Zinc sulfide

Zinc sulfide

ZnS powders containing different concentrations of sulfur vacancies
Names
Other names Zincblende Wurtzite
Identifiers
CAS Number	1314-98-3 Y
PubChem	14821
RTECS number	ZH5400000
Properties
Chemical formula	ZnS
Molar mass	97.474 g/mol
Density	4.090 g/cm3
Melting point	1,185 °C (2,165 °F; 1,458 K) (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
Vapor pressure	{{{value}}}
Related compounds
Other anions	Zinc oxide Zinc selenide Zinc telluride
Other cations	Cadmium sulfide Mercury sulfide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Y verify (what is YN ?)
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

Sphalerite, the more common polymorph of zinc sulfide

Wurtzite, the less common polymorph of zinc sulfide

ZnS exists in two main crystalline forms, and this dualism is often a salient example of polymorphism. In each form, the coordination geometry at Zn and S is 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. 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

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 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. 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 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

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

Catalyst

Fine ZnS powder is an efficient photocatalyst, which produces hydrogen gas from water upon illumination. Sulfur vacancies can be introduced in ZnS during its synthesis; this gradually turns the white-yellowish ZnS into a brown powder, and boosts its the photocatalytic activity through enhanced light absorption.

Semiconductor properties

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

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. 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.

Production

Mixtures of zinc and sulfur react pyrotechnically, leaving behind zinc sulfide.

Zinc sulfide is usually produced from waste materials from other applications. Typical sources include smelter, slag, and pickle liquors. 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. 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.

External links

• Zinc and Sulfur at The Periodic Table of Videos (University of Nottingham)
• Composition of CRT phosphors
• University of Reading, Infrared Multilayer Laboratory optical data