Cerium Compounds Research Articles

Effects of amorphous silica coating on cerium oxide nanoparticles induced pulmonary responses

Recently cerium compounds have been used in a variety of consumer products, including diesel fuel additives, to increase fuel combustion efficiency and decrease diesel soot emissions. However, cerium oxide (CeO2) nanoparticles have been detected in the exhaust, which raises a health concern. Previous studies have shown that exposure of rats to nanoscale CeO2 by intratracheal instillation (IT) induces sustained pulmonary inflammation and fibrosis. In the present study, male Sprague–Dawley rats were exposed to CeO2 or CeO2 coated with a nano layer of amorphous SiO2 (aSiO2/CeO2) by a single IT and sacrificed at various times post-exposure to assess potential protective effects of the aSiO2 coating. The first acellular bronchoalveolar lavage (BAL) fluid and BAL cells were collected and analyzed from all exposed animals. At the low dose (0.15mg/kg), CeO2 but not aSiO2/CeO2 exposure induced inflammation. However, at the higher doses, both particles induced a dose-related inflammation, cytotoxicity, inflammatory cytokines, matrix metalloproteinase (MMP)-9, and tissue inhibitor of MMP at 1day post-exposure. Morphological analysis of lung showed an increased inflammation, surfactant and collagen fibers after CeO2 (high dose at 3.5mg/kg) treatment at 28days post-exposure. aSiO2 coating significantly reduced CeO2-induced inflammatory responses in the airspace and appeared to attenuate phospholipidosis and fibrosis. Energy dispersive X-ray spectroscopy analysis showed Ce and phosphorous (P) in all particle-exposed lungs, whereas Si was only detected in aSiO2/CeO2-exposed lungs up to 3days after exposure, suggesting that aSiO2 dissolved off the CeO2 core, and some of the CeO2 was transformed to CePO4 with time. These results demonstrate that aSiO2 coating reduce CeO2-induced inflammation, phospholipidosis and fibrosis.

The stannides RE 3Au6Sn5 (RE = La, Ce, Pr, Nd, Sm) – synthesis, structure, magnetic properties and 119Sn Mössbauer spectroscopy

Abstract The Ce3Pd6Sb5-type rare earth stannides RE 3Au6Sn5 (RE = La, Ce, Pr, Nd, Sm) were synthesized by arc-melting of the elements and subsequent annealing in open tantalum crucibles within sealed evacuated silica ampoules. The polycrystalline samples were studied by powder X-ray diffraction. The structures of three crystals were refined from single crystal X-ray diffractometer data: Pmmn, a = 1360.3(9), b = 455.9(2), c = 1023.6(4) pm, wR2 = 0.0275, 1069 F 2 values, 48 variables for Ce3Au6Sn5, a = 1352.4(4), b = 455.1(1), c = 1023.7(3) pm, wR2 = 0.0367, 1160 F 2 values, 48 variables for Nd3Au6Sn5, and a = 1339.8(2), b = 452.80(7), c = 1012.4(2) pm, wR2 = 0.1204, 1040 F 2 values, 49 variables for Sm3Au5.59(2)Sn5.41(2). One of the gold sites of the samarium compound shows a significant degree of Au/Sn mixing. The RE 3Au6Sn5 structures are composed of three-dimensional [Au6Sn5] polyanionic networks with the two crystallographically independent rare earth atoms in larger cages, i.e., RE1@Au10Sn6 and RE2@Au8Sn8. The [Au6Sn5] network is stabilized by Au–Sn (266–320 pm), Au–Au (284–301 pm) as well as Sn–Sn (320 pm; distances given for the cerium compound) interactions. Temperature-dependent magnetic susceptibility measurements reveal an antiferromagnetic ordering only for Sm3Au6Sn5, while the other compounds exhibit Curie–Weiss paramagnetism. 119Sn Mössbauer spectroscopy shows resonances in the typical range for intermetallic tin compounds where tin takes part in the polyanionic network [isomer shifts between 1.73(1) and 2.28(1) mm·s−1]. With the help of theoretical electric field gradient calculations using the WIEN2k code it was possible to resolve the spectroscopic contributions of all three crystallographically independent atomic tin sites in the 119Sn spectra of RE 3Au6Sn5 (RE = La, Ce, Pr, Nd, Sm).

