Analysis of rare earth mixtures

The spectra thus produced are relatively simple, so that a spectrometer of 0.5 m focal length is adequate for the analysis of rare earth mixtures (D Silva.el 0.1 1964a). Preliminary studies indicate that the induction-coupled plasma (ICP) described by Fassel and Kniseley (1974) provides spectra which are similar to those obtained with dc arc excitation. Consequently, a spectrometer with greater dispersion capabilities than can be obtained with a 0.5 m focal length instrument will probably be necessary. Superior powers of detection have been reported for several of the rare earth elements by Fassel et al. (1973) and by Souilliart and Robin (1972) when aerosols of rare earth containing solutions are injected into inductively coupled plasmas. This excitation source possesses additional advantages, which will be discussed in section 2.2.4. 

Electrical flames or electrically generated flame-like plasmas possess physical and spectroscopic properties that make them potentially very useful as free atom generators and excitation sources for the determination of the rare earths. The ultimate potential of these plasmas for the analysis of rare earth mixtures has not been evaluated, but the preliminary result so far obtained in our laboratories are indeed encouraging. For example, the detection limits that have been measured in an electrodeless induction coupled plasma (ICP) (see table 37D.3 in section 2.2.5) are at least two to three orders of magnitude lower than the lowest values so far reported by flame emission. 

Analysis of rare earth mixtures 4.1. Arc and spark excitation... 

Stewart and Kato presented spectral data for the analysis of rare-earth mixtures in acid aqueous solutions. 

D. C. Stewart and D. Kato, Analysis of Rare Earth Mixtures by Recording Spectrophotometer, Anal. Chem. 30, 164, 1958. 

Elderfield and Greaves [629] have described a method for the mass spectromet-ric isotope dilution analysis of rare earth elements in seawater. In this method, the rare earth elements are concentrated from seawater by coprecipitation with ferric hydroxide and separated from other elements and into groups for analysis by anion exchange [630-635] using mixed solvents. Results for synthetic mixtures and standards show that the method is accurate and precise to 1% and blanks are low (e.g., 1() 12 moles La and 10 14 moles Eu). The method has been applied to the determination of nine rare earth elements in a variety of oceanographic samples. Results for North Atlantic Ocean water below the mixed layer are (in 10 12 mol/kg) 13.0 La, 16.8 Ce, 12.8 Nd, 2.67 Sm, 0.644 Eu, 3.41 Gd, 4.78 Dy, 407 Er, and 3.55 Yb, with enrichment of rare earth elements in deep ocean water by a factor of 2 for the light rare earth elements, and a factor of 1.3 for the heavy rare earth elements. 

This is a classic method for the analysis of rare earths. L-spectra of the elements in the region 1500-2500 A show that for each element it is possible to select 2-5 lines for analysis. These analytical lines are given in Table 1.38. By this method rare earths in a complex mixture can be analyzed. The emission method has a sensitivity of 0.1 to 0.01 %. The time of analysis is 1.5-2.0 h. The method has been used in the analysis of minerals, alloys, etc. 

The discussions of various flame analysis techniques in section 2.2 are equally applicable to the determination of rare earth elements in a complex mixture of these elements./Net intensity or absorbance measurements usually provide adequate precision, so that an added reference element is not needed. In addition, there is no evidence of inter-element effects, and line interferences, even in small monochromators, are rarely a serious problem. This contrasts sharply with the selective enhancement and absorption effects observed in X-ray fluorescent spectrometric measurements. Analyses of rare earth mixtures by AAS have been described by Jaworowsk et al. (1967), Kriege and Welcher (1968) and many others. 

Several methods of dealing with absorption and enhancement effects are commonly employed in X-ray spectrometry. One approach is the preparation of standard samples with major constituent concentrations similar to those of the samples to be analyzed (Lytle et al., 1957). When mixtures consisting of a wide range of concentrations are encountered, it is necessary to prepare a large number of standard mixtures of known concentration. The closer these standard mixtures approximate the actual constitution of the sample, the better the analysis will be. Although the preparation of these standard mixtures is often tedious, time consuming, and expensive, this technique may in certain instances still be the most advantageous for analysis of some types of rare earth mixtures. 

Table 7-12. Semiquantitative Analysis of a Rare-Earth Mixture by X-ray Emission Spectrography...

For preparation of alloys nickel by cleanliness of 99.99 %, magnesium by cleanliness of 99.95 %, lanthanum by cleanliness of 99.79 %, and mishmetall (industrial mixture of rare-earth metals (REM) Ce - 50, La - 27, Nd - 16, Pr - 5, others REM - 2wt. %) were used. The melting of metal charge was carried out in the vacuum-induction furnace under fluxing agent from eutectic melt LiCl-KCl. The composition of alloys was supervised by the chemical analysis and the X-ray testing. 

