① Elemental silicon
In 1823, Bezelius of Sweden used silicon fluoride or potassium fluorosilicate and potassium to obtain powdered silicon and determined it as an element. The symbol of silicon is Si, atomic number 14, atomic weight 28.086, peripheral electron arrangement 3s²3p², located in group IV of the third cycle, covalent radius 117pm, ion radius 42pm, first ionization energy 786.1kJ/mol, electronegativity 1.8, there is Both crystalline and amorphous allotropes, density 2.33kg/m3, melting point 1410°C, boiling point 2355°C, hardness 7, crystalline silicon is silver-grey, with obvious metallic luster, the crystal lattice is the same as diamond, hard and brittle, It is a semiconductor. Elemental silicon is inactive at low temperatures and does not react with air, water and acid. The surface is oxidized at room temperature to form a 1000pm silicon dioxide protective film. It can react with all halogens at high temperature to produce silicon tetrahalide, and when it burns with oxygen above 700°C to produce silicon dioxide. It reacts with hydrogen chloride at 500°C to produce trichlorosilane and hydrogen gas. The low boiling point of trichlorosilane (31.8°C) is used to separate it from other substances by Siemens chemical method. Silicon is widely distributed in nature. The percentage of silicon atoms in the earth’s crust is 16.7%, and the mass fraction is 27.6%. Silicon in nature is composed of three stable isotopes of silicon 28, silicon 29, and silicon 30. Silicon is a basic element that composes rock minerals, mainly in the form of quartz sand or silicate.
Silicon is mainly present in quartz and sand in the form of silicon dioxide. The chemical formula of silicon dioxide is SiO2, the molecular weight is 60.08, and it is also called silica, which is a hard and insoluble solid. Most of the 16km down from the ground are ore. Silica in its natural form is either an independent quartz mineral or sandstone in the form of silica and silica. Silica may contain limonite, hematite, pyrite, feldspar and clay ore. Natural silica is divided into two categories: crystalline and amorphous. Crystalline silica is mainly found in quartz ore. Pure quartz is a colorless crystal, and large and transparent prismatic quartz is a crystal. Silica is an atomic crystal with a tetrahedral structure formed by silicon atoms and four oxygen atoms. The entire crystal can be regarded as a huge molecule. SiO2 is the simplest form and does not mean a single molecule. Amorphous silica is a white solid or powder with a melting point of 1723°C±5°C and a boiling point of 2230°C. Its chemical properties are very stable. It is insoluble and does not react with water. It is an acidic oxide and does not react with general acids. Hot strong alkali solution or molten alkali reacts to form silicate and water, and reacts with a variety of metal oxides at high temperature to form silicate, which is used to make quartz glass, optical instruments, chemical utensils, ordinary glass, refractory materials, Optical fiber, ceramics, etc.
Silica with high purity is quartz, trigonal crystal system, the crystals are hexagonal columnar, often in the form of crystal clusters, granular, massive and other monomers or groups. Colorless and transparent crystals are called crystals, milky white is called milk quartz, purple is called amethyst, smoky yellow is called smoky crystal or citrine, and black is called smoky crystal. The crystal contains white or other color radiation. It is called the Venus Stone. The complete crystals of quartz are produced in rock geodes, and the massive ones are often produced in hydrothermal veins. They are also an important part of various rocks such as granite, gneiss and sandstone. Quartz crystals can also be made artificially. Well-crystallized crystals can be used in optical instruments and piezoelectric materials; various other quartz variants can be used in the manufacture of glass, enamel, abrasive materials, and building materials.