Magnesium fluoride

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.

Magnesium fluoride[1]
Names
Other names
Sellaite
Irtran-1
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.029.086
EC Number
  • 231-995-1
RTECS number
  • OM3325000
UNII
Properties
MgF2
Molar mass 62.3018 g/mol
Appearance White tetragonal crystals
Density 3.148 g/cm3
Melting point 1,263 °C (2,305 °F; 1,536 K)
Boiling point 2,260 °C (4,100 °F; 2,530 K)
0.013 g/100 mL
5.16⋅10−11
Solubility Insoluble in ethanol
−22.7⋅10−6 cm3/mol
1.37397
Structure
Rutile (tetragonal), tP6
P42/mnm, No. 136
Thermochemistry
61.6 J⋅mol−1⋅K−1
57.2 J⋅mol−1⋅K−1
Std enthalpy of
formation (ΔfH⦵298)
 −1124.2 kJ⋅mol−1
−1071 kJ/mol
Hazards[2][3]
Safety data sheet ChemicalBook
GHS pictograms
GHS Signal word Warning
GHS hazard statements
 H303, H315, H319, H335
P261, P304+340, P305+351+338, P405
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 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
0
3
0
Lethal dose or concentration (LD, LC):
2330 (rat, oral)
Related compounds
Other anions
 Magnesium chloride
Magnesium bromide
Magnesium iodide
Other cations
 Beryllium fluoride
Calcium fluoride
Strontium fluoride
Barium fluoride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

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. The structure of the compound is similar to that in rutile, featuring octahedral Mg2+ centers and 3-coordinate fluoride centres.[4]

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 $3/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.[4]

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⋅cm.[5]

Safety

Chronic exposure to magnesium fluoride may affect the skeleton, kidneys, central nervous system, respiratory system, eyes and skin, and may cause or aggravate attacks of asthma.[6]

References
  1. Lide, David R. (1998), Handbook of Chemistry and Physics (87 ed.), Boca Raton, Florida: CRC Press, pp. 4–67, 1363, ISBN 0-8493-0594-2
  2. "Magnesium Fluoride Material Safety Data Sheet". Science Labs. May 21, 2013. Retrieved October 13, 2017.
  3. "Magnesium fluoride". CAS DataBase List. ChemicalBook. Retrieved October 13, 2017.
  4. Aigueperse, Jean; Mollard, Paul; Devilliers, Didier; Chemla, Marius; Faron, Robert; Romano, Renée; Cuer, Jean Pierre (2005), "Fluorine Compounds, Inorganic", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, doi:10.1002/14356007.a11_307
  5. J. Chem. Soc., Faraday Trans., 1996, 92, 2753 - 2757. doi:10.1039/FT9969202753
  6. "Magnesium Fluoride Material Safety Data Sheet". ESPI Metals. August 2004. Retrieved October 13, 2017.
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