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About Silicon

Silicon Bohr

Silicon is truly ubiquitous, but is almost never found as the free element in nature. Instead, it occurs mostly as silicon dioxide, more commonly known as sand or quartz, or in silicate minerals, generally in the found in the forms of clay or rock. It was first proposed that silica sand was likely the oxide of a previously unknown element by Antoine Lavoisier in 1787. In 1808, Sir Humphry Davy named this hypothetical element “silicium”, combining the Latin silex, meaning stone, with the traditional -ium ending often given to metallic elements. The name was changed to silicon in 1817, as the -on ending suggested its closer relation to the non-metallic elements boron and carbon, but it wasn’t until 1823 that the Swedish chemist Jons Jacob Berzelius finally succeeded in preparing pure amorphous silicon and as the first to do so was given credit for “discovering” the element.

The vast majority of silicon used commercially is never separated out of the materials in which it occurs naturally, which are often processed fairly minimally before use. Silicate clays are used to produce whiteware ceramics such as porcelain and in the making of ceramic bricks and cement used as building materials. Silicate-containing rock such as granite is used directly in structural and decorative applications, and silica sand mixed with gravel and cement produces concrete. Sand is also used widely as an abrasive and as a filler in plastics, rubber, and paints. Additionally, diatomaceous earth, a form of silica rock consisting of fossilized remains of diatoms, has many direct commercial applications, especially as an absorbent, a filtration medium, a mild abrasive, and a natural pesticide.

More refined silicon products account for a much smaller portion of commercial silicon usage, but nonetheless are extremely important economically. Common silica sand is the starting point for production of a variety of refined silica products, other silicon compounds, silicon-containing alloys, and elemental silicon at various levels of purity, all of which play significant roles in industry. The following paragraphs give an overview of the major categories of silicon end uses, but do not constitute an exhaustive list.

Silicon in Alloys

Silicon is commonly used as an alloying element. Silica sand is reduced with carbon in the presence of iron to produce ferrosilicon, which can then be used in silicon-containing steels. In molten iron, silicon aids in maintaining carbon content within narrow limits required for a given steel grade. Used in larger amounts, as in electrical steel, silicon favorably influences resistivity and ferromagnetic properties of the material.

For use in non-ferrous alloys, metallurgical grade silicon is produced by reacting high-purity silica with carbon in an electric arc furnace. The most common non-ferrous silicon alloys are aluminum-silicon alloys. The appropriate proportions of aluminum and silicon produce a material that exhibits very little thermal contraction during solidification, making it ideal for casting applications. Metallurgical-grade silicon is also used as a minor alloying agent in a number of other alloys designed for specialized applications.

High-Strength Ceramics

First produced synthetically in the nineteenth century, silicon nitride has been known to science for about as long as silicon carbide, but nonetheless took a much slower path to commercial exploitation. The potential of silicon nitride> as a refractory material was first recognized in the 1950s, and in fact the material came to be used as a binder in silicon carbide ceramics, a use which continues to some extent today. However, pure silicon nitride ceramics proved extremely difficult to fabricate, and early production methods either resulted in materials with less-than-ideal or unreliable mechanical properties, or used production methods that severely limited the types of parts that could be produced. Today, sintered silicon nitride ceramic components can be produced with excellent mechanical properties, but this requires extremely pure silicon nitride nanopowder and precisely controlled manufacturing conditions, both of which contribute to the high cost of this material. These materials have excellent shock resistance, and have come to be used in small engine components. Additionally, silicon nitride can be used to produce ball bearings that can tolerate corrosive environments, high operating temperatures, and low lubrication all while performing better and weighing less than alternatives.

Sialons, ceramics produced with aluminum oxide, silicon nitride and sometimes rare-earth oxides, were first developed in response to difficulties in producing sintered silicon nitride ceramics. Many variations on sialons exist, as variations in starting compositions as well as in production techniques can produce materials with vastly different properties, which result from differences in crystal structure. Some of these variations retain many of the desirable properties of silicon nitride while also providing the added benefit of easier production processes. Other variations are formulated to provide additional properties, such as electrical conductivity or resistance to damage in specific chemical environments. Currently, sialons are used primarily in cutting tools and industrial machine components subjected to extreme conditions.

