Silicon tetrachloride

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Silicon tetrachloride
Silicon tetrachloride.svg
Silicon-tetrachloride-3D-vdW.png
Names
IUPAC name
Silicon (IV) chloride
Other names
Silicon tetrachloride
Tetrachlorosilane
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.030.037
EC Number
  • 233-054-0
PubChem CID
RTECS number
  • VW0525000
UNII
UN number 1818
Properties
SiCl4
Molar mass 169.90 g/mol
AppearanceColourless liquid
Density 1.483 g/cm3
Melting point −68.74 °C (−91.73 °F; 204.41 K)
Boiling point 57.65 °C (135.77 °F; 330.80 K)
Reaction
Solubility soluble in benzene, toluene, chloroform, ether [1]
Vapor pressure 25.9  kPa at 20 °C
88.3·10−6 cm3/mol
Structure
Tetrahedral
4
Thermochemistry
240 J·mol−1·K−1 [2]
−687 kJ·mol−1 [2]
Hazards
Safety data sheet See: data page
MSDS
Irritant (Xi)
R-phrases (outdated) R14, R36/37/38
S-phrases (outdated) (S2), S7/8, S26
NFPA 704 (fire diamond)
Flammability code 0: Will not burn. E.g. waterHealth code 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasReactivity code 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g. white phosphorusSpecial hazard W: Reacts with water in an unusual or dangerous manner. E.g. sodium, sulfuric acidSilicon tetrachloride
0
3
2
W
Related compounds
Other anions
Silicon tetrafluoride
Silicon tetrabromide
Silicon tetraiodide
Other cations
Carbon tetrachloride
Germanium tetrachloride
Tin(IV) chloride
Titanium tetrachloride
Related chlorosilanes
Chlorosilane
Dichlorosilane
Trichlorosilane
Supplementary data page
Refractive index (n),
Dielectric constantr), etc.
Thermodynamic
data
Phase behaviour
solidliquidgas
UV, IR, NMR, MS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
X mark.svgN  verify  (what is  Yes check.svgYX mark.svgN ?)
Infobox references

Silicon tetrachloride or tetrachlorosilane is the inorganic compound with the formula SiCl4. It is a colourless volatile liquid that fumes in air. It is used to produce high purity silicon and silica for commercial applications.

Contents

Preparation

Silicon tetrachloride is prepared by the chlorination of various silicon compounds such as ferrosilicon, silicon carbide, or mixtures of silicon dioxide and carbon. The ferrosilicon route is most common. [3]

In the laboratory, SiCl4 can be prepared by treating silicon with chlorine: [1]

Si + 2 Cl2 → SiCl4

It was first prepared by Jöns Jakob Berzelius in 1823.

Brine can be contaminated with silica when the production of chlorine is a byproduct of a metal refining process from metal chloride ore. In rare occurrences, the silicon dioxide in silica is converted to silicon tetrachloride when the contaminated brine is electrolyzed. [4]

Reactions

Like other chlorosilanes, silicon tetrachloride reacts readily with water:

SiCl4 + 2 H2O → SiO2 + 4 HCl

In contrast, carbon tetrachloride does not hydrolyze readily. The reaction can be noticed on exposure of the liquid to air, the vapour produces fumes as it reacts with moisture to give a cloud-like aerosol of hydrochloric acid. [5]

With alcohols and ethanol it reacts to give tetramethyl orthosilicate and tetraethyl orthosilicate:

SiCl4 + 4 ROH → Si(OR)4 + 4 HCl

Polysilicon chlorides

At higher temperatures homologues of silicon tetrachloride can be prepared by the reaction:

Si + 2 SiCl4 → Si3Cl8

In fact, the chlorination of silicon is accompanied by the formation of Si2Cl6. A series of compounds containing up to six silicon atoms in the chain can be separated from the mixture using fractional distillation. [1]

Reactions with other nucleophiles

Silicon tetrachloride is a classic electrophile in its reactivity. [6] It forms a variety of organosilicon compounds upon treatment with Grignard reagents and organolithium compounds:

4 RLi + SiCl4 → R4Si + 4 LiCl

Reduction with hydride reagents afford silane.

Uses

Silicon tetrachloride is used as an intermediate in the manufacture of polysilicon, a hyper pure form of silicon, [3] since it has a boiling point convenient for purification by repeated fractional distillation. It is reduced to trichlorosilane (HSiCl3) by hydrogen gas in a hydrogenation reactor, and either directly used in the Siemens process or further reduced to silane (SiH4) and injected into a fluidized bed reactor. Silicon tetrachloride reappears in both these two processes as a by-product and is recycled in the hydrogenation reactor. Vapor phase epitaxy of reducing silicon tetrachloride with hydrogen at approximately 1250oC was done:

SiCl
4
(g) + 2 H
2
(g) → Si(s) + 4 HCl(g) at 1250oC [7]

The produced polysilicon is used as wafers in large amounts by the photovoltaic industry for conventional solar cells made of crystalline silicon and also by the semiconductor industry.

