- Lithium fluoride (LiF) is an inorganic compound composed of lithium (Li⁺) and fluoride (F⁻) ions. It appears as a white, crystalline solid that is highly stable and possesses a high melting point of approximately 845 °C. Structurally, LiF crystallizes in the cubic NaCl-type lattice, where each lithium ion is surrounded by six fluoride ions and vice versa, forming a dense, symmetrical arrangement.
- Among alkali metal halides, lithium fluoride is unique due to its strong ionic bond and small ionic radii, which contribute to its distinct physical and chemical properties.
- LiF is known for its extreme chemical stability and low solubility in water compared to other alkali metal halides. It is only sparingly soluble in water and practically insoluble in most organic solvents. The compound is also highly resistant to heat, chemical attack, and radiation damage, making it suitable for use in harsh environments. Lithium fluoride is chemically inert under most conditions but will react with strong acids to form hydrogen fluoride (HF), a highly corrosive and toxic gas.
- One of the most important uses of lithium fluoride is in optics and photonics. Due to its wide bandgap and excellent transparency across a broad range of wavelengths—from the vacuum ultraviolet (VUV) to the infrared (IR)—LiF is commonly used in UV optics, lenses, and windows. It is particularly valued in spectroscopic applications where transmission below 200 nm is required, such as in X-ray and vacuum ultraviolet spectrometry. Its low refractive index and resistance to laser damage also make it useful in laser and high-energy photon applications.
- In the nuclear industry, lithium fluoride is employed as a component in molten salt reactors (MSRs) and in fluoride salt mixtures, such as FLiBe (LiF-BeF₂), which serve as coolants or fuel carriers. The high thermal stability and chemical inertness of LiF under reactor conditions make it ideal for withstanding intense radiation and high temperatures. Additionally, LiF is used in dosimetry, where it functions as a thermoluminescent material (particularly in the form of doped LiF, e.g., with Mg or Ti), storing energy upon exposure to ionizing radiation and releasing it as light when heated. This property is exploited for measuring radiation doses in medical, industrial, and environmental monitoring.
- In ceramics and metallurgy, LiF serves as a fluxing agent, helping to lower the melting point of mixtures and improve the flow and formation of metal alloys or ceramic materials. It is also used in the production of aluminum, where it acts as a flux in the electrolytic reduction of alumina during the Hall–Héroult process, often in combination with cryolite (Na₃AlF₆).
- LiF is considered relatively safe when handled correctly, but it does pose health risks. Inhalation or ingestion can be harmful due to the fluoride ion, which is toxic at high levels. Chronic exposure to fluoride compounds can lead to fluorosis, while contact with acid can release hydrogen fluoride, which is highly corrosive and hazardous. Thus, proper protective equipment and ventilation are essential when handling lithium fluoride in industrial or laboratory settings.