Flotation recovery of rare-earth metal compounds from dilute aqueous solutions

The possibility of flotation extraction of lanthanum and cerium (III) compounds from diluted sulfate solutions was shown by using finely dispersed solid solutions of different radical phosphine oxide in paraffin. Optimal conditions for conducting the flotation have been determined. The effect of electrolyte additions on the process efficiency was studied. In addition, the mechanism of interaction of rare earth metal compounds with flotation collector was proposed.

A ligand field series for the 4f-block from experimental and DFT computed Ce(IV/III) electrochemical potentials.

Understanding of the sensitivity of the reduction potential of cerium(IV) cations to ligand field strength has yet to benefit from systematic variation of the ligand environment. Detailed analyses for a series of seven cerium(IV) tetrakis(pyridyl-nitroxide) compounds and their cerium(III) analogues in varying ligand field strengths are presented. Electrochemical, spectroscopic, and computational results reveal a close correlation of electronic properties with ligand substituents. Together with electrochemical data for reported eight-coordinate compounds, DFT calculations reveal a broad range of the cerium(IV/III) redox potentials correlated to ligand field strengths, establishing a semiempirical, predictive model for the modulation of cerium redox thermodynamics and ligand field strengths. Applications over a variety of scientific disciplines make use of the fundamental redox thermodynamics of cerium. Such applications will benefit from a combined experimental and theoretical approach for assessing redox cycling of cerium compounds.

In Situ AFM and Electrochemical Study of a Waterborne Acrylic Composite Coating with CeO2 Nanoparticles for Corrosion Protection of Carbon Steel

The corrosion protection of a waterborne acrylic composite coating with 1 wt% ceria nanoparticles (CeNP) coated on carbon steel in 3 wt% NaCl solution was investigated by ex-situ and in situ as well as electrochemical atomic force microscopy (AFM) observations, combined with open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) measurements. The synthesized CeNP were stabilized by acetic acid. The transmission electron microscopy characterization showed fine nano-size of as-synthesized CeNP, the ex-situ AFM imaging revealed uniform dispersion of the CeNP in the composite coating and greatly reduced nano-sized pinholes in the coating. The in situ and electrochemical (EC) AFM investigations indicate release of some CeNP and aggregates from the coating surface and then precipitation of some particles and cerium-compounds during the exposure. The OCP and EIS results demonstrated that the addition of 1 wt% CeNP leads to a significantly improved long term barrier type corrosion protection of the waterborne acrylic composite coating for carbon steel in 3 wt% NaCl solution. The beneficial effect of the CeNP is attributed to the blocking of nano-sized defects and inhibition by the cerium compounds originated from the acetic acid stabilized CeNP.

Anomalous change of the magnetic moment direction by hole doping inCeRu2Al10

We present a detailed investigation of the hole (3% Re) doping effect on the polycrystalline ${\mathrm{CeRu}}_{2}{\mathrm{Al}}_{10}$ sample by magnetization, heat capacity, resistivity, muon spin relaxation ($\ensuremath{\mu}\mathrm{SR}$), and neutron scattering (both elastic and inelastic) measurements. ${\mathrm{CeRu}}_{2}{\mathrm{Al}}_{10}$ is an exceptional cerium compound with an unusually high N\'eel temperature of 27 K. Here we study the stability of the unusual magnetic order by means of controlled doping, and we uncover further surprising attributes of this phase transition. The heat capacity, resistivity, and $\ensuremath{\mu}\mathrm{SR}$ measurements reveal an onset of magnetic ordering below 23 K, while a broad peak at 31 K (i.e., above ${T}_{N}$) has been observed in the temperature dependent susceptibility, indicating an opening of a spin gap above ${T}_{N}$. Our important finding, from the neutron diffraction, is that the compound orders antiferromagnetically with a propagation vector $\mathbf{k}=(1,0,0)$ and the ordered state moment is 0.20(1) ${\ensuremath{\mu}}_{B}$ along the $b$ axis. This is in sharp contrast to the undoped compound, which shows AFM ordering at 27 K with the ordered moment of 0.34--0.42 ${\ensuremath{\mu}}_{B}$ along the $c$ axis. Similar to ${\mathrm{CeRu}}_{2}{\mathrm{Al}}_{10}$ our inelastic neutron scattering study on the Re-doped compound shows a sharp spin gap-type excitation near 8 meV at 5 K, but with slightly reduced intensity compared to the undoped compound. Further the excitation broadens and shifts to lower energy ($\ensuremath{\le}4$ meV) near 35 K. These results suggest that the low temperature magnetic properties of the hole-doped sample are governed by the competition between the anisotropic hybridization effect and the crystal field anisotropy as observed in hole-doped ${\mathrm{CeOs}}_{2}{\mathrm{Al}}_{10}$.

