1、 Chemical precipitation method
Principle: Using silicates (such as sodium silicate) as raw materials, silica precipitates are generated through chemical reactions, and then dispersed in a solvent to form a suspension.
Steps:
Prepare silicate solution and precipitant (such as ammonium chloride).
Under suitable conditions (such as sodium silicate concentration of 0.4 mol/L, ethanol to water volume ratio of 1:8, pH value of 8.5), the precipitant is added to the silicate solution to generate silica precipitate.
After washing and drying the precipitate, disperse it in a solvent (such as deionized water) to form a silica suspension.
Characteristics: Simple operation, low cost, able to prepare amorphous nano silica suspension with small particle size and good dispersion.
2、 Sol gel method
Principle: Metal alkoxides (such as ethyl orthosilicate) are hydrolyzed in acidic or alkaline alcohol solutions to form oxide sols, which are then subjected to post-treatment such as aging and drying to obtain silica particles. Finally, they are dispersed in a solvent to form a suspension.
Steps:
Prepare ethyl orthosilicate, alcohol solution (such as ethanol), acid or base catalyst.
Add ethyl orthosilicate to an alcohol solution and initiate a hydrolysis reaction by adding a catalyst, resulting in the formation of silica sol.
The sol is aged for a period of time to form gel.
The gel is dried and ground to obtain silica particles.
Disperse the particles in a solvent to form a silica suspension.
Characteristics: It can prepare pure and uniformly distributed ultrafine silica particles, but the preparation time is relatively long.
3、 Condensation method (ion exchange method)
Principle: Using sodium silicate as raw material, impurity ions are removed through ion exchange resin to generate a polysilicic acid solution, which is further prepared into a silica suspension.
Steps:
Prepare sodium silicate solution and ion exchange resin.
Exchange the sodium silicate solution through cation exchange resin to remove sodium ions and other cationic impurities, and obtain a polysilicic acid solution.
Continue to pass the polysilicic acid solution through anion exchange resin to remove anionic impurities.
Prepare the processed polysilicic acid solution into a mother liquor to complete the generation of crystal nuclei.
Add the remaining polysilicic acid solution to the mother liquor at a certain speed to complete the growth of grains.
Concentrate using a certain process to achieve the desired concentration of silica suspension.
Characteristics: It can prepare silica suspension with small particle size, uniformity, less agglomeration, and high stability, but the process flow is complex and difficult to control.
4、 Microfluidic technology
Principle: Using microfluidic chips to control fluid flow, prepare monodisperse silica suspension droplets, and then obtain silica suspension through subsequent processing.
Steps:
Prepare silica powder and solvent (such as deionized water) to form a suspension with a certain mass fraction.
Use a microinjection pump to inject the suspension and dimethyl silicone oil into the innermost and outermost tubes of the microfluidic chip, respectively.
Set the appropriate flow rate to obtain monodisperse silica suspension droplets.
Place the droplets in an oven to evaporate the water, while the internal silica nanoparticles self assemble into a three-dimensional ordered structure.
Wash the obtained silica particles multiple times with solvent to remove residual dimethyl silicone oil around them, and obtain a silica suspension.
Characteristics: It can prepare silica suspension with good monodispersity, and can control the droplet size by adjusting the flow rate, thereby changing the final size of silica particles.