Airgel – the future of insulating material

We are in the exploration of outer space, \”new race\” among the new material is always in the forefront of technological advances. Look at the demand for space suit, it has to protect astronauts from the extreme temperatures of space, while also thin and light as possible, in order to enhance flexibility. 专栏:气凝胶——未来的绝缘材料 United States National Aeronautics and Space Administration (NASA) developed airgel insulation material used in space exploration, but in recent years, aerogels have been commercialized, and has been applied in many other areas. Airgel is an excellent insulation material. Here, a piece of airgel can protect the flowers from the blowtorch damage. Airgel material is an advanced, due to its super-porous structure, not only can the design engineer new aircraft and space suits insulating material, may also be designed as a filter, battery, solar collectors and the like. However, \”airgel\” are not material. Rather, they are a special form of a solid, may be made of silica, a polymer, an oxide, carbon and other materials. Although aerogels are solid, they contain many small voids or \”pores\”, they are mostly consisting of air. So, what is airgel? How to make airgel? What are the main characteristics of the airgel is? Which applications airgel there?

What is airgel?

Aerogels are super porous material, which means that, although they are solid, but they are full of fine pores inside. These pores are the key to the unique properties of aerogels. Although many materials are also porous, and certain ceramics such as foam, but airgel is an extreme example. In aerogels, pores accounted for the majority of materials, lightweight solid material formed. Airgel pores very small, much smaller than a human hair, the naked eye is difficult to see. It is because of Aerogels are so light and translucency, that they have frozen smoke (frozen smoke), smoke solid state (solid smoke), solid state air (solid air) and blue smoke (blue smoke) so nickname. Samuel Stephens Kistler invention airgel in 1931. And all this is because of a bet between him and Charles Learned. At that time the two of them being in the game who should gel with the liquid component of the gas is not replaced by contraction of the partitions foam collapse. Finally Kistler did.

What are the main characteristics of the airgel is?

Aerogels are porous so that air is 95% by volume, which gives them a variety of unusual properties. They are the lightest material ever developed or discovered, which makes them particularly useful in aerospace applications, because in these applications, weight is crucial.

low density airgel

Despite their names airgel, but they are not a gel, they are highly porous solids, mainly consists of air. Aerogels a liquid initially, it is converted to a gel, and then removing the liquid. Their unique pore structure is formed by binding fine particles stored in the liquid phase is formed is formed. The trick is to remain in the space between the particles while removing the liquid. These voids became the airgel pores. Although airgel has had a gum words, but in fact it is hard and dry substance, its physical properties and colloid is not similar. It is known as glue, because of its manufacturing process is extracted from the gel.

Aerogels pressure resistance

filed fingertips gently press it on the surface of the gel, and will not leave marks; if aggravating the force pressing cause permanent depression; and will add enough power scattered like glass breaking it into pieces. This is what we know fragility. Although it has a tendency to break, but structural terms it is still very strong. It is excellent load capacity due to the composition of the molecule: approximately 2 to 5 nm size spherical polymeric particles bonded to each other into a small unit, and then combined into a three-dimensional structure dendritic microstructure. These small cells form a chain fractal three dimensional structure therebetween filled with a large number of holes, each hole size of not greater than 100 nanometers. While the packing density of the holes and the average size of an individual capable of being controlled by the manufacturing process.

airgel very low thermal conductivity

airgel is an excellent thermal insulator, airgel consists of three almost block the two kinds of heat transfer (heat conduction, convection, radiation) of the belt to heat transfer. The proportion of air in the gel composition comprises at least 95% or more, and the air is a poor conductor of heat, so that they are good thermally conductive insulating material (metal gel but not so effective in use as an insulator). For example silicone gel, since the silicon is also poor conductor of heat, which barrier properties and a more favorable. On the way in terms of thermal convection,Since air can not cross the gel surface convection row, they are also good convection heat insulating material. General airgel thermal radiation can not afford much effect. However, the carbon gel is a good heat radiating insulating material, because carbon at standard temperature capable of absorbing infrared radiation emitted during heat transfer. Therefore, nowadays the best properties of the airgel is silica gel fraction of carbon incorporated.