Polyol Synthesis and Investigation of Ce1−xRExO2−x/2 (RE = Sm, Gd, Nd, La, 0 ≤ x ≤ 0.25) Electrolytes for IT‐SOFCs

In this study, we aimed to examine the effect of dopant type and concentration on the ionic conductivity of ceria‐based electrolytes. Ceria electrolytes doped with samarium (SDC), gadolinium (GDC), neodymium (NDC), and lanthanum (LDC) for solid oxide fuel cells were prepared through the polyol process. Acetate compounds of cerium and dopants were used as starting materials, and triethylene glycol was used as a solvent. Prepared powders and pellets were characterized by TG/DTA, XRD, FTIR, SEM, EIS, and EDS techniques. The results of the TG/DTA and XRD indicated that a single‐phase fluorite structure formed at the relatively low calcination temperature of 500°C. The relative densities of the pellets were higher than 90% and these finding were supported by the SEM images. The lattice parameters of the samples increased with the dopant concentration. According to the electrochemical analysis results, the samples with maximum conductivity values were SDC‐20, GDC‐15, NDC‐15, and LDC‐15. The results of the impedance spectroscopy revealed that the SDC‐20 sample exhibited the highest ionic conductivity with a value of 4.29 × 10−2 S/cm at 800°C in air.

Crystal fields and Kondo effect: Specific heat for Cerium compounds

The thermodynamic Bethe ansatz equations for the N=6 Coqblin-Schrieffer model with crystal fields have been solved numerically. The realistic case of three Kramers doublets with arbitrary splittings has been studied for the first time. The specific heat has been calculated for representative combinations of the ionic energy splittings providing ample material for comparison with experimental results for Cerium impurities and compounds.

Kinetics of water oxidation with cerium(IV) compounds catalyzed by a tetranuclear ruthenium complex

The kinetics and mechanism of water oxidation with cerium(IV) compounds catalyzed by a tetranuclear ruthenium complex containing two polyoxotungstate ligands are reported. Four water molecules are oxidized via an eight-electron process to form two oxygen molecules.

Neutron diffraction studies on structural and magnetic properties of RE2NiGe3 (RE=La, Ce)

We report the crystallographic properties of RE2NiGe3 (RE=La, Ce) synthesized by arc melting. Rietveld refinement on the powder neutron diffraction (ND) data suggest both compounds are isostructural and crystallize in the non-centrosymmetric Er2RhSi3 type structure having hexagonal space group P6¯2c. In the crystal structure of RE2NiGe3, two dimensional arrangements of nickel and germanium atoms lead to the formation of hexagonal layers with rare earth atoms sandwiched between them. Magnetic susceptibility measurements performed in low fields exhibit antiferromagnetic ordering in cerium compound around (To=) 3.2K. Neutron diffraction measurements at 2.8K (i.e., at T<To) neither show any change in the intensities of the diffraction lines nor indicate the appearance of any new diffraction lines in the Q-range of 0.47–7.34Å−1, thus ruling out any long-range magnetic order.

Interactive effects of cerium oxide and diesel exhaust nanoparticles on inducing pulmonary fibrosis

