Physical Properties of Silica Aerogels

Note: Most of the properties listed here are significantly affected by the conditions used to prepare the aerogel and any subsequent post-processing.

Property Value Comments
Apparent Density 0.003-0.35 g/cm3 Most common density is ~0.1 g/cm3
Internal Surface Area 600-1000 m2/g As determined by nitrogen adsorption/desorption
% solids 0.13-0.15% Typically 5% (95% free space)
Mean Pore Diameter ~20 nm As determined by nitrogen adsorption/desorption (varies with density)
Primary Particle Diameter 2-5 nm Determined by electron microscopy
Index of Refraction 1.0-1.05 Very low for a solid material
Thermal Tolerance to 500 C Shrinkage begins slowly at 500 C and increases with temperature. Melting point is >1200 C
Coefficient of Thermal Expansion 2.0-4.0 x 10-6 Determined using ultrasonic methods
Poisson’s Ratio 0.2 Independent of Density. Similar to dense silica
Young’s Modulus 106-107 N/m2 Very small ( <10 4x) compared to dense silica
Tensile Strength 16 kPa For density = 0.1 g/cm3
Fracture Toughness ~0.8 kPa*m1/2 For density = 0.1 g/cm3. Determined by 3-point bending
Dielectric Constant ~1.1 For density = 0.1 g/cm3. very low for a solid material
Sound Velocity Through the Medium 100 m/sec For density = 0.07 g/cm3. One of the lowest velocities for a solid material

Special thanks to the Lawrence Berkeley Laboratory’s Microstructured Materials Group for permission to use this paper.


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