Silicon dioxide

General Description

Silicon dioxide occurs almost everywhere on earth. It is one of the most important and abundant oxides on earth, constituting about 60% weight of the earth’s crust as silica itself or in combination with other metal oxides in silicates. It commonly is found as sand in the vast ocean and river shores, their beds, deserts, rocks, and minerals.
Silicon dioxide exists in several structural forms: polymorphic crystalline silica, synthetic quartz crystals, amorphous silica, and vitreous silica. This classification is not complete as there are other forms of silica synthesized for specialized applications.

Uses

Chemical Properties

Diatomaceous earth is a transparent to gray, odorless amorphous powder.

Chemical Properties

Amorphous silica, the noncrystalline form of SiO2, is a transparent to gray, odorless, amorphous powder

Chemical Properties

white crystals or powder

Physical properties

Colorless amorphous (i.e., fused silica) or crystalline (i.e., quartz) material having a low thermal expansion coefficient and excellent optical transmittance in far UV. Silica is insoluble in strong mineral acids and alkalis except HF, concentrated H₃PO₄, NH₄ HF₂ , concentrated alkali metal hydroxides. Owing to its good corrosion resistance to liquid metals such as Si, Ge, Sn, Pb, Ga, In, Tl, Rb, Bi, and Cd, it is used as crucible container for melting these metals, while silica is readily attacked in an inert atmosphere by molten metals such as Li, Na, K Mg, and Al. Quartz crystals are piezoelectric and pyroelectric. Maximum service temperature 1090°C.

Uses

manufacture of glass, water glass, refractories, abrasives, ceramics, enamels; decolorizing and purifying oils, petroleum products, etc.; in scouring- and grinding-compounds, ferrosilicon, molds for castings; as anticaking and defoaming agent.

Uses

Silica (SiO2) (RI: 1.48) is mined from deposits of diatomaceous soft chalk-like rock (keiselghur). This is an important group of extender pigments, which is used in a variety of particle sizes. They are used as a flatting agent to reduce gloss of clear coatings and to impart shear thinning flow properties to coatings. They are relatively expensive.

Uses

silica is also known as silicone dioxide. Silica has a variety of applications: to control a product’s viscosity, add bulk, and reduce a formulation’s transparency. It can also function as an abrasive. In addition, it can act as a carrier for emollients, and may be used to improve a formulation’s skin feel. Spherical silica is porous and highly absorbent, with absorption capabilities roughly 1.5 times its weight. A typical claim associated with silica is oil control. It is found in sunscreens, scrubs, and wide range of other skin care, makeup, and hair care preparations. It has been successfully used in hypoallergenic and allergy-tested formulations.

Uses

Functionalized RAFT agent for controlled radical polymerization; especially suited for the polymerization of styrene; acrylate and acrylamide monomers. Azide group can be used to conjugate to a variety of alkyne-functionalized biomolecules. Chain Transfer Agent (CTA).

Uses

SDS mixture of sodium alkyl sulfates consisting chiefly of sodium lauryl sulfate

Uses

Silicon(IV) oxide, amorphous is used as carriers, processing aids, anti-caking and free-flow agents in animal feed. Defoamer applications such as paint, food, paper, textile and other industrial applications. Synthetic silicon dioxides are used as a rheology control agent in plastics. It is also used to manufacture adhesives, sealants and silicones.

Definition

ChEBI: A silicon oxide made up of linear triatomic molecules in which a silicon atom is covalently bonded to two oxygens.

General Description

contains sodium stabilizing counterion

Hazard

Not toxic if ingested, inhaled silica dust can cause silicosis; carcinogen.

Agricultural Uses

Silica is silicon dioxide, one of the most abundant materials on the earth's crust. Quartz is an example of silica. It is used as a filler in fertilizers, and also, in the manufacture of glass, ceramics, abrasives, rubber and cosmetics.

Safety Profile

The pure unaltered form is considered a nuisance dust. Some deposits contain small amounts of crystahne quartz and are therefore fibrogenic. When diatomaceous earth is calcined (with or without fluxing agents) some sdica is converted to cristobalite and is therefore fibrogenic. Tridymite has never been detected in calcined batomaceous earth. See also other silica entries

Potential Exposure

Diatomaceous earth is used as a filtering agent and as a filler in construction materials, pesticides, paints, and varnishes. The calcined version (which has been heat treated) is the most dangerous and contains crystallized silica, and should be handled as silica. See also other entries on silica

Shipping

This material is not singled out by DOT in its Performance-Oriented Packaging Standards.

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].

Derivatives

Precipitated silica is obtained like silica gel by acidifying an aqueous solution of sodium silicate. Precipitated silica is used as filler in rubber for automobile tires and reinforcement particulate in elastomers, and as a flatting agent in paints and coatings for improving the flatness of coatings.

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.

Waste Disposal

Sanitary landfill.