Aerogel is considered to be the lightest solid in the world, has excellent thermal insulation effect, and can even help astronauts resist the severe cold in space, so it has become a aerospace material favored by NASA, and is known as a kind of aerospace material. The "magic material that changes the world" has been listed as a national strategic emerging industry by the National Development and Reform Commission.

Among the aerogels, SiO2 aerogels are the easiest to prepare and the most widely used. They use air as the main component and amorphous SiO2 as the basic skeleton, and have ultra-high porosity (up to 80-99.8 %), showing unique properties in mechanics, heat, electricity, optics, acoustics, etc. For example, its thermal conductivity at room temperature can be as low as 0.013w/(m·k). At the same time, it also includes the properties of low thermal conductivity, low density, high porosity, high light transmittance, high specific surface area, low refractive index and low sound velocity, so it has broad application prospects in many fields.

Regarding the application of SiO2 aerogel, the main product forms are as follows: aerogel powder/particle, aerogel felt, aerogel sheet, etc. With the increase of coating usage and the improvement of coating performance requirements , SiO2 aerogel as a functional filler of coatings has also attracted the attention of many researchers. Today, I will focus on this part.

Preparation of Aerogel Thermal Insulation Coatings

The main components of aerogel thermal insulation coatings include film formers such as cross-linked acrylic emulsion, fillers such as SiO2 aerogel, and various additives. Among them, SiO2 aerogel is used as an important part of the coating, which will make the coating have special functions such as heat insulation, high temperature resistance, fire protection, adsorption, photocatalysis, sound insulation and sound absorption, so its quality will greatly affect the coating. performance.

At present, there are many preparation methods for SiO2 aerogel, and the main process includes preparing SiO2 wet gel by sol-gel method and drying to obtain SiO2 aerogel. The preparation process of SiO2 wet gel is similar, and the main difference is the drying method. The properties and quality of SiO2 aerogel prepared by different drying techniques will be different. Then, on the basis of the preparation of SiO2 aerogel, additives such as stabilizers and dispersants are added, and SiO2 aerogel slurry is first prepared by various dispersion methods, and then mixed with film-forming resin, auxiliary agent, solvent and other The pigments and fillers are mixed, and finally the SiO2 aerogel coating can be obtained by high-speed dispersion.

In the whole preparation process, the preparation process of SiO2 aerogel slurry is the most critical step, and it is also the direct influence factor of whether the performance of SiO2 aerogel coating is superior or not. This process needs to solve the problem of the agglomeration of nanoparticles in the medium, so that the SiO2 aerogel nanoparticles are uniformly and stably dispersed in the solvent.

Application of Aerogel Thermal Insulation Coatings

Although the preparation process of various SiO2 aerogel coatings is roughly the same, if the properties of SiO2 aerogel used as fillers are different, and the formulas of added pigments, fillers and additives are also different, the resulting SiO2 aerogel will condense. Adhesive coatings also have differences in main functions. At present, the more common development directions are heat insulation, fire prevention, adsorption, photocatalysis, and sound insulation.

1. Thermal Insulation Coatings

Due to the structural characteristics of SiO2 aerogel itself, SiO2 aerogel thermal insulation coating can effectively reduce heat transmission, improve the environment and reduce energy consumption. The nanopores and three-dimensional network structure of SiO2 aerogel destroy the heat conduction path of the matrix, which is an important reason for its extremely low thermal conductivity. The unique nano-pore structure restricts the free flow of air molecules and inhibits the convection conduction of air. The infinite number of hole walls form the reflection and refraction surfaces of heat radiation, with the "infinite heat shield effect", which maximizes the inhibition of heat radiation. Radiant heat conduction. Therefore, the use of SiO2 aerogel with excellent thermal insulation properties in thermal insulation coatings will greatly improve the thermal insulation effect of the coating film.

The test results show that the 1mm thick aerogel thermal insulation coating has better thermal insulation performance than the 8cm thick polystyrene foam board, so it has been used for thermal insulation of building exteriors, building curtain walls, walls and roofs, etc. Applications in many fields such as industrial medium and low temperature pipelines, storage tanks, communication base stations, ships, and automobile transportation industries.

