Fabrication Of Strontium Ferrite Magnetic Material Through Wet Processing.
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
FABRICATION OF STRONTIUM FERRITE
MAGNETIC MATERIAL THROUGH WET
PROCESSING
Thesis submitted in accordance with the partial requirements of the Universiti Teknikal Malaysia Melaka for the Bachelor
Of Manufacturing Engineering (Engineering Materials) with Honours
By
Nik Norzaliza binti Long Hassan
Faculty of Manufacturing Engineering May 2008
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UTeM Library (Pind.1/2007)
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
BORANG PENGESAHAN STATUS LAPORAN*
JUDUL: Fabrication of Strontium Ferrite Magnetic Material through Wet Processing.
SESI PENGAJIAN: 2007/2008
Saya Nik Norzaliza Binti Long Hassan
mengaku membenarkan tesis (PSM/Sarjana/Doktor Falsafah) ini disimpan di Perpustakaan Universiti Teknikal Malaysia Melaka (UTeM) dengan syarat-syarat kegunaan seperti berikut:
1. Tesis adalah hak milik Universiti Teknikal Malaysia Melaka dan penulis.
2. Perpustakaan Universiti Teknikal Malaysia Melaka dibenarkan membuat salinan untuk tujuan pengajian sahaja dengan izin penulis.
3. Perpustakaan dibenarkan membuat salinan tesis ini sebagai bahan pertukaran antara institusi pengajian tinggi.
4. **Sila tandakan (√) SULIT
TERHAD
TIDAK TERHAD
(Mengandungi maklumat yang berdarjah keselamatan atau kepentingan Malaysia yang termaktub di dalam AKTA
RAHSIA RASMI 1972)
(Mengandungi maklumat TERHAD yang telah ditentukan oleh organisasi/badan di mana penyelidikan dijalankan)
(TANDATANGAN PENULIS)
Alamat Tetap:
Lot 506, Kampong Kemasin, Perupok, 16300 Bachok, kelantan
Disahkan oleh:
(TANDATANGAN PENYELIA)
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FAKULTI KEJURUTERAAN PEMBUATAN
Rujukan Kami (Our Ref) : 20 Mei 2008
Rujukan Tuan (Your Ref):
Pustakawan
Perpustakawan Universiti Teknikal Malaysia Melaka UTeM,No 1, Jalan TU 43,
Taman Tasik Utama, Hang Tuah Jaya, Ayer Keroh, 75450, Melaka
Saudara,
PENGKELASAN TESIS SEBAGAI SULIT/TERHAD
- TESIS SARJANA MUDA KEJURUTERAAN PEMBUATAN (Department of Materials Engineering): Nik Norzaliza Binti Long Hassan.
TAJUK: Fabrication of Strontium Ferrite Magnetic Material through Wet Processing.
Sukacita dimaklumkan bahawa tesis yang tersebut di atas bertajuk “Fabrication of Strontium Ferrite Magnetic Material through Wet Processing” mohon dikelaskan sebagai terhad untuk tempoh lima (5) tahun dari tarikh surat ini memandangkan ia mempunyai nilai dan potensi untuk dikomersialkan di masa hadapan.
Sekian dimaklumkan. Terima kasih.
“BERKHIDMAT UNTUK NEGARA KERANA ALLAH”
Yang benar,
... DR AZIZAH SHAABAN
Pensyarah,
Fakulti Kejuruteraan Pembuatan (Penyelia Bersama)
No telefon: 06-2332122 Email : azizahs@utem.edu.my
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
Karung Berkunci 1200, Ayer Keroh, 75450 Melaka Tel: 06-233 2421, Faks : 06 233 2414
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DECLARATION
I hereby declare that this report entitled FABRICATION OF STRONTIUM FERRITE MAGNETIC MATERIAL THROUGH WET PROCESSING is the result of my own
research except as cited in the references.
Signature : ………
Author’s Name : Nik Norzaliza Binti Long Hassan
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APPROVAL
This report is submitted to the Faculty of Manufacturing Engineering of UTeM as a partial fulfillment of the requirements for the degree of Bachelor of Manufacturing Engineering (material engineering). The members of the supervisory committee are as
follow:
………..
