Is vapor-phase white carbon black better, or precipitation white carbon black?

White carbon black is the general term for white amorphous powdery silicic acid and silicate products, mainly refers to precipitated silica, fumed white carbon black, ultrafine silica gel and aerogel, and also includes powdered synthetic silica calcium, aluminum and the like
.
White carbon black is roughly divided into precipitation method white carbon black and gas phase method white carbon black (scientific name: fumed silica) according to the production method
.
? Gas phase method white carbon black is white amorphous flocculent translucent solid colloidal nanoparticles under normal conditions, non-toxic, and has a huge specific surface area (100-400m2/g)
.
The fumed white carbon black is all nano-scale silica, the product purity is over 99.
8%, and the primary particle size is 10-40nm; the precipitation method white carbon black is divided into the traditional precipitation method white carbon black and the special precipitation method white carbon black.
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 the use of supergravity technology, sol-gel method, chemical crystal method, secondary crystallization method or reverse Silicon dioxide produced by special methods such as phase micelle microemulsion method
.
? Comparison of vapor-phase method white carbon black and precipitation method white carbon black? 1.
The difference in structure between vapor-phase method white carbon black and precipitation method white carbon black.
The vapor-phase method white carbon black is neither simply crushed nor produced by special drying.
Come out
.
In any case, the smallest particle is the primary particle, but it will agglomerate more or less (because of the large amount of silanol on its surface).
The special surface is its most important property
.
Silica gel has a large internal surface area, which is why it has a strong adsorption capacity
.
In contrast, the primary particles of fumed silica are hydrolyzed by flame, and they only have an external surface area
.
This also explains why the rheological properties of many systems have been greatly improved after the combination of gas-phase white carbon black, such as the application of gas-phase white carbon black in powder coatings
.
Table 1 shows the particle size of the fumed silica particles
.
?? Figure 1 Comparison of the structural models of vapor-phase white carbon black and precipitation white carbon black?? Second, the difference in the number of silicon hydroxyl groups of vapor-phase white carbon black and precipitation white carbon black The difference in the drying loss of white carbon black Product characteristics and product application performance have a great impact
.
The lower the drying loss requirement of silica, the better.
For example, the lower the drying loss, the better the insulation of the silicone rubber used for cables
.
Low drying loss can increase the stability of adhesives and sealants added with white carbon black during storage
.
In fact, the main difference between white carbon blacks lies in their different silicon hydroxyl numbers (that is, SiOH/nm2)
.
The number of silanol groups of hydrophilic fumed silica is between 2 and 3, while the silanol content of precipitation silica is about 6.
The surface-modified silica (hydrophobic silica ) The silanol content is less than 1
.
? Third, the difference in silicon purity between vapor phase white carbon black and precipitation white carbon black The difference in purity of white carbon black is also worth noting
.
As far as anions are concerned, fumed silica only contains trace amounts of chloride ions and metal oxide impurities
.
The anions of precipitated white carbon black include acid radical ions, alkaline ions and alkaline earth metal ions (approximately 1000 ppm)
.
The difference in process technology leads to different product purity
.