Greetings to all you readers out there! Also wishing all the Indians, Koreans, Liechtensteiners(I don’t know if that’s correct) and people from the Republic of Congo, A very Happy Independence day!(a belated one,that is! 🙂 )
So today’s post deals with Aerogels. I’m sure you might have heard of this term earlier. If not, no worries.
So what is an aerogel anyway, you may ask. Well, the word aerogels can be split into two parts- “aero” and “gel”. As you may have figured out, aero signifies air and gel is basically something that’s semisolid or gooey. That’s partially correct as aerogels are a solidified form of gels with about 98% of air within them. Aerogels are typically ultralight solid materials with very high electrical and thermal and acoustic insulating capacities.
There is no fixed chemical composition of Aerogels and the term itself is used to refer to a very diverse class of ultralight materials. Aerogels are generally made of highly porous combinations of silica, metals, metal oxides, organic materials and nano-tubes. Silica aerogels are the most common and are typically bluish in colour, followed by metal oxide aerogels which are generally coloured according to the metallic element inside.
Many Aerogels possess properties that are very much unique to them. These include a very low density, a high thermal, acoustic and electrical insulating ability, ultra-low weight and almost transparent nature.
Here are some of the properties of some specially-formulated silica aerogels (which held the world records till 2011):
- Low density solid (0.0011 g cm-3)
- Low optical index of refraction (1.002)
- Low thermal conductivity (0.016 W m-1 K-1)
- Low speed of sound through a material (70 m s-1)
- Low dielectric constant from 3-40 GHz (1.008)
Aerogels are highly thermal resistant because of the extraordinary amount of air contained within them. The porous nature of the material tends to prevent heat transfer via convection and conduction. The high amount of air, which is a bad conductor of heat, causes a very low amount of heat to pass through the material. In silica aerogels, this effect is further amplified as silica itself is also a bad conductor of heat. However, heat transfer by radiation occurs relatively easily in aerogels as the heat carrying infrared radiation can pass quite easily through it.
The following video demonstrates the extraordinary insulation properties of aerogels.
Despite of their highly porous nature, aerogels can be pretty strong. The following picture shows a 2.5 kg Brick being supported on the 2.5 gram aerogel block! This example illustrates that static loading on aerogels can be very well sustained. However, the aerogel block is highly susceptible to dynamic loading. This is a major disadvantage of aerogels. The aerogels are inherently very brittle and can break apart if subjected to shear or extreme tensile loading. Integrating polymers onto the surface or within the structure can greatly increase the strength of the Aerogels.
Silica Aerogels are very hydrophillic and desiccant. This property causes them to start absorbing water immediately on contact with moisture in the air. The absorption of moisture causes them to shrink and become cloudy over time. However, aerogels can be made hydrophobic or water repellant by special external treatments.
So how do you make an aerogel? An aerogel is most commonly manufactured by the sol-gel process. In this process, a liquid solution is made with the required composition present as a dissolved solute. Then, this mixture is condensed in controlled conditions to form inter-molecular bonds. The inter-molecular bonding forms a gel which is typically semi-liquid. This gel is then exposed to a very high temperature and pressure, by which the liquid present inside the gel gasifies immediately, leaving behind the solidified structure of the bonded solute, which is nothing but the aerogel. This method is called supercritical drying.
Now, you must be wondering where such a material would come into use. The following list shows the numerous applications of aerogels:
- NASA has used silica aerogels in its comet probe spacecraft Stardust. The spacecraft successfully gathered the released icy dust from the tail of the comet “Wild 2” and returned to Earth in 2006!
NASA’s Stardust spaceprobe’s space dust collecting surface
- Semi-transparent Skylights which insulate and provide lighting
- As a chemical adsorber of oil spills
- As a thickening agent in paints and cosmetics
- In water purification for absorbing the heavy metal pollutants mercury, lead, and cadmium from water.
- As an insulator in diving suits and space suits.
Well, that’s it for this article! Hope this was useful and fun to read!
Until Next Time!!