Dr Azizah Shaaban
(Main Supervisor)
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ABSTRACT
The purpose of doing this project is to evaluate the phase composition for calcined ferrite using SEM-EDX and XRD and to evaluate microstructure effects on calcined materials. The raw material used in this study is strontium ferrite which is combination between strontium carbonate and iron oxide. The material was mill and mixed with ethanol during ball milling process. The next process continues with calcined in 12500C of temperature and followed by crushing process. First sample is
sintered at 12500C and second sample sintered at 12700C. Then the calcined powder is
mixed by using 2 different percentages of Nickel using Tambling mixing. Third sample consist of 1% of Nickel and 99% of calcined powder and fourth sample is consisting 2% of Nickel and 98% of calcined powder. Both of third and fourth samples are sintered at 12700C. The grains size of ferrite is analysis with Scanning Electron Microscope (SEM)/
EDX and XRD. Backscattered image is carried out from the EDX to evaluate the chemical analysis and morphology. Physical analysis of the sample is carried out using Electronic densimeter to measure the density. The main phase compositions in calcined powder are strontium ferrite and Fe2O3. SEM indicated that a continuous network of pores exist in the microstructure make the value of density low. Besides, it could be observed that there were small amount of Nickel on the surface of grains boundaries. Addition of Nickel as additive strongly affects the structural and morphological of the samples.
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ABSTRAK
Projek ini adalah bertujuan untuk menilai komposisi fasa pengkalsinan ferrite dengan menggunakan SEM-EDX dan XRD dan untuk menilai kesan pengkalsinan ke atas struktur mikro bahan. Bahan mentah yang di gunakan dalam kajian ini ialah strontium ferrite di mana terhasil daripada kombinasi antara strontium carbonate dan iron oxide. Bahan ini mesti di kisar dan dicampur dengan ethanol semasa proses pengisar bebola. Proses di ikuti dengan pengkalsian pada suhu 12500C dan seterusnya
dengan proses penggempuran. Sampel pertama disinter pada 12500C dan sampel kedua
disinter pada suhu 12700C. Kemudian bahan pengkalsinan di campur dengan dua jenis
peratusan Nikel yang berbeza secara ‘tambling’. Sampel ketiga terdiri daripada 1% Níkel dan 99% serbuk pengkalsinan. Sampel keempat pula terdiri daripada 2% Nickel dan 98% serbuk pengkalsinan. Sampel ketiga dan keemapat kemudiaanya di sinter pada suhu 12700C. Saiz butiran ferit di analisis dengan mengunakan Scanning Electron
Microscope (SEM)/ EDX dan XRD. Imej backscattered dilakukan dengan EDX untuk manjalankan analisis kimia dan morfologi. Analisis fizik sampel dijalankan menggunakan Elektronik densimeter untuk mengukur ketumpatan. Fasa utama yang terdapat dalam serbuk pengkalsinan adalah stontium feritte dan Fe2O3. SEM
menunjukkan rangkaian liang-liang yang wujud dalam mikrostruktur menyebabkan nilai ketumpatan menjadi rendah. Selain itu, boleh diperhatikan terdapat unsur Nikel di permukaan sempadan butir tapi hanya dalam jumlah yang kecil. Secara jelasnya penambahan Nikel sebagai bahan tambahan dalam serbuk pengkalsinan menjejaskan struktur dan mofologikal sampel.
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A
CKNOWLEDGEMENT
I would like to express my appreciation to the individuals who had played a part in ensuring a successful occurrence and flow of activities throughout the duration of my final year project. Endless appreciation and gratitude to my supervisor, Dr Azizah Shaaban and to my first panel Dr Warikh for their encouragement and support and for spending quite some time with myself, providing a lot of guidance and ideas for my project research. Their knowledge and experience really inspired and spurred myself. I truly relished the opportunity given in working with them. Last but not least, my appreciation to Mr. Mohd Azhar Shah b. Abu Hassan , Mr. Hairulhisham b. Rosnanm Mr Mahader bin Muhamad, Mr Sarman and all technicians involved to complete this project. Finally, my sincere appreciation is dedicated to my parents and family and as well as the friends for their priceless assistance and patronage throughout the process of data gathering.
