Application of SiO2 Aerogels Materials in Construction
SiO2 aerogels materials is a kind of nanostructured material with high transparency and very low thermal conductivity. These properties make this material has a wide range of applications in the construction field. This paper mainly introduces the performance characteristics of aerogel materials, the research and application status of this material at home and abroad, and discusses the problems to be solved in the further application of SiO2 aerogel materials in building materials.
SiO2 aerogel material
Aerogels, a porous, lightweight material that was discovered 70 years ago, Kistler S. of the Pacific University of California in 1931 used supercritical drying to remove moisture from the hydrogel and got the first There is no shrinkage of the aerogel material and many potential good properties of the aerogel material have been developed over the course of many years of development and evolution. Now we are saying that the SiO2 aerogel materials is composed of a nano-SiO2 framework It has a porosity of 99%, a density of 0.05-0.2 g / cm3, a gel size of less than 50 nm, a pore diameter less than the mean free path of the molecule, a thermal conductivity of 0.03-0.05 W / m K Therefore, the best application is its porosity and super thermal insulation properties.
Construction Industry around the world on the application of SiO2 aerogels materials
The application of SiO2 aerogels materials in construction is still blank in China. The current research mainly focuses on the development of high value-added application products such as aerospace and pharmaceutical carriers. In foreign countries, since 2000 for the construction of aerogel materials have been a certain amount of research and application. Now the main research directions are air-energy-saving windows, aerogelcoatings, aerogel new panels and roof solar collectors.
1. Aerogel energy-saving window
In 2000, a Russian company first developed a new type of aerogel glass used in the field of building materials. This kind of glass looks similar to ordinary glass in terms of appearance and transparency, but it has extremely high heat resistance, flame retardant, anti-radioactive radiation, and can also tone and absorb sound.
Filling a double layer of glass with a transparent insulating material is a way to reduce heat transfer through the glass layer. SiO2 aerogels materials have a very small pore structure, much smaller than the wavelength of visible light. In aerogel, air occupies about 95% to 99% of the volume in pores that are smaller than the mean free path of air. As the aerogel has sufficient compressive strength, can balance the outside air pressure, vacuum aerogel window can be used as a transparent separator. And since the evacuated aerogel is opaque to most infrared radiation, the net radiative heat loss through the aerogel window is minimal. At present, the research on aerogels focuses on the development of thermal insulation products with high transparency, good durability, large blocks and low cost.
Reim M and others at the ISOTEG joint project have developed a new architectural aerogel for roofing insulation that meets both thermal and optical properties and is starting to be used.
2.SiO2 aerogel material sheet
The use of SiO2 aerogel materials production of new insulation panels is now one of the focuses of research at home and abroad. It is a moisture-proof, mildew-proof, germicidal, UV-resistant, fully recyclable material that is non-flammable and has no damaging effect on the ozone layer during its production. Its granular morphology can be tightly compressed into a sandwich structure with a composite structure. The new sheet has a light transmission of 20% and a heat transfer coefficient of only 0.05 W / (m2 · K).
In January 2003, a new roof skylight system from Kalwall was installed on the roof of an indoor hot tub at a small hotel in Manchester. The system achieved good results with the new technology Nanogel sandwich panels instead of the Kalwall sandwich panels that have been used for decades. The new sunroof system at the same time enhance the translucency and did not produce ventilation in its insulation effect, but also does not lose heat in the heavy snow in winter, the hot pool temperature can not melt the snow covered skylight .
3 Roof solar collector
Abroad, aerogel has been used in roof solar collectors for a long time. In the civilian sector, the efficient insulation of solar water heaters and other heat-collecting devices has become a key factor in further enhancing the energy efficiency of solar installations and further enhancing their practicality. As the production technology of nanoporous super insulation material continues to mature and production costs continue to decline, the material is first applied to solar water heaters in homes and units. The application of nanoporous super thermal insulation to water heaters in water storage tanks, pipelines and collectors will more than double the heat gain of existing solar water heaters and reduce heat loss to less than 30% of existing levels.
A new type of aerogel vacuum collector was developed in 2001. The front of the collector is filled with granular aerogel and the back is made of opaque amorphous silicon as the insulation material. The main feature of this particle-filled aerogel is the production process and particle collocation. There are pores between the particles, and the thermal conductivity of the obtained aerogel material is somewhat different from that of the bulk aerogel. Therefore, to control the particle collocation in the aerogel manufacturing process, the air gap can be minimized.
The current problem to be solved
1. The supercritical production line requires a large investment, high cost, high-pressure equipment operation danger.
2. The use of atmospheric drying and supercritical drying shrinkage problems.
3. Solvent exchange / surface modification, atmospheric drying process For large-scale production of aerogel, how to steadily improve the reaction rate and speed up the permeability of the modified liquid.
4. In the construction of the application, should consider what kind of application form.
Conclusion
SiO2 aerogels materials with excellent heat insulation, sound insulation and good light transmission make it a foundation for the development of new eco-friendly building materials. Although this eco-friendly building materials in the construction market is still in the promotion stage, but its development prospects are very optimistic. As China's building energy efficiency requirements continue to increase, and the academic community of SiO2 aerogelis materials also deepening understanding of the development of SiO2 aerogel-based raw materials for ecological materials is our future research direction.