What is the difference between Fumed Silica and Precipitated Silica?
They are produced by different raw materials and by different production process. The fumed silica is with high purity and small particle size, as well as the rigidly structure. However regarding the precipitated silica, its moisture contents and ion contents are high due to the limited of its production technology. In additional, their appearance and surface chemical are different.
What are the influence factors of High Temperature Vulcanization Silicone Rubber (HTV) with Fumed Silica?

The influence factors of silica rubber, including the fumed silica’s bet specific surface, dosage and whether give surface treatment or not and so on. (fumed silica’s moisture content can affect the reinforcement and rheology and transparency, etc).

How to fix the surface hydroxyl of fumed silica?
The surface hydroxyl number of fumed silica is fixed commonly by the method of infrared, lithium reagent and Karl fischer reagent, also by method of thermogravimetric analysis.
There are three phases for the Fumed silica’s losing of weight. The first phase, it will lost the dissociative adsorbed water under the room temperature - 190 ℃. The second phase, it will lost the adsorbed water which is formed the hydrogen bond with silica hydroxyl under the temperature 190-197 ℃. The third phase, it will lost the water which formed after hydroxyl’s condensation under the temperature 917-1320 ℃.
The number of surface hydroxyl can be calculated according to the weight lost date. The unit of testing is generally stated by (a/nm2)
How to deal the surface treatment to the fumed silica and what are the primer types?
Regarding the surface treatment of fumed silica, it gets the chemical reaction between some certain chemicals and hydroxyl of fumed silica by the surface treatment technology.  It makes the primer to join the surface of fumed silica through chemical bond and get permanent surface properties,
There are mainly two methods of treatment. One is to heat the fumed silica and primer, which makes the primer boiling. It is also named Wet Process. One is to touch and react the dry fumed silica and primer steam. It is also named Dry Process.
Most foreign companies adopt the continuous treatment of Dry Process. The shortcoming of Wet Process includes the difficulty to separate and purify the product as well as the serious pollution.
The surface treatment primer is generally used by organic silicon compounds, alcohols, amine and polymer grafting, etc