What Are the Unique Structure and Properties of Fumed Silica?

As we all know, fumed silica is an ultrafine powder material obtained by the high-temperature hydrolytic condensation of halosilanes in a hydroxide flame. Due to its unique preparation process, it has a different structure and unique properties from other silica products.

So what are the unique structure and properties of fumed silica?

(1) Unique "three-dimensional dendritic" structure

As fumed silica in the production process, the first is the hydrolysis of halosilane condensation into a single silica particles, and then gradually grow into 7-40 nanometers of spherical particles, the particles are called "primary particles" (Primary Particle) of silica.

The "primary particle" in the reaction furnace with the direction of the flame continues to move forward, the particles collide with each other, at this time, because the temperature in the reaction furnace is still relatively high, the particles are still close to the molten state, the particles collide and fuse together, forming a three-dimensional dendritic structure of multiple spherical particles fused together, known as the silica "Aggregate" (Aggregate Particle). Since the particles in the aggregates are fused together, they are stable structures that are almost impossible to separate.

The silica "Aggregate Particle" continues to move forward and collide with the airflow in the pipe, and then joins together to form a flocculent, fluffy powder called the silica "Agglomerate Particle". Because the temperature inside the pipe is low, the connection between the "aggregates" is only connected together by physical adsorption, which is an unstable structure, and under certain mechanical force, it is separable (dispersable).

(2) High surface activity

Fumed silica in the process of high-temperature hydrolysis condensation, the surface also has some residual silicon hydroxyl (Si-OH), the existence of surface silicon hydroxyl, so that the surface of fumed silica polarity is strong, the surface activity is high.

The presence of "siloxyl" and "silicon hydroxyl" on the surface of fumed silica, in which the silicon hydroxyl has high activity, can form hydrogen bonds, or react with other groups, which also ensures the formation of a stable network between the silica particles, and at the same time has good interaction with other media, so that the silica presents good strengthening, toughening; thickening thixotropy and anti-settling properties.

In addition, the existence of silica hydroxyl groups also provides the possibility of surface modification of fumed silica, the choice of different structures of surface modifiers and silica hydroxyl groups for reaction, grafting some functional groups to the surface of fumed silica, thus making the fumed silica more diverse functions.

(3) Small particle size and large specific surface area

The "native particle size" of fumed silica is 7-40nm, what is this concept? We can understand it from the data comparison in the following table. If we enlarge a fumed silica particle to the size of a standard soccer, we need to enlarge it about 30 million times; if we enlarge a soccer about 30 million times in equal proportion, it will become about the size of Mars.

Due to the small particle size of fumed silica, its specific surface area is very large, usually the specific surface of fumed silica is 100-400m2/g. Usually we have a 150m2 house, its indoor area is only about 120m2, that is, using the current market general * low specific surface area of fumed silica products (such as HL-150), less than 1g, its specific surface area can cover The entire indoor area of the house! And if the product with high specific surface area (such as HL-380), only 18.8g, its specific surface area is equivalent to the area of a standard soccer field!

It is because of the small particle size and large specific surface area of fumed silica, making it has good adsorption properties, can be widely used with catalysts, food, medicine, insulation materials and other fields, playing the adsorption, anti-caking, heat insulation and other functions.

In addition, fumed silica also has a series of unique properties such as small bulk density and high porosity, which are inseparable from the unique production process of fumed silica; and these unique structures and properties also bring unique application properties for fumed silica that are different from other silica.