Spherical silica micro powder has excellent properties such as high transparency, high dielectric, high moisture resistance, high filling amount, low expansion, low stress, and low friction coefficient. It is widely used in many fields such as epoxy molding materials, catalysts, copper clad panels, adhesives, and aerospace.
At present, the mainstream methods for preparing spherical silicon micro powders include flame forming method, high-temperature melt spraying method, etc. The flame spheroidization method mainly involves crushing, screening, purification, fine grinding of quartz ore, and then feeding it into the high-temperature field generated by gas for high-temperature melting. Through surface tension spheroidization, spherical silicon micro powder is finally obtained by cooling. The disadvantage of this method is that the process is complex, and the quartz ore is difficult to remove completely, with low purity, and high energy consumption in the final high-temperature balling stage. The high temperature melting spray method is to melt the silicon oxide into liquid at more than 2000 degrees, and then form spherical silicon powder after spray cooling. This method is mainly adopted in the United States and Japan, which requires strict equipment.
The present invention discloses a solid spherical silicon micro powder and a preparation method thereof, wherein the preparation method comprises:
(1) Synthesis of silica sol
Silica sol with low solid content (1-5%) was synthesized by solution ‑ gel method, using tetraethyl orthosilicate as the organic silicon source, heating and stirring under alkaline conditions.
(2) Silica sol concentration
Heat and concentrate the low solid content silica sol mentioned above to obtain a high solid content silica sol (15% -50%).
(3) Material mixing and compounding
The high solid content silica sol and thickener were mixed and compounded under heating and stirring conditions to form a silica sol solution containing 0.001% -5% thickener. The selected thickener in this case is a specific thickener containing carboxyl or amide groups, such as polyacrylamide, carboxymethyl cellulose, carboxyethylcellulose, polyacrylic acid, polymethyl acrylic acid, carbomer, etc., which is easy to adsorb or react with the silicon hydroxyl groups on the surface of silica, thereby facilitating the aggregation of nano silica particles. Thickeners do not contain sodium or potassium ions to avoid cationic interference. The optimal content of thickener is 0.05% -2%, and the most optimal is 0.1% -1%.
(4) Spray drying
After the compounded silica sol is dried by spray (both pneumatic and centrifugal), spherical silica powder can be obtained, but at this time, the moisture content is 5% ‑ 10%, and the specific thickening agent is removed by high-temperature calcination.
(5) Heat treatment
The product obtained after spray drying is sent to muffle furnace for high temperature heat treatment to burn off the excess thickener. After that, it is cooled to room temperature and taken out to obtain the target high-purity spherical silicon powder.
Through the above process, spherical silica micro powder with a purity of 99.999% can be obtained, and the preparation process is simple and easy, with low energy consumption and low cost.
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