Abstract
The effect of electrolysis temperature on the resistivity change of cathode graphite during and after electrolysis of alumina molten salt was investigated. The resistivity decreased along with electrolysis and increased after the electrolysis ended. For electrolysis at 910 and 920°C, ρ/ρ0, the resistivity normalized by the original value, decreased to ~0.80 at first and then showed a plateau at ρ/ρ0~0.40 during electrolysis. On the other hand, for electrolysis at 950 and 980°C, only a plateau at ρ/ρ0~0.80 was observed. Formation of the stage 8 sodium-graphite intercalation compounds was confirmed for the phase with ρ/ρ0~0.40, in contrast to the random stage structure for the phase with ρ/ρ0~0.80. The SEM-EDX measurement of the phase with ρ/ρ0~0.40 showed that sodium was detected not only in the vicinity of the surface but also the inner part of the cathode. The signal intensity of sodium was almost uniform in the cross section of cathode, indicative of sodium intercalation all over the graphite. The cathode was continuously kept at the electrolysis temperature for long time after interruption of electrolysis current until the resistivity showed a steady value. The resistivity determined after cooling to room temperature was larger than that before electrolysis.
