Zinc Sulfide (ZnS) is a naturally occurring salt that appears in liquid form as a yellowish-white powder. It has two common crystalline forms, which are Sphalerite (zinc blende) and Wurtzite. Sphalerite has a cubic crystal structure, and this form is the predominant form in nature. Meanwhile, wurtzite has a hexagonal crystal which is made by heating the sphalerite to 1020°C. Zinc sulfide is commonly employed as a pigment for paint, plastic, and rubber. It is also phosphorescent, which makes it useful for several decorative and electronic applications, such as luminescent cosmetics, x-ray, glowing paint, etc.
Zinc sulfide is obtained as by-product from the synthesis of ammonia from methane. The hydrogen sulfide impurities in the natural gas reacts with the zinc oxide to form zinc sulfide.
ZnO + H2S → ZnS + H2O
Another method is through the reaction of zinc sulfate and sodium sulfide, followed by calcination. The zinc sulfide is produced as the hydrogen sulfide passes the zinc salt formed from the initial reaction.
Elemental zinc and sulfur can also be reacted together to form zinc sulfide. However this is a violent reaction and is accompanied by rapid evolution of gas, light, and heat.
It can be used as a white pigment for paint, linoleum, or synthetic leather.
Zinc sulfide is used as a luminiscent material or phosphor for cathode ray tubes, X-ray screens and other glow-in-the-dark products. The zinc sulfide can be used as pigment to dental rubber.
Both the polymorphs of zinc are intrinsic, wide-bandgap semiconductors. They are identified as prototypical II-VI semiconductors, and they adopt structures related to many of the other semiconductors, such as gallium arsenide. The sphalerite has a band gap of about 3.54 electron volts at 300 kelvins, while the wurtzite has a band gap of about 3.91 electron volts. It can be doped as either an n-type semiconductor or a p-type semiconductor.
Zinc sulfide can be used as an infrared optical material and an efficient photocatalyst. It is also used as phosphor in television screens and watches. Due to its versatility as a white pigment it can also be used in manufacture of cosmetics.