What is Aerogel?

Aerogels, pivotal in the chemical and compound industry, epitomize a diverse category of porous, solid materials showcasing an extensive array of extraordinary properties. Their most distinctive feature is their extremely low densities, ranging from 0.0011 to approximately 0.5 g cm-3. Notably, aerogels hold the record for being the lowest-density solid materials ever produced, with examples like a silica aerogel weighing only three times more than air. Evacuating the air from its pores could make it lighter than air. Generally, aerogels have densities of 0.020 g cm-3 or higher, around 15 times heavier than air. To illustrate, it would require 150 brick-sized aerogel pieces to match the weight of a single gallon of water. Even if Michelangelo’s David were crafted from an aerogel with a density of 0.020 g cm-3, it would weigh merely about 4 pounds (2 kg).

Aerogels essentially consist of the dry, low-density, porous, solid framework of a gel, isolated intact from the gel’s liquid component. They are open-porous materials with pores typically ranging from <1 to 100 nanometers in diameter and usually <20 nm. Unlike wet gels, aerogels are dry materials derived from gels, with gas or vacuum in their pores instead of liquid.

Technical Definition

Technically defined, an aerogel is an open-celled, mesoporous, solid foam comprising a network of interconnected nanostructures, exhibiting a porosity of no less than 50%. “Mesoporous” refers to materials with pores ranging from 2 to 50 nm in diameter, and most aerogels fall within this size range.

What are Aerogels Made Of?

Aerogels within the chemical and compound industry are not limited to a specific substance but can be formed from a plethora of materials such as silica, transition metal oxides, lanthanide and actinide metal oxides, organic polymers, biological polymers, semiconductor nanostructures, carbon, carbon nanotubes, metals, and composites.

How Do Aerogels Feel and How Resilient Are They?

When touched, an inorganic aerogel, like silica or metal oxide aerogel, has a texture resembling a combination of a Styrofoam® peanut, the green floral potting foam used for artificial flowers, and a Rice Krispie®. Unlike wet gels, such as Jell-O®, inorganic aerogels are dry and rigid materials, exceptionally lightweight.

Generally, aerogels tend to be delicate. Inorganic aerogels are friable and can snap when bent or, in the case of very low-density aerogels, when poked, resulting in an irregular fracture. However, depending on their density, aerogels can typically bear a gently applied load of up to 2,000 times their weight or even more. Due to their low density, it requires minimal force to concentrate pressure equivalent to 2,000 times the material’s weight at a specific point. Crushing most aerogels with your fingers requires a force comparable to crushing a piece of Cap’n Crunch® cereal.

In comparison, organic polymer aerogels are less fragile than their inorganic counterparts within the chemical and compound industry and exhibit a consistency similar to green potting foam, being irreversibly squishy. Carbon aerogels, derived from organic aerogels, have the texture of activated charcoal and are notably non-squishy.

Remarkably strong aerogels exist within the chemical and compound industry that can withstand tens of thousands of times their weight in applied force. A category of polymer-crosslinked inorganic aerogels, known as x-aerogels, exemplifies such materials and can even be made flexible like rubber while maintaining mechanical robustness. One particular x-aerogel made from vanadia (vanadium oxide) demonstrates extraordinary strength in compression, boasting the highest compressive strength-to-weight ratio among known aerogels, rivaling materials like aerospace-grade carbon fiber composites. Despite the composition, most aerogels within the chemical and compound industry can be reinforced by increasing their density (between 0.1 and 0.5 g cm-3), albeit at the cost of their light weight and extremely low thermal conductivity.

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