Silica aerogel is a lightweight nanoporous amorphous material with nanoporous structure, high specific surface area, high porosity, low density and very low thermal conductivity. It has broad application prospects in aerospace, military, medical, thermal insulation, electronics, environmental protection, industrial catalysis and other fields.
What is silica aerogel
Silica aerogel is a new miracle material in the 21st century. Although it is a solid, 99% of its composition is made of gas.Currently the lightest silica aerogel is only 3 milligrams per cubic centimeter, three times heavier than air, so it's also called "frozen smoke" or "blue smoke." Silica aerogel is a kind of nano-porous lightweight material with controllable structure. It is the lightest solid material known at present.Among them, silica aerogel is a new type of nano-porous super thermal insulation material, with powder and block, its hole rate up to 80 % ~ 99.8%, is a low density nano-porous amorphous material.Because silica aerogel contains nano-scale particles and pore structure (1-100nm), it has great specific surface area (200-1000m2 /g), high porosity (80-99.8%), low density (1-500kg /m3) and low thermal conductivity (0.02wm-1k-1).This shows unique properties in mechanics, acoustics, heat, optics and other aspects, for example, strong adsorption, small thermal conductivity, low refractive index, low elastic modulus, low acoustic impedance, typical parting structure.They are widely used in the fields of optics, electricity, acoustic impedance materials, catalysis, environmental protection, thermal insulation, medicine and life sciences.
How to make silica aerogel
The preparation of silica aerogel can be divided into three processes: gel preparation, gel aging and gel drying.
Gels are prepared by sol-gel method, generally by catalytic hydrolysis of solutions containing silicon.The dispersion media can be divided into water-sol, alcohol-sol and aerosol.Gel aging refers to the sols aging in the mother liquor for a period of time to strengthen its network structure and minimize the shrinkage in the drying process.In the drying process, the solvent in the sol pore structure should be removed and the pore structure should not change. Therefore, special drying process is required.
(1) Gel preparation
Gels are prepared by sol-gel method, generally by catalytic hydrolysis of solutions containing silicon.The dispersion media can be divided into water-sol, alcohol-sol and aerosol.The raw materials of gel preparation are also very important. At present, the main precursors are sodium silicate and silanolate.
(2) Gel aging
Gel aging is the process of dissolving and recondensation of heterogeneous gel particles.In the process of silica aerogel sol-gel, there are few link bonds between the secondary particles of silica, and only a few siloxane bonds connect the secondary particles together.After the dissolution and recondensation of the gel particles, the links between the secondary particles can be increased, and larger aggregate particles can be obtained to enhance the aerogel skeleton.Gel aging usually involves soaking the gel in an alcohol/water mixture of the original sol.The results showed that the gel aging was more complete and the gel skeleton strength was enhanced by increasing aging time and temperature.
Choosing suitable aging medium will also make the pore distribution more uniform and improve the pore structure.Increasing the alkalinity of the aging medium will enlarge the porosity and minimize the shrinkage of silica aerogel.
(3) Drying treatment technology
Drying is very important in the preparation of silica aerogel.In this process, the solvent in the silica aerogel pores should be removed, and the pore structure should not be damaged by capillary force to maintain the integrity of the pore structure.The main methods are supercritical drying, atmospheric drying and vacuum freeze-drying.