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研究生:余文懷
研究生(外文):Wen-Hwai Yu
論文名稱:共沉澱法合成細顆粒鈦酸鋇
論文名稱(外文):Synthesis of Barium Titanate Fine Powders by Coprecipitation
指導教授:陳郁文陳郁文引用關係
指導教授(外文):Yu-Wen Chen
學位類別:碩士
校院名稱:國立中央大學
系所名稱:化學工程與材料工程研究所
學門:工程學門
學類:化學工程學類
論文種類:學術論文
論文出版年:2002
畢業學年度:90
語文別:英文
論文頁數:90
中文關鍵詞:鈦酸鋇共沉澱草酸擴散形狀和顆粒大小控制
外文關鍵詞:Barium titanatecoprecipitationmorphology and particle size controldiffusionBTO
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摘 要
自從Clabaugh 等人在1956年,首先發現將BaTiO(C2O4)2‧4H2O (BTO) 於800℃下鍛燒,可以得到高純度的鈦酸鋇 (BaTiO3)。許多相關的研究也於其後陸續發表,然而大部份的研究者都將研究重心放在BTO的熱分解機構上,對於探討影響BTO顆粒大小和形狀的研究並不多。本研究主要探討影響BTO顆粒大小和形狀的因素,包括不同反應溫度、進料速度、pH值以及進料混合方式等;並利用擴散以及不同醇水比等方式製備BTO,以期得到細顆粒的鈦酸鋇粉末,並對其形狀做一定的控制。使用SEM分析沉澱的顆粒大小和形狀,使用XRD和TGA等儀器分析沉澱物的晶相和熱分解機構。研究發現BTO可於800℃鍛燒後得到立方晶相的鈦酸鋇,但聚集形狀卻和原BTO類似。進料速度愈快所得到的BTO 顆粒愈大,高溫下容易得到大顆粒的BTO沉澱。改變進料混合方式雖可以得到細顆粒(0.2μm)且分散的沉澱,但於800℃鍛燒後卻有BaTi2O5的雜相存在。另外以擴散方式可以得到類似葉片狀的BTO,並可利用快速攪拌得到顆粒約0.5 μm的BTO。在乙醇/水比等於1時,可以得到片狀的BTO沉澱,而在丙醇/水比大於1下所得沉澱於800℃鍛燒後會有BaT2iO5存在。本研究並指出BTO應為Ti(OH)22+嵌入Ba(HC2O4)2‧2H2O的結構中,並和極性水分子反應所得到的錯和物Ba(HC2O4)2‧2H2O-TiO(OH)2。此外在pH大於4之下所得
到的沉澱應該是BaC2O4和TiO(OH)2的混合物。


Abstract
Many research reports had been reported that high purity of barium titanate (BaTiO3) could be prepared by calcined BaTiO(C2O4)2‧4H2O (BTO) at 800℃.However, most of the researchers put the emphasis on the mechanism of the thermal decomposition of BTO, only a few researchers discussed the morphology and particle size of BTO. In this study, several experiments had been conducted to investigate the factor that affected the morphology and particle size of BTO. The effect of investigated different reaction-temperature, adding rate, pH values, and adding order were used. BTO was also prepared by way of diffusion and different alcohol/water ratios in order to control the morphology and to obtain small particle size of BTO. SEM was used to examine the morphology and particle size of the precipitates. XRD and TGA were used to study the phase and thermal decomposition mechanism of the precipitates. It has been found that cubic barium titanate could be prepared by calcining BTO at 800℃, the particle size and morphology of agglomerated barium titanate was similar to that of BTO. The faster the adding rate the bigger the particle size of BTO. It is easy to form BTO with larger particle size at higher reaction temperature. Small particle size (0.2 μm) and dispersed BTO could be prepared by changing the adding order, however some BaTi2O5 was present after calcining the precipitates at 800℃. Furthermore, leaf-like BTO could be prepared by diffusion without stirring. BTO with particle size of 0.5 μm could be prepared by diffusion with vigorous stirring. Flake-like BTO could be prepared at ethanol/water of 1, and some BaTi2O5 was present after calcining the precipitates which were prepared at propanol/water>1. In this study, it was also found that BTO might be a compound which Ba(HC2O4)2 inserted with TiO(OH)22+, and then reacted with dipole molecular H2O to form the compound Ba(HC2O4)2‧2H2O-TiO(OH)2. Besides, the precipitates prepared at pH>4 were the mixture of BaC2O4 and TiO(OH)2.


