1. Definition and origin of aerogels
The term "aerogel" derives from its unique properties. Among them, "aero" means flight, while "gel" means gel, which together means a gel like substance capable of light flight. This material undergoes special drying processes to remove internal solvents while maintaining its original shape. It also has high porosity and low density, allowing it to float lightly in the air.
Aerogel is the lightest solid in the world, with its pore size reaching nanometer level, covering many categories such as silicon, carbon, sulfur, metal oxide and metal systems. Although American scientist Kistler had made aerogel in 1931, it was not until recent years that small-scale production was realized with the development of supercritical technology.
The microstructure of aerogel is a nano porous network formed by the coalescence of colloidal particles or polymer molecules. Its porosity is as high as 80% to 99.8%, and the pore size is between 1 and 100 nm. This gives it a specific surface area of up to 200 to 1000 square meters per gram and a density of 3 to 600 kilograms per cubic meter. This three-dimensional nano network porous material is almost entirely filled with gas inside, giving it a unique visual effect. For example, placing SiO ₂ aerogel on a dark background will show blue, while it will be almost transparent on a light background. Although it is not as transparent as glass, it has attracted much attention due to its high concealment and low visibility.

2. Unique characteristics of aerogel
Aerogels are famous for their lightweight texture, high porosity and low density. This material not only presents a unique visual effect, but also demonstrates its extraordinary qualities in concealment and visibility. Although its transparency is less than that of glass, the high concealment and low visibility of aerogel make it an ideal choice for many fields.
1) Excellent thermal insulation performance
Aerogel stands out for its excellent thermal insulation. Its thermal conductivity ranges from 0.012 to 0.024W/(m · K), which is 2 to 3 orders of magnitude lower than traditional insulation materials. This is due to its uniform and dense nanopores as well as multi-level fractal pore structure, which work together to effectively block air convection and reduce thermal radiation and conduction. Specifically, the thermal insulation mechanism of aerogel is reflected in three aspects: (1) no convection effect: its nano pores make the internal air lose the ability of free flow; (2) Countless shielding effect: There are numerous nanoscale pore walls, which minimize radiative heat transfer; (3) Infinite path effect: Heat conduction mainly occurs along the pore walls, while the length of nanoscale pore walls tends towards infinity.
2) Energy conservation and emission reduction, high material utilization rate
The thermal insulation performance of SiO ₂ aerogel thermal insulation felt is significantly better than that of traditional materials, which can be improved by 2 to 8 times. Taking pipe insulation as an example, for pipes with a diameter of 150mm, to achieve the same insulation effect, the thickness of expanded perlite, calcium silicate, rock wool and aerogel felt is 90mm, 76mm, 64mm and only 20mm respectively. It can be seen that aerogel has significant advantages in energy conservation, emission reduction and efficient utilization of materials.
3) Excellent durability
The durability of aerogel is about four times that of traditional thermal insulation materials. Traditional insulation materials, such as rock wool and polyurethane, are prone to absorbing water during long-term use, resulting in uneven distribution and damaging the insulation effect and service life. However, the hydrophobic rate of aerogel is up to 99%, which ensures that it can still maintain a stable structure and excellent thermal insulation performance in long-term use.
4) Strength and toughness need to be improved
Although aerogels perform well in many aspects, they also have some shortcomings, such as relatively low strength and poor toughness. To overcome these drawbacks, researchers often enhance their mechanical properties by adding reinforcing materials such as particles and fibers. At the same time, in order to enhance the shielding ability of aerogel, carbon black, ceramic fiber and other shading agents will also be introduced. Based on these improvements, aerogel products were born. They not only retain the excellent thermal insulation performance of aerogel, but also enhance other required characteristics. These products cover a variety of forms, such as aerogel felt, aerogel paper, aerogel cloth and board, providing a variety of options for different application scenarios.

4. Aerogel is widely used
As a high performance thermal insulation material, aerogel has a wide range of applications. It can not only be used in the aerospace industry, but also widely applied in multiple industries such as energy, chemical, and construction. At the same time, improved aerogel products, such as aerogel felt and aerogel paper, also provide more possibilities for the application of aerogel. These products not only retain the excellent thermal insulation performance of aerogel, but also enhance other required properties, thus meeting the needs of different application scenarios.
1) Applications in the Aerospace Field
Compared with traditional thermal insulation materials, aerogel shows significant advantages in the aerospace field with its excellent thermal insulation performance. Its lightweight and compact characteristics make it possible to significantly reduce the weight of aeroengines while providing excellent thermal insulation protection under the same thermal insulation effect.
2) Application in the field of industrial insulation
In the field of industrial insulation, aerogel also shows its unique advantages. Due to the limitations of some specific parts and environments, such as weight, volume and space, aerogels play a key role in these occasions due to their excellent thermal insulation performance. In addition, aerogel also has the characteristics of high temperature resistance and fire resistance, making it a more appropriate choice for thermal insulation of equipment in the chemical field.
3) Applications in the field of architecture
Aerogel and its composite materials, such as gel felt/board, aerogel thermal insulation mortar, aerogel gel sunlight board and aerogel gel thermal insulation coating, have shown excellent energy-saving effect in the construction field. The application of these materials effectively improves the insulation performance of buildings and reduces energy consumption.
4) Applications in the field of transportation
Aerogels play an important role in the field of transportation, especially vehicles such as automobiles, high-speed railways and subways. Its fireproof, heat-insulating, and noise reducing layer can significantly improve the safety of vehicles. At the same time, the use of large capacity battery pack fireproof, waterproof, and insulation boxes also provides strong guarantees for the safety performance of new energy vehicles. In addition, the thermal insulation and fireproof layer of aerogel also plays a vital role in special transport vehicles such as hazardous chemical transport vehicles and liquefied natural gas transport ships.
5) Applications in the field of environment
With its huge specific surface area and unique nano porous network structure, aerogels show excellent adsorption capacity, which is 6 times that of activated carbon. Therefore, it has a wide range of applications in wastewater treatment, water purification, oil pollution adsorption, and VOCs gas adsorption, and its green and environmentally friendly characteristics are also highly praised.
6) Applications in other fields
Because of its excellent thermal insulation performance, aerogel is often used as the filling layer of insoles, sports shoes and clothing to achieve effective thermal insulation in low temperature environment. In addition, the high-end cosmetics industry and sporting goods industry have also integrated aerogels into their products, using their unique properties to improve the performance of products.

5 Conclusion
At present, the price of aerogel and its composites is relatively high, especially the price of aerogel felt, which reaches nearly 200 yuan/m2, resulting in its low penetration rate in the building energy conservation market. Nevertheless, the application of aerogel in high-end cosmetics and sporting goods has gradually become popular, showing its unique performance advantages. According to the estimated output value of 1.59 billion yuan in the domestic aerogel industry in 2020 and the demand of about 7% in the construction industry, the sales volume of aerogel for building materials is about 100 million yuan. Further analysis of the market demand for building exterior wall insulation materials shows that the permeability of aerogel is only 0.02% in 2020. Assuming that by 2025, this penetration rate can increase to 0.12%, then the demand for aerogel in the domestic building exterior wall insulation market will reach 137000 m3. With people's in-depth understanding of aerogels and the continuous improvement of technological maturity, its application market will undoubtedly usher in greater development space.