For a chemical element with serial number 14, which is in the periodic table in group IV of period 3 and row III, the formation of two silicon oxides consisting of two elements Si and O is possible:
- silicon monoxide, in which Si is divalent, the chemical formula of this oxide can 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 a transparent crystal. The density of SiO2 is 2.648 g / cm³. The substance melts in the temperature range from 1600 to 1725 ° C, boils at a temperature of 2230 ° C.
Silicon oxide SiO2 has been known for its hardness and strength since ancient times, most common in nature in the form of sand or quartz, as well as in the cell walls of diatoms. The substance has many polymorphic modifications, most often found in two forms:
- crystalline - in the form of a natural mineral of quartz, as well as its varieties (chalcedony, rock crystal, jasper, agate, flint); quartz is the basis of quartz sand; it is an indispensable building material and raw material for the silicate industry;
- amorphous is found in the form of the natural mineral opal, the composition of which can be described by the formula SiO2 • nH2O; earthy forms of amorphous SiO2 are tripoli (mountain flour, ciliates) or diatomite; artificial amorphous anhydrous silica is silica gel, which is made from sodium metasilicate.
Silicon oxide SiO2 is an acid oxide. It is this factor that determines its chemical properties.
Fluorine reacts with silicon dioxide: SiO2 + 4F → SiF4 + O2 to form a colorless gas of silicon tetrafluoride and oxygen, while other gases (halogens Cl2, Br2, I2) react less actively.
Silicon oxide IV interacts with hydrofluoric acid to produce hydrofluoric acid: SiO2 + 6HF → H2SiF6 + 2H2O. This property is used in the semiconductor industry.
Silicon (IV) oxide dissolves in hot concentrated or molten alkali to form sodium silicate: 2NaOH + SiO2 → Na2SiO3 + H2O.
Silicon dioxide reacts with basic metal oxides (for example, with oxides of sodium, potassium, lead (II), zinc or a mixture of oxides used in the manufacture of glass). For example, we can give the reactions of sodium oxide and SiO2, as a result of which sodium orthosilicate 2Na2O + SiO2 → Na4SiO4, sodium silicate Na2O + SiO2 → Na2SiO3, and glass Na2O + 6SiO2 + XO → Na2O: XO: 6SiO2 can be formed. Examples of such glass of commercial importance are sodium-calcium glass, borosilicate glass, lead glass.
Silicon dioxide at high temperatures interacts with silicon, resulting in a gaseous monoxide: Si + SiO2 → 2SiO ↑.
Most often, silicon oxide SiO2 is used to produce elemental silicon. The process of interaction with elemental carbon proceeds at high temperature in an electric arc furnace: 2C + SiO2 → Si + 2CO. It is quite energy intensive. However, its product is used in semiconductor technology for the manufacture of solar cells (convert light energy into electrical energy). Pure Si is also used in metallurgy (in the production of heat-resistant and acid-resistant silicon steels). Thus obtained elemental silicon is necessary to obtain pure silicon dioxide, which is of great importance for a number of industries. Natural SiO2 is used in the form of sand in those industries where its high purity is not required.
When inhaling finely divided dust of crystalline SiO2, even in very small quantities (up to 0.1 mg / m³), silicosis, bronchitis or cancer can develop over time. Dust becomes dangerous when it enters the lungs, constantly annoying them, thereby reducing their function. In the human body, silicon oxide in the form of crystalline particles does not dissolve during clinically significant periods of time. This effect can create a risk of occupational disease for people working with sandblasting equipment or products that contain crystalline silica powder. Children, asthmatics of any age, suffering from allergies, as well as older people can get sick much faster.