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

Abstract

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...

Anodic behavior of nickel-based alloys in the electrolytic production of NF3

“…For the purpose of prevention from anodic dissolution, the nickel-oxide composite materials, such as Ni-NiO 1+x (0 < x< 0.5), Ni-Co 3 O 4 , Ni-MnO 2 , Ni-Ag 2 O, Ni-Y 2 O 3 , Ni-La 2 O 3 , Ni-Nd 2 O 3 and Ni-Sm 2 O 3 , were used as the anodes for electrolytic production of NF 3 . Although Ni-NiO 1+x , Ni-La 2 O 3 , Ni-MnO 2 and Ni-Ag 2 O composites were effective for preventing nickel from anodic dissolution, the current efficiencies for NF 3 formation on these composite anodes were somewhat smaller compared with that on the nickel sheet anode except Ni-La 2 O 3 composite anode [2,3]. Therefore, it is important to develop another nickel-based composite anode without decreasing the current efficiency for NF 3 formation.…”