Magnesium fluoride


Magnesium fluoride
Magnesium fluoride[1]
Identifiers
CAS number 7783-40-6 YesY
PubChem 24546
ChemSpider 22952 YesY
RTECS number OM3325000
Jmol-3D images 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
Related compounds
Other anions Magnesium chloride
Magnesium bromide
Magnesium iodide
Other cations Beryllium fluoride
Calcium fluoride
Strontium fluoride
Barium fluoride
 YesY fluoride (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 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.

Contents

Production and structure

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

MgO + (NH4)HF2 → MgF2 + NH3 + H2O

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]

Magnesium fluoride can also be prepared from the following simple reaction[3]

MgCl2 + 2((NH4)F) → MgF2 + 2(NH4Cl)

Different with other developments, the use of MgCl2 and (NH4)F allows the fabrication of nano to submicrometer MgF2 with controllable morphology (spherical and cubical)

Uses

Optical properties

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.

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

Thin layers of MgF2 are frequently applied to the surfaces of optical elements as part of optical coatings such as anti-reflective coatings.

References

  1. ^ a b 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. ^ A.B.D. Nandiyanto; F. Iskandar; T. Ogi; and K. Okuyama (2010), "Nanometer to Submicrometer Magnesium Fluoride Particles with Controllable Morphology", Langmuir 26 (14): 12260–12266, doi:10.1016/j.actamat.2009.09.004, PMID 20557055. 
  4. ^ J. Chem. Soc., Faraday Trans., 1996, 92, 2753 - 2757. doi:10.1039/FT9969202753

External links


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