ABSTRACT
Magnesium has a close-packed hexagonal lattice elongated along the six-fold axis with a c/a ratio of 1.856. It has specialized applications in engineering by virtue of its useful properties and characteristics. Sources of magnesium suitable for extraction are dolomite, CaCO3 · MgCO3, and MgCl2 obtained from seawater by ion exchange. The corrosion of pure magnesium is sensitive to impurities, particularly iron, copper and nickel, which have vanishingly small solubilities in solid magnesium and appear in the structure as cathodic intermetallic phases. Alloy specifications are devised to improve the mechanical properties and casting characteristics. A former important application of magnesium was as cladding material for uranium rods in early designs of Magnox gas cooled nuclear reactors, by virtue of its transparency to neutrons and fairly high melting point combined with adequate corrosion resistance to the gas coolant. There is a fairly substantial literature describing experiments designed to identify mechanisms of stress-corrosion cracking in magnesium alloys.
