What Is Aerogel?
Aerogels have been in existence for more than 80 years. Invented in 1931 by Dr. Samuel Kistler at the College of the Pacific in California, silica aerogel is a lightweight solid derived from gel in which the liquid component of the gel has been replaced with gas. When the liquid is removed, what remains is “puffed-up sand,” with up to 99% porosity. The result is an extremely low density solid with several remarkable properties, most notably its effectiveness as a thermal insulator. Aerogels also have value in emerging applications such as energy storage, filtration and carbon capture.
The solids in silica aerogels are poor conductors, consist of very small, three-dimensional, intertwined clusters that comprise only 3% of the volume. Conduction through the solid is therefore very low. The remaining 97% of the volume of aerogels is composed of air in extremely small nanopores. The air has little room to move, inhibiting both convection and gas-phase conduction. These characteristics make aerogels the world’s lightest solid material and most effective thermal insulator.
Aerogels also exhibit incredibly high internal surface area—in fact, a typical piece of aerogel the size of an ice cube has about half a football field’s worth of surface area wrapped up inside its pores. This makes electrically conductive aerogels such as carbon aerogels particularly interesting as electrodes for batteries, supercapacitors, and desalination systems.
Aerogels are generally available in four form factors
Monolithic aerogel or monoliths are continuous solid materials with a defined shape. This includes the ethereal blue “NASA-type” silica aerogel people typically think about when they hear the word “aerogel”. Monoliths include aerogel discs, blocks, spheres, cubes, cylinders, rods, etc. Monolithic aerogels such as classic silica aerogels have incredibly high strength-to-weight ratios but often exhibit low fracture toughness and so they tend to be very fragile. That said, monolithic aerogels can withstand several thousand times their weight in applied force if applied compressively and gently.
Aerogel particles include millimeter-sized granules, which are used in skylights to allow light to diffuse through but not heat, and micron-sized particles, which are used as performance additives for insulative coatings, safety coatings, and matte finish coatings. Aerogel particles exhibit strength and toughness properties similar to monolithic aerogels, however with such small dimensions they pour and handle just like other particulate materials. Aerogel particles are strong in compression and can withstand vacuum as well as the compressive forces exerted on them when packed tightly into, for example, a double-pane skylight.
Aerogel composite blankets are the most common type of insulation made with aerogels and are composed of woven or non-woven fibers coated or embedded with aerogel. These materials can be rolled, cut, and sewn and offer three to five times better thermal performance than other insulating materials. Aerogel blankets, are flexible, resilient, and withstand the force of being handled and stepped on, however may shed some dust in the process.
Airloy™ Ultramaterials such as Airloy X103 are the strongest aerogels available and are mechanically robust and non-brittle. They are strong enough to be used in many applications where plastics and composites are used today. Airloys can be machined, drilled, tapped, flexed, and, in some cases, thermoformed.
How Safe Are Aerogels?
Most aerogel blankets, particles, and monoliths are based on silica aerogel, which is comprised of synthetic amorphous silica. As a substance, synthetic amorphous silica has been found to not be harmful to humans—it is non-toxic and non-carcinogenic.
What Are Aerogel’s Applications?
Aerogels have been used since the 1960’s in space travel, but are now finding uses across a whole range of industries. From superinsulation and daylighting to catalysts, and batteries, aerogels offer a wide range of unique material properties that make next generation energy-efficiency and scientific applications possible.
Mechanically robust aerogels such as Airloy® Ultramaterials are now being used as ultralight replacements to plastics. Airloys are 3-15x lighter than plastics yet have greater strength and durability. They offer up to 50% better thermal insulating performance than foams and up to 1000x better soundproofing properties than any other material.
This technology is not only limited to space and home applications, but is also starting to be used for outdoor apparel. You can get aerogel gear including jackets, gloves, and snow pants from companies like OROS.