Small Amounts Of Ce Research Articles

The incorporation of Nd or Ce in CaZrTi2O7 zirconolite: Ceramic versus glass-ceramic

Three sets of the zirconolite ceramic and glass-ceramic systems have been investigated including Ca1−xZr1−xNd2xTi2O7, Ca1−xNdxZrTi2-xAlxO7 and CaZr1−xCexTi2O7 (x = 0 − 0.5). The zirconolite formation is compared between ceramics sintered at 1300 °C for 12 h and glass-ceramics sintered at 1250 °C for 3 h. Powder X-ray diffraction, Raman and scanning electron microscopy techniques are used to analyze the crystal structure, morphologies and composition distribution. Ca1−xNdxZrTi2-xAlxO7 can incorporate 0.5 formula unit of Nd in dominant zirconolite in both ceramic and glass-ceramic samples with baddeleyite as minor phase and slight amount of sphene in glass-ceramics, with more than 86% of the Nd initially introduced staying in zirconolite phase. Less Nd can be doped in zirconolite dominated Ca1−xZr1−xNd2xTi2O7 system with perovskite as a minor phase in ceramics and sphene as a minor phase in glass-ceramics. Only small amounts of Ce (x ≤ 0.1) can be incorporated in CaZr1−xCexTi2O7 zirconolite ceramic and glass-ceramics without obvious minor phases.

Influence (Ce and Sm) co-doping ZnO nanorods on the structural, optical and electrical properties of the fabricated Schottky diode using chemical bath deposition

Schottky diodes based on ZnO nanorods, undoped and co-doped with different concentrations (0.0, 0.2, 0.4, 0.6 and 0.8 at.%) of Ce and Sm, were fabricated on glass and on n-Si (111) substrates using chemical bath deposition assisted with the sol-gel spin coating. The ZnO maintained its hexagonal shape up to higher levels of doping (0.8 at.%) with the growth rate being suppressed by Ce and Sm co-doping. The as-synthesized nanorods were found to be highly crystalline and no impurities or peaks related to Ce and Sm or their oxides were observed. Room temperature Raman spectroscopy revealed that the prominent E2 high peak shifted towards a lower wave number and the intensity decreased upon doping. X-ray photoelectron spectroscopy studies at room temperature showed that the presence of Zn and O in all samples with small amounts of Ce and Sm being detected at doping levels of 0.8 at.%. Photoluminescence studies at room temperature revealed a weak ultraviolet emission and a strong deep level (visible) emission. Deconvolution of the visible emission spectra showed that more than one defect contributed to the visible emission. The I–V characteristics of the fabricated Schottky diode devices measured at room temperature showed that the Ce and Sm co-doping increased the generation-recombination process in the fabricated Schottky diodes. Furthermore, the current transport mechanism in the fabricated Schottky devices at a lower voltage (0.0–∼ 0.6 V) was dominated by ohmic conduction mechanism, while at voltages greater than 0.6 V, the space charge limited current and the trap filled limit voltage mechanism dominated.

Measurement of fossil deep-sea coral Nd isotopic compositions and concentrations by TIMS as NdO+, with evaluation of cleaning protocols

