How do they make aerogel

It is important to note, however, that most of the liquids used in the preparation of gels are organic solvents such as methanol, ethanol, acetone, and acetonitrile, and such liquids are potentially dangerous at the temperatures and pressures required to make them supercritical.

To make the aerogelification process less dangerous, the liquid component of a gel can be exchanged with a non-flammable solvent that mixes well with organic solvents—liquid carbon dioxide see below. For more information about supercritical drying , see The Science of Aerogel section. Arlon Hunt at Lawrence Berkeley National Laboratory developed a technique for preparing aerogels without needing to supercritically extract potentially explosive solvents.

In this technique, a gel containing an organic solvent such as methanol, ethanol, acetone, or acetonitrile is soaked under liquid carbon dioxide to replace the liquid in the gel with liquid CO 2.

This is compared with, say, methanol, which is very flammable and has a critical point of One drawback, however, is that unlike methanol or other organic solvents, CO 2 does not exist as a liquid at ambient conditions. In fact, dry ice, the solid form of CO 2 which you can buy at some gas stations and grocery stores , sublimes directly to gaseous CO 2 at atmospheric pressure instead of melting.

As a result, in order to work with liquid CO 2 so that we can soak a gel in it, we have to use CO 2 at a pressure where it can exist as a liquid around 58 times atmospheric pressure at room temperature.

To perform CO 2 exchange, a gel is placed in a pressure vessel which is then sealed and slowly pressurized with a tank of liquid CO 2 equipped with a siphon tube like a liquid soap dispenser.

Liquid CO 2 siphon tanks are common, and can be found in almost any restaurant or bar as the source of carbonation in a soda fountain system. At that point, liquid CO 2 will siphon into the vessel and cover the gel. Depending on the size of the vessel and the gel, it is common to pre-fill the vessel with organic solvent whatever is in the gel to prevent the gel from drying out while waiting for CO 2 to siphon in. This organic solvent is then drained off as soon as CO 2 starts to siphon in.

After liquid CO 2 has siphoned in, the gel is simply allowed to soak for a number of hours. The liquid in the vessel is drained out and replaced with new liquid every few hours for a period of time of days for small samples and up to a week or two for large samples.

As the gel soaks in the liquid CO 2 , the organic solvent held within its pores diffuses out, and liquid CO 2 diffuses in its place. Learn how to build a supercritical dryer of your own and find a fully-illustrated step-by-step process of performing supercritical drying with CO 2 under the Make section. Just as you can only bake a pie as big as your oven, you can only supercritically dry an aerogel as large as your pressure vessel.

This means one of three things—either you need a big supercritical dryer, you limit yourself to making small aerogels, or you use a non-supercritical drying technique see below. Additionally, large continuous volumes such as cubes or spheres are generally difficult to make since it takes exponentially longer for solvent from the interior of the gel to diffuse out of the gel as the gel thickness is increased. This said, there are many techniques for preparing aerogel materials called ambigels often just referred to as aerogels with subcritical drying techniques.

Subcritical drying techniques typically require specially-modified gels, in which the solid framework of the gel is chemically changed so that liquid is less able to stick to it and thus exerts only minimal stress on the gel upon evaporation. Aerogels are extremely low-density materials, typically This means aerogels have very little mass through which heat can conduct.

Additionally, the solid part of an aerogel is highly disordered and thus makes conduction of heat through the little solid that is there inefficient. Additionally, aerogels have extremely tiny pores, typically between nm in diameter. These pores are actually so tiny that they are smaller than the mean free path of air at room temperature and pressure, that is, the average distance a molecule of air can travel before hitting another air molecule is greater than the width of the pores in a typical aerogel.

As a result, air has an extremely difficult time diffusing through and thus carrying heat energy through an aerogel by convection. This phenomenon, called the Knudsen effect, differentiates aerogels from traditional foams, which typically have pore sizes of tens to thousands of microns in diameter and thus allow more heat through by convection. Aerogels are not necessarily good at stifling radiative transport, however, and so at high temperatures, heat can pass through aerogels in the form of infrared energy.

This helps limit radiative transport, making aerogel insulators excellent insulators at high temperatures as well as room temperature. The maximum operating temperature of an aerogel material depends on its composition. At hotter temperatures, silica aerogels will eventually melt. See our page about Airloy materials properties for specific information about different Airloy product temperature ratings.

First, not all aerogels are easy to break! Airloy aerogels are hundreds of times stronger and stiffer than classic aerogels and simultaneously durable and fracture tough.

Unlike legacy aerogels, Airloy aerogels can be machined drilled, tapped, turned, milled and bent without breaking. The strength, stiffness, thermal conductivity, and other properties of Airloy aerogels depend on the product series. See our page about Airloy materials properties for specific information about the mechanical properties of different Airloy products. Aerogels are open-celled materials with typical average pore sizes of less than 50 nm in diameter typically nm —about 3, to 30, times smaller than the diameter of a hair.

Some aerogel materials are waterproof and some are not. Classic silica aerogels and other oxide-based aerogels are not natively waterproof but can be modified to not only be waterproof, but superhydrophobic. The flexibility of an aerogel material depends on its composition and density. Classic silica, metal oxide, and carbon aerogels are not flexible and are usually very fragile.

Specially-formulated polymer and silica aerogels and aerogel composites with extreme flexibility can also be made, with flexibility ranging from cloth-like to marshmallow-like. Aerogel materials vary in price depending on form factor and composition. Once very costly due to specialty manufacturing processes and lack of commercial availability, today aerogel materials of various types are produced commercially on massive scales at prices that are in many instances competitive with traditional materials technologies.

Sub-bulk pricing for these and other aerogel products is available at BuyAerogel. This product is pliable and can withstand knocks. Such a battery could thus even be introduced into pieces of clothing.

Perhaps it could even be used for new kinds of three-dimensional chips to bring about a space-saving miniaturisation of electronics. These unusual product ideas are in any case probably unsuited to mass production. At present, mass production is anyway only possible for silica-based aerogels. These are the class of aerogels that have been investigated the most and that are the most widespread. They are also the only aerogels that are commercially available at the moment.

Their processing technology is already at an advanced stage of technological maturity, way beyond the laboratory stage, says Koebel. But if this silica aerogel is to have any chance of being used to insulate houses, making it will have to become quicker and cheaper. To this end, Koebel and his team are now working on more efficient production processes.

When you produce silica aerogel, says Koebel, first you have to dissolve a precursor material like silicon dioxide in a liquid such as alcohol.

After its solid particles have linked up to form a gel, the wet material then has to be dried. And there are different ways of doing this. The solvent is dried under pressure in a kind of drying tunnel.

The problem with this method is that the gel then shrinks a little, and cracks also form in it. That in turn means there are lots of small particles at the end. But at least you can stick the granules together later to form larger pieces, like with polystyrene beads. Up to now, the drying process has usually involved exchanging the one solvent with another. In one variant, for example, you can replace the alcohol with carbon dioxide — typically at a pressure of roughly a hundred atmospheres and at a temperature of over 50 degrees Celsius.