Abstract: A CeCl 3 /H 2 O 2 aqueous solution treatment is assessed for the formation of conversion coatings on a AZ63 magnesium alloy. The coating composition and morphology are examined. The conversion coating appears to consist of a thin and cracked coating with ‘dry-mud’ morphology with large agglomerates over cathodic intermetallic particles. The corrosion resistance in NaCl solution has been investigated. The cerium-based conversion process improves the pitting potential of the alloy. Better corrosion resistant surfaces are obtained when the samples are submitted to repeated immersions in the conversion bath for 30 s up to 180 s of total immersion time. The thickness of the cerium conversion coating rapidly grows up in the first 30 s; afterwards it remains nearly constant. An increase of both hydrogen peroxide concentration and immersion time produces a worsening of the alloy to corrosion.

Abstract: This paper reviews progress in the development of oxygen storage materials for automotive exhaust catalysts. The research was mainly conducted as a study and development exercise in the author's laboratory in Japan. Ceria-lanthana solid solutions (CL) and the first generation of ceriazirconia solid solutions (CZ) were developed as excellent oxygen storage materials for automotive catalysts in the 1980s. These materials consist of ceria doped with less than 20 mol% of La4+ or Zr4+. An increase in oxygen defects in CL and CZ under reductive conditions is responsible for an enhanced oxygen storage capability on the cerium atoms. An accurate measure of the oxygen storage capacity (OSC) per cerium is very important for theoretical and practical treatments of the catalyst. The term “partial OSC” was introduced to describe this capacity and to differentiate it from the usual definition of the OSC, known also as the “total OSC”. After the development of CL and CZ, a new technology was developed to dissolve more than 20 mol% of zirconia in the ceria, allowing second generation CZ and third generation CZ (known as ACZ, which is doped with alumina) to be successfully developed in the 1990s. The partial OSC of these materials increases with increasing amounts of zirconia dissolved in the ceria, and also with decreasing material particle size after an engine durability test. In the case of ACZ, alumina was added to CZ based on the “diffusion barrier concept”, in which a diffusion barrier layer inhibits the coagulation of CZ and A when the material is required for duty at high temperature in air. Furthermore, the relationship between the total or partial OSC and the structure of the ceriazirconia solid solutions is explained in this paper. For ceriazirconia solid solutions composed of equimolar CeO2 and ZrO2(Ce/Zr=1), the total or partial OSC of the κ-phase CeZrO4, in which the cerium and zirconium ions are regularly distributed, was about twice as large as that of a ceriazirconia solid solution with a relatively irregular distribution of cerium and zirconium ions, and about five times larger than that of a mixture of ceria powder and zirconia containing only a small amount of ceriazirconia solid solution. It corresponds to about 89% of the theoretical maximum value. For a ceriazirconia solid solution composed of non-equimolar CeO2 and ZrO2(Ce/Zr ≠ 1), the partial OSC of a ceria-κ-phase solid solution with a zirconia content of between 30 and 50mol% is much higher than that of a ceriazirconia solid solution of the same zirconia content. The partial OSC of a κ-phase and zirconia mixed oxide, which is formed by reducing the material at 1200 °C, reaches a value above 0.20 mol-O2/mol-Ce (about 80% of the theoretical maximum value of the partial OSC), when the zirconia content is between 50 and 80 mol%. The Toyota Motor Corp. has put automotive three-way catalysts containing the first, second and third generations of CZ into practical use on a global basis.

Abstract: Oxidative coupling of methane (OCM) catalyzed by a series of rare earth oxides (REO) and mixtures of REO was studied using a continuous-flow quartz reactor at atmospheric pressure, 650–900 °C and variable gas flow rates of methane and air. The mixtures of the rare earth oxides available industrially (as intermediate products in commercial RE metal manufacturing) revealed good efficiency in the OCM. Catalytic performance of the light group of REO consisting of lanthanum, praseodymium, neodymium and cerium oxides with 5.5 wt.% of ceria is comparable to that of the individual oxides (samaria, ytterbia and europia). Addition of 10 wt.% of ceria to pure lanthana unexpectedly enhanced the efficiency of the catalyst. Raman spectroscopy as well as XRD suggested an oxide–oxide interaction between lanthana and ceria providing formation of additional oxygen vacancies.

Abstract: Synchrotron-based time-resolved x-ray diffraction (TR-XRD), x-ray absorption near edge spectroscopy (XANES), Raman spectroscopy (RS), and first-principles density functional (DF) calculations were used to study the structural and electronic properties of Ce–Ca mixed-metal oxides. The XRD results and DF calculations show that doping with calcium induces relatively minor variations (<0.05 A) in the cell dimensions of ceria. However, the presence of Ca leads to slightly distorted tetragonal structures, a substantial strain in the lattice of the oxide and a tendency to form O vacancies in an ideal Ce1−xCaxO2 solid solution. The two latter effects can be a consequence of the large number of oxygen neighbors that Ca is forced to have in Ce1−xCaxO2 and differences in the electronic charges of calcium and cerium cations. The Ce1−xCaxO2−x systems are not fully ionic. Cation charges derived from the DF calculations indicate that these systems obey the Barr model for charge redistribution in mixed-metal oxides. The Ca atoms in Ce1−xCaxO2−x are more electropositive than the cations in CaO, while the Ce cations of Ce1−xCaxO2−x are less electropositive than those of CeO2. These trends are consistent with XANES measurements at the Ca K- and Ce LIII-edges. The cation charge redistributions should be taken into consideration when explaining or predicting the chemical and catalytic properties of Ce1−xCaxO2−x. Ca induces structural and electronic perturbations on ceria quite different from those found after doping with Zr. The behavior of Ce1−xCaxO2−x illustrates the drastic effects that doping with an electropositive element can have on the properties of ceria.

Abstract: This study concerns the effect of lanthanum substitution by cerium on the catalytic activity of La1-xCexMnO3 catalysts and its relation to their physico-chemical characteristics. Samples of pure and cerium-substituted lanthanum manganese perovskites. La1-xCexMnO3 with x = 0.1-0.5 and LaCexMnO3 with x = 0.1, 0.2 and 0.3, were prepared by the citrate method and calcined 5 h at 973 or 1073 K. All samples were characterized by XRD, XPS and oxygen TPD and had their specific surface area (SSA) determined by nitrogen adsorption. The catalytic activity was determined, using 0.1 g catalyst, 1% methane in air at a flow rate of 75 ml/min (GHSV = 45,000 ml/g(cat) h). Substitution with cerium affects significantly the physico-chemical properties of individual compositions. It slows the rate of perovskite phase formation, increases the SSA, has an effect on thermal stability and modifies the oxygen desorption characteristics. However, these changes do not correlate in the expected way with changes in activity for methane combustion. Substitution with cerium or addition of cerium over the formal stoichiometry were positive only for x = 0.1 in samples calcined 5 h at 973 K. Higher x values resulted in lower activity. (C) 2002 Elsevier Science B.V. All rights reserved.

Abstract: Blueshifts in the ultraviolet absorption spectra have been observed in cerium oxide nanocrystallites. The mechanism of the absorption is a charge-transfer optical transition. The relationships among the blueshift, valence state of cerium ions, and the particle size are formulated. The blueshifts are well explained for diameters down to less than a few nanometers by the change in the electronic band structure.

Abstract: The results of preparation, characterization and in vitro bioactivity evaluation of phosphosilicate glasses based on Bioglass 45S5 (SiO2 45; Na2O 24.5; CaO 24.5; P2O5 6 wt%) doped during melting with (1.5–13.5 wt%) cerium dioxide (CeO2), has been reported. The choice of cerium was related to its low toxicity associated with bacteriostatic properties; cerium-doped bioactive glasses could be useful when implantation concerns local infected areas. The maximum value that permitted forming a homogeneous glass was 13.5 wt% and enabled us to get a better insight into CeO2 effect on the chemical behaviour of glasses. The as-quenched glasses were characterized by means of magnetic and spectroscopic measurements that revealed the prevailing presence of cerium (III). The bioactivity of the glasses was tested by soaking them in a simulated body fluid at 37 C, under continuous stirring. ICP measurements were carried out for ion concentration determinations and the solution/glass interface was investigated by scanning electron microscopy equipped with energy dispersive analyzer (SEM/EDS technique) to check morphological modifications; the solids were investigated by means of X-ray powder diffraction and IR techniques. The results indicated that at low cerium content the glass degradation and repolymerization gave rise to an internal silicon-based layer and an external calcium-phosphatebased layer formed on the glass surface; high cerium content retards the glass degradation and gave rise to cerium– phosphate layer instead of calcium one. The cerium was never found in solution. For the reacted glasses, in the external layer, at 10% and 13.5% CeO2 contents the molar ratio Ca/P were � 1 and 0.8 respectively and the molar ratio Ce/P was � 0.3 in both cases. On the surface of the glasses with the highest cerium content it could distinguish new regular aggregates mainly formed by cerium and phosphate (Ce=P � 3:5, Ca=P � 0:6). In the cerium-free glass and with low cerium content (1.5 wt%) the calculated Ca/P ratio was 1.67, as calculated for pure hydroxyapatite. At low cerium content (BG-1.5 Ce) the glass behaviour was strictly similar to that of Bioglass 45S5. 2003 Elsevier Science B.V. All rights reserved.

Abstract: The influence of calcination and redox cycles on the structural modification and redox properties of a ceria–zirconia mixed oxide of nominal composition Ce 0.6 Zr 0.4 O 2 were investigated by XRD and Rietveld refinement, by BET measurement, TPR and OSC analyses. The material is characterized by high total OSC and retains this property after several redox and calcination cycles up to 1273 K, despite the loss of porosity and the decrease of surface area. The Rietveld analysis of the diffractograms allowed to establish that at least two solid solutions are present in the as-prepared sample: a cubic phase, space group Fm-3m, richer in cerium compared to the nominal composition, a tetragonal phase (t′) richer in zirconium. The first redox treatment modifies the composition towards two different solid solutions with composition closer to the nominal one: a cubic Ce 0.65 Zr 0.35 O 2 and a tetragonal (t′) Ce 0.47 Zr 0.53 O 2 . No changes are noticed after four further redox cycles, while the successive calