Science Fair Project Encyclopedia
Silicon dioxide
| General | |
|---|---|
| Name | Silicon dioxide |
| Chemical formula | SiO2 |
| 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 | |
| ΔfH0gas | -305.43 kJ/mol |
| ΔfH0liquid | -899.86 kJ/mol |
| ΔfH0solid | -910.86 kJ/mol |
| S0gas, 1 bar | 228.98 J/mol·K |
| S0liquid, 1 bar | ? J/mol·K |
| S0solid | 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. | |
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.
Further reading
- R. K. Iler, The Chemistry of Silica (ISBN 047102404X)
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