Chemical Properties
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.
Chemical Properties
Amorphous silica, the noncrystalline form of SiO2, is a transparent to gray, odorless, amorphous powder
Uses
Synthetic Amorphous Silica has interesting thickening and thixotropic properties, and an enormous external surface area. It is produced by a vapor phase hydrolysis process using chlorosilanes or substituted silanes such as, silicon tetrachloride in a flame of hydrogen and oxygen. This material is formed and collected in a dry state. This product contains no detectable crystalline silica.
Production Methods
Colloidal silicon dioxide is prepared by the flame hydrolysis of
chlorosilanes, such as silicon tetrachloride, at 18008℃ using a
hydrogen–oxygen flame. Rapid cooling from the molten state
during manufacture causes the product to remain amorphous.
Definition
ChEBI: Silicon dioxide is a silicon oxide made up of linear triatomic molecules in which a silicon atom is covalently bonded to two oxygens.
General Description
Fumed silica may be synthesized by high temperature hydrolysis of SiCl
4 in O
2(N
2)/H
2 flame. It is amorphous in nature and possesses very high specific area. The micro droplets of amorphous silica fuse into a branch and form a chain like agglomerate.
Pharmaceutical Applications
Colloidal silicon dioxide is widely used in pharmaceuticals,
cosmetics, and food products. 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
in a number of processes such as tableting 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. 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 viscosity1.
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. Colloidal
silicon dioxide is frequently added to suppository formulations
containing lipophilic excipients to increase viscosity, prevent
sedimentation during molding, and decrease the release rate.
Colloidal silicon dioxide is also used as an adsorbent during the
preparation of wax microspheres; as a thickening agent for
topical preparations; and has been used to aid the freeze-drying
of nanocapsules and nanosphere suspensions.
Safety Profile
Poison by intraperitoneal, intravenous, and intratracheal routes. Moderately toxic by ingestion. An inhalation hazard. Much less toxic than crystalhe forms. Questionable carcinogen with experimental carcinogenic data. Mutation data reported. Does not cause silicosis. See also other silica entries
Safety
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.
LD
50 (rat, IV): 0.015 g/kg
LD
50 (rat, oral): 3.16 g/kg
Potential Exposure
Amorphous fumed silica is used as a mineral, natural or synthetic fiber. A potential danger to those involved in the production and handling of fumed silica for paint pigments or catalysts. Diatomaceous earth is used in clarifying liquids, in manufacture of fire brick and heat insulators; used as a filtering agent; as a filler in construction materials; pesticides, paints, and varnishes. A potential danger to those involved in mining of diatomaceous earth or fabrication of products there from.
storage
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. Colloidal silicon dioxide
powder should be stored in a well-closed container.
Purification Methods
Purification of silica for high technology applications uses isopiestic vapour distillation from concentrated volatile acids and is absorbed in high purity water. The impurities remain behind. Preliminary cleaning to remove surface contaminants uses dip etching in HF or a mixture of HCl, H2O2 and deionised water [Phelan & Powell Analyst 109 1299 1984].
Incompatibilities
Silica, amorphous is a noncombustible solid. Generally unreactive chemically. Incompatible with fluorine, oxygen difluoride, chlorine trifluoride. Soluble in molten alkalis and reacts with most metallic oxides at high temperature.
Incompatibilities
Incompatible with diethylstilbestrol preparations.
Waste Disposal
Sanitary landfill.
Regulatory Status
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 in the Canadian List of Acceptable Nonmedicinal
Ingredients.
