Effects of particle size of silica aerogel on its nano-porous structure and thermal behaviors under both ambient and high temperatures

Silica aerogel as the most commonly used aerogel has attracted increasing attention from both academia and industries due to its extraordinary performances and potentials. Through this study, influences of the particle size (38–880 μm) on its nano-porous structure and thermal behaviors were addressed based on a series of experimental tests under both ambient and high temperatures (i.e., 1000 °C). It was known from the experimental results that the fractional densities of samples with particle sizes of 270–880 μm were similar, which were about 40% of the sample with a particle size of 38 μm. The ratio of densification was found decrease to about 10–40% when heating time increased from 10 to 90 min. For those samples with 150 μm or finer particles, SiC crystal with 70.8 nm particles was generated, and the pore shape was slit in the silica aerogel. The Brunauer–Emmett–Teller (BET) surface area, cumulative pore volume, and average pore diameter of those heated samples with over 75 μm diameter were about 40%, 20%, and 50% of those unheated (virgin) samples, respectively. Virgin samples showed 18% lower thermal conductivity for 75 μm particles compared to that of 38 μm, while for the heated samples, 38 μm particles showed a 28% lower thermal conductivity than that with 880 μm. Mixture of silica aerogel and other inorganic material particles are recommended for high-temperature applications, while the silica aerogel with different-sized particles are observed better for applications under ambient temperature.