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Aerogels are among the lightest materials in the world and are highly porous with strong absorption capacity and low thermal conductivity which make them highly suitable for applications oil-spill cleaning, personal care products like diapers and heat, and sound insulation.
“Aerogel is what NASA uses to insulate the space shuttles, Mars rovers and other things in space,” Michael Markesbery says. “Space is negative 4550° F. This insulation is surviving the best torture test in the universe, but it isn’t being used in apparel.” Markesbery and Venna plan to disrupt the outdoor and performance apparel industry with Oros’ exclusive Solarcore insulation, the brand name for the company’s use of NASA’s aerogel material on which it has filed several patents.
The high air content (99.98% air by volume) makes it one of the world’s lightest solid material. Aerogels can be made from a variety of chemical compounds, and are a diverse class of materials with unique properties. Silica aerogels are nanomaterials with excellent thermal insulations properties because 99.98% of their volume can be pure air. They usually have low density and low thermal conductivity.
Silica aerogels could be considered as the ecofriendly “plastic” of the 21st century because they can find application in any field. Common applications include enhancing the thermal performance of energy-saving materials and sustainable products for buildings, acting as a high performance additive to coatings, prevention of corrosion under insulation, uses in imaging devices, optics, and light guides, thermal breaks and condensation control, architectural lighting panels, outdoor and sports gear and clothing.
Aerogels, when manufactured, can exhibit varying degrees of opacity, including both translucency and transparency, thereby enabling a diverse variety of applications for insulation in buildings that might require access to daylight or exploit sunlight for energy.
They may also find use as temperature-resistant windows, and in the space industry. As aerogels are phenomenal energy savers they could be the paradigmatic materials for designing the insulation for future sustainable space habitats. One of the most promising applications for aerogels is as a shock-absorbing medium in safety equipment.
Aerogel is created by combining a polymer with a solvent to form a gel, and then removing the liquid from the gel and replacing it with gas (usually air).
The greatest obstacle to the widespread use of aerogels is cost. The cost of aerogels is not inherent in their composition; silica is one of the most common minerals on Earth. The cost results from the time and energy it takes to produce them. Aerogel production involves two main steps: the preparation of a wet silica gel, and the removal of the wet matrix by supercritical fluid drying, a process requiring high temperatures and pressures.
Physical and chemical properties
The most obvious property of aerogels is their extremely low density. Aerogels have been produced with densities of 0.003g/cm3. Densities of around 0.1g/cm3, however, are more common; this is about 10% of the density of water.
Chemically, they are identical to silica glass, but they have a very porous internal structure, which leads to a number of interesting properties. They are excellent thermal insulators; they have a huge internal surface area; they are transparent; they can absorb a large amount of kinetic energy.
The most studied property of aerogels is their thermal resistance. Aerogels can withstand temperatures up to 500ºC, above which they begin to shrink. Their melting point is around 1200ºC.
The internal surface area of an aerogel can be as high as 1000m2/g. This property allows to be used to absorb some gases and fluids.
The chemical makeup of aerogels strongly affects their adsorbent properties. Aerogels can be made hydrophilic or hydrophobic, depending on which drying process is used. Alcohol drying (now uncommon because of the high temperature and pressure required) results in pore surfaces covered with alkoxy-groups (an oxygen atom attached to a non-polar organic mer). These hydrophobic aerogels, if sealed, are completely impervious to water, and will float indefinitely.
Carbon dioxide drying results in pore surfaces covered with hydroxyl (OH) groups. When one of these hydrophilic aerogels is placed in a humid environment, it adsorbs water into its pores, up to 20% of its mass. The water may be released simply by heating the sample. These aerogels, however, cannot be used to adsorb liquid water. The high surface tension of water, upon entering the tiny pores, tears them apart. The aerogel seems to disappear; it has become a fine powder, less than 5% of the volume of the gel.
Another property that is fairly obvious is transparency. Aerogels have a very low index of refraction. While some have a milky appearance, others are as transparent as glass.
One of the disadvantages of aerogels is their brittleness. Being a form of solid silica, aerogels are basically an exotic form of glass. However they have different mode of brittle failure. Most brittle substances, including regular glass, fracture almost instantly. Aerogels, due to their low density and high porosity, fail much more slowly.
Military Applications
Aerogels products have demonstrated numerous performance advantages in defence applications translating to tremendous savings on topside weight and volume. Aerogels Insulation delivers superior value where weight, space and performance are paramount. Whether it’s protecting low temperature composite structures or providing signature reduction to hot engine components, Aerogels provides unmatched performance.
Aerogels are already used in spacesuits, now we can expect outdoor clothing with an unparalleled level of insulation. Aerogels provide much better ballistic protection, weight for weight, than steel. NASA’s Stardust mission used a block of aerogel to soft-catch high-speed comet particles.
