The preparation of Si0₂ aerogel insulation material is usually composed of sol-gel, aging and drying.

1. Sol-gel process

In the sol-gel process, silicon-containing raw materials are dispersed in a specific solvent and hydrolyzed, and the resulting active monomers form nanocluster structure sol through polymerization reaction. After standing for a period of time, the clusters adhere to each other and form a gel with a network space structure. The gel is filled with the remaining liquid reagent after the chemical reaction, and the low-density Si0₂ aerogel material is properly aged, dry and porous, disordered, and has a nanocontinuous network spatial structure.

2. Silicon source

The silicon source of Si0₂ aerogel material can be divided into silicate silicon source with water glass as the main, and silanol silicon source with ethyl orthosilicate and methyl orthosilicate as the precursor.

Water glass is a soluble alkali metal silicate formed by the combination of alkali metal oxides and silicon dioxide. According to the types of alkali metals, water glass can be divided into sodium water glass and potassium water glass. Si02 aerogel was prepared from water glass with an average pore size of 6.3 nm and a specific surface area of 297. 7m²/g.

Compared with water glass, high-purity silanol-containing salt is expensive, but the Si0₂ aerogel prepared by it has good morphology and better performance, and is often used in the preparation of high-end Si02 aerogel. Commonly used silica-containing alkols are mainly ethyl orthosilicate, methyl orthosilicate, methyl triethoxysilane, methyl trimethoxysilane, polysiloxane, sesquisilane and so on. Si02 aerogel with higher optical transparency and lower thermal conductivity was prepared by hydrolysis of methyl orthosilicate into a mixture of methanol and distilled water.

3. Drying process

Drying treatment is an important step in the preparation of Si0₂ aerogel. Si0₂ aerogel will bear huge shrinkage pressure during drying. Improper drying method will cause Si0₂ aerogel to shrink, crack and deform. At present, there are three commonly used drying methods: freeze drying, supercritical drying and atmospheric drying.

The method of freezing the solvent in the gel pores at low temperature and then removing the frozen solvent by sublimation is called freeze drying method. This method can eliminate the stress of liquid bending surface and avoid the collapse phenomenon caused by skeleton shrinkage. However, when the liquid is frozen, the crystal or grain formed will destroy the mesh structure of the gel, the drying effect is poor, and it is difficult to form a block aerogel.

Supercritical drying is to control the pressure and temperature, so that the solvent reaches the supercritical state, in this state there is no gas-liquid interface between the liquid and the gas fluid, can ignore the capillary force between the solvent and the gel pores to discharge it, without destroying the structure of the gel. Although the aerogel produced by supercritical drying method has excellent performance, the expensive drying equipment, harsh process conditions and high operational risk of this method also limit the industrial mass production of aerogel.

Under normal pressure conditions, the temperature is raised to the boiling point of the solvent, so that it evaporates out of the method is the atmospheric pressure drying method. Although the atmospheric pressure drying process is simple, safe and low cost, the gel prepared is prone to cracking. The key point of this method is to overcome the damage of the gel mesoporous caused by the surface tension of solvent evaporation.