Dr.-Ing. Semiramis Friedrich, Dipl.-Ing. Danilo Curtolo, Prof. Dr.-Ing. Dr. h.c. Bernd Friedrich
Aluminum, in highly pure form, has increasingly been used in highly corrosion resistant applications
or as an alternative to copper in conductive parts, especially for high voltage cables and transformers
due to its inherent electrical conductivity characteristics. These properties also enables the use of high
purity Aluminum in the production of electronic capacitor hard-disks, sputtering targets as well as in
LCD-displays. The most common methodology to produce ultrapure Aluminum is through a combination
of a three-layer electrolytic refining process together with fractional crystallization, mostly
commonly Zone Melting. In order to achieve a purity of up to 6N with the aid of zone melting, many
passes have to be performed, taking several hours to be accomplished.
This paper introduces for the first time an alternative approach for the purification of Aluminum,
offering a high potential to meet the same purification degree and quality aspects while reducing the
overall process time. Firstly, distribution coefficients of main impurities in Aluminum – a deciding
factor to forecast and assess the removal behavior of impurities – were studied theoretically as a
function of temperature using thermochemical calculation in FactSage™. Secondly, this innovative
method using a rotating and gas cooled crystallizer (“cooled finger”) was developed to validate the
principle and an experimental distribution coefficient values were obtained and compared with theoretical
values.
Investigation of Temperature Effect on Impurities’ Distribution Coefficient in Molten Aluminum through Theoretical Calculation and Experimental Fractional Crystallization