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)
THERMAL INSULATION • Conduction • Convection • Radiation
HIGH STRENGTH TO WEIGHT RATIO • Low Density • High Compressive Strength
Conclusion • Aerogel will probably be a common household name in the next decade although it is not yet ready for commercial use. • Eco friendly building design ( replace glass pane)