M - Magnesium and Alkaline-Earth Oxides

Abstract

This chapter discusses the properties and extraction of magnesium and alkaline-earth oxides. Magnesia does not occur naturally but is an important material that finds use in a variety of industries. The alkaline-earth oxides are mainly ionic in character and crystallize with the NaCl-type structure. The lattice parameter of the unit cell increases with the radius ratio Mg 2+ : O 2− , and the oxide density at first decreases and then increases in the series. The octahedral coordination of the metal ions in the structure persists throughout the series and the increasing radius ratio results in a distorted configuration of oxygen ions around each cation and the oxides become more basic. Thermal decomposition of magnesium and calcium hydroxides and carbonates at temperatures just above their decomposition temperatures results in the formation of an oxide that is crystallographically oriented with respect to the parent hydroxide or salt. Lime, produced commercially on a large scale by calcining limestone in kilns, finds wide use in the production of Portland cement, glass, enamels, and glazes, Barium oxides is a constituent of many glasses, usually being added as the sulfate and it is also used as a fluxing agent in glazes.