At present, aerogel materials that are more common and studied in the market mainly include oxide aerogel, carbon aerogel gel (its high temperature resistance can reach 3000 ℃), and carbide aerogel gel.
1. Oxide aerogel material
The oxide aerogel material will appear crystal transformation and particle sintering under high temperature environment (over 1000 ℃), resulting in its weak temperature resistance. However, they exhibit lower thermal conductivity in the medium to high temperature range (below 1000 ℃). This type of material mainly includes SiO2, Al2O3, TiO2, ZrO2, and CuO.
1) SiO2 aerogel material
The research of SiO2 aerogel in the field of thermal insulation is quite extensive and the technology is mature. Its porosity is as high as 80% 99.8%, the typical pore size range is 1100nm, the specific surface area reaches 200-1000m2/g, and the density is as low as 3kg/m3, resulting in a thermal conductivity of only 12mW/(m · K) at room temperature. In order to further improve the thermal insulation and mechanical properties of SiO2 aerogels, they are usually compounded with infrared light blocking agents and reinforcements. This type of composite material not only has significant nanopore super insulation effect, but also has excellent insulation and mechanical properties, making it widely used for insulation and heat preservation in various fields such as aerospace, military, electronics, construction, home appliances, and industrial pipelines. Among them, commonly used infrared shading agents include silicon carbide, TiO2 (rutile and anatase), carbon black, potassium hexatitanate, etc., while reinforcing materials such as ceramic fibers, alkali free ultrafine glass fibers, polycrystalline mullite fibers, aluminum silicate fibers, and zirconia fibers are selected.
2) ZrO2 aerogel material
Compared with SiO2 aerogels, ZrO2 aerogels exhibit lower thermal conductivity at high temperatures, so they are particularly suitable for high temperature insulation. Its pore size is smaller than the average free path of air molecules, which effectively avoids air convection in the aerogel. Meanwhile, its extremely high porosity and low solid volume ratio together endow it with excellent thermal insulation performance. Although there are few reports on the application of ZrO2 aerogel in the field of thermal insulation, researchers are actively exploring the optimization of its preparation process in order to further expand its application potential for high-temperature thermal insulation.
3) Al2O3 aerogel material
Alumina aerogel material is famous for its unique nano porous structure, which endows it with lightweight and efficient thermal insulation performance. Its high porosity, large specific surface area, and open weave structure make it show potential application value in the field of catalysts and their supports. In addition, alumina aerogels can also be used as high-voltage insulation materials, substrates for high-speed or overspeed integrated circuits, isolation media for vacuum electrodes, and ideal choices for supercapacitors.

2. Carbon aerogel and carbide gel materials
Carbon aerogel stands out for its temperature resistance of up to 2000 ℃ in inert and vacuum environment, and it can reach 3000 ℃ after graphitization. Its carbon nanoparticles exhibit excellent absorption capacity for infrared radiation, similar to the effect of infrared shading agents, which reduces high-temperature thermal conductivity. However, it should be noted that in the aerobic environment, carbon aerogels will be oxidized when the temperature exceeds 350 ℃, which to some extent limits their application in the field of high-temperature insulation. However, with the progress of high oxidation resistance coating technologies such as SiC, MoSi2, HfSi2, TaSi2, etc., the application scope of these carbon aerogels will be significantly expanded by covering the surface of these carbon aerogels with dense coatings to prevent oxygen intrusion.
On the other hand, although carbide materials have excellent oxidation resistance, their thermal conductivity is relatively high. In order to solve this problem, researchers try to make it into three-dimensional three-dimensional network like aerogel structure, so as to significantly reduce the thermal conductivity and further optimize the thermal insulation performance. Although the research on carbide aerogels at home and abroad is still in its infancy, especially the research on well formed blocky carbide aerogels is even rarer, its potential as an efficient thermal insulation material has begun to emerge.
Next, we will discuss the preparation method of SiO2 aerogel.
As SiO2 aerogel is the most mature product in industrialization at present, its preparation mainly adopts drying method and sol gel method. At present, drying technology has become a core technology in industrialization.
Drying technology is a key link in the preparation of aerogels. At present, supercritical drying technology and atmospheric drying technology have become the mainstream of industrialization. Although technologies such as vacuum freeze-drying and subcritical drying have not yet achieved large-scale production, they are constantly developing and improving.
Supercritical drying technology is an early technology to realize batch preparation of aerogels. After years of development and improvement, it is now quite mature. This technology can ensure that the gel maintains its original skeleton structure during the drying process, so as to obtain stable aerogel materials.
Atmospheric drying technology is a new technology for preparing aerogels. In recent years, this technology has received extensive attention and research, and is regarded as the most promising batch production technology of aerogel. Its unique feature is that the gel skeleton is modified by introducing hydrophobic groups to enhance the elasticity of gel and reduce the surface tension. In this way, high performance aerogel materials can be obtained by direct drying under normal pressure.
Compared to supercritical drying technology, atmospheric drying technology exhibits significant advantages in both equipment cost and silicon source cost. Although there is a certain technical threshold, it is very suitable for large-scale mass production of aerogel in the later stage.
