Aerogel seems to be an unreal material. Although it looks empty and ethereal, it can easily withstand the heat of a blowtorch or the weight of a car. As the name suggests, this is a colloid in which the liquid is completely replaced by air, which is why it looks like a cloud of smoke. Aerogels can be made of any number of substances, including silica, metal oxides, and graphene. Since air accounts for most of the weight, aerogel is also an excellent insulator. Its structure also gives it ultra-high strength and toughness.

However, aerogels also have a fatal flaw: brittleness, especially when the raw material is silica. But NASA scientists are already experimenting with a flexible aerogel made of polymer as an insulating material for spacecraft as they pass through the atmosphere. Adding other compounds to silica aerogel can enhance its flexibility, coupled with its own lightness, toughness and insulation, which will make it an incredible material.

Silica aerogel is a lightweight nanoporous amorphous solid material with excellent thermal and thermal insulation properties. Its porosity is as high as 80-99.8%, the typical size of the pores is 1-100nm, and the specific surface area is 200-1000m2. /g, and the density can be as low as 3kg/m3, and the room temperature thermal conductivity can be as low as 0.012W/(mk). It is precisely because of these characteristics that aerogel materials have a broad application potential in thermal, acoustics, optics, microelectronics, and particle detection.

Five characteristics of silica aerogel

1. Thermal insulation

Silica aerogel materials have extremely low thermal conductivity, which can reach 0.013-0.016W/(mK), which is lower than the thermal conductivity of static air (0.024W/(mK)) and lower than the corresponding inorganic insulating materials. -3 orders of magnitude, its thermal conductivity is only 0.043W/(mK) even at a high temperature of 800℃. It does not decompose at high temperature and emits no harmful gas. It is a green and environmentally friendly material. After SiO2 silicon aerogel is compounded with various heat-resistant fibers, it can be made into various forms of insulation materials. It can be widely used in industry, construction, pipeline, automobile, aerospace and other fields.

2. Sound insulation

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 (103-107kg/m2.s), and is an ideal acoustic resistance coupling material for ultrasonic detectors. Preliminary experimental results show that silica aerogel with a density of about 300kg/m3 as a coupling material can increase the sound intensity by 30dB. If a silica aerogel with a density gradient is used, a higher sound intensity gain can be expected.

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 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.

4. Filtration and catalytic properties

Nanostructured aerogel can also be used as a new type of gas filtration. The difference from other materials is that the material has a uniform pore size distribution and high porosity, making it a high-efficiency gas filtration material. Because the material is particularly large than the surface product. Aerogels also have broad application prospects as new catalysts or catalyst carriers

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