Zinc sulfide

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Zinc sulfide
Sphalerite, the more common polymorph of zinc sulfide
Wurtzite, the less common polymorph of zinc sulfide
Identifiers
CAS number 1314-98-3 YesY
PubChem 14821
RTECS number ZH5400000
Properties
Molecular formula ZnS
Molar mass 97.474 g/mol
Density 4.090 g/cm3
Melting point 1185 °C (sublime)
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
Flammability code 0: Will not burn. E.g., water Health code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentine Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point Non-flammable
Related compounds
Other anions Zinc oxide
Zinc selenide
Zinc telluride
Other cations Cadmium sulfide
Mercury sulfide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Zinc sulfide (or zinc sulphide) is an inorganic compound with the chemical formula of ZnS. 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.

Structure[edit]

ZnS exists in two main crystalline forms, and this dualism is often a salient example of polymorphism. In both polymorphism, the coordination geometry at Zn and S are tetrahedral. The more stable 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 celsius. A tetragonal form is also known as the very rare mineral called polhemusite, with the formula (Zn,Hg)S.

Applications[edit]

Luminescent material[edit]

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 nanometers. Using manganese yields an orange-red color at around 590 nanometers. Copper gives long-time glow, and it has the familiar greenish glow-in-the-dark. Copper-doped zinc sulfide ("ZnS plus Cu") is used also in electroluminescent panels.[2] It also exhibits phosphorescence due to impurities on illumination with blue or ultraviolet light.

Optical material[edit]

Zinc sulfide is also used as an infrared optical material, transmitting from visible wavelengths to just over 12 micrometers. 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 this is sold as FLIR-grade (Forward Looking IR), where the zinc sulfide is in a milky-yellow, 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[edit]

Zinc sulfide is a common pigment, sometimes called sachtolith. When combined with barium sulfate, zinc sulfide forms lithopone.[3]

Semiconductor properties[edit]

Both sphalerite and wurtzite are intrinsic, wide-bandgap semiconductors. These are prototypical II-VI semiconductors, and they adopt structures related to many of the other semiconductors, such as gallium arsenide. The cubic form of ZnS has a band gap of about 3.54 electron volts at 300 kelvin, but the hexagonal form has a band gap of about 3.91 electron volts. ZnS can be doped as either an n-type semiconductor or a p-type semiconductor.

History[edit]

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[edit]

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[edit]

It is easily produced by igniting a mixture of zinc and sulfur.[6] Since zinc sulfide is insoluble in water, it can also be produced in a precipitation reaction. 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[edit]

  1. ^ Wells, A. F. (1984), Structural Inorganic Chemistry (5th ed.), Oxford: Clarendon Press, ISBN 0-19-855370-6 
  2. ^ Karl A. Franz, Wolfgang G. Kehr, Alfred Siggel, Jürgen Wieczoreck, and Waldemar Adam "Luminescent Materials" in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a15_519
  3. ^ a b Gerhard Auer, Peter Woditsch, Axel Westerhaus, Jürgen Kischkewitz, Wolf-Dieter Griebler and Marcel Liedekerke "Pigments, Inorganic, 2. White Pigments" in Ullmann's Encyclopedia of Industrial Chemistry 2009, Wiley-VCH, Weinheim. doi: 10.1002/14356007.n20_n01
  4. ^ Sidot, T. (1866). ". Sur les propriétés de la blende hexagonale". Compt. Rend. 63: 188–189. 
  5. ^ Greenwood, Norman N.; Earnshaw, Alan (1984). Chemistry of the Elements. Oxford: Pergamon Press. p. 1405. ISBN 0-08-022057-6. 
  6. ^ Sur un nouveau procédé de préparation – du sulfure de zinc phosphorescent" by R. Coustal, F. Prevet, 1929
  7. ^ Mendham, J.; Denney, R. C.; Barnes, J. D.; Thomas, M. J. K. (2000), Vogel's Quantitative Chemical Analysis (6th ed.), New York: Prentice Hall, ISBN 0-582-22628-7 

External links[edit]