No abstract

The effects of metallic impurities added and dissolved from the structure 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°C by galvanostatic electrolysis. A mixed gas composed of NF3 and N2 with a small amount of N2F2,N2F4,N2O , and O2 was liberated at the nickel anode during electrolysis at 25 mA/cm2. The current efficiencies for NF3 formation and the overall generation of anode gas under steady‐state conditions depended on the structural material, i.e., the current efficiency of the copper cell was high compared with those of the steel and nickel cells. On the other hand the current loss caused by the anodic dissolution of nickel in the copper cell was larger than that in the steel and nickel cells Water in the melt retarded not only the anode consumption but also the current efficiency for NF3 formation. Although the addition of complexes such as NH4NiF3 and false(NH4)3FeF6 in the melt was effective for minimizing the anode consumption, the NF3 formation was affected seriously. Therefore, we estimate that the allowable contents of Ni2+ and Fe3+ in the melt should be no more than 0.06 and 0.03 mole percent, respectively.

The hydrogen bonding features of Si(100) surfaces treated with BHF (NH4F/HF/H2O) have been studied by Fourier transform infrared attenuated total reflection spectroscopy (FT-IR-ATR). The amount of residual silicon-fluorine bonds on Si(100) surfaces has been evaluated by X-ray photoelectron spectroscopy (XPS). It is found that Si-H3 bonds appears to be preferentially removed by OH ions so as to increase the surface SiH2 and SiH bonds. On the other hand, it is likely that fluorine-containing ionic species such as HF2 might attack the backbonds of surface hydrides to produce Si-H3 and Si-F bonds. ATR spectra have shown that a BHF treated Si(100) surface in 5∼10% NH4F with molar ratios of HF/NH4F=0.37∼0.56 (pH=3.7∼4.0) at a treatment time of 5 minutes is atomically flatter than that treated in BHF containing 15∼20% NH4F. This is because the amount of residual Si-F bonds on Si(100) increases with HF2 concentration in BHF and these Si-F bonds enhance attacking of silicon backbonds of Si-F bond by OH− and HF2− ions.