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HISTORICAL ORIGINS
• Aerogel was invented some time between 1930 by Dr Samuel Stephen Kistler
• But actual commercial production was not done till late 1990s .
WHAT IS AEROGEL …?
• Aerogels are a diverse class of porous, solid materials which exhibit an uncanny array of extreme materials properties
• Silica Aerogel• Organic and Carbon Aerogels• Metal Oxide Aerogels• Metal Aerogel
SPECIAL PROPERTIES OF AEROGEL
• extraordinarily strong in compression • highest compressive strength to
weight ratio of any known material• Very high thermal insulation
RECORDS HELD BY AEROGEL
• Lowest density solid (0.0011 g /cm3)• Lowest optical index of refraction
(1.002)• Lowest thermal conductivity (0.016W
/mK)• Lowest speed of sound through a
material (70 m/s)• Lowest dielectric constant from 3-40
GHz (1.008)
MANUFACTURING OF AEROGEL
• Preparation of a hydrogel (gels with water as a solvent) in reaction of sodium silicate with hydrochloric acid.
• Removal of sodium and chlorine ions. This step involves a long and tedious soaking of the gel.
• Converts the hydrogel into alcogel by replacing water with ethyl alcohol in a lengthy process of solvent replacement.
• Drying at above critical conditions for ethyl alcohol. • The balanced chemical equation for the formation of a silica
gel from TEOS is:• Si(OCH2CH3)4 (liq.) + 2H2O (liq.) = SiO2 (solid) + 4HOCH2CH3
(liq.)
• The Critical Point• Surface Tension and Capillary Stress• Shrinkage• Properties of Supercritical Fluids• CH3OH Methanol 239.50C
79.783atm• CO2 Carbon dioxide 31.130C
72.786atm
High-Temperature Supercritical Drying
Most organic solvents have relatively high critical temperatures of 300-600°C with critical pressures of 50-100 atm, and are dangerously flammable and potentially explosive at these conditions.
Low-Temperature Supercritical Drying from Carbon Dioxide (the Hunt
Process)• Instead of using flammable, explosive solvents, a
safer, non-flammable solvent can be used instead–carbon dioxide. In this process, the organic solvent in a gel is replaced with liquid carbon dioxide by soaking. The liquid carbon dioxide can supercritically extracted at a much lower temperature (31.1°C) than an organic
solvent and without the risk of combustion.
APPLICATIONS
• SPACE APPLICATIONS • ELECTRICAL AND ELECTRONIC
APPLICATIONS • ACOUSTICAL AND MECHANICAL
APPLICATIONS • OPTICAL PROPERTY APPLICATIONS • OPTICAL PROPERTY APPLICATIONS • THERMAL APPLICATIONS ( Superinsulator)