Technics And Properties Of SiO₂ Aerogel Based Thermal Insulation Composite

Due to their nano-networks and nano-pore structure, SiO₂ aerogels gains great thermal insulation properties, In this paper, SiO₂ aerogels with massive structure were prepared by using TEOS as precursor, through hydrolysis, polycondensation, aging and drying procedure, with the methods at ambient pressure drying separately. The SiO₂ aerogels composites strengthened by fiber-felts were also prepared. The integrity, internal pore size distribution and surface modification of SiO₂ aerogels prepared were analyzed using nitrogen adsorption-desorption method, infrared spectroscopy method and X-Ray analysis. The microstructure of SiO₂ aerogels composites was investigated with scanning electron microscopy, transmission electron microscope and thermal analyzer.In this paper, influencing factor of preparing SiO₂ aerogels with massive structure is explored by controlling doses of acid and base catalyst. The results showed that using NH3·H2O of 0.04mol/L as base catalyst massive structure can be well gained with specific surface area over 700m2/g, density below 0.15g/cm3 and an average pore diameter around 10nm which has homogeneous distribution. As a acid catalyst, content of oxalate is a minor factor. When it is below 0.08mol/L, massive structure can be gained.The SiO₂ aerogels prepared with drying under the ambient pressure were amorphous and lyophobic at room temperature, contact angle stay above 140°,The methyl on the skeletal surface were burned off before 400℃, and the aerogels became hydrophobic from hydrophilic. The author believe that SiO₂ aerogels can be used as heat insulation metrial repeatedly used below 900℃. Above 900℃SiO₂ aerogels shrinks obviously and get worse as temperature grows. Glass-transition temperature of SiO₂ aerogels is around 950℃, and shrinkage over 50% is obtained at 1100℃. Though SiO₂ aerogels stay amorphous after heat treated at 1200℃for 1h, the skeleton collapse and lose its multiple nano-pore structure.SiO₂ aerogels composites whose surfaces are flat and smooth are prepared using quartz fiber felt and ceramic particles of Al2O3,BN,TiO₂ as reinforcements. The flexibility and intensity are greatly improved. And dielectrical property of SiO₂ aerogels composites is excellent,ε<2 and transmissivity of infrared is less than 10%. In this paper, the influence of thermal isolation properties by the types and content of ceramic particles is researched. Numerical simulation result shows heat conductivity of the composites at 430℃and 820℃are between 0.02⁰.05W/(m·K), to which ceramic particles contribute a lot.