Aerogel has become the best material for studying fractal structure and its dynamic behavior

 Aerogel overview

Aerogel is a solid material form, the smallest dense solid in the world. The density is 3 kilograms per cubic meter. The most common aerogel is silicon aerogel, which was first made by American scientist Kistler in 1931 because of a bet with his friends. 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, which means flying, and gel is obviously a gel. Literally means a flying gel. The gel of any substance can be called an aerogel as long as it can be dried and removed from 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, the lightest aerogel is only 0.16 mg per cubic centimeter, which is slightly less dense than 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 just like the sky (if there are no other things in it), and it looks a little red if it looks at the light. (The sky is blue, and the evening sky is red). Since more than 80% of the aerogel is generally 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 not be damaged at all. 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 one of the latest application examples. The aerogel used in this detector has the characteristics of a 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.

SiO2 aerogel is a nano-porous material with ultra-light and super thermal insulation properties. It is the best quality, lightest, and most heat-insulating solid material. It is difficult to ensure the formability of foam concrete when the foam content is large. Simply increase, and the aerogel prepared by adding aerogel reduces the density and thermal conductivity of concrete, high cost, density, and lower thermal conductivity are limited. By mixing lightweight, porous, super-hydrophobic aerogel powder in foamed concrete, the thermal conductivity is lower than that of air, and it is expected to be prepared under the condition of low porosity and low density. The formability of foamed concrete has a high porosity. On the basis of prefabricated foam to prepare foamed concrete, a new type of aerogel foamed concrete preparation method is added, and the preparation parameters affect the performance of foamed concrete aerogel. The results of the study are as follows:

(1) Using aerogel as the filler, a new type of aerogel foamed concrete was successfully prepared by the prefabricated foam mixing method. Under the premise of meeting the requirements of the compressive strength index, its density and thermal conductivity were significantly reduced. It is 222kg/m3, the aerogel content is 13.0kg/m3, the foam content is 70%, the minimum density is 270.2kg/m3, and the minimum thermal conductivity is 0.069W/m·K.

(2) The dry bulk density of gel foam concrete with a porosity of 40% is 58.6% lower than that of ordinary foamed concrete, which meets the dry bulk density of 400 kg/m3. Foamed concrete only needs 66% of the aerogel porosity. 82% of the foamed concrete needs pores, which can improve the formability and compressive strength of the foamed concrete.

(3) The ratio of aerogel and bubbles has a great influence on the performance of aerogel foam concrete. Under the condition of 50% foam volume ratio, when the amount of aerogel increases from 9.2 kg/m3 to 22.1 kg/m3, the density decreases by 13.7%, the thermal conductivity decreases by 18.5%, and the compressive strength decreases by 0.91. Mpa.

(4) There is a strong correlation between the dry bulk density, thermal conductivity, and compressive strength of aerogel foamed concrete. The fitting of the empirical relationship between the two can provide a reference for the prediction of engineering application performance.

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 with the increase of the scale. 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 make the correlation length change within two orders of magnitude. Therefore, silica aerogel has become the best material for studying the fractal structure and its dynamic behavior. 

1. In the "863" high-tech and strong laser research

Nanoporous materials have important application values. 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 the new porous target with a microspherical node structure to achieve The rapid cooling of the three-dimensional adiabatic expansion of the plasma can increase the gain coefficient of the x-ray laser generated by the electronic recombination mechanism, and use ultra-low density materials to adsorb nuclear fuel, which can constitute a high-gain freezing target for laser inertial confinement fusion. Aerogel's slender nanoporous network structure, huge specific surface area, and mesoscopic structure controllable become the best candidate material for the development of new low-density targets.

2. As 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. The nano-pores suppress the contribution of gas molecules to heat conduction. The refractive index of silicon aerogel is close to l, 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 from 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 0.013 w/m·K at room temperature and pressure, which is the solid material with the lowest thermal conductivity. It is expected to replace polyurethane foam as a new type of refrigerator insulation material. Incorporating titanium dioxide can make silicon aerogel become a new type of high-temperature 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. The 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 can be 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 highly efficient gas filtration material. Because the material is particularly large than the table and accumulate. Aerogels also have broad application prospects as new catalysts or catalyst carriers.

3. In terms of energy storage devices

After the organic aerogel is processed by the sintering process, carbon aerogel will be 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). /g) and high conductivity (10-25 s/cm). Moreover, the density has a wide range (0.05-1.0 g/cm3). If an appropriate electrolyte is filled in the micropores, a new type of rechargeable battery can be made, which has excellent characteristics such as large storage capacity, small internal resistance, lightweight, strong charging and discharging ability, and repeated use. Preliminary experimental results show that the charging capacity of the 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 the 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 means to form nanocomposite phase materials.

In addition, silica aerogel is a material with an 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, metal-aerogel hybrid materials for the preparation of high-performance catalysts, high-temperature superconducting materials, Ultra-fine ceramic powder, etc.

The price of aerogel

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Aerogel supplier

As a global supplier of nano-SiO2 aerogels, Tanki New Materials Co., Ltd. has extensive experience in the performance, application, and cost-effective manufacturing of advanced technology and engineering materials. The company has successfully developed a series of powder materials (including oxides, carbides, nitrides, single metals, etc.), high-purity targets, functional ceramics, and structural devices, and provides OEM services.