Sol gel method is to construct SiO2 gel with three-dimensional network structure through hydrolysis and polycondensation of silicon source material. In this process, the polymer with the main body of ∨ Si-O-Si ∨ gradually formed, and after the aging stage, the gel network structure was stabilized. By adjusting the pH of the reaction solution, the rate of hydrolysis and polycondensation can be finely controlled, and then the structure of gel can be affected. In acidic environments, hydrolysis reactions are more rapid, which is conducive to the formation of more nucleation reactions; In alkaline environments, it is more conducive to the growth and cross-linking of nuclei, thereby forming dense colloidal particles. It is worth noting that strong alkali or high temperature conditions will increase the solubility of SiO2, resulting in the final formation of gel structure in the form of colloidal aggregates.
In order to overcome the inherent shortcomings of low strength and high brittleness of aerogel materials, the modification of aerogel materials has become an indispensable process. At present, doping is the most commonly used modification method, which is to prepare composite aerogels by adding dopants or reinforcing/toughening materials. The preparation methods of these composites include directly adding doped materials in the gel process, or first preparing aerogel particles or powders, and then adding doped materials and binders for secondary molding.
Aerogel can be compounded with glass fiber, ceramic fiber or carbon fiber to enhance the bonding force of the system and prevent surface embrittlement and pulverization. For example, air gel glass fiber felt, air gel ceramic fiber felt, preoxidized fiber and other products have been widely used in heat insulation fields such as pipe furnace body, and they can replace traditional flexible heat insulation materials that are not environmentally friendly and have poor heat insulation performance, such as polyurethane foam, asbestos heat insulation pad, silicate fiber and so on.
Composite with higher strength and toughness materials on the surface of aerogel matrix materials can significantly improve the strength of the entire material system, and further expand its application fields. Although pure fiber felt has a certain insulation effect, its surface fibers are prone to breakage and pulverization, leading to floating fibers or powder pollution, which limits its long-term use in high temperature, compression, and vibration environments. To solve this problem, an innovative aerogel material composite method has emerged in the market. This method covers the outer surface of the aerogel composite layer with a layer of materials with higher strength and toughness, such as the composite layer of expanded polytetrafluoroethylene and flame retardant PET fiber, making this material suitable for special fields such as automobile heat insulation.
In addition, aerogel materials can also be used as coating materials to provide thermal insulation protection for the matrix. By mixing aerogel particles with adhesives, flame retardants, foaming agents, etc., an aerogel adhesive composition is prepared, and a heat reflective layer is coated on its surface, which can significantly improve the heat resistance of raw materials.
At the same time, the synergistic use of aerogel materials and flame retardants can also achieve better flame retardancy, and enhance the strength and toughness of materials. For example, Sb2O3-SiO2 composite aerogel inorganic flame retardant has a large specific surface area, and has a strong interface adhesion with polymer matrix such as plastics and rubber, which improves the dispersion and fluidity of flame retardant in polymer melt, thus enhancing the flame retardant effect and reducing the impact of inorganic flame retardant on the mechanical properties of polymer matrix.
In addition, the aerogel material can also be combined with textile fibers such as non-woven fabric, polyester staple fiber, nylon, etc. to make clothing fabrics suitable for down jacket, cotton padded jacket, outdoor supplies, fireproof clothing, aerospace clothing and special work clothes. This fabric has excellent insulation, heat resistance, wear resistance, waterproof and windproof properties, with a thermal conductivity of less than 0.05W/(m · K), even lower than that of down and wool.
In the aerospace field, nano porous aerogel super thermal insulation material has achieved equivalent thermal insulation effect due to its lightweight and compact characteristics. This material performs well in the insulation of aircraft engines, providing excellent insulation and effectively reducing the weight of the engine.
Application of Nanoporous Aerogel Super Thermal Insulation Materials in Aerospace Field
In addition, this nano porous aerogel super thermal insulation material also plays an important role in industrial and building thermal insulation fields. Thermal equipment is widely present in industries such as electricity, petrochemicals, chemicals, metallurgy, building materials, and civil construction. In these fields, nanoporous aerogels have made important contributions to industrial energy conservation due to their excellent thermal insulation performance. Especially in some special locations and environments, due to weight, volume or space constraints, the efficient thermal insulation performance of nanoporous aerogels is particularly important.
At the same time, as a hydrogen storage material with high specific surface area, low density and continuous network structure, carbon aerogel has small pore size and is connected with the outside world, showing excellent hydrogen absorption and desorption performance. This characteristic makes carbon aerogels have potential application value in the field of hydrogen storage. It is understood that the US Department of Energy has set up a special organization to study metal doped carbon aerogel hydrogen storage technology, and has given financial support.

3. Application of carbon gas gel in the field of hydrogen storage and thermal battery
Carbon aerogels, due to their high specific surface area, low density and unique continuous network structure, are widely used in the field of hydrogen storage materials. Its pore size is moderate and connected to the outside world, making it excellent in hydrogen absorption and release performance, bringing new possibilities to the field of hydrogen storage. In addition, carbon aerogel gel can also be used in the field of thermal batteries, as a high-temperature resistant aerogel insulation material, which can effectively extend the working life of the thermal battery and prevent the heat generated inside the battery from affecting the surrounding components.