What is aerogel?
Silica Aerogel is a lightweight nano-solid material with a nanoporous network structure and a network skeleton filled with a large amount of gaseous dispersion medium. Thanks to the special characteristics of its structure, aerogel materials have a wide range of applications, among which silica aerogel materials are the result of the exploration of SiO2 applications based on aerogel technology. Compared with other aerogel materials, SiO2 aerogel has abundant raw material sources, a simple process and good controllability; in terms of performance, it has the characteristics of high transparency, low thermal conductivity and high specific surface area.
Basic properties of SiO2 aerogel
The unique properties of SiO2 aerogel determine its excellent properties in thermal, optical, electrical and acoustic aspects.
Thermal properties
The uniform nanoparticle skeleton structure and size pore size distribution of SiO2 aerogel material give it an extremely low density and thermal conductivity, so SiO2 has an excellent performance in thermal protection. Studies have shown that the thermal convection effect of silica aerogel is negligible, and in general silica aerogel its thermal conductivity consists of gaseous heat conduction, solid state heat conduction and thermal radiation. The gas in the pores of the material at atmospheric pressure can be negligible for heat conduction, so the heat conduction of silica aerogel is mainly determined by solid-state heat conduction and radiation heat conduction. The extremely low density increases the solid heat conduction pathway and effectively reduces the solid state heat conduction; while the addition of shading agents can greatly increase the specific extinction coefficient and reduce the radiation heat conduction, thus giving it a very low thermal conductivity.
Optical properties
Most silica aerogels can be made into fully transparent or translucent materials. It has no reflective presence to incident light, blocks thermal infrared radiation from ambient temperature, has good transparency, and is a good thermal insulation and transparent material.
Electrical properties
The dielectric constant of silica aerogel is low, and its dielectric constant has a certain relationship with both density and porosity. Research shows that the dielectric constant decreases as the porosity increases.
Acoustic properties
Generally, the resistance of silica aerogel porous materials to acoustic waves is related to their pore size and particle size. The density of most silica aerogels is very low, so the sound propagation rate is very small, and the longitudinal sound velocity can be as low as 100m/s order of magnitude, and the acoustic impedance of silica aerogels has a large variable range, and the corresponding silica aerogels can be prepared by controlling the density to control the different acoustic resistance z.
Preparation method of SiO2 aerogel
The main process of preparing silica aerogels consists of three parts:
Sol-gelation process: The sol is obtained by the precursor reaction of the silica source and then hydrolytic condensation occurs by adding a catalyst to obtain the wet gel.
Aging of the gel: The wet gel is aged in the mother liquor to improve its mechanical strength and stability.
Drying process: The liquid dispersion medium in the gel has to dry the gas from the pores to form silica aerogel.
Application of silica aerogel
Silica aerogel is a material with a wide range of applications. It consists of extremely fine silica particles with high porosity and surface area, which can adsorb moisture, organic molecules and other substances. Therefore, it is widely used in the following fields:
1. Thermal insulation material: The low thermal conductivity and excellent thermal insulation properties of silica aerogel make it an excellent thermal insulation material. It is widely used in the construction, aerospace and automobile industries.
2. Adsorbent: The high porosity and surface area of silica aerogel make it an excellent adsorbent. It can be used in the fields of water treatment, air purification, drug separation and catalytic reaction.
3. Electronic material: silica aerogel has good insulating performance and electrical conductivity, and is widely used in electronic components, batteries and solar cells, etc.
4. Medical use: silica aerogel has excellent biocompatibility and adsorption ability, and is used in the preparation of medical adsorbents, artificial organs and drug slow-release systems.
5. Petrochemicals: SiO2 aerogel can be used for the separation and purification of petrochemicals, as well as for catalytic reactions and hydrogen storage materials.
Application fields of SiO2 aerogel
People make use of the microstructure to give the properties of silica aerogel, and through the appropriate processing of silica aerogel materials, then a wide range of applications in the field of thermal insulation, optical field, electrical field, catalytic field and medical field.
Heat insulation field
With extremely low density, silica aerogel can achieve the same thermal insulation effect with lighter mass and smaller volume compared with traditional thermal insulation materials, and nowadays it has shown broad application prospects in aerospace, military and civil fields. For example, the British "Jaguar" fighter jet is using silica aerogel insulation composite material as the cabin insulation layer. The use of silica aerogel insulation composites on weapon power units can not only effectively prevent the diffusion of heat sources, but also facilitate the anti-infrared detection of the weapon itself. In the field of building materials, silica aerogel is also an excellent environmentally friendly and efficient heat and sound insulation lightweight construction material. Better transparency and good insulation properties also make it a promising material for window insulation.
Optical field
The nanoporous structure of silica aerogel gives it a long average free range in the visible range and good light transmission, and the reflected light loss is negligible when it is used as a light transmission material. The optical reflective film prepared by using the optical properties of silica aerogel can be applied to high-power laser system optical components, display devices and solar cell protection glass.
Electrical field
The ultra-low dielectric constant of silica aerogel has led to a large number of applications in the field of electricity as a high-temperature wave-transparent material for missiles.
Catalytic field
The unique nanoporous three-dimensional network structure, resulting in ultra-fine particles, high porosity, high specific surface area, low density and other characteristics, which makes it has a strong adsorption, in terms of activity, selectivity and life of the loaded catalyst greatly superior to the traditional catalyst, and therefore has great application value in the field of catalysis.
Medical field
Silica aerogels have extremely high porosity, as well as certain bio-organism compatibility and biodegradability, and thus can be used in biomedical fields such as diagnostic agents, artificial tissues, human organs, and organ components. For example, carrying drugs through adsorption-related solutions can be applied to medical behaviors such as drug delivery and controlled release systems. Moreover, the sensitive response of silica aerogel-loaded enzymes to the reaction and the presence of organisms can be used to fabricate biosensors.
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