本研究以檸檬酸先驅物法來製得磁性鐵酸鋇粉體。硝酸鋇與硝酸鐵依化學計量比溶解於去離子水中後，加入過量檸檬酸以鏊合溶液裡的金屬離子。溶液之酸鹼值藉由添加氨水來調整。起始溶液共有6種不同之酸鹼值，分別為0.8 (未加氨水)、3、5、7、8及10。之後提升溶液溫度至90℃並加入回流裝置，促使鏊合反應完全。經200℃乾燥24小時及不同熱處理溫度後，以XRD、FT-IR、TEM、SEM、TG-DSC、和SQUID做性質分析。本文將探討溶液酸鹼值及熱處理溫度對鐵酸鋇之影響。從XRD之分析，可得有添加氨水於起溶液中，則增加檸檬酸之解離，促使鋇離子與鐵離子鏊合反應更均勻；而未添加氨水(pH=0.8)，反應不完全，在高溫熱處理後還有中間相態存在。在溶液酸鹼值大於8以上，鏊合反應完全且均勻，使得在650℃時便可得到單一相態鐵酸鋇。在pH值為3時，反應過程中得到中間相態γ-Fe2O3，γ-Fe2O3易與BaCO3形成鐵酸鋇粉體，且在700℃時磁性質表現也較其他pH值高。

Magnetic BaFe12O19 powder with crystallite sizes in nanometers was produced via citric acid precursor method. Citric acid was added into an aqueous solution, containing nitrates of iron and barium in stoichimetric ratios to form the required barium ferrite, to chelate the metallic ions. The pH value of starting aqueous solutions was adjusted using NH4OH. The solutions with six different pH values were prepared; they were the solutions of pH = 0.8 (without NH4OH additions), 3, 5, 7, 8, and 10, respectively. After drying, the solid citrate precursors were obtained. The solid citrate precursors were then calcined in air at different temperature. Effects of pH of the starting solution and calcination temperatures of the solid precursors on characteristics of resultant particles were investigated using XRD, FT-IR, TEM, SEM, TG-DSC and SQUID. The XRD analysis indicates that adding NH4OH into the starting solution will increase the ionization of citric acid and provide more carboxyl groups to chelate Ba2+ and Fe3+. Without NH4OH additions, no sufficient carboxyl groups, ionized from citric acid, were available to completely and simultaneously chelate iron and barium ions. The starting solutions at pH≧8 contained enough number of carboxyl groups to have both Fe3+ and Ba2+ be completely and homogeneously chelated, resulting in the direct formation of single crystalline phase of BaFe12O19 at calcinations temperatures as low as 650℃. At pH=3, resulting in the formation of crystalline γ-Fe2O3 intermediate. γ-Fe2O3 easily reacts with BaCO3 to form BaFe12O19.  The results of magnetic measurements show that the calcined sample at 700℃ gives the highest Ms, Mr and Hc than those using other pH values.

CONTENTS
CHAPTER 1 INTRODUCTION	1
CHAPTER 2 CHARACTERS OF BARIUM FERRITE AND LITERATURE REVIEW	3
2-1 MOLECULAR STRUCTURE OF BAFE12O19	3
2-2 MAGNETIC CHARACTERISTICS OF BAFE12O19	4
2-2-1 Saturation magnetization	4
2-2-2 Coercivity	6
2-3 THEORETICAL DENSITY	7
2-4 LITERATURE REVIEW	8
2-4-1 Solid-State methods	8
2-4-2 Sol-gel methods	8
2-4-3 Chemical Co-precipitation Methods	10
2-4-4 Hydrothermal methods	11
2-4-5 Microwave methods	11
2-4-6 Aerosol routes	12
2-4-7 Citrate methods	13
CHAPTER 3 EXPERIMENTAL PROCEDURES	17
3-1 EXPERIMENTAL	17
3-2 CHARACTERISTIC ANALYSES	20
3-2-1 X-ray diffraction (XRD)	20
3-2-2 Thermogravimetric analysis (TGA)	21
3-2-3 Differential scanning calorimeter (DSC)	21
3-2-4 Scanning electron microscopy (SEM)	22
3-2-5 Transmission electron microscopy (TEM)	22
3-2-6 Infrared Spectroscopy (IR)	23
CHAPTER 4 RESULTS AND DISCUSSION	26
4-1 PHASE DEVELOPMENT	26
4-2 THERMAL BEHAVIOR OF DERIVED PARTICLES	30
4-3 MAGNETIC PROPERTIES	39
CHAPTER 5 CONCLUSIONS	62
REFERENCES	64
APPENDIX  A	68
APPENDIX  B	70
CONTENTS OF FIGURES

