The effects of metallic impurities added and dissolved from the struct
ure of the cell on the current efficiencies for NF3 formation and the
overall generation of anode gas, and on the consumption of the nickel
anode were studied in molten NH4F . 2HF at 120 degrees C by galvanosta
tic electrolysis. A mixed gas composed of NF3 and N-2 with a small amo
unt of N2F2, N2F4, N2O, and O-2 was liberated at the nickel anode duri
ng electrolysis at 25 mA/cm(2). The current efficiencies for NF3 forma
tion and the overall generation of anode gas under steady-state condit
ions depended on the structural material, i.e., the current efficiency
of the copper cell was high compared with those of the steel and nick
el cells. On the other hand, the current loss caused by the anodic dis
solution df nickel in the copper cell was larger than that in the stee
l and nickel cells. Water in the melt retarded not only the anode cons
umption but also the current efficiency for NF3 formation. Although th
e addition of complexes such as NH4NiF3 and (NH4)(3)FeF6 in the melt w
as effective for minimizing the anode consumption, the NF3 formation w
as affected seriously Therefore, we estimate that the allowable conten
ts of Ni2+ and Fe3+ in the melt should be no more than 0.06 and 0.03 m
ole percent, respectively.