Rare earth elements crystallization

Various other techniques are available to assess the quality of crystals. Residual resistance ratio provides a useful criterion by which overall chemical purity can be quantified and is particularly employed for the highest quality rare earth element crystals values up to 1000 were reported by Jones et al. (1982). Similar... 

Ternary tellurides of rare earth elements crystallize in structure types which are derivatives of the NaCl-, SC2S3- and EuEr2Tc4-type structure, as well as in the Th3P4-type structure (Eliseev et al. 1980, Sadovskaya et al. 1985) (table 16). 

Anhydrous ammonium oxalate is obtained when the monohydrate is dehydrated at 65°C. The monohydrate is a colorless crystal or white powder, and dissolves in water at 0°C up to 2.17 wt %, and 50°C up to 9.63 wt %. It is slightly soluble in alcohol and insoluble in ether. It is used for textiles, leather tanning, and precipitation of rare-earth elements. 

The total cerium content in the single crystal samples on the basis of rare-earth elements is determined by photometry after Ce(III) oxidation by ammonium persulfate. The Ce(III) content is calculated from the difference. Comparison of the determination results of the total cerium content obtained by photometric and atomic emission methods for Li GdlBO ljiCe demonstrated the elaborated procedure precision and systematic error absence. 

SPECTROPHOTOMETRIC DETERMINATION OF RARE EARTH ELEMENTS IN MONO CRYSTALS AND STARTING LEAD MOLYBDATE RAW MATERIAL... 

The crystal chemistry of A3RF6 and A2RF5 compounds with A=alkali and R=rare earth elements. O. Greis, Rev. Inorg. Chem., 1982, 4, 87—i01 (55). 

For small extents of crystallization, the maximum change, and thereby the most valuable information on F, will be obtained from elements with high Dt (compatible elements) such as Ni in basaltic olivine. Elements with ), 1 (incompatible elements), such as Th, Ba or rare-earth elements in basaltic systems, will provide basically no clue to F variations. In addition, information carried by incompatible elements, which do not fractionate with respect to each other, is entirely redundant. This is better shown by taking the relative change in the ratio of two elements il and i2 per increment of crystallization... 

Due to the great similarity of the chemical properties of the rare earth elements, their separation represented, especially in the past, one of the most difficult problems in metallic chemistry. Two principal types of process are available for the extraction of rare earth elements (i) solid-liquid systems using fractional precipitation, crystallization or ion exchange (ii) liquid-liquid systems using solvent extraction. The rare earth metals are produced by metallothermic reduction (high purity metals are obtained) and by molten electrolysis. 

Abell, J.F. (1989) Preparation and crystal growth of rare earth elements and intermetallic compounds. In Handbook on the Physics and Chemistry of Rare Earths, eds. Gschneidner Jr., K.A. and Eyring, L.R. (North-Holland, Amsterdam), Vol. 12. 

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. 

Prior to the proposal of the Periodic Table, there was no information available on how many chemical elements could possibly exist. Even after the appearance of the numerous periodic tables of chemical elements, the rare earth elements were an especially difficult case because they could not be properly arranged into any of the Tables. Until the twentieth century, fractional crystallization was the only method of purification of elements. In most cases, this required thousands of recrystallizations involving months of work. As a result, there is a long list of various false claims among the rare earth elements, some of which are detailed below. 

So far, the bonding and surface structure aspects of electrocatalysis have been presented in a somewhat abstract sort of way. In order to make electrocatalysis a little more real, it is helpful to go through an example—that of the catalysis of the evolution of oxygen from alkaline solutions onto substances called perovskites. Such materials are given by the general formula RT03, where R is a rare earth element such as lanthanum, and T is a transition metal such as nickel. In the electron catalysis studied, the lattice of the perovskite crystal was replicated with various transition metals, i.e., Ni, Co, Fe, Mn, and Cr, the R remaining always La. 

In its precipitation reactions ameiicium(IIl) is very similar to the other tripositive actinide elements and to the rare earth elements. Thus the fluonde and the oxalate are insoluble and the phosphate and iodate are only moderately soluble in acid solution, whereas the nitrates, halides, sulfates, sulfides, and perchlorates are all soluble. Americium(VI) can be precipitated with sodium acetate giving crystals isostructural with sodium uranyl acetate,... 

Because, of the veiy heavy ionic, weight (250) of the perrhenate ion, it is one of the heaviest simple anions obtainable in readily soluble salts. It has found use as a precipitant for potassium and some other heavy univalent ions also as a precipitant for such complex ions as Co(NH )( "+. and for the separation of alkaloids and organic bases. Perrhenate also is used in the fractional crystallization ot the rare-earth elements. 

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