吳乃立臺灣大學：化學工程學研究所翁瑩潔Weng, Ying-ChiehYing-ChiehWeng2007-11-262018-06-282007-11-262018-06-282006http://ntur.lib.ntu.edu.tw//handle/246246/52177本實驗利用電凝聚法製造奈米晶體氧化鐵，此氧化物的微結構成長過程可大略分成三階段: 缺陷粒子的成核與成長，聚集，粗粒化。其反應機制牽涉到了在自由粒子的成核與成長和骨架的粗化之間的競爭。此競爭造成了晶粒大小在成長過程中的成長平台。另外,利用改良的電凝聚法亦合成了超微氧化鐵粒子(直徑小於10 nm) 。此粒子展現了超順磁特性，其飽和磁化率為64.5 emu/g。此晶體特性由XRD， TEM， DLS， SQUID鑑定分析。接著，利用電解液中添加聚乙烯醇製造出磁流體。聚乙烯醇會抑制晶體的成長使晶粒大小降至5 nm。此磁流體亦顯現出超順磁特性，由於聚乙烯醇的包覆及晶體些微氧化，其飽和磁化率降至4.57 emu/g。Nanocrystalline magnetite powders were synthesized by an electrocoagulation technique and the microstructure of the oxide powder was found to evolve in roughly three stages: formation and growth of severely defective colloidal crystallites, agglomeration, and coarsening. A mechanism involving competition between nucleation and growth of free colloids and coarsening of the skeletal framework was proposed to explain the temporary level-off in crystallite size during the synthesis. A modified method was developed to synthesize ultrafine magnetite (less than 10 nm) revealing superparamagnetism with saturation magnetization of 64.5 emu/g. The crystallites were characterized by XRD, TEM, DLS, and SQUID. The ferrofluid was also synthesized in the presence of PVA. The PVA will inhibit the growth of magnetite and the magnetite crystallite size reduced to 5 nm. The particles also show a superparamagnetic behavior with saturation magnetization of 64.5 emu/g. to 4.57 emu/g due to the PVA-coated layer and the oxidation.摘要 I Abstract II Table of Contents III List of Figures VI List of Tables X Chapter 1. Introduction and Background 1 1.1 Introduction to Magnetite 2 1.1-1 The Physical Properties and Crystal Structure of Magnetite 2 1.1-2 Applications of Magnetite 5 1.1-3 Methods to Synthesize Magnetite 6 1.2 Introduction to Electrocoagulation 10 1.2-1 Electrocoagulation Process in Wastewater Treatment 10 1.2-2 Using Electrocoagulation to Synthesize Magnetite Particles 12 1.3 Introduction to Superparamagnetism 15 1.3-1 Basic Concept 15 1.3-2 Size Effect 16 1.3-3 Blocking Temperature 18 1.3-4 Applied Field Effect 19 1.3-5 Applications 19 1.4 Magnetite Ferrofluid with Superparamagnetic Behavior 24 1.4-1 The Development of Ferrofluid 24 1.4-2 PVA as the Surfactant 25 1.5 Summary 26 Chapter 2. Experimental 28 2.1 Synthesis of Magnetite Particles 28 2.1-1 Electrocoagulation 28 2.1-2 A modified EC method 31 2.1-3 A modified EC Method in the Presence of PVA 34 2.2 Reagents 35 2.3 Analysis 36 2.3-1 Phase Identification 36 2.3-2 Morphology 37 2.3-3 Surface Area and Pore Characteristics 39 2.3-4 Size Distribution 41 2.3-5 Magnetic Properties 42 Chapter 3. Results and Discussion 44 3.1 Magnetite Powders Synthesized by EC 44 3.1-1 Structural Characterization 44 3.1-2 Morphology 49 3.1-3 Surface Area and Pore Characterization 52 3.1-4 Magnetic Properties 54 3.1-5 Mechanism 56 3.1-6 Summary 59 3.2 Magnetite particle/film by a modified EC method 60 3.2-1 Structural Characterization 61 3.2-2 Morphology 63 3.2-3 Size Distribution 68 3.2-4 Magnetic Properties 70 3.2-5 Summary 75 3.3 The Effect of Adding PVA 76 3.3-1 Structural Characterization 76 3.3-2 Surface Morphology 80 3.3-3 Size Distribution 80 3.3-4 Magnetic Properties 83 3.3-5 Summary 87 Chapter 4. Conclusion 88 References 904610361 bytesapplication/pdfen-US四氧化三鐵奈米電凝聚法超順磁Magnetitenanocrystallineelectrocoagulationsuperparamagnetismthesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/52177/1/ntu-95-R92524018-1.pdf