A microtube of yttria‐stabilized zirconia of ca. 100 μm diameter was prepared. An yttria‐stabilized zironia film was formed over a surface‐oxidized nickel wire with a diameter of 10 μm by electrochemical vapor deposition using zirconium tetrachloride and yttrium trichloride as metal sources, and nickel oxide as an oxygen source for the reaction. The YSZ‐coated wire was then immersed in aqueous 11.5 mol.L‐1 hydrochloric acid to dissolve the nickel and nickel oxide, and a microtube of 80 mol? yttria‐stabilized zirconia with a cubic crystal structure was obtained. The surface of the microtube was rough, but was pinhole‐free, from SEM observation. The thickness of the zirconia layer was about 3 μm.

The electrolytic formation of NF, from molten salt, NH,F-HF, KF-NH4F-HF, and CsF-NH,F-HF, with different anodes, was compared. The current efficiencies for NF, formation on a Ni anode and a LiF impregnated carbon (LiF/C) anode in the NH,F-HF melt increased with an increase of the current density and became constant at current densities higher than 120 and 50 mA/cm', respectively Current efficiencies on the Ni anode were greater than those on the LiE/C anode in the range of current density higher than 30 mA/cm'. On the other hand, the presence of KF in the melt reduced the NF, current efficiency on both the Ni and the LiF/C anodes, and the NF, current efficiency on the LiF/C anode in the KF-NH4F-HF melt decreased with an increase of the current density According to the surface analyses, the oxide film on the Ni anode polarized in the NH4-F-HF melt was composed of nickel difluoride, some highly oxidized nickel fluoride, and nickel oxide or oxyfluoride having plural valences. Consequently highly oxidized nickel fluoride on the Ni anode is considered to function as a mediator of the electrochemical fluorination under discussion.

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