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HEXAFLUOROSILICIC ACID

Hexafluorosilicic acid is an inorganic compound with the chemical formula H2SiF6.
Aqueous solutions of hexafluorosilicic acid consist of salts of the cation and hexafluorosilicate anion.
These salts and their aqueous solutions are colorless.

Hexafluorosilicic acid is produced naturally on a large scale in volcanoes.
Hexafluorosilicic acid is manufactured as a coproduct in the production of phosphate fertilizers.
The resulting hexafluorosilicic acid is almost exclusively consumed as a precursor to aluminum trifluoride and synthetic cryolite, which are used in aluminium processing.
Salts derived from hexafluorosilicic acid are called hexafluorosilicates.

CAS: 16961-83-4
European Community (EC) Number: 241-034-8

IUPAC Name: hexafluorosilicon(2-);hydron

Molecular Formula: H2SiF6
Molecular Weight: 144.091 g/mol

Hexafluorosilicic acid is mainly produced as a precursor to aluminum trifluoride and synthetic cryolite.
Hexafluorosilicic acid is commonly used as a source of fluoride for water fluoridation.
Hexafluorosilicic acid is also converted to a variety of useful hexafluorosilicate salts.
The potassium salt is used in the production of porcelains, the magnesium salt.

Experimental Properties:

Boiling Point: 212 °F at 760 mmHg (water) approx.
Melting Point: -4 °F
Solubility: in water: miscible
Density: 1.3 at 77 °F

Hexafluorosilicic Acid is a water insoluble Silicon source for use in oxygen-sensitive applications, such as metal production.
In extremely low concentrations (ppm), fluoride compounds are used in health applications.
Fluoride compounds also have significant uses in synthetic organic chemistry.
They are commonly also used to alloy metal and for optical deposition.
Certain fluoride compounds can be produced at nanoscale and in ultra high purity forms.
Hexafluorosilicic Acid is generally immediately available in most volumes.
Ultra high purity and high purity compositions improve both optical quality and usefulness as scientific standards.

Hexafluorosilicic acid is a kind of inorganic acid.
Hexafluorosilicic acid is majorly used for the fluoridation of water in United State to minimize the incidence of dental caries and dental fluorosis.
For chemical synthesis, hexafluorosilicic acid is majorly used for the manufacturing of aluminum fluoride and cryolite as well as many kinds of hexafluorosilicate salts.
Hexafluorosilicic acid can also be used for the production of silicon and silicon dioxide.
Hexafluorosilicic acid can also be used as an electrolyte in the Betts electrolytic process for refining lead.
Hexafluorosilicic acid is also a specialized reagent in organic synthesis for cleaving Si–O bonds of silyl ethers.

Fluosilicic acid, H2SiF6, also known as hydrofluorosilicic acid, is a colorless liquid that is soluble in water.
Fluosilicic acid is used in water fluoridation, electroplating, and in manufacturing enamels and cement.

Hexafluorosilicic acid is commonly used as a source of fluoride.
Hexafluorosilicic acid is converted to a variety of useful hexafluorosilicate salts.
Hexafluorosilicic acid is also used as an electrolyte in the Betts electrolytic process for refining lead.
Hexafluorosilicic acid is an important organic reagent for cleaving Si-O bonds of silyl ethers.
Further, Hexafluorosilicic acid is used as wood a preservation agent and also used in surface modification of calcium carbonate.

A 1-2% solution is used widely for sterilizing equipment in brewing and bottling establishments.
Other concentrations are used in the electrolytic refining of lead, in electroplating, for hardening cement, crumbling lime or brick work, for the removal of lime from hides during the tanning process, to remove molds, as preservative for timber.

