Fumed Silica Applications & Industrial Solutions

Fumed silica (pyrogenic silica) is produced by flame hydrolysis of silicon tetrachloride at >1000°C, resulting in amorphous SiO₂ with ultra-high purity (>99.8%), primary particle size 7–40 nm, and BET surface area 100–400 m²/g. Silica gel is a porous, granular material used primarily as a desiccant — not a functional additive. Precipitated silica is produced by a wet chemical process, has larger particle size, and lower purity. For rheology control, reinforcement, and pharmaceutical applications, fumed silica is the preferred form.

Hydrophilic fumed silica has surface silanol groups (Si–OH) that interact well with water and polar solvents. It is used in waterborne coatings, powder coatings, food, pharmaceutical, and cementitious applications. Hydrophobic fumed silica has been surface-treated to replace silanols with non-polar groups (PDMS, DDS, or HMDS treatment), making it compatible with solventborne resins, silicones, and non-polar organic systems like adhesives and potting compounds.

Anti-sag dosage depends on film thickness and coating density. For industrial primers at 100–200 µm WFT, 1–2% fumed silica achieves TI 3–5. For high-build marine coatings at 300–500 µm WFT, 2–3.5% is needed. For epoxy cove base, 1.5–3%. Use a sag tester (ASTM D4400) to verify — target no sag at your specified WFT on a vertical glass panel. Measure Thixotropic Index (Brookfield at 0.5 rpm / 5 rpm) to characterize the thixotropic network.

Yes. SEMISIL hydrophilic grades meet: Ph. Eur. (pharmaceutical grade, silicon dioxide), USP/NF (monograph for Colloidal Silicon Dioxide), and EU food additive E551 (silicon dioxide) under Regulation (EC) No 1333/2008 with FDA GRAS status under 21 CFR 172.480. Full Certificates of Analysis, REACH declarations, and compliance letters are available. Contact our team for regulatory documentation for your specific application category.

Higher BET surface area = stronger thixotropic network at lower loading. SEMISIL 150 m²/g: mild thixotropy, easy processing; 200 m²/g: most versatile, standard grade for coatings and adhesives; 300 m²/g: high efficiency, use at lower loading; 380 m²/g: maximum thixotropy for demanding applications. For reinforcement (silicone rubber), 200–300 m²/g is standard. For pharmaceutical glidant, 200–300 m²/g. For food anti-caking, 200 m²/g is the most common grade.

Yes, but grade selection matters. Hydrophilic grades (SEMISIL 200, 300) disperse readily in waterborne systems (aqueous latex, waterborne epoxy, water-based coatings) through high-shear mixing. Hydrophobic grades (SEMISIL R202, R272, R620) are preferred for solventborne systems (solventborne alkyd, epoxy, PU) and non-polar systems. Using the wrong type results in agglomeration, poor dispersion, and loss of thixotropic performance.