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Study on the Metal/Silicon Dioxide Composite Aerogels and Low Cost Preparation of Hydrophobic Silicon Dioxide Aerogels

Author: ChenYiMin
Tutor: XieKai
School: National University of Defense Science and Technology
Course: Materials Science and Engineering
Keywords: metal silicon dioxide composite aerogel hydrophobic ambient drying sol-gel method
CLC: TB383.1
Type: PhD thesis
Year: 2005
Downloads: 1191
Quote: 8
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Abstract


Aerogels that have fascinating such as high porosity, large surface area, low density and low thermal conductivity have been used in numerous application fields including microfilters, adsorbents,controlled realease of drug, especially for thermal insulation and catalyst or support of catalysts. In order to use more widely aerogels, it is necessary to improve preparing technique and properties of aerogels, and to reduce cost of aerogels.In situ eaction method, in which metal-containing tetraethoxysiliane（M-TEOS, M: Fe, Co, Ni or Cu） were used as the sol-gel precursors, was firstly applied to prepare the metal/SiO2 composite aerogels with high metal content in this paper. It was found that metal-oxygen bond in metal-oxygen-silicon bridge-containing aerogels broke in reduction process at high temperature to obtain metal/SiO2 composite aerogels. Because metal is linked to silicon dioxide gel network by metal-oxygen-silicon bridge, it is possible to prepare metal/SiO2 composite aerogels with high metal content. In situ reaction method can effectively reserve metal to the extent 90%. Therefore, Metal/SiO2 composite aerogels with expected metal content can be conveniently prepared by controlling metal content of M-TEOS.The effect of M-TEOS sol-gel conditon on sol-gel process and the structure and properties of metal/SiO2 composite aerogels were completely investigated. Compared to metal-oxygen- silicon bridge-containing aerogels, both pore diameter and pore volume of metal/SiO2 composite aerogels increased, but their specific surface area decreased. With the increase of metal content, specific surface area of metal/SiO2 composite aerogels decrease and vary in the range of 200620m2/g. Metal/SiO2 composite aerogels, the particle diameters of which are mostly less than 10nm, have pore diameter of 035nm and are characteristic of typically mesoporous structure.Fe, Co, Ni or Cu/SiO2 composite aerogels can obviously catalyse carbon deposition of acetylene pyrogenation in chemical vapor depostion（CVD）. The effect of metal sort and content on carbon deposition velocity and configuration of carbon are detailedly investigated. Fe-Ni/SiO2 composite aerogels can more effectively catalyse carbon deposition than Fe or Ni/SiO2 composite aerogels whose catalysis activity is higher than that of Cu/SiO2 composite aerogels. However, vapor grown carbon fibers（VGCFs） were prepared from carbon deposition of

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