Silicon tetrachloride can also be hydrolysed to fumed silica. High purity silicon tetrachloride is used in the manufacture of optical fibres. This grade should be free of hydrogen containing impurities like trichlorosilane. Optical fibres are made using processes like MCVD and OFD where silicon tetrachloride is oxidized to pure silica in the presence of oxygen.

Safety and environmental issues

Pollution from the production of silicon tetrachloride has been reported in China associated with the increased demand for photovoltaic cells that has been stimulated by subsidy programs. [8] The MSDS notes that one should "avoid all contact! In all cases consult a doctor! ... inhalation causes sore throat and Burning sensation". [9]

See also

Related Research Articles

Silicon Chemical element with atomic number 14

Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard and brittle crystalline solid with a blue-grey metallic lustre; and it is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic table: carbon is above it; and germanium, tin, and lead are below it. It is relatively unreactive. Because of its high chemical affinity for oxygen, it was not until 1823 that Jöns Jakob Berzelius was first able to prepare it and characterize it in pure form. Its melting and boiling points of 1414 °C and 3265 °C respectively are the second-highest among all the metalloids and nonmetals, being only surpassed by boron. Silicon is the eighth most common element in the universe by mass, but very rarely occurs as the pure element in the Earth's crust. It is most widely distributed in dusts, sands, planetoids, and planets as various forms of silicon dioxide (silica) or silicates. More than 90% of the Earth's crust is composed of silicate minerals, making silicon the second most abundant element in the Earth's crust after oxygen.

Silane is an inorganic compound with chemical formula, SiH4, making it a group 14 hydride. It is a colourless, pyrophoric gas with a sharp, repulsive smell, somewhat similar to that of acetic acid. Silane is of practical interest as a precursor to elemental silicon.

Trichlorosilane chemical compound

Trichlorosilane is an inorganic compound with the formula HSiCl3. It is a colourless, volatile liquid. Purified trichlorosilane is the principal precursor to ultrapure silicon in the semiconductor industry. In water, it rapidly decomposes to produce a silicone polymer while giving off hydrochloric acid. Because of its reactivity and wide availability, it is frequently used in the synthesis of silicon-containing organic compounds.

Tungsten(VI) fluoride, also known as tungsten hexafluoride, is an inorganic compound with the formula WF6. It is a toxic, corrosive, colorless gas, with a density of about 13 g/L (roughly 11 times heavier than air.) It is one of the densest known gases under standard conditions. WF6 is commonly used by the semiconductor industry to form tungsten films, through the process of chemical vapor deposition. This layer serves as a low-resistivity metallic "interconnect". It is one of seventeen known binary hexafluorides.

Chlorosilanes are a group of reactive, chlorine-containing chemical compounds, related to silane and used in many chemical processes. Each such chemical has at least one silicon-chlorine bond. Trichlorosilane is produced on the largest scale. The parent chlorosilane is Silicon tetrachloride.

Tantalum(V) chloride chemical compound

Tantalum(V) chloride, also known as tantalum pentachloride, is an inorganic compound with the formula TaCl5. It takes the form of a white powder and is commonly used as a starting material in tantalum chemistry. It readily hydrolyzes to form tantalum(V) oxychloride (TaOCl3) and eventually tantalum pentoxide (Ta2O5); this requires that it be synthesised and manipulated under anhydrous conditions, using air-free techniques.

Hafnium tetrachloride chemical compound

Hafnium(IV) chloride is the inorganic compound with the formula HfCl4. This colourless solid is the precursor to most hafnium organometallic compounds. It has a variety of highly specialized applications, mainly in materials science and as a catalyst.

Phosphoryl chloride chemical compound

Phosphoryl chloride (commonly called phosphorus oxychloride) is a colourless liquid with the formula POCl3. It hydrolyses in moist air releasing phosphoric acid and fumes of hydrogen chloride. It is manufactured industrially on a large scale from phosphorus trichloride and oxygen or phosphorus pentoxide. It is mainly used to make phosphate esters such as tricresyl phosphate.

Chloroplatinic acid chemical compound

Chloroplatinic acid (also known as hexachloroplatinic acid) is an inorganic compound with the formula [H3O]2[PtCl6](H2O)x (0≤x≤6). A red solid, it is an important commercial source of platinum, usually as an aqueous solution. Although often written in shorthand as H2PtCl6, it is the hydronium (H3O+) salt of the hexachloroplatinate anion (PtCl2−
6
).. Hexachloroplatinic acid is highly hygroscopic.

Organosilicon organometallic compound containing carbon–silicon bonds

Organosilicon compounds are organometallic compounds containing carbon–silicon bonds. Organosilicon chemistry is the corresponding science of their preparation and properties. Most organosilicon compounds are similar to the ordinary organic compounds, being colourless, flammable, hydrophobic, and stable to air. Silicon carbide is an inorganic compound.

Tellurium tetrachloride chemical compound

Tellurium tetrachloride is the inorganic compound with the empirical formula TeCl4. The compound is volatile, subliming at 200 °C at 0.1 mmHg. Molten TeCl4 is ionic, dissociating into TeCl3+ and Te2Cl102−.

