Silicon dioxide

(Redirected from Silica)

**Properties**
General
Name	Silicon dioxide
Chemical formula	Si O₂
Appearance	Transparent solid
Physical
Formula weight	60.1 amu
Melting point	1986 K (1713 °C)
Boiling point	2503 K (2230 °C)
Density	2.6 ×10³ kg/m³
Crystal structure	Quartz, cristobalite or tridymite
Solubility	0.012 g in 100g water
Thermochemistry
Δ_fH⁰_gas	-305.43 kJ/mol
Δ_fH⁰_liquid	-899.86 kJ/mol
Δ_fH⁰_solid	-910.86 kJ/mol
S⁰_{gas, 1 bar}	228.98 J/mol·K
S⁰_{liquid, 1 bar}	? J/mol·K
S⁰_solid	41.46 J/mol·K
Safety
Ingestion	Low hazard.
Inhalation	Irritation, long term exposure of the crystalline form causes silicosis.
Skin	May cause irritation.
Eyes	May cause irritation.
More info	Hazardous Chemical Database
SI units were used where possible. Unless otherwise stated, standard conditions were used. Disclaimer and references

The chemical compound silicon dioxide, also known as silica, is the oxide of silicon, chemical formula SiO₂.

It is found in nature in several forms, including quartz and opal. In fact, silica has 17 crystalline forms. Also, many forms of life include silica structures, including microorganisms such as diatoms, plants such as horsetail, and animals such as hexactinellid sponges.

It is manufactured in several forms including glass (in colorless high purity form called fused silica), synthetic amorphous silica and silica gel (used e.g. as desiccants in brand new clothes and leather goods). Silica is a major ingredient of Portland cement. The ceramic re-entry heat protection tiles mounted on the bottom side of the Space Shuttles are made mostly of silica, as are the firebricks used in steel processing.

Inhaling crystalline silica dust can lead to silicosis.

Silicon dioxide

Further reading