Fumed Silica
Fumed silica (pyrogenic silica) is a high-purity amorphous SiO₂ produced by gas-phase flame hydrolysis. Ultra-fine 7-40 nm primary particles and BET 100-400 m²/g make it the dominant reinforcing filler for HTV/RTV silicone rubber and the leading thixotropic additive for paints, adhesives, and gel-coats.
Key Properties at a Glance
| Primary Particle Size | 7 – 40 nm |
|---|---|
| BET Surface Area | 100 – 400 m²/g |
| SiO₂ Purity | ≥99.8% |
| Tap Density | 30 – 70 g/L (hydrophilic) / 50 – 90 g/L (hydrophobic) |
| pH (4% slurry) | 3.7 – 4.5 (hydrophilic) / 4 – 9 (hydrophobic) |
| Carbon Content | 0% (hydrophilic); 0.5 – 5.0% (hydrophobic) |
| Common Tradenames | Aerosil 200/300 (Evonik) / HDK N20/T30 (Wacker) / Cab-O-Sil M-5/EH-5 (Cabot) |
Range shown is category-wide; refer to individual grade COA for precise specs.
Featured Grades
Aerosil 200 / HDK N20 — Hydrophilic Fumed Silica 200 m²/g
CAS 112945-52-5
Hydrophilic fumed silica with BET surface area of 200 m²/g is the most widely used grade globally — a versatile thickener and reinforcing filler for unsaturated polyester resins, epoxy adhesives, sealants, and paints. Equivalent grades: Evonik Aerosil 200, Wacker HDK N20, Cabot CAB-O-SIL M-5.
Aerosil 300 / HDK T30 — Hydrophilic Fumed Silica 300 m²/g
CAS 112945-52-5
High surface area hydrophilic fumed silica (BET 300 m²/g). Used where stronger thickening, higher transparency, or maximum reinforcement in HTV silicone rubber is required. Equivalent grades: Evonik Aerosil 300, Wacker HDK T30, Cabot CAB-O-SIL HS-5.
Aerosil R972 — Hydrophobic Fumed Silica (DMDCS-treated)
CAS 68611-44-9
Hydrophobic fumed silica surface-treated with dimethyldichlorosilane (DMDCS). The dimethylsilyl surface modification provides moisture resistance, anti-settling performance in non-aqueous systems, and superior dispersion in solvent-borne paints and powder coatings. Equivalent: Wacker HDK H17, Cabot TS-720.