126 / 390
Figure 13:
Laser light diffraction data of an aqueous dispersion of pyrogenic silica of
300 m
2
/g SSA stirred at 3000 rpm (internal stirrer of Mastersizer 3000) for different
periods of time.
Under these mild shear conditions, the particle size distribution shows a bimodal
distribution with one mode in the nm-range and a second mode in the μm-range. With
increasing stirring time, the sub-micron mode increases in intensity. The intensity of
the coarse particle peak (μm-mode) strongly decreases.
Applications of pyrogenic silica
Main industrial applications of pyrogenic silica are summarized in table 1.
Table 1:
Main industrial applications of pyrogenic silica.
Application
desired effect
dosage / wt%
reinforcing filler
Improving mechanical properties of
silicone elastomers
ca. 30
rheological additive
Flow control of sealants, adhesives,
and coatings
1 – 10
thermal insulation
High and low temperature insulation
ca. 80
anti-blocking additive
Free flow of adhesive powders
0.05 – 1
charge regulation additive
Charge regulation of toner particles
ca. 0.5 – 1
pharmaceutical excipient
Improved powder handling, tabletting,
and tablet disintegration
ca. 1
submicron mode
μm-mode
0
1
2
3
4
5
6
volume density [%]
12 min stirring
24 min stirring
36 min stirring
48 min stirring
60 min stirring
118