Aluminium sulfide

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. 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.

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.