Direct acidification method:
Generally, dilute water glass is used to remove Na⁺ through ion exchange resin to prepare active silica sol. The active silica sol is heated and kept warm for a period of time to form a certain crystal nucleus of the sol, directly acidified, and the appropriate reaction conditions are controlled to make the crystal grow, so that a dilute large-particle silica sol can be prepared. After concentration and purification, a large-particle, high-concentration silica sol can be obtained.
Ion exchange method (particle growth method):
The ion exchange method uses water glass as a raw material, removes Na⁺ and other metal cations in the water glass through ion exchange reaction, and generates a polysilicic acid solution. Prepare seed crystals, generate particle growth reaction, and then remove other anions in the water glass through anion exchange resin. If high-purity silica sol is to be made, multiple exchanges are required to obtain active dilute silica sol. The active dilute silica sol is stabilized, and then reacted under normal pressure or high temperature and high pressure to generate a large-particle silica sol. Finally, it is concentrated to obtain a large-particle, high-concentration silica sol.
Pressurized heating method: Under special requirements, pressurized heating is required to further polymerize polysilicic acid, and the particle size continues to grow to obtain large-particle silica sol. Under heating or high pressure conditions, a large number of active silica molecules will undergo dehydration polymerization to form silica colloid particles, and will also undergo polymerization with the formed silica colloid particles (mother core), causing the particle size of the mother core silica colloid particles to continue to grow.