The semiconductor properties of silicon carbide have been known since the early twentieth century, when the material found use in radio detectors and the first LEDs. However, these and several other uses were developed in the very early days of semiconductor devices, and alternative materials with properties more suited to these applications have since been developed, largely displacing silicon carbide from its historical functions. Research developing silicon carbide as a semiconductor has since explicitly focused on exploiting its strengths, which include its ability to perform at high temperatures and in strong electrical fields. These properties theoretically allow for the production of much smaller, faster, more energy efficient, and more heat-tolerant electronic devices than are possible with traditional silicon based technologies. Initially difficulties producing silicon carbide crystals without defects hampered development of sophisticated silicon carbide electronics, but functional silicon carbide diodes and transistors are now commercially available, and development of these technologies is ongoing.

Amorphous silicon nitride, which can be produced in thin layers using chemical vapor deposition, is an important material in integrated circuits manufacturing, where it is used as structurally as an electrical insulator or protective passivation layer, or as an etch mask in the machining process. Additionally, doped silicon nitrides are being investigated for use as a semiconductor in devices such as LEDs, and both silicon nitride and sialon can be doped to produce phosphors.

Silica glasses

In common usage, glass refers to soda-lime glass, a silica-based glass produced by melting quartz sand along with sodium carbonate, lime, dolmite, and aluminum oxide. This is the glass commonly used in window panes and beverage containers. Most other products commonly known as glass are also silica based, but have differing compositions intended to produce properties favorable for specific uses. For example, borosilicate glasses, often sold under the name Pyrex, contain boron oxide, are notable for their superior ability to withstand thermal shock, and are used for laboratory glassware, household cookware, and optical components. Aluminosilicate glass, another common variety, is used in the composite material fiberglass, and in shatter-resistant glass used for windshields of high-speed vehicles and, increasingly, exposed glass surfaces on portable electronic devices such as mobile phones.

Alternatively, glass can be produced from pure silicon dioxide with no other compounds added. The resulting material is known as fused quartz, and compared to soda lime glass is stronger, has better optical properties, and better resists thermal shock. It also melts at a much higher temperature. This property, though often desirable, makes it considerably more costly to produce than other types of glass. It is therefore used primarily for applications which require these improved properties, which include the production of precision optical components such as high-quality lenses and optical fibers, photolithography masks, and refractory materials for use in high-temperature laboratory and industrial processes.

Synthetic quartz

Quartz is a natural piezoelectric material that finds use in crystal oscillators used to mark time in clocks and digital devices, and to standardize frequency in radio frequency devices. Quartz for this use is generally produced synthetically from silica sand, as this allows for precision engineering of crystal properties.

Silicones

Silicones are mixed organic-inorganic polymers generally consisting of a silicon-oxygen backbone connected to hydrocarbon side groups. Varying the hydrocarbon groups present, silicon-oxygen chain lengths, and the degree of crosslinking can produce a wide range of materials, from silicone oil lubricants to hard silicone resins, but all tend to exhibit low thermal conductivity, chemical reactivity, and toxicity. The wide range of consistencies possible and ease of fabrication, as well as their polymeric structure, prompts comparison to hydrocarbon-based plastics, and in household devices the materials are sometimes used interchangeably. However, the low toxicity and high heat stability of silicone products allow for a broader range of uses in cookware and medical devices. Silicones are additionally used for electrical and thermal insulation, adhesive, sealant, industrial lubricants, dry-cleaning solvent, and personal care products.

Ultra high purity silicon in electronics and photovoltaics

Despite the fact that wafer silicon used in semiconductor devices accounts for only a tiny fraction of the commercial use of the element, this single application is the one most intimately tied to public conceptions of silicon, as its influence on modern life has been profound. Though neither the first integrated circuits (germanium) nor the first solar cells (selenium) contained silicon, for most of the history of both industries, high-purity silicon has been the unquestionably dominant semiconductor material.

For integrated circuit applications, even tiny crystal defects interfere with tiny circuit paths, necessitating the use of monocrystalline silicon. This material is produced using the Czochralski crystal growth process, which requires slow growth of a single enormous crystal from molten high-purity silicon in a carefully controlled environment. Integrated circuits are build using thin wafers cut from these crystals, as are the highest efficiency silicon photovoltaic cells. Other semiconductor devices generally do not require monocrystalline silicon, but still require high-purity to control electrical properties of the material. High-purity amorphous or polycrystalline silicon is found in most silicon photovoltaic cells, and some other large area semiconductor devices.

Synthetic silica products

There are many forms of synthetic silicon oxide, including precipitated silica, colloidal silica, silica gel, fumed silica, and silica fume. Though each product is primarily silicon dioxide, each is produced as a result of a different industrial process, and they vary in particle size. Commonly, these products are employed as mild abrasive agents, anti-caking or thickening agents in food, absorbants, or as filler material in plastics, rubbers, silicones, or cement, though precise end uses vary by form.

