Civil Engineering Reference
In-Depth Information
Table 1
Physical properties of silica aerogels (adapted from Riffat and Qiu
2012
)
Properties
Values range
Pore diameter (nm)
5-100 (about 20 in general)
Porosity (%)
85-99.8 ([90 in general)
Density (kg/m
3
)
50-200 (about 100 in building applications)
Surface area (m
2
/g)
100-600
Optical behaviour (-)
Opaque (blankets)
Translucent (granular)
Transparent (monolithic)
Thermal conductivity (W/m K)
0.008-0.020 (depending on temperature, pressure,
and production process)
Sound speed (m/s)
40-300
Table 2 Main features of
Lumira nanogel
(adapted
from Cabot
2012
)
Properties
Values range
Particle size (mm)
0.07-4
Pore diameter (nm)
About 20
Porosity (%)
[90 air
Density (kg/m
3
)
65-85 (bulk); 120-180 (particle)
Surface area (m
2
/g)
600-800
Surface chemistry
Fully hydroscopic
Optical behaviour
Translucent
China, Japan, and Russia. Cabot Corporation (USA) seems to be the main manu-
facturer of granular translucent aerogels. The company developed an innovative
manufacturing process and allowed a production on large scale since 2003 in a plant
in Frankfurt, Germany; it can produce about 10,000 t per year (Werner and Brand
2010
; Aegerter et al.
2011
). The translucent aerogels manufactured by Cabot,
Lumira
TM
aerogel, formerly Nanogel
aerogel, are characterized by grain size in
the 0.07-4 mm range (Table
2
).
3 Silica Aerogels Thermal and Lighting Performance
3.1 Thermal Properties
Silica aerogel has the lowest thermal conductivity k among solid materials, despite
the silica skeleton structure value being relatively high (in the 1.3-1.4 W/m K
range). The overall value is very low: it ranges from 0.018 W/m K for granular
silica aerogel to 0.004 W/m K for evacuated monolithic silica aerogel (Koebel
et al.
2012
; Bouquerela et al.
2012
). Table
3
shows the thermal conductivity of
silica aerogel, compared to different insulation products: nowadays, only vacuum
technology has a thermal conductivity of the same order of aerogel.
