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研究生:辜喬治
研究生(外文):george endri kusuma
論文名稱:固態氧化物燃料電池鉍摻雜釔安定氧化鋯基電解質之微觀與電性研究
論文名稱(外文):Investigation of microstructural and electrical properties Bi2O3 added 8YSZ electrolyte for SOFZ
指導教授:周振嘉
指導教授(外文):Chen-Chia Chou
學位類別:碩士
校院名稱:國立臺灣科技大學
系所名稱:機械工程系
學門:工程學門
學類:機械工程學類
論文種類:學術論文
畢業學年度:96
語文別:英文
論文頁數:103
中文關鍵詞:釔安定氧化鋯電解質氧化鉍
外文關鍵詞:8YSZElectrolyteBi2O3
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Development of SOFC single cell using 8YSZ as an electrolyte component is one of the major issue. We developed a new electrolyte material for SOFC using Bi2O3 as dopant and sintering aid to 8YSZ for decreasing the sintering temperature and increasing electrical property especially at ionic conductivity. Bismuth oxide added yttria stabilized zirconia as electrolyte material for SOFC was investigated using x-ray diffraction, scanning electron microscopy, transmission electron microscopy and AC impedance spectroscopy.
It was found that the small addition of Bi2O3 was effective in reducing the sintering temperature and promoting the densification rate of the ceramics. At lower sintering temperatures, Bi2O3 phase is found to act as a wetting agent of the grain boundaries. The majority of Bi2O3 was segregated at the grain boundaries which formed Bi2O3 - rich liquid films on the basis of STEM/EDS analysis and the thin Bi2O3 -rich liquid film is found to serve as a diffusion path for the sintering.
XRD analysis reveals the coexistence of cubic and monoclinic phases in pure 8YSZ and Bi2O3 doped 8YSZ at lower sintering temperatures. But, at higher sintering temperatures, 8YSZ electrolyte and low content of Bi2O3 doped 8YSZ electrolyte show pure cubic phase in micro-scale observation. This might be due to appropriate sintering temperature and Bi2O3 content.
Microstructural study shows bimodal grains. Bismuth rich is found in smaller grains. Transmission electron micrographs revealed the similar behavior. But, the diffraction pattern of big grain show cubic phase and smaller grain resulted in monoclinic phase. Though the monoclinic phase is not observed in XRD analysis, the nanoscale analysis using TEM has shown the existence of monoclinic phase even at higher sintering temperatures.
AC impedance analysis indicates better grain boundary conduction in doped 8YSZ. Grain boundary conduction was significantly improved in our observation. The total conductivity of 8YSZ was evidently increased 26% compare to pure 8YSZ by doping small amount of Bi2O3. The change in conductivity by the addition of dopant Bi2O3 in these material systems was correlated with microstructure analysis. The experimental results demonstrate better density, improved microstructure, higher ionic conductivity and lower activation energy in bismuth oxide doped 8YSZ electrolytes compared to that of pure 8YSZ. The results on conventional sintered samples indicate that the minimum processing temperature needed to stabilize the cubic phase is above 1300oC for 8YSZ and 0.5mol% Bi2O3 added 8YSZ to use these materials as electrolytes in the solid oxide fuel cells.
Microwave sintering was also carried out on microwave sintering in order to reduce the evaporation of Bi2O3 rate during sintering process. Microwave sintering is found to suppress the evaporation rate of Bi2O3. Compared to conventional furnace, significant improvement in density of zirconia ceramics at lower sintering temperature, rapid heating rate and short sintering time were observed. Microwave sintering was proved to overcome the problems with the evaporation of Bi2O3 during sintering process. By using microwave sintering at the same sintering temperature the total density of 8YSZ+10% Bi2O3 was evidently increased 4.59 % in comparison to YSZ+10% Bi2O3 sintered with conventional furnace and the total ionic conductivity was enhanced by 6.578 % in microwave sintering process.
Abstract I
Acknowledgments III
Vitae IV
Table of Contents V
List of Table XII
Introduction 1
Literature Review 4
2.1 Sintering Process 4
2.2 Yttria Stabilized Zirconia (YSZ) 7
2.2.1 Pure ZrO2 7
2.2.2 Phase stability of ZrO2-Y2O3 system 9
2.2.3 Microstructures of YSZ 11
2.3 Pure Bi2O3 12
2.3.1 Structure Bi2O3 12
2.3.2 The Structure of α-Bi2O3 13
2.3.3 The structure of ��-Bi2O3 14
2.3.4 The structure of β and ��-Bi2O3 16
2.3.5 Thermal expansion of ��, β, �� and �� Bi2O3 17
2.3.6 The electrical properties of Bi2O3 17
2.4 Bi2O3-ZrO2 system 19
2.5 Bi2O3-Y2O3 system 20
2.6 ZrO2-Y2O3-Bi2O3 System 29
2.7 Electrochemical Impedance Spectroscopy (EIS) 31
2.7.1 AC Circuit Theory and Representation of Complex Impedance Values. 32
2.7.2 Impedance spectroscopy in application in electrolyte resistance 34
Experimental Procedures 35
3.1 Material 35
3.2 Characterization of the raw powder 36
3.3 Identification Specimen Result 36
3.3.1 Experimental Density Measurement 36
3.3.2 Phase identification (XRD) 37
3.3.3 Microstructure and Compositional analysis 37
3.3.4 Ionic Conductivity Properties Measurement 39
3.4 Design of Result 40
Experimental Results and Discussion 41
4.1 Characterizations of raw powder 41
4.1.1 Raw powder 8YSZ 41
4.1.2 Raw Powder Bi2O3 42
4.2 XRD data analysis result of 8YSZ+Bi2O3 System 45
4.2.1 Data analysis sintering at 1000°C-1300°C 45
4.2.2 Data analysis of Specimen Sintered with Various mol % Bi2O3 addition and Different Time 50
4.3 Microstructure investigation and analysis 55
4.3.1 SEM analysis 8Y-ZrO2–Y2O3 sintering at 1300°C/2 hours 55
4.3.2 TEM Analysis 8Y-ZrO2–Y2O3 sintering at 1300°C/2 hours 57
4.3.3 Microstructure analysis of 8YSZ + Bi2O3 58
4.3.4 BEI and SEI Technique Investigation 60
4.3.5 Investigation at 8YSZ+10% Bi2O3 using EDS 64
4.3.6 TEM-EDS analysis at 8Y-ZrO2- Bi2O3 system 66
4.3.7 SADP analysis of 8YSZ+10%Bi2O3 68
4.3.8 TEM Element Mapping 71
4.4 Electrical characterization using AC impedance analyzer 72
4.5 Microwave Sintering Process 85
4.5.1 Microwave Sintering Result Analysis 85
4.5.2 Microstructural Analysis of Microwave Sintering 8YSZ+10% Bi2O3 89
4.5.3 TEM investigation 8YSZ+10% Bi2O3 90
Summary and Conclusion 92
Bibliography 94
Appendixes 99
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