Magnesium fluoride

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Magnesium fluoride[1]
Other names

Sellaite
Irtran-1

Identifiers
CAS number 7783-40-6 YesY
PubChem 24546
ChemSpider 22952 YesY
RTECS number OM3325000
Jmol-3D images {{#if:[Mg+2].[F-].[F-]|Image 1
Properties
Molecular formula MgF2
Molar mass 62.3018 g/mol
Appearance white tetragonal crystals
Density 3.148 g/cm3
Melting point 1263 °C [1]
Boiling point 2260 °C (decomp)
Solubility in water 0.013 g/100 mL
Solubility product, Ksp 5.16·10-11
Solubility soluble in nitric acid
insoluble in ethanol
Refractive index (nD) 1.37397
Structure
Crystal structure Rutile (tetragonal), tP6
Space group P42/mnm, No. 136
Thermochemistry
Std enthalpy of
formation ΔfHo298		 -1124.2 kJ·mol-1
Standard molar
entropy So298		 57.2 J·mol-1·K-1
Specific heat capacity, C 61.6 J·mol-1·K-1
Hazards
R-phrases R20, R22
NFPA 704
0
3
0
Related compounds
Other anions Magnesium chloride
Magnesium bromide
Magnesium iodide
Other cations Beryllium fluoride
Calcium fluoride
Strontium fluoride
Barium fluoride
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Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references

Magnesium fluoride is an inorganic compound with the formula MgF2. The compound is a white crystalline salt and is transparent over a wide range of wavelengths, with commercial uses in optics that are also used in space telescopes. It occurs naturally as the rare mineral sellaite.

Production and structure

Magnesium fluoride is prepared from magnesium oxide with sources of hydrogen fluoride such as ammonium bifluoride:

MgO + (NH4)HF2 → MgF2 + NH3 + H2O

Related metathesis reactions are also feasible.

The compound crystallizes as tetragonal birefringent crystals. Its structure is similar to that in rutile, featuring octahedral Mg2+ centers and 3-coordinate fluoride centres.[2]

Uses

Optics

Magnesium fluoride is transparent over an extremely wide range of wavelengths. Windows, lenses, and prisms made of this material can be used over the entire range of wavelengths from 0.120 μm (vacuum ultraviolet) to 8.0 μm (infrared). High quality synthetic VUV grade MgF2 is quite expensive, in the region of $3000/kg (2007) but the real cost of optics in this material is due to relatively low volume manufacture. However, with lithium fluoride it is one of the two materials that will transmit in the vacuum ultraviolet range at 121 nm (Lyman alpha) and this is where it finds its application. Lower grade MgF2 is sometimes used in the infrared but here it is inferior to calcium fluoride. MgF2 is tough and works and polishes well, but it is slightly birefringent and should be cut with the optic axis perpendicular to the plane of the window or lens.[3]

Due to its having a suitable refractive index of 1.37, thin layers of MgF2 are very commonly used on the surfaces of optical elements as inexpensive anti-reflective coatings.

The Verdet constant of (MgF2) at 632.8 nm is 0.00810 arcmin G−1 cm−1.[4]

References

  1. ↑ 1.0 1.1 Lide, David R. (1998), Handbook of Chemistry and Physics (87 ed.), Boca Raton, FL: CRC Press, pp. 4–67; 1363, ISBN 0-8493-0594-2 
  2. ↑ Aigueperse, Jean; Paul Mollard, Didier Devilliers, Marius Chemla, Robert Faron, Renée Romano, Jean Pierre Cuer (2005), "Fluorine Compounds, Inorganic", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, doi:10.1002/14356007.a11_307 
  3. ↑ Aigueperse, Jean; Paul Mollard, Didier Devilliers, Marius Chemla, Robert Faron, Renée Romano, Jean Pierre Cuer (2005), "Fluorine Compounds, Inorganic", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, doi:10.1002/14356007.a11_307 
  4. ↑ J. Chem. Soc., Faraday Trans., 1996, 92, 2753 - 2757. doi:10.1039/FT9969202753

External links

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