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 1ϩx 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.A large amount of nitrogen trifluoride (NF 3 ) is consumed as a dry etchant and a cleaner gas for the chemical vapor deposition ͑CVD͒ chamber by the electronic industry in Japan. Pure NF 3 free from carbon tetrafluoride (CF 4 ) can be obtained by the electrolysis of NH 4 F•2HF with a nickel anode to meet the demand. However, a relatively large corrosion rate and passivation of the nickel anode are problems for electrolytic production of NF 3 . According to the previous works, 1-3 the nickel dissolution is diminished by a trace of water in the melt whereas the current efficiency for NF 3 formation decreases. The surface layer on the anode formed in a molten salt containing water was dense and adhesive, and its oxygen content was high. 2,3 When the oxidized layer on the nickel anode has a high content of nickel oxide, it has a higher electric conductivity and a higher resistance to corrosion. 4 Although a LiNiO 2 -coated Ni sheet anode prepared by atmospheric plasma spraying technique has almost same current efficiency for NF 3 formation as that on the Ni sheet anode and a relatively small anode consumption, the LiNiO 2 layer having the thickness of 20 to 50 m is dissolved during electrolysis for only 120 h, so that the lifetime of the LiNiO 2 layer in a dehydrated melt of NH 4 F•2HF may be insufficient. 5 Hence, a Ni-NiO 1ϩx (0 Ϲ x Ͻ 0.5) composite was prepared from mixture of Ni and LiNiO 2 or NiO powders by hot isostatic pressing ͑HIP͒.This paper deals with the effect of the content of nickel oxide in the composite on the current efficiency for NF 3 formation and the anode consumption.
ExperimentalA mixture of LiNiO 2 ͑particle size of 1 to 3.3 m͒ and Ni ͑purity of 99.9%, particle size of 74 m͒ powders and that of NiO ͑purity of 97.0%, particle size of 1 m͒ and Ni ͑purity of...