Colloidal silicon dioxide

• BPColloidal Anhydrous Silica
• JPLight Anhydrous Silicic Acid
• Ph. Eur.Silica, Colloidal Anhydrous
• USP–NFColloidal Silicon Dioxide

Aerosil; Cab-O-Sil; colloidal silica; fumed silica; HDK; light anhydrous silicic acid; pyrogenic silica; silicic anhydride; E551

Silica · [7631-86-9]

UNII ETJ7Z6XBU4 · PubChem CID 24261

SiO2 · 60.08

Glidant

Typical concentrations: 0.1–1% · Dosage forms: Solid, Semi-solid

Used mainly as a glidant to improve the flow of powders in tablet and capsule manufacture, and as an anticaking agent, adsorbent and viscosity-increasing or thixotropic agent in liquids, gels, ointments and suppositories. Typical concentrations: glidant 0.1–1.0%; aerosols 0.5–2.0%; emulsion stabiliser 1.0–5.0%; suspending and thickening agent 2.0–10.0%. It is also used to convert oily liquids into free-flowing powders.

A light, loose, bluish-white, odourless and tasteless amorphous powder made of submicroscopic fumed silica particles that form loose aggregates. It has a very large specific surface area and a very low bulk density.

Primary particle size

about 7–40 nm, depending on grade

Specific surface area (BET)

about 50–400 m²/g, depending on grade (about 200 m²/g for common pharmaceutical grades)

Bulk density

very low, of the order of 0.03–0.05 g/cm³

pH

3.5–5.5 (4% w/v aqueous dispersion)

Solubility

practically insoluble in water, organic solvents and acids (except hydrofluoric acid); dissolves in hot solutions of alkali hydroxides

Hygroscopic, but adsorbs large quantities of water without liquefying. Its thickening effect in aqueous systems is greatest in the acidic to neutral range and is lost at strongly alkaline pH, where silica begins to dissolve. Store in a well-closed container.

Reported to be incompatible with diethylstilbestrol preparations. Its high surface area can adsorb drugs or preservatives, which may matter at low drug loads.

Made by vapour-phase hydrolysis of silicon tetrachloride in an oxygen–hydrogen flame at high temperature (about 1800 °C); the resulting fumed silica is collected as a fluffy powder.

Essentially non-toxic and non-irritant after oral or topical use, and not absorbed from the gut. Unlike crystalline silica, amorphous colloidal silica has not been linked to silicosis, but inhalation of the fine dust should still be avoided. Local tissue reactions have been seen after injection.

Observe normal precautions for the quantity handled. The very fine, light powder is easily airborne; wear eye protection, gloves and a suitable respirator, and use local exhaust ventilation.

Accepted as a food additive in Europe (E551). Included in the FDA Inactive Ingredient Database (oral capsules, suspensions and tablets; transdermal, vaginal and other non-parenteral routes) and in non-parenteral medicines licensed in Europe.

Hydrophobic colloidal silica; silicon dioxide (precipitated silica); magnesium trisilicate; talc.

A glidant works best at low levels; above about 1% flow often stops improving and may even worsen. Because of its low bulk density it should be pre-sieved or pre-blended with part of the formulation to avoid agglomerates and poor distribution.