Aerogel is a new generation of high-efficiency energy-saving thermal insulation material. Aerogel is a solid material with a nanoporous network structure and a gaseous dispersion medium in the pores. It is the lightest solid in the world. Due to its unique structure, aerogel has excellent performance in many fields such as thermal, acoustic, optical, electrical, and mechanical. At present, the commercial application of aerogel is mainly based on its high-efficiency heat resistance. It is used in many fields such as petrochemical, thermal network, lithium battery, construction materials, outdoor clothing, aerospace, and military industry.
The heat resistance principle of aerogel is the non-convection effect, infinite shielding effect, and infinite path effect brought by its independent structure. The thermal conductivity of aerogel is 0.012~0.024W/(m·K), which is 2~3 orders of magnitude lower than that of traditional thermal insulation materials. The principle of thermal insulation is that the uniform and dense nanopores and multi-level fractal pore microstructure can effectively prevent air convection and reduce thermal radiation and heat conduction:
1) No convection effect: the pores of aerogel are nanoscale, and the internal air loses the ability to flow freely;
2) Infinite baffle effect: nanoscale pores, infinite pore walls, and radiation heat transfer is reduced to a minimum;
3) Infinite path effect: heat conduction is carried out along the pore wall, and the nanoscale pore wall is infinitely long.
Compared with traditional thermal insulation materials, the thermal insulation performance of silica aerogel insulation felt is 2-8 times that of traditional materials, so the amount of aerogel used is less under the same thermal insulation effect. Taking the pipeline as an example, if a pipeline with a diameter of 150mm needs to achieve the same insulation effect, the thickness of the corresponding insulation materials, expanded perlite, calcium silicate, rock wool, and aerogel felt, are 90mm, 76mm, 64mm, and 20mm, respectively. According to the calculation of Sinopec Tahe Refining, after the atmospheric coking unit was transformed from traditional insulation materials to a combination of "silicon dioxide aerogel insulation felt + single-sided aluminum foil glass fiber cloth insulation material", the heat loss was reduced by 34.7%, and the thickness of the insulation layer was reduced by more than 50% compared with traditional insulation materials.
In addition, aerogel has the advantage of a longer service life, which is about 4 times that of traditional insulation materials. Traditional insulation materials such as rock wool and polyurethane are easy to absorb water during long-term use, which affects the insulation effect on the one hand, and on the other hand, the insulation material is unevenly distributed due to gravity after absorbing water, especially in the use scenario of pipeline insulation, which easily causes the insulation material to accumulate at the bottom of the pipeline, ultimately affecting the service life. Aerogel has excellent waterproof effect, with a water repellency of more than 99%, and can maintain a stable structure and thermal insulation effect during long-term use.
Currently, commercial aerogels are usually composite products with various forms. Aerogels have disadvantages such as low strength and poor toughness, so it is necessary to improve the strength and toughness by adding reinforcements such as particles and fibers, and to improve the radiation shielding ability by adding sunscreens such as carbon black and ceramic fibers. Therefore, the aerogel products currently on sale are often made of aerogel materials and substrates. According to the product form, aerogel products can be divided into aerogel felt, aerogel paper, aerogel cloth, aerogel sheet, aerogel powder, aerogel slurry, aerogel coating, etc.
1. The lowest density of solid <1.5mg/mL
2. The smallest pore size 1~100nm
3. The highest porosity >99.9%
4. The highest specific surface area 200-1000 m2/g
5. The lowest thermal conductivity: up to 0.013 w/(km) at room temperature and pressure
6. Excellent fire resistance: fire rating A1, smoke rating AQ1
7. Super hydrophobicity: water increase rate >99%
8. The lowest sound propagation speed <70m/s
9. The lowest dielectric constant <1.003
10. The lowest refractive index <1.0003

There are many types of aerogel materials, among which SiO2 aerogel has the most mature commercial application. Aerogels can be divided into seven categories according to the precursor: oxides, carbides, polymers, biomass, semiconductors, non-oxides, and metals. Many different precursors can be used to prepare aerogels with different properties, which greatly enriches the diversity of aerogel varieties and expands the application range of aerogels. At present, the application of SiO2 aerogel is the most mature in the market. In 2019, the global silica aerogel accounted for as much as 69%.
Silica aerogel precursors can be divided into organic silicon sources and inorganic silicon sources. Commonly used organic silicon sources are functional silanes such as methyl orthosilicate and ethyl orthosilicate, and inorganic silicon sources include silicon tetrachloride and water glass. Compared with inorganic silicon sources, organic silicon sources are more expensive, but they have high purity and good process adaptability, and can adapt to supercritical drying and atmospheric pressure drying. Although the price of inorganic silicon source water glass is lower, it has more impurities and is currently mainly used in atmospheric pressure drying.
Aerogel products use nano-aerogels and glass fiber, ceramic fiber and other substrates to perfectly combine aerogels with excellent performance with flexible substrates, maximize the retention of aerogels' lightweight, heat insulation and other characteristics, and give aerogels flexibility and toughness. With the additional characteristics of ultra-long service life, super insulation performance, ultra-high fire resistance, and super mechanical properties, aerogel products are widely used in military aerospace, thermal pipe network, petrochemical, new energy vehicles, power batteries, rail transit, consumer electronics, and textiles.
1. Ceramic fiber-based aerogel insulation pad (temperature resistance 1050℃)
SiO2, aerogel composite materials based on ceramic fiber are made by embedding silicone frame laminating process.
2. Pre-oxidized silk-based aerogel insulation pad (temperature resistance 450℃)
SiO2 aerogel composite materials based on pre-oxidized silk. It is made by embedding silicone frame laminating process. It can also be directly applied by spraying flame retardant adhesive.
3. Glass fiber-based aerogel insulation pad (temperature resistance 650℃)
SiO2, aerogel composite materials based on glass fiber are made by embedding silicone frame laminating process.