).
Thus, advancements in nanotechnology and novel synthesis approaches should play a huge role in order to develop a stable hybrid nanofluids with an extremely high thermal conductivities to be used in various cooling applications.
