二氧化矽氣凝膠與二氧化矽複合氣凝膠之探討與二氧化矽氣凝膠薄膜之應用

Study of SiO2 Aerogels, SiO2 Hybrid/Composite Aerogels, and SiO2 Aerogel Films

張坐福(Mark Chang)

指導教授 ： 呂世源

國立清華大學/工學院/化學工程學系/碩士(2007年)

https://doi.org/10.6843/NTHU.2007.00130

摘要

氣凝膠擁有需多的特殊性質如，低密度，高孔隙率，高比表面積，以及低熱傳導係數。本研究針對塊材氣凝膠的孔隙率，接觸角，比表面積，材料熱重分析，以及熱傳導係數，進行研究及探討。 氣凝膠及其它電化學製備的多孔性薄膜部分，針對表面型態，反射率，以及接觸角進行研究及探討。
研究中使用的二氧化矽氣凝膠、二氧化矽/聚乙烯吡咯烷酮混和氣凝膠、以及二氧化矽/氧化鉛混和氣凝膠主要是在常壓常溫下製備。 添加聚乙烯吡咯烷酮的主要目的是要改善氣凝膠的整體性及機械性質，而氧化鉛可以降低氣凝膠在高溫的熱傳導係數。氣凝膠薄膜主要是用來當作以電化學的方式製備的多孔性薄膜的基板.
實驗結果發現氣凝膠的比表面積會隨著使用的乙醇濃度增加而減少，混和氣凝膠有較好的整體性但是孔隙率較低、熱傳導係數較高。二氧化矽氣凝膠、含有0.14 wt%聚乙烯吡咯烷酮的二氧化矽/聚乙烯吡咯烷酮混和氣凝膠、含有0.5 wt%氧化鉛二氧化矽/氧化鉛混和氣凝膠在室溫的熱傳導係數分別是0.031、0.046、和0.037 W/K-m。5.0 wt%二氧化矽/氧化鉛混和氣凝膠在500 ℃有最低的熱傳導係數0.075 W/K-m。在400℃時，混和氧化鉛及二氧化鈦的二氧化矽氣凝膠的熱傳導係數比在300 ℃時還低，這個現象相信是混和氧化鉛及二氧化鈦的二氧化矽氣凝膠在400 ℃時的消光係數比在300 ℃時還高所造成。
常壓製備出來的氣凝膠薄膜的厚度為~200 nm。此研究中，以氣凝膠薄膜分別成功製備出聚咇咯、鎳、銀以及二氧化鈦多孔性薄膜。製備出來的多孔性薄膜分別使用掃瞄式電子顯微鏡、可見紫外線反射率以及接觸角量測做性質的探討。

關鍵字

氣凝膠 ； 熱傳導 ； 薄膜 ； 氧化鉛

並列摘要

Aerogels have been known for its low density, high porosity, high specific surface area, low dielectric constant, and low thermal conductivity for decades. Porosity, contact angle, BET surface area, TGA, and thermal conductivity of aerogel monolith, morphology, UV-vis reflection spectra, and contact angle of aerogel film with different synthesizing parameters or composition are studied in this thesis.
Monolithic SiO2 aerogels, SiO2-PVP hybrid aerogels, and SiO2-PbO composite aerogels were prepared and dried under ambient pressure. PVP is added as a mechanical strength enhancing additive to improve monolithicity of aerogels, and PbO is selected to lower thermal conductivity at high temperature, when radiation is prominent. Aerogel films are prepared to investigate the feasibility to serve as inverse structure for preparation of porous film electrochemically.
Experimental results showed that monolithic aerogels with lower molar ratio of ethanol used have higher BET surface area. Hybrid/composite aerogels have better monolithicity, but lower porosity and higher thermal conductivity. Thermal conductivities of SiO2 aerogel, 0.14 wt% SiO2-PVP hybrid aerogel, and 0.5 wt% SiO2-PbO composite aerogel at ambient temperature are 0.031, 0.046, and 0.037 W/K-m, respectively. 5.0 wt% SiO2-PbO composite aerogel have the lowest thermal conductivity at 500 ℃, which is 0.075 W/K-m. An unusual phenomenon is found for all SiO2-PbO and SiO2-TiO2 composite aerogels, thermal conductivity of composite aerogels at 400 ℃ are all lower compared to thermal conductivity at 300 ℃, and the phenomenon is expected to be caused by enhancement of extinction coefficient of composite aerogels is by addition of opacifier at 400 ℃.
Thickness of aerogel films prepared is ~200 nm. Polymer, metal, metal with magnetic property, and oxide porous film were successfully prepared, polypyrrole, silver, nickel, and TiO2¬ are selected respectively. Porous films prepared are characterized with SEM, UV-vis reflectance and contact angle measurement.

並列關鍵字

Aerogel ； thermal conductivity ； film ； PbO ； PVP

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