Zinc Sulfide Overview and its properties

Zinc Sulfide Zinc sulfide is an inorganic compound with the chemical formula of ZnS, and its molar mass is 97.47 g/mol. The chemical structure of ZnS is simple and consists of the zinc metal attached to a sulfur atom through a polar covalent bond. This is the main form of zinc found in nature, where it mainly occurs as the mineral sphalerite. Although this mineral is usually black because of various impurities, the pure material is white, and it is widely used as a pigment. In its dense synthetic form, zinc sulfide can be transparent, and it is used as a window for visible optics and infrared optics. Zinc sulfide appears as a yellowish-white powder in a liquid. Insoluble in water and denser than water. The primary hazard is to the environment. Immediate steps should be taken to limit spread to the environment. Easily penetrates the soil to contaminate groundwater and nearby waterways.
Solid zinc sulfide is found in two different crystal forms, alpha (wurtzite) and beta (sphalerite), which have hexagonal and cubic structures, respectively. The beta crystalline (sphalerite) is the more stable form of ZnS.
Zinc sulfide Occurrence:
Zinc sulfide occurs naturally as the mineral zinc blende, also called sphalerite, which is a mixture of iron and zinc sulfides. In nature, zinc oxide is found as the mineral “zincite.” In fluorescence, light energy is absorbed and then rapidly reemitted. After turning the UV light “off” we see the evidence of phosphorescence emission from the zinc sulfide in the form of an “eerie green” glow.

Zinc sulfide Preparation:
Zinc sulfide is commonly prepared through several simple reactions, such as the combustion of a mixture of zinc and sulfur, reacting zinc sulfate (ZnSO4) with sodium sulfide (Na2S), or by passing hydrogen sulfide (H2S) gas into aqueous solution of any Zn2+ salt to precipitate the insoluble ZnS. It is also prepared by reacting zinc oxide with hydrogen sulfide:
ZnO + H2S – ZnS + H2O
Zinc sulfide Physical properties:
Zinc sulfide is found in two different crystal forms, as mentioned above. The wurtzite form exists as white or yellowish-white crystals, while the sphalerite form exists as greyish white crystals. It has a density of 4.09 g/mL, and melting point of 1,185 degC.
Zinc sulfide Chemical properties:
Zinc sulfide is completely insoluble in water. It decomposes in the presence of acids and strong oxidizing agents. At temperatures higher than 900 degC, it decomposes with the release of zinc and sulfur fumes, and it also reacts with strong acids to release hydrogen sulfide gas. When heated to a temperature of 102 degC, the stable beta crystalline form of ZnS (sphalerite) changes into the alpha form (wurtzite). ZnS is a luminescent material, and exhibits phosphorescence when illuminated with UV light.
Zinc sulfide Uses:
Zinc sulfide has several applications due to its luminescent property. It is doped with different activators and used for making phosphorescent and electroluminescent materials. Zinc sulfide is used as a pigment, infrared optical material, and for making optical windows and lenses. It is also a wide-bandgap semiconductor and an efficient photo catalyst.
The most common use of ZnS is as a pigment for paints, plastics, and rubber. Lithopone, a mixture of ZnS and barium sulfate (BaSO4), is a widely used pigment for low-gloss paints. ZnS is phosphorescent, which makes it useful for several electronic and decorative applications.
Zinc sulfide hazards:
Zinc sulfide is not very hazardous for humans and mainly causes irritation of skin, eyes and respiratory tract upon exposure. However, it is considered a serious environmental hazard as it is highly toxic to aquatic organisms.

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