Cerium compounds have been used as a fuel-borne catalyst to lower the generation of diesel exhaust particles (DEPs), but are emitted as cerium oxide nanoparticles (CeO2) along with DEP in the diesel exhaust. The present study investigates the effects of the combined exposure to DEP and CeO2 on the pulmonary system in a rat model. Specific pathogen-free male Sprague–Dawley rats were exposed to CeO2 and/or DEP via a single intratracheal instillation and were sacrificed at various time points post-exposure. This investigation demonstrated that CeO2 induces a sustained inflammatory response, whereas DEP elicits a switch of the pulmonary immune response from Th1 to Th2. Both CeO2 and DEP activated AM and lymphocyte secretion of the proinflammatory cytokines IL-12 and IFN-γ, respectively. However, only DEP enhanced the anti-inflammatory cytokine IL-10 production in response to ex vivo LPS or Concanavalin A challenge that was not affected by the presence of CeO2, suggesting that DEP suppresses host defense capability by inducing the Th2 immunity. The micrographs of lymph nodes show that the particle clumps in DEP+CeO2 were significantly larger than CeO2 or DEP, exhibiting dense clumps continuous throughout the lymph nodes. Morphometric analysis demonstrates that the localization of collagen in the lung tissue after DEP+CeO2 reflects the combination of DEP-exposure plus CeO2-exposure. At 4weeks post-exposure, the histological features demonstrated that CeO2 induced lung phospholipidosis and fibrosis. DEP induced lung granulomas that were not significantly affected by the presence of CeO2 in the combined exposure. Using CeO2 as diesel fuel catalyst may cause health concerns.

Anisotropic magnetic, transport and thermodynamic properties of novel tetragonal Ce2RhGa12 compound

We report on a comprehensive study of the magnetization, resistivity and heat capacity on the single crystals of Ce2RhGa12 synthesized using Ga flux. Single crystal X-ray diffraction data confirm the tetragonal Pb/nbm structure of Ce2RhGa12, which is isostructural to Ce2PdGa12. Ce2RhGa12 orders antiferromagnetically at TN=3.5K and exhibits anisotropic magnetic behavior, inferred from the magnetization and resistivity data, taken along the two principal crystallographic directions of the crystal, viz., along [100] and [001]. The anisotropic magnetic response of Ce2RhGa12 establishes [001] as the easy axis of magnetization, and a weak meta-magnetic transition is also observed in the magnetic isotherm at 2K along the same axis. A sharp peak in specific heat signals the bulk antiferromagnetic transition at TN=3.5K, which shifts to lower temperatures in low applied fields. The electrical resistivity along the two directions shows metallic behavior from 300K down to 1.8K and establishes Ce2RhGa12 as a normal, trivalent cerium compound.

The Promising Synthetic Route Hydrothermal Synthesis of Non-Stoichiometric Cerium and Boron Containing Compounds and Characterization

Cerium, the most abundant rare earth element, and boron containing mineral (lithium tetraborate pentahydrate) were used for synthesizing rare earth borates. Alternatively, for preparing rare earth borates, hydrothermal technique can be used. The non-stoichiometric cerium and boron containing compounds were synthesized by hydrothermal method using cerium sulphate and lithium tetraborate pentahydrate in appropriate molar ratio. Characterizations were done by X-ray di raction, Fourier transform infrared spectroscopy, scanning electron microscopy/energy dispersive X-ray analysis, and thermogravimetric/di erential thermal analysis.

Variation of electronic transitions and reduction potentials of cerium(IV) complexes.

The trivalent compound K[Ce[N(SiHMe2)2]4] was synthesized and oxidized, providing a convenient route to the reported cerium(IV) compound Ce[N(SiHMe2)2]4. Protonolysis reactions of Ce[N(SiHMe2)2]4 with tert-butanol, substituted benzyl alcohols, and 2,6-diphenylphenol yielded the neutral tetravalent compounds Ce(O(t)Bu)4(py)2, Ce2(OCH2C6R5)8(thf)2 (R = Me, F), and Ce(Odpp)4 (dpp = 2,6-(C6H5)2-C6H3). Spectroscopic and electrochemical characterization of the monometallic cerium(IV) silylamide, alkoxide, and aryloxide compounds revealed variable ligand-to-metal charge transfer transitions and metal-based reduction potentials. Computational bonding analyses were performed to complement the physical characterization of the complexes.

Thermoelectric composite materials based on intermediate-valence cerium and ytterbium intermetallic compounds

An important thermoelectric characteristic-the power factor of composite thermoelectric materials—is calculated on the basis of performed measurements of the thermopower, electric conductivity, thermal conductivity, and reference data. The investigated composites consist of intermediate-valence CeNi and YbAl3 intermetallic systems and elementary metals, nickel and chromium. On account of the specific transport properties of a heterogeneous medium, it becomes possible to increase the value of the power factor in composites at a sufficiently low concentrations of rare-earth-element-based intermetallic compounds. The dependences of the composite-thermoelectric-material power factor on the temperature and the mass fraction of valence-instable components are obtained.

