1. Rubber carbon black | The difference in structure between fumed silica and precipitated silica
Fumed silica is not produced through simple crushing and special drying. In any case, the primary particle is the smallest particle, but it is prone to agglomeration (because there are a large number of silanol groups on the surface), and the special surface is its most important property. The large internal surface area of silica gel is the main reason for its strong adsorption capacity. The primary particles of fumed silica are produced by flame hydrolysis, and it only has an outer surface area. This is also the reason for the improved rheology of many systems combined with fumed silica, such as the application of fumed silica in powder coatings.
2. Rubber carbon black | The difference in the number of silicon hydroxyl groups between fumed silica and precipitated silica
Differences in product properties and product application performance are influenced by drying loss of silica. The lower the drying loss requirement of silica, the better, for example, the lower the drying loss, the better the insulation of silicone rubber for cables; the stability of adhesives and sealants during storage is increased. The difference in silanol number (that is, SiOH/nm2) is the main reason for the difference between silica. The number of silanol groups of hydrophilic fumed silica is between 2 and 3, while the silanol content of precipitated silica is around 6, and the silanol content of hydrophobic silica is less than 1.
3. Rubber carbon black | The difference in silicon purity between fumed silica and precipitated silica
The difference in purity of silica is also worth noting. Fumed silica anions contain only a very small amount of chloride ions and metal oxide impurities. The anions of precipitated silica contain acid ions, basic ions and alkaline earth metal ions. This is because the difference in process technology leads to the difference in product purity.