Magnesium sulfide

Magnesium sulfide is the chemical compound with the formula MgS. It is a colorless crystalline material but often is encountered in an impure form that is brown and non-crystalline powder.

Preparation
MgS forms by the reaction of sulfur or hydrogen sulfide with magnesium. In the BOS steelmaking process, sulphur must be removed, and is the first element to be. Sulphur is removed from the impure blast furnace iron by the addition of several hundred kilograms of magnesium powder by a lance. The magnesium reduces the sulphur to form magnesium sulphide (MgS). The ionic equations are:

Mg --> Mg2+ + 2e-

S + 2e- --> S2-

General properties
MgS crystallizes in the rock salt structure, although the zinc blende structure might be anticipated. The chemical properties of MgS resemble those of related ionic sulfides such as those of Na, Ba, Ca: 1) MgS reacts readily with oxygen to form the corresponding sulfate, magnesium sulfate. 2) MgS reacts with water to give hydrogen sulfide and magnesium hydroxide.

Applications

 * MgS is a wide band-gap direct semiconductor of interest as a blue-green emitter, a property that has been known since the early 1900's.
 * During the purification of iron, sulfur must be extracted. To achieve this, a "lance" is introduced into the molten metal, and powdered magnesium is poured in. In a violent exothermic reaction ensues, resulting in MgS, which is then raked off as a component of the slag.
 * MgS is claimed to slow labor (childbirth).

Safety
MgS evolves hydrogen sulfide upon contact with moisture.