zinc sulfide

Zinc sulfide
Other names Zincblende Wurtzite
Identifiers
CAS number	1314-98-3 Y
PubChem	14821
RTECS number	ZH5400000
Properties
Molecular formula	ZnS
Molar mass	97.474 g/mol
Density	4.090 g/cm3
Melting point	1185 °C (sublim)
Solubility in water	negligible
Band gap	3.54 eV (cubic, 300 K) 3.91 eV (hexagonal, 300 K)
Structure
Crystal structure	see text
Coordination geometry	Tetrahedral (Zn2+) Tetrahedral (S2−)
Thermochemistry
Std enthalpy of formation ΔfHo298	−204.6 kJ/mol
Hazards
MSDS	ICSC 1627
EU Index	Not listed
NFPA 704	0 1 0
Flash point	non-flammable
Related compounds
Other anions	Zinc oxide Zinc selenide Zinc telluride
Other cations	Cadmium sulfide Mercury sulfide
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Zinc sulfide (or zinc sulphide) is a inorganic compound with the formula ZnS. ZnS is the main form of zinc in nature, where it mainly occurs as the mineral sphalerite. Although the mineral is black owing to impurities, the pure material is white and is in fact used widely as a pigment.

Structure of ZnS

ZnS exists in two main forms, and this dualism is often a textbook example of polymorphism. In both polymorphs, the coordination geometry at Zn and S are tetrahedral. The more stable form cubic form is known also as zinc blende or sphalerite. The hexagonal form is known as the mineral wurtzite, although it also can be produced synthetically.^[1] The transition from the sphalerite form to the wurtzite form occurs at around 1020 °C. A tetragonal form is also known as the very rare mineral called polhemusite, with the formula (Zn,Hg)S.

Applications

Luminescent material===

Zinc sulfide, with addition of few ppm of suitable activator, is used as phosphor in many applications, from cathode ray tubes through x-ray screens to glow in the dark products. When silver is used as activator, the resulting color is bright blue, with maximum at 450 nm. Manganese yields an orange-red color at around 590 nm. Copper provides long glow time and the familiar glow-in-the-dark greenish color. Copper-doped zinc sulfide ("ZnS+Cu") is used also in [[electroluminescence|electroluminescent panels.^[2] It also exhibits phosphorescence due to impurities on illumination with blue or ultraviolet light.

Optical material

Zinc sulfide is also used as an infrared optical material, transmitting from visible wavelengths to over 12 micrometres. It can be used planar as an optical window or shaped into a lens. It is made as microcrystalline sheets by the synthesis from hydrogen sulfide gas and zinc vapour and sold as FLIR (Forward Looking IR) grade ZnS a pale milky yellow visibly opaque form. This material when hot isostatically pressed (HIPed) can be converted to a water-clear form known as Cleartran (trademark). Early commercial forms were marketed as Irtran-2 but this designation is now obsolete.

Pigment

Zinc sulfide is a common pigment. When compounded with barium sulfate, zinc sulfide forms lithopone.^[3]

Semiconductor properties

Both sphalerite and wurtzite are intrinsic, wide-bandgap semiconductors. It is a prototypical II-VI semiconductors and adopts structures related to many other semiconductors such as gallium arsenide. The cubic form has a band gap of 3.54 eV at 300 K whereas the hexagonal form has a band gap of 3.91 eV. It can be doped as both n-type semiconductor and p-type semiconductor.

History

The phosphorescence of ZnS was first reported by the French chemist Théodore Sidot in 1866. His findings were presented by A. E. Becquerel, who was renowned for the research on luminescence.^[4] ZnS was used by Ernest Rutherford and others in the early years of nuclear physics as a scintillation detector, because it emits light upon excitation by x-rays or electron beam, making it useful for X-ray screens and cathode ray tubes.^[5]

Production

Zinc sulfide is usually produced from waste materials from other applications. Typical sources include smelter, slag, and pickle liquors.^[3] It is also a by-product of the synthesis of ammonia from methane where zinc oxide is used to scavenge hydrogen sulfide impurities in the natural gas:

ZnO + H₂S → ZnS + H₂O

Laboratory preparation

It is easily produced by igniting a mixture of zinc and sulfur.^[6] Since zinc sulfide is insoluble in water, solutions containing Zn²⁺ salts readily form a precipitate ZnS in the presence of sulfide ions (e.g., from H₂S).

Zn²⁺ + S²⁻ → ZnS

This reaction is the basis of a gravimetric analysis for zinc.^[7]

References

External links

• Composition of CRT phosphors
• University of Reading, Infrared Multilayer Laboratory optical data