High temperature resistant gas gel insulation material
Aerogel is a high-quality and efficient thermal insulation material with high porosity, which can effectively reduce the solid phase heat conduction of the material. Its pore size is mainly distributed in the mesoporous range (2-50nm), effectively inhibiting the gas phase heat transfer. Aerogel materials can be divided into oxide gel materials, carbon gel materials (high temperature resistance up to 3000 ℃) and carbide gel materials according to different components. The following sections introduce the above three high-temperature resistant gas gel insulation materials。
1、 Overview of aerogel materials
The high porosity of aerogel materials and the mesoporous structure formed by the interconnection of nano network skeletons determine that aerogel materials have excellent thermal insulation performance, and are used as efficient thermal insulation materials in military and civil fields such as high-temperature catalyst carriers, high-temperature kilns, and ultra-high sound velocity aircraft. Aerogel materials have thermal insulation, sound insulation, nonlinear optical properties, filtration and catalytic properties.
Thermal insulation characteristics
The porosity of gel material is more than 90%, and the pore size of gel is in the range of 2-50nm mesopore. This special structure determines that it has excellent thermal insulation characteristics. At the same time, the gel material can maintain the integrity of its network structure at high temperatures, and is not easy to sinter at high temperatures.
Al2O3 high temperature resistant aerogel material
Sound insulation
The low sound speed of silicon aerogel makes it an ideal acoustic delay or high temperature sound insulation material. The variable range of acoustic impedance of this material is relatively large (103-107kg/m2 · s), making it an ideal acoustic impedance coupling material for ultrasonic detectors.
nonlinear optical properties
Silicon aerogel has a nano network quantum dot structure. After doping Si and C60 by chemical vapor infiltration, strong visible light emission can be observed. Further use of the structure of silicon aerogel and the nonlinear optical effect of C60 can further develop a new type of laser protective mirror.
Filtration and catalytic properties
The nanostructured aerogel can be used as a new type of gas filtration material. Unlike other materials, the material has uniform pore size distribution and high porosity, so it is an efficient gas filtration material. Due to the large specific surface area of this material, aerogel also has broad application prospects as a new catalyst or catalyst carrier.
2、 High temperature resistant gas gel insulation material
Aerogel materials can be divided into oxide gel materials, carbon gel materials (high temperature resistance up to 3000 ℃) and carbide gel materials according to different components.
Oxide aerogel material
Oxide aerogels are prone to crystal transformation and particle sintering in high temperature region (>1000 ℃), and their temperature resistance is relatively poor, but they have low thermal conductivity in medium and high temperature region (<1000 ℃).
Oxide aerogel materials mainly include SiO2, Al2O3, TiO2, ZrO2, CuO, etc.
(1) SiO2 aerogel material
SiO2 aerogel is a kind of high temperature resistant aerogel that has been studied most and maturely in the field of thermal insulation at present. Its porosity is as high as 80%~99.8%, the typical size of the pores is 1~100nm, the specific surface area is 200~1000m2/g, the density can be as low as 3kg/m3, and the thermal conductivity at room temperature can be as low as 12m. W/(m · K).
SiO2 aerogel material
SiO2 aerogel materials are usually compounded with infrared light blocking agents and reinforcements to improve the thermal insulation and mechanical properties of SiO2 aerogel, so that it is not only a practical nano porous super thermal insulation material, but also has good thermal insulation and mechanical properties. It is mainly used for thermal insulation in aerospace, military, electronics, architecture, home appliances, industrial pipelines and other fields.
Common infrared light blocking agents include silicon carbide, TiO2 (rutile and anatase), carbon black, potassium hexatitanate, etc; Common reinforcement materials include ceramic fibers, alkali free ultrafine glass fibers, polycrystalline mullite fibers, aluminum silicate fibers, zirconia fibers, etc.
(2) ZrO2 aerogel material
The pore diameter of ZrO2 aerogel material is smaller than the average free path of air molecules, there is no air convection in the aerogel, the porosity is very high, and the volume ratio of solids is very low, so the thermal conductivity of the aerogel is very low. Compared with SiO2 aerogel material, ZrO2 aerogel has lower thermal conductivity at high temperature, which is more suitable for thermal insulation application at high temperature section, and has great application potential as high-temperature thermal insulation material. At present, there are few reports on the application of ZrO2 aerogel in the field of thermal insulation, and researchers mainly focus on the research of the preparation process of ZrO2 aerogel gel.
