As we all know, the heat energy on the earth's surface mainly comes from sunlight, and the spectrum of sunlight is mainly concentrated in the range of 200-2500nm, of which: the range of 200-400nm is ultraviolet, its energy accounts for about 5% of the total energy of sunlight, and the range of 400-720nm The inner part is visible light, whose energy accounts for about 45% of the total energy of sunlight, and the range of 720-2500nm is infrared, whose energy accounts for half of the total energy of sunlight.
Infrared rays are invisible to the human eye. Therefore, how to effectively block the infrared rays and improve the heat insulation performance of glass without affecting the transmission of visible light is one of the most difficult points in domestic and foreign technology research and development. At present, the research and development of high-quality, high-permeability heat-insulating film is mainly concentrated in developed countries such as the United States and Japan. "Although there are many methods for blocking sunlight in the prior art, each has many problems." Lu Fei said.
Lu Fei explained its shortcomings to reporters by taking Low-E glass (Low-E), the most commonly used building insulation glass, as an example. This type of glass achieves the thermal insulation effect by coating the surface of ordinary glass. However, after extensive use of this type of glass on the exterior wall of the building, although it has good heat preservation and heat insulation properties for the building itself, it will reflect a lot of sunlight and cause a lot of light pollution problems.
People working in a light-polluted environment for a long time can cause vision loss, dizziness, insomnia, heart palpitations, decreased appetite, and depression, which seriously affect people's physical and mental health. In addition, Low-E glass cannot obtain heat insulation on the surface of the glass through post-painting and other methods. In addition, due to the oxidation of the metal layer, the life of the surface layer is much lower than that of the glass itself, which makes Low-E glass unable to be used as It is used to upgrade the existing architectural glass.
In addition, colored glass absorbs visible light while absorbing heat. It will greatly sacrifice visible light transmittance while achieving heat insulation, and present obvious colors, which greatly limits its need for high visible light such as car front windshields. Through the application of the scene.
"At present, cesium tungsten bronze, a widely used infrared absorbing material in commercial applications, has a good infrared absorbing effect. However, it will exhibit photochromic phenomenon under ultraviolet radiation, and will interact with water and oxygen under heating. An irreversible oxidation reaction occurs, generating tungsten trioxide and losing its infrared absorption properties." Yin Jian said.
A new thermal insulation coating comes out
From the above analysis, it can be seen that the thermal insulation principle of traditional Low-E glass and glass products is to achieve the thermal insulation effect by coating the surface of ordinary glass. After coating, Low-E glass can reflect far infrared rays with wavelengths above 2500nm. , But it can also cause pollution. Absorbing photons may be a better choice.
"We are also inspired by the phenomenon of localized surface plasmon resonance (LSPR), because the surface electrons of gold nanobelts with a certain aspect ratio can resonate with incident photons of a certain frequency, and strongly absorb the incident photons before passing through Adjusting the particle size and morphology of the material can achieve selective absorption of infrared photons, which can be made into infrared absorbing materials." Lu Fei said.
According to Lu Fei, the coating they made is based on rare earth compounds. On the one hand, because boron atoms have strong electronegativity, they can form a strong force with rare earth elements, making the rare earth nano thermal insulation materials formed. Good acid and alkali resistance; on the other hand, in the formed rare earth nano boride material, the outer layer electrons of the rare earth element itself provide a large number of free electrons. When the photons of incident light are excited, the free electrons resonate with the incident photons. Thus, the macroscopic performance is the heat absorption capacity.
In addition, by adjusting the type and doping amount of rare earth elements, the wavelength range where incident photons resonate can be further controlled. Using this method, the R&D team successfully developed a high-performance rare earth nanocomposite thermal insulation material with good weather resistance, which solved the problem of insufficient environmental stability of existing materials and the inability to absorb infrared spectra.
"The coating we developed has a red and ultraviolet barrier greater than 90%, a visible light transmittance greater than or equal to 70%, and its thermal insulation effect, convenience and stability are superior to similar glass films, Low-E glass and insulating glass. Products.” Wen Yongqing said. They have also done several experiments. Taking the comparison of the effects of LOW-E insulating glass and thermally insulating rare earth laminated glass as an example, under the same conditions, the double silver LOW-E insulating glass and thermally insulating rare earth The laminated glass is placed in front of the infrared lamp, the infrared heat value of double silver LOW-E insulating glass is 3417, the ultraviolet value of double silver LOW-E insulating glass is 4857, the blocking rate is 50%, and the infrared heat value of thermal insulation rare earth laminated glass It is 320, the ultraviolet value of the insulating rare earth laminated glass is 19.4, and the barrier rate is as high as 99.8%.
It can be seen that even the double-silver LOW-E insulating glass with excellent performance on the market currently lags behind the single-layer RE laminated glass using heat-insulating rare earth technology in terms of heat insulation, sun protection and energy saving.
Coating application helps my country's green development
In November 2019, the Rare Earth Research Institute and Yitujiewei Technology established a joint laboratory for thermal insulation rare earths to jointly promote the industrialization of new rare earth nano thermal insulation coatings. The preparation technology of new rare earth nano thermal insulation materials and coating industries has made breakthroughs. .
"At present, we have built the first domestic pilot production demonstration line of rare earth nano thermal insulation slurry with a monthly output of 800 kg, which can save energy by 25%-40%." said Yang Jue, general manager of EasyTujiewei Technology, the developed coating The index is equivalent to or even better than that of foreign products. At the technical level, it has realized "curve overtaking", filled the gap of domestic insulation glass coating materials, and can completely replace imported products.
As we all know, solar heat mainly exists through infrared radiation, and has the characteristics of high temperature to low temperature transfer.
Therefore, the outdoor high temperature in summer will rush indoors, causing the air conditioning load to increase, and red/ultraviolet rays can make the human skin feel hot; the coating can produce plasma resonance effect with light waves in the range of 200-400nm and 700-2500nm, radiating heat energy Can not penetrate the coating, it can achieve good heat insulation and sun protection performance. At the same time, because the radiant heat energy is blocked, the indoor temperature cannot rise rapidly and continuously, which reduces the air conditioning load, greatly saves air conditioning costs, and achieves energy saving. purpose.
In winter, the essence of indoor heat source heating is still infrared light, which is the internal vibration of particles propagating electromagnetic waves. Therefore, heating electromagnetic waves cannot effectively penetrate the heat-insulating rare earth coating (plasma resonance), and the heat source is left in large quantities. Indoors, the heating will heat up faster, the locking and heat preservation will be better, super energy saving.
The problem of building energy consumption is particularly severe in China. The total building area in our country is huge, and more than 90% of it uses ordinary glass. According to my country’s energy-saving targets in 2010, an average of about 1.32 billion square meters of thermal insulation glass is added every year, and the market demand for rare earth nano thermal insulation materials is huge.