Technology Oct 28

Rare earth coating for glass can save energy by 25-40%, Baotou says

Researchers from the Chinese group's research institute believe they have developed a product that can help to greatly reduce the amount energy used by buildings all across the country

Rare earth coating for glass can save energy by 25-40%, Baotou says
The town of Baotou in Inner Mongolia is the hub of rare earth production in China, which dominates the global trade in the 17 rare earth minerals partly because countries like the US lack processing plants. File photo by AFP.

(ATF) In a news release in China, the Baotou Rare Earth Research Institute has announced the group's main innovations in the use and application of rare earth elements. One finding considered of national significance is a compound that, when applied to glass, can stop heating loss by 20-45%.

China’s housing stock mostly lacks insulation so this new compound could make a significant difference in the country’s drive to upgrade its carbon footprint. The compound is already in production, and will likely go into widespread use in the near future as the scale of production is ramped up.

Baotou scientists named the heat-insulating rare-earth glass coating ‘EASTO.1098’.

"The reason why our material is new is that in terms of functionality, it can be directly coated on the surface of glass, [and provide] a maximum adjustable temperature of 7-15 degrees, and energy saving capability of 25-40%," Baotou rare earth scientist Dr Yin Jian said, who is based at the Tianjin Branch of the Research Institute.

By way of comparison, double glazing, when used traditionally in Western Europe saves about 10% of energy loss. So, this discovery could be a significant find.

Baotou says that the coating is a stable and classed it as a "high-performance rare earth nano-composite thermal insulation coating" product. It was reportedly developed by the Rare Earth Research Institute and Chengdu Yitujiewei Technology Co Ltd. 

"We have successfully developed more than 10 kinds of rare earth nano-thermal insulation slurry industrial preparation technologies. Currently, for this technology, Baotou has published two domestic papers, and applied for three domestic invention patents, and one appearance design patent," Senior Engineer Lu Fei of Baotou Rare Earth Research Institute said.

Fei added that that the coating is ahead of similar products such as glass film, low-E glass and insulating glass in the market currently for thermal insulation, convenience and stability.

'Optimising glass insulation is imperative'

In China’s 13th Five-Year Plan, Chinese officials sought to conserve energy use in buildings. For building energy conservation and "Green Building Development", they proposed that by 2020, the energy efficiency of new urban buildings in China should increase by 20%, and that the proportion of "green building areas" should exceed 50%.

So, this is an issue clearly designated as being of national significance.

Approximately 40% of building energy is estimated to be lost through glass doors and windows, so improving the thermal insulation performance of glass is a critical factor in energy conservation.

Heat energy on the earth's surface comes mainly from sunlight, and the spectrum of sunlight is mainly concentrated in the range of 200-2500nm. Within that, the range of 200-400nm is ultraviolet, and its energy accounts for about 5% of the total energy of sunlight, while the range from 400-720nm is visible light energy, which accounts for about 45% of the total energy of sunlight. The range from 720-2500nm is infra-red, and its accounts for half of the total energy of sunlight.

Infra-red rays are invisible to the human eye. Therefore, to effectively block infra-red rays and improve the heat insulation performance of glass without affecting the transmission of visible light is one of the most difficult aspects 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 [techniques], each has many problems." Lu Fei said.

Lu Fei explained the shortcomings of low-emissivity glass (Low-E), the most commonly used building insulation glass, which achieves thermal insulation effects 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 also reflects a lot of sunlight and causes a lot of light pollution problems, the researcher said.

People working in a light-polluted environment for a long time can experience loss of vision, dizziness, insomnia, heart palpitations, decreased appetite, and depression, which seriously affects people's physical and mental health. Also, Low-E glass cannot manage heat insulation on the surface of the glass through post-painting and other methods. And, 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 to upgrade existing architectural glass.

On top of this, coloured glass absorbs visible light while absorbing heat. It greatly sacrifices visible light transmittance while achieving heat insulation, and present obvious colours greatly limit the need for high visible light, which is important for car front windshields. 

Yin Jian said: "At present, the most widely used infra-red absorption material is cesium tungsten bronze material, which has the best infra-red absorption effect. However, it isn’t good with ultraviolet radiation, and will interact badly with water and oxygen under heat. An irreversible oxidation reaction occurs, generating tungsten trioxide, and losing its infra-red absorption properties."

A new thermal insulation coating emerges

The new technology sounds quite revolutionary in its field.

Lu Fei said: "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 infra-red photons, which can be made into infrared absorbing materials."

Lu Fei said the coating they made is based on rare earth compounds. On the one hand, because boron atoms have extremely strong electro-negativity, they can form a strong force with rare earth elements, resulting in the final formation of rare earth nano-thermal insulation materials. It has excellent acid and alkali resistance. 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 photon of the incident light is excited, the free electron resonates with the incident photon, which manifests as heat absorption in the macroscopic view."

It also has good weather resistance.

The coating 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.

In November 2019, the Rare Earth Research Institute and Yitujiewei Technology established a joint laboratory for creating 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%," Yang Jue, general manager of E-Tube Technology, said.

They plan to ramp up production according to demand.

Yang Jue said: “The problem of building energy consumption is particularly severe in China. The total building area in the country is huge, and more than 90% of it uses ordinary glass. According to the calculation of China’s energy-saving goals in 2010, an average of about 1.32 billion square metres of thermal insulation glass is added every year, and the market demand for rare earth nano-thermal insulation materials is huge.

"After the product goes on the market, it can be widely used in energy-saving and environmentally-friendly automobiles and energy-saving architectural glass.

"It can effectively solve the problems of high internal temperature of automobiles and buildings and large energy consumption of air-conditioning,” Yang Jue said.

He added that at present, they have established 11 branches and signed product agency agreements with more than 80 cities in more than 10 provinces across China.

The glass coating is expected to achieve sales of nearly 30 million yuan (US$4.47 million) this year.

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Rare earth Rare-earth compound Glass coating Glass insulation Building energy Energy saving China Baotou research facility