Aerogel, a miraculous material that has won the title of "the lowest density solid in the world" in the Guinness World Record, although it is light in appearance, it has amazing durability and can withstand the pressure of thousands of times its own mass. This feature has aroused the strong interest of scientists all over the world, who have devoted themselves to the research of aerogels. Aerogel is also highly praised by the international top authoritative academic journal Science for its excellent performance, is listed as one of the top ten popular science and technology, and is praised as "a magic material that can change the world". We have reason to expect that aerogel will lead many industries and disciplines to a new historical chapter. Next, let's explore the magical world of aerogels.
First, let's understand the concept of "gel". At a certain concentration, the viscosity of polymer solution or sol will gradually increase under specific conditions, and eventually lose its fluidity, thus forming an elastic semi-solid with uniform appearance and a certain form, which is called gel. The jelly we often eat in our daily life is an example of gel, but it is filled with water or other liquids. When the filler becomes gas, the so-called "aerogel" is born. Compared with ordinary porous materials, the unique feature of aerogels is that their skeleton size is at the nanometer level. Because of this, when visible light penetrates, its scattering effect is very small, making the aerogel look like "solidified smoke".
Types of aerogels
Aerogels, a unique material, can be mainly divided into three categories according to the difference of its composition: oxide gel, carbon gel and carbide gel. Next, we will discuss the characteristics and applications of various aerogels one by one.
Oxide aerogel
Oxide aerogels, such as SiO2 and ZrO2, are famous for their high porosity, large specific surface area and low thermal conductivity. SiO2 aerogel has the most extensive research in the field of thermal insulation, and its technology is relatively mature. It is widely used in aerospace, military, electronics, architecture and other fields. Although there are few reports on the application of ZrO2 aerogel in thermal insulation, its unique physical properties have shown great potential in high-temperature thermal insulation materials.
Carbon aerogel
Carbon aerogels stand out for their temperature resistance up to 2000 ℃ in inert or vacuum environments, and they can withstand 3000 ℃ after graphitization. This kind of aerogel has a broad application prospect in the field of high temperature insulation. However, the oxidation problem during its preparation process, especially the oxidation reaction above 350 ℃ in aerobic environment, has become the main obstacle to its further application.
Carbide aerogel
Carbide aerogels have attracted much attention due to their excellent oxidation resistance. Although the research on it is still in its infancy at home and abroad, especially for the well formed blocky carbide aerogels, its unique properties have predicted that it may have broad application prospects in the future.
Preparation method of aerogel
Generally speaking, the preparation of aerogel includes two key steps: first, wet gel is prepared through a specific process; Secondly, wet gel is subjected to special drying treatment to obtain aerogel. This process involves multiple technical details that are crucial for the performance of the final product.
Wet gel preparation
The traditional and commonly used method for the preparation of wet gel is the sol gel method. This method involves dispersing highly chemically active compounds in solvents, and generating active monomers through hydrolysis reaction. These monomers are further polymerized to form sol, and finally transformed into gel with specific spatial structure. In addition, there are other methods to prepare wet gel, such as hydrothermal method and in-situ reduction method, which use different reaction conditions and mechanisms to synthesize gel.
Wet gel drying technology
supercritical fluid drying
Supercritical fluid drying technology is the most mature method for large-scale preparation of aerogels at present. This method requires high-pressure equipment, and the process is more complex, but because the surface tension disappears, the gel structure will not be damaged.
Freeze-drying
Freeze drying technology is quite common in the drying process of bio based carbon aerogel. Use vacuum or negative pressure environment to sublimate water molecules in gel directly, so as to achieve efficient drying. Its processing capacity is large and the process is simple.
ambient pressure drying
Atmospheric drying, that is, the treatment of wet gel samples at room temperature or high temperature under normal pressure, has attracted much attention due to its mild conditions and simple equipment. Although economic, maintaining the structure poses significant challenges.
Preparation Issues and Challenges
Aerogel, a solid material with extremely low thermal conductivity, has excellent thermal insulation performance due to its high porosity porous structure composed of nano particles. However, this characteristic also leads to relatively weak mechanical performance, making it susceptible to the risk of collapse and breakage. In order to enhance the mechanical strength of aerogels, researchers need to use a variety of methods, which undoubtedly increases the complexity of preparation. In the future, there is an urgent need to simplify the process and reduce costs.
Application of aerogel
The microstructure of aerogel is unique, similar to a bird's nest, in which nano particles build a skeleton, and the skeleton is filled with air. This special nano porous network structure endows aerogels with extremely low density, thermal conductivity, high porosity and high specific surface area. Therefore, aerogels are widely used in thermal insulation materials, catalysts and carriers, sound barrier materials and other fields.
Application in the field of thermal insulation
Aerogel insulation blanket
The aerogel can be made into thermal insulation felt, which is soft and easy to cut, has small density, inorganic fire resistance, overall hydrophobic and green. Air gel thermal insulation felt is environmentally friendly and superior to traditional materials in thermal insulation, especially suitable for green buildings and ultra low energy consumption buildings. Air gel concrete and thermal insulation coating
Among building materials, SiO2 aerogel material is relatively new in the application of thermal insulation felt. In particular, in special scenarios where space and weight constraints exist, or in applications such as pipelines that need thermal insulation, SiO2 aerogel thermal insulation felt shows significant advantages. At the same time, the balance between its mechanical strength and thermal insulation remains challenging.
Wastewater treatment and phase change insulation substrate
Carbon gas gel has unique potential in the field of environmental protection and high temperature protection due to its rich micropore structure and strong natural adsorption capacity. Especially in dealing with marine oil spill pollution, it has demonstrated significant advantages.
Other applications of aerogels
Aerogel shows unique advantages in hydrogen storage, supercapacitor, environmental protection and other fields. Its addition can enhance the hydrogen storage capacity and stability of the material, and perform excellently in supercapacitors and electromagnetic shielding materials.
Current research status and prospects at home and abroad
International Research and Development
Developed countries such as the United States, Europe and Japan have made remarkable progress in the research and application of aerogels. LLNL Laboratory, JPL Laboratory, SNL Laboratory in the United States, as well as California Institute of Technology, Aspen Corporation, and others, are all in a global leading position in material innovation, large-scale production, cross disciplinary applications, and market expansion.
Domestic research and development
In China, Tongji University, National University of Defense Technology, Nanjing University of Technology, Tsinghua University, Xiamen University, Zhejiang University, Harbin Institute of Technology, Chinese Academy of Sciences and other research institutions have also made important breakthroughs in the field of aerogels. China keeps pace with the world in the R&D and application of aerogels, with great market potential. Looking forward to the future, with the development of the concept of energy conservation and environmental protection, the application prospect of aerogel will be more bright.