Activation analysis was first applied by von Hevesy and Levi two years after the discovery of artificial radioactivity (38). Determination of 0.1% dysprosium in rare earth mixtures was made by activation with neutrons from a 300-millicurie radium emanation-beryllium neutron source. The 2.3-hr half-life induced activity due to Dy was compared with that induced in mixtures of known dysprosium content. A similar method was used to determine europium in gadolinium. 

The quantitative aspect of the EXAFS technique is also well known and the literature gives several studies where chemisorption and EXAFS measurements are compared (see for example We can illustrate this particular contribution of the spectroscopy by a study of rare earth transition metal catalysts prepared from intermetallic LaNij-type compounds. The three classical preparation steps are here skipped with a carbon monoxide hydrogenation reaction. The intermetallic phase is transformed into a rare earth oxide upon which the transition metal is left as metallic clusters which form the active species. This transformation has been followed as a function of the time reaction In Fig. 5 we plot the Fourier transforms of CeNij at the nickel edge before the reaction (a), after 10 hours (b) and after 27 hours (c) under the CO + H2 mixture. These are all compared to elemental nickel (d). The increase of the amplitude of the first peak and the growth of three new ones at greater distances are the consequence of the formation of nickel particles. A careful analysis of these four shells has allowed us quantitatively to estimate the fraction of extracted nickel during the reaction as 30% after 10 hours and 80% after 27 hours on a CO + flux at 350 °C. 

X-ray spectroscopy rivals visible spectroscopy as a tool for elemental analysis. Because the energies of x-rays are much higher than those of visible radiation, however, x-rays usually cause transitions of inner-shell electrons rather than of valence-shell electrons. There are many advantages of this method in spectrochemical analysis. A quantitative analysis of a mixture of rare-earth oxides may be performed or a crystal structure may be determined. A specimen that contains two elements widely separated in atomic number may be studied, or the thickness of a very thin layer of tin plating may be measured. The most widespread use of x-rays has been in the field of metallurgy, but x-rays may also be used to analyze metals, minerals, liquids, glasses, ceramics, or plastics. 

Analytical lines for flame emission analysis of complex rare earth mixtures. 

Muster TH, Lau D, Wrubel H, Sherman N, Hughes AE, et al. (2010) An investigation of rare earth chloride mixtures combinatorial optimisation for AA2024-t3 corrosion inhibition Surface and Interface Analysis, 42,170-174. 

Gas chiomatograplty of rare-earth j8-diketonates is not only of interest for the separation of mixtures of rare earths. The method can also be used for trace metal analysis. First, formation of the volatile chelates is achieved by extraction of the rare-earth ions with the )8-diketonate ligands from an aqueous solution into an immiscible organic solvent Alternatively, direct reaction between the ligand and the metal ions in the aqneons solntion can be used (in the absence of a solvent). After elntion, the volatile rare-earth j3-diketonate complexes can be detected by conventional detectors such as the flame ionization detector (FID) or the thermal condnctivity detector (TCD). Because the [R(tfac)3] and the R(fod)3] complexes contain electronegative fluorine atoms, they can be selectively detected at low concentrations by an electron capture detector (ECD) (Sievers and Sadlowski, 1978). Bnigett and Fritz (1972, 1973) studied the separation and quantitative determination of rare earths by gas chromatography of [R(thd)3(dbso)3] complexes. 

Rare earths, analysis of mixture of, by x-ray emission spectrography, 204, 205... 

Carbide cluster ions (MC + - M = matrix element) have been measured by investigating them directly from the solid carbides (B4C,46 SiC) or by analyzing metal oxide/graphite mixtures (for M = rare earth element,3 Si,46 Th or U36). Figure 9.60 shows the distribution of silicon carbide cluster ions (SiC +) in laser ionization mass spectrometry by the direct analysis of compact SiC in comparison to the carbide cluster ion distribution of LaC + and SrC + in spark source mass spectrometry, by investigating a metal oxide/graphite mixture. 

Analysis of vanadium-loaded model materials (such as EuY, amorphous aluminosilicate gels and EuY-gel mixtures) by electron paramagnetic resonance (EPR) has provided information concerning metal oxidation state and stereochemistry (67). EPR data has indicated that when vanadyl cations are introduced in the form of vanadyl naphthenate, they were stabilized in a zeolite with the faujasite structure as pseudo-octahedral V02+ even after calcination at 540°C. Upon steaming, these V02+ cations were then converted almost entirely to V+5 species (67). The formation of EuV04 was verified but the concentration of this vanadate was never proportional to the total rare-earth content of the zeolite. In EuY-gel mixtures the gel preferentially sorbed vanadium where it was stabilized mainly in the form of V205. 

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