Thorium Borides

When a mixture of thoria with boron is heated in a carbon boat in an electric furnace a bronze-yellow to red product is obtained from which two borides of thorium, ThB₄ and ThB₆ can be isolated.

Thorium Tetraboride, ThB₄, is a yellow, metallic-looking powder consisting of fragments of prismatic crystals, and having a density of 7.5 at 15° C. It is dissolved by cold hydrochloric and nitric acids and by hot sulphuric acid.

Thorium Hexaboride, ThB₆, is an amorphous, reddish violet, metallic- looking substance having a density of 6.4 at 15° C. It is not dissolved by concentrated hydrochloric and sulphuric acids, but dissolves readily in hot nitric acid.