Antimony Trisulfide

There are only a few examples of antimony sulfide compounds with useful applications. The most important among the limited selection of sulfide compounds is antimony trisulfide. After antimony trisulfide, antimony pentasulfide has the next most practical significance.

Sb₂S₃ has two forms, namely a crystalline form and an amorphous form. The crystalline variety has a grey color with a metallic luster. It is rhombic in structure and generally occurs as stibnite ore in a number of antimony deposits. It has a density of 4.65 g/cm³, a melting point of 550° C, and a boiling point of roughly 1085° C. Finally, its solubility in water is less than two-thousandths of a percent.

The amorphous form can be grey, black, red, yellow, brown, or purple. The final color depends on the material’s grain size, production method, and trace impurities.

One chemical reaction can produce either form. First, you need to pass hydrogen sulfide gas through a solution of antimony halide. This results in antimony sulfide and hydrochloric acid. Now, if you were to quickly melt the product you can arrive at the crystalline material or the amorphous substance depending in the rate of cooling. A slow, controlled cooling allows for large, black crystals to form. On the other hand, rapidly cooling the melt prevents crystal formation and the end product is amorphous antimony sulfide.