Aerogels translucency

Since the vast majority of air airgel, therefore, most of the airgel material having translucency. Because the effects of Rayleigh scattering of tiny airgel in dendritic structure will filter a small portion of the visible spectrum in a shorter wavelength, and this had its soft color: blue dissemination of dough in a dark environment, bright the environment exudes slightly yellow.

and a hydrophilic airgel hydrophobic aerogels

with the nature of the airgel itself is hydrophilic, it may also be by means of a chemical process changes its hydrophobic. In the process of the gradual absorption of moisture gel, a molecular structure undergoes changes, such as size reduction, or even completely destroyed. By means of changing the gel for acceptance of water vapor in order to improve the destruction phenomenon. While the hydrophobic process can promote the convenience of the colloid process, easy to use water jet cutting. Because airgel natural hygroscopic nature, feels Dry gel, and showed a strong ability to absorb water, for a long time holding the gel people to wear gloves to prevent skin surface phenomenon of dehydration.

How to make airgel?

专栏:气凝胶——未来的绝缘材料 airgel by liquid component is withdrawn from the gel inside the supercritical drying method. This method will make the liquid is slow coming out, but not so in the solid structure of the gel because of the capillary action is pressed along broken. The main component of the world\’s first airgel is silica gel. Kistler subsequently fashioned aluminum, chromium, tin oxide gel-based substances. The first carbon gel to the late 1980s was only later developed. The most common type of silica airgel by \”Sol-Gel\” process made:

  1. The fine solid particles with a liquid solvent prepared by mixing \”sol.\”
  2. By adding a catalyst, the sol is made to a kind of \”gel\”, which allows the catalyst particles are bonded to each other, so that the mixture was solidified.
  3. removed by dryingTo liquid solvent, leaving only the solid airgel.

airgel processing unique crucial microstructure formed. If no semi-liquid gel phase ultrafine hole left by the airgel would not have such a low density, will not have such excellent insulation properties. Which applications

Aerogels have?

airgel is not a special material, but a processed so as to have an additional porous material. Aerogels are most commonly made of silica, but graphene airgel, iron oxide, and the like made from the polymer. Airgel also appeared in various forms, including thick brick flexible plate and the thin coating. Aerogels can be used for many purposes and has been marketed as an insulating material.

airgel insulation

airgel low thermal conductivity and low density makes it an excellent insulating material. In addition, airgel is very light, almost does not increase the weight of the structure, which makes them well suited for space travel, because each kilogram of airgel will need to spend money to rise space. Airgel is an excellent insulator, can be used for the thin layer structure requires flexibility, as the suit. NASA Widespread use of airgel insulation material as the main spacesuit, and to protect electronic equipment from damage under extreme conditions. 专栏:气凝胶——未来的绝缘材料 Some of aerogels are translucent, which means that they can be used in place of conventional insulating materials can not be used, such as windows and solar panels. Whether they are used for building skylight ground or future space habitats windows, aerogels can transmit light, but can hinder the transfer of heat. This makes them ideal for heating and cooling the structure is easy to make, but also allow more natural light enters. Airgel is also used as next-generation solar collector coating, in this case, allowing light to pass through the airgel, but prevent heat loss. Airgel ability to stop the flow of heat also makes it an effective form of camouflage, and airgel coating has been tested and found to be as a way to avoid the infrared camera.

airgel and adsorbent filter

airgel micropores inside that they have a particularly high specific surface area, which means that a large amount of solid material can be in contact with its surroundings. When the airgel to attract and adhere to certain molecules or particles is made of a material, they are useful as adsorbents and filters, the material trapped in the hole. 专栏:气凝胶——未来的绝缘材料 is an excellent desiccant silica gel, chemically safe, can be used in a common food airgel adsorbent \”close\” is silica, it is often used as a desiccant of moisture removed from the air. Most people are familiar with keeping food and other goods dried silica gel bags for use in air conditioning systems and other applications. When silica gel is saturated with water, it can be \”charged\” by heating in an oven, the water may evaporate so that the surface of the pores, it remains dry and used again. Generally, the amount of water absorbed by the desiccant increases with increasing specific surface area increases. Since aerogels have a higher specific surface area than conventional silicone gel, a greater improvement in the ability to retain moisture.

