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In the production process, the liquid silicon compound is first mixed with a liquid solvent capable of rapid evaporation to form a gel, which is then dried in an apparatus (autoclave) similar to a pressurized cooker and heated and depressurized, forming a porous sponge-like structure. Dr. Jones obtained 99.8% of the total air volume in the final airgel. The main components and glass is also the same as silicon dioxide, but because it is 99.8% air, so the density of only one thousandth of the glass. 

Effect of water amount on sol-gel of silicon dioxide:

It was found that the gelation time decreased linearly with the increase of TEOS, which was in agreement with the hydrolysis rate of TEOS. However, if the water relative to the TEOS hydrolysis of the theoretical amount of material than 4 after the water as a polycondensation reaction of the product will make the gel time is gradually extended. It is found that the relative increase in water content has a significant negative effect on the finished product properties (such as density). It is believed that the increase in water content in the gel increases the difficulty of the subsequent process and leads to a significant increase in shrinkage.

The temperature rise is favorable for the collisions of the colloidal particles, which is considered to be in inverse proportion to the gel time. However, the high temperature easily leads to the unevenness and coarseness of the structure, so the gel temperature should be lower than 70 ℃. 

It was found that the sol-gel reaction could be carried out at low temperature, and the time of the sol-gel viscosity was prolonged obviously, and the stable sol could be preserved for a long time. The sol is molded and aged, and the critical fluid is dried to obtain a silicon oxide airgel without cracking, transparency and high porosity.

 

 

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