Heavy RE Research Articles

A new partitioning process for high-level liquid waste by extraction chromatography using silica-substrate chelating agent impregnated adsorbents

To separate the long-lived minor actinides (MA(III) = Am(III), Cm(III)) and some specific fission products (FP) such as Pd(II), Mo(VI), Cs(I) and Sr(II) from high-level liquid waste (HLLW), we have been studying a new partitioning process by extraction chromatography using several novel silica-based extraction resins. In this work, we examined the separation behavior of the elements contained in a simulated MA-effluent by the CMPO/SiO 2 P packed column. In addition, as an attempt to further isolate Am(III) and Cm(III) from the heavy RE(III) such as Eu(III), Gd(III) and Dy(III) contained in the MA-effluent, we investigated the possibility of separation by using a silica-based cationic exchange resin. Furthermore, to isolate Sr(II) from the HLLW, adsorption and separation performances of Sr(II) and some other FP elements were studied by using a novel silica-based crown ether extraction resin, DtBuCH18C6/SiO 2 P. The experimental results demonstrated that the elements in the simulated MA-effluent can be successfully separated to (1) Pd, (2) MA-hRE and (3) Zr–Mo, by CMPO/SiO 2 P packed column using water and a dilute DTPA solution as eluents. Am(III) and Cm(III) are expected to be effectively separated from light RE(III) and Y(III) by the SiSCR cationic resin. However, more effective separation between Am(II), Cm(III) and heavy RE(III) such as Eu(III), Gd(III) and Dy(III) needs further approach. DtBuCH18C6/SiO 2 P showed a highly selective adsorption for Sr(III) so that the Sr(II) could be completely separated from other FPs except a portion of Ba(II).

Crystal structure and magnetic properties of Pr 5Si 4− xGe x compounds

The magnetic properties of Pr 5Si 4− x Ge x ( x=0.0, 1.0, 2.0, 2.5, 3.0, 3.5, 4.0) were investigated by magnetic measurements. The compounds Pr 5Si 4− x Ge x crystallize in the tetragonal Zr 5Si 4-type structure for x=0.0 and 1.0, in the monoclinic Gd 5Si 2Ge 2-type structure for x=2.0 and 2.5; and in the orthorhombic Sm 5Ge 4-type structure for x=3.0–4.0. Unlike the heavy rare earth RE 5Si 4− x Ge x (RE=Gd, Tb, Dy) system, the Curie temperature of this system exhibits the following features: the Curie temperature of the compound increases with the increasing of the Ge content in the tetragonal phase region, whereas it shows a weak dependence on the Ge content in the monoclinic phase region and decreases in the orthorhombic phase region. All of the compounds in this system may have a canted magnetic structure.

Growth and microstructure of MTG REBa 2Cu 3O 7/RE [formula omitted]BaCuO 5 with heavy rare earth elements

New melt textured REBa 2Cu 3O 7/RE ′ 2 BaCuO 5 composites, have been obtained by top seeding melt-texturing growth. Two different starting mixtures of REBa 2Cu 3O 7 superconducting powders and insulating Y 2BaCuO 5 phase were used. On one hand RE is a natural mixture of heavy rare earth elements (Y, Yb, Lu, Er, Dy, Tm, Ho) extracted from the Brazilian mineral “Xenotime”, and on the other hand, RE is thulium. In both cases melt textured REBa 2Cu 3O 7/RE ′ 2 BaCuO 5 composites have been obtained where RE and RE ′ are different mixtures of heavy rare earth/yttrium and Tm/yttrium. The composition analysis shows different areas within the RE ′ 2 BaCuO 5 as a consequence of an inhomogeneous RE distribution, due to the differential solubility of each rare earth in the high temperature semisolid state. During the crystallization process a profound inversion of the rare earth composition between the superconducting matrix and the insulating precipitates occurs. Yttrium is selectively located in the 123 matrix and RE in the 211 particles. Heavy RE ions can substitute yttrium in MTG REBCO without degradation of the superconducting properties. A model for the crystallization process is proposed.

Melt growth and microstructure development of high critical current REBa2Cu3O7 superconductors with a natural mixture of rare earths

A natural mixture of heavy rare earth oxides has been used to prepare high critical current bulk superconducting ceramics which may be used in electrotechnical devices. Melt processing of a starting mixture of REBa2Cu3O7 and Y2BaCuO5 powders (RE denotes natural mixture of rare earth elements), leads to a final ceramic composite REBa2Cu3O7/RE2′BaCuO5, where RE and RE′ are different mixtures of heavy rare earths and yttrium. It is found that the superconducting matrix and the core of the large RE2′BaCuO5 particles are yttrium rich while the small RE2′BaCuO5 particles are rich in heavy RE ions. The differential solubility of the rare earths in the high-temperature semisolid state leads to a strong inversion of the rare earth composition between the superconducting matrix and the insulating precipitates which is originated during the melt growth process. The superconducting properties of the new compound having natural RE mixtures are found to be very similar to those of pure YBa2Cu3O7/Y2BaCuO5 melt textured composites.

