is manufactured electrochemically from a salt melt, which consists of a mixture of fluoride and hydrofluoric acid in a molar ratio of 1:2.0 to 1:2.2. The temperature of the salt melt is ca. 70 to 130 °C. provides the necessary melt conductivity, the hydrogen fluoride consumed being continuously replenished during the electrolysis.

Description of the Electrolysis Cell:

The cathodes and cell are usually made of Monel alloys or steel, the anodes of degraphitized carbon. The cathodic and anodic compartments are not separated by a diaphragm, but by "steel skirts" suspended from the lid into the melt. Fig. 1.7-1 shows a cross-section through an industrial fluorine cell.

Technical data:

The lifetime of the anodes is, for example, 40 to 80^.10⁶ Ah in the type developed by the US Atomic Energy Commission. Since the voltage applied is well above the theoretical value, considerable amounts of heat, ca. 35 MJ/kg fluorine, have to be dissipated. On the other hand, the cooling water temperature must be maintained above the melting point of the electrolyte to prevent its solidification.

The fluorine and hydrogen produced contain ca. 10% by volume of hydrogen fluoride. Cooling below -100 °C strongly reduces the hydrogen fluoride content. The residual hydrogen fluoride in the hydrogen is removed by an alkaline scrubber and that in the fluorine further reduced, if necessary, by passing over sodium fluoride. The fluorine thereby obtained is directly processed further (to uranium hexafluoride, sulfur hexatluoride) or liquefied (b.p. -188 °C) and filled into pressure cylinders. Pressure cylinders with mixtures of fluorine and nitrogen, with 10 or 20% by volume of fluorine, are widely marketed (utilized, for example, for the surface fluorination of vehicle fuel tanks). The worldwide fluorine capacity is estimated to be ca. 7.5^.10³ t/a, of which 60% is in the USA, 25% in Europe and 15% in Japan. Ca. 75% of the fluorine manufactured is utilized in the manufacture of uranium hexafluoride, 22.5% in the manufacture of sulfur hexafluoride and 2.5% in the manufacture of tetrafluoromethane. In 1986 ca. 100 t of fluorine was utilized in the manufacture of fluorographite (high conductivity) for use in batteries.