For a chemical element with the serial number 14, which is in the periodic table in the IV group of the 3rd period and the third row, it is possible to form two silicon oxides consisting of two elements Si and O:
- 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 recorded as SiO2.
Silicon (IV) oxide in appearance representstransparent crystals. The density of SiO2 is 2.648 g / cm3. The substance melts within the limits of temperatures from 1600 to 1725 ° C, boils at a temperature of 2230 ° C.
Silicon oxide SiO2 was known for its hardnessand strength since ancient times, is most common in nature in the form of sand or quartz, as well as in the cell walls of diatom algae. The substance has many polymorphic modifications, most often found in two forms:
- crystalline - in the form of a natural mineralquartz, 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 occurs as a natural mineralopal, the composition of which can be described by the formula SiO2 • nH2O; earthy forms of amorphous SiO2 are trefoil (mountain meal, diatomaceous earth) or diatomite; Artificial amorphous anhydrous silica is silica gel, which is made from sodium metasilicate.
Silicon oxide SiO2 is an acidic 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 is reacted with hydrofluoric acid to produce fluorosilicic acid: SiO2 + 6HF → H2SiF6 + 2H2O. This property is used in the semiconductor industry.
Silicon (IV) oxide dissolves in hot concentrated or melted alkali to form sodium silicate: 2NaOH + SiO2 → Na2SiO3 + H2O.
Silicon dioxide reacts with basic oxidesmetals (for example, with oxides of sodium, potassium, lead (II), zinc or a mixture of oxides, which is used in the production of glass). For example, the reactions of sodium oxide and SiO2, which can result in the formation of: sodium orthosilicate 2Na2O + SiO2 → Na4SiO4, sodium silicate Na2O + SiO2 → Na2SiO3, and glass Na2O + 6SiO2 + XO → Na2O: XO: 6SiO2. Examples of such glasses of commercial importance are sodium-calcium glass, borosilicate glass, lead glass.
Silicon dioxide reacts with silicon at high temperatures, resulting in a gaseous monoxide: Si + SiO2 → 2SiO ↑.
Most often, SiO2 is used forproduction of elemental silicon. The process of interaction with elemental carbon proceeds at a 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 manufacturing solar cells (converting light energy into electrical energy). Also, pure Si is used in metallurgy (in the production of heat-resistant and acid-resistant siliceous steels). The elemental silicon thus obtained is necessary for the production of 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.
Upon inhalation of finely divided dustcrystalline SiO2, even in very small amounts (up to 0.1 mg / m³), with the passage of time, silicosis, bronchitis or cancer can develop. Dust becomes dangerous when it enters the lungs, constantly irritates them, thereby reducing their function. In human body, the 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 diseases for people working with sandblasting equipment or products that contain a powder of crystalline silicon oxide. Children, asthmatics of any age, suffering from allergies, and also elderly people can get sick much faster.