NaF-BaF₂-AIF₃系溶融塩の電気伝導度

アルミニウムの電解精製に関する研究 (第5報)

抄録

The molten salts, sodium fluoride-barium fluoride-aluminum fluoride system, are known as “Hoopes' bath” in the electrolytic refining of aluminum.
The melting points and densities of this system were already reported by the author.
In this paper, the electrical conductivities of some compositions of the above-mentioned system were determined.
1) As a conductance cell of the molten fluoride salts, a platinum crucible combined with a platinized platinum wire was used.
To prevent errors due to polarization, we adopted
(i) An electrode of platinized platinum wire.
(ii) Resistances measured at 2, 500, 5, 000, 10, 000 cycles/sec were plotted against 1/√f and the linear extrapolations to infinite frequency were used.
Then we calculated both the electrical conductivities of the molten salts and the resistance of the lead wire by using the next formula;
R ∝ =R₀+K/k
2) The measuring value of the specific conductivity of the molten cryolite was 2.92 ohm^-1cm^-1 at 1, 050°C and 2.87 ohm^-1 cm^-1 at 1, 000°C.
3) The values of the molten mixtures of the ternary system NaF-BaF₂-AIF₃ are 5.0-1.0 ohm^-1cm^-1 at 1, 000°C and 950°C.
When the content of barium fluoride is kept constant, the specific conductivity decreases almost linearly with the increase of aluminum fluoride content, and when the content of barium fluoride increases, the conductivity decreases also.
4) The specific conductivity of the Hoopes' bath is 1.70 ohm^-1cm^-1 at 1, 000°C and 1.47 ohm^-1 cm^-1 at 950°C.
5) When we assume the formation of the compound NaBaAIF₆ and calculate the specific conductivities of these ternary molten salt mixtures, these values accord well with measured ones.
6) In this system, the following compositions show the comparatively low melting temperatures and have the same value as that of th, e Hoopes' bath.
NaF 50-57%, BaF₂ 30-40%, AIF₃ 8-18%
The densities of ihese salt mixtures also range between that of the anode alloy and the refined aluminum.