Preliminary Study Of SiO₂ Aerogel Hollow Microsphere Preparation

In the present thesis, low density SiO₂ aerogels for ICF targets via sol-gel process were disclosed. On the basis of SiO₂ aerogels preparation methodology, the micro-fluid technology was used to fabrication hollow aerogels microsphere. In order to reveal the microstructures of aerogel shell, scanning electron microscopy (SEM), transmission electron microscope (TEM) and optical microscope were employed.Firstly, silica aerogels were obtained by acid-base 2-step hydrolysis-condensation in tetraethoxysilane (TEOS) ethanol solution. The synthesis parameter was denoted as TEOS: EtOH: H2O: Catalysts (HCl or HNO3) in some content ratio to hydrolyze the siloxane precursor, the NH4OH was used to adjust the system at pH value was 7⁸, then the viscosity liquid was poured into plastic molds. When the gels formed in the molds, the gels were kept in closed containers to age 3⁶ days. After aging process, the gels were removed from the molds and soaked in ethanol for several days. Finally, the wet-gels were transferred into the autoclave vessel, and use the high purity CO2 as supercritical fluid media to obtain the as-synthesis aerogels. The aerogels densities were between 20 mg/cm3¹50 mg/cm3 in ethanol solution system. These aerogel could be used as filler materials in ICF targets. The microstructure of aerogels was characterized by SEM , HRTEM and N2 isotherm adsorption-desorption methods.Then,in order to obtained SiO₂ aerogel hollow microsphere, we built a double-T micro-channel device to control micro-fluid process parameter. In this process, the TEOS was used as silica precursor, the precursor reaction solution was employed as an intermediate water phase, poly dimethyl silicone oil as the inner and outer oil phase, adjusting the flow rate of the different phase was and preparing with a diameter 0.5 2.0mm, wall thickness 0.030 0.180mm, SiO₂ aerogel hollow microspheres. The micro emulsion particle sizes were affected by the device parameters, and horizontal water bath heating technology was used to increase the survival rate of the double micro emulsion particles. Ether was selected to replace the silicone oil in the microspheres. Then the wet-gel spheres were soaked in acetone to make them become acetone-gel. Finally, the acetone-gel spheres were dried in supercritical CO2 fluid to obtained low-shrinkage aerogel shells. In solvent exchange and drying process, there exist diameter and wall thickness shrinkage. The average shrinkage ratios of diameter and wall thickness were 9.78% and 6.5%, respectively, before and after solvent exchange. The average shrinkage ratios of diameter and wall thickness were 3.75% and 2.94% , respectively , after supercritical drying. Finally , optical microscopy , FESEM , high-resolution transmission electron microscopy (HRTEM) were used to determined the SiO₂ hollow aeogel microspheres morphology and size, the results show that the obtained spherical SiO₂ hollow microspheres greater than 99%, less than 5% of de-concentricity, which agreed with the demand of ICF experiments.