Magnetic properties of Tl9LnTe6, Ln = Ce, Pr, Tb and Sm

After introducing the thermoelectric properties of Tl10−xLnxTe6, the magnetic properties of the allegedly formally electron precise (Tl+)9Ln3+(Te2−)6 materials with Ln=Ce, Pr, Sm and Tb were investigated using a SQUID magnetometer. All the compounds were found to be paramagnetic with experimental magnetic moments of 2.07, 3.25 and 9.67μB for Tl9CeTe6, Tl9PrTe6 and Tl9TbTe6, respectively. The lower magnetic moment for the cerium compound points towards the possibility of the presence of mixed valent Ce in Tl9CeTe6.

Tuning Reactivity and Electronic Properties through Ligand Reorganization within a Cerium Heterobimetallic Framework

Cerium compounds have played vital roles in organic, inorganic, and materials chemistry due to their reversible redox chemistry between trivalent and tetravalent oxidation states. However, attempts to rationally access molecular cerium complexes in both oxidation states have been frustrated by unpredictable reactivity in cerium(III) oxidation chemistry. Such oxidation reactions are limited by steric saturation at the metal ion, which can result in high energy activation barriers for electron transfer. An alternative approach has been realized using a rare earth/alkali metal/1,1'-BINOLate (REMB) heterobimetallic framework, which uses redox-inactive metals within the secondary coordination sphere to control ligand reorganization. The rational syntheses of functionalized cerium(IV) products and a mechanistic examination of the role of ligand reorganization in cerium(III) oxidation are presented.

A Cerium(IV)–Carbon Multiple Bond

Straightforward access to a cerium(IV)-carbene complex was provided by one-electron oxidation of an anionic "ate" cerium(III)-carbene precursor, thereby avoiding decomposition reactions that plague oxidations of neutral cerium(III) compounds. The cerium(IV)-carbene complex is the first lanthanide(IV)-element multiple bond and involves a twofold bonding interaction of two electron pairs between cerium and carbon.

Investigation of AA2024-T3 surfaces modified by cerium compounds: A localized approach

The precipitation of cerium compounds on polished AA2024-T3 surfaces was investigated following an electrochemical and microstructural localized approach. It was found that cerium precipitation occurs on the entire surface covering intermetallic particles and the matrix as well. The matrix is the region where the precipitation of cerium is less favoured. The highest amount of cerium was observed on magnesium-rich intermetallic particles. The localized analyses suggest that precipitation of cerium on magnesium-rich intermetallic particles could happen following two mechanisms: the former based on a potential reversal of the intermetallic particles and the latter due to a partial magnesium dissolution.

Structural and Optical Behavior of nanoCe&lt;sub&gt;2&lt;/sub&gt;(SO&lt;sub&gt;4&lt;/sub&gt;)&lt;sub&gt;3&lt;/sub&gt;, CeF&lt;sub&gt;3&lt;/sub&gt; and CePO&lt;sub&gt;4&lt;/sub&gt;:Tb&lt;sup&gt;3+&lt;/sup&gt; Composites Embedded in PVOH Matrix

Embedding rare earth compounds and inorganic materials in polymer matrix are of great interest due to its various applications in sensors, optical batteries etc. The hydrated form of optical compounds possesses interest due to the possibility of crystal field effect on the electronic and magnetic field structure of the 4f shell. The stiochiometric cerium compounds have attracted attention due to its high temperature phase stability, high melting point, low thermal conductivity, optical fluorescence etc. In this paper we discuss the synthesis of cerrous sulphate Ce2(SO4)3, Cerium fluoride CeF3 and Cerium Phosphate doped with terbium Ce1-xPO4:Tbx composites and dependence of their structural and optical behavior on particle size. Cerrous sulphate exists in several phases, mostly hydrated. In polymer composite the anhydrous phase of Ce2(SO4)3 is observed. Also CePO4 composites crystallize to monazite phase. The significant changes in Ce3+ emission and absorption spectra are observed due to this phase change. Cerium fluoride composites prepared with different concentration show three absorption peaks around 237, 275 and 265nm. The lower concentration of CeF3 shows different absorption. CePO4 composites doped with various concentrations of terbium shows intense green emission at 543 nm and maximum energy transfer for 10 mol % of Tb3+. The Ce3+ emission is shifted to 337nm. The S.E.M. photograph of the composite shows well separated particles with average size 300nm.