Binary silicon-hydrogen compounds saturated silicon hydrides, analogues of the alkanes; i.e. compounds of the general formula SiₙH₂ₙ₊₂

Binary silicon-hydrogen compounds are saturated chemical compounds with the empirical formula SiHn. All contain tetrahedral silicon and terminal hydrides. They only have Si–H and Si–Si single bonds. The bond lengths are 146.0 pm for a Si–H bond and 233 pm for a Si–Si bond. The structures of the silanes are analogues of the alkanes, starting with silane, SiH
4
, the analogue of methane, continuing with disilane Si
2
H
6
, the analogue of ethane, etc.

Dichlorosilane chemical compound

Dichlorosilane, or DCS as it is commonly known, is a chemical compound with the formula H2SiCl2. In its major use, it is mixed with ammonia (NH3) in LPCVD chambers to grow silicon nitride in semiconductor processing. A higher concentration of DCS:NH3 (i.e. 16:1), usually results in lower stress nitride films.

Dimethyldichlorosilane is a tetrahedral, organosilicon compound with the formula Si(CH3)2Cl2. At room temperature it is a colorless liquid that readily reacts with water to form both linear and cyclic Si-O chains. Dimethyldichlorosilane is made on an industrial scale as the principal precursor to dimethylsilicone and polysilane compounds.

Polysilicon hydrides are polymers containing only silicon and hydrogen. They have the formula where 0.2 ≤ n ≤ 2.5 and x is the number of monomer units. The polysilicon hydrides are generally colorless or pale-yellow/ocher powders that are easily hydrolyzed and ignite readily in air. The surfaces of silicon prepared by MOCVD using silane (SiH4) consist of a polysilicon hydride.

Polysilicon halides are silicon-backbone polymeric solids. At room temperature, the polysilicon fluorides are colorless to yellow solids while the chlorides, bromides, and iodides are, respectively, yellow, amber, and red-orange. Polysilicon dihalides (perhalo-polysilenes) have the general formula (SiX2)n while the polysilicon monohalides (perhalo-polysilynes) have the formula (SiX)n, where X is F, Cl, Br, or I and n is the number of monomer units in the polymer.

Lead tetrachloride chemical compound

Lead tetrachloride, also known as lead(IV) chloride, has the molecular formula PbCl4. It is a yellow, oily liquid which is stable below 0 °C, and decomposes at 50 °C. It has a tetrahedral configuration, with lead as the central atom. The Pb–Cl covalent bonds have been measured to be 247 pm and the bond energy is 243 kJ⋅mol−1.

Hexachlorodisilane chemical compound

Hexachlorodisilane is the inorganic compound with the chemical formula Si2Cl6, It is a colourless liquid that fumes in moist air. It has specialty applications in as a reagent and as a volatile precursor to silicon metal.

Chlorotrifluorosilane is an organic gaseous compound with formula SiClF3 composed of silicon, fluorine and chlorine.

Tris(trimethylsilyl)silane chemical compound

Tris(trimethylsilyl)silane is the organosilicon compound with the formula (Me3Si)3SiH (where Me = CH3). It is a colorless liquid that is classified as a hydrosilane since it contains an Si-H bond. The compound is notable as having a weak Si-H bond, with a bond dissociation energy estimated at 84 kcal/mol. For comparison, the Si-H bond in trimethylsilane is 94 kcal/mol. With such a weak bond, the compound is used as a reagent to deliver hydrogen atoms. The compound has been described as an environmentally benign analogue of tributyltin hydride.

References

  1. 1 2 3 P. W. Schenk (1963). "Phosphorus(V) fluoride". In G. Brauer (ed.). Handbook of Preparative Inorganic Chemistry, 2nd Ed. 1. NY,NY: Academic Press. pp. 282–683.
  2. 1 2 Zumdahl, S. S. (2009). Chemical Principles (6th ed.). Houghton Mifflin. p. A22. ISBN   0-618-94690-X.
  3. 1 2 Simmler, W. "Silicon Compounds, Inorganic". Ullmann's Encyclopedia of Industrial Chemistry . Weinheim: Wiley-VCH. doi:10.1002/14356007.a24_001.
  4. White, George Clifford (1986). The handbook of chlorination (2nd ed.). New York: Van Nostrand Reinhold. pp. 33–34. ISBN   0-442-29285-6.
  5. Clugston, M.; Flemming, R. (2000). Advanced Chemistry. Oxford University Press. p. 342. ISBN   978-0199146338.
  6. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN   978-0-08-037941-8.
  7. Morgan, D. V.; Board, K. (1991). An Introduction To Semiconductor Microtechnology (2nd ed.). Chichester, West Sussex, England: John Wiley & Sons. p. 23. ISBN   0471924784.
  8. "Solar Energy Firms Leave Waste Behind in China". The Washington Post. 9 March 2008.
  9. "International Chemical Safety Cards Tetrachlorosilane".