The Electrolytic Production of Fluorine

Abstract

Fluorine was first prepared in quantity by H. Moissan2 by the electrolysis of anhydrous hydrofluoric acid rendered conducting by the addition of potassium hydrogen fluoride. Moissan began with a platinum U-tube as his electrolyzing vessel, the openings in which were closed with fluorite stoppers in which the electrodes of platinum-iridium were set. Later he found that copper would serve equally well as an electrolyzing vessel but that platinum electrodes must be used, Fig, I. With copper electrodes, polarization took place due

The Action of Elementary Fluorine upon Organic Compounds.

“…While it is probable that a further electrolysis of this kind of melt at higher current densities, using more than 10 amp., would ultimately dehydrate it before the exhaustion of the charge, it certainly would not remain anhydrous for any considerable time if left standing exposed to the air, either heated or frozen. Incidentally, it has been found entirely practicable to regenerate an exhausted charge by passing anhydrous hydrogen fluoride into it, contrary to the earlier report (3). It should also be clear that the limitations just outlined would apply not only to the Mathers type of generator, but to all units in which strictly anhydrous conditions cannot be or are not maintained.…”

“…Many years later Ruff (72) studied the Moissan generator intensively, and found that under the best conditions the electrical efficiency with respect to fluorine was only 30 per cent, while that with respect to hydrogen was only 40 per cent, thus lending support to Moissan's observation that they were not far from the same. These very low values were found to be due to (1) the reaction of fluorine with the platinum anode, (2) the reaction of hydrogen with platinum compounds progressively dissolved by the bath, (3) the simultaneous liberation of some hydrogen and some fluorine in the anode and cathode chambers, respectively, and (4) the presence of water in the electrolyte. All of these considerations taken together leave a slight uncertainty as to the exact quantitative composition of the fluorine gas originally obtained when the element was discovered.…”

“…Perhaps a short sketch covering the broad outlines of the work done in this field for the purpose of orienting the reader may not be out of place at this point. In general, direct fluorination using the element itself as the reagent can be carried out in four quite different ways, and these, listed in the approximate order of decreasing importance at the present time, are (1) in the vapor phase, over a metal screen packing, (£) in solution in an inert solvent, (3) in the liquid phase, by counter-current flow, and (4) in the solid phase, mixed with a solid, inert diluent.…”

Role of elemental fluorine in nuclear field

“…Argo in 1919 [5] used a salt of Frémy with a composition of KF-HF at 250 8C. A copper cathode and a graphite anode electrode (unusable in the Moissan's operating conditions) were used.…”

The chemistry of fluorine

“…Production.-Moissan originally prepared gaseous fluorine by the electrolysis of solutions of potassium fluoride in liquid hydrogen fluoride, and this inconvenient method, requiring cooling of the solution to prevent evaporation of the liquid, was used until 1919. In that year Argo, Mathers, Humiston, and Anderson (7) introduced the use of molten potassium hydrofluoride, KHF2, as an electrolyte, and their method, or its modification using KF(HF)3 as suggested by Lebeau and Damiens (8), is in most general use today. The hydrofluoride method, which is largely responsible for the present rapid development of the chemistry of fluorine, will be the one described here.…”