The main preparation method of ZrO2 aerogel is a series of hydrolysis polycondensation of zirconium salt precursor. Its preparation mainly includes two parts: preparation of wet gel and drying. Generally, supercritical drying and freeze drying are used. The commonly used wet gel preparation methods include zirconium alkoxide hydrolysis, precipitation, alcohol water solution heating, dropping epoxy propane and inorganic dispersed sol gel. The preparation of ZrO2 aero gel with cheap inorganic zirconium salt as precursor and how to improve the thermal stability of zirconia aero gel at high temperature are one of the research focuses of researchers.
(3) Al2O3 aerogel material
Al2O3 aerogel material
Alumina aerogel material has nano porous structure, which makes it have lighter weight and smaller volume to achieve equivalent thermal insulation effect. At the same time, it has high porosity, high specific surface area and open texture structure, which has potential application value in catalyst and catalytic carrier. Alumina aerogel can also be used as high-voltage insulation material, substrate material of high-speed or overspeed integrated circuits, isolation medium of vacuum electrode and supercapacitor.
Carbon aerogel material
The biggest feature of carbon aerogel is its temperature resistance up to 2000 ℃ under inert and vacuum atmosphere, and the temperature resistance after graphitization can even reach 3000 ℃. In addition, the carbon nanoparticles in carbon aerogel itself have excellent absorption performance for infrared radiation, thus producing an effect similar to infrared sunscreen, so its high temperature thermal conductivity is low. However, in the presence of oxygen, the oxidation of carbon aerogels occurs above 350 ℃, which greatly limits their application in the field of high temperature insulation. With the development of high oxidation resistant coatings such as SiC, MoSi2, HfSi2, TaSi2, etc., coating dense oxidation resistant coatings on the surface of carbon aerogel materials to prevent the further diffusion of oxygen will make the materials have great application prospects.
Carbide aerogel material
Carbide materials have excellent oxidation resistance, but their own thermal conductivity is high. Making them into aerogels with three-dimensional network structure can greatly reduce the thermal conductivity of materials and further improve the thermal insulation performance of materials. However, the research on carbide aerogels at home and abroad is relatively few, especially the research on blocky carbide aerogels with good formability is still in the initial stage, and the research on them as efficient thermal insulation materials is also relatively scarce, which is limited to the preparation and characterization of this material.
Multi-component aerogel materials
Multicomponent aerogel materials mainly include SiO2/Al2O3, TiO2/SiO2, C/SiC, C/SiO2, Si-C-O, Al-C-O, etc.
SEM pictures of graphene oxide alumina composite aerogel
3、 Application of high temperature resistant gas gel thermal insulation material
1. Aerospace field
Nanoporous aerogel super thermal insulation material can achieve equivalent thermal insulation effect with lighter weight and smaller volume. This characteristic gives it a significant advantage in the fields of aviation and aerospace applications. Used as insulation material for aircraft engines, it not only provides excellent insulation but also reduces the weight of the engine.
Application of Nanoporous Aerogel Super Thermal Insulation Materials in Aerospace Field
2. Industrial and building insulation field
High temperature resistant aerogel thermal insulation materials have a wide range of potential applications in industrial and civil fields. Firstly, thermal equipment is commonly found in the power, petrochemical, chemical, metallurgical, building materials industries, and other industrial sectors. In industrial energy conservation, nanopore super insulation materials also play a very important role, and some special parts and environments urgently need efficient super insulation materials due to weight, volume, or space limitations.
High temperature resistant aerogel thermal insulation material applied to pipeline laying
3. Hydrogen storage materials
Carbon aerogels have high specific surface area, low density, continuous network structure, small pore size and communication with the outside world, and have excellent hydrogen absorption and desorption properties. It is understood that the US Department of Energy has set up a special organization to study metal doped carbon aerogels for hydrogen storage and provided financial support.
Application of carbon aerogel in hydrogen storage materials
4. Thermal battery field: High temperature resistant gas gel thermal insulation material is applied to battery thermal insulation material, which can extend the working life of the thermal battery and prevent the generated heat from affecting the components around the thermal battery.
High temperature resistant gas gel thermal insulation material applied to battery thermal insulation material
