1. Aerogel: The King of Insulation Materials
1.1 Aerogel is called "blue smoke", a magical material that changes the world

Aerogel was officially launched in 1931. It is currently known as a solid material with the lowest thermal conductivity and lowest density. It is also known as "blue smoke" because of its lightness and blue color. Heat insulation performance, ultra-high fire resistance, etc., are known as "magic materials that change the world".

The specific surface area of ​​conventional aerogels is ~700m2/g, the porosity is 95%-99.8%, and the evenly distributed nano-scale pore structure almost isolates heat conduction and heat convection, giving it far better thermal insulation performance than other traditional materials, and the lowest thermal conductivity can reach 0.012-0.016 W/(m•K), only equivalent to 1/2 of air.

There are many types of aerogels, and most of them have a density of no more than 3mg/cm3; for example, the density of all-carbon aerogels is as low as 0.16mg/cm3, which is only 1/6 of the air density at normal temperature and pressure.

1.2 The unique structure of aerogels endows many excellent properties

Aerogel is a three-dimensional continuous porous material composed of nano-holes and nano-framework, and its unique structure endows it with super thermal insulation properties.

Compared with other insulation materials, aerogel has the lowest thermal conductivity, the lightest weight and higher heat resistance temperature.

To achieve the same thermal insulation effect, the thickness of the aerogel is less than 1/3 of the other materials; the thickness is thinner, the heat dissipation area is smaller, the temperature drop of the pipeline is lower, the thermal efficiency is higher, and the space is saved to the greatest extent; if the underground pipeline is insulated, the opening and closing are greatly reduced. dig volume.

In addition to light weight and excellent thermal insulation properties, aerogel also has many other advantages: good fire resistance, hydrophobicity, sound insulation, adsorption, green environmental protection, etc.

Fireproof and hydrophobic: It can reach the national building material A1 non-combustible standard, and the water repellency rate is N98%;

It has weather resistance: the aerogel insulation material is hydrophobic as a whole, and it is not easy to absorb hydrolysis, and its service life can reach more than 10 years, which is 3-5 times longer than that of traditional insulation materials;

Sound insulation and shock resistance: The three-dimensional porous network structure of aerogel can play the role of sound absorption, noise reduction and shock absorption;

Health and environmental protection: The product has passed RoHS, REACH, ELV testing, and does not contain substances harmful to the human body; it is an ideal adsorption material.

1.3 The downstream application of aerogel is widely, mainly based on thermal insulation

Due to its super thermal insulation and other properties, aerogels were mainly used in aerospace, military and national defense fields in the early days, and then gradually expanded to petrochemical, industrial, construction, transportation, daily use and other fields; in electrode carrier materials, catalytic materials, sensing materials , nano-sterilization materials, drug release and many other emerging fields have been widely studied.

At present, the downstream of aerogel is concentrated in industrial pipeline insulation, such as oil and gas projects, industrial insulation, and building construction insulation. With the continuous expansion of application fields, new energy vehicles, Japanese outdoor and other fields will gradually open up the market.

1.4 There are many kinds of aerogels, and they have become a huge family of aerogels

Aerogels have developed from the original SiO2 aerogels into a huge family of aerogels.

According to the appearance of aerogel, it can be divided into block, powder and film; according to the preparation method of aerogel, it can be divided into aerogel, xerogel, and cryogel; according to different microstructures, it can be divided into microporous (<2nm), mesoporous (2~50nm) and hybrid porous aerogels; according to the matrix, can be divided into inorganic, organic, hybrid and composite aerogels; the most commonly used aerogel classification method is to distinguish by components , which can be divided into single-component and multi-component aerogels.

Single-component aerogels include oxide aerogels, carbide aerogels, nitride aerogels, graphene aerogels, quantum dot aerogels, metal aerogels, polymer-based organic aerogels, Biomass-based organic and carbon aerogels, sulfide aerogels, etc.

Multi-component aerogel (composite aerogel) refers to an aerogel composite composed of two or more single-component aerogels or a combination of fibers, whiskers, nanotubes and other reinforcements and aerogel matrix. Material. For example, organic fiber-SiO2 composite aerogels, etc. Aerogels with different compositions and structures exhibit unique properties and are suitable for specific application scenarios.