Hexafluorosilicic acid is a chemical that can be used for the treatment of water.
Hexafluorosilicic acid is typically used when there is too much fluoride in the water.
Hexafluorosilicic acid reacts with the fluoride ion to form hexafluorosilicate, which precipitates out of solution.
This process removes 75% of the fluoride from the water in an hour.
Hexafluorosilicic acid also has been shown to be effective against sulfa drugs and phosphorus pentoxide, making it useful for wastewater treatment as well as analytical chemistry.
The chemical stability and reaction mechanism of hexafluorosilicic acid make it a good choice for use in industry.

Hydrofluorosilicic Acid is a colorless, fuming liquid and is the most commonly used fluoridation methods for treating drinking water.

Uses:

- Water Fluoridation
- Disinfecting Copper & Brass Vessels
- Sterilizing Bottling & Brewing
- Cement
- Ceramics
- Wood Preservative

Hexafluorosilicic acid is a chemical compound that is an acid.
Hexafluorosilicic acid's chemical formula is H2SiF6.
Hexafluorosilicic acid is made by the reaction of hydrofluoric acid with silicon dioxide when the hydrofluoric acid is produced.
Hexafluorosilicic acid can be reacted with bases such as sodium hydroxide to produce a fluorosilicate salt such as sodium fluorosilicate.
Hexafluorosilicic acid is used to make artificial cryolite.
Hexafluorosilicic acid releases hydrogen fluoride when it is heated, so it is toxic like hydrofluoric acid.
Hexafluorosilicic acid is used in fluoridation of water.

Structure:
Hexafluorosilicic acid has been crystallized as various hydrates.
These include (H5O2)2SiF6, the more complicated (H5O2)2SiF6·2H2O, and (H5O2)(H7O3)SiF6·4.5H2O.
In all of these salts, the octahedral hexafluorosilicate anion is hydrogen bonded to the cations.

Aqueous solutions of hexafluorosilicic acid are often described as H2SiF6.

Production and principal reactions:

Hexafluorosilicic acid is produced commercially from fluoride-containing minerals that also contain silicates.
Specifically, apatite and fluorapatite are treated with sulfuric acid to give phosphoric acid, a precursor to several water-soluble fertilizers.
This is called the wet phosphoric acid process.
As a by-product, approximately 50 kg of hexafluorosilicic acid is produced per tonne of HF owing to reactions involving silica-containing mineral impurities.

Some of the hydrogen fluoride (HF) produced during this process in turn reacts with silicon dioxide (SiO2) impurities, which are unavoidable constituents of the mineral feedstock, to give silicon tetrafluoride.
Thus formed, the silicon tetrafluoride reacts further with HF.
The net process can be described as:

6 HF + SiO2 → SiF2−6 + 2 H3O+

Hexafluorosilicic acid can also be produced by treating silicon tetrafluoride with hydrofluoric acid.

Reactions:
In water, hexafluorosilicic acid readily hydrolyzes to hydrofluoric acid and various forms of amorphous and hydrated silica ("SiO2").
At the concentration usually used for water fluoridation, 99% hydrolysis occurs and the pH drops.
The rate of hydrolysis increases with pH.
At the pH of drinking water, the degree of hydrolysis is essentially 100%.

H2SiF6 + 2 H2O → 6 HF + "SiO2"

Near neutral pH, hexafluorosilicate salts hydrolyze rapidly according to this equation:

SiF2−6 + 2 H2O → 6 F− + SiO2 + 4 H+

Alkali and alkaline earth salts:

Neutralization of solutions of hexafluorosilicic acid with alkali metal bases produces the corresponding alkali metal fluorosilicate salts:

H2SiF6 + 2 NaOH → Na2SiF6 + 2 H2O

The resulting salt Na2SiF6 is mainly used in water fluoridation.
Related ammonium and barium salts are produced similarly for other applications.
At room temperature 15-30% concentrated hexafluorosilicic acid undergoes similar reactions with chlorides, hydroxides, and carbonates of alkali and alkaline earth metals.