Precise and accurate measurements of Nd concentrations and isotopic compositions of small sample masses (≤30ng Nd) are increasingly necessary in the geosciences. Here, we present a combined chemical separation and TIMS (thermal ionisation mass spectrometry) NdO+ method adapted for fossil deep-sea corals, which represents a significant improvement in precision compared to existing methods, with additional assessment of potential contamination of coral aragonite by external encrustations. After digesting and spiking samples, we purified sample Nd using RE and Ln-spec separation chemistries, and tested the efficiency of these on aliquots of USGS BCR-2. In addition, we prepared a matrix-matched in-house coral reference material to monitor the analytical precision on coral carbonate. Using a micro-loading technique and TaF5 activator on single W filaments, ion beam sizes of up to 0.60V per ng on mass 160 are achievable, but decline with increasing age of the activator. The long-term average for NdO+ measurements of 5ng and 15ng loads of the pure metal oxide JNdi-1 reference material (Geological Survey of Japan) was 0.512106±6 for 143Nd/144Nd (12ppm 2RSD, n=44), with an overall deviation from the reference value of 17ppm (0.512115±7; Tanaka et al., 2000). BCR-2 aliquots of 10ng and 30ng generated an average 143Nd/144Nd of 0.512643±8 (16ppm 2RSD, n=14), which is identical within uncertainty to the reference value (0.512637±12; Weis et al., 2006). Very similar external reproducibility was obtained on 10ng and 30ng aliquots of the in-house coral standard, with an average 143Nd/144Nd of 0.512338±8 (16ppm 2RSD, n=13). Precision and accuracy of Nd oxide measurements depend on well-characterised oxygen isotopic compositions over the range of measurement temperatures, and very small amounts of Ce and Pr in final chemistry cuts. Whilst the former is laboratory-specific, and can be determined precisely using a column-purified 150Nd spike (e.g. 17O/16O=0.000390±3 and 18O/16O=0.002073±8 for this study; n=12), our method shows that interference corrections for Ce and Pr are tolerable up to higher values than previously reported (e.g. 156/160 ratios≤0.148 and 157/160 ratios≤0.68). In reality, however, our separation was always better than this.An important issue with fossil corals concerns their apparently higher Nd concentrations compared to modern counterparts (~7–310ppb vs. ~3–51ppb respectively). Variable to high Nd concentrations could arise for a number of reasons, but here we focus solely on evaluating the effectiveness of coral cleaning to remove external, Nd-rich encrustations. To test this, we measured major and trace metal concentrations (Ca, Fe, Mn, Ti, Al, Ce, Nd, Th, U) in paired aragonite and FeMn coatings from the same samples. Mass balance calculations reveal negligible influence of FeMn coatings on the final εNd, although four samples showed some degree of contamination as demonstrated by elevated Fe, Mn, Ti and Th concentrations.

Collapse-Like Decrease of RKKY Interaction and Kondo Effect in Heavy Fermion Compounds (Ce1-XGdX)Ni (0.03≤X ≤0.20)

Small amounts of Ce were substituted by Gd and the (Ce-Gd)Ni heavy fermion compounds were investigated in detail from viewpoint of magnetism in Gd-poor region between 3 at% and 20 at%. Magnetizations showed peculiar linear relationship as a function temperature and were sensitive to the applied magnetic field in common. These characteristic natures were analyzes employing molecular field analysis by changing three exchange interaction energies, JGd-Gd, JGd-Ni and JNi-Ni. The unique solution for the linear relationship in the temperature dependence of magnetization M(T) was found to be attributed to the collapselike decrease of JGd-Gd and the decrease of JGd-Gd can explain the sensitivity to applied magnetic field. However this peculiar decrease of JGd-Gd did not effect on the inverse susceptibilities above the Curie temperatures and the χ-1(T) behaved normally as ferri-magnet.

PERFORMANCE OF Ce-INCORPORATED KIT-6 SUPPORTED COBALT CATALYSTS FOR FISCHER–TROPSCH SYNTHESIS

A series of Ce -incorporated structure of cubic large mesoporous molecular sieves, KIT-6, with different Ce contents were synthesized by a direct hydrothermal process. A sample of Ce -loaded KIT-6 material was synthesised by incipent wetness impregnation. Similarly, catalysts with 15 wt.% Co loading on the above supports were also synthesized by incipient wetness impregnation. The supports and catalysts were characterized by X-ray diffraction, diffuse reflectance UV-vis, solid-state 29Si magic-angle spinning nuclear magnetic resonance, H2 -temperature programmed reduction, H2 -temperature programmed desorption and oxygen titration. The structure of the KIT-6 support was well retained after Ce incorporation. Small amounts of Ce in the Co catalyst were found to improve the activity and increase the selectivity to C5+ hydrocarbons for Fischer–Tropsch synthesis, while larger amounts of Ce had the reverse effect. Meanwhile, methane selectivity shows an opposite trend as compared with that of C5+ selectivity. Ce -loaded KIT-6 supported Co catalyst showed lower activity than KIT-6 supported Co catalyst.

