Silica airgel thermal properties and its application
aerosil is a synthetic amorphous silica, and crystalline silica are significantly different. Silicone molecule is composed of a silicon atom and two oxygen atoms. Shown, there are two basic forms of silica gel follows: amorphous silica and crystalline silica. If the silicone molecule may be arranged neatly and the repetitive pattern is formed, compared with the crystalline silica. If silica gel molecular irregular arrangement, compared with amorphous silica. Silica Aerogels also known as \”blue smoke\”, \”solid smoke\”, it is the lightest known solid material, and so far the best insulation performance material. Because of its low density (3 ~ 250kg / m3), low dielectric constant (1.1 to 2.5), low thermal conductivity (0.013 ~ 0.025W / (m · k)), nano-porous structure having high porosity (1 ~ 100nm), (80 to 99.8%), high specific surface area (500 ~ 1000m2 / g), etc., shown in the aspects of mechanical, acoustic, thermal, optical and other unique properties, in the aerospace, military, oil, chemicals, minerals, communications, medical, building materials, electronics, metallurgy and other fields have a wide range and great value, known as \”change the world of magical material.\” a, thermal characteristics and applications 1, silica thermal properties of nanoporous airgel structure has excellent thermal insulation performance, thermal conductivity than air and even to lower the thermal conductivity of air at room temperature vacuum state was 0.026W / (m · k), and the thermal conductivity of the airgel at normal temperature and pressure is generally less than 0.020W / (m · k), vacuuming under the state, the thermal conductivity may be as low as 0.004W / (m · k). The reason why so airgel has good thermal insulation properties and its high porosity related. The heat conduction mainly takes place via three routes, gas-conducting, solid conduction, radiation, conduction. In these three ways, the heat conduction by the gas is small, so most of the gas has a very low thermal conductivity. Commonly used insulating material is a porous structure, is the use of air which occupies a portion of the volume of the solid material, thus reducing the overall thermal conductivity of the material. Porosity aerogels heat insulating material is much greater than the average, more than 95% are constituted by the air, which determines the air having the same low thermal conductivity. Also included in the airgel pores of large diameter is smaller than 70nm, 70nm isAir, nitrogen and oxygen, the main component of free path (the elapsed time between two collisions of gas molecules from the statistical average), and therefore means that the air convection in the airgel can not be achieved, so that the further gaseous thermal conductivity reduce. The content of the solid framework of the airgel is very small by the nanoparticles, the contact area is very small, so that the same airgel has an extremely small thermal conductivity of a solid. Radiation heat conduction airgel infrared radiation mainly occurs in the region 3-5μm, which can effectively block the infrared radiation at ordinary temperature, but with increasing temperature, infrared radiation enhanced permeability. To further reduce infrared radiation temperature, typically added opacifiers, such as carbon black, titanium dioxide and the like to the airgel, the use of sunscreens can greatly reduce infrared radiation at high temperatures. 2, a silica airgel as a SiO2 airgel nanoporous super thermal insulation material, in addition to having a very low thermal conductivity also have high thermal properties and ultra-light stability, it is of industrial, civil, construction, aerospace and military fields has a very wide range of applications. 1), the conventional industrial fields such as petrochemical industry, chemical industry, metallurgy, etc., piping, furnaces and other thermal equipment prevalent alternative to conventional insulating material airgel insulation material, energy the effect is obvious. Aerogels have a height solar energy transmittance, and low thermal conductivity is almost no reflection loss of incident light, sunlight can be transmitted efficiently, and therefore particularly suitable for use airgel solar collectors and other heat collecting apparatus insulation material, when sunlight enters through the airgel inside the collector, the internal systems of sunlight energy into thermal energy, aerogels can effectively prevent heat loss. 2), since the construction of energy-saving airgel having both heat insulating properties, but also has sound absorption characteristics, and has a light-transmissive, and therefore the airgel can be sandwiched between the sandwich is made of double-glazing glass, its insulating effect than ordinary double glazing several times, and has a noise reduction effect. Such glass windows for houses, can greatly reduce heat loss, a significant energy saving effect, an interlayer airgel glazing rate of heat loss (hydrogen filling ratio of the best window based and low emission of indium oxide or silver as a coating) but also two-thirds reduction. If the airgel glass for high-rise buildings instead of the general glass curtain wall, will greatly reduce the weight of buildings, and can play a role in fire prevention.3), compared with the conventional aerospace insulation materials, SiO2 airgel insulation material may be lighter mass, smaller volume to achieve better insulation effect, this characteristic has a pole aerospace applications big advantage. Airgel insulation can be used as sound deadening material used on the aircraft. According to reports, the space shuttle and spacecraft during re-entry to undergo high-temperature incandescent thousands of degrees Celsius, its safe return to Earth to protect the insulation material is the SiO2 airgel. In the United States NASA \”Mars Rovers\” design, the use of the SiO2 aerogels as insulation, to withstand the extremely low temperatures of the Martian night. 4), military field SiO2 airgel insulation layer material may be used as an aircraft cabin. Efficient heat insulating material can be used as submarines, missile destroyers steam power reactors, evaporators, steam boilers as well as complex high-temperature piping system can be enhanced thermal insulation effect, reducing the temperature of the cabin, while effectively reducing the amount of insulating material, by the use of large cabin space, improve various work environments. 5), with the appliance substituted massive, granular or powdered aerogels flon polyurethane foam as heat insulating material emptive cryogenic refrigerator systems, gas leakage can be prevented Freon destroy the ozone layer, to protect the survival of mankind surroundings. 6), the silica airgel as garment linings warm winter clothing may cause both light and warm clothing.