Name: Colloidal Silicon Dioxide
CAS No: Silica [7631-86-9]
BP: Colloidal Anhydrous Silica JP: Light Anhydrous Silicic Acid PhEur: Silica, Colloidal Anhydrous USP-NF: Colloidal Silicon Dioxide
Aerosil; Cab-O-Sil; Cab-O-Sil M-5P; colloidal silica; fumed silica; fumed silicon dioxide; hochdisperses silicum dioxid; SAS; silica colloidalis anhydrica; silica sol; silicic anhydride; silicon dioxide colloidal; silicon dioxide fumed; synthetic amorphous silica; Wacker HDK
Silica [7631-86-9]
SiO2 60.08
See Section 4
Colloidal silicon dioxide is widely used in pharmaceuticals, cosmetics, and food products; see Table I. Its small particle size and large specific surface area give it desirable flow characteristics that are exploited to improve the flow properties of dry powders(1) in a number of processes such as tableting(2–4) and capsule filling. Colloidal silicon dioxide is also used to stabilize emulsions and as a thixotropic thickening and suspending agent in gels and semisolid preparations.(5) With other ingredients of similar refractive index, transparent gels may be formed. The degree of viscosity increase depends on the polarity of the liquid (polar liquids generally require a greater concentration of colloidal silicon dioxide than nonpolar liquids). Viscosity is largely independent of temperature. However, changes to the pH of a system may affect the viscosity; see Section 11. In aerosols, other than those for inhalation, colloidal silicon dioxide is used to promote particulate suspension, eliminate hard settling, and minimize the clogging of spray nozzles. Colloidal silicon dioxide is also used as a tablet disintegrant and as an adsorbent dispersing agent for liquids in powders.(6) Colloidal silicon dioxide is frequently added to suppository formulations containing lipophilic excipients to increase viscosity, prevent sedimentation during molding, and decrease the release rate.(7,8) Colloidal silicon dioxide is also used as an adsorbent during the preparation of wax microspheres;(9) as a thickening agent for topical preparations;(10) and has been used to aid the freeze-drying of nanocapsules and nanosphere suspensions.(11)
Colloidal silicon dioxide is a submicroscopic fumed silica with a particle size of about 15 nm. It is a light, loose, bluish-white-colored, odorless, tasteless, amorphous powder.
See Table II
Acidity/alkalinity pH = 3.8–4.2 (4% w/v aqueous dispersion) and 3.5–4.0 (10% w/v aqueous dispersion) for Cab-O-Sil M-5P Density (bulk) 0.029–0.042 g/cm3 Density (tapped) see Tables III, IV, and V. Melting point 16008C Moisture content see Figure 1.(12,13) Particle size distribution Primary particle size is 7–16 nm. Aerosil forms loose agglomerates of 10–200 mm. See also Figure 2. Refractive index 1.46 Solubility Practically insoluble in organic solvents, water, and acids, except hydrofluoric acid; soluble in hot solutions of alkali hydroxide. Forms a colloidal dispersion with water. For Aerosil, solubility in water is 150 mg/L at 258C (pH 7). Specific gravity 2.2 Specific surface area 100–400 m2 /g depending on grade. See also Tables III, IV,and V. Several grades of colloidal silicon dioxide are commercially available, which are produced by modifying the manufacturing process. The modifications do not affect the silica content, specific gravity, refractive index, color, or amorphous form. However, particle size, surface areas, and densities are affected. The physical properties of three commercially available colloidal silicon dioxides, Aerosil (Evonik Degussa Corp.), Cab-O-Sil (Cabot Corporation), and Wacker HDK (Wacker-Chemie GmbH) are shown in Tables III, IV and V, respectively
Colloidal silicon dioxide is hygroscopic but adsorbs large quantities of water without liquefying. When used in aqueous systems at a pH 0–7.5, colloidal silicon dioxide is effective in increasing the viscosity of a system. However, at a pH greater than 7.5 the viscosityincreasing properties of colloidal silicon dioxide are reduced; and at a pH greater than 10.7 this ability is lost entirely since the silicon dioxide dissolves to form silicates.(14) Colloidal silicon dioxide powder should be stored in a well-closed container
Incompatible with diethylstilbestrol preparations.(15)
Colloidal silicon dioxide is prepared by the flame hydrolysis of chlorosilanes, such as silicon tetrachloride, at 18008C using a hydrogen–oxygen flame. Rapid cooling from the molten state during manufacture causes the product to remain amorphous.
Colloidal silicon dioxide is widely used in oral and topical pharmaceutical products and is generally regarded as an essentially nontoxic and nonirritant excipient. However, intraperitoneal and subcutaneous injection may produce local tissue reactions and/or granulomas. Colloidal silicon dioxide should therefore not be administered parenterally. LD50 (rat, IV): 0.015 g/kg(16) LD50 (rat, oral): 3.16 g/kg
Observe normal precautions appropriate to the circumstances and quantity of material handled. Eye protection and gloves are recommended. Considered a nuisance dust, precautions should be taken to avoid inhalation of colloidal silicon dioxide. In the absence of suitable containment facilities, a dust mask should be worn when handling small quantities of material. For larger quantities, a dust respirator is recommended. Inhalation of colloidal silicon dioxide dust may cause irritation to the respiratory tract but it is not associated with fibrosis of the lungs (silicosis), which can occur upon exposure to crystalline silica.
GRAS listed. Included in the FDA Inactive Ingredients Database (oral capsules, suspensions, and tablets; transdermal, rectal, and vaginal preparations). Also approved by the FDA as a food additive and for food contact. Included in nonparenteral medicines licensed in the UK. Included i
Hydrophobic colloidal silica.
Colloidal silicon dioxide is one of the materials that have been selected for harmonization by the Pharmacopeial Discussion Group. For further information see the General Information Chapter <1196> in the USP32–NF27, the General Chapter 5.8 in PhEur 6.0, along with the ‘State of Work’ document on the PhEur EDQM website, and also the General Information Chapter 8 in the JP XV. The PhEur 6.0 also contains a specification for hydrated colloidal silicon dioxide. The incidence of microbial contamination of colloidal silicon dioxide is low(17) due to the high production temperatures and inorganic precursor materials. Note that porous silica gel particles may also be used as a glidant, thickener, dispersant and to adsorb moisture, which may be an advantage for some formulations. Syloid 244FP meets the USP– NF requirements for silicon dioxide, and Syloid 244 FP-BU meets the PhEur and JP requirements for silicon dioxide.(18) Another CAS number that is used for colloidal silicon dioxide is 112945-52-5. The EINECS number for colloidal silicon dioxide is 231-545-4. The PubChem Compound ID (CID) for colloidal silicon dioxide is 24261.