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"The technological elements of the process – electrolysis of fused salts to produce metals (including aluminum), the use of cryolite as a flux to dissolve alumina, and the use of carbon electrodes – had been exploited for some time prior to 1886. The workable electrolytic process was discovered independently, and almost simultaneously, in early 1886 by CHARLES MARTIN HALL in Oberlin, Ohio, and PAUL L. T. HÉROULT in Gentilly, France. Both these young scientists were familiar with the work of SAINTE-CLAIRE DEVILLE.

The Hall-Héroult process has produced aluminum with a purity as great as 99.95 %.
All commercial production of aluminum today is done in Hall-Héroult cells. Two major types of cells are currently in use: those employing prebaked carbon anodes and those employing self-baking Söderberg anodes.

The electrolyte contained 25 – 30 % sodium fluoride, 30 – 38 % aluminum fluoride, and 30 – 38 % barium fluoride to increase the electrolyte's density so that pure aluminum would float to the top.

In 1932 the Pechiney Company in France operated .. The electrolyte consisted of 17 % sodium fluoride, 23 % aluminum fluoride, and 60 % barium chloride.

Super-purity aluminum is produced by another fractional crystallization process [1]. In the first step, peritectic elements are removed from molten aluminum by reacting them with boron to form borides, which are precipitated and settled before the metal is transferred to a second furnace. Here the surface of molten aluminum is cooled with forced air, causing metal to crystallize. When the furnace is nearly filled with crystals, the remaining impure aluminum is drained. Then the crystals are remelted to yield very pure metal. Aluminum of purity higher than 99.995 % has been produced from 99.9 % pure smelting-grade aluminum by this process.

Pure cryolite melts at about 1010 °C. Alumina and other additives lower the melting point, allowing operation at 940 – 980 °C. The cryolite-aluminum fluoride-alumina system [2] has binary eutectic points at 961 °C and 694 °C and a ternary one at 684 °C. Calcium fluoride and lithium fluoride further reduce the liquidus temperature [2]. Calcium fluoride is seldom added intentionally. Because of a small amount of calcium oxide impurity in the alumina, it attains a steady-state concentration of 3 – 8 % in the melt. At this level calcium is codeposited into the aluminum and emitted in the off-gas at a rate equal to its introduction. Magnesium fluoride accumulates to 0.1 – 0.3 %, in the electrolyte by the same mechanism as calcium fluoride. Some operators add up to 5 % MgF2 because it expels carbon dust from the electrolyte by decreasing the electrolyte's ability to wet carbon. "


[1] S. C. Jacobs, US Patent 3303019 1967.
[2] P. A. Foster, Jr.: "Phase Diagram of a Portion of the System Na3AlF6-AlF3-Al2O3, J. Am. Ceram. Soc. 58 (1975) no. 7 – 8, 288 – 291.

Ефектност? не съм чувал тоз термин, сигурен ли си че има разлика с ефективност?
Флуора като че ли се използва за нискотемпературни тройни или четворни евтектики.
При тези условия които е дал бдимов, нищо няма да стане.

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