Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B1/00—Electrolytic production of inorganic compounds or non-metals
  • C25B1/01—Products
  • C25B1/24—Halogens or compounds thereof
  • C25B1/245—Fluorine; Compounds thereof
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
  • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material

Definitions

• the invention relates to anodes for electrochemical fluorination and fluorine generation and to a method for their production.
• Electrochemical fluorination in anhydrous or low-water condensed hydrofluoric acid is a technically important process, particularly for organic compounds, and is very gentle and selective compared to fluorination with elemental fluorine.
• the decisive technical problem with this method is the corrosion or passivation of the anode, which is usually made of pure nickel.
• the service life of the anodes is very short, especially at higher current densities, and on the other hand, because of the considerable polarization effects, much higher voltages must be applied than would be expected due to the thermodynamics of the fluorination reactions.
• the invention relates to metal anodes for electrofluorination or for electrochemical fluorine generation, which have an electron-conducting or at least semiconducting layer made of one or more compounds of the metal or metals on which the anode is based, on which there may be another layer made of one or more fluorine compounds Anode of the underlying metal or metals.
• Oxides or sulfides of the metal are preferred as metal compounds for the electron or at least semiconducting layer.
• preferred metals for the anodes are also Cu, Nb, Ta, V, Mo, W, Ti, Zr, Hf, Fe, La and Th or their alloys.
• Another object of the invention is a method for producing the metal anodes according to the invention, which is characterized in that the metals on which the anodes are based are oxidized on their surface to produce a layer and, if appropriate, the oxidized metal anodes are subsequently fluorinated to produce a further layer, e.g. in hydrofluoric acid.
• the oxidation is preferably carried out thermally in air.
• the oxidation for nickel anodes preferably takes place at temperatures above 800 ° C. (between 800 and 1300 ° C.).
• the fluorination of the oxidized metal electrodes to produce the further layer can be carried out separately before the actual process of electrofluorination or fluorine generation or else during the process of electrofluorination or fluorine generation.
• the advantage of the metal anodes according to the invention is that they are particularly corrosion-resistant over a longer period of time and that they allow a higher current density or have a lower overvoltage.
• An electrode made of pure nickel (Ni> 99.7) is annealed in air at 1200 ° C for two hours.
• the electrode turns blue-black due to the formation of oxide on the surface.
• the thickness of the oxide layer is about 10 ⁇ m.
• the electrode can then be used as an anode in a solution of 1 mol / l KF in practically anhydrous condensed hydrofluoric acid without further treatment. After 21 hours of exposure to 4.5 mA / cm2, no corrosion damage can be seen on the electrode with the naked eye.
• the electrode is practically unchanged smooth and blue-black and free of nickel fluoride incrustations. At 50x magnification, the light microscope shows only a few minimal signs of corrosion or discoloration.
• a comparative electrode made of non-pretreated pure nickel is encrusted with nickel fluoride after an identical 21-hour exposure.
• An electrode made of pure nickel is annealed in air at 1200 ° C. as in Example 1, but for a period of 3 hours.
• An electrode made of pure nickel is annealed for 2 hours while adding pure oxygen at approx. 1200 ° C.
• the nickel oxide surface layer that forms is greenish black.
• An electrode made of pure nickel is galvanically coated with an approx. 5 ⁇ m thick layer of copper. The mixture is then heated to 1200 ° C. in air for 2 hours.
• the electrode turns blue-black.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Electrodes For Compound Or Non-Metal Manufacture (AREA)
• Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)

Applications Claiming Priority (2)

Publications (1)

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Citations (2)

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• 1990
  • 1990-04-05 DE DE4010961A patent/DE4010961A1/de active Granted
• 1991
  • 1991-03-23 EP EP91104625A patent/EP0451589A1/de not_active Withdrawn
  • 1991-04-03 JP JP3096086A patent/JPH05140783A/ja active Pending

Patent Citations (2)

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