Spraying process of aerogel thermal insulation coating

2. High temperature resistant coating

SiO2 aerogel high temperature resistant coating refers to a functional coating that can be used in a high temperature environment above 200 ° C for a long time, can protect the substrate, and the physical and chemical properties of the coating itself can still remain relatively stable. SiO2 aerogel can maintain good porous network structure characteristics below 900 °C, but when the temperature reaches above 900 °C, sintering will occur, the Si-O-Si network structure will shrink and agglomerate, and the pore structure will be destroyed. In order to realize that SiO2 aerogel maintains the original nanopore network structure at ultra-high temperature, and maintains its low thermal conductivity and high porosity, high temperature resistant composite materials are generally prepared by doping other high temperature resistant materials.

SiO2 aerogel high temperature resistant coating has the characteristics of thin thickness, high temperature resistance, heat insulation, etc. In high temperature environment, the thickness of the coating film can be selected according to the ambient temperature and the cooling range to be achieved. It can be applied to high temperature steam pipes, High temperature furnace, oil cracking equipment, engine parts and metal high temperature protection in metallurgical industry, etc.

3. Fire retardant coating

SiO2 aerogel fire retardant coating is a kind of special functional coating that is coated on the surface of flammable substrate, which can effectively prevent the transfer of heat, reduce the flammability of the substrate, delay or even prevent the spread of fire, and can improve the fire resistance limit of the coated substrate. The fire prevention mechanism of SiO2 aerogel fireproof coating is mainly that SiO2 aerogel itself is a flame-retardant substance, so that the coating has flame-retardant properties. The pore size of SiO2 aerogel is between 2 and 50 nm, and the mean free path of the main components of nitrogen and oxygen in the air is about 70 nm. If the coating is dense enough, it can effectively prevent the direct contact between the protected substrate and the air.

The extremely low thermal conductivity of SiO2 aerogel can greatly reduce the flame temperature, so that the protected substrate cannot reach its own ignition point. Using SiO2 aerogel as functional filler, it is evenly dispersed in the stable system of the coating. When the coating is painted to form a coating, it can effectively play a good role in thermal insulation protection, thereby improving its fire resistance and playing a role in fire prevention. , can be used to protect buildings, equipment, personnel safety, etc.

4. Adsorption paint

SiO2 aerogel has a nanoporous network structure and its huge internal surface area, which makes it have the structural characteristics that the adsorption material should have. Adsorbents (activated carbon, silica gel, alumina, molecular sieve, etc.) are even better. At the same time, due to the large number of surface atoms and the lack of adjacent atoms to combine with it, the surface atoms of SiO2 aerogel have high chemical activity, and it is very easy to adsorb other atoms, so it has a strong adsorption effect. Because SiO2 aerogel adsorption coating is recyclable, green economy, and has excellent development potential, it can be widely used in air purification, sewage treatment, water vapor adsorption, medical filtration, seawater desalination and other fields, and has broad application prospects.

5. Photocatalytic coating

SiO2 aerogels prepared by sol-gel method have a porosity of up to 99.8% and a specific surface area of ​​up to nearly 1000 m2/g. These inherent properties make them highly concerned in the application of catalysts. SiO2 aerogel photocatalytic coating can have catalytic reaction function under the irradiation of a certain wavelength of light. This coating has the functions of decomposing toxic substances, sterilizing, degrading organic substances and purifying the air. The special properties of SiO2 aerogel make it possible to establish an efficient catalytic degradation system and realize high-level utilization of aerogel, and also provide a theoretical basis for studying the photocatalytic mechanism and new application prospects of SiO2 aerogel materials for pollutants. .

6. Sound insulation and sound absorption paint

SiO2 aerogel has the characteristics of low sound speed and can be used as sound-absorbing and sound-insulating material. Its mechanism of action is that it has a large number of tiny interconnected pores. It can be converted into heat energy to achieve sound insulation effect. However, at present, SiO2 aerogel is rarely used alone as a sound-absorbing material. Generally, it is combined with other materials to form a sound-absorbing material, or the SiO2 aerogel coating is coated on the surface of other sound-absorbing materials to make the sound-absorbing effect stronger. soundproofing material.