Basic Concepts
Aerogel is a lightweight solid material that is composed of nano-colloidal particles that aggregate to form a nano-skeleton and nano-porous network structure, and the pores are filled with gaseous dispersion medium image
Development History
Origin: In 1931, American chemist Samuel Stephens Kistler prepared the world's first aerogel.
Early limitations: Since then, due to the nano-scale pore size of the gel, the low mass transfer rate, the inefficient and time-consuming steps such as water washing and alcohol-water exchange, the product purity is difficult to guarantee, and the actual application value was not found at that time, its application research was limited.
Development breakthrough: In 1968, Nicoloan et al. in France used methyl orthosilicate to prepare silica aerogel by a one-step sol-gel method, shortening the drying cycle. In 1985, the Lawrence Berkeley National Laboratory in the United States used less toxic ethyl orthosilicate instead of methyl orthosilicate as a silicon source precursor, and used CO2 instead of ethanol as a supercritical drying medium, which improved production safety and promoted the commercialization of aerogel.
Characteristics
Low density: It is one of the lowest density solids in the world. The lightest aerogel is only 0.16 mg/cm3, which is slightly lower than the density of air.
High porosity: 99% of the interior is composed of gas, and the pores are extremely small, generally around a few nanometers.
Low thermal conductivity: It has a very good thermal insulation effect. An inch thick aerogel is equivalent to the thermal insulation function of 20 to 30 ordinary glasses.
Low acoustic impedance: It has special acoustic properties and has certain advantages in sound insulation.
High specific surface area: It has a large specific surface area, which makes it perform well in adsorption, catalysis, etc.
Preparation method
Sol-gel method: By controlling the hydrolysis and polycondensation reaction conditions of the solution, nanoclusters with different structures are formed in the solution, and the clusters adhere to each other to form a gel, and then aerogel is obtained after drying.
Supercritical drying technology: Place the gel in a pressure vessel and heat it to increase the pressure, so that the liquid in the gel undergoes a phase transition to a supercritical fluid, the gas-liquid interface disappears, and the surface tension no longer exists. At this time, the supercritical fluid is released from the pressure vessel to obtain a porous, disordered, low-density aerogel material with a nanoscale continuous network structure.
Classification
Silicon-based aerogels: such as silica aerogels, are the most common type of aerogels, with good thermal insulation and chemical stability 2.
Carbon-based aerogels: such as all-carbon aerogels, have extremely low density and relatively good mechanical properties.
Sulfur-based aerogels: have their own unique physical and chemical properties and have application potential in certain specific fields.
Metal oxide-based aerogels: including aerogels such as aluminum oxide and iron oxide, with high hardness and high temperature resistance.
Metal-based aerogels: such as aerogels composed of nickel, which have special metallic properties.
Application fields
Aerospace: used for heat shields of vehicles, flexible thermal protection systems of reducers, insulation layers of cryotubes in space propulsion systems, space suits, etc. For example, the Russian "Mir" space station, the US "Mars Pathfinder" probe, China's "Long March 5" launch vehicle and the "Zhurong" Mars rover have all used aerogel as thermal insulation materials.
Automotive batteries: used for thermal runaway insulation of ternary batteries to delay or prevent heat diffusion and flame spread; it can also protect the cells in lithium iron phosphate batteries from external low temperatures and improve battery performance.
Architecture: It can be used to make new high-efficiency thermal insulation composite materials for energy-saving buildings, with properties such as heat insulation, fire retardant, sound insulation, and light transmission; it can also be combined with ordinary glass to make a film to improve energy-saving and thermal insulation effects, and can also be used in high-rise buildings to reduce building quality.
Electronic and electrical engineering: As a dielectric material with a low dielectric constant, it can solve problems such as crosstalk, interconnection delay, and increased power loss that are easy to occur inside the circuit; it can also be used as a microwave dielectric material, such as a microstrip antenna, to improve antenna gain and bandwidth.
Adsorption and environmental protection: Functional cellulose aerogel has natural advantages in adsorbing gases such as carbon dioxide and formaldehyde, as well as removing heavy metal ions, organic dyes, organic solvents and oily wastewater from wastewater.
Energy storage: The conductivity of aerogel enables its internal three-dimensional network skeleton structure to provide a higher specific surface area, providing a high-end conductive channel for charge transport, and can be used for supercapacitors, lithium-ion battery electrode materials, etc.
Development trend
With the continuous improvement of preparation technology and the continuous development of science and technology, the production cost of aerogel is expected to decrease, and its application in more fields will be expanded and deepened. For example, in the field of clothing, although it currently faces some technical difficulties, researchers are working hard to improve its mechanical properties and processing technology to achieve its large-scale application in daily cold-proof and warm clothing.