silicon - Purification, Different forms of silicon, Compounds

Si, element 14, melting point 1410°C. A grey solid non-metal, the second most common element in the crust of the Earth, 26% by weight. It is the second element in the carbon group, and like carbon it forms mainly covalent compounds, with a valence of 4. It does not occur uncombined in nature. In addition to a large number of minerals which are essentially SiO₂, it occurs in many alumino-silicates. Very pure silicon is widely used in electronic devices. It is also doped with controlled amounts of aluminium, phosphorus, and other elements to alter its conductivity. Silicates are the main constituents of brick, stone, cement, and glass.

14 aluminium ← silicon → phosphorus C ↑ Si ↓ Ge Periodic Table - Extended Periodic Table
General
Name, Symbol, Number	silicon, Si, 14
Chemical series	metalloids
Group, Period, Block	14, 3, p
Appearance	dark gray, bluish tinge
Atomic mass	28.0855(3) g/mol
Electron configuration	[Ne] 3s
Electrons per shell	2, 8, 4
Physical properties
Phase	solid
Density (near r.t.)	2.33 g·cm−3
Liquid density at m.p.	2.57 g·cm−3
Melting point	1687 K (1414 °C, 2577 °F)
Boiling point	3538 K (3265 °C, 5909 °F)
Heat of fusion	50.21 kJ·mol−1
Heat of vaporization	359 kJ·mol−1
Heat capacity	(25 °C) 19.789 J·mol
Vapor pressure P/Pa 1 10 100 1 k 10 k 100 k at T/K 1908 2102 2339 2636 3021 3537
Atomic properties
Crystal structure	Diamond Lattice
Oxidation states	4 (amphoteric oxide)
Electronegativity	1.90 (Pauling scale)
Ionization energies (more)	1st: 786.5 kJ·mol−1
	2nd: 1577.1 kJ·mol−1
	3rd: 3231.6 kJ·mol−1
Atomic radius	110 pm
Atomic radius (calc.)	111 pm
Covalent radius	111 pm
Van der Waals radius	210 pm
Miscellaneous
Magnetic ordering	nonmagnetic
Thermal conductivity	(300 K) 149 W·m
Thermal expansion	(25 °C) 2.6 µm·m
Speed of sound (thin rod)	(20 °C) 8433 m/s
Young's modulus	47 GPa
Bulk modulus	100 GPa
Mohs hardness	6.5
CAS registry number	7440-21-3
Selected isotopes
Main article: Isotopes of silicon iso NA half-life DM DE (MeV) DP 28Si 92.23% Si is stable with 14 neutrons 29Si 4.67% Si is stable with 15 neutrons 30Si 3.1% Si is stable with 16 neutrons 32Si syn 132 y β- 13.020 32P
References

Not to be confused with Silicone.

Silicon (IPA: /ˈsɪlikən/, Latin: silicium) is the chemical element in the periodic table that has the symbol Si and atomic number 14.

Silicon and alloys

The largest application of pure silicon (metallurgical grade silicon) is in aluminum - silicon alloys, often called "light alloys", to produce cast parts, mainly for automotive industry (this represents about 55% of the world consumption of pure silicon). The second largest application of pure silicon is as a raw material in the production of silicones (about 40% of the world consumption of silicon) Pure silicon is also used to produce ultrapure silicon for electronic and photovoltaic applications : Semiconductor - Ultrapure silicon can be doped with other elements to adjust its electrical response by controlling the number and charge (positive or negative) of current carriers.

Purification

The use of silicon in semiconductor devices demands a much greater purity than afforded by metallurgical grade silicon. The earliest method of silicon purification, first described in 1919 and used on a limited basis to make radar components during World War II, involved crushing metallurgical grade silicon and then partially dissolving the silicon powder in an acid.

In zone melting, also called zone refining, the first silicon purification method to be widely used industrially, rods of metallurgical grade silicon are heated to melt at one end.

Chemical methods

Today, silicon is instead purified by converting it to a silicon compound that can be more easily purified than silicon itself, and then converting that silicon element back into pure silicon.

At one time, DuPont produced ultrapure silicon by reacting silicon tetrachloride with high-purity zinc vapors at 950 °C, producing silicon according to the chemical equation

SiCl4 + 2 Zn → Si + 2 ZnCl2

However, this technique was plagued with practical problems (such as the zinc chloride byproduct solidifying and clogging lines) and was eventually abandoned in favor of the Siemens process.

Different forms of silicon

Granular silicon	Polycrystal silicon	Silicon monocrystal	Silicon nanopowder
Silicon Ingot

One can notice the color change in silicon nanopowder.

Compounds

For examples of silicon compounds see silicate, silane (SiH4), silicic acid (H4SiO4), silicon carbide (SiC), silicon dioxide (SiO2), silicon tetrachloride (SiCl4), silicon tetrafluoride (SiF4), and trichlorosilane (HSiCl3).