Magnesium sulfide reacts with oxygen to form the corresponding sulfate, magnesium sulfate. MgS reacts with water to give hydrogen sulfide and magnesium hydroxide. In the BOS steelmaking process, sulfur is the first element to be removed. Sulfur is removed from the impure blast furnace iron by the addition of several hundred kilograms of magnesium powder by a lance. Magnesium sulfide is formed, which then floats on the molten iron and is removed. MgS is a wide band-gap direct semiconductor of interest as a blue-green emitter, a property that has been known since the early 1900s. The wide-band gap property also allows the
Magnesium oxychloride at about 23 °C, the completely liquid region has vertices at the following triple equilibrium points (as mass fractions, not molar fractions): The other vertices are pure water, magnesium chloride hexahydrate, and the saturated solution (0.0044 MgO + 0.9956 by mass). The anhydrous forms decompose when heated above 450-500 °C by decomposition of the hydroxide and chloride anions, releasing water and hydrogen chloride and leaving a magnesium oxide residue, by the reactions: Extended exposure of magnesium oxychlorides to water leaches out the soluble , leaving hydrated brucite . On exposure to the atmosphere, the oxychlorides will slowly react with carbon