Aerogel

This page is in progress. Please do not cite or link

Description

An aerogel is an open-celled, mesoporous, solid foam that is composed of a network of interconnected nanostructures and that exhibits a porosity (non-solid volume) of no less than 50%. Despite the name, aerogels are solid, rigid, and dry materials that do not resemble a gel in their physical properties: the name comes from the fact that they are made from gels. Aerogels are a class of synthetic porous ultralight material derived from a gel, in which the liquid component for the gel has been replaced with a gas, without significant collapse of the gel structure.[1] The result is a solid with extremely low density[2] and extremely low thermal conductivity. Aerogels can be made from a variety of chemical compounds.[3] Silica aerogels feel like fragile expanded polystyrene to the touch, while some polymer-based aerogels feel like rigid foams. A generic term for a material Aerogels are 3-D nanostructures of non-fluid colloidal interconnected porous networks consisting of loosely packed bonded particles that are expanded throughout its volume by gas and exhibit ultra-low density and high specific surface area. Aerogels are normally synthesized through a sol–gel method followed by a special drying technique such as supercritical drying or ambient pressure drying. The fascinating properties of aerogels like high surface area, open porous structure greatly influence the performances of energy conversion and storage devices and encourage the development of sustainable electrochemical devices. Therefore, this review describes on the applications of inorganic, organic and composite aerogel nanostructures to dye-sensitized solar cells, fuel cells, batteries and supercapacitors accompanied by the significant steps involved in the synthesis, mechanism of network formation and various drying techniques. Silica aerogels are the most common type of aerogel, and the primary type in use or study.[18][19] It is silica-based and can be derived from silica gel or by a modified Stober process. Nicknames include frozen smoke,[20] solid smoke, solid air, solid cloud, and blue smoke, owing to its translucent nature and the way light scatters in the material. The lowest-density silica nanofoam weighs 1,000 g/m3,[21] which is the evacuated version of the record-aerogel of 1,900 g/m3.[22] The density of air is 1,200 g/m3 (at 20 °C and 1 atm).[23] As of 2013, aerographene had a lower density at 160 g/m3, or 13% the density of air at room temperature.[24]

The silica solidifies into three-dimensional, intertwined clusters that make up only 3% of the volume. Conduction through the solid is therefore very low. The remaining 97% of the volume is composed of air in extremely small nanopores. The air has little room to move, inhibiting both convection and gas-phase conduction.[25]

The first documented example of an aerogel was created by Samuel Stephens Kistler in 1931,[4] as a result of a bet[5] with Charles Learned over who could replace the liquid in "jellies" with gas without causing shrinkage.[6][7]

Aerogels are produced by extracting the liquid component of a gel through supercritical drying or freeze-drying. This allows the liquid to be slowly dried off without causing the solid matrix in the gel to collapse from capillary action, as would happen with conventional evaporation. The first aerogels were produced from silica gels. Kistler's later work involved aerogels based on alumina, chromia and tin dioxide. Carbon aerogels were first developed in the late 1980s.[8] Aerogel has not languished inside labs. You may find it inside modern rugs, cosmetics, paints, pipes, wetsuits, and roofs, merely to name only a couple of products. And now inventors are creating new recipes and production techniques for aerogel, resulting in novel applications which have thin yet incredibly warm (and trendy ) coats and petroleum spill-cleanup kits. Without The fortuitous discovery of aerogel from the early 1900s of Samuel Stephens Kistler, however, we may still be dreaming about the incredible substance’s occurrence. they cycle moist aerogel through multiple stages of heating and cooling under pressure, which keeps the silica system’s shape even after completely drying out Aerogels have an extremely higher nano-porosity and so exhibit extraordinary properties: high pore volume (up to 99 per cent), ultralow density (0.2 — 0.5 g/cm3), higher surface area (up to 1200 m2/g). They can be synthesized from organic or inorganic precursors. Silica aerogels are the most often used and have a broad selection of applications. Aerogels are the best known thermal insulators (thermal conductivity < 5 mW/mK) and are nearly inert against molten metal. Kistler won the wager and ended up discovering aerogel as a fortuitous bonus. He went on to release his first study about aerogels in the journal Nature in 1931, then patented that the way of generating aerogel on Sept. 21, 1937. From the early 1940s, Kistler signed a contract with Monsanto Company — now an agricultural firm known for selling and developing genetically modified plants. A Monsanto plant in Massachusetts made the first silica-based aerogel products under the trade names Santocel, Santocel-C, Santocel-54, and Santocel-Z. Their first program: a Thickening agent for napalm, makeup, and paints. Aerogel made its way to freezer insulation and cigarette filters.

Organic polymers can be used to create aerogels. SEAgel is made of agar. AeroZero film is made of polyimide. Cellulose from plants can be used to create a flexible aerogel.[34]

An Aerogel 3-layer mat consisting of a core of Pyrogel XTE encompassed between layers of E-Glass Needle Mat fiberglass tissue (Skanacid A/S) was found to provide optimal fire protection in a 2023 study (Praestegaard et al.) when used as a cover over a wooden chair.

Applications

• Fire protection
• Thermal and sound insulation
• Thickener

Physical and Chemical Properties

• Can withstand temperatures up to 1200C
• Very lightweight

Working Properties

• Cannot be fashioned into shaped covers inhouse; must be sewn to measurement by the factory
• Constructed 3-layer mat is very heavy, dense and hard to fold

Resources and Citations

• Praestegaard L., G. Sorig Thomsen, K. Woer 'Before the Fire: Experiments on Fire-Protecting Cover Materials', Studies in Conservation, Vol. 68 (1), pp. 1-8, 2023.
• Alwin, S., Sahaya Shajan, X. Aerogels: promising nanostructured materials for energy conversion and storage applications. Mater Renew Sustain Energy 9, 7 (2020).
• Skanacid A/S: www.skanacid.dk
• Supedium: The Incredible Aerogel
• Wikipedia: https://en.wikipedia.org/wiki/Aerogel
• Aerogel: What is Aeogel?