Science of Silica Aerogels
Physical Properties
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 ~0.1g/cm3. |
| Internal Surface Area | 600-1000 m2/g | As determined by nitrogen adsorption/desorption. |
| % Solids | 0.13-15% | 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, increases with inc. 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 (<104x) 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. |
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