二氧化硅气凝胶的性能受热过程的影响

Effect of Thermal Process on Microstructure and physical properties of silica aerogels

摘要:

本文成功的以水玻璃为硅源，经乙醇溶剂替换及六甲基二硅醚(hexamethyl disiloxane)和盐酸(hydrochloric acid )的混合液对二氧化硅(SiO2)湿凝胶表面基团改性后，常压干燥制备出低密度（约0.116 g/cm3）、高比表面积（871 m2/g）、超疏水（疏水角约为145°）、低热导率（0.025 w/(m•K)）的高性能SiO2气凝胶块体。SiO2气凝胶在室温至400°C附近具有稳定的疏水性能，460 °C附近气凝胶由疏水型完全转变成亲水型。本文重点研究了室温至400 °C之间，SiO2气凝胶的微观结构（表面形貌、孔径分布）和物理性能（热学、力学性能）受热处理过程的影响。SiO2气凝胶即使经过400°C高温热处理后，仍能保持优异的疏水性能（约为125°）、较高的比表面积(530 m2/g)和较低的热导率(0.049 W/ (m K))等。

Abstract:

The experimental results of changing heat treatment temperature on the microstructure and thermodynamic properties of hydrophobic silica aerogels are reported and discussed. Prepared with sodium silicate precursor, ethanol (EtOH)/ hexamethyldisiloxane (HMDSO) /hydrochloric acid (HCL) as solvent exchange and surface modification agent, the crack-free and high hydrophobic silica aerogel monoliths were obtained. Silica aerogels possessed the superior properties, such as low density (0.116 g/cm3), high surface area (871 m2/g), high hydrophobicity (~145°) and low thermal conductivity (0.025 W(m K)−1). Silica aerogel monoliths maintained hydrophobic behavior up to a maximum temperature of 460°C above which they become hydrophilic. After a thermal process changing from room temperature to 400°C, the final product was still remained hydrophobic (~125°) and presented good performance with surface area of 530 m2/g. Thermal conductivity coefficients of silica aerogel monoliths changed from 0.025 to 0.049 W/ (m K) as temperature increased from 25 to 400°C, revealed an excellent heat insulation effect during thermal process.