Calculation of dipole fields at interstices of rare-earth metals

An effective method for calculating the sum of dipole magnetic fields of lattice sites is developed using the threefold axial symmetry and performing summation over hexagonal planes. The values of fields in octahedral and tetrahedral interstices of an hcp lattice are determined for spiral structures of heavy RE metals and for samarium. It is shown that the absence of an experimentally observed jump in the dipole field at the point of ferro-antiferromagnetic transition in the disposition is due to the small angle of rotation of the spiral magnetic structure. The problem of interpretation of the Lorentz macroscopic field is discussed on the basis of calculation of microscopic fields in a homogeneous continuous medium.

On the localization of the transition metal atoms in HoFe0.5Si2 and in the related RFexSi2 (R=heavy RE element) compounds

Neutron diffraction and 57Fe Mössbauer spectroscopy were used to establish the crystal structure of HoFe0.5Si2. Our data strongly suggest that this compound crystallizes in the CeNiSi2-type structure. This study removes the uncertainties concerning the localization of the transition metal in the heavy rare earth RFeXSi2 (R=Tb, Dy, Ho, Er, Lu) compounds, previously described in the TbFeSi2-type structure.

‘Lu-paradox’ as a consequence of the different magnetic ground states of the R(Co,Al)2 (R  heavy RE and Y) and Lu(Co,Al)2 compounds

The low temperature magnetic characteristics of the Y1−tLut(Co0.88Al0.12)2 system were determined. The drastic change from a weakly to strongly ferromagnetic ground state observed at t = 0.38 is discussed in the itinerant model by using the Landau expression for free energy expanded up to the eighth power of magnetization. The ‘Lu-paradox’, that the Curie temperature of Lu(Co1−xAlx)2 is higher than that of isostructural R(Co1−xAlx)2 with some heavy RE and Y (for x > 0.12), is interpreted considering the magnetic ground state of the itinerant electron subsystem to be strongly ferromagnetic in the Lu-based system and weakly ferromagnetic in the RE-based ones.

Resistivity and thermopower of monocrystalline TbIn 3 and DyIn 3

We report the results of resistivity and thermoelectric power measurements of TbIn 3 and DyIn 3 in temperature range 5K–300K. Both the results are consistent with our previously reported data of the REIn 3 compounds with other heavy RE elements and confirm a similarity in electronic properties of the heavy REIn 3 compounds.

Original magnetization processes in the artificial ferrimagnet Y-Co/Gd-Co/Y-Co

Sandwiches consisting of three amorphous layers, each about 1000 Å thick, have been prepared by dc triode sputtering. The approximate composition of each layer is R 0.33Co 0.67. These systems are such that the Co moments are coupled parallel to each other throughout the thickness of the sandwich while the RE moments are alligned either parallel (for light RE) or antiparallel (for heavy RE) to the Co moments. In this paper, we report experimental and analytical results obtained on the model system Y-Co/Gd-Co/Y-Co. In low fields, both Y-Co and Gd-Co magnetizations are saturated in opposite directions, the Gd moments being antiparallel to the field. As a result, the macroscopic magnetization alternates from one layer to another giving rise to a macroscopic ferrimagnetic arrangement (artificial ferrimagnet). When a field is applied, the magnetization of the Gd-Co layer reverses in the direction of the field. This transition is retarted by the necessary creation of planar Bloch walls at the two interfaces within the Co sublattice. In higher fields, the whole approach to saturation is governed by the reversible shrinking or broadening of these two Bloch walls.

Thermoelectric power of the REIn 3 single crystals where RE = La, Ce, Pr, Nd, Sm, Gd, Ho, ErIn3, TmandLu

We report the thermopower for the REIn 3 compounds in temperature range between 5 K and 300 K. We show that differences in thermopower observed for compounds containing either light or heavy RE element can be interpreted in terms of differences in topology of their Fermi surface. Beyond the well known anomalies observed in low temperatures the presence of an additional crystal field effect is suggested.

Separate resistive loading of the respiratory phases during mild hypercapnia in man.