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TABLE OF CONTENT
DECLARATION ii APPROVAL iii ABSTRACT iv ABSTRAK v ACKNOWLEDGEMENT viTABLE OF CONTENTS vii
LIST OF FIGURES xi
LIST OF TABLES xv
LIST OF ABBREVIATIONS, SYMBOLS, SPECIALIZED NOMENCLATURES
xvi
CHAPTER 1 INTRODUCTION
1.1 Background of the project 1 1.2 Problem Statement 1
1.3 Objectives 2
1.3 Introduction on Magnetic material 2 1.4.1 Ceramic material 2 1.4.2 Ceramic magnet 3 1.4.3 Properties of magnetic material 4 1.4.4 Application of magnetic material 6
CHAPTER 2 LITERATURE REVIEW
2.1 Type of magnetism 7 2.1.1 Diamagnetism 7 2.1.2 Paramagnetism 8 2.1.3 Antiferromagnetism 8 2.1.4 Ferrimagnetism 8 2.1.5 Ferromagnetism 9 2.2 Type of ferrites 10 2.2.1 Hard ferrite 11 2.2.2 Soft ferrite 12 2.2.3 Other type of magnetic materials 12 2.3 Starting material for strontium ferrite 15 2.3.1 Strontium carbonate 15
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2.3.2 Iron oxide 15 2.3.3 Ethanol 16 2.3.4 Nickel 16 2.4 Previous research on strontium ferrite 17
2.4.1 Process parameter selection for strontium ferrite sintered magnets using Taguchi L9 orthogonal design.
17
2.4.2Barium and Strontium ferrite perpendicular thin film media with a sendust soft magnetic underlayer.
18
2.4.3Fine powders of SrFe12O19 with SrTiO3 additive prepared via a quasi-dry combustion synthesis route
19
2.4.4 Microstructure of pre-sintered permanent magnetic strontium ferrite powder
19
CHAPTER 3 METHODOLOGY
3.1 Powder processing 21 3.1.1 Milling and mixing 22 3.1.2 Calcinations 24 3.1.3 Crushing 25
3.1.4 Sieving 25
3.1.5 Mixing 26
3.1.6 Compact 26
3.1.7 Sintering 28 3.2 Sample Characterization 28
3.2.1 Sample preparation for microstructure evaluation
28
3.2.2 Microstructure evaluation 30 3.2.1.2 Optical microscope 30 3.2.1.2 Scanning Electron Machine
(SEM)
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CHAPTER 4 RESULT AND DISCUSION
4.1 Observation on powder 37 4.1.1 As-received material 37 4.1.1.1 Iron Oxide 37 4.1.1.2 Strontium carbonate 38 4.1.2 Milled powder 39 4.1.3 Calcined powder 40 4.2 Composition Study on Strontium Ferrite 41 4.3 Sintered Strontium Ferrite 43 4.3.1 Final Specimens 44 4.3.2 Optical Observation
4.3.3 SEM observation
45
4.3.3.1 Strontium ferrite sinter at 1250oC 46
4.3.3.2 Strontium ferrite sinter at 1270oC 48
4.3.3.3 Strontium ferrite + 1% Nickel sintered at 1270oC
49
4.3.3.4 Strontium ferrite + 2% Nickel sintered at 1270oC
50
4.3.4 EDX microstructure
4.3.3.2 Strontium ferrite sinter at 1270oC 51
4.3.3.3 Strontium ferrite + 1% Nickel sintered at 1270oC
52
4.3.3.4 Strontium ferrite + 2% Nickel sintered at 1270oC
53
4.3.5 Phase analysis 54 4. 3.6 Physical properties 56 4.3.6.1 Mass and Volume measurement 57 4.3.6.2 Density measurement 57 4.4 Defect on sample 58
CHAPTER 5 CONCLUSION AND RECOMMENDATION 60
REFERENCES 62
APPENDIX A 65
APPENDIX B 67
APPENDIX C 69
APPENDIX D 71
APPENDIX E 71
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LIST OF FIGURES
Figure 1.1(a) Ceramic Blocks 3
Figure 1.1(b) Ceramic Discs 3
Figure 1.1(c) Ceramic Rings 3
Figure 1.2 Generic hysteretic plot of magnetization as a
function of magnetic material. 5
Figure 2.1 Ferrite magnet 11
Figure 3.1 Processing Flow 21
Figure 3.2 Ball milling machine 23
Figure 3.2.1(a) mixing process 24
Figure 3.2.1(b) filtration 24
Figure 3.2.1(c) Powder after filtration and drying 24
Figure 3.3(a) Powder in aluminum bowl 25
Figure 3.3(b) Furnace 25
Figure 3.4 Alumina mortar 25
Figure 3.6(a) Oil strainer 26
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Figure 3.7 Hydraulic Press Machine 27
Figure 3.8 Sintering profile 28
Figure 3.9 Diamond cutter 29
Figure 3.10 Figure shows steps for sample preparation. Figure 30
shows sinter specimens; (a) grinding and (b) etching
Figure 3.11(a) Optical microscope 31
Figure 3.11(b) Schematic diagram of the optical micrograph 31
Figure 3.12(a) SEM component 33
Figure 3.12(b) SEM operating 33
Figure 3.13 Electronic Densimeter 35
Figure 4.1 Figure shows SEM image for as-received Iron oxide 37
with different magnification; (a) 500x (b) 2500x.
