Silicon dioxide

Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula SiO2, most commonly found in nature as quartz.[5][6] 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 as a compound of several minerals and as a synthetic product. Notable examples include fused quartz, fumed silica, silica gel, opal and aerogels. It is used in structural materials, microelectronics (as an electrical insulator), and as components in the food and pharmaceutical industries.

"Silica" redirects here. For other uses, see Silica (disambiguation).
Silicon dioxide

A sample of silicon dioxide
Names
IUPAC name
Silicon dioxide
Other names
  • Quartz
  • Silica
  • Silicic oxide
  • Silicon(IV) oxide
  • Crystalline silica
  • Pure Silica
  • Silicea
  • Silica sand
Identifiers
ChEBI
ChemSpider
ECHA InfoCard 100.028.678 Edit this at Wikidata
EC Number
  • 231-545-4
E number E551 (acidity regulators, ...)
200274
KEGG
MeSH Silicon+dioxide
RTECS number
  • VV7565000
UNII
  • InChI=1S/O2Si/c1-3-2 checkY
    Key: VYPSYNLAJGMNEJ-UHFFFAOYSA-N checkY
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[1]
Melting point 1,713 °C (3,115 °F; 1,986 K) (amorphous)[1]: 4.88  to
Boiling point 2,950 °C (5,340 °F; 3,220 K)[1]
−29.6·10−6 cm3/mol
Thermal conductivity 12 (|| c-axis), 6.8 (⊥ c-axis), 1.4 (am.) W/(m⋅K)[1]: 12.213 
1.544 (o), 1.553 (e)[1]: 4.143 
Hazards
NFPA 704 (fire diamond)
0
0
0
NIOSH (US health exposure limits):
PEL (Permissible)
 TWA 20 mppcf (80 mg/m3/%SiO2) (amorphous)[2]
REL (Recommended)
 TWA 6 mg/m3 (amorphous)[2]
Ca TWA 0.05 mg/m3[3]
IDLH (Immediate danger)
 3000 mg/m3 (amorphous)[2]
Ca [25 mg/m3 (cristobalite, tridymite); 50 mg/m3 (quartz)][3]
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[4]
−911 kJ·mol−1[4]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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