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New Star in the Material World Aerogel
- Time of issue:2023-02-13 20:13
New Star in the Material World Aerogel
n January 2023, the scientists of Chinese and foreign scientific research institutions obtained the latest research results of "Mars Sunrise" through the data transmitted from Tianwen 1.
In 2021, Tianwen 1 landed on Mars and started the Mars exploration journey. This is not an easy journey. Tianwen 1 must go through the test of "ice and fire" - when landing, the heat generated by the engine will suddenly increase the ambient temperature to more than 1000 ℃; At the inspection stage, the Mars rover Zhurong carried by Tianwen 1 had to work at about - 130 ℃.
What kind of material can withstand such extreme heat and cold? What kind of material can make the scientific load on the Mars rover carry out Mars exploration smoothly in such a bad environment?
The following will introduce you: aerogel, a new star in the world of materials.
1、 The wonderful birth of aerogel
Aerogel is a kind of lightweight solid material, in which nano colloidal particles gather together to form a nano framework and a nano porous network structure, and the pores are filled with gaseous dispersion media. The internal structure of the aerogel is like the steamed bread we eat everyday, with many holes and a skeleton formed by flour. Different from steamed bread, in the internal structure of aerogel, the pore size is relatively more uniform, and the pore size is about 1 million times smaller than that of steamed bread, and most of the pores in aerogel are connected with each other. Similarly, the skeleton size of aerogel is about 1000 times smaller than that of flour skeleton.
Due to this special structure, aerogel presents a smoke like state in the air. Therefore, it is also called "frozen smoke". Mark Miodonick, a material scientist, described his feeling of encountering aerogel for the first time in the laboratory: "It is transparent, but strangely milky white, much like the hologram of jewelry, and it is an unreal substance... I can't help but wonder if it was snatched from an alien spaceship?"
The birth of aerogel came from a genius's whim.
In 1931, American scientist Kistler and his friend made a bet: they met to see who could change the liquid in the gel into gas without changing the solid structure.
Take jelly for example. If you want to separate the liquid and solid in the gel by evaporation, it will inevitably cause jelly shrinkage and structural collapse. However, after repeated experiments, Kistler finally solved this problem through supercritical alcohol drying technology, and the world's first aerogel was born. However, the preparation process of aerogel at this time was time-consuming and difficult, and it was not widely used.
Until the 1970s, scientists used methanol solvent as the supercritical drying medium to prepare silica aerogels, which greatly simplified the preparation process of aerogels. The research field of aerogels, which had been dormant for more than 40 years, began to wake up.
Nowadays, aerogels have formed a huge family. This family is mainly divided into three parts: inorganic aerogels, organic aerogels and organic-inorganic hybrid aerogels gel.
Inorganic aerogel, as its name implies, is based on inorganic substances. Inorganic aerogels can withstand high temperatures, and the use temperature can generally reach more than 600 ℃.
Organic aerogels are mainly composed of organic substances, and generally have the characteristics of high strength and good flexibility. They are often used at medium and low temperatures (no more than 400 ℃).
The organic-inorganic hybrid aerogel, on the other hand, uses the advantages of organic and inorganic materials to realize the special functions of aerogel materials. For example, silica aerogel is an excellent thermal insulation material with ultra-low thermal conductivity and high temperature resistance. However, it is difficult to use directly due to its low strength and brittle material. Organic aerogels generally have good toughness. Therefore, the combination of organic gel and silica gel can enhance the strength of silica gel, and also endow hybrid gel with specific functions due to the change of organic structure.
In 2021, the international top authoritative academic journal Science listed aerogel as one of the top ten popular science and technology. In 2022, the International Union of Pure and Applied Chemistry listed aerogel as one of the top ten emerging technologies in the chemical field in 2022. Up to now, the birth of aerogels has been nearly a century, but the research on aerogels in the scientific community is still hot.
2、 Integrator of excellent characteristics
The English name of aerogel is "aerogel". "Aero" means flying, and "gel" means gel, which together is a flying gel. The name alone shows how light aerogel is. Over the years, scientists have continuously prepared more advanced aerogels, breaking the record of "the lightest solid in the world" again and again. Among the currently reported aerogels, the lowest density can reach 0.00016g/cm3, which is far lower than the density of air. After vacuuming, it can even float in the air.
The super high proportion of air in the structure of aerogel makes it have high specific surface area and high porosity. It is understood that the specific surface area of aerogels can be as high as 1000m2/g. That is to say, the surface area of one piece of aerogel the size of a table tennis ball is equivalent to that of a football field. At the same time, the porosity of 80%~99.8% also means that in the aerogel with a volume of 1m3, the volume of nano pores is more than 0.8m3. This makes aerogels have excellent adsorption properties. Its adsorption capacity is far greater than that of ordinary sponge, which can be called "ultimate sponge".