Eleven human subjects were studied during steady state, controlled mild hypercapnia with resistive loading of either inspiration (RI) or expiration (RE). Minute ventilation and frequency were significantly reduced by RI (P = less than 0.01) and even more so by RE (P = less than 0.001). Tidal volume was unchanged. Both RI and RE reduced mean flow in the loaded phase - an effect relatively greater with RE. Neither RI nor RE altered mean flow in the unloaded phase. Although mean inspiratory flow was unchanged with RE, mouth occlusion pressure (P0.1) was increased (P = less than 0.01). Functional residual capacity (seven subjects) was increased with RE, but not with RI (P = less than 0.05). Five additional subjects were similarly studied with and without RE in whom transdiaphragmatic pressure (PDi) and peak diaphragmatic EMG (EMGDi) were examined. Changes in ventilation, breathing pattern and P0.1 were similar to those described above. Neither PDi nor EMGDi were significantly altered by RE, but with RE, diaphragmatic EMG activity began 50-190 ms before inspiratory flow. In conclusion, ventilation is reduced more by RE than by RI due to greater respiratory phase time. Moderately heavy RE does not augment inspiratory drive as reflected by mean flow, PDi or EMGDi. With RE and increased FRC, P0.1 does not accurately reflect inspiratory drive because of dissociation between EMG and flow.

X-RAY ABSORPTION SPECTROSCOPY (L3 EDGES, XANES, EXAFS) ON 4f MIXED-VALENT COMPOUNDS

X-RAY ABSORPTION SPECTROSCOPY (L₃ EDGES, XANES, EXAFS) ON 4f MIXED-VALENT COMPOUNDS

Electronic structure, chemical bonding and X-ray photoelectron spectra of light rare-earth oxides

The electronic structure of the heavy RE sesquioxides from Sm2O3 to Lu2O3 has been studied by the cluster discrete variational Xα method and X-ray photoelectron spectroscopy. The interpretation of XPS spectra basing on the MO model is given. An analysis of the dependence of Ln 4f orbitals contribution to chemical bonding on the lanthanide atomic number and bond lengths is made.

Magnetic anomalies of thermal expansion in (rare-earth) Ni 2 intermetallic compounds

The thermal expansion of eight RENi 2 intermetallic compounds (RE = La, Nd, Sm, Tb, Dy, Ho, Er, Tm) and YNi 2 have been measured between 3.8 and approx. 300 K. The anomalies found at the paramagnetic-magnetically ordered phase transition have allowed an accurate determination of the Curie temperatures. From the low temperature comparison of the thermal expansion of the light RE compounds with that of LaNi 2, and of the heavy RE compounds with that of YNi 2, the Debye temperatures have been obtained. In the case of the compounds DyNi 2, TbNi 2 and HoNi 2 the contributions from crystal field and exchange interactions to the spontaneous volume strain at the magnetically ordered phase have been calculated, the agreement between experiment and calculation being good.

Macroscopic shape effect due to quadropole orientation in single crystals of Mg with heavy RE impurities

The magnetostriction of dilute Mg Tb, Mg Dy, Mg Ho and Mg Tm alloys was measured at 4.2 K and found to be comparable, per RE ion, to that of concentrated RE systems. The contribution of these impurities to the low-temperature thermal expansion of Mg was also measured between 1.5 and 15 K. Quadrupole orientation accounts only for the results on Mg Tb; in Mg Ho we find very strong indications for an effect of higher-order multipoles.

Magnetization processes caused by iron substitution in cubic laves phases

The magnetic properties of cubic Laves phases RE(Fe, M) 2, M = Al, Co, Rh are discussed. Pauli-paramagnetism is obtained for all three YM 2 compounds. The appearance of a percolation limit for the onset of long-range ferromagnetic order which depends strongly on the matrix susceptibility is characteristic for all investigated series Y (Fe, M) 2. Mictomagnetic behaviour can be deduced from magnetic, Mössbauer- and neutron depolarization measurements below the percolation limit. A Co moment of approximately 1 μ B is induced in RECo 2 compounds, RE = Gd, Dy, Ho. On the contrary Rh has no magnetic moment in these compounds. Within the RE(Fe, Co) 2 series a Co moment is induced by both the RE and Fe atoms, whereas within RE(Fe, Rh) 2 the Rh atoms will only be influenced by the substituted Fe. In all compounds the spin of the heavy RE atoms couples antiparallel to the spin of the transition metal atoms. Local environment effects are important for all Fe containing series whereas the properties of RECo 2 compounds evidence itinerant electron metamagnetism.