Figure 4.2 Figure shows SEM image for as-received 38
Strontium carbonatewith different magnification;
(a) 500x (b) 2500x.
Figure 4.3 Figure shows SEM image of Strontium ferrite after 39
milledwith different magnification; (a) 500x (b) 2500x
Figure 4.4 SEM image of strontium ferrite powder after 40
calcined; (a) particles size (b) microstructure
with 2500 x magnification. Yellow circle indicates
powder agglomeration.
Figure 4.5 XRD patterns of strontium ferrite calcined 41
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at.1250oC 50C/min
Figure 4.6 Figure shows for all specimens after mounting; 44
(a) Strontium ferrite + 1% Ni sinter at 1270,
(b) Strontium ferrite sinter at 1270,
(c) Strontium ferrite + 2% Ni sinter at 1270,
(d) Strontium ferrite sinter at 1250
Figure 4.7 All figure shows the observation using optical 45
microscopy using 20 X magnification
(a) Strontium ferrite sinter at 1250
(b) Strontium ferrite sinter at 1270 oC
Figure 4.8 Figure shows SEM image for Strontium ferrite 47
sintered at 1250oC with different magnification
(a) 800x (b) 1500x (c) 5000x.
Figure 4.9 Figure shows SEM image for Strontium ferrite 48
sintered at 1270 oC with different magnification;
(a) 1500x ( b) 2500x (c) 5000x.
Figure 4.10 Figure shows SEM image for Strontium ferrite + 49
1% Nickel sintered at 1270 oC with different
magnification; (a)1500x (b) 2500x (c) 5000x.
Figure 4.11 Figure shows SEM image for Strontium ferrite + 50
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Figure 4.13 EDX result of Strontium ferrite + 1% Nickel 52
sintered at 1270 oC
Figure 4.14 EDX result of Strontium ferrite + 2% Nickel 53
sintered at 1270 oC
Figure 4.3.15(a) SEM Backscattered image of strontium ferrite 54
sintered at 1270 without nickel with 2500 x magnification.
Figure 4.3.15(b) SEM Backscattered image of strontium ferrite + 55
1 % Nickel sintered at 1270 oC with 2500 x magnification
Figure 4.3.15(c) SEM Backscattered image of strontium ferrite + 56
2 % Nickel sintered at 1270 oC with 2500 x magnification.
Figure 4.16(a) Specimen after sinter at 1250oC 58
Figure 4.16(b) Strontium ferrite sinter at 1270 oC 58
Figure 4.16(c) Strontium ferrite + 1% Nickel sinter at 1270oC 58
Figure 4.16(d) Strontium ferrite + 2% Nickel sinter at 1270oC 58
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LIST OF TABLES
Table 1.1 Typical Magnetic and Physical Properties
of ferrite Magnet Material 5
Table 2.1 Magnetic Material Classification 7
Table 2.2 Summary of different types of magnetic behavior 9
Table 2.3 Physical Properties of hard ferrite 12
Table 2.4 Selected process parameters and their respective
levels in the present experimental design. 18
Table 4.1 Data of mass and volume 57
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LIST OF ABB
REVIATIONS, SYMBOLS,
NOMENCLATURES
SEM - Scanning Electron Machine EDX - Energy Dispersive X-ray Analysis XRD - X-ray diffraction
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CHAPTER 1
INTRODUCTION
1.1 Background of the project
The fabrication of the strontium ferrite magnetic material through wet processing is doing by mixing the strontium carbonate with iron oxide powder in wet milling. Wet milling is the grinding of materials with sufficient liquid to form slurry. The mixing of both as received powder is doing in ball mill machine and then calcined at certain temperature. The calcined powder is mix with the different percentage of additives and then sintered at certain temperature. The microstructure effect and the phase composition of the samples are evaluated using SEM-EDX and XRD.
