The rare earth elements form a transition series including the elements of atomic number 57 through 71, all having three outer electrons and differing only in the inner electronic structure. Because chemical properties are determined by the outer electronic structure, it is evident why these metals are chemically alike. Although not truly members of this series, scandium and yttrium (atomic numbers 21 and 39, respectively) are frequently included with this grouping.
Scandium and yttrium occur together in nature with the rare earths and are similar in properties.
Yttrium oxide and cerium sulfide are highmelting refractories. Yttria-stabilized zirconia ceramic materials with excellent properties are commercially available. In cast iron it opposes graphitization and produces a malleablized iron. It removes the sulfur and the oxides and completely degasifies steel. In stainless steel it is used as a precipitation-hardening agent. An important use of misch metal is in magnesium alloys for castings. From 3 to 4% of misch metal is used with 0.2 to 0.6% zirconium, both of which refine the grain and give sound castings of complex shapes.
The rare earth elements are metals possessing distinct individual properties that make them potentially valuable as alloying agents. They can also be reduced electrolytically from fused-salt baths.
The rare earths may be hot-worked, and some of them can be fabricated cold.
Applications of the rare earths may be divided into two general categories: the long-established uses and the newer developments that frequently require the higher-purity separated elements.
