Aluminium sulfide

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Aluminium sulfide
CAS number 1302-81-4
Molecular formula Al2S3
Molar mass 150.158076 g/mol
Appearance colorless
Density 2.0 g/cm3, solid
Melting point


Boiling point

1500°C (sublimes)

Solubility in water decomposes
Solubility in other solvents none
EU classification not listed
NFPA 704

NFPA 704.svg

Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)

Infobox disclaimer and references

Aluminium sulfide is the name for the chemical compound with the formula Al2S3. This colorless species has an interesting structural chemistry, existing in three different forms. The material is sensitive to moisture, hydrolyzing readily to hydrated aluminium oxides/hydroxides.[1] The hydrolysis reaction also generates the odoriferous and toxic gas hydrogen sulfide (H2S).

Unlike Al2O3, in which the Al(III) centers occupy octahedral holes, the more expanded framework of Al2S3 stabilizes the Al(III) centers into one third of the tetrahedral holes of a hexagonally close-packed arrangement of the sulfide anions. At higher temperature, the Al(III) centers become randomized to give a "defect wurtzite" structure. And at still higher temperatures stabilize the γ-Al2S3 forms, with a structure akin to γ-Al2O3.

Molecular derivatives of Al2S3 are not known. Mixed Al-S-Cl compounds are however known. Also Al2Se3 and Al2Te3 are also known.


Aluminium sulfide is readily prepared by ignition of the elements:

2Al + 3S → Al2S3

This reaction is extremely exothermic and it is not necessary or desirable to heat the whole mass of the sulfur-aluminium mixture; (except possibly for very small preps). The product will be created in a fused form; that is at greater than 1100°C and may melt its way through steel. The cooled product is very hard.


  1. Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.



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