Preparation of a Nickel-Nickel Oxide Composite by Hot Isostatic Pressing and Its Application for Anodes Used in Electrolytic Production of Nitrogen Trifluoride.

The nickel-nickel oxide [Ni-NiO 1+ ≤(0 ≤ x < 0.5)] composites prepared from a mixture of Ni and LiNiO 2 or NiO powders at 900°C under 2000 atm for 2 h by hot isostatic pressing were employed as the anode for electrolytic production of NF 3 . In electrolysis of a molten NH 4 F.2HF with and without LiF at 100°C and at 25 mA/cm 2 , the anode gas generated at the Ni-NiO 1+x composite anode was composed of N 2 , O 2 , NF 3 , N 2 F 2 , N 2 F 4 , and N 2 O, and its composition was almost the same as that at the Ni sheet anode. The current efficiency for NF 3 formation on the Ni-NiO composite anode from mixture of NiO and Ni powders was high compared with that on the Ni-NiO 1+x composite anode from the mixture of LiNiO 2 and Ni powders. The best current efficiency for NF 3 formation was ca. 53% on the Ni 5 mol % NiO composite anode, and it was almost the same as that of the Ni sheet anode. The addition of LiF in a molten NH 4 F-2HF increased it, presumably because of deposition of Li 2 NiF 6 on the anode. On the other hand, the anode consumption of the Ni-NiO composite was much smaller compared with that of the Ni sheet electrode. Also, the oxygen content in the oxidized layer formed on the Ni-NiO composite anode was high compared with that on the Ni sheet anode. The scanning electron microscope observation revealed that the surface of the Ni-NiO composite anode was covered with the compact film having some defects. From these results, it is concluded that the Ni-NiO composite anode is favorable for electrolytic production of NF 3 , and that the oxidized layer on the anode has a high resistance to corrosion, because of the compact film containing a higher content of oxygen formed on the anode.