White carbon black is the general term for white amorphous powdered silicic acid and silicate products, mainly referring to precipitated silica, fumed silica, ultra-fine silica gel and aerogel, as well as powdered synthetic aluminum silicate and calcium silicate. According to the production method, white carbon black can be divided into precipitation white carbon black and vapor phase white carbon black (scientific name: vapor phase silica).


Fumed silica is white amorphous flocculent translucent solid colloidal nanoparticles in normal state, non-toxic, and has a huge specific surface area (100~400m2/g). The fumed silica is all nano silica, the purity of the product is more than 99.8%, and the primary particle size is 10~40nm; Precipitated silica can be divided into traditional precipitated silica and special precipitated silica. The former refers to silica produced with acid (sulfuric acid, hydrochloric acid, etc.), CO2 and water glass as basic raw materials, and the latter refers to silica produced by special methods such as high gravity technology, sol-gel method, chemical crystal method, secondary crystallization method or reversed micelle microemulsion method.


1. production method of white carbon black

The traditional method of preparing white carbon black is to use sodium silicate, silicon tetrachloride and tetraethyl orthosilicate as silicon sources. Except for sodium silicate, other costs are high. The new method uses cheap nonmetallic ore as silicon source, which greatly reduces the production cost of silica.

1.1 gas phase method

Mainly chemical vapor deposition (CAV) method, also known as pyrolysis method, dry method or combustion method. Its raw materials are generally silicon tetrachloride, oxygen (or air) and hydrogen, which are formed by reaction at high temperature. The reaction formula is:

SiCl4＋ 2H2＋ O2—>SiO2＋4HCl

The air and hydrogen are sent to the synthetic hydrolysis furnace after drying, dedusting and filtration respectively. Send silicon tetrachloride raw material to evaporator for heating and evaporation, and send it to synthetic hydrolysis furnace with dried and filtered air as carrier. After silicon tetrachloride is gasified at high temperature, it is hydrolyzed with a certain amount of hydrogen and oxygen (or air) at high temperature; At this time, the generated fumed silica particles are very fine and form aerosols with the gas, which is not easy to capture. Therefore, it is first aggregated into larger particles in the aggregator, then collected by the cyclone separator, and then sent to the deacidification furnace. The fumed silica is purged with hot air or auxiliary steam until the pH value is above 3.6.

1.2 precipitation method

Precipitation method, also known as sodium silicate acidification method, uses water glass solution to react with acid to obtain white carbon black through precipitation, filtration, washing, drying and calcination. The reaction formula is:

Na2SiO3 + 2h+ - > silica + 2na+ + H20

White carbon black is an indispensable reinforcing material in the rubber industry. It is widely used in industrial fields such as tires, rubber products, resins, coatings, inks, pesticides, papermaking, pharmaceuticals and so on. At present, more than 90% of China's white carbon black is used in the rubber industry, of which 60% is used in the shoemaking industry.

2. comparison between fumed silica and precipitated silica

2.1 structural differences between fumed silica and precipitated silica

Fumed silica is not produced by simple crushing or special drying. In any case, the smallest particle is the primary particle, but it will be reunited more or less (because there are a large number of silicon hydroxyl groups on its surface). The special surface is its most important property. Silica gel has a large internal surface area, which is the reason for its strong adsorption capacity. In contrast, the primary particles of fumed silica are hydrolyzed by flame and only have surface area. This also explains why the rheology of many systems has been greatly improved after they are combined with fumed silica, such as the application of fumed silica in powder coatings. Table 1 shows the particle size of fumed silica.