REE used in Metallurgical alloys

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Rare Earth used in Metallurgical alloys REE have major applications in metallurgical alloys. In 2010 this use accounted for 18 per cent of global consumption by volume. One of the oldest uses of REE as an alloy is in mischmetal, a pyrophoric alloy containing only REE metals. The individual REE are present in the same proportions as they naturally occur in the bastnasite concentrates. Typical composition is about 50 per cent cerium and 25 per cent lanthanum with small amounts of neodymium and praseodymium. The most common use of this alloy is in the flint ignition device of many lighters and torches, although for this purpose it is blended with iron oxide and magnesium oxide since the REE alloy alone is too soft. Mischmetal and cerium are commonly used as minor alloying additives for controlling inclusions in cast irons and steels. The cerium combines with the sulphide inclusions to form more rounded particles which are less likely to promote cracking. Superalloys are a class of heat resistant alloys used in applications involving intense, high-temperature oxidizing environments such as in gas turbine engines and electric generators. Adding REE enhances the alloy's oxidation resistance. In M-chromium-yttrium alloys (where M is iron, nickel or cobalt), yttrium is the active component but lanthanum and cerium are also used in certain nickel and cobalt superalloy compositions. Less than one per cent of REE metal in a superalloy can dramatically improve its performance. The use of REE as a method of storing hydrogen was identified in 1969 when it was discovered that the intermetallics REM5 (where RE is the rare earth and M is iron, cobalt or nickel) could absorb a large amount of hydrogen at room temperature. Solid state storage of hydrogen is better than storage as cryogenic and compressed gas in terms of safety, volume, weight, pressure and energy savings. REE are used in nickel metal hydride (NiMH) rechargeable batteries that power many electronic products. A mixed rare earth metal alloy is used as the anode in the NiMH battery, representing about 26 per cent of the battery's weight. Lanthanum is the main REE used in the NiMH battery. These batteries in addition to many other REE bearing components are particularly important for hybrid cars such as the Toyota Prius (Figure 1). It has been calculated that each Toyota Prius battery uses 10 to 15 kilograms of lanthanum.