1.2 Problem statement
The objectives of this project are to evaluate microstructure effect and the phase composition of the samples using SEM-EDX and XRD. The interaction of Nickel powder as additive material in calcined material influence the grains size of the sample after sintered. This evaluation will focus on three areas. First, microstructure
evaluation using SEM-EDX and phase analysis by XRD. Second, the percentages of
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1.3 Objectives
The objectives of this project are:
i. To evaluate the phase composition for calcined ferrite using SEM-EDX and XRD
ii. To evaluate microstructure effects on calcined materials.
1.4 Introduction on Magnetic material
Materials may be classified according to some of their basic magnetic properties, particularly whether or not it is magnetic and how behave in the vicinity of an external magnetic field. When a material is placed within a magnetic field, the magnetic forces of the material's electrons will be affected. This effect is known as Faraday's Law of Magnetic Induction. However, materials can react quite differently to the presence of an external magnetic field. This reaction is dependent on a number of factors, such as the atomic and molecular structure of the material, and the net magnetic field associated with the atoms. The magnetic moments associated with atoms have three origins. These are the electron orbital motion, the change in orbital caused by an external magnetic field and the spin of the electrons. In most atoms, electrons occur in pairs. Electrons in a pair spin in opposite directions. So, when electrons are paired together, their opposite spins cause their magnetic fields to cancel each other. Therefore, no net magnetic field exists. Alternately, materials with some unpaired electrons will have a net magnetic field and will react more to an external field
1.4.1 Ceramic material
Ceramics is a singular noun referring to the art of making things out of ceramic materials. The technology of manufacturing and usage of ceramic materials is part of the
field of ceramic engineering. Many ceramic materials are hard, porous and brittle.
Ceramic materials are usually ionic or covalently-bonded materials, and can be crystalline or amorphous. A material held together by either type of bond will tend to
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fracture before any plastic deformation takes place, which results in poor toughness in these materials. Additionally, because these materials tend to be porous, the pores and other microscopic imperfections act as stress concentrators, decreasing the toughness further, and reducing the tensile strength. These combine to give catastrophic failures, as opposed to the normally much more gentle failure modes of metals. These materials do show plastic deformation. However, due to the rigid structure of the crystalline materials, there are very few available slip systems for dislocations to move, and so they deform very slowly. With the non-crystalline (glassy) materials, viscous flow is the dominant source of plastic deformation, and is also very slow. It is therefore neglected in many applications of ceramic materials.
1.4.2 Ceramic magnet
Ferrite magnets are combination between strontium, barium or plumbum
carbonate and iron oxide. They are charcoal gray in color and usually appear in the forms of discs, rings, blocks, cylinders, and sometimes arcs for motors. Figure 1.1(a), (b) and (c) below are the type of form of ceramic magnetic.
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Figure 1.1(c): Ceramic Rings Sources: http://www.allmagnetics.com/ceramic.htm Attributes of Ceramic Magnets:
• High intrinsic coercive force
• Tooling is expensive
• Least expensive material compared to alnico and rare earth magnets
• Limited to simple shapes due to manufacturing process
• Lower service temperature than alnico, greater than rare earth
• Finishing requires diamond cutting or grinding wheel
• Lower energy product than alnico and rare earth magnets
• Most common grades of ceramic are 1, 5 and 8 (1-8 possible)
• Ceramic grade 8 shown in Table 1.1 is the strongest ceramic material available.
1.4.3 Properties of magnetic material.
When ferromagnetic materials are magnetized, demagnetized, and re-magnetized, they exhibit a hysteretic behavior illustrated as shown in Figure 1.2. Important and often
quoted features of these graphs are the saturation magnetization Ms, remanent
magnetization Mr, coercivity Hc, and saturating field Hs. With these parameters,
ferromagnetic materials can be divided into so-called soft magnetic materials (i.e., with a small coercivity and low saturation field) and hard magnetic materials (i.e., with a large coercivity and high saturation field).
