Effect of Glycerol in the Preparation of Silica Aerogels by Ambient Drying Method
- 주제(키워드) aerogel , silica
- 발행기관 고려대학교 대학원
- 지도교수 남 산, 오영제
- 발행년도 2008
- 제출일 2008-07-07
- 학위수여년월 2008. 8
- 학위명 석사
- 학과 일반대학원 신소재공학과
- 세부전공 신소재공학전공
- 원문페이지 67 p
- 본문언어 영어
- 제출원본 000045504298
초록/요약
Silica aerogels have extraordinary properties and their potential applications in wide variety technological areas. Silica aerogel is a nanostructured material with high specific surface area, high porosity, low density, low dielectric constant and excellent heat insulation properties. The synthesis of silica aerogels can be divided into 3 general steps; gel preparation, aging of the gel and drying of the gel. The silica aerogel is obtained by sol-gel process. The sol is prepared by silica source solution and addition of catalyst. The aging process after gelation strengthens the gel, so that shrinkage during the drying step is kept to minimum. In drying process of the gel, the gel should be freed of the pore liquid. To prevent the collapse of the gel structure, drying is made to take place under special condition. The ambient drying process, cost effective way, for silica aerogels and aerogel consists two step process with solvent exchange and surface modification in alkoxide. In this study, silica hydrosol was synthesized by a sol-gel process using metal alkoxide precursor. After gelation, the fluid solvent in hydrogel was exchanged with various solvents to minimize drying shrinkage. And small amount of glycerol was added for DCCA(Drying Control Chemical Additive) to prevent cracks in silica aerogels. The crack-free silica aerogels were showed 0.18-0.71 g/cm3 of bulk densities, ~1015 m2/g of specific surface area and ~36-149 Å of average pore diameter.
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Contents
Abstract ⅰ
List of Figure ⅴ
List of Table ⅵ
1. Introduction 1
2. Theory of aerogel 6
2.1. Mechanism of aerogel network 6
2.1.1. Supercritical Drying 15
2.1.2. Ambient Drying 16
2.1.3. Freeze-drying 18
2.2. Properties of Aerogels 18
2.2.1. Dielectric Property 20
2.2.3. Optical Property 22
2.2.3. Thermal Property 24
2.2.4. Surface Chemical Property 25
3. Experimental Procedure 28
3.1. Preparation of TEOS based Silica sols 28
3.2. Solvent Exchange and Surface Modification 30
3.3. Ambient Pressure Drying 32
3.4. Analysis 33
4. Results and Discussion 34
4.1. Properties of Silica sol 34
4.2. Mechanism and Effectiveness of Surface Modification 37
4.3. Drying of Wet Gels 41
4.4. Effectiveness of Glycerol for DCCA 42
4.5. Characteristics of Silica Aerogels 45
4.5.1. Thermal Property 45
4.5.2. Microstructure of Silica Aerogel 47
5. Conclusion 54
References 55
