Aerogel (aerogels) usually refers to the nano-scale ultrafine particles aggregate to form a nano-porous network structure, and the network pores are filled with gaseous dispersion medium of light nano-solid materials. Aerogel is a solid, but 99% is made up of gas and looks like a cloud. Aerogels are sometimes referred to as "solid smoke" or "frozen smoke" because of their translucent color and ultra-light weight ".

A common aerogel is a silica aerogel. SiO2 aerogel is a light nano-porous amorphous solid material with excellent heat protection and heat insulation performance. Its porosity is as high as 80-99.8%, the typical pore size is 1-100nm, the specific surface area is 200-1000 m2/g, the density can be as low as 3kg/m3, and the room temperature thermal conductivity can be as low as 0.012W/(m k). It is precisely because of these characteristics that aerogel materials in thermal, acoustic, optical, microelectronics, particle detection has a very broad application potential.

Properties of 1. Aerogels

1. Heat insulation

SiO2 aerogel material has a very low thermal conductivity, which can reach 0.013-0.016W/(m · K), which is lower than that of static air (0.024W/(m · K)) and 2-3 orders of magnitude lower than that of corresponding inorganic insulating materials. Even at a high temperature of 800 ° C., its thermal conductivity is 0.043W/(m · K). High temperature does not decompose, no harmful gas release, belongs to the green environmental protection material. After SiO2 silica aerogel is compounded with various heat-resistant fibers, it can be made into various forms of thermal insulation materials. It can be widely used in industry, construction, pipeline, automobile, aerospace and other fields.

2. Sound insulation

Silica aerogel is also an ideal acoustically retarding or high temperature sound insulation material due to its low acoustic velocity properties. The material has a wide range of acoustic impedance (103-107kg/m2 · s), and is an ideal acoustic impedance coupling material for ultrasonic detectors.

Silicon aerogel with a density of about 300kg/m3 can be used as a coupling material to increase the sound intensity by 30dB.silica aerogelIt is expected to get a higher sound intensity gain.

3. Nonlinear optical properties

Due to the formation of quantum dot structure in the nano network of silicon aerogel, the results of chemical vapor infiltration method doped with Si and solution method doped with C60 show that the dopant is in the form of nano-grains, and a strong visible light emission is observed, which provides strong evidence for the quantum confinement effect 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.

4. Filtration and catalytic properties

Nanostructured aerogels can also be used as a new type of gas filtration, which is different from other materials in that the material has uniform pore size distribution and high porosity. Due to the material is particularly large than the table and product. Aerogels also have broad application prospects as new catalysts or catalyst carriers.

5. Refractive index adjustability

The refractive index of silica aerogel is close to 1, and the ratio of the annihilation coefficient of infrared and visible light is more than 100. It can effectively pass through the visible light part of sunlight and block the infrared light part. It has become an ideal transparent heat insulation material, which has been applied in solar energy utilization and building energy saving.

2.aerogelThe use

(1) Industrial field

In the petroleum, chemical and metallurgical industries, pipelines, furnaces and other thermal equipment are widespread, using SiO2 aerogel and its composite materials to replace the traditional insulation materials for their insulation, can greatly reduce the loss of heat energy, improve the utilization rate of heat energy. It can also be used as a thermal insulation material for liquid natural gas tanks and oil storage tanks, as well as engines and exhaust pipes of automobiles and airplanes.

(2) Civilian areas

Doped SiO2 aerogels with extremely low thermal conductivity can be used as heat insulation materials for refrigerators, and can also be used for heat insulation and sound insulation materials for buildings. Commonly used building insulation materials are polystyrene, polyurethane and other polymer foam materials, the material size is thick, to the construction and the later stability of many problems, and polymer insulation materials are flammable, easy to cause fire. SiO2 aerogel can withstand high temperature, generally at 800 ℃, the structure and performance of no obvious change, is a kind of safety, energy saving, environmental protection super insulation material.

(3) Solar collector

Aerogels with high light transmittance and low thermal conductivity have almost no reflection loss to incident light, can effectively transmit sunlight, and aerogels can effectively prevent heat loss. Therefore, aerogels are particularly suitable for use as thermal insulation materials for solar collectors and other heat collection devices. The application of aerogel insulation materials to water heater storage tanks, pipes and collectors will increase the heat collection efficiency of existing solar water heaters by more than 1 times, and the heat loss will be reduced to less than 30% of the existing level.

(3) Aerospace field

Aerogel super thermal insulation material has excellent quality and thermal insulation effect, and has a good application prospect in aviation and aerospace applications. Aluminum silicate refractory fiber/SiO2 aerogel composite insulation tile has been used in the space shuttle, aerogel is being used for the first landing on Mars in the space suit to develop a thermal insulation lining.

Aerogels are also used to collect cometary particles. Like an extremely soft baseball glove, it can gently reduce the speed of comet stardust, causing it to slowly stop after gliding a distance equivalent to 200 times its own length. After entering the "aerogel glove", the stardust will leave a carrot-like track. Because the aerogel is almost transparent, scientists can easily find these particles according to the track.

(4) Military industry

Bulletproof is another important use of the new aerogels. If a layer of aerogel about 6mm thick is added to the metal sheet, then even if it is directly blasted by explosives, the metal sheet will not be injured.

(5) Filtration and catalytic applications

In terms of environmental protection and chemical industry, nanostructured aerogels can also be used as a new type of gas filtration. Unlike other materials, the material has uniform pore size distribution and high porosity, and is a gas filtration material. Aerogels can also be used as adsorption materials, such as adsorption of CO2 gas, adsorption of chemical toxic gases such as benzene, adsorption of explosive wastewater, etc. Due to the material is particularly large than the table and product. Aerogels also have broad application prospects as new catalysts or catalyst carriers.

(6) Application in other areas

   SiO2 aerogelWith high specific surface area and porosity, it has been widely used in Cerenkov detectors in recent years to detect high-energy charged particles. SiO2 aerogels have also been used in plasma studies as target components for inertial confinement melting test bodies.

SiO2 aerogels composed of light atomic weight elements with low density and uniform micropore distribution have good adsorption properties for neon, thus providing a new way to develop high gain targets for inertial confinement fusion experiments, which is of great significance for obtaining cheap and clean energy by using controlled thermonuclear fusion reactions.