Lithium fluoride

Manufacturing

LiF is prepared from lithium hydroxide or lithium carbonate with hydrogen fluoride.

Applications

Precursor to lithium hexafluorophosphate for batteries

Lithium fluoride is reacted with hydrogen fluoride (HF) and phosphorus pentachloride to make lithium hexafluorophosphate , an ingredient in lithium ion battery electrolyte.

The lithium fluoride alone does not absorb hydrogen fluoride to form a bifluoride salt.

In molten salts

Fluorine is produced by the electrolysis of molten potassium bifluoride. This electrolysis proceeds more efficiently when the electrolyte contains a few percent of LiF, possibly because it facilitates formation of an Li-C-F interface on the carbon electrodes. A useful molten salt, FLiNaK, consists of a mixture of LiF, together with sodium fluoride and potassium fluoride. The primary coolant for the Molten-Salt Reactor Experiment was FLiBe; (66 mol% of LiF, 33 mol% of ).

Optics

Because of the large band gap for LiF, its crystals are transparent to short wavelength ultraviolet radiation, more so than any other material. LiF is therefore used in specialized optics for the vacuum ultraviolet spectrum. (See also magnesium fluoride.) Lithium fluoride is used also as a diffracting crystal in X-ray spectrometry.

Radiation detectors

It is also used as a means to record ionizing radiation exposure from gamma rays, beta particles, and neutrons (indirectly, using the (n,alpha) nuclear reaction) in thermoluminescent dosimeters. 6LiF nanopowder enriched to 96% has been used as the neutron reactive backfill material for microstructured semiconductor neutron detectors (MSND).

Nuclear reactors

Lithium fluoride (highly enriched in the common isotope lithium-7) forms the basic constituent of the preferred fluoride salt mixture used in liquid-fluoride nuclear reactors. Typically lithium fluoride is mixed with beryllium fluoride to form a base solvent (FLiBe), into which fluorides of uranium and thorium are introduced. Lithium fluoride is exceptionally chemically stable and LiF/ mixtures (FLiBe) have low melting points (360 to) and the best neutronic properties of fluoride salt combinations appropriate for reactor use. MSRE used two different mixtures in the two cooling circuits.

Cathode for PLED and OLEDs

Lithium fluoride is widely used in PLED and OLED as a coupling layer to enhance electron injection. The thickness of the LiF layer is usually around 1 nm. The dielectric constant (or relative permittivity, ε) of LiF is 9.0.

Natural occurrence

Naturally occurring lithium fluoride is known as the extremely rare mineral griceite.

References

References

1. (June 18, 2018). "CRC Handbook of Chemistry and Physics". CRC Press.
2. "Lithium fluoride - Product Specification Sheet". Merck KGaA.
3. "Lithium fluoride". [[National Library of Medicine.
4. (2005). "Ullmann's Encyclopedia of Industrial Chemistry". Wiley-VCH.
5. (2012). "Improved High Efficiency Stacked Microstructured Neutron Detectors Backfilled With Nanoparticle ⁶LiF". [[IEEE Transactions on Nuclear Science.
6. (2000). "Fluorine Compounds, Inorganic".
7. (2012). "Lithium Fluoride (LiF) Optical Material".
8. (2013). "Present status of microstructured semiconductor neutron detectors". Journal of Crystal Growth.
9. (1970). "Low-Frequency Dielectric Constant of LiF, NaF, NaCl, NaBr, KCl, and KBr by the Method of Substitution". [[Physical Review B.
10. "Griceite mineral information and data".