Preparation method of colloidal silica

At present, the main production methods of silica sol are: dissolution method, ion exchange method, peptization method, dispersion method, etc.

1. Silicon dissolution method: The method of preparing silica sol by using inorganic or organic bases as catalysts and reacting elemental silicon with pure water is called silicon dissolution method. The advantage of this method is that there is less impurity content in the finished silica sol product, and the colloidal particle shape, particle size, viscosity, p H value, density,

The purity is easy to control, the shape of the colloidal particles is round and uniform, the structure is compact, and the stability of the silica sol is good.

2. Ion exchange method: The ion exchange method is currently the most researched and most mature process, usually divided into the following two steps ① Preparation of active silicic acid ② Colloidal particle growth and concentration This method should be noted that there are generally a small amount of impurities in the finished product exists and needs to be purified. An effective way to remove impurities is centrifugation.

3. Electrolysis and electrodialysis: The preparation of silica sol by electrolysis and electrodialysis is an electrochemical method. Add electrolyte in the electrolytic electrodialysis cell, adjust the pH value of the electrolyte solution, control the current density, temperature and other reaction conditions of the electrolytic electrodialysis reaction, and in the electrolytic electrodialysis cell equipped with suitable electrodes (such as hydrogen evolution electrode, oxygen cathode) After the reaction, the finished silica sol can be prepared. The main advantage of this method is that the operating conditions for the preparation of silica sol can be controlled, and it is convenient to optimize the quality of the finished silica sol. It is an electrochemical method with development value.

4. Peptization method: The preparation of silica sol by the peptization method is to neutralize the water glass solution with acid to form a gel, and the obtained gel is filtered, washed with water, and then added with a dilute alkali solution, and the gel is dissolved under pressure and heating to obtain the sol . Main advantages and disadvantages: The silica sol prepared by this method has a wide particle size distribution and low purity.

5. Acid neutralization method: The acid neutralization method generally uses dilute water glass (Na2O . xSiO2) as the starting material, and inorganic acids such as dilute sulfuric acid as the acidifying agent [13]. Depending on the amount of acid used, acidic or alkaline silica sol can be prepared. The specific process steps include ion exchange to remove sodium ions, preparation of crystal nuclei, acid neutralization reaction, and grain growth. Main disadvantages: Silica sol prepared by acid neutralization generally has high content of impurity ions and poor stability.

6. Dispersion method: Dispersion method is a physical method that uses machinery to disperse SiO2 particles in water to prepare silica sol. The specific steps are as follows: Weigh a certain amount of deionized water into a dry and clean plastic cup, and fix it on a high-speed disperser. Start the high-speed disperser, add a certain amount of gas-phase SiO2 powder continuously to the cup, and cover the cup with a plastic film to prevent water evaporation and SiO2 powder from flying. After adding the SiO2 powder, add a certain amount of deionized water, adjust the high-speed dispersion speed, and keep it for 1.5h to obtain a SiO2 water dispersion. After aging the SiO2 aqueous dispersion overnight, disperse at a high speed for 2 h, add the additive solution, continue to disperse at a high speed for 2 h, and filter with a 300-mesh filter to obtain silica sol with good performance. Main advantages and disadvantages: Pan Helin et al. use appropriate dispersion process and additives to combine

Gas-phase SiO 2 powder is dispersed in aqueous solution to obtain a high-performance silica sol with a stability of up to one year and a viscosity as low as 0.01Pa..s, and its various performance indicators meet the requirements.