Metallic Antimony - Chemical Properties

Metallic antimony is a relatively stable compound. Under standard conditions, antimony will keep its luster because it does not readily oxidize. Even in moist air and elevated temperatures in the range of 100 - 250° C, it resists oxidization. However, at temperatures above its melting point, powered antimony ignites and burns with a white-green flame. This reaction forms the pure metal into antimony trioxide, Sb₂O₃. At 750 - 800° C, molten antimony can decompose steam to liberate hydrogen.

Antimony does not dissolve in water, and is relatively stable in dilute hydrochloric acid and concentrated hydrofluoric acid. It forms SbCl₃ and Sb₂(SO₄)₃ respectively when brought in contact with concentrated hydrochloric acid and hot concentrated sulfuric acid (90 - 95°:).

Concentrated nitric acid will oxidize antimony, forming Sb₂O₃ or Sb₂O₅. It is believed the reaction mechanism centers around the intermediary formation of nitrous acid. A layer of oxide material forms on the surface of the metal and subsequently blocks any further reaction.

To conclude, antimony will dissolve in aqua regia, a fresh mixture of concentrated nitric and hydrochloric acids, or in a mixed solution of nitric acid and tartaric acid. It sparingly dissolves in phosphoric acid and some organic acids.

Introduction to Metallic Antimony

Metallic antimony readily crystallizes. During production, molten antimony is poured into molds. As the liquid antimony cools, a thin coating of easily melt-able material, a couverture, forms on the surface of the cooling metal. This couverture is notable for the fern pattern of crystals that appears on the surface of the solidified antimony. It is said that these crystals sparkle or twinkle like stars. Consequently, the resulting product is called "star antimony". Many people consider the sharpness of the fern pattern to be an indicator of the quality of the material. However, there is no scientific basis for this conclusion as ambient conditions and cooling rate will have a significant impact on crystal size of metallic antimony.