Everything about Fluorine totally explained
The derivation of elemental fluorine from hydrofluoric acid is exceptionally dangerous, killing or blinding several scientists who attempted early experiments on this halogen. These men came to be referred to as "fluorine martyrs". For Moissan, it earned him the 1906 Nobel Prize in chemistry (Moissan himself lived to be 54, and it isn't clear whether his fluorine work shortened his life).
The first large-scale production of fluorine was needed for the
atomic bomb Manhattan project in
World War II where the compound
uranium hexafluoride (UF
6) was needed as a gaseous carrier of uranium to separate the
235U and
238U
isotopes of
uranium. Today both the
gaseous diffusion process and the
gas centrifuge process use gaseous UF
6 to produce
enriched uranium for
nuclear power applications. In the Manhattan Project, it was found that elemental fluorine was present whenever UF
6 was, due to the spontaneous decomposition of this compound into UF
4 and F
2. The corrosion problem due to the F
2 was eventually solved by electrolytically coating all UF
6 carrying piping with nickel metal, which resists fluorine's attack. Joints and flexible parts were made from
teflon, then a very recently discovered
fluorocarbon plastic which wasn't attacked by F
2.
Preparation
Industrial fluorine production starts with
fluorspar (CaF
2), which is heated with
sulfuric acid (H
2SO
4) to produce anhydrous
hydrogen fluoride (HF). The hydrogen fluoride is added to
potassium fluoride (KF) to make
potassium bifluoride (KHF
2). Electrolysis of potassium bifluoride produces fluorine gas at the anode, and hydrogen gas at the cathode. This is essentially the same method employed by Moissan in 1886; the use of potassium bifluoride rather than hydrogen fluoride itself aids electrolysis by greatly increasing the conductivity.
» 2 CaF
2 + H
2SO
4 → 2 HF + CaSO
4
HF + KF → KHF
2 » 2 KHF
2 → 2 KF + H
2 + F
2
In 1986, when preparing for a conference to celebrate the 100th anniversary of the discovery of fluorine,
Karl Christe discovered a purely chemical preparation involving the reaction of solutions in anhydrous HF, K
2MnF
6, and
SbF5 at 150 °C:
» F
6 + 2F
5 → 2F
6 + F
3 + ½F
2
Though not a practical synthesis, it demonstrates that electrolysis isn't essential.
Safety
Elemental fluorine
Elemental fluorine (fluorine gas) is a highly toxic, corrosive oxidant, which can cause organic material, combustibles, or other flammable materials to ignite. It must be handled with great care and any contact with
skin and
eyes should be strictly avoided. Fluorine gas has a characteristic pungent odor that's detectable in concentrations as low as 20
ppb. As it's so reactive, all materials of construction must be carefully selected. All metal surfaces must be
passivated before exposure to fluorine.
Fluoride ion
Fluoride ions are also highly toxic and must also be handled with great care and any contact with
skin and
eyes should be strictly avoided.
Hydrogen fluoride and hydrofluoric acid
Contact of exposed skin with
hydrofluoric acid solutions poses one of the most extreme and insidious industrial threats—one which is exacerbated by the fact that hydrofluoric acid damages nerves in such a way as to make such burns initially painless. The HF molecule is a weaker acid which is significantly non-dissociated in water, and the intact molecule is capable of rapidly migrating through lipid layers of cells which would ordinarily stop an ion or partly ionized acid, and the burns it produces are typically deep. HF may react with calcium, permanently damaging the bone . More seriously, HF reaction with the body's calcium inside cells can cause cardiac arrhythmias, followed by cardiac arrest brought on by sudden chemical changes within the body (
hypocalcaemia). These can't always be prevented with local or intravenous injection of calcium salts. Hydrofluoric acid spills over just 2.5% of the body's surface area (about 75 in
2 or 5 dm
2), despite copious immediate washing, have been fatal. If the patient survives, hydrofluoric acid burns typically produce open wounds of an especially slow-healing nature.
Anhydrous
hydrogen fluoride will rapidly form hydrofluoric acid on contact with moisture; its physiological effects are then the same.
Organic fluorides
Perfluorocarbons are generally inert and nontoxic, but there are many other fluorine compounds that have physiological effects, both good and bad. For example,
fluoroacetic acid (one of the very few natural fluorine compounds) is very poisonous, while
fluorouracil is an anti-cancer drug.
Further Information
Get more info on 'Fluorine'.
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