More efficient heating insulation, more robust building materials, more environmentally sustainable energy production
– which is particularly important in winter – are all due primarily to
the rapid progress in materials and energy management. Nanotechnology is
increasingly playing a critical role.
“Daily high temperatures near freezing, snow, and sleet will cause
slick streets – also expect strong and stormy winds”: When you’re
sitting in a well heated living room, you may suddenly appreciate the
importance of building techniques.
Effective thermal insulation is central to a comfortable indoor
climate, while consuming the minimum possible amount of energy.
Governments are enacting increasingly rigid energy consumption
ordinances for new as well as existing buildings. It’s no wonder in
times of urgent climate discussions – nearly a fifth of all CO2
emissions in Germany is attributable to buildings. In private households
in Germany, an average 75 percent of energy consumption is used for
indoor heating alone.
Nanopores keep heat where it belongs
To drive down exterior wall heating requirements to near passive
house levels, it is possible to install 20 to 30-centimeter thick layers
of conventional insulating material, such as polystyrene – but this
approach has undesirable effects on aesthetics and space requirements.
It is also possible to use more intelligent insulating materials.
Today, silica-aerogels are available – highly porous, noncombustible
solids made of silicon dioxide and air: over 90 percent of the volume
consists of pores, which are only a few nanometers in size. Similar
nanoporous foams based on synthetics are currently in development.
From an oven to a research station in Antarctica
Nanopores make aerogels rigid, somewhat translucent, and lend them a
remarkably large interior surface area, often totaling over 1,000 square
meters per gram – which makes this class of materials attractive for a
wide variety of applications. Their structure ensures extremely low
thermal conductivity: there are far too many small amounts of the base
material present to transmit significant heat, and heat conductivity is
effectively impeded.
Such nanoporous foams can be applied to conventional insulating
panels that have been previously installed on building façades to retain
heat inside buildings – to keep boilers hot or keep a refrigerator cold
that is near an oven. Likewise, material in the form of granulate can
be used as spray insulation or, with even greater effectiveness, as a
filler for vacuum insulation panels. A unique example is the use of
aerogel as a translucent filler between glass panels, which results in
diffuse, translucent, heat- and sound-insulating building components.
It’s not only a good idea for our latitudes: a British research station
in Antarctica has installed this distinctive type of glazing.
Steel that does not rust
Probably the most important and most commonly used material in
construction is concrete, which is essentially a mixture of cement,
water, and gravel (aggregate). Maximum structural performance is
achieved by optimizing concrete at the nanotechnological level. Pores
form in concrete, which cause compression strength to diminish. The
surface area subject to concrete-damaging substances can corrode and
become larger. Adding the right particle can provide protection by
filling the tiny cavities, making the concrete more compact, harder, and
more durable.
To achieve this, over the last decade researchers in the town of
Kassel in Germany systematically studied the nanostructure of concrete.
In order to find the optimum mixture, they measured possible particle
additives on a scale of nanometers. When tensile strength is increased
by adding steel fibers, the result is a material with the properties of
steel that does not rust: ultra high performance concrete (UHPC).
The material has already been used to construct several bridges,
including the Gärtnerplatz Bridge in Kassel, Germany and numerous
smaller bridges in the American state of Iowa. The advantages:
structures last longer and require less material thickness. This
conserves raw materials and helps protect the climate: the production of
cement is responsible for nearly five percent of global CO2 emissions.
Better solar cells
As an emissions-free source of energy, electricity from sunlight is
playing an increasingly important role. A key objective is to continue
optimizing solar cells in terms of material consumption, effectiveness,
and cost. One approach makes use of thin-layer cells made from silicium
that are up to 1,000 times thinner than conventional photovoltaic
elements – and save a corresponding amount of materials. The problem is,
if they are too thin, too much sunlight can pass through unimpeded,
instead of producing electricity. A current technique is to disperse the
light with zinc oxide crystals, so that the path distance within the
silicium layer becomes greater. It was a challenge to force zinc oxide
crystals into the correct nanoscaled shape, so that the technique could
function properly. Researchers have however found an efficient solution:
they produce a negative of the desired structure and allow zinc oxide
crystals to form on it. The nanolayer can then be removed.
Another path of development is the Grätzel cell. Inventor Michael
Grätzel won the 2010 Millennium Prize – in essence the Nobel Prize for
engineers – for developing the technology. It generates electricity not
in semiconductor layers but instead in special dyes, based on a process
borrowed from natural photosynthesis. The Grätzel cell promises
inexpensive, flexible, and transparent solar panels – even a window
could become a photovoltaic cell. “Nano” is also found is this
development: titanium dioxide is a necessary component, which captures
the electrons that are set free from the dye by sunlight and transmits
them to the electrical circuit.
Titanium dioxide is a nanoporous material or a material occurring in
nanoparticles. It is used extensively as a white color pigment in wall
paint and as a UV reflector in sunscreen lotions.
