Brauer and Mitius modified a method developed by Honigschmid and prepare ThSi3 by the following procedure. Intimate mixtures of Al, Th and Silumin (13% Si, 87% Al) powders are compressed into tablets 10 mm long and 5 mm thick, placed in alumina crucibles and fused at 1100°C in high vacuum. Slow cooling (from 1100°C to 800°C in four hours) produces good product crystals within the aluminium ingot. These are freed of excess Al by alternate treatments with dilute hydrochloric acid and potassium hydroxide (moderate heating), followed by washing with water and alcohol. Since most of the silicide particles form cohesive granules with the Si and SiO2 contaminants, the crystallites are pulverized in an agate mortar and separated from foreign matter (particularly SiO2, which cannot be removed by chemical means) by flotation with bromoform (d 2.9). The bromoform must be continuously renewed. Evaporation with hydrofluoric acid is not practical, since it destroys the silicide.
