Behavior of impurities during distillation and melting of pure magnesium

In order to understand the contamination of molten pure magnesium by various crucibles, at first 99.9% magnesium was distilled under reduced pressure conditions. Then the distilled magnesium was melted in the magnesia, alumina, zirconia with Y2O3, calcia, low carbon steel and stainless steel crucibles in an argon gas atmosphere. The Zn, Al, Si and Mn in the pure magnesium were effectively eliminated by the distillation. Melting in the magnesia, zirconia and SUS430 stainless steel crucibles makes no change of impurities. When alumina and low carbon steel crucibles are used, however Al and Fe contents increase by melting, because the alumina crucible and FeO or Fe in the low carbon steel crucible are reduced or attacked by the molten magnesium. Furthermore, Ca and Al contents increase by melting in the calcia crucible. It is confirmed by an X-ray diffraction method that the calcia crucible contains Ca(OH)2 and Al2O3. Therefore, it is considered that the Ca(OH)2 decompose and dissolve into the molten magnesium and the Al2O3 is reduced by the molten magnesium.