Specific process of gas phase hydrolysis for preparing Sodium Colloidal Silica/Silica Sol

In the vast field of chemical material preparation, gas phase hydrolysis has an important position in the preparation of Sodium Colloidal Silica with its unique advantages. This method can accurately control the particle size distribution and purity of the product, and can also ensure that the produced silica sol has good dispersibility and stability.

The main raw materials of gas phase hydrolysis are chlorosilane, such as silicon tetrachloride (SiCl₄), and water vapor as a reaction medium. These raw materials need to be strictly screened and pretreated to ensure its purity and reactivity. It is also necessary to prepare an appropriate amount of hydrogen or oxygen as a carrier gas to deliver the raw materials into the reaction zone.

The reaction process of gas phase hydrolysis is as follows.
Mixing and heating: Chlorosilane and water vapor are mixed in a certain proportion and heated to the high temperature required for the reaction through a preheating system. This temperature range is usually between 1000℃ and 2000℃, depending on the type of reactants and reaction conditions.
Gas-phase hydrolysis: At high temperatures, chlorosilanes undergo violent gas-phase hydrolysis reactions with water vapor. In this process, the silicon-chlorine bond in the chlorosilane molecule breaks and combines with the hydroxide in the water molecule to generate silicon dioxide (SiO₂) and hydrogen chloride (HCl). The reaction equation can be simplified as: SiCl₄ + 2H₂O → SiO₂ + 4HCl.
Nucleation and growth: As the reaction proceeds, the generated silicon dioxide particles begin to nucleate and gradually grow. These particles remain suspended in the gas phase and form larger particles through collision and polymerization. The hydrogen chloride gas generated by the reaction is promptly discharged from the reaction system to avoid adverse effects on the reaction process.
Cooling and collection: The silicon dioxide particles generated by the reaction enter the cooling zone with the air flow, cool rapidly and solidify at low temperatures, and are absorbed by water to form silica sol. In order to improve the stability and dispersibility of the silica sol, the solution may need to be further treated, such as adding stabilizers or adjusting the pH value.

Silica sol prepared by gas phase hydrolysis usually needs a series of subsequent treatments to remove impurities, adjust particle size distribution and improve product performance. These treatment steps may include filtration, washing, drying and dispersion. The final Sodium Colloidal Silica/Silica Sol has good physical and chemical properties and is widely used in precision casting, coating industry, papermaking industry and catalyst carrier.