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, building 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 its thermal insulation lies in the uniform and dense nanopores and multi-level fractal pore microstructures, which 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 less aerogel is used under the same thermal insulation effect. Taking the pipeline as an example, if the pipeline with a diameter of 150mm needs to achieve the same insulation effect, the thickness of the corresponding insulation materials used, such as 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 combined insulation method 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.
Core advantage of aerogel materials - thermal insulation
In addition, aerogel has the advantage of a long service life, which is about 4 times that of traditional thermal insulation materials. Traditional thermal insulation materials such as rock wool and polyurethane are easy to absorb water during long-term use, which affects the thermal insulation effect on the one hand, and on the other hand, the thermal insulation materials are unevenly distributed due to gravity after absorbing water, especially in the use scenario of pipeline insulation, which easily causes the thermal insulation materials to accumulate at the bottom of the pipeline, ultimately affecting the service life. Aerogel has excellent waterproof effect, and its hydrophobicity is more than 99%, which can still maintain a stable structure and thermal insulation effect during long-term use.
Currently, commercial aerogels are usually composite products and have 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 their precursors: 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 share of silica aerogel was as high 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 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 relatively low, it has more impurities and is currently mainly used in atmospheric pressure drying.
Core advantage of aerogel materials - thermal insulation
Aerogel products use nano-aerogels and glass fiber, ceramic fiber and other substrates to perfectly combine aerogels with excellent performance with flexible substrates, which maximizes the retention of aerogels' lightweight and thermal insulation properties, and gives aerogels flexibility and toughness. With the additional characteristics of ultra-long service life, super thermal insulation, 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 substrate aerogel insulation pad (temperature resistance 1050℃)
SiO2, aerogel composite material with ceramic fiber as the substrate is made by embedding silicone frame laminating process.
2. Pre-oxidized silk substrate aerogel insulation pad (temperature resistance 450℃)
SiO2 aerogel composite material with pre-oxidized silk as the substrate. 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°C)
The SiO2-aerogel composite material based on glass fiber is made by embedding in a silicone frame and coating.
