Yellow Antimony and Explosive Antimony

The final two unstable allotropic forms of antimony are yellow and explosive.

Much like its arsenic and phosphorus analogs, yellow antimony exhibits mostly nonmetal properties. The oxidization, either by air or oxygen, of liquid antimony hydride produces yellow antimony and black antimony. Yellow antimony is only stable below -90° C. At temperatures between -90° C and -50° C, the yellow allotrope will degrade into its black counterpart. At temperatures above -50° C, yellow antimony rapidly converts into regular metallic antimony.

Explosive antimony is produced by the electrolysis of the aqueous solution of antimony halide. It is believed that this is because of the presence high concentrations of antimony ions in the solution. Explosive antimony deposits on the cathode at a current density of 200 A/m² in a hydrochloric acid solution containing 17 - 33% SbCl₃. Explosive antimony has a steel-gray color and a smooth, soft surface. Its density is 5.64 -5.97 g/cm³. It will produce a vigorous explosion when it is gently struck, rubbed, treated with thermal radiation, or heated to 125° C. The explosion is the result of instant liberation of crystalline heat when a foreign force is applied and will occur even under water.

Black Antimony Allotrope

Antimony’s three unstable allotropes are black, yellow, and explosive. An allotrope is a variation of the molecular structure of a single element. Differences in chemical structure will give an element different physical properties depending on the allotropic form. For example, carbon has two common allotropes; diamond and graphite. In the diamond form the carbon atoms are arranged in a tetrahedral lattice configuration. In the graphite form, on the other hand, carbon atoms are bonded in layers of a hexagonal lattice.

Black antimony is an amorphous black powder, with a specific gravity of 5.3. It can be obtained when metallic antimony vapor is shock cooled or when liquid antimony hydride is oxidized by air or oxygen at -40° C. Black antimony is more volatile than grey antimony. Chemically active, it oxidizes in the air at atmospheric temperature. When heated to 400° C in the absence of air, black antimony transforms rapidly into ordinary antimony crystals.