Determination of rare earth impurities

The application of SSMS to the semiquantitative survey of all impurities in rare earth matrices is very useful. All of the recent innovations for improvement of performance (Ahearn, 1972) are applicable to the analysis of rare earth matrices. The determination of rare earth impurities in rare earth matrices presents no unusual difficulties and the quantification of these impurity levels can be performed with relative ease if standards are prepared. Quantification of non-rare earth impurities in rare earth matrices by comparison with specially prepared standards has not been reported. These determinations are based frequently upon RSC s determined from non-rare earth metal standards or upon RSC s determined from dry blended preparations of rare earth oxide samples. 

Determination of rare earth impurities in a rare earth... 

The application of an inductively coupled plasma system to the determination of rare earth impurities in a pure rare earth has not to our knowledge been reported. However, preliminary experiments in our laboratories indicate that trace rare earth spectral line intensities are essentially independent of the major constituent. Thus, a calibration curve for the determination of one rare earth in a matrix may well be valid for other rare earth matrices so long as spectral line interferences do not occur. Additional comments on these observations may be found in section 4. 

Herman, E., W3, Determination of Rare Earth Impurities in Pure Rare Earths by Means of Extraction Chromatography, in hfichelsen, O.B. ed.. Analysis and Application of Rare Earth Materials (Uni-versitetsforlaget, Oslo) pp. 39-53. 

Cao, X., Yin, M., and Li, B. (1999). Determination of rare earth impurities in high purity gadolinium oxide by inductively coupled plasma mass spectrometry after 2-ethylhexyl-hydrogen-ethylhexy phosphonate extraction chromatographic separation. Talanta 48(3), 517. 

The purity of rare earth oxides is an important factor for the reliability on the characterization of their basic properties. In some earlier works, the presence of impurities in the oxides led to erroneous determinations of stmcture and polymorphism. However, due to development of effective separation technologies such as liquid/liquid extraction and precipitation/crystallization purification processes, high purity rare earth oxides can now be easily supplied for higher reliability studies as well as industrial manufacturing. 

The information about nanocrystalline ferroic powders fabricated by various chemical synthesis technologies is reported in Table 5.2. Their possible applications are also listed. Powders of the same ferroics for two different applications might be obtained by different techniques since the requirements of size distribution, morphology, agglomeration and impurity composition are determined by different technological conditions. For example, barium titanate is a dielectric with high dielectric constant and it is widely used in multilayer ceramic capacitors, whereas semiconducting properties of rare-earth doped BaTiOs are important for thermistors. 

Rare-earth impurities in high-purity Ce02 were determined by ICP/MS after separation by liquid-liquid extraction, avoiding interferences of CeH" with the detection of Pr and CeO and CeOH with Gd and Tb isotopes (B. Li et al. 1997). The Ce was oxidized to Ce with KMn04 at pH 4 and all of the rare-earth elements were extracted into 0.05 M ethylhexyl(ethylhexyl)phosphonic acid/cyclohexane. The trivalent rare earths were stripped with 1.5 M HNO3, while 99.81 0.01% of the Ce ", which is more strongly extracted, remained in the organic phase. The separation was sufficient to allow detection of each rare-earth impurity at 20-90 ppb, despite some interference of CeOH+ in the determination of the only stable isotope of terbium, Tb. 

Further analytical work by SSMS on the sample is considered if certain rare earth impurities require lower error limits. Internal referencing is employed in which the reference is an appropriately selected rare earth. The rare earth levels, determined with internal referencing, are then compared to the determinations for these same elements in the original sample. The ratios of these determinations should be constant and this constant can be used as a correction factor for all of the determinations in the original sample. The Laboratory is presently changing the internal standardization step to incorporate the use of isotope dilution when it is practical. 

The determination of non-rare earth impurities in rare earth matrices is complicated not only by the complex spectra of many of the rare earth elements but also by the very different volatilization rates of the impurities to be determined. Simple dc arc excitation methods are usually found to suiter from poor precision if a matrix element spectral line is used for internal standardization, because the impurity and matrix elements will likely be present in the arc column at different times, and will therefore experience different arc fluctuations. Four approaches have been used to improve precision. The first is to add reference elements to the sample with vaporization rates similar to the rates of the impurity elements to be determined. 

A general procedure for the DC carbon arc determination of trace rare earth impurities in highly purified rare earth materials... 

G. J. Oestreich, 1974, X-Ray Excited Optical Luminescence Methods for the Determination of Trace Level Rare Earth Impurities in Cerium and Lutetium, in Harchke, J.M. and... 

Physical Properties. An overview of the metallurgy (qv) and soUd-state physics of the rare earths is available (6). The rare earths form aUoys with most metals. They can be present interstitiaUy, in soUd solutions, or as intermetaUic compounds in a second phase. Alloying with other elements can make the rare earths either pyrophoric or corrosion resistant. It is extremely important, when determining physical constants, that the materials are very pure and weU characteri2ed. AU impurity levels in the sample should be known. Some properties of the lanthanides are Usted in Table 3. 

Investigated is the influence of the purity degree and concentration of sulfuric acid used for samples dissolution, on the analysis precision. Chosen are optimum conditions of sample preparation for the analysis excluding loss of Ce(IV) due to its interaction with organic impurities-reducers present in sulfuric acid. The photometric technique for Ce(IV) 0.002 - 0.1 % determination in alkaline and rare-earth borates is worked out. The technique based on o-tolidine oxidation by Ce(IV). The relative standard deviation is 0.02-0.1. 

The basis for the claim of discovery of an element has varied over the centuries. The method of discovery of the chemical elements in the late eightenth and the early nineteenth centuries used the properties of the new sustances, their separability, the colors of their compounds, the shapes of their crystals and their reactivity to determine the existence of new elements. In those early days, atomic weight values were not available, and there was no spectral analysis that would later be supplied by arc, spark, absorption, phosphorescent or x-ray spectra. Also in those days, there were many claims, e.g., the discovery of certain rare earth elements of the lanthanide series, which involved the discovery of a mineral ore, from which an element was later extracted. The honor of discovery has often been accorded not to the person who first isolated the element but to the person who discovered the original mineral itself, even when the ore was impure and that ore actually contained many elements. The reason for this is that in the case of these rare earth elements, the earth now refers to oxides of a metal not to the metal itself This fact was not realized at the time of their discovery, until the English chemist Humphry Davy showed that earths were compounds of oxygen and metals in 1808. 

The ZSA phase diagram and its variants provide a satisfactory description of the overall electronic structure of stoichiometric and ordered transition-metal compounds. Within the above description, the electronic properties of transition-metal oxides are primarily determined by the values of A, and t. There have been several electron spectroscopic (photoemission) investigations in order to estimate the interaction strengths. Valence-band as well as core-level spectra have been analysed for a large number of transition-metal and rare-earth compounds. Calculations of the spectra have been performed at different levels of complexity, but generally within an Anderson impurity Hamiltonian. In the case of metallic systems, the situation is complicated by the presence of a continuum of low-energy electron-hole excitations across the Fermi level. These play an important role in the case of the rare earths and their intermetallics. This effect is particularly important for the valence-band spectra. 

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