Lithium fluoride

Description

lithium fluoride is a strong irritant to the eyes and skin; potassium bromide is toxic by ingestion and inhalation; sodium chloride is table salt, a medical concern when ingested in excess, but certainly of no significant hazard to emergency responders.

Chemical properties

Lithium fluoride is a white crystalline solid. It is not hygroscopic as are the other lithium halides and is not affected by exposure to the air. Lithium fluoride is the least soluble of the alkali metal fluorides. This characteristic likens it to the alkaline earth fluorides. Lithium fluoride is different from the other lithium halides in that it does not form hydrates which can be isolated from solution. Lithium fluoride does show an increase in solubility as hydrofluoric acid is added to an aqueous solution. Under these conditions the fluoride ion is converted to the bifluoride ion, HF-2, allowing further dissolving of the solid lithium fluoride.

Physical properties

White cubic crystals; refractive index 1.3915; density 2.635 g/cm³; melts at 845°C; vaporizes at 1,676°C; very slightly soluble in water 0.27 g/100g at 18°C; soluble in hydrofluoric acid; insoluble in alcohol.

The Uses of Lithium fluoride

The important uses of lithium fluoride are as flux in glasses, vitreous enamels and glazes; in soldering and welding aluminum; and its prisms in infrared spectrophotometers. The compound also is used for storing solar energy.

The Uses of Lithium fluoride

As flux for soldering and welding aluminum, in the manufacture of vitreous enamels and glazes. Lithium fluoride prisms are used in infrared spectrophotometers.

The Uses of Lithium fluoride

Lithium fluoride is widely used in many fields. It is used in the soldering progress for glass lining as a cosolvent. It finds application as an additive of aluminum electrolysis and rare earth electrolysis as a crystal in X-ray spectrometry. It is also used in specialized UV optics due to its large band gap and transparency to short wave length ultraviolet radiation. It is involved to record ionizing radiation exposure from gamma rays, beta particles and neutrons in thermoluminescent dosimeters. In nuclear reactors, lithium fluoride is mixed with beryllium fluoride to form a base solvent, which is used in molten-salt reactor experiment (MSRE). Additionally, it is useful as a coupling layer to enhance electron injection in polymer light-emitting diodes (PLED) and organic light-emitting diode (OLED).

Preparation

Lithium fluoride is prepared by treating an aqueous solution of lithium hydroxide or lithium carbonate with aqueous hydrofluoric acid: LiOH + HF → LiF + H2O.

Flammability and Explosibility

Non flammable

Safety Profile

Poison by ingestion and subcutaneous routes. When heated to decomposition it emits toxic fumes of F-. Used as a flux in enamels, glasses, glazes, and weldmg. See also FLUORIDES and LITHIUM COMPOUNDS.

Purification Methods

Possible impurities are LiCO3, H2O and HF. These can be removed by calcining it at red heat, then pulverizing it with a Pt pestle and storing it in a paraffin bottle. Its solubility in H2O is 0.27% at 18o. It volatilises between 1100-1200o. [Kwasnik in Handbook of Preparative Inorganic Chemistry (Ed. Brauer) Academic Press Vol I p 235 1963].

Structure and conformation

The space lattice of LiF belongs to the cubic system, and its rock salt structure has a lattice constant of a=0.40173 nm and Li-F=0.201 nm. The cleavage plane is (100).