Aspen Aerogels is a NASA spin-off dedicated to bringing aerogel to the market. They have succeeded in creating a far more robust, flexible form of aerogel that looks like the ultimate insulation. One of the military applications of their aerogel blanket can be used to radically cut infrared emissions from helicopters, making it much harder for heat-seeking missiles to lock on to them.
This work was done under contract to Aspen Systems and Bell Helicopter. This program focused on the use and optimization of aerogels as a high performance insulation material, encapsulated in innovative, lightweight packaging. The aerogel blanket insulation system, with a weight of only 5 pounds, demonstrated a 40 percent reduction in aircraft IR signature during flight demonstrations on an Army OH–58D Kiowa
They can be used in Fixed-Wing and Rotary-Wing Aircraft Thermal, Acoustic, IR & Fire Protection systems and Shipboard Fire & Thermal Protection. They have 40% weight savings over conventional fire rated insulation systems used shipboard, 50% reduction in thickness and significantly enhanced acoustic performance. They are used for thermal signature reduction for hot engine components and aircraft skins and lightweight thermal insulation for exhaust, ducting, and nacelle applications.
Aerogels offers a more efficient, lighter weight, water repellent alternative to tent insulation systems now in the field. Efficient insulation in severe conditions means a 30-50% reduction in fuel consumption for necessary heating/cooling operations. Additionally, inherent acoustic performance and IR Suppression capabilities make Aerogels a perfect fit for higher performance military shelters.
For Marine applications, the superior thermal insulating power and hydrophobic properties make them the ideal solution for chill water lines as well as steam pipe insulation shipboard.
Graphene aerogels
Graphene aerogel, also known as aerographene, is considered to be the least dense solid in existence (graphene aerogels are light enough to be balanced on small plants!).
Graphene aerogels are quite elastic and can easily retain their original form after some compression. In addition, the low density of graphene aerogels makes them very absorbent (to the point where it can even absorb more than 850 times its own weight). This means that it could be useful for environmental clean-ups like oil spills, and the aerogels only need to be picked up later after absorbing the spilled material.
Graphene aerogel may also have some applications in both the storage and the transfer of energy by enabling the creation of lighter, higher-energy-density batteries. This is because graphene aerogels are promising materials for energy systems due to their porous hierarchical structure which affords rapid electron/ion transport, superior chemical and physical stability, and good cycle performance. Areas of application include supercapacitors, Li-batteries, H2 and thermal energy storage, fuel cells and solar cells.
Aerogels Made From Recycled Cotton
Researchers from the National University of Singapore (NUS) Faculty of Engineering have created a fast, cheap and green method to convert cotton-based fabric waste—including unwanted clothing— into highly compressible and ultralight cotton aerogels, while also demonstrating the application of the material to keep military water bottles cold and to effectively control rapid bleeding.
One of the challenges in aerogels is to lower its production cost, that is leading to a push to find new ways to improve the manufacturing and consumption of different types of aerogels. NUS’s new cotton aerogels can be easily compressed and quickly recover up to 97 percent of their original size when placed in water.
“This new eco-friendly cotton aerogel is a major improvement from the aerogel that our team had previously developed using paper waste,” associate professor Hai Minh Duong said in a statement. “It is highly compressible, hence storage and transportation costs could be greatly reduced.
“Furthermore, these cotton aerogels can be fabricated within eight hours— this is nine times faster than our earlier invention and about 20 times faster than current commercial fabrication processes,” he added. “They are also stronger, making them more suitable for mass production. While we have demonstrated novel application of the cotton aerogels for effective haemorrhage control and heat insulation, we will continue to explore new functions for this advanced material.”
To effectively control rapid bleeding, the researchers developed highly compressible hybrid cotton aerogel pellets, which are more effective than cellulose-based sponges for treatment of deep haemorrhagic wounds.
The pellets are comprised of an optimal mix of cotton and cellulose aerogels coated with chitosan. They are simple, biocompatible and cost-effective to produce and can be easily integrated into a clinical syringe to be used as a haemorrhage control device.
Each cotton aerogel pellet can expand to 16 times its size in 4.5 seconds – larger and more than three times faster than existing cellulose-based sponges – while retaining their structural integrity,” Duong said. “The unique morphology of the cotton aerogels allows for a larger absorption capacity, while the compressible nature enables the material to expand faster to exert pressure on the wound.”
The researchers also developed a lightweight thermal jacket to maintain the temperature of ice slurry—crushed ice and liquid water—at 0.1 to 1.0 degree Celsius for more than four hours. The jacket, which weighs just 200 grams, consists of a cotton aerogel layer embedded within commonly used fabrics to provide heat insulation.
“The heat insulation property of the novel cotton aerogels can be applied to various consumer products, such as cooler bags to keep food items fresh,” professor Nhan Phan-Thien said in a statement. “We also foresee tremendous potential for other high value applications, such as pipeline insulation and transportation of liquefied natural gas which needs to be stored at a low temperature.”
