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Silica

Silicon dioxide
Sample of silicon dioxide.jpg
Names
IUPAC name
Silicon dioxide
Other names
Quartz

Silica
Silicic oxide
Silicon(IV) oxide

Crystalline silica
Identifiers
7631-86-9 YesY
ChEBI CHEBI:30563 YesY
ChemSpider 22683 YesY
ECHA InfoCard 100.028.678
EC Number 231-545-4
E number E551 (acidity regulators, ...)
200274
KEGG C16459 N
MeSH Silicon+dioxide
PubChem 24261
RTECS number VV7565000
UNII ETJ7Z6XBU4 YesY
Properties
SiO2
Molar mass 60.08 g/mol
Appearance Transparent solid (Amorphous) White/Whitish Yellow (Powder/Sand)
Density 2.648 (α-quartz), 2.196 (amorphous) g·cm−3
Melting point 1,713 °C (3,115 °F; 1,986 K) (amorphous) to
Boiling point 2,950 °C (5,340 °F; 3,220 K)
−29.6·10−6 cm3/mol
Thermal conductivity 12 (|| c-axis), 6.8 (⊥ c-axis), 1.4 (am.) W/(m⋅K)
1.544 (o), 1.553 (e)
Hazards
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 0: Exposure under fire conditions would offer no hazard beyond that of ordinary combustible material. E.g., sodium chloride Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
US health exposure limits (NIOSH):
PEL (Permissible)
TWA 20 mppcf (80 mg/m3/%SiO2) (amorphous)
REL (Recommended)
TWA 6 mg/m3 (amorphous)
Ca TWA 0.05 mg/m3
IDLH (Immediate danger)
3000 mg/m3 (amorphous)
Ca [25 mg/m3 (cristobalite, tridymite); 50 mg/m3 (quartz)]
Related compounds
Related diones
Carbon dioxide

Germanium dioxide
Tin dioxide
Lead dioxide

Related compounds
Silicon monoxide

Silicon sulfide

Thermochemistry
42 J·mol−1·K−1
−911 kJ·mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YesYN ?)
Infobox references

Silica
Silicic oxide
Silicon(IV) oxide

Germanium dioxide
Tin dioxide
Lead dioxide

Silicon sulfide

Silicon dioxide, also known as silica (from the Latin silex), is a chemical compound that is an oxide of silicon with the chemical formula SiO2. It has been known since ancient times. Silica is most commonly found in nature as quartz, as well as in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and most abundant families of materials, existing both as several minerals and being produced synthetically. Notable examples include fused quartz, crystal, fumed silica, silica gel, and aerogels. Applications range from structural materials to microelectronics to components used in the food industry.

Silicon dioxide is mostly obtained by mining and purification of quartz. Quartz comprises more than 10% by mass of the earth's crust. This product is suitable for many purposes while for others chemical processing is required to make a purer or otherwise more suitable (e.g. more reactive or fine-grained) product.

Pyrogenic silica (sometimes called fumed silica or silica fume) is a very fine particulate or colloidal form of silicon dioxide. It is prepared by burning SiCl4 in an oxygen rich hydrocarbon flame to produce a "smoke" of SiO2.

This product is obtained as byproduct from hot processes like ferro-silicon production. It is less pure than fumed silica and should not be confused with that product. The production process, particle characteristics and fields of application of fumed silica are all different from those of silica fume.


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