Aerogel: From Preparation to Application, the "Frozen Smoke" Revolution in Industry
Like "frozen smoke", it is light and yet can withstand temperatures of 1300℃; with a thickness of only a few millimeters, its heat insulation effect far exceeds that of traditional materials - this is aerogel. It has entered the civilian sector from the aerospace black technology, and behind this lies not only its unparalleled performance but also the breakthrough in the preparation process. Today, let's start from the preparation process and dissect how this "material界的 hexagonal warrior" reshapes industrial energy conservation and safety. 
I. Comprehensive Analysis of the Preparation Process of Aerogels: Key Technologies and Influencing Factors from Sol-Gel to Drying
The core of aerogel preparation is to form a wet gel through the sol-gel method, then remove the solvent in the pores through the drying process, and finally obtain aerogels with high porosity. The entire process requires strict control of reaction conditions to prevent the gel structure from collapsing during drying. 
(1). Core Process (Taking Silica-based Aerogel as an Example)
The preparation of aerogels mainly consists of three stages: sol preparation, gel formation, and drying treatment. The specific steps are as follows: 
1. Stage 1: Sol Preparation
The objective of this stage is to uniformly disperse the precursor in the solvent and initiate the initial reaction, thereby forming a stable sol system. 
· Raw material mixing: Mix the precursor (such as tetraethyl orthosilicate TEOS) with the solvent (such as ethanol, water) in a certain proportion and stir until evenly combined. 
· Catalyst addition: Add acid (such as hydrochloric acid) or base (such as ammonia water) as the catalyst to adjust the pH value of the system (acid catalysis usually has a pH < 2, while base catalysis usually has a pH > 8), and control the rate of the hydrolysis reaction. 
· Hydrolysis reaction: The precursor undergoes hydrolysis under the action of a catalyst, generating small molecules with hydroxyl groups (such as silicic acid). The solution gradually changes from a transparent liquid to a gel with a certain viscosity. 
2. Stage 2: Gelation
The small molecules in the sol undergo condensation reactions to form a three-dimensional network structure, and the liquid is encapsulated within the pores, resulting in a wet gel. 
· Condensation reaction: The hydroxyl molecules in the sol connect with each other (condensation dehydration / dehydroxylation), gradually forming a continuous solid network framework. 
· Aging treatment: The formed wet gel is left to stand in a constant temperature environment for several hours to several days, allowing the network structure to further grow and strengthen, thereby reducing the shrinkage during subsequent drying. 
3. Third stage: Drying
This is the crucial step that determines the performance of the aerogel. It involves removing the solvent from the pores while preserving the three-dimensional network structure. There are mainly two technical routes: 
(II). Key Influencing Factors
1. Raw Material Ratio: The proportions of precursor, solvent, and water directly affect the concentration of the sol. An excessive ratio may result in a dense gel structure, while an insufficient ratio may cause the framework to be fragile. 
2. Catalyst and pH value: Acid catalysis results in gel pores with small diameters and uniform distribution; while base catalysis leads to larger pores and faster reaction rates. The choice depends on the desired performance. 
3. Aging time: Insufficient aging will result in low strength of the framework and it is prone to collapse during drying; excessive aging may cause the pore size to be too large, thereby affecting properties such as heat insulation. 
4. Drying conditions: Supercritical drying requires precise control of temperature and pressure; Atmospheric pressure drying needs to strictly control the heating rate (typically 1-5℃/h) to prevent structural damage caused by rapid solvent evaporation. 
(III). Common Types of Aerogels and Differences in Preparation Processes
Apart from the most basic silicon-based aerogels, the preparation of other types of aerogels will involve adjustments in raw materials and processes: 
· Carbon-based aerogel: Using phenolic resin, graphene, etc. as precursors, the sol-gel process is followed by high-temperature carbonization (typically at 800-1200°C), and then drying. 
· Metal oxide aerogels (such as Al₂O₃, TiO₂): The precursor is a metal alcohol salt (such as isopropanol aluminum), and after hydrolysis, the pH value needs to be controlled to prevent the precipitation of metal ions. The drying process is similar to that of silicon-based aerogels. 
· Organic aerogels (such as polyurethane aerogels): Using polymer monomers as raw materials, a gel is formed through polymerization reaction. No high-temperature treatment is required; it can be dried at normal pressure. 
II. New Energy Vehicles: The "Firewall" for Battery Safety
The core value of aerogel in new energy vehicles lies in the low thermal conductivity and stability conferred by its preparation process. In lithium battery modules, the aerogel sheets embedded between the battery cells can be regarded as a "fire barrier", capable of blocking the spread of thermal runaway at 1300℃. A 2.5mm thickness can reduce the temperature to 180℃, effectively preventing chain explosions. Companies like Geely and BYD have already adopted it on a large scale. 
Under the same level of insulation effect, the thickness of the aerogel is only 1/5 of that of traditional materials. This not only saves space in the battery pack but also reduces the overall vehicle weight, indirectly improving the range. In cold regions, it can also keep the battery warm and prevent the degradation of low-temperature performance. 
III. Architecture and Industry: The "Invisible Helper" for Energy Saving and Consumption Reduction
In the field of architecture, the aerogel produced by the atmospheric pressure drying process has achieved large-scale application. The aerogel coating applied to the walls has a fire resistance rating of A grade and can also enhance the compressive strength and water resistance of building materials. However, the application of transparent aerogel in energy-saving windows still requires optimization of the light transmission parameters during the sol-gel process. 
In industrial settings, the high-performance aerogels produced through supercritical drying serve as the "energy-saving outer layer" for petrochemical subsea pipelines and heating networks. They can significantly reduce heat loss and also lower the construction difficulty in harsh environments. When used in cold storage facilities, they not only minimize heat loss but also prevent pipeline condensation. 
IV. Aerospace and Electronics: "Shield" for Extreme Scenarios
The aerospace industry has the highest requirements for the performance of aerogels. The silica aerogel used in NASA's Mars rover was produced through supercritical drying, with a density of only 20 kg/m³. It can withstand the extremely low temperatures of -123°C on Mars and the extremely high temperatures of thousands of degrees during landing; isotope temperature difference batteries also rely on it to reduce heat energy loss. 
In the field of consumer electronics, aerogels prepared under normal pressure have lower costs and are used as heat insulation layers for mobile phone chips, with their low thermal conductivity of 0.013W/(m・K) effectively blocking heat. They are also used to replace polyurethane foam in refrigerators, resulting in even better energy-saving effects. 
V. Future Trends: Cost Reduction Drives Popularization
In the past, aerogels were only used in high-end fields due to the high cost of the supercritical drying process. Now, the atmospheric pressure drying process has significantly reduced costs, and the flash synthesis technology of the Chinese Academy of Sciences has further achieved a cost reduction of 99%, accelerating its popularization in the fields of construction and automobiles. 
Multifunctional composites are the other direction: By improving the sol-gel process, aerogels with both insulation and adsorption properties have been developed, which can be used for oil-water separation and heavy metal adsorption. With the increasing demand for new energy vehicles, it is expected that the global market size of aerogels will reach 1.5 billion US dollars by 2031. 
From the "scaffold construction" of sol-gel to the "cost breakthrough" of drying processes, every step of the application expansion of aerogels is closely linked to the innovation of preparation technologies. This "frozen smoke" is writing a new chapter of industrial energy conservation and safety with its dual advantages of process and performance. 




Source: Lianjing Composite Materials