Fluorine is the most electronegative and chemically reactive nonmetal, a pale-yellow gas at room temperature with a density around 1.696 g/L. It reacts with almost every element, so elemental fluorine does not exist in nature and must be produced from minerals such as fluorite. Its largest industrial role is in fluorinated refrigerants and blowing agents: since chlorofluorocarbons were phased out, hydrofluorocarbons and hydrofluoroolefin replacements continue to support the refrigeration cycles of air conditioners, refrigerators and automotive climate control, valued for being non-toxic, non-flammable and thermally stable. Fluoropolymers are another high-value market: polytetrafluoroethylene (PTFE, sold as Teflon) has an extremely low coefficient of friction and resists strong acids, strong bases and high temperatures, and is used as the non-stick inner layer of cookware, in gaskets, chemical pipe linings and wire insulation.
In the nuclear industry, fluorine, in the form of uranium hexafluoride (UF6), converts natural uranium into a gas so that U-235 enrichment can proceed by gas centrifuge, making it a key step in the nuclear fuel cycle. The electronics industry uses hydrofluoric acid to etch SiO2 and glass wafers, and fluorinated specialty gases for plasma etching and cleaning that directly determine chip line width and yield. Lithium hexafluorophosphate (LiPF6), the electrolyte of lithium-ion batteries, is an indispensable component of today's mainstream traction batteries. In consumer products, fluoridated toothpaste forms an acid-resistant fluorapatite layer on teeth, and water and salt fluoridation are used to prevent dental caries. Fluoroplastics, fluoroelastomers and fluorosurfactants also support aerospace seals, semiconductor gas piping and high-performance water- and oil-repellent textile finishes.
Hydrofluoric acid (HF) is fluorine's most fundamental acid; because it dissolves silicon dioxide, it is uniquely used in glass etching and semiconductor wafer cleaning, and is also a key acid in refinery alkylation and uranium conversion. Calcium fluoride (CaF2) is fluorite, or fluorspar—the starting ore for virtually the entire fluorine industry; treated with sulfuric acid it yields hydrofluoric acid, which is then processed into refrigerants, fluoropolymers and fluorinated specialty gases. Polytetrafluoroethylene (PTFE) is the representative fluoropolymer, with an extremely low coefficient of friction and extraordinary corrosion resistance, used in non-stick coatings, seals and chemical linings. Sulfur hexafluoride (SF6) has outstanding insulating and arc-quenching properties and is used as the insulating gas in high-voltage switchgear, gas-insulated substations and ring-main units. Uranium hexafluoride (UF6) is the working fluid for gas-centrifuge enrichment of uranium isotopes and is an irreplaceable compound in the nuclear fuel cycle.
