Fumed silica powder
Fumed silica is a nano-scale white powder produced by the high-temperature hydrolysis of silicon halide in a hydrogen-oxygen flame. It is an amorphous silica product with a primary particle size of 7~40nm. The aggregate particle size is about 200-500 nanometers, and the specific surface area is 100-400m2/g. The purity of fumed silica is high – the content of SiO2 is not less than 99.8%. The untreated fumed silica aggregates contain a variety of silanol groups.
Primary particle size and powder
In the preparation process of fumed silica powder, silicon tetrachloride, hydrogen and air undergo high-temperature reactions in a reactor to form primary particles with a particle size of 7 to 40 nm. Because the primary particles are extremely fine, they generate aerosols with gases, which are difficult to capture. In order to facilitate packaging, storage and transportation, first use an agglomerator to aggregate the particles into larger particles, that is, fumed silica powder.(* This picture is just for a better reading experience, not the actual fumed silica molecular structure)
Packing of fumed silica powder
Even after polymerization in the agglomerator, the fumed silica powder is very fluffy and has extremely high requirements for moisture resistance. It is difficult to package the silica powder with traditional processes. Vacuum packaging technology solves this problem well. The pressure difference between the vacuum chamber and the feeding device is used to suck fumed silica into the packaging bag so that the powder can be packaged in a sealed vacuum state, and the powder is not exposed. in the air. This can accurately control the weight, achieve a good moisture-proof effect, and solve the problem of dust leakage.
The disperse of fumed silica powder
Due to the polysiloxane inside the fumed silica and the active silanol on the outer surface, it has extremely strong water absorption, making it hydrophilic, and it is difficult to wet and disperse in the organic phase. Moreover, due to the presence of hydroxyl groups on the surface, the surface energy is relatively large, and the aggregates tend to aggregate, which adversely affects the application performance. In some fields that require high dispersibility, in order to achieve an ideal dispersion effect, it is necessary to use a dispersing machine and a specific dispersing process.
Hydrophobic fumed silica is a new type of fine inorganic material with a special structure, which has almost all the superior properties of ordinary fumed silica, and due to its hydrophobicity and special surface structure, the application field is greatly expanded.