MEASUREMENT AND THERMODYNAMIC ANALYSIS OF REFERENCE ELECTRODE POTENTIALS IN A FEW FLUORIDE MELTS CONTAINING HF

摘要

Potential on a copper reference electrode was measured at 100 deg C in each dehydrated melt of a KF centre dot 2HF, a NH_4F centre dot KF centre dot 4HF, and a NH_4F centre dot 2HF against hydrogen evolution potential on a Pt rod by voltammetry with a sweep rate of 5 to 10 mV/s. Its value on a fresh copper reference electrode was unstable for first 30 days, whereas those on the anodically oxidized and the thermally fluorinated copper reference electrodes became stable for the shorter time. The stable value of potential on the thermally fluorinated copper reference electrode in a KF centre dot 2HF melt was 0.402 + - 0.003 V vs. H_2. On the other hand, the theoretical value of potential calculated from thermodynamic data was 0.388 V. It has a little difference from observed value of it, and it may be caused by coexistence of CuF with CuF_2 on the surface of a copper reference electrode. Although the theoretical potential on a Ni/NiF_2 reference electrode was -0.248 V, the observed potential on a nickel reference electrode in a KF centre dot 2HF melt at 100 deg C was 0.096 + - 0.010 V vs. H_2. It was different from the calculated potential of a Ni/NiF_2 electrode. From these results, it is concluded that a new type of a copper electrode designated as Cu/CuF_(2-x) (0