Materialists have adjusted the chemical state of the aerogel framework to make it selective in adsorption. For example, the adsorption capacity of silica aerogel for common harmful gases such as toluene is more than twice that of activated carbon and silica gel, which can be used to remove indoor harmful gases; The oil absorption capacity of carbon aerogel can reach 40~160 times of its own weight, and it is an ideal material for treating oil pollution at sea.
Aerogel has excellent thermal insulation performance due to its structural characteristics. Its nano-skeletal structure disperses the way of solid heat transfer, and the smaller nanopores hinder the heat transfer of gas molecules. Therefore, when the heat passes through the aerogel, it is like walking on a winding and rugged path, and the heat transfer speed is extremely slow. Thermal insulation performance has always been one of the focuses of all walks of life. Taking the commonly used aerogel thermal insulation blanket in industry as an example, compared with traditional thermal insulation materials, the thermal insulation performance of silica aerogel thermal insulation blanket is 2~8 times that of traditional materials.
In addition, aerogels also have unparalleled catalytic properties. Its specific surface structure enables the active components to be very evenly dispersed in the carrier. At the same time, the aerogel has good thermal stability, which can effectively reduce the occurrence of side reactions. Therefore, aerogels are often used as catalysts or catalyst carriers. At the beginning, aerogel catalyst was mainly used for some organic reactions with industrial application background, such as acetic acid conversion to acetone, propionic acid conversion to diethyl acetone, etc. In recent years, aerogel catalysts have been widely used. For example, graphene based aerogels have broad application prospects in fuel cells, dye-sensitized solar cells, microbial electrolytic cells and electrochemical sensors due to their excellent electrochemical activity and catalytic properties.
3、 The king of materials
Nowadays, aerogels are everywhere, from aerospace and national defense industries to knee pads and insoles in daily life.
Aerogels have been widely used in space exploration. The Chinese Zhurong Mars rover, the Russian Mir space station and the US Mars Pathfinder probe all use aerogel as thermal insulation material.
The application of aerogels in the aerospace field goes beyond this. As early as the end of the 20th century, aerogel had been made into a dust collector to collect cometary dust in the universe.
Scientists believe that the comet dust in the universe contains the most primitive and oldest material in the solar system, which can help people understand the history of the sun and planets more clearly. But collecting comet dust is not an easy task. The volume of comet dust is smaller than that of sand particles, but its movement speed is at least 6 times that of rifle bullets. Contact with other substances at such a high speed may change their physical and chemical composition, or even completely evaporate.
The characteristics of silica aerogels can solve this problem well. It is like an extremely soft baseball glove. Its extremely low density can slow down the dust slowly without damage. Its intricate structure can play a good cushioning effect, making it slide 200 times its length and then stop slowly. After entering the "aerogel glove", the stardust will leave a carrot shaped track. Because the aerogel is almost transparent, scientists can easily find these particles according to the track.
The Stardust spacecraft launched by NASA in 1999 carried a dust collector made of aerogel. In 2006, Stardust returned to Earth with the first batch of cometary dust samples obtained by humans. The captured dust particles were clearly visible, and the aerogel units were intact. This proves that silica aerogel is worthy of the collection artifact of interstellar dust.
The common electric vehicles in people's daily life are also inseparable from aerogel.
Li-ion batteries are mainly used as power batteries for electric vehicles. Under extreme conditions, thermal runaway of battery is the primary safety problem of electric vehicle. The application of aerogel thermal insulation materials has greatly improved the use safety of new energy vehicles.
Aerogel heat insulation sheet is an aerogel composite heat insulation material based on silica aerogel and ceramic fiber substrate. It is used to block the heat transfer between the heating part and the equipment shell. Aerogel felt has the characteristics of low thermal conductivity, good heat insulation effect and incombustibility. Compared with traditional thermal insulation materials, aerogel felt only needs 1/5~1/3 thickness to achieve the same thermal insulation effect. At present, many automobile power battery manufacturers use silica aerogel thermal insulation composite felt as the separation material of power battery components on a large scale.
In addition, aerogel is also widely used in production and life: thin and light cold clothing made of aerogel can resist liquid nitrogen injection at - 196 ℃; Functional cellulose aerogels have natural advantages in adsorbing carbon dioxide, formaldehyde and other gases, as well as removing heavy metal ions, organic dyes, organic solvents and oily sewage from wastewater
At present, there are a variety of aerogels that can be prepared by human beings. Each aerogel has its own unique and interesting performance, and has been successfully applied in high-tech equipment and daily life. With the continuous improvement of the preparation process and the continuous development of science and technology, the development cost of aerogels has gradually decreased. In the near future, aerogels will be more widely used in all walks of life, bringing surprising changes to all fields.