Figure 2-1 The crystal structure of barium ferrite.	3
Figure 2-2 The saturation magnetization Ms of BaFe12O19 as a function of temperature, after Smit and Wijn.52	……………………………………………………5
Figure 3-1 The experimental procedures used to prepare BaFe12O19.	19
Figure 3-2 Diffraction of X-rays by a crystal.	21
Figure 4-1 XRD patterns for different pH values obtained by drying in 200℃ for 24hr.	42
Figure 4-2 XRD patterns for different pH values obtained by heating the precursor in                
         600℃ for 5hr.	43
Figure 4-3 XRD patterns for different pH values obtained by heating the precursor in     
         650℃ for 5hr.	44
Figure 4-4 XRD patterns for different pH values obtained by heating the precursor in 
         700℃ for 5hr.	45
Figure 4-5 XRD patterns for different pH values obtained by heating the precursor in
         800℃ for 5hr.	46
Figure 4-6 Thermal analysis of the citrate precursor of pH=0.8: (a) TG-DSC curve, (b) 
         DTG-DDSC.	47
Figure 4-7 The FT-IR pattern of different calcinations temperature at pH=0.8.	48
Figure 4-8 Thermal analysis of the citrate precursor of pH=3: (a) TG-DSCcurve, (b)
DTG-DDSC.	49
Figure 4-9 The FT-IR pattern of different calcinations temperature at pH=3.	50
Figure 4-10 Thermal analysis of the citrate precursor of pH=5: (a) TG-DSC curve, (b)
          DTG-DDSC.	51
Figure 4-11 The FT-IR pattern of different calcinations temperature at pH=5.	52
Figure 4-12 Thermal analysis of the citrate precursor of pH=7: (a) TG-DSC curve, (b)
          DTG-DDSC.	53
Figure 4-13 The FT-IR pattern of different calcinations temperature at pH=7.	54
Figure 4-14 Thermal analysis of the citrate precursor of pH=8: (a) TG-DSC curve, (b) 
          DTG-DDSC.	55
Figure 4-15 Thermal analysis of the citrate precursor of pH=10: (a) TG-DSC curve, (b)
          DTG-DDSC.	56
Figure 4-16 The FT-IR pattern of different calcinations temperature at pH=8.	57
Figure 4-17 The FT-IR pattern of different calcinations temperature at pH=10.	58
Figure 4-18 Hysteresis loops of the sample heated at 700℃ for 5hr, using the solution 
          of (a) pH=0.8, (b) pH=3, (c) pH=5, (d) pH=7, (e) pH=8, (f) pH=10.	59
Figure 4-19 TEM photomicrographs of sample pH=3 heating at (a) 600℃, (b) 650℃,    
          (c) 700℃, (d) 800℃, (e) 900℃ for 5hr.	60
Figure 4-20 SEM photomicrographs of sample pH=3 heating at (a) 700℃, (b) 800℃ and (c) 900℃ for 5hr.	…………………………………………………..61
Figure A-1 Hysteresis loops of the sample heated at 800℃ for 5hr, using the solution             
          of (a) pH=0.8, (b) pH=3, (c) pH=5, (d) pH=7, (e) pH=8, (f) pH=10.	68
Figure A-2 Hysteresis loops of the sample heated at 900℃ for 5hr, using the solution 
          of (a) pH=0.8, (b) pH=3, (c) pH=5, (d) pH=7, (e) pH=8, (f) pH=10.	69
Figure B-1 TEM and SEM of the sample heated at 700℃ for 5hr.	70
Figure B-2 TEM and SEM of the sample heated at 800℃ for 5hr.	71
Figure B-3 TEM and SEM of the sample heated at 900℃ for 5hr.	72
CONTENTS OF TABLES
Table 2-1 The site, amount, sublattice and moment direction of Fe3+ in BaFe12O19      5
Table 3-1 The techniques used to characterize the specimens     25
Table 4-1 Crystalline phases and the corresponding crystallite sizes existed in the specimens obtained at different pH and  calcination temperatures      29
Table 4-2-1 The FT-IR analysis obtained at different calcination temperatures by pH=0.8     36
Table 4-2-2 The FT-IR analysis obtained at different pH and calcination temperatures      37
Table 4-3 Thermal analysis of the investigated precursors    38
Table 4-4 Thermal analysis of the investigated precursors    38
Table 4-5 Magnetic characteristics of the specimens of different pH at different calcination temperatures     41

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