Silica gel is the form of synthetic silica most familiar to consumers. These microporous silica beads are commonly found in small paper packets that included in packaging of variety of products to absorb excess moisture. The same absorption properties are exploited for use in cat litter. Silica gel is also used in chemistry laboratories as a stationary phase for chromatography or, when modified with covalently bound functional groups, as a reducing or chelating agent.

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Compounds
Organosilicon & Organometallics

High Purity (99.999%) Silicon (Si) Sputtering Target Silica, as sand, is a principal ingredient of glass--a material with excellent mechanical, optical, thermal, and electrical properties. Ultra high purity silicon can be doped with boron, gallium, phosphorus, or arsenic to produce silicon for use in transistors, solar cells, rectifiers, and other solid-state High Purity (99.999%) Silicon Oxide (SiO2)Powder devices which are used extensively in the electronics industry. Silcones, a large family of synthetic polymers, are important products of silicon. These range from liquids to hard glass-like solids with many useful properties. Silicon is available as metal and compounds with purities from 99% to 99.999% (ACS grade to ultra-high purity). Elemental or metallic forms include pellets, rod, wire and granules for evaporation source material purposes. Silicon oxides are available in powder and dense pellet form for such uses as optical coating and thin film applications. Silicon fluoride is an insoluble silicon source for uses in which the oxide is undesirable such as metallurgy, chemical and physical vapor deposition and in some optical coatings. Silicon is also available in soluble forms including chloridesand acetates. These compounds can be manufactured as solutions at specified stoichiometries.

Silicon Properties

Silicon (Si) atomic and molecular weight, atomic number and elemental symbolSilicon is a Block P, Group 14, Period 3 element. The number of electrons in each of Silicon's shells is 2, 8, 4 and its electron configuration is [Ne] 3s2 3p2. The silicon atom has a radius of 111.pm and its Van der Waals radius is 210.pm. In its elemental form, silicon's CAS number is 7440-21-3. Silicon Elemental Silicon makes up 25.7% of the earth's crust, by weight, and is the second most abundant element, exceeded only by oxygen.Silicon Bohr Molecule Silicon was discovered and first isolated by Jöns Jacob Berzelius in 1823. It is rarely found in pure crystal form and is usually produced from the iron-silicon alloy Ferrosilicon. The name Silicon originates from the Latin word "silex" which means flint or hard stone.

