| SiO2 aerogels belong to a kinds of non-crystal solid material which consist of SiO2 colloid particles molecule and form continuous random and porous network structure filled with gaseous dispersive medium. Because of their nano-size particles and porous characteristic, aerogels have many potential applications especially as super-insulation materials in modern aerospace and industrial fields.However, at ambient and higher temperatures, aerogel has poor thermal insulating property because it is highly transparent in the 2-8μm wavelength regions and the infrared electromagnetic wave can transmit in the SiO2 aerogels,therefore the radiative thermal conductivity will increase with the temperature increasing, which limits its actual application at high temperature.Due to its high transmittance in the infrared region at elevated temperature, this paper select TiO2 and K2Ti6O13 whisker as main opacifiers, considering it is an efficient opacifer due to its high reflection index and thermal stability. The pure and composite aerogels were fabricated by sol-gel method and subsequent non- supercritical drying technique (usually it maybe called as xerogels prepared with this method).The microstructure and physicochemical properties of the prepared aerogels were investigated by the menas of XRD, SEM, TEM, HRTEM, as well as Nitrogen gas adsorption, BET and FTIR method. Moreover, the MS method was adopted to simulate and analyze the interfacial and bonding properties between the SiO2 xerogels matrix and doped TiO2 particle or K2Ti6O13 whisker. Also the thermal insulation properties of the pure and doped-opacifer aerogels were evaluated using oxy-acetylene heating equipment.In the course of sol-gel, two-step acid-base catalyzed silica gels were prepared by using of tetraethoxysiliane (TEOS) as precursor, absolute alcohol as solvent, 0.2mol/L hydrochloric acid (diluting with absolute ethanol) and ammonia as acid and base catalyzer respectively. The results show that the most optimal molar ratio of TEOS, H2O, alcohol is 1: 4: 8. The hydrolyzation and condensation temperature is 50℃, and the hydrolysis time is 15min under acid solution. The most optimal molar ratio of TEOS and NH3·H2O is 1:0.036 under alkaline condition and the gel time is less than 2 min.Silica aerogels doped nano-sized TiO2 particle belong to amorphous and nano-porous network materials. TiO2 particles are physically embedded by silica aerogel and most TiO2 particles were adhered to silica aerogels.The average diameter of the pores obtained by BET analysis was about 30-50 nm. The BET surface area was in excess of 1000 m2/g for the doped TiO2 is less than 5wt%, while the specific surface area was slightly decreased to 785 m2/g for the doped TiO2 reaches 5wt%. The results showed that the SiO2 aerogel doped TiO2 can effectively scatter and adsorb the infrared electromagnetic wave between 2-8μm wavelengths, which results in the reducing infrared transmittance.Silica aerogels doped K2Ti6O13 whisker also have a characteristic of amorphous and nano-porous structure. The maximum BET surface area was 843 m2/g for the doped K2Ti6O13 whisker is 1wt%, and the specific surface area was slightly decreased compared with the doped-TiO2 aerogels. The average diameter of the pores for the doped content between 1wt% and 8wt% obtained by BET analysis was about 20-30 nm. The doped K2Ti6O13 whisker can greatly reduce the crystallization temperature, and thus the SiO2 crystalline was found at 870℃. The results showed that the SiO2 aerogel doped K2Ti6O13 whisker can also scatter and adsorb the infrared electromagnetic wave effectively between 2-8μm wavelengths, which results in the reducing infrared transmittance.The MS method was adopted to simulate and analyze the microstructural feature and interfacial energy between the SiO2 xerogels matrix and doped TiO2 particle or K2Ti6O13 whisker. The results revealed that the interfacial energy between TiO2/SiO2 is only 0.601J/m2, showing that no obvious chemical reaction on interface when the TiO2 is added into SiO2 aerogel. However, the interfacial energy between TiO2/ K2Ti6O13 whisker increased to 3.32 J/m2, although it is also attributed to weak interfacial bonding. It is noticeable that the some K+ can diffuse into the SiO2 aerogel and therefore displace its original position, which will result in interfacial reconstitution. This phenomenon will explain the reason that the SiO2 crystalline occur at relatively low temperature.The transient temperature distribution of honeycomb structure filled with and without doped TiO2 or K2Ti6O13 whisker aerogel was simulated by finite element modeling (FEM) analysis. Moreover, the modeling results were compared with the experimental equipment by oxy-acetylene heating system. The experimental and simulated results showed that the heat transfer style is mainly air convection and radiation transfer. However, the heat transfer of the doped-opacifer TiO2 or K2Ti6O13 can effectively inhibit the occurrence of the above two transferring style. The heat was mainly transferred by the small-area honeycomb wall and greatly delays the time to reach the back surface.
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