AEROGELS-THE MATERIAL SCIENCE OF CONSTRUCTION
New buildings are rising everywhere, burning energy by the second and this demand for power pushes up greenhouse gases and pollution. 40% of the buildings energy consumption is used for heating and cooling.
Being civil engineers it becomes imperative on our part to device some modern construction methodology to contribute our bit to prevent further worsening of the condition.
Buildings alone waste 13% of the global energy production because of poor insulation. That’s equals to nearly four billion barrels of oil a year. Its an unbelievable waste just to heat up the sky. After years of research scientists have revealed the technology in the form of aerogels that could transform our cities and usher in better future.
What is aerogel?
Aerogel is made from a jelly like substance partly liquid partly solid. Solids are fine chain of silica surrounded by alcohol. It is then supercritically dried to transform it into aerogel.It is basically a form of nanotechnology.It is also known as frozen smoke or blue smoke because of its blue colour.
History of aerogels:
The first aerogels were produced in 1931 by Samuel Kistler, an undergraduate instructor at the College of the Pacific in Stockton, California. Accidently, Kistler found a way to remove the fluid from a wet silica gel, leaving behind its solid structure. The first commercial aerogels were produced in 1942 by the Mosanto corporation, under the trade name Santocel. The process involved soaking a sodium silicate solution in sulfuric acid, then repeatedly washing it in alcohol before drying it at high pressure. Since then, lot of researches has been done in aerogels and technology to use aerogel as a commercial product is invented.

Making of aerogels:
Aerogels are made using sol-gel chemistry. Aerogel is prepared in two simple steps:-
Step 1:-
A small amount of silica is taken in a flask to it a solvent (ethanol) is added. After a solution of catalyst + water as second reagent is added which leads to hydrolysis and cross- linking of silica chains.

Step2:-
The next step in the making of aerogel is the super-critical drying. It is the most critical step, as the fluid must be removed without destroying the solid framework of the gel. This is achieved by the process of supercritical fluid drying. When a fluid is raised to its supercritical point (a specific combination of high pressure and high temperature), it exhibits some properties of a liquid, and some of a gas. This allows the fluid to boil out of the gel gently, without tearing the cell walls. To supercritically dry the gel, alcohol is replaced with liquid CO2 under high pressure as the pressure drops liquid CO2 becomes gas, it bubbles away and leaves behind tiny air pockets.
Various terms associated with aerogel formation:- 1. Gel Point:
The point in time at which the network of linked oxide particles spans the container holding the Sol . At the gel point the Sol becomes an Alcogel.

2. Alcogel (wet gel):
At the gel point, the mixture forms a rigid substance called an alcogel. The alcogel can be removed from its original container and can stand on its own. An alcogel consists of two parts, a solid part and a liquid part. The solid part is formed by the three-dimensional network of linked oxide particles. The liquid part (the original solvent of the Sol) fills the free space surrounding the solid part. The liquid and solid parts of an alcogel occupy the same apparent volume.

3. Supercritical fluid:
A substance that is above its critical pressure and critical temperature . A supercritical fluid possesses some properties in common with liquids (density, thermal conductivity) and some in common with gases (fills its container, does not have surface tension).

4. Xerogel:
What remains when the liquid part of an alcogel is removed by evaporation, or similar methods . Xerogels may retain their original shape, but often crack. The shrinkage during drying is often extreme (~90%) for xerogels.

Structure of aerogel:
Aerogels are porous inorganic polymers. The main component of this material is air, which is surrounded by a three dimensional solid network. This solid network is built from inorganic nanoparticles, which are connected with each other.
Aerogels are open-cell polymers with pores less than 50 nanometers in diameter .The aerogel particles are so small that an average sand grain particle have to be reduced by 30,000 times to make up an aerogle particle.
Initial concerns with aerogel is that it is very fragile i.e. can be broken into chunk of pieces very easily. But after years of researc , scientist came up with a very simple solution to tackle this problem which is, by providing a blanket of polyester. Polyester act as a skeleton, making it strong and flexible . In compression, aerogel an take a weight up to 4,000 times its own weight.
Properties:
* Aerogels are good thermal insulators because they almost nullify the three methods of heat transfer (convection, conduction, and radiation). They are good conductive insulators because they are composed almost entirely from a gas, and gases are very poor heat conductors. If a flame of temp. around 1000 degree celcius is applied at the bottom of 6 mm thick aerogel ,then the temp. at top will be only 100 degree celcius. * They are excellent absorbents for hydrogen. * Because of their hygroscopic nature, they can act as strong dessicant. * They have the largest surface area of any known solid. One gram of aerogel can have up to 1500 metre square of surface area. * Sound is impeded in its passage through an aerogel and slowed to a speed of 100 to 300 meters per second. Thus it can also be utilized to make soundproof building materials.

Applications: How aerogels are used in building construction?
As energy-efficiency standards for buildings become increasingly stringent, using a traditional insulation material often means having to accept increasingly thick layers of insulation in walls, floors, and roofs. This consumes valuable floor space in new construction. In renovation projects, if it is even possible to increase insulation thickness at all, significant aesthetic and functional compromises are often required to retrofit more insulation on the inside or outside of the building envelope.
Nanogel aerogel can help building owners and architects break away from these compromises. For constructional purposes its available as a flexible, nanoporous aerogel blanket insulation that reduces energy loss while conserving interior space in residential commercial building applications.
It can be used for:- * Wall exterior * Wall interior * Floor * Roofs * Framing

Aerogels blanket are manufactured by various companies.One of the product features are:- * Available thickness 3.5mm/6mm/8mm * other thicknesses available upon request * Width Standard 56cm * Length Rolls up to 100m * Density ~70kg/m3 (5.6 - 6.2lb/ft3) * Tensile strength ~517kPa (~75lbs/in2) * Fiber composition Polyester and polyethylene * Operating temperature -200° to 125°C continuous

Safety:
Nanogel aerogel is reusable, safe for human and ecologicalsystems, and is created through a closed loop process with little to no impact on the environment.It is bio –degradable.

Cost:
Aerogel is a very expensive material that’s why its use is limited in building construction.Researches are on progress to make it as cheaper as possible.According to NASA,in 2050, aerogel would be as common as simple building materials like plastic.

Practical applications which can be seen are:-

* The first residential use of aerogel as an insulator is in the Georgia Institute of Technology's Solar Decathlon House where it is used as an insulator in the semi-transparent roof. * A school in Ohio has sky lights made up of aerogel in both multipurpose and library room.

Other commercial use of aerogel are:- * Military ultra warm sleeping bags. * Aero insoles in shoes in extremely cold areas. * Insulation for oil pipelines in cold environment.

Recent developments in aerogels: * Research are on progress to make aerogel transparent enough to be used as window panes in buildings because 30% of the heat dissipates through windows alone. * A special type of aerogel (SEAGEL) is made which is even lighter than air as well as environmental safe.

Conclusion:-

Centre of alternative technology crunches the no. providing the impact of this technology on carbon emission and this astonishing material scored 29% reduction in carbon emission.Therefore ,it can be said that aerogels is an exotic material which can combat the phenomenon of global warming to a great extent.