Table of Contents
Abstract…………………………………………………………………..i
List of Contents………………………………………………………….iii
List of Tables…………………………………………………………….v
List of Figures…………………………………………………………...vi
Chapter 1. Introduction…………………………………………...1
1.1Application of barium titanate……………………………………....1
1.2Barium titanate structure and phase transition………………………2
1.3Basic theory and definition of dielectric properties…………………6
1.4The theoretical density and ideal powder of barium titanate………….17
Chapter 2 Literature review…………………………………….……...20
2.1 The preparation method……………………………………………..20
2.2 The pyrolysis of BTO……………………………………………….24
2.3 The effect of pH value…………………………………………………….28
2.4 The structure of BTO…………………………………………………...…32
Chapter 3. Experimental…………………………………………35
3.1 Chemicals………………………………………………………….…..35
3.2 Preparation………………………………………………………………....35
3.3 Characterization…………………………………………………………....37
3.3.1. X-ray diffraction (XRD)…………………………………………...37
3.3.2. Thermogravimetric analysis (TGA)…………………………...38
3.3.3. Scanning electron microscopy (SEM)…………………………38
Chapter 4. Results and discussion……………………………….…….39
4.1. Preparation in aqueous solution…………………………………………….39
4.1.1. BTO prepared by oxalate route………………………………..39
4.1.2. Effect of titration-rate………………………………………….45
4.1.3. Effect of reaction temperature…………………………………48
4.1.4. Effect of mixed order………………………………………….52
4.1.5. Effect of pH value……………………………………………..58
4.2 Preparation BTO by diffusion………………………………………69
4.3 Preparation with different RH ratio…………………………………81
4.3.1 RH ratio of ethanol solution……………………………………81
4.3.2 RH ratio of n-propanol…………………………………………83
Chapter 5. Conclusion………………………………………………….………85
Reference…………………………………………………………..………...86
List of Tables
Table 1-1. Comparison of measured values of critical size for the c→t phase transformation and method of BaTiO3 powder preparation………………………………………………….3
Table 4-1. Decomposition schemes and TGA data of BTO under air.……………………………………………………………..….41
Table 4-2. The identification of XRD peaks analyzed of cubic BaTiO3……………………………………………………..42
Table 4-3. The identification of XRD peaks of tetragonal BaTiO3……………………………………………………...44
Table 4-4. The crystalline size of BaTiO3 prepared at various reaction temperature………………………………………………...50
Table 4-5. Decomposition schemes and TGA data of co-precipitated materials at pH=1, under air……………………………….52
Table 4-6. Decomposition schemes and TGA data of co-precipitated materials at pH=2, under air……………………………….53
Table 4-7. Decomposition schemes and TGA data of co-precipitated materials at pH=4, under air……………………………….55
Table 4-8. Decomposition schemes and TGA data of co-precipitated materials at pH=5, under air……………………………….58
Table 4-9.The possible decomposition schemes of co-precipitated material prepared by the third adding order……………….65
Table 4-10. The crystalline size of barium titanate prepared at different RH (ethanol to water ) ratios…………………………………...81
List of Figures
Fig. 1-1. Ion position in ideal perovskite structure……………………….….5
Fig. 1-2. Crystallographic changes of BaTiO3…………………………….5
Fig. 1-3. (a) Dimension of pseudocubic unit cell of BaTiO3.
(b) Temperature dependence of dielectric constant of single crystals of barium titanate………………………………………....7
Fig. 1-4. Dielectric constant of barium titanate ceramic as a function of temperature……………………………………………………..9
Fig. 1-5 Dielectric constant as a function of grain size of ceramic BaTiO3………………………………………………………….9
Fig. 1-6. Schematic representation of polarization by dipole chains and boundcharges…………………………………………………11
Fig. 1-7. Schematic representation of different mechanisms of polarization………………………………………………………..…….……11
Fig. 1-8. Microstructure of barium titanate ceramic. Different ferroelectric domain orientation are brought out by etching…………………………………………………………………………………………….16
Fig. 1-9. A typical ferroelectric hysteresis loop………………………………….16
Fig. 1-10. The change in barium titanate ferroelectric hysteresis loop shape with temperature……………………………………….….16
Fig. 2-1. pH diagrams for the Ti-Ba-H2O system at 25℃…………….......30
Fig. 2-2. pH diagram for the Ti-H2O and Ba-H2O system at 25℃………..…30
Fig. 2-3. (a) pH diagram of Ti-H2C2O4-H2O system at 25℃, (b) pH diagram of Ti-H2C2O4-H2O system at 25℃………………......31
Fig. 2-4. pH diagrams for the Ti-Ba-H2C2O4 system at 25℃ with different metal concentration……………………………...31