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Figure 1.2: Generic hysteretic plot of magnetization as a function of magnetic material. Sources: Judy and Myung (2001)
Table 1.1: Typical Magnetic and Physical Properties of ferrite Magnet Material
Magnetic Materials Density Maximum Energy Product BH (max) Residual Induction Br Coercive Force Hc Intrinsic Coercive Force Hc Normal Maximum Operating Temp. Curie Temp.
lbs/in g/cm MGO Gauss Oersteds Iersteds F° C° F° C°
Ceramic 1 0.177 4.9 1.05 2300 1860 3250 842* 450 842 450
Ceramic 5 0.177 4.9 3.4 3800 2400 2500 842* 450 842 450
Ceramic 8 0.177 4.9 3.5 3850 2950 3050 842* 450 842 450
Sources: http://www.allmagnetics.com/ceramic.htm
All magnet materials demonstrate reversible strength loss as they approach Maximum operating temperature.
* NOTE: Unshielded open circuit ceramic magnets should not be subjected to more than 400°F.
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1.4.4 Application of magnetic material
Applications of ferrite Magnets are Speaker magnets, DC brushless motors, Magnetic Resonance Imaging (MRI), Magnetos used on lawnmowers and outboard motors, DC permanent magnet motors (used in cars), Separators (separate ferrous material from non-ferrous), Used in magnetic assemblies designed for lifting, holding, retrieving, and separating.
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CHAPTER 2
LITERITURE REVIEW
2.1 Type of magnetism
Magnetic materials can be classified according to their magnetic susceptibility χ =
M / H and relative permeability μr = (χ / μ0 + 1) into several categories: ferromagnetic,
ferrimagnetic, antiferromagnetic, paramagnetic, diamagnetic, and superconducting materials. Listed in Table 2.1 are the typical ranges of χ / μ0 for each category of magnetic material and examples of each are identified (Parker 1989).
Table 2.1: Magnetic Material Classification
Category χ/μ0 Examples
Ferromagnetic 107 to 102 Ni, Fe, Co, NiFe, NdFeB
Ferrimagnetic 107 to 101 Fe3O4 Ferrite, garnets
Antiferromagnetic small MnO, NiO, FeCO3
Paramagnet 10-3 to 10-6 Al, Cr, Mn, Pt, Ta, Ti, W
Diamagnetic 10-6 to -10-3 -Ag, Au, C, H, Cu, Si, Zn
Sources from Parker(1989)
2.1.1 Diamagnetism
If the net magnetic moment of each atom in a material is zero because of mutually canceling electronic movement within the atom, then the net flux density within the
material, due to an applied external field, is slightly less th an it w o u ld b e in s p ac e
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1.3 Objectives
The objectives of this project are:
i. To evaluate the phase composition for calcined ferrite using SEM-EDX and XRD
ii. To evaluate microstructure effects on calcined materials.
1.4 Introduction on Magnetic material
Materials may be classified according to some of their basic magnetic properties, particularly whether or not it is magnetic and how behave in the vicinity of an external magnetic field. When a material is placed within a magnetic field, the magnetic forces of the material's electrons will be affected. This effect is known as Faraday's Law of Magnetic Induction. However, materials can react quite differently to the presence of an external magnetic field. This reaction is dependent on a number of factors, such as the atomic and molecular structure of the material, and the net magnetic field associated with the atoms. The magnetic moments associated with atoms have three origins. These are the electron orbital motion, the change in orbital caused by an external magnetic field and the spin of the electrons. In most atoms, electrons occur in pairs. Electrons in a pair spin in opposite directions. So, when electrons are paired together, their opposite spins cause their magnetic fields to cancel each other. Therefore, no net magnetic field exists. Alternately, materials with some unpaired electrons will have a net magnetic field and will react more to an external field
1.4.1 Ceramic material
Ceramics is a singular noun referring to the art of making things out of ceramic materials. The technology of manufacturing and usage of ceramic materials is part of the field of ceramic engineering. Many ceramic materials are hard, porous and brittle. Ceramic materials are usually ionic or covalently-bonded materials, and can be crystalline or amorphous. A material held together by either type of bond will tend to
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fracture before any plastic deformation takes place, which results in poor toughness in these materials. Additionally, because these materials tend to be porous, the pores and other microscopic imperfections act as stress concentrators, decreasing the toughness further, and reducing the tensile strength. These combine to give catastrophic failures, as opposed to the normally much more gentle failure modes of metals. These materials do show plastic deformation. However, due to the rigid structure of the crystalline materials, there are very few available slip systems for dislocations to move, and so they deform very slowly. With the non-crystalline (glassy) materials, viscous flow is the dominant source of plastic deformation, and is also very slow. It is therefore neglected in many applications of ceramic materials.