The use of airgel

airgel high specific surface area, which means that the material in contact with the surrounding environment may be particularly high. This makes it very useful in a large airgel chemical and electrochemical processes, these processes can be improved by maximizing the area of ​​contact between the solution and the solid matrix. These techniques include use as a catalyst or catalyst substrate in various industrial chemical processes, as well as an electrode in the next generation supercapacitors. NASA using airgel to capture the \”Stardust\” space dust particles on the spacecraft. The particle vaporizes and passes through a gas upon impact with a solid, but trapped in the airgel. NASA also uses airgel insulation on Mars. The early 1980s, particle physicists recognize SiO2 airgel airgel will be cut over the dielectric material Cherenkov counter (Aerogel Cherenkov Counter) particle identification device (see Cherenkov effect), and requires a lot of trial transparent SiO2 airgel. TMOS method they use, creating two large detectors: one is the TASSO detector at the DESY laboratory in Hamburg, Germany, uses 1700 liters airgel; the other is the detector CERN (CERN) manufacturing , using 1000 liters of airgel made from Lund University in Sweden. Japanese KEK B meson factory Belle experiment detector also used airgel Cherenkov counter. This detector utilizes the airgel low refraction index between the liquid and the gas properties and the nature of its high transmittance and a solid, is superior to the traditional practice of using high pressure air or cryogenic liquids. Airgel is also detected in space has many uses in RussiaSri Lanka on the Mir space station and Mars Pathfinder United States has used this material. Since aerogels are made of a structure of a variety of materials may be, researchers continue to develop new aerogels and new method to use it. As more new airgel material is made, which will promote the development of new technologies, such as a new super capacitor, an antimicrobial coating, oil absorbent pad, bone implants. Because of its low thermal conductivity, low density, high surface area and unique combination of translucency, the aerogels being developed as materials of various advanced technologies. Finally, let\’s look at the current hot topic: whether the novel coronavirus aerosol can spread? On joint prevention and control mechanism of the State Council held a press conference on February 9, a researcher at the Infectious Diseases Control and Prevention, Chinese Center for Disease Control and Prevention recorded Feng Zhao said that there is currently no evidence that the novel coronavirus spread by aerosol. \”Currently, the main route of transmission of novel coronavirus transmission or respiratory droplets and contact, such as aerosols and fecal-oral pending further clarified.\” Feng Zhao said the record, \”through epidemiological survey shows that more cases can be traced to the confirmed cases had a short distance in close contact, which is consistent with the characteristics of the droplets and contact transmission. \”Feng call record describes aerosol droplets spread refers to the loss of moisture in the air during suspension while the remaining proteins and pathogens composition nuclei formed droplet nuclei, can float to distant form of an aerosol, resulting in the propagation distance. There is currently no evidence that the novel coronavirus spread by aerosol. The latest National Health health committee issued a \”novel coronavirus pneumonia treatment program (Trial Fifth Edition Revision)\” in which the expression of virus transmission also showed that \”the digestive tract such as aerosols and transmission need to be clarified.\” China CDC epidemiology chief expert WU Zun said that the general public, in general the working and living conditions, protective measures taken to prevent the spread of droplets right to wear masks, enough to be effectively protected. \”In public places, especially in a confined environment wearing masks, washing hands is the most effective protective measures.\” Extraordinary times for epidemic prevention and control, we need attention, but do not panic. Confidence, solidarity, scientific control, precision Shi policy, we will be able to win this epidemic prevention and control warfare. .

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