05-07-2013, 03:12 PM
A seminar on aerogel
aerogel.pptx (Size: 3.18 MB / Downloads: 110)
Introduction:
Aerogel is a synthetic ultralight material derived from a gel, in which the liquid component of the gel has been replaced with a gas. The result is a solid with extremely low density and thermal conductivity.
Aerogels are produced by extracting the liquid component of a gel through supercritical drying. This allows the liquid to be slowly dryed off without causing the solid matrix in the gel to collapse from capillary action, as would happen with conventional evaporation. The first aerogels were produced from silica gels. Kistler's later work involved aerogels based on alumina, chromia and tin dioxide.
Metal aerogel properties
High specific surface area
Electrically conductive!
Enhanced catalytic activity
Surprisingly capable thermal insulator
Types of aerogel
SILICA
Silica aerogel is the most common type of aerogel and the most extensively studied and used. It is a silica-based substance, derived from silica gel.
The world’s lowest-density solid is a silica Nano foam at 1 mg/cm3, which is the evacuated version of the record-aerogel of 1.9 mg/cm3.
Silica aerogel strongly absorbs infrared radiation. It allows the construction of materials that let light into buildings but trap heat for solar heating.
Carbon
Carbon aerogels are composed of particles with sizes in the nanometer range, covalently bonded together & have very high porosity and surface areas ranging between 400–1000 m²/g.
They are often manufactured as composite paper: non-woven paper made of carbon fibres, impregnated with resorcinol-formaldehyde aerogel, and pyrolyzed.
MANUFACTURING
Aerogels are formed by a process known as supercritical drying, in which the liquid from the gel base is removed and replaced by a gas, leaving a solid structure.
It is prepared by mixing a liquid silicon compound and a fast-evaporating liquid solvent, forming a gel that is then dried in an instrument similar to a pressure cooker.
The mixture thickens, and then careful heating and depressurizing produce a glassy sponge of silicon.
CONCLUSION
Aerogels are the strong, flexible, and robust against folding, creasing, crushing and the least dense solids, possess compressive specific strength similar to aerospace grade graphite composite, and provide the smallest thermal conductivity for any solid.
Overall, the mechanical properties are rather like those of a synthetic rubber, save that the aerogel has the same properties with only about 10 per cent of the weight. So it can be used in case of synthetic rubber.