Silicon tetrafluoride or tetrafluorosilane is a

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

with the formula Si F₄. This colorless gas is notable for having a narrow liquid range: its boiling point is only 4 °C above its melting point. It was first prepared in 1771 by

Carl Wilhelm Scheele Carl Wilhelm Scheele (, ; 9 December 1742 – 21 May 1786) was a Swedish German pharmaceutical chemist. Scheele discovered oxygen (although Joseph Priestley published his findings first), and identified molybdenum, tungsten, barium, hydroge ...

by dissolving silica in

hydrofluoric acid Hydrofluoric acid is a solution of hydrogen fluoride (HF) in water. Solutions of HF are colourless, acidic and highly corrosive. It is used to make most fluorine-containing compounds; examples include the commonly used pharmaceutical antidepress ...

., later synthesized by John Davy in 1812. It is a tetrahedral molecule and is corrosive.

Preparation

is a by-product of the production of

phosphate In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid . The phosphate or orthophosphate ion is derived from pho ...

fertilizer A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...

s wet process production, resulting from the attack of HF (derived from

fluorapatite Fluorapatite, often with the alternate spelling of fluoroapatite, is a phosphate mineral with the formula Ca5(PO4)3F (calcium fluorophosphate). Fluorapatite is a hard crystalline solid. Although samples can have various color (green, brown, bl ...

protonolysis) on silicates, which are present as impurities in the phosphate rocks. The

and silicon dioxide (SiO₂) react to produce hexafluorosilicic acid: : 6 HF + SiO₂ → H₂SiF₆ + 2 H₂O In the laboratory, the compound is prepared by heating barium hexafluorosilicate (Ba iF₆ above whereupon the solid releases volatile , leaving a residue of . : Alternatively, sodium hexafluorosilicate () may also be thermally decomposed at — (optionally in inert nitrogen gas atmosphere) :

Uses

This volatile compound finds limited use in microelectronics and

organic synthesis Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...

. It's also used in production of

fluorosilicic acid Hexafluorosilicic acid is an inorganic compound with the chemical formula . Aqueous solutions of hexafluorosilicic acid consist of salts of the cation and hexafluorosilicate anion. These salts and their aqueous solutions are colorless. Hexafluo ...

(see above). Staying in the 1980s, as part of the Low-Cost Solar Array Project by Jet Propulsion Laboratory, it was investigated as a potentially cheap feedstock for polycrystalline silicon production in

fluidized bed reactor A fluidized bed reactor (FBR) is a type of reactor device that can be used to carry out a variety of multiphase chemical reactions. In this type of reactor, a fluid (gas or liquid) is passed through a solid granular material (usually a catalyst ...

s. Few methods using it for the said production process were patented.

The Ethyl Corporation process

In 80s the Ethyl Corporation came up with a process that uses hexafluorosilicic acid and sodium

aluminium hydride Aluminium hydride (also known as alane and alumane) is an inorganic compound with the formula Al H3. Alane and its derivatives are common reducing (hydride addition) reagents in organic synthesis that are used in solution at both laboratory and ...

(NaAlH₄) (or other

alkali metal The alkali metals consist of the chemical elements lithium (Li), sodium (Na), potassium (K),The symbols Na and K for sodium and potassium are derived from their Latin names, ''natrium'' and ''kalium''; these are still the origins of the names ...

hydride) to produce silane (SiH₄).

Occurrence

Volcanic plumes contain significant amounts of silicon tetrafluoride. Production can reach several tonnes per day. Some amounts are also emitted from spontaneous coal fires.Kruszewski, Ł., Fabiańska, M.J., Ciesielczuk, J., Segit, T., Orłowski, R., Motyliński, R., Moszumańska, I., Kusy, D. 2018 – First multi-tool exploration of a gas-condensate-pyrolysate system from the environment of burning coal mine heaps: An in situ FTIR and laboratory GC and PXRD study based on Upper Silesian materials. Science of the Total Environment, 640-641, 1044-1071; DOI: 10.1016/j.scitotenv.2018.05.319 The silicon tetrafluoride is partly hydrolysed and forms hexafluorosilicic acid.

Safety

In 2001 it was listed by

New Jersey New Jersey is a U.S. state, state in the Mid-Atlantic States, Mid-Atlantic and Northeastern United States, Northeastern regions of the United States. It is bordered on the north and east by the state of New York (state), New York; on the ea ...

authorities as a hazardous substance that is corrosive and may severely irritate or even burn skin and eyes. It is fatal if inhaled.

References