Aerogels in Aerospace: An Overview

Table 1

Physical properties of conventional silica aerogel and Maerogel.

Property	Conventional aerogel	Maerogel	Comments
Apparent density	0.003–0.35 g/cm^3	0.03 g/cm^3	Commonly ~0.1 g/cm^3 for conventional aerogels; Usually 0.03 g/cm^3 for Maerogel
Internal surface area	600–1000 m^2/g	700–900 m^2/g
Mean pore diameter	20 nm	20.8 nm	Varies with density
Particle diameter	2–5 nm	5 nm	Determined by electron microscopy
Thermal tolerance	500°C	500°C	Shrinkage begins gradually at 500°C
Melting point	>1200°C	>1200°C
Typical thermal conductivity	0.015 W/mK	0.02 W/mK
Coefficient of thermal expansion	2.0–4.0 × 10^−6	2.0–4.0 × 10^−6	Determined using ultrasonic techniques
Poisson’s ratio	0.2	0.2	Independent of density
Young’s modulus	10^6–10^7 N/m^2	10^6–10^7 N/m^2	Insignificant compared to dense silica
Tensile strength	16 kPa	16 kPa	For density of 0.1 g/cm^3
Fracture toughness	0.8 kPa⋅m^0.5	0.8 kPa⋅m^0.5	For density of 0.1 g/cm^3
Index of refraction	1.0–1.05	1.0–1.05
Dielectric constant	~1.1	~1.1	For density of 0.1 g/cm^3
Sound velocity	100 m/s	100 m/s	For density of 0.07 g/cm^3