Rare earth alloying elements

An interesting stage in the development of primer mixes was the use of pyrophoric metal alloys, first patented in 1936 and improved in 1964. These rare earth alloys, as used in cigarette lighter flints, give a shower of sparks when lightly scraped. A typical pyrophoric alloy is misch metal, which has the following approximate composition cerium 50%, lanthanum 40%, other rare earth elements 3%, and iron 7%. 

Extensive solid-solution formation in the binary rare earth alloy systems is summarized in fig. 14. If the solid solubility at any temperature in any polymorphic form is >5at.% of either R (a trivalent rare earth metal) in M (a non-rare earth metal) or M in R, the solid solubility is considered to be extensive, and limited when it is <5at.%. Since both europium and ytterbium are divalent in their elemental... 

High pressure studies on magnetic transitions in rare earth metals, intra-rare earth alloys and compounds (the monochalcogenides, ferrites, spinels (RFe204) and garnets (R3Fe50i2 where R is a rare earth element)) have been numerous and all the work prior 1969 has been reviewed by Bloch and Pavlovic (1969). For the discussion on pressure studies of magnetic transition in this chapter, much material has been drawn from the above review. 

Solid state recrystallisation methods are particularly applicable to the elements and intra-rare earth alloys while melt growth techniques have found application for certain of the elements, but most particularly for intermetallic compounds use of the vapour-solid approach has been limited to the higher vapour pressure... 

There is little information concerning the thermodynamic data of binary intra-rare-earth alloys. However the interactions between the rare-earth elements are small, and when thermodynamic data have been obtained they show either slight positive or negative deviations from ideality. 

As mentioned in the last section the ordering temperatures of the amorphous alloys differ significantly from crystalline compounds of the same composition. Tables 16.2-16.4 list the Curie temperatures (Tc) and moment compensation temperatures (Tcomp) of many of the amorphous rare earth alloys studied along with the equivalent crystalline compounds. In the tables an element name under the compensation temperature indicates that its sublattice moment is dominant... 

Role of structure and rare earth (RE) elements on the corrosion of magnesium (Mg) alloys... 

Abstract This chapter discusses the effect of microstructure and rare earth (RE) elements on the corrosion of magnesium (Mg) alloy. Firstly, this chapter discusses the effect of P-phase and microcrystallization on the corrosion behavior of magnesium. Secondly, it describes the roles of RE elements on the corrosion behavior of Mg alloys. 

In materials science, the relationship between the properties, microstructure, composition and manufacture is described as tetrahedroid. This chapter discusses the factors of microstructure and composition (rare earth (RE) elements) on the corrosion process of magnesium (Mg) alloy. 

Mg alloys incorporate rare earth (RE) elements [128] to improve (i) creep resistance, which is primarily achieved by RE-containing phases along grain boundaries [129,130], (ii) castability, (iii) age hardening [131], and corrosion resistance [132]. Chang et al. [132] reported that Mg-3Nd-0.2Zn-0.4Zr had a corrosion rate lower than AZ91D. Nordlien et al. [133] reported that RE elements improved passivation. Krishnamurthy et al. [134] suggested that pseudo-passivation in rapidly solidified Mg-Nd was due to Nd enrichment at the surface. 

Gr. neos, new, and didymos, twin) In 1841, Mosander, extracted from cerite a new rose-colored oxide, which he believed contained a new element. He named the element didymium, as it was an inseparable twin brother of lanthanum. In 1885 von Welsbach separated didymium into two new elemental components, neodymia and praseodymia, by repeated fractionation of ammonium didymium nitrate. While the free metal is in misch metal, long known and used as a pyrophoric alloy for light flints, the element was not isolated in relatively pure form until 1925. Neodymium is present in misch metal to the extent of about 18%. It is present in the minerals monazite and bastnasite, which are principal sources of rare-earth metals. 

Figure 10 presents the Curie temperature (T ) vs the TM-content (x) for Co- and Fe-based biaary alloys. Alloying rare-earth elements with small amounts of transition metals (x < 0.2) leads to a decrease ia Curie temperature. This is particularly obvious ia the Gd—Co system where it corresponds to a nonmagnetic dilution similar to that of Cu (41,42). This iadicates that TM atoms experience no exchange coupling unless they are surrounded by a minimum number j of other TM atoms. The critical number is j = 5 for Fe and j = 7 for Co. The steep iacrease of for Co-based alloys with x about 0.7 is based on this effect. 

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