Sodium hexafluorosilicate for instance may be produced by treating sodium chloride (NaCl) by hexafluorosilicic acid:

2NaCl + H2SiF6 (27 °C)→Na2SiF6↓ + 2 HCl
BaCl2 + H2SiF6 (27 °C)→BaSiF6↓ + 2 HCl

Heating sodium hexafluorosilicate gives silicon tetrafluoride:

Na2SiF6 (>400 °C)→SiF4 + 2 NaF

Uses
The majority of the hexafluorosilicic acid is converted to aluminium fluoride and synthetic cryolite.
These materials are central to the conversion of aluminium ore into aluminium metal.
The conversion to aluminium trifluoride is described as:

H2SiF6 + Al2O3 → 2 AlF3 + SiO2 + H2O

Hexafluorosilicic acid is also converted to a variety of useful hexafluorosilicate salts.
The potassium salt, Potassium fluorosilicate, is used in the production of porcelains, the magnesium salt for hardened concretes and as an insecticide, and the barium salts for phosphors.

Hexafluorosilicic acid and the salts are used as wood preservation agents.

Lead refining
Hexafluorosilicic acid is also used as an electrolyte in the Betts electrolytic process for refining lead.

Rust removers
Hexafluorosilicic acid (identified as hydrofluorosilicic acid on the label) along with oxalic acid are the active ingredients used in Iron Out rust-removing cleaning products, which are essentially varieties of laundry sour.

Niche applications

Hexafluorosilicic acid is a specialized reagent in organic synthesis for cleaving Si–O bonds of silyl ethers.
Hexafluorosilicic acid is more reactive for this purpose than HF.
Hexafluorosilicic acid reacts faster with t-butyldimethysilyl (TBDMS) ethers than triisopropylsilyl (TIPS) ethers.

Treating concrete
The application of hexafluorosilica acid to a calcium rich surface such as concrete will give that surface some resistance to acid attack.

CaCO3 + H2O → Ca2+ + 2 OH− + CO2
H2SiF6 → 2 H+ + SiF2−6
SiF2−6 + 2 H2O → 6 F− + SiO2 + 4 H+
Ca2+ + 2 F− → CaF2
Calcium fluoride (CaF2) is an insoluble solid that is acid resistant.

Natural salts
Some rare minerals, encountered either within volcanic or coal-fire fumaroles, are salts of the hexafluorosilicic acid.
Examples include ammonium hexafluorosilicate that naturally occurs as two polymorphs: cryptohalite and bararite.

Applications
Hexafluorosilicic acid is commonly used as a source of fluoride.
Hexafluorosilicic acid is converted to a variety of useful hexafluorosilicate salts.
Hexafluorosilicic acid is also used as an electrolyte in the Betts electrolytic process for refining lead.
Hexafluorosilicic acid is an important organic reagent for cleaving Si-O bonds of silyl ethers.
Further, Hexafluorosilicic acid is used as wood a preservation agent and also used in surface modification of calcium carbonate.

SYNONYMS:

Hexafluorosilicic acid
Fluorosilicic acid
Dihydrogen hexafluorosilicate
Silicate(2-), hexafluoro-, dihydrogen
Hydrofluosilicic acid
Hydrofluorosilicic acid
Silicon hexafluoride dihydride
Fluorosilicic acid (H2SiF6)
hexafluorosilicon(2-); hydron
MFCD00036289
FLUOROSILIC ACID
Kieselfluorwasserstoffsaure
FLUOSILICIC ACID [MI]
53V4OQG6U1
DTXSID2029741
Dihydrogen hexafluorosilicate(2-)
OHORFAFFMDIQRR-UHFFFAOYSA-P
NSC-16894
hexakis(fluoranyl)silicon(2-); hydron
FT-0626488
HYDROGEN HEXAFLUOROSILICATE (H2SIF6)
HEXAFLUOROSILICATE(2-)HYDROGEN (1:2)
FLUOSILICIC ACID (HYDROFLUOSILICIC ACID)
A811126
Q411250
J-521443