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Aerogels - an exceptional light weight material

Introduction

Aerogel was created by Steven Kistler in 1931 and it has become a material of interest to scientists in recent decades due to its light weight. Aerogel is a synthetic porous ultralight material derived from a gel, in which the liquid component of the gel has been replaced with a gas. It is an advanced material which holds 15 entries in the Guinness Book of Records for properties such as lowest density solid and best insulator. It is a silica-based substance, consisting of a loose dendritic network of the atom silicon.

According to Electronics.ca research network, the market for aerogels by 2013 is estimated to be $646.3 million with a compound annual growth rate of 50.8 per cent. Aerogel is also called as ‘Frozen smoke’ and it consists of 99.8 per cent of air. It can be used at temperatures between -200°C to +600°C. Aerogel is having following characteristics

Characteristics of aerogel

Low thermal conductivity
Hardness
Heat resistance
Transparency
Elasticity
Insulation
Durability
Flexibility

Types of aerogel

Aerogels can be divided into following types based on composition from which they are made

Silica Aerogel – it contains silica-based substances

Metal Oxide Aerogel – these can acts as catalysts

Carbon Aerogel

Organic Aerogel – it is comprised of organic polymers such as

Resorcinol
Formaldehyde
Phenol formaldehyde
Melamine formaldehyde
Cresol formaldehyde
Phenol furfuryl alcohol
Polyacrylamides
Polyacrylonitriles
Polyacrylates
Polycyanurates
Polyfurfural alcohol
Polyimides
Polyacrylates
Polycyanurates
Polyfurfural alcohol
Polyvinyl alcohol dialdehyde
Polystyrenes
Polyurethanes
Agar agar
Agarose

Alumina Aerogels – it contain aluminium oxide

Semiconducting Metal Chalcogenide Aerogels

Metal Aerogels

Cryogels Aerogels – it is used in

Sub-ambient piping and equipment
Cryogenic storage
Sea transport
Industrial gases
Liquefied natural gas (LNG) import/export pipelines
Chilled water systems
Gloves
Jackets
Sleeping bags

Spaceloft Aerogels – it is used in

Building and construction
Heating, water and conditioning systems
Household appliances

Pyrogel Aerogel – it is used in

Aerospace and aeronautic transportation
Fire protection equipment
Industrial and petrochemical equipment
Power generation equipment

Preparation

Aerogels can be prepared by using

Alumina
Chromia
Tin oxide
Carbon

But apart from these materials used for making of aerogel, silica based aerogel is preparation is easier and reliable.

4 to 30 times more water is added to Tetraethylorthosilicate (TEOS) in the presence of ethanol it leads to the further chemical reaction

Si (OCH₂CH₃)₄ _(liq.) + 2(H₂O) _(liq.) → SiO₂ _(solid) + 4(HOCH₂CH₃) _(liq.)

Fig. 1) Aerogel preparation method

Final product density is mainly depends on the concentration of silicon alkoxide monomers in the solution. After gelification, the gel is left undisturbed in the solvent for 48 hours to complete the reaction. Once reaction will complete the alcogel product will form. The alcogel is then submitted to supercritical drying.

The final products formed in this reaction are

Aerogel
Xerogel

Applications of aerogel

Aerogels are being used by NASA for collecting micrometeoroids in space. As aerogels are highly transparent, the captured micrometeoroids and their paths through the material can be studied easily.

Aerogels are being developed as catalysts to promote chemical reactions and as