for the chemical element with atomic number 14, located in the periodic table in Group IV 3 periods and III series, the formation of two oxides of silicon, consisting of two elements Si and O:
- monoxide, silicon, in which Si is bivalent, chemicalokisda this formula may be represented as SiO;
- silicon dioxide - is the highest silicon oxide in which Si is tetravalent, its chemical formula is written as SiO2.
silicon (IV) oxide in appearance is transparent crystals.The density of SiO2 is equal to 2,648 g / cm³.The substance melts in a temperature range from 1600 to 1725 ° C and boils at 2230 ° C.
Silica SiO2 was known for its hardness and strength since ancient times, the most common in nature as sand or quartz, as well as in the cell walls of diatoms.The substance has many polymorphs, most often found in two forms:
- Crystal - a natural mineral quartz and its varieties (chalcedony, rock crystal, jasper, agate, flint);Quartz is the basis of quartz sand, it is an essential building material and raw materials for silicate industry;
- amorphous occurs as a natural mineral opal, which structure can be described by the formula SiO2 • nH2O;earthy forms of amorphous SiO2 are tripoli (rock flour, diatomaceous earth) and diatomaceous earth;synthetic amorphous anhydrous silica - is silica gel, which is made of sodium metasilicate.
Silica SiO2 is an acidic oxide.This factor determines the chemical properties.
Fluorine reacts with silica: SiO2 + 4F → SiF4 + O2 to form colorless silicon tetrafluoride gas and oxygen, while the other gases (halogens Cl2, Br2, I2) responsive less active.
silicon oxide IV is reacted with hydrofluoric acid to produce fluorosilicic acid: SiO2 + 6HF → H2SiF6 + 2H2O.This property is used in the semiconductor industry.
Silicon (IV) oxide dissolved in the molten or hot concentrated alkali to form a sodium silicate: 2NaOH + SiO2 → Na2SiO3 + H2O.
silica reacts with the basic metal oxides (e.g., oxides of sodium, potassium, lead (II), or a mixture of zinc oxide that is used in glass production).For example, the reaction of sodium oxide and SiO2, as a result of which may be formed: sodium orthosilicate 2Na2O + SiO2 → Na4SiO4, sodium silicate Na2O + SiO2 → Na2SiO3, and glass Na2O + 6SiO2 + XO → Na2O: XO: 6SiO2.Examples of such glass having commercial value, are the soda-lime glass, borosilicate glass, leaded glass.
silica at high temperatures, is reacted with the silicon, resulting in a monoxide gas: SiO2 + Si → 2SiO ↑.
most cases silicon oxide SiO2 is used for the production of elemental silicon.The process of interaction with elemental carbon proceeds at a high temperature in the electric furnace: SiO2 + 2C → Si + 2CO.It is quite energy intensive.However, its product is used in semiconductor technology for the manufacture of solar cells (light energy is converted into electrical energy).Also pure Si used in the industry (in the production of heat-resistant and acid-resistant silicon steel).The thus obtained elemental silicon necessary for obtaining pure silica, which is important for a number of industries.Natural SiO2 as sand used in those industries where it is not required high purity.
Inhalation of dust finely divided crystalline SiO2, even in very small quantities (up to 0.1 mg / m³), with the passage of time can develop silicosis, bronchitis or cancer.Dust becomes dangerous if it enters the lungs, constantly irritates them, reducing their function.In humans, the silica in the form of crystalline particles is not dissolved within clinically relevant time periods.This effect may create a risk of occupational diseases for people working with the sandblasting equipment or products that contain crystalline silica powder.Children of any age with asthma, allergies, and older people can become ill more quickly.
