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Properties and applications of silica aerogels
- Time of issue:2022-04-08 16:56
Properties and applications of silica aerogels
Silica Aerogels have excellent properties such as high porosity, low density, very low sound transmission speed, very low dielectric constant, and high specific surface area. Due to these outstanding characteristics, aerogels are expected to be "magic materials to change the world". They have broad application prospects in the fields of heat, optics, acoustics, microelectronics, catalysis, aeronautics and Astronautics, energy saving building and so on.
The microstructure of aerogels determines its thermal conductivity in a very low range, which is an important feature of aerogels. For example, the thermal conductivity of SiO2 aerogels is usually 0.015W/m. K, which is an excellent thermal insulation material. It can be widely used in the field of thermal insulation, such as equipment insulation, pipeline insulation, building external wall insulation, etc. This is the main application direction of large-scale aerogel production.
Silica Aerogel materials are increasingly used in Aeronautics and Astronautics and navigation as insulation materials. It is reported that during the operation of spacecraft, the temperature at night will generally be lower than - 70 degrees Celsius, and when the aerogel composite material is used to heat the spacecraft, the temperature inside the spacecraft can be kept at room temperature (around 25 degrees Celsius). This way, when the external temperature is extremely low, the electronic equipment inside the spacecraft will not be affected by temperature and can perform the task normally.
Application in acoustic field
The sound propagation in silicaaerogel materials depends on the porosity and aerogel density in the gel gap. In the process of gel network propagation, the sound wave is attenuated due to the gradual transfer of wave energy, so the amplitude and speed are greatly weakened. This makes aerogels very suitable for acoustic insulation devices. Because of its low sound speed, silica aerogels are ideal acoustic delay and high temperature sound insulation materials.
Application in optical field
The optical transmission and scattering properties of silica aerogels are another important characteristic of aerogels. They can make aerogel materials into transparent thermal insulation windows, which not only have the function of conventional glass, but also play a role of thermal insulation. They are expected to be widely applied in buildings and buildings. In addition, although there is a certain degree of scattering, the transparency and visible light transmittance of aerogels are very high and can be used as a window for high temperature observation.
Application in the field of electricity and catalysis
The relative permittivity of aerogel is very low (1<e<2), and the dielectric constant can be adjusted by changing its density. Therefore, aerogels can be made into ultra-low dielectric constant IC materials. The dielectric constant is very low and can be adjusted. Its thermal expansion coefficient is similar to that of silicon material, so the stress is very small. Moreover, compared with polyimide, aerogels have good high temperature stability. Therefore, if the substrate material used in the integrated circuit is changed into aerogel film, its operation speed can be increased by 3 times, and aerogels show great potential in the field of electricity.
Adsorption and storage performance
Because aerogels are composed of nanoparticle framework, high permeability three-dimensional nanostructure, high specific surface area and porosity, and holes are interlinked with the outside world, it has very good adsorption characteristics, and has great application value in gas filters and adsorption media.
The ultra-high porosity of aerogels makes them exhibit high brittleness and fragility in mechanical properties, especially for many inorganic aerogels. The weak mechanical properties are the key factors hindering their application. At present, the mechanical properties of inorganic aerogels are enhanced from 3 aspects. From the macro level, the elastic properties of composite aerogels can be significantly improved by using fiber as substrate and inorganic aerogels. From the particle level, by combining inorganic aerogels with some organic compounds, such as epoxy resin and polystyrene, the skeleton structure of inorganic aerogels can be enhanced, so as to enhance its mechanical properties. From the molecular level, the use of precursors containing different organic substituents can improve the mechanical properties of inorganic aerogels, which is widely used in the preparation of silica aerogels.
In addition to the characteristics of high brittleness and friability, another important mechanical property of aerogels is that these materials have very low modulus. The Young 's modulus of aerogels is 106N/m2 order of magnitude, 4 orders of magnitude lower than that of the corresponding glass state. The extremely low modulus makes aerogels possess the characteristics of shock resistance and impact resistance. If it is further made into block material with gradient density, it can be applied to the capture of high speed particles in space.
Application in medical field
Silica Aerogels in carbon aerogels have high porosity and biocompatibility and biodegradability, so they are widely used in medical field. Possible applications include diagnostic agents, artificial tissues, artificial organs, organ components, etc. The biological characteristics of aerogels are especially suitable for drug controlled release systems. They have high drug loading and are suitable for the low toxicity and high efficiency of the extra gastrointestinal drug delivery system.