Aluminium sulfide

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Aluminium sulfide
Identifiers
CAS number	[1302-81-4]
Properties
Molecular formula	Al₂S₃
Molar mass	150.158076 g/mol
Appearance	colorless
Density	2.0 g/cm³, solid
Melting point	1100°C
Boiling point	1500°C (sublimes)
Solubility in water	decomposes
Solubility in other solvents	none
Hazards
EU classification	not listed
NFPA 704	0 4 2
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 Al₂ S₃. 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.

[edit] Preparation

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.