page_title: Silicon dioxide
section_title: Chemical reactions
hierarchical_section_title: Silicon dioxide / Chemical reactions
caption_attribution_description: English: Fibre optic strands
context_page_description: Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula SiO₂, most commonly found in nature as quartz and 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 as a compound of several minerals and as synthetic product. Notable examples include fused quartz, fumed silica, silica gel, and aerogels. It is used in structural materials, microelectronics, and as components in the food and pharmaceutical industries.
  Inhaling finely divided crystalline silica is toxic and can lead to severe inflammation of the lung tissue, silicosis, bronchitis, lung cancer, and systemic autoimmune diseases, such as lupus and rheumatoid arthritis. Inhalation of amorphous silicon dioxide, in high doses, leads to non-permanent short-term inflammation, where all effects heal.
context_section_description: Silica is converted to silicon by reduction with carbon.
  Fluorine reacts with silicon dioxide to form SiF₄ and O₂ whereas the other halogen gases (Cl₂, Br₂, I₂) are essentially unreactive.
  Silicon dioxide is attacked by hydrofluoric acid (HF) to produce hexafluorosilicic acid:
  HF is used to remove or pattern silicon dioxide in the semiconductor industry.
  Under normal conditions, silicon does not react with most acids but is dissolved by hydrofluoric acid.
  Silicon is attacked by bases such as aqueous sodium hydroxide to give silicates.
  Silicon dioxide acts as a Lux–Flood acid, being able to react with bases under certain conditions. As it does not contain any hydrogen, it cannot act as a Brønsted–Lowry acid. While not soluble in water, some strong bases will react with glass and have to be stored in plastic bottles as a result.
  Silicon dioxide dissolves in hot concentrated alkali or fused hydroxide, as described in this idealized equation:
  Silicon dioxide will neutralise basic metal oxides (e.g. sodium oxide, potassium oxide, lead(II) oxide, zinc oxide, or mixtures of oxides, forming silicates and glasses as the Si-O-Si bonds in silica are broken successively). As an example the reaction of sodium oxide and SiO₂ can produce sodium orthosilicate, sodium silicate, and glasses, dependent on the proportions of reactants:
   .
  Examples of such glasses have commercial significance, e.g. soda-lime glass, borosilicate glass, lead glass. In these glasses, silica is termed the network former or lattice former. The reaction is also used in blast furnaces to remove sand impurities in the ore by neutralisation with calcium oxide, forming calcium silicate slag.
  Silicon dioxide reacts in heated reflux under dinitrogen with ethylene glycol and an alkali metal base to produce highly reactive, pentacoordinate silicates which provide access to a wide variety of new silicon compounds. The silicates are essentially insoluble in all polar solvent except methanol.
  Silicon dioxide reacts with elemental silicon at high temperatures to produce SiO:
caption: Bundle of optical fibers composed of high purity silica.
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