1.4.2 Ceramic magnet
Ferrite magnets are combination between strontium, barium or plumbum
carbonate and iron oxide. They are charcoal gray in color and usually appear in the forms of discs, rings, blocks, cylinders, and sometimes arcs for motors. Figure 1.1(a), (b) and (c) below are the type of form of ceramic magnetic.
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Figure 1.1(c): Ceramic Rings Sources: http://www.allmagnetics.com/ceramic.htm Attributes of Ceramic Magnets:
• High intrinsic coercive force
• Tooling is expensive
• Least expensive material compared to alnico and rare earth magnets
• Limited to simple shapes due to manufacturing process
• Lower service temperature than alnico, greater than rare earth
• Finishing requires diamond cutting or grinding wheel
• Lower energy product than alnico and rare earth magnets
• Most common grades of ceramic are 1, 5 and 8 (1-8 possible)
• Ceramic grade 8 shown in Table 1.1 is the strongest ceramic material available. 1.4.3 Properties of magnetic material.
When ferromagnetic materials are magnetized, demagnetized, and re-magnetized, they exhibit a hysteretic behavior illustrated as shown in Figure 1.2. Important and often quoted features of these graphs are the saturation magnetization Ms, remanent magnetization Mr, coercivity Hc, and saturating field Hs. With these parameters, ferromagnetic materials can be divided into so-called soft magnetic materials (i.e., with a small coercivity and low saturation field) and hard magnetic materials (i.e., with a large coercivity and high saturation field).
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Figure 1.2: Generic hysteretic plot of magnetization as a function of magnetic material. Sources: Judy and Myung (2001)
Table 1.1: Typical Magnetic and Physical Properties of ferrite Magnet Material
Magnetic Materials Density Maximum Energy Product BH (max) Residual Induction Br Coercive Force Hc Intrinsic Coercive Force Hc Normal Maximum Operating Temp. Curie Temp.
lbs/in g/cm MGO Gauss Oersteds Iersteds F° C° F° C°
Ceramic 1 0.177 4.9 1.05 2300 1860 3250 842* 450 842 450
Ceramic 5 0.177 4.9 3.4 3800 2400 2500 842* 450 842 450
Ceramic 8 0.177 4.9 3.5 3850 2950 3050 842* 450 842 450
Sources: http://www.allmagnetics.com/ceramic.htm
All magnet materials demonstrate reversible strength loss as they approach Maximum operating temperature.
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1.4.4 Application of magnetic material
Applications of ferrite Magnets are Speaker magnets, DC brushless motors, Magnetic Resonance Imaging (MRI), Magnetos used on lawnmowers and outboard motors, DC permanent magnet motors (used in cars), Separators (separate ferrous material from non-ferrous), Used in magnetic assemblies designed for lifting, holding, retrieving, and separating.
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CHAPTER 2
LITERITURE REVIEW
2.1 Type of magnetism
Magnetic materials can be classified according to their magnetic susceptibility χ = M / H and relative permeability μr = (χ / μ0 + 1) into several categories: ferromagnetic, ferrimagnetic, antiferromagnetic, paramagnetic, diamagnetic, and superconducting materials. Listed in Table 2.1 are the typical ranges of χ / μ0 for each category of magnetic material and examples of each are identified (Parker 1989).
Table 2.1: Magnetic Material Classification
Category χ/μ0 Examples
Ferromagnetic 107 to 102 Ni, Fe, Co, NiFe, NdFeB
Ferrimagnetic 107 to 101 Fe3O4 Ferrite, garnets
Antiferromagnetic small MnO, NiO, FeCO3
Paramagnet 10-3 to 10-6 Al, Cr, Mn, Pt, Ta, Ti, W
Diamagnetic 10-6 to -10-3 -Ag, Au, C, H, Cu, Si, Zn Sources from Parker(1989)
2.1.1 Diamagnetism
If the net magnetic moment of each atom in a material is zero because of mutually canceling electronic movement within the atom, then the net flux density within the material, due to an applied external field, is slightly less th an it w o u ld b e in s p ac e