Luminescence and creation of electron centers in UV-irradiated YAlO3 single crystals

Luminescence and defect creation processes were studied by the photoluminescence, thermally stimulated luminescence, and electron paramagnetic resonance methods in the UV-irradiated single crystals of undoped YAlO3, containing small amounts of Ce, Mo, and Ti ions as accidental impurities. The luminescence of the electron antisite YAl2+-type centers of different structures was found around 2.45 eV and studied at 4.2–500 K. The luminescence of the Ti3+-related centers (2.03 and 1.73 eV) and Ti4+ centers (2.78 eV) was observed as well. Dependences of the number of the YAl2+-type and Ti3+-related centers on the UV irradiation energy, temperature, and duration, as well as on various crystal heat-treatment procedures were examined. As a result of the photostimulated electron transfer from the O2− ligand ions to Mo4+ and Ti4+ ions, the paramagnetic hole O−-type centers and electron Ti3+ and Mo3+ centers are created. The antisite YAl2+-type centers are created due to the photostimulated release of electrons mainly from the Mo3+ centers to the conduction band and their subsequent trapping at the YAl3+ ions located near an oxygen vacancy or a defect at the neighboring Y3+ site.

Reactivity of Fe/M (M = Ce, Mn, Al) oxide-hydroxides for hydrosulfide removal in anoxic and oxic solutions

The reactivity toward hydrosulfide (HS −) of seven iron-containing oxide-hydroxides (FeMOx) with different Fe/M (M = Ce, Mn, Al) molar ratios (0.9, 0.5, 0.1) was studied for alkaline pH in a batch slurry reactor to identify the fittest material aimed at the removal of H 2S from the pulp and paper atmospheric effluents. The materials were optimized by varying the calcination temperature to maximize the surface area. FeAlOx0.9 achieved the highest surface area (286.8 m 2/g), followed by FeCeOx0.9 (241.5 m 2/g) and FeMnOx0.9 (217.9 m 2/g). In anoxic solutions, combination of Fe with small amounts of Ce or Mn improved HS − oxidation. Increasing Mn (respectively, Fe) content in FeMnOx (respectively, FeCeOx) increased HS − conversion both in oxic and anoxic solutions. The majority of FeMOx showed improved reactivity towards HS − in oxic conditions while dissolved oxygen (DO 2) accelerated HS − conversion by re-oxidizing Fe(II) to active Fe(III) as well as by homogeneously converting the polysulfides into thiosulfate. The gain in efficiency of FeCeOx in oxic versus anoxic environments correlated negative-linearly with the Fe/Ce ratio, and Ce was found to enhance the electron transfer between Fe(II) sites and DO 2. The gain in efficiency of FeMnOx in oxic versus anoxic solutions correlated linearly with Fe/Mn ratio suggesting reoxidation for Fe(II) and Mn(II) to occur at different rates. Therefore, even if Mn exhibited superior reactivity toward HS − than Fe, the greater reoxidation ability of Fe(II) elects FeCeOx materials for a redox-scrubbing process aiming at the removal of H 2S from Kraft atmospheric effluents.

FCC SOx Additives Deactivation

The relative importance of possible factors leading to the deactivation of a commercial SOx emission reduction additive used in the fluid cracking process was evaluated individually. This additive was based on mixed oxides of Mg and Al and contained small amounts of Ce and V. The laboratory deactivation simulation was an extended hydrothermal treatment of the additive by steam with or without the presence of sources of possible poisons such as Si, V, and S. It was observed that a reduction of the area and sintering and migration of V from the catalyst to the additive did not affect the performance of the additive. However, migration of Si from a fresh catalyst or sulfate from an impregnated catalyst drastically reduced the SOx adsorption capacity of the additives. As the migration of Si was important mainly with fresh catalyst, which is present in the inventory of the unit in very small quantity compared to the large amount of equilibrium catalyst, the main factor leading to deactivation of the SOx additives in the industrial operation can be attributed to formation of stable sulfates.

