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Specific gravity (true density) is the mass-to-volume ratio of a material.  Bulk density refers to how much material is in a package of a certain volume, so air pockets are included. While the specific gravity of Cabot silicas and aluminas are high relative to water (with a specific gravity of 1.0 g/cm³), the bulk density of these products is quite low. This difference is because of the size and shape of these products.  Bulk density for Cabot silicas and aluminas range from 50 to 200 g/l.

The refractive index of fumed silica matches that of many organic solvents, oils and polymers making it an ideal rheology control or reinforcing additive for applications requiring clarity.

 

Products Refractive Index Specific Gravity g/cm³
CAB-O-SIL® Treated and Untreated Fumed Silicas ~1.46 ~2.2
CAB-O-SIL™ Treated Colloidal Silicas ~1.46 ~2.2
SpectrAl ®Treated and Untreated Fumed Aluminas ~1.77 ~3.6

 

Fumed Silica Interactive Learning Module

Take this self-guided tour to learn more about the functionality of fumed silica. Learn