Thorium Fluoride, ThF₄

Anhydrous thorium fluoride, ThF₄, is obtained as a white, amorphous powder by passing hydrogen fluoride over the chloride or bromide, heated to 350°-400° C.

The hydrated fluoride ThF₄.4H₂O is formed as a gelatinous precipitate, passing into a heavy white powder, when hydrofluoric acid is added to a solution of a thorium salt. Unlike zirconium fluoride, thorium fluoride is insoluble in hydrofluoric acid; this difference furnishes a means for the quantitative separation of the two metals. When strongly ignited in air.the fluoride leaves a residue of thoria.