Study On The Metal/Silicon Dioxide Composite Aerogels And Low Cost Preparation Of Hydrophobic Silicon Dioxide Aerogels

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...