Symbol: Si
Atomic Number: 14
Atomic Weight: 28.09
Element Category: metalloid
Group, Period, Block: 14, 3, p
Color: dark gray with a bluish tinge
Other Names: Silicium, Silicio
Melting Point: 1414°C, 2577.2°F, 1687.15 K
Boiling Point: 3265°C, 5909°F, 3538.15 K
Density: 2330 kg/m3
Liquid Density @ Melting Point: 2.57 g·cm3
Density @ 20°C: 2.33 g/cm3
Density of Solid: 2330 kg·m3
Specific Heat: 0.168 Cal/g/K @ 25°C
Superconductivity Temperature: N/A
Triple Point: N/A
Critical Point: N/A
Heat of Fusion (kJ·mol-1): 39.6
Heat of Vaporization (kJ·mol-1): 383.3
Heat of Atomization (kJ·mol-1): 451.29
Thermal Conductivity: 1.49 W/cm/K @ 298.2 K
Thermal Expansion: (25 °C) 2.6 µm·m-1·K-1
Electrical Resistivity: 3-4 µΩ-cm @ 0°C
Tensile Strength: N/A
Molar Heat Capacity: 19.789 J·mol-1·K-1
Young's Modulus: 51-80 GPa
Shear Modulus: N/A
Bulk Modulus: 97.6 GPa
Poisson Ratio: 0.064 - 0.28
Mohs Hardness: 7
Vickers Hardness: N/A
Brinell Hardness: N/A
Speed of Sound: (20 °C) 8433 m·s-1
Pauling Electronegativity: 1.9
Sanderson Electronegativity: 2.14
Allred Rochow Electronegativity: 1.74
Mulliken-Jaffe Electronegativity: 2.28 (sp3 orbital)
Allen Electronegativity: 1.916
Pauling Electropositivity: 2.1
Reflectivity (%): 28
Refractive Index: N/A
Electrons: 14
Protons: 14
Neutrons: 14
Electron Configuration: [Ne] 3s2 3p2
Atomic Radius: 111 pm
Atomic Radius,
non-bonded (Å):
2.1
Covalent Radius: 111 pm
Covalent Radius (Å): 1.14
Van der Waals Radius: 210 pm
Oxidation States: 2, 4, -4
Phase: Solid
Crystal Structure: diamond cubic
Magnetic Ordering: diamagnetic
Electron Affinity (kJ·mol-1) 134.115
1st Ionization Energy: 786.52 kJ·mol-1
2nd Ionization Energy: 1577.15 kJ·mol-1
3rd Ionization Energy: 3231.61 kJ·mol-1
CAS Number: 7440-21-3
EC Number: 231-130-8
MDL Number: MFCD00085311
Beilstein Number: N/A
SMILES Identifier: [SiH4]
InChI Identifier: InChI=1S/Si
InChI Key: XUIMIQQOPSSXEZ-UHFFFAOYSA-N
PubChem CID: 5461123
ChemSpider ID: 4574465
Earth - Total: 15.12%
Mercury - Total: 7.05%
Venus - Total: 15.82%
Earth - Seawater (Oceans), ppb by weight: 1000
Earth - Seawater (Oceans), ppb by atoms: 220
Earth -  Crust (Crustal Rocks), ppb by weight: 2.7E+08
Earth -  Crust (Crustal Rocks), ppb by atoms: 2E+08
Sun - Total, ppb by weight: 900000
Sun - Total, ppb by atoms: 40000
Stream, ppb by weight: 5000
Stream, ppb by atoms: 180
Meterorite (Carbonaceous), ppb by weight: 1.4E+08
Meterorite (Carbonaceous), ppb by atoms: 1E+08
Typical Human Body, ppb by weight: 260000
Typical Human Body, ppb by atom: 58000
Universe, ppb by weight: 700000
Universe, ppb by atom: 30000
Discovered By: Jöns Jacob Berzelius
Discovery Date: 1823
First Isolation: Jöns Jacob Berzelius (1823)

Health, Safety & Transportation Information for Silicon

Silicon is not toxic but can cause chronic respiratory problems if inhaled as a fine silica or silicate dust. Asbestos silicates are carcinogenic. Safety data for Silicon and its compounds can vary widely depending on the form. For potential hazard information, toxicity, and road, sea and air transportation limitations, such as DOT Hazard Class, DOT Number, EU Number, NFPA Health rating and RTECS Class, please see the specific material or compound referenced in the Products tab. The below information applies to elemental Silicon.

Safety Data
Material Safety Data Sheet MSDS
Signal Word Warning
Hazard Statements H228
Hazard Codes F
Risk Codes 11
Safety Precautions 16-33-36
RTECS Number VW0400000
Transport Information UN 1346 4.1/PG 3
WGK Germany 2
Globally Harmonized System of
Classification and Labelling (GHS)
Flame-Flammables

Silicon Isotopes

Silicon has three stable isotopes: 28Si, 29Si and 30Si.

Nuclide Isotopic Mass Half-Life Mode of Decay Nuclear Spin Magnetic Moment Binding Energy (MeV) Natural Abundance
(% by atom)
22Si 22.03453(22)# 29(2) ms ß+ to 22Al; ß+ to 21Mg 0+ N/A 130.35 -
23Si 23.02552(21)# 42.3(4) ms ß+ to 23Al 3/2+# N/A 146.81 -
24Si 24.011546(21) 140(8) ms ß+ to 24Al; ß+ to 23Mg 0+ N/A 167.93 -
25Si 25.004106(11) 220(3) ms ß+ to 25Al; ß+ to 24Mg 5/2+ N/A 182.53 -
26Si 25.992330(3) 2.234(13) s EC to 26Al 0+ N/A 201.79 -
27Si 26.98670491(16) 4.16(2) s EC to 27Al 5/2+ N/A 215.46 92.2297
28Si 27.9769265325(19) STABLE - 0+ 0 232.85 4.6832
29Si 28.976494700(22) STABLE - 1/2+ -0.55529 240.93 3.0872
30Si 29.97377017(3) STABLE - 0+ 0 251.81 -
31Si 30.97536323(4) 157.3(3) min ß- to 31P 3/2+ N/A 258.02 -
32Si 31.97414808(5) 132(13) y ß- to 32P 0+ N/A 267.03 -
33Si 32.978000(17) 6.18(18) s ß- to 33P (3/2+) N/A 271.38 -
34Si 33.978576(15) 2.77(20) s ß- to 34P 0+ N/A 279.46 -
35Si 34.98458(4) 780(120) ms ß- to 35P; ß- + n to 34P 7/2-# N/A 281.95 -
36Si 35.98660(13) 0.45(6) s ß- to 36P; ß- + n to 35P 0+ N/A 288.17 -
37Si 36.99294(18) 90(60) ms ß- to 37P; ß- + n to 36P (7/2-)# N/A 290.66 -
38Si 37.99563(15) 90# ms [>1 µs] ; ß- + n to 37P; ß- to 38P 0+ N/A 295.94 -
39Si 39.00207(36) 47.5(20) ms ß- to 39P 7/2-# N/A 297.5 -
40Si 40.00587(60) 33.0(10) ms ß- to 40P 0+ N/A 302.78 -
41Si 41.01456(198) 20.0(25) ms ß- to 41P 7/2-# N/A 302.48 -
42Si 42.01979(54)# 13(4) ms ß- to 42P 0+ N/A 305.9 -
43Si 43.02866(75)# 15# ms [>260 ns] Unknown 3/2-# N/A 305.59 -
44Si 44.03526(86)# 10# ms Unknown 0+ N/A 307.15 -
Silicon Elemental Symbol

