NaF-BaCl2-AlF3系溶融塩の電気伝導度について

アルミニウムの電解精製に関する研究 (第7報)

抄録

The molten salts, sodium fluoride-barium chloride-aluminum fluoride system, are known as “Gadeau's 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 NaF-BaCl₂ binary system and NaF-BaCl₂-AlF₃ ternary system were determined by using a conductance cell of a platinum crucible combined with a platinized platinum wire.
1) The measuring values of the specific conductivity of the molten mixtures of the binary system NaF-BaCl₂ are 5.17-2.18 ohm-1 cm^-1 at 1000°C.
When the content of barium chloride increases, the specific conductivity decreases.
2) In the binary system, the following displacement reaction occurs.NaF+BaCl₂=NaCl+BaFCl
Calculated specific conductivities of this binary system, assuming the additivity of the conductivity of each salt and the displacement reaction, accord well with measured ones.
3) The values of the molten mixtures of the ternary system NaF-BaCl_2-AlF₃are 3.3-0.6 ohm^-1cm^-1at 850°C
When the content of barium chloride is kept constant, the specific conductivity decreases almost linearly with the increase of aluminum fluoride content, because of the formation of the compound Na₃AlF₆and NaAlF₄. And when the content of barium chloride increases, the conductivity decreases also because of the decrease of the sodium fluoride content and the formation of BaFCl.
4) The specific conductivity of the Gadeau's bath is 0.88 ohm^-1 cm^-1at 850°C and 0.82 ohm^-1cm^-1 at 800°C
5) In this ternary system, the following compositions show the comparatively low melting temperatures and suitable densities as the refining electrolyte and have better specific electrical conductivities than that of the Gadeau's bath partially.
NaF 10-35%, BaCl₂50-70%, AlF₃5-25%.