Formation of secondary phases after long-term corrosion of simulated HLW glass in brine solutions at 190 °C

SummaryThe behavior of rare earth elements (REE) as chemical analogues for actinides during glass corrosion was studied with static long-term batch experiments (7.5 years) at 190 °C. Corrosion tests were carried out using a simulated inactive high level waste (HLW) glass powder. Two different highly concentrated salt solutions (NaCl-rich and MgCl2-rich) have been used to simulate the potential corrosion by aqueous solutions in geological salt formations. Samples with surface-to-volume ratios (S/V) of 1000 m−1and 10000 m−1were investigated. The chemical composition of the aqueous solution and the formation of secondary phases at the glass/solution interface as well as their elemental composition, especially with respect to the behavior of REE was studied. The glass corrosion behavior and secondary phase formation was significantly different in the two brines. In the MgCl2-rich salt solution, with a final pH < 3.5, hydrous Mg-silicates and (Ba,Sr)SO4solid solutions with considerable amounts of Sr (up to 15 wt.%) have been observed. Further, REE-sulfates and REE-molybdates with an indication of dissolution (etch pits) as secondary phases could be identified. In the NaCl-rich solution with a final high pH, REE-containing hydrous silicates (up to 35 wt.%) and (Ba,Sr)SO4solid solutions with small amounts of Ce (up to 5 wt.%) have been observed. Frequently observed Ca-molybdates (powellite) did not contain detectable amounts of REE.

Calibration of LiBaF 3:Ce scintillator for fission spectrum neutrons

The scintillator LiBaF 3 doped with small amounts of Ce +3 has the ability to distinguish heavy charged particles (p, d, t, or α) from beta and/or gamma radiation based on the presence or absence of nanosecond components in the scintillation light output. Since the neutron capture reaction on 6Li produces recoil alphas and tritons, this scintillator also discriminates between neutron induced events and beta or gamma interactions. An experimental technique using a time-tagged 252Cf source has been used to measure the efficiency of this scintillator for neutron capture, the calibration of neutron capture pulse height, and the pulse height resolution—all as a function of incident neutron energy.

Metallurgy and superconductivity in bronze-processed Nb/sub 3/Sn doped cerium and cerium-titanium

Metallurgy and superconductivity in Ce-doped and Ce-Ti-doped Nb/sub 3/Sn samples were investigated. The wires containing Ce-bronze and Ce-Te-bronze were not noticeably difficult to draw. The addition of Ce to the bronze not only enhances the growth rate of the Nb/sub 3/Sn layer but also improves the composition distribution within the wire. The critical temperature T/sub c/ of Ce-doped samples treated at 700 degrees C is obviously higher than that of pure Nb/sub 3/Sn. The J/sub c/ difference between samples with small amounts of Ce and pure Nb/sub 3/Sn is not obvious. J/sub c/ decreases slightly in low field with increasing Ce content. >

Crystal-field splitting and single-ion exchange of Ce and Yb impurities in dilute monopnictides

We report measurements on the resistivity, susceptibility and ESR vs. temperature of monopnictides MZ (with M=Sc, Y, La and Z=As, Sb, Bi) which contain small amounts of Ce- or Yb-ions as doping material. Metallic conductivities are found in all of these systems. With increasing covalent character of the MZ host we observed: an increasing conductivity, a decreasing crystal-field splitting of the Ce 3+- or Yb 3+-ionic state and for both 4f-ions an increase of the negative 4f-conduction electron exchange constant.

Orthorhombic and Trigonal Electron-Spin-Resonance Spectra ofCe3+Ions in CaF2

Two new electron-spin-resonance spectra, one having trigonal and the other having orthorhombic symmetry, have been observed in Ca${\mathrm{F}}_{2}$ doped with small amounts of Ce${\mathrm{O}}_{2}$. The $x$ and $y$ axes of the orthorhombic spectrum lie in the (110) plane and are tilted by an angle $\ensuremath{\delta}=13.8\ifmmode\pm\else\textpm\fi{}{0.2}^{\ensuremath{\circ}}$ from the [$\overline{1}10$] and the [001] axes, respectively, and the $z$ axis lies along the [110] axis. The components of the $g$ tensor for the two spectra are: orthorhombic, ${g}_{x}=0.844\ifmmode\pm\else\textpm\fi{}0.001$, ${g}_{y}=0.22\ifmmode\pm\else\textpm\fi{}0.05$, ${g}_{z}=3.286\ifmmode\pm\else\textpm\fi{}0.001$; trigonal, ${g}_{\ensuremath{\parallel}}=3.673\ifmmode\pm\else\textpm\fi{}0.0021$, ${g}_{\ensuremath{\perp}}\ensuremath{\le}0.3$.