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51
ZEB
annual report 2014
Glass materials are used extensively in
today’s buildings, and the use will probably
increase even more in the coming years.
Large window and glazing areas are often
preferred, e.g. with respect to daylight
admittance and visual expressions. On the
other hand, windows may also be responsible
for large heat losses from buildings and
contrary overheating of buildings from
incoming solar radiation. Thus, the various
properties of glass materials will be very
important. Furthermore, it will also be of
crucial interest if it is possible to improve these
properties significantly. That is, for future
glass materials and their application in e.g.
zero energy and zero emission buildings, it
will be important to address properties related
to e.g. solar radiation throughput, thermal
conductivity, mass density and mechanical
strength.
Hence, the objective of our study presented
herein has been to attempt to develop a new
aerogel glass material for energy-efficient
buildings with low mass density, low thermal
conductivity, high visible transparency and
satisfactory high mechanical strength.
Experimentally, in short, new aerogel glass
materials were successfully prepared by
sintering monolithic silica aerogel precursors
at elevated temperatures (Gao et al. 2014ab).
These new aerogel glass materials were
characterized by high visible transparency (T
vis
≈ 91 – 96 % at 500 nm) (Fig.1), low thermal
conductivity (k≈ 0.17 – 0.18 W/(mK)) (Fig.2),
low mass density (ρ ≈ 1.60 – 1.79 kg/dm
3
),
and enhanced mechanical strength (typical
elastic modulus Er ≈ 2.0 – 6.4 GPa and
hardness H = 0.23 – 0.53 GPa).
These new and improved properties,
summarized in Table 1, were derived
from a series of successive gelation and
ageing steps during the desiccation of
silica aerogels. The involved ”sol → gel
→ glass” transformation was investigated
by means of thermo-gravimetric analysis
(TGA), scanning electron microscopy (SEM),
nanoindentation, and Fourier transform
infrared (FTIR) spectroscopy. Strategies of
improving further the mechanical strength
of the obtained aerogel glass materials
are also being discussed. As compared to
monolithic silica aerogels that have a typical
thermal conductivity of about 0.013 W/(mK),
there seems to be a huge potential to further
decrease the thermal conductivity and thus
enhance the thermal insulation performance
of aerogel glass materials by optimizing
their structural properties, such as the
The future glass materials may be a
lot different from today’s materials...
LIGHTWEIGHT AEROGEL GLASS
|
LETT AEROGEL GLASS
Tao Gao (NTNU) and Bjørn Petter Jelle (NTNU and SINTEF)