Recent Research & Development for Silicon

  • Coherent Visible-Light-Generation Enhancement in Silicon-Based Nanoplasmonic Waveguides via Third-Harmonic Conversion. 2015 Jun 5 Sederberg S, Elezzabi AY. Phys Rev Lett. 2015 Jun 5
  • Photoluminescent Mesoporous Silicon Nanoparticles with siCCR2 Improve the Effects of Mesenchymal Stromal Cell Transplantation after Acute Myocardial Infarction. 2015 Jun 25 Lu W, Xie Z, Tang Y, Bai L, Yao Y, Fu C, Ma G. Theranostics. 2015 Jun 25
  • Optical Polarization of Nuclear Spins in silicon carbide. 2015 Jun 19 Falk AL, Klimov PV, Ivády V, Szász K, Christle DJ, Koehl WF, Gali Á, Awschalom DD. Phys Rev Lett. 2015 Jun 19
  • Compact models for carrier-injection silicon microring modulators. 2015 Jun 15 Wu R, Chen CH, Fedeli JM, Fournier M, Cheng KT, Beausoleil RG. Opt Express. 2015 Jun 15
  • Free-carrier electro-refraction modulation based on a silicon slot waveguide with ITO. 2015 Jun 15 Baek J, You JB, Yu K. Opt Express. 2015 Jun 15
  • Frequency comb offset detection using supercontinuum generation in silicon nitride waveguides. 2015 Jun 15 Mayer AS, Klenner A, Johnson AR, Luke K, Lamont MR, Okawachi Y, Lipson M, Gaeta AL, Keller U. Opt Express. 2015 Jun 15
  • Influence of BaTiO<sub>3</sub> ferroelectric orientation for electro-optic modulation on silicon. 2015 Jun 15 Castera P, Tulli D, Gutierrez AM, Sanchis P. Opt Express. 2015 Jun 15
  • Free-Standing Kinked silicon nanowires for Probing Inter- and Intracellular Force Dynamics. 2015 Jul 22 Zimmerman JF, Murray GF, Wang Y, Jumper JM, Austin JR 2nd, Tian B. Nano Lett. 2015 Jul 22
  • Anomalous Stagewise Lithiation of Gold-Coated silicon nanowires: A Combined In-Situ Characterization and First-Principles Study. 2015 Jul 21 Chou CY, Seo JH, Tsai YH, Ahn JP, Paek E, Cho MH, Choi IS, Hwang GS. ACS Appl Mater Interfaces. 2015 Jul 21
  • Mapping Local Cytosolic Enzymatic Activity in Human Esophageal Mucosa with Porous Silicon Nanoneedles. 2015 Jul 21 Chiappini C, Campagnolo P, Almeida CS, Abbassi-Ghadi N, Chow LW, Hanna GB, Stevens MM. Adv Mater. 2015 Jul 21
  • A Highly Responsive Silicon Nanowire/Amplifier MOSFET Hybrid Biosensor. 2015 Jul 21 Lee J, Jang J, Choi B, Yoon J, Kim JY, Choi YK, Myong Kim D, Hwan Kim D, Choi SJ. Sci Rep. 2015 Jul 21