Neodymium earths

Praseodymium is soft, silvery, malleable, and ductile. It is somewhat more resistant to corrosion in air than europium, lanthanum, cerium, or neodymium, but it does develop a green oxide coating that spalls off when exposed to air. As with other rare-earth metals, it should be kept under a light mineral oil or sealed in plastic. 

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. 

The element may be obtained by separating neodymium salts from other rare earths by ion-exchange or solvent extraction techniques, and by reducing anhydrous halides such as NdFs with calcium metal. Other separation techniques are possible. 

The metal has a bright silvery metallic luster. Neodymium is one of the more reactive rare-earth metals and quickly tarnishes in air, forming an oxide that spalls off and exposes metal to oxidation. The metal, therefore, should be kept under light mineral oil or sealed in a plastic material. Neodymium exists in two allotropic forms, with a transformation from a double hexagonal to a body-centered cubic structure taking place at 863oC. 

Neodymium has a low-to-moderate acute toxic rating. As with other rare earths, neodymium should be handled with care. 

Other catalytic uses of rare-earth compounds have not reached the same development. Neodymium salts are, however, used for mbber manufacturing (22). Divalent samarium haHdes are employed in organic synthesis (23). 

Solid-State Lasers. Sohd-state lasers (37) use glassy or crystalline host materials containing some active species. The term soHd-state as used in connection with lasers does not imply semiconductors rather it appHes to soHd materials containing impurity ions. The impurity ions are typically ions of the transition metals, such as chromium, or ions of the rare-earth series, such as neodymium (see Lanthanides). Most often, the soHd material is in the form of a cylindrical rod with the ends poHshed flat and parallel, but a variety of other forms have been used, including slabs and cylindrical rods with the ends cut at Brewster s angle. 

Polyisoprenes of 94—98% as-1,4 content were obtained with lanthanum, cerium, praseodymium, neodymium, and other rare-earth metal ions (eg, LnCl ) with trialkyl aluminum (R3AI) (34). Also, a NdCl 2THF(C2H3)3A1 catalyst has been used to prepare 95% <7j -l,4-polyisoprene (35). <7j -l,4-Polyisoprene of 98% as-1,4 and 2% 3,4 content was obtained with organoalurninum—lanthariide catalysts, NdCl where L is an electron-donor ligand such as ethyl alcohol or butyl alcohol, or a long-chain alcohol, and is 1 to 4 (36). 

Figure 16 shows the charge-discharge cycle characteristics of alloys in which part of the nickel component was replaced with cobalt. Misch metal (Mm), which is a mixture of rare earth elements such as lanthanum, cerium, praseodymium, and neodymium, was used in place of lanthanum. It was found that the partial replacement of nickel with cobalt and the substi-... 

The valences of the rare-earth metals are calculated from their magnetic properties, as reported by Klemm and Bommer.14 It is from the fine work of these investigators that the lattice constants of the rare-earth metals have in the main been taken. The metals lutecium and ytterbium have only a very small paramagnetism, indicating a completed 4/ subshell and hence the valences 3 and 2, respectively (with not over 3% of trivalent ytterbium present in the metal). The observed paramagnetism of cerium at room temperature corresponds to about 20% Ce4+ and 80% Ce3+, that of praseodymium and that of neodymium to about 10% of the quadripositive ion in each case, and that of samarium to about 20% of the bipositive ion in equilibrium with the tripositive ion. 

We found that completely soluble compounds can be obtained in two ways. The first method, which is widely applicable, is to react a rare earth carboxylate with a small amount of an aluminum alkyl (11). Neodymium octoate can be converted into a product which is completely soluble in cyclohexane by reacting one mole of it with 1 to 5 moles of triethylaluminum. We also found that the rare earth salts of certain tertiary carboxylic acids are very readily soluble in non-polar solvents (12). In conjunction with a Lewis acid and aluminum alkyls, these compounds form highly active catalysts for the polymerization of butadiene. The neodymium Lewis acid aluminum alkyl molar ratio is within the range 1 (0.4-2.0) (10-40). 

In. he industrial processes for the production of polybutadiene with Ti, Co, or Ni catalysts it can be controlled to only a very small extent. In comparison with the commercially available polybutadienes, SE-BR (SE stands for Seltene Erden, which means rare earths) has a broader molecular- weight distribution, which can be altered, however, by varying the ratio of Lewis acid to neodymium. Table II shows that an increase of this ratio from 0.8 to 2.0 increases the molecular weight distribution from 7 (which is close to that of Ni-BR) to 27. 

The compounds of the rare earth elements are usually highly colored. Neodymium s compounds are mainly lavender and violet, samarium s yellow and brown, holmium s yellow and orange, and erbium s rose-pink. Europium makes pink salts which evaporate easily. Dysprosium makes greenish yellow compounds, and ytterbium, yellow-gold. Compounds of lutetium are colorless, and compounds of terbium are colorless, dark brown, or black. 

Some rare-earth-activated materials do show strong fluorescence phenomena at temperatures even up to IOOO°C with a lifetime long enough to be detected without particular difficulties, as demonstrated in the cases of neodymium yttrium-aluminum-garnet(Nd YAG) andScPC>4 Eu3+ by Grattan etal.m and Bugos etal.,m respectively. 

Bau M, Dulski P (1996) Distribution of yttrium and rare-earth elements in the Penge and Kuruman iron-formations, Transvaal Supergroup, South Africa. Precam Res 79 37-55 Bau M, Hohndorf A, Dulski P, Beukes NJ (1997) Sources of rare-earth elements and iron in Paleoproterozoic iron-formations from the Transvaal Supergroup, South Africa evidence from neodymium isotopes. J Geol 105 121-129... 

Rare earth. One of a group of 15 chemically related elements lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. 

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