Thermal Properties and Application of Silica Aerogel
2018-01-09 14:47:06 From: Tradematt-Aerogel
Silica aerogel is a synthetic amorphous silica gel that is significantly different from crystalline silica gel. Silicone molecules consist of one silicon atom and two oxygen atoms. As shown below, there are two basic forms of silica gel: amorphous silica and crystalline silica gel. If the silicone molecules are arranged neatly and form a repeatable pattern, it is crystalline silica gel. If the silicone molecules are not aligned, then amorphous silica gel.
Silica aerogel, also known as "blue smoke", "solid smoke", is the lightest solid material known to date and is by far the best thermal insulation material. Because of its high porosity (1 ~ 100nm), low density (3 ~ 250kg / m3), low dielectric constant (1.1 ~ 2.5) and low thermal conductivity (0.013 ~ 0.025W / (m · k) (80-99.8%) and high specific surface area (500-1000m2 / g). It has unique properties in mechanics, acoustics, heat and optics, and has unique properties in aerospace, military, petroleum, chemical, Medical, building materials, electronics, metallurgy and other fields have a wide range of great value, known as "the magic of changing the world."
- The thermal properties of silica aerogel
Aerogel nano-porous structure so that it has excellent thermal insulation properties, the thermal conductivity even lower than air, air at room temperature vacuum thermal conductivity of 0.026W / (m · k), while the aerogel Glue at room temperature and pressure under the general thermal conductivity of less than 0.020W / (m · k), in the vacuum state, the thermal conductivity can be as low as 0.004W / (m · k).
The reason why the aerogel has such a good thermal insulation properties is related to its high porosity. Aerogel porosity is much greater than conventional insulation, and more than 95% of it is made of air, which determines that it will have the same low thermal conductivity as air. Moreover, aerogels contain a large number of pores with a pore size of less than 70 nm. 70 nm is the free path of nitrogen and oxygen as the main components in the air, which means air can not be convected in the aerogel and the gaseous thermal conductivity is further reduced. A very small amount of aerogel solid skeleton is also composed of nanoparticles, the contact area is very small, making the aerogel also has a very small solid state thermal conductivity. The thermal radiation conduction of aerogels mainly occurs in the 3-5 μm region of infrared radiation, which can effectively block the infrared heat radiation at room temperature, but with the increase of temperature, infrared radiation transmittance enhancement.
- The application of silica aerogel
As a nanoporous super thermal insulator, SiO2 aerogels not only have extremely low thermal conductivity, but also have super light weight and high thermal stability. They are very useful in industrial, civil, architectural, aerospace and military fields Wide range of applications.
1, The traditional industrial areas
Such as petrochemical industry, chemical industry, metallurgical industry, etc., pipelines, furnaces and other thermal equipment ubiquitous, with aerogel insulation materialto replace the traditional insulation materials, energy-saving effect is obvious. Solar aerogel with a high degree of light transmittance and low thermal conductivity of the incident light with little reflection loss, can effectively penetrate the sun, so the aerogel is particularly suitable for use as a solar collector and other heat collection device Thermal insulation materials, when sunlight through the aerogel into the collector, the internal system of solar energy into heat, aerogel and can effectively prevent the loss of heat.
2, Energy-saving building
As the aerogel has both adiabatic characteristics, but also has sound absorption properties, and has translucency, so the aerogel can be sandwiched between double-glazing made of sandwich glass, the insulation effect than ordinary double-glazed glass Several times, and has a noise reduction effect. The use of such glass for windows in houses can greatly reduce heat loss and provide significant energy savings. aerogel interlaced glazings have a higher heat loss rate than the best window systems currently available (hydrogen filling and low emission Rate of indium oxide or silver coating) is also reduced by two-thirds. If the aerogel glass is used in high-rise buildings instead of the general glass curtain wall, will greatly reduce the weight of the building, and can play a fireproof role.
Compared with traditional insulation material, SiO2 aerogel insulation material can achieve better thermal insulation effect with lighter mass and smaller volume, which has great advantages in aviation and aerospace applications. Aerogel can be used as an aircraft insulation sound-deadening material. According to reports, spacecraft and spacecraft to go back to the atmosphere to go through incandescent temperatures of thousands of degrees Celsius, to protect their safety back to Earth insulation material is SiO2 aerogel. NASA in the United States in the "Mars rover" design, the use of SiO2 aerogel insulation layer, used to resist Mars night cryogenic.
4, The military field
SiO2 aerogel can be used as the aircraft cabin insulation material. Can be used as nuclear submarines, steam destroyer nuclear reactors, evaporators, boilers and complex high-temperature steam pipe system, efficient insulation materials, can enhance the insulation effect, reduce the cabin temperature, while reducing the amount of insulation materials, increased Large space within the use of space, effectively improve the working environment.
5, Home appliances
Replacing Freon-made polyurethane foam with chunky, granulated or powdered aerogels as a heat insulation material for refrigerators and other cryogenic systems can prevent Freon gas from leaking and destroying the atmospheric ozone layer, thus protecting the human environment.
Using silica aerogel as a lining for winter warm clothing can make the garment lightweight and warm.