Praseodymium impurity

Figure 38. Double>difIerential scattering cross section for neodymium at 110° photon scattering angle. Spectra were taken for primary energies of 43.01, 43.18, and 43.35 keV and a bandwidth of 40 eV. Points are experimental data as recorded by an intrinsic Ge planar detector. Curves are theoretical spectra. L X-L-RRS M X-M-RRS R Rayleigh scattering a, p Ka, XjO-fluorescence of a praseodymium impurity in the sample. (From Ref. 113.)...

Praseodymium di-iodide, Prl2, can essentially be made in the same way. If sufficient care is taken to exclude air and moisture, oxidic impurities can be avoided. To avoid the formation of Pr2ls, praseodymium metal is used in excess as chunks to easily remove the unreacted metal after the reaction is completed. The pure compound Prl2 is thus obtained, with a reaction temperature well above the peritectic temperature, around 800 °C. Reaction times seem not to matter much, a few days are usually sufficient, perhaps even less. The cooling procedure, however, is crucial as it determines the phases (I through V) that are formed and their relative quantities. Section 4.3 will deal with this issue. 

Properties Pink crystals. Soluble in water. Technical grade contains 75% neodymium salt, principal impurities praseodymium and samarium compounds. 

Neodymium, being one of the more abundant rare earth metals, is more easily obtained in pure cum pounds, Thu last impurity to be removed is usually praseodymium, which is separated by the methods already given. The following methods are also valuable Fractionation of the meta-nitrobenznnte, of the simple nitrates in strong nitric acid, or the fractional precipitation of the chloride by HC1 gas. 

Whilst there have been several theoretical investigations of the effect of hybridisation on the crystal-field excitations within the ground multiplet (Maekawa et al. 1985, Lopes and Coqblin 1986), there have been relatively few in which the spin-orbit level is explicitly included. Cox et al. (1986) have shown, in the context of the Anderson impurity model, that when is comparable to the spin-orbit splitting, the inelastic peak is broadened and shifted to lower energies. Given that the cross-section is weak, at about half the intensity of the praseodymium spin-orbit cross-section, they concluded that the transition was unlikely to be seen except in heavy-fermion compounds with low values of This appears to be confirmed by the failure to observe such a transition in CePdj in recent measurements on HET (Osborn, unpublished). On the other hand, the... 

Fig. 8.22. Temperature dependence of the tensile and compressive strength properties of praseodymium. Love (1959) as-cast 2640 ppm impurities including 1400 ppm oxygen. Owen and Scott (1977) worked and annealed <307 ppm impurities including 148 ppm oxygen 5 fim grain size. Skudnov et al. (1969a) claimed 90.2% Pr worked and annealed.

Fig. 4.33 Configurational coordinate diagram representing the structure of Pr in the host, which is represented by the impurity (praseodymium)-trapped exciton PTE a represents the situation at ambient pressure, b at pressure P i (reprinted from Ref. [202], copyright 2013, with permission from Elsevier), and c at pressure P2- The radiative and nonradiative transitions are indicated by solid and dashed arrows, respectively...

Among these materials, cerium dioxide (ceria) is of particular importance. Very pure ceria forms a white powder, but more often, it appears pale yellow, and less pure samples can even be brownish. A brownish coloration could be an indicative for the presence of impurities such as praseodymium... 

The phase diagram for the praseodymium-neodymium system has been investigated by Markova et al. (1963) and by Lundin et al. (1964 ). Markova et al. used 97 (wt )% pure praseodymium and 98% pure neodymium. The impurities present in their metals consisted of other rare earth metals, plus Cu, Fe and Ca in unspecified amounts. Their methods of investigation included thermal analysis, metallography. X-ray diffraction and hardness measurements. Their alloys were annealed at 600°C for 20 hr before measurements were made. Terekhova (1963) has published a similar phase diagram that would appear to be based on the same research. Both Russian diagrams show complete solid solubility for both the dhep and the bcc structures and a definite two-phase region (liquid plus solid) between the liquidus and solidus lines. 

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