1.4.1 Oxide aerogel is the most mature, and SiO2 is at the forefront of industrialization

At present, the technology and application of oxide aerogels are the most mature. On the basis of the original excellent properties of oxides, the characteristics of light weight and high porosity of aerogels are added. The production process usually uses alkoxides and salts as precursors, and then catalyzes the preparation under acid and alkali conditions. At present, SiO2, ZrO2, Al2O3 and conformal aerogels are the most studied. Among them, SiO2 aerogel was discovered first, and it is also the most widely used and industrialized aerogel.

1.4.2 Non-oxide aerogels have great application prospects in high temperature thermal insulation and other fields

Traditional SiO2 aerogels will shrink and agglomerate at temperatures above 800 °C, resulting in material densification and loss of their original excellent properties; other oxides will also shrink and sinter when approaching 1000 °C, which greatly limits the use of oxide aerogels in high temperature applications.

Carbon materials and carbides have relatively higher hardness and melting points, and the highest heat-resistant temperature of carbide aerogels can reach 3000°C. It is currently the most promising aerogel material in the temperature range above 1200 °C. Carbides also have extremely high chemical stability, expanding the application of aerogels to aerospace, high-temperature furnaces, nuclear energy and other fields that require high-temperature heat insulation.

Carbide, carbon materials and other types of aerogels also have more potential applications due to their intrinsic properties. For example, SiC aerogels can be used as electromagnetic absorption materials; carbon material aerogels can be used as materials for supercapacitors.

1.5 Mainstream preparation process of aerogel: sol-gel + drying

At present, the large-scale industrialization is SiO2 aerogel, and the preparation process of aerogel is introduced as an example.

The preparation of aerogel usually includes two main processes: sol-gel and drying: the first step is to prepare wet gel through the sol-gel process; the second step is to replace the liquid substance in the gel with a certain drying method. gaseous state to produce aerogels.

Introducing fiber reinforcement in the sol-gel process, or using a cross-linking agent for cross-linking, can improve the mechanical properties of aerogels and is a common modification method.

The silicon source is the main raw material for the aerogel. Including inorganic silicon sources and organic silicon sources.

Solvents include water, ethanol, etc., and ethanol is used as a co-solvent to promote uniform mixing.

In the initial stage of the reaction, the silicon source is hydrolyzed to obtain the active monomer silicic acid, and then the silicic acid is locked to form a polymer (sol) with silicon-oxygen (-Si-O-Si-) sites, and then cross-linked with each other to form a Three-dimensional network structure of gel skeleton.

There are a large number of pores between the gel skeletons, which are filled with solvent molecules such as ethanol and water.

After the wet gel is prepared and aged, the liquid solvent in the gel needs to be replaced by a gaseous substance through a drying process, so as to prepare an aerogel. This process is the most critical step in determining the quality of the product. Drying methods include atmospheric drying, supercritical drying, high temperature drying, freeze drying and microwave drying.

At present, the main methods used in the industry are supercritical drying and atmospheric drying. The former is the most mainstream drying method since the invention of aerogel, with harsh conditions and high equipment requirements; atmospheric drying has low equipment requirements, but the drying time is long and the process is cumbersome. Freeze drying, high temperature drying and microwave drying are new methods proposed this year.

1.6 Aerogel modification learns from each other’s strengths and needs to continue to optimize in the future

In the preparation process of SiO2 aerogel, fiber compounding and flexibility modification can be used to improve the mechanical strength, hydrophobic modification to increase hydrophobicity, and doping modification to improve the stability at high temperature, thereby making up for the mechanical properties of SiO2 aerogel itself Poor, the structure is easy to collapse after absorbing water and so on.

As a relatively mature product, the current development direction of SiO2 aerogel is mainly to reduce costs, increase production capacity, and design and develop commercial products with better comprehensive performance.

1.7 The heat of aerogel research and development continues, and the number of patent applications grows rapidly

From 2000 to 2021, a total of 14,550 aerogel-related patents have been published in my country.

In 2000, 15 aerogel-related patents were published, and by 2010, there were only 91 patents; after that, the number of patents increased rapidly, reaching 3,079 in 2021. From 2010 to 2021, the average annual compound growth of the number of patent publications was 37.7%, which fully demonstrated aerogelation. The research interest of glue and the potential huge commercial value.