Fig. 2-5. The structure of BaTiO(C2O4)2…………………………………..34
Fig. 4-1. XRD pattern of the BaTiO(C2O4)2‧4H2O……………………..40
Fig. 4-2. TGA curve of BaTiO(C2O4)2‧4H2O……………………….40
Fig. 4-3. XRD patterns of BTO calcined at 800℃/4h…………………..43
Fig. 4-4. XRD pattern of BaTiO3 calcined at 1350℃/4h……………….43
Fig. 4-5. SEM photographs of (a) The morphology of as-dried BTO, (b) The morphology of BTO calcined at 800℃/4h, (c) The surface of as-dried BTO, (d) The surface of BTO calcined at 800℃/4h…………………………………………………………….46
Fig. 4-6. The SEM photographs of BTO with adding-rate of (a) 10ml/min, (b) 30ml/min, (c) Flash-mixing…………………………………...47
Fig. 4-7. The SEM photographs of BTO prepared by reaction-temperature of (a) 5℃, (b) 25℃, (c) 50℃…………………………………...49
Fig. 4-8. The XRD patterns of the precipitates prepared by different reaction temperature and calcined at 800℃.(1) 5℃, (2) 20℃, (3) 50℃……………………………………………………………...51
Fig. 4-9. TGA curve of co-precipitated materials at pH=1……………..……53
Fig. 4-10. TGA curve of co-precipitated materials at pH = 2……………..53
Fig. 4-11. TGA curve of co-precipitated materials at pH = 3……………..56
Fig. 4-12. TGA curve of co-precipitated materials at pH = 4…………..……56
Fig. 4-13. TGA curve of co-precipitated materials at PH = 5………………..57
Fig. 4-14. the XRD patterns of the precipitates prepared by different pH values and calcined at 800 ℃. (1) pH =1, (2) pH=2, (3) pH=3, (4) pH=4, (5) pH=5……………………………………………....57
Fig. 4-15. The SEM photographs of BTO prepared by different adding order (a) BTO prepared by the first adding order, (b) BTO prepared by the second adding order, (c) BTO prepared by the third adding order, (d) The surface of BTO prepared by the third adding order………………………………………………..59
Fig. 4-16. XRD patterns of different adding order (1) The first adding order, (2) The second adding order, (3) The third adding order…………………………………………………………..60
Fig. 4-17. SEM photographs of BTO prepared by adding order one without stirring. (a) BTO calcined at 800℃/4h,
(b) BTO……………………………………………………..….66
Fig. 4-18. TGA curve of oxalate prepared by the third adding order…………………………………………………………….....66
Fig. 4-19. (a) SEM photograph of the precipitates prepared by the third adding order with Ba:Ti=1:2, (b) XRD pattern of precipitates calcined at 800℃ for 4h…………………………………..68
Fig. 4-20. SEM photograph of the precipitates prepared by way of diffusion with Ba:Ti:C2O4=1.05:1:2.2………………………..71
Fig. 4-21. shows XRD pattern of the precipitates prepared by diffusion with Ba:Ti:C2O4=1.05:1:2.2 and calcined at 800℃ for 4h……………………………………………………………..71
Fig. 4-22. XRD pattern of the precipitates prepared by diffusion with Ba:Ti:C2O4 = 1:4:2.2……………………………………………73
Fig. 4-23. TGA curve of the precipitates prepared by diffusion with Ba:Ti :C2O4= 1:4:2.2……………………………………………73
Fig. 4-24. (a) XRD patterns of precipitates prepared by the second adding order and calcined at 800℃for 4h, (b) XRD patterns of precipitates prepared by the third adding order and calcined at 800℃for 4h…………………………………………………..75
Fig. 4-25. XRD patterns of precipitates prepared by increasing the amount of barium chloride in water solution and calcined at 800℃for 4h. (1) Ba/Ti=1, (2) Ba/Ti=2, (3) Ba/Ti=3, (4)Ba/Ti=4, (5)BaTi=5……………………………………….76
Fig. 4-26. XRD patterns of the precipitates prepared by diffusion with Ba: Ti: C2O4 = 1.05: 1: 6……………………………………………78
Fig. 4-27. TGA pattern of the prepared by diffusion with Ba: Ti: C2O4 = 1.05: 1: 6……………………………………………………...78
Fig. 4-28. XRD pattern of precipitates prepared by diffusion with Ba: Ti: C2O4 = 1.05: 1: 6 and calcined at 800℃ for 4h……………...79
Fig. 4-29. (a) SEM photograph of precipitates prepared by diffusion with Ba:Ti:C2O4 = 1.05:1:6, (b) the surface of the precipitates prepared by diffusion with Ba:Ti:C2O4 = 1.05:1:6…………...80
Fig.4-30. SEM photograph of BTO and BaTiO3 prepared by way of diffusion and with very quickly stirred rate, Ba:Ti:C2O4 = 1.05:1:6.(a) BTO, (b) BaTiO3………………………………..80
Fig.4-31. SEM photographs of precipitates prepared by different RH (ethanol to water) ratios, (a) RH=1, (b) RH=2,
(c) RH=3……………………………………………………..82
Fig. 4-32. XRD patterns of barium titanium prepared with different RH (ethanol to water) ratios, (1) RH=1, (2) RH=2,
(3) RH=3……………………………………………………..82
Fig. 4-33. XRD patterns of precipitates prepared by different RH ratio of n-proponal. (1) RH=1, (2) RH=2, (3) RH=3…………………..84


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