Characteristics of nanoporous silica aerogel under high temperature from 950 °C to 1200 °C

Silica aerogel is a unique three-dimensional nano-porous material and its characteristics have attracted much attention from both engineers and researchers. However, their structural behaviors under high temperature are not well known yet. The structure of silica aerogel under high temperature from 950 °C to 1200 °C was investigated based on pycnometry, scanning electron microscope (SEM), Brunauer-Emmett-Teller (BET) analysis, Fourier transform infrared (FTIR) spectroscopy, and X-ray diffraction patterns (XRD). It was obtained that the structure of silica aerogels was strongly affected by heating temperature and time. It was known based on experimental results that the changes of silica aerogel during 950-1200 °C can be divided into three steps: expansion of primary particles at sample surface (step I), atrophy and pore collapse of primary particles at the surface (step II), and atrophy and pore collapse of primary particles inside the sample (step III). Change rate was found significantly dependent on the moving rate of expansion region, while during the first two steps only limited changes were observed about three dimensional nanoporous structures. During Step III, the structure of silica aerogel was completely destructed, while the density can reach to about 1600 kg/m3.