Silica-based aerogel boards
Aerogels are open porous, nanostructured materials manufactured by sol-gel technologies from water-rich solutions containing suitable chemical precursors. After their reaction a wet gel body containing nanosized particles being connected in3D like strings of pearls appear. Drying suitably conserves their solid skeleton and leaves materials with fascinating properties. They have a low density, very high inner surfaces area, low thermal conductivity and a high capability of sound absorption. They can be brittle like ceramics but also flexible like rubber. Their operation temperatures range from -200°C to 1400°C, depending on the precursors. Aerogels can be functionalized: they can by hydrophobic or hydrophilic, electrical insulators or electrically conductive, transparent in wavelength range from 400nm to 2000 nm or opaque, they can be colored, made ferroelectric or superparamagnetic. Their specific surface area is in the range form 100 to 2000 m2/g
Possible applications are superisolating materials for many kinds of aerospace applications, in cars, trains and any kind of earth bound vehicles, passive isolation of buildings or even passive isolation in high temperature applications (exhausts of engines or furnaces), superefficient heat pumps, new kinds of filters for clean air inside cars, trains and airplanes, superlight, multifuncti-onal construction materials which isolate not only thermally but also acoustically..
Microstructure of a acid catalyzed, brittle thermoset aerogel
Since almost 20 years DLR performs research on aerogels on the basis of oxides, thermosettings resins, biopolymers and Carbon. We especially explore technologies for their synthesis and manufacturing, to optimize routines and reduce costs and using environmentally friendly processes and precursors. Heat insulation is realized in buildings, in air condition systems, heat storage devices, motors, exhausts, industrial and kitchen furnaces, refrigerators use porous materials made form polymers and ceramics either as foams or fiber bats or felts. Aerogels outperform these materials, since the heat conduction via the solid network is reduced, since the particles just have nano-contacts, the conduction of air through the pores is reduced, since the gas molecules are scattered at the pores walls and loose their energy, and radiation heat losses are reduced, if the materials is opaque. Today’s standard isolation materials are outperformed by aerogels by a factor of 2 to 3. Wherever the available space in a construction is limited, aerogel solutions for isolation are best and also save mass and weight.
Organic and inorganic aerogels belong lightest solids, even lighter than most polymeric foams. They can have porosities up to 99.9 %, typically the porosity is between 93% and 97%. Their thermal conductivity is at room temperature between 0.005 and 0.03 W/Km. Therefore they are the best available isolation materials. They are only outperformed by vacuumisolationpanels (VIPs), but aerogels are open for humidity exchange.
Oxide aerogels are typically fragile, brittle and break easily under inhomogeneous stresses. They can be pulverized between the fingers. Depending on their density and chemistry, they can, however, also be of low elasticity and be deformed like rubber. Oxide aerogels typically have a low compression and shear strength. Many inorganic aerogels have a bad haptic; one feels uncomfortable on touching them. They release dust on touching and adsorb water or fat from the skin surface. Organic aerogels instead made from thermosetting resins or biopolymers, like cellulose, chitin or alginates do not have these negative properties. But their operation temperature is restricted to mostly 200°C. All materials currently available on the market have drawbacks that we are aiming to overcome by our research to finally bring this new class of materials into many applications for the benefit of us.