English aerogel,also known as xerogel.When most of the solvent is removed from the gel,the liquid content in the gel is much less than the solid content,or the medium in the spatial network structure of the gel is gas and the appearance is solid.This is a dry gel. It is called aerogel. Aerogel is a solid material form,the smallest dense solid in the world.The density is 3kg per cubic meter.The common aerogel is silicon aerogel,which was first produced in 1931 by the American scientist Kistler.There are many types of aerogels, including silicon,carbon,sulfur,metal oxide,metal and so on.Aerogel is a compound word,where aero is an adjective,meaning flying,and gel is obviously gel. Literally means a flying gel. Gel of any substance can be called an aerogel as long as it can be dried and removed the internal solvent,but can basically keep its shape unchanged,and the product has high porosity and low density.
Because of its extremely low density,currently the lightest silica aerogel is only 0.16 mg per cubic centimeter slightly lower than the density of air, so it is also called "frozen smoke" or "blue smoke".Since the particles inside are very small (on the order of nanometers),visible light scatters less when passing through it (Rayleigh scattering), just like sunlight passing through the air.Therefore, it looks bluish like the sky (if there is nothing mixed in it),and it looks a little red if it looks at the light. (The sky is blue, and the sun looks a bit red). Since more than 80% of the aerogel is air, it has a very good thermal insulation effect. An inch thick aerogel is equivalent to the thermal insulation function of 20-30 pieces of ordinary glass.Even if the aerogel is placed between the rose and the flame,the rose will be intact. Aerogel also has many uses in space exploration. It is used in the Russian Mir space station and the Mars Pathfinder probe of the United States. Aerogel is also used as a detector for the Cherenkov effect in particle physics experiments. A particle discriminator called Aerogel Cherenkov Counter (ACC) in the Belle Experimental Detector of the High Energy Accelerator Research Institute B Meson Factory is a recent application example.The aerogel used in this detector has the characteristics of low refractive index between liquid and gas,as well as its high light transmittance and solid properties,which is better than the traditional method of using cryogenic liquid or high-pressure air.At the same time, its lightweight nature is also one of the advantages.
What is the scope of application of aerogel?
In the research of fractal structure. As a nanoporous material with a controllable structure,silicon aerogel has a density that obviously depends on the scale size. Within a certain scale, its density tends to be scale-invariant, that is, the density decreases as the scale increases,and With a self-similar structure, the structure in the dynamics research of aerogel fractal structure also shows that in different scales,there are three excitation regions with significantly different dispersion relations, corresponding to the excitation of phonons,fractals and particle modes. Changing the preparation conditions of aerogels can change the correlation length within two orders of magnitude.Therefore,silica aerogel has become the best material for studying the fractal structure and its dynamic behavior.
In the "863" high-tech and strong laser research. Nanoporous materials have important application value. For example,the use of porous target materials below the critical density can improve the beam quality of the X-ray laser generated by electron collision excitation,save driving energy,and use a new porous target with a micro-spherical node structure.The rapid cooling of the three-dimensional adiabatic expansion of the plasma improves the gain coefficient of the x-ray laser generated by the electronic recombination mechanism,and the use of ultra-low-density materials to adsorb nuclear fuel can form a high-gain freezing target for laser inertial confinement fusion. Aerogel's slender nanoporous network structure, huge specific surface area, and controllable structure on the mesoscopic scale have become the best candidate material for the development of new low-density targets.
In terms of being a thermal insulation material.The slender nano network structure of silicon aerogel effectively limits the propagation of local thermal excitation, and its solid-state thermal conductivity is 2-3 orders of magnitude lower than that of the corresponding glassy materials.Nano-pores suppress the contribution of gas molecules to heat conduction.The refractive index of silicon aerogel is close to 1, and the ratio of the annihilation coefficient to infrared and visible light is more than 100. It can effectively transmit sunlight and prevent infrared heat radiation at ambient temperature, making it an ideal transparent heat insulation material ,Has been applied in solar energy utilization and building energy saving.By means of doping, the radiant heat conduction of silicon aerogel can be further reduced.The thermal conductivity of carbon-doped aerogel can be as low as 0.013w/m·K at normal temperature and pressure,and it is currently the lowest thermal conductivity solid material It is expected to replace polyurethane foam as a new type of refrigerator insulation material. Doping with titanium dioxide can make silicon aerogel become a new type of high-temperature thermal insulation material. The thermal conductivity at 800K is only 0.03w/m·K, and it will be further developed as a new material for military products.
Due to its low sound velocity,silicon aerogel is also an ideal acoustic delay or high temperature sound insulation material. This material has a large acoustic impedance variable range (103-107 kg/m2·s),and is an ideal acoustic resistance coupling material for ultrasonic detectors. For example, the commonly used acoustic resistance turns Zp=1. 5×l07 kg/ Piezoelectric ceramics of m2·s are used as ultrasonic generators and detectors, while the acoustic resistance of air is only 400 kg/m2·s. Silicon aerogel with a thickness of 1/4 wavelength is used as the acoustic resistance coupling material between piezoelectric ceramics and air. It can improve the transmission efficiency of sound waves and reduce the signal-to-noise ratio in device applications. Preliminary experimental results show that silica aerogel with a density of about 300 kg/m3 as a coupling material can increase the sound intensity by 30 dB. If a silica aerogel with a density gradient is used,a higher sound intensity gain is expected.
In environmental protection and chemical industry.Nano-structured aerogel can also be used as a new type of gas filtration.The difference from other materials is that the material has uniform pore size distribution and high porosity.It is a high-efficiency gas filtration material. Because the material is particularly large than the table product.Aerogels also have broad application prospects as new catalysts or catalyst carriers.
In terms of energy storage devices. After the organic aerogel is processed by the sintering process,carbon aerogel is obtained.This conductive porous material is a new type of carbon material developed after fibrous activated carbon. It has a large specific surface area (600-1000 m2). /kg) and high conductivity (10-25 s/cm). And the head. The density has a wide range (0.05-1.0 g/cm3). If the micropores are filled with appropriate electrolyte, a new type of rechargeable battery can be made. It has excellent characteristics such as large storage capacity,small internal resistance, light weight, strong charging and discharging ability, and repeated use. Preliminary experimental results show that the charging capacity of carbon aerogel is 3×104/kg2, the power density is 7 kw/kg, and the repeated charge and discharge performance is good.
In the research of quantum size effect of materials. Due to the formation of quantum dot structure in the nano network of silicon aerogel,the results of chemical vapor infiltration method doping Si and solution method doping C60 show that the dopant exists in the form of nanocrystalline particles, and strong visible light emission is observed.It provides strong evidence for the quantum confinement effect of porous silicon to emit light. Using the structure of silicon aerogel and the nonlinear optical effect of C60, new laser protective glasses can be further developed. The doping method is also an effective way to form nanocomposite phase materials.
In addition,silica aerogel is a material with adjustable refractive index.Using aerogel media of different densities as Cherenkov threshold detectors can determine the mass and energy of high-energy particles. Because high-speed particles can easily penetrate into porous materials and gradually slow down to achieve a "soft landing",if a transparent aerogel is used to capture high-speed particles in space, the blocked and captured particles can be observed with the naked eye or a microscope.
As a new type of nanoporous material, in addition to silicon aerogels, other units, binary or multiple oxide aerogels, organic aerogels and carbon aerogels have been developed. As a unique material preparation method, related processes have been widely used in the development of other new materials,such as the preparation of porous silicon with extremely high porosity,the preparation of high-performance catalysts of metal-aerogel hybrid materials, high-temperature superconducting materials, Superfine ceramic powder, etc. At present, international research work on aerogel materials is mainly concentrated in Würzburg University in Germany, BASF Company, Lorenz Livermore National Laboratory in the United States, Sandia National Laboratory, and Montpellier in France Angstrom Materials Research Center, Japan National Laboratory for High Energy Physics, etc. Domestically, it is mainly concentrated in the Ball Solid State Physics Laboratory of Tongji University, National University of Defense Technology, Tsinghua University, Tongji University, Zhejiang Shaoxing Nano Technology Co., Ltd. and Guangdong Alison High-tech Co., Ltd. Also Guangdong Alison High-tech Co., Ltd. Currently the largest aerogel product manufacturer in China.
Aerogel fold other uses
1.Making Mars expedition spacesuit
In 2002,NASA established a company that specializes in the production of stronger and more resilient aerogels. NASA has now determined that during the 2018 Mars expedition, astronauts will wear spacesuits made of new aerogels. The company's senior scientist Mark Krajeowski said that as long as an 18 mm thick aerogel layer is added to the spacesuit, it can help astronauts withstand the high temperature of 1300 ℃ and the ultra-low temperature of minus 130 ℃. "This is the most effective thermostatic material I have ever seen." Mark said.
2.Bulletproof is not afraid of being bombed
Bulletproof is the second important use of new aerogels.The NASA company is testing homes and military vehicles built with aerogel. According to the laboratory's test situation, if a layer of aerogel with a thickness of about 6 mm is added to the metal sheet,then even if the explosive is directly exploded, it will not damage the metal sheet.
3.Can handle ecological disasters
Environmental protection is the third important role of the new aerogel.Scientists affectionately call aerogel "super sponge" because it has millions of small holes on its surface,so it is an ideal material for adsorbing pollutants in water.The aerogel newly invented by American scientists can now absorb lead and mercury in water.According to the scientist,this aerogel is an excellent material for dealing with ecological disasters. For example, after the sinking of the "Sea Express" tanker in 1996,72,000 tons of crude oil leaked out. If this material was used at that time, then it would not Will cause serious pollution to the entire coast.
4.Tennis racket has stronger ability to hit the ball
New aerogels will also enter each of us in our daily lives in the future. For example, Dunlop Sports Equipment in the United States has successfully developed tennis rackets containing aerogel.This tennis racket is said to be more capable of hitting the ball;at the beginning of this year,the 66-year-old Bob Stoker became the first British person to use aerogel for housing: "The effect of heat preservation and heating is very good,I will use air conditioning The temperature dropped by 5°C,and as a result,the indoor temperature is still very comfortable."Climbers are also full of hope for the use of aerogel.The shoes worn by British mountaineer Anne Parment when he climbed Mount Everest last year used some aerogel materials,and there was a layer of this new material in his sleeping bag.
The price of aerogel:
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