Aerogel is the lowest density solid substance in the world. The density is 3kg/ m3. The common aerogel is silicon aerogel, which was first made by American scientist Kistler in 193 1 year. There are many kinds of aerogels, including silicon, carbon, sulfur, metal oxides, metals and so on. Aerogel is a combination word, in which Aero is an adjective, which means flying, and gel is obviously gel. Literally means flying gel. As long as the gel of any substance can be dried to remove the internal solvent, the shape can remain basically unchanged, and the product has high porosity and low density, it can be called aerogel.
Because of its extremely low density, the lightest silica aerogel is only 0. 16 mg per cubic centimeter, which is slightly lower than the density of air, so it is also called "frozen smoke" or "blue smoke". Because the particles inside are very small (nano-scale), visible light scatters less (Rayleigh scattering) when it passes through, just like sunlight passes through the air. So it looks as blue as the sky (if it is not doped with other things), and it looks a little red just by looking at it. The sky is blue, while the evening sky is red. Because aerogel is more than 80% air, the heat insulation effect is very good. An inch thick aerogel is equivalent to 20 to 30 pieces of ordinary glass. Even if aerogels are placed between roses and flames, roses will remain intact. Aerogels are also used in space exploration, such as the Russian space station "Peace" and the American Mars Pathfinder. Aerogels are also used as detectors of cherenkov effect in particle physics experiments. A particle discriminator named Aerogel Cherenkov Counter (ACC) located in Belle experimental detector of B meson factory, a high-energy accelerator research institution, is the latest application example. This detector takes advantage of the low refractive index between liquid and gas, as well as its high transmittance and solid state, which is superior to the traditional method of using low-temperature liquid or high-pressure air. At the same time, its lightweight is also one of the advantages.
characteristic
Aerogel, as the lightest solid in the world, has been selected into Guinness World Records. The density of this new material is only 3.55 kilograms per cubic meter, which is only 2.75 times that of air. The density of dry pine (500 kilograms per cubic meter) is 140 times that of it. This substance looks like solidified smoke, but its composition is similar to that of glass. Because of its extremely low density, it is very suitable for aerospace.
At NASA's Jet Propulsion Laboratory, Dr. Jones developed a new type of aerogel, which is mainly composed of pure silica. In the manufacturing process, a liquid silicon compound is mixed with a liquid solvent that can evaporate rapidly to form a gel, and then the gel is dried in an instrument similar to an autoclave, heated and decompressed to form a porous sponge-like structure. The proportion of air in aerogels finally obtained by Dr Jones is 99.8%.
Aerogel is sometimes called "solid smoke" or "frozen smoke" because of its translucent color and ultra-light weight. This new material looks fragile, but it is actually very durable and can withstand the highest temperature of 1400 degrees Celsius. These characteristics of aerogels have many uses in space exploration. Aerogel materials are used in the Russian space station "Peace" and the American Mars Pathfinder.
A new type of aerogel developed by NASA, with a density of only 3 mg per cubic centimeter, has been officially selected as the "lowest density solid in the world" in the Guinness Book of World Records.
This kind of aerogel is translucent and light blue, and its weight is extremely light, so people also call it "solid smoke". This new aerogel was developed by Dr. Steven Jones, a material scientist at NASA's Jet Propulsion Laboratory. Its main component is glass-like silica, but because it is 99.8% air, its density is only one thousandth of that of glass.
Aerogels seem to be "fragile", but they are actually very durable. It can withstand thousands of times its own mass and will not melt until the temperature reaches 1200 degrees Celsius. In addition, its thermal conductivity and refractive index are also very low, and its insulating ability is 39 times stronger than that of the best glass fiber. Because of these characteristics, aerogel has become an irreplaceable material in space exploration, and it has been used for heat insulation in the Russian space station "Peace" and the American Mars Pathfinder.
The application of aerogels in space goes far beyond these. NASA's Stardust spacecraft is carrying out a very important task in space-collecting comet particles. Scientists believe that comet particles contain the most primitive and oldest substances in the solar system, and studying it can help people understand the history of the sun and planets more clearly. In 2006, the spacecraft Stardust will return to Earth with the first samples of comets from Stardust.
However, it is not easy to collect comet dust, which is six times faster than rifle bullets. Although it is smaller than sand, when it comes into contact with other substances at such a high speed, its physical and chemical composition may change or even be completely evaporated. Now that scientists have aerogels, the problem becomes very simple. It is like an extremely soft baseball glove, which can gently slow down the speed of the "Stardust" comet and make it slowly stop after sliding for 200 times its own length. After entering the "aerogel gloves", stardust will leave a carrot-shaped trajectory. Because aerogels are almost transparent, scientists can easily find these particles according to their trajectories.
use
1, studying fractal structure. As a kind of nano-porous material with controllable structure, the apparent density of silicon aerogels obviously depends on the size. In a certain scale range, its density tends to be scale-invariant, that is, its density decreases with the increase of scale, and it has a self-similar structure. The study of structural fractal dynamics of aerogels also shows that there are three excitation regions with obviously different dispersion relations in different scales, which correspond to the excitation of phonons, fractals and particle modes respectively. By changing the preparation conditions of aerogels, the correlation length can be changed within two orders of magnitude. Therefore, silica aerogel has become the best material to study fractal structure and its dynamic behavior.
2. In the research of "863" high-tech intense laser. Nano-porous materials have important application value. For example, the use of porous target materials with lower critical density is expected to improve the beam quality of X-ray laser generated by electron collision excitation and save driving energy. A new porous target with microsphere node structure can quickly cool the three-dimensional adiabatic expansion of plasma and improve the gain coefficient of X-ray laser generated by electron recombination mechanism. Using ultra-low density materials to adsorb nuclear fuel can form a high-gain frozen target for laser inertial confinement fusion. Aerogel is the best candidate for developing new low-density targets because of its fine nanoporous network structure, huge specific surface area and controllable mesoscopic structure.
3. As a thermal insulation material. The fine nano-network structure of silicon aerogel effectively limits the propagation of local thermal excitation, and its solid thermal conductivity is 2-3 orders of magnitude lower than that of the corresponding glassy materials. Nanopores inhibit the contribution of gas molecules to heat conduction. The refractive index of silica aerogel is close to L, and the extinction coefficient ratio of infrared to visible light is above 100, which can effectively transmit sunlight and prevent infrared heat radiation at room temperature. As an ideal transparent thermal insulation material, silica aerogel has been applied in the fields of solar energy utilization and building energy conservation. By doping, the radiation heat conduction of silicon aerogels can be further reduced. The thermal conductivity of doped carbon aerogels can be as low as 0.01.3w/m k at normal temperature and pressure. It is a solid material with the lowest thermal conductivity at present, and is expected to replace polyurethane foam as a new type of refrigerator insulation material. Doping titanium dioxide can make silicon aerogel a new type of high-temperature thermal insulation material, and its thermal conductivity at 800K is only 0.03 W/m·k, which will further develop into a new supporting material for military products.
4. Silicon aerogel is an ideal sound insulation material for sound delay or high temperature because of its low sound velocity. The acoustic impedance of this material can vary widely (103-107 kg/m2 s), and it is an ideal acoustic impedance coupling material for ultrasonic detectors. For example, piezoelectric ceramics with acoustic impedance turns ZP =1.5× l07kg/m2 s are often used as ultrasonic generators and detectors, while the acoustic impedance of air is only 400 kg. Using silicon aerogel with the thickness of 1/4 wavelength as the acoustic resistance coupling material between piezoelectric ceramics and air can improve the transmission efficiency of sound waves and reduce the signal-to-noise ratio in device application. The preliminary experimental results show that the sound intensity can be improved by 30 dB by using silica aerogel with a density of about 300 kg/m3 as the coupling material. If silica aerogels with density gradient are used, higher sound intensity gain can be expected.
5. In environmental protection and chemical industry. Nanostructured aerogels can also be used as a new type of gas filtering material. Different from other materials, this material has uniform pore size distribution and high porosity, and is an efficient gas filtration material. Aerogel has a great specific surface area, and has a broad application prospect as a new catalyst or catalyst carrier.
6. In the energy storage device. Carbon aerogels is a conductive porous material, which is obtained by sintering organic aerogels. It is a new type of carbon material developed after fibrous activated carbon. Large specific surface area (600- 1000m2/kg) and high electrical conductivity (10-25s/cm). And the density varies widely (0.05- 1.0g/cm3). If the micropores are filled with appropriate electrolyte, a new type of rechargeable battery can be made, which has the excellent characteristics of large storage capacity, small internal resistance, light weight, strong charging and discharging ability and reusability. The preliminary experimental results show that the charging capacity of carbon aerogels is 3× 104/kg2.
7. In the study of quantum size effect of materials. Due to the formation of quantum dot structure in silicon aerogel nano-network, the results of chemical vapor infiltration doping Si and solution doping C60 show that the dopant exists in the form of nanoparticles, and strong visible light emission is observed, which provides strong evidence for quantum confinement effect luminescence of porous silicon. Using the structure of silica aerogel and the nonlinear optical effect of C60, a new type of laser protective mirror can be further developed. Doping is also an effective means to form nanocomposites.
8. In addition, silica aerogels are materials with adjustable refractive index. Using aerogels with different densities as Cherenkov threshold detectors can determine the mass and energy of high-energy particles. Because high-speed particles easily penetrate porous materials and gradually slow down, a "soft landing" is realized. If transparent aerogels are selected to capture high-speed particles in space, the blocked and captured particles can be observed with naked eyes or microscopes.
9. As a new nano-porous material, besides silicon aerogel, other units, binary or multi-oxide aerogels, organic aerogels and carbon aerogels have been developed. As a unique material preparation method, related technologies have been widely used in the development of other new materials, such as porous silicon with extremely high porosity, metal-aerogel mixed materials for preparing high-performance catalysts, high-temperature superconducting materials, ultrafine ceramic powders and so on.
Research unit
In 20 13, the international research work of aerogel materials was mainly concentrated in the University of Wü rzburg, BASF, Lorenz Livermore National Laboratory, Sandia National Laboratory, Montpellier Materials Research Center, France, and Japan National Laboratory of High Energy Physics. China is mainly concentrated in Bohr Solid State Physics Laboratory of Tongji University, National University of Defense Technology, Tsinghua University, Zhejiang University, Nanotechnology Co., Ltd. and Guangdong Ailisheng High-tech Co., Ltd.
Other uses
1, making a Mars exploration spacesuit
In 2002, NASA set up a company to produce stronger and more elastic aerogels. In 20 13, NASA has confirmed that astronauts will wear spacesuits made of new aerogels when exploring Mars in 20 18. Mark Krajewski, a senior scientist of the company, said that as long as an aerogel layer with a thickness of18mm is added to the spacesuit, it can help astronauts resist the high temperature of 1.300℃ and the ultra-low temperature of-1.30℃. "This is the most effective thermostatic material I have ever seen," Mark said.
2. Bulletproof and not afraid of being bombed
Bulletproof is the second important use of new aerogels. NASA is testing houses and military vehicles built with aerogels. According to the laboratory test, if a layer of aerogel with a thickness of about 6 mm is added to the metal sheet, even if the explosive is blown directly, it will not hurt the metal sheet.
3. Be able to cope with ecological disasters
Environmental protection is the third important function of new aerogels. Scientists affectionately call aerogel "super sponge" because it has millions of small holes on its surface, so it is an ideal material to absorb pollutants in water. The aerogels newly invented by American scientists can actually absorb lead and mercury from water. According to the scientist, this kind of aerogel is an excellent material to deal with ecological disasters. For example, 72,000 tons of crude oil leaked after the sinking of 1996 "Haikuai" oil tanker. If this material had been used at that time, it would not have caused serious pollution to the whole coast.
Tennis racket has better hitting ability.
In the future, new aerogels will also enter our daily life. For example, Deng Lupu Sports Equipment Company has successfully developed tennis rackets containing aerogels. This kind of tennis racket is said to have better hitting ability; At the beginning of 20 12, 66-year-old Bob Stoke became the first Englishman to use aerogels in houses: "The effect of heat preservation and heating is very good. I reduced the air conditioning temperature by 5 C, and the indoor temperature is still very comfortable. " Climbers are also full of hope for the use of aerogels. Anne Palmer, a British mountaineer, used some aerogel materials in her shoes when she climbed Mount Everest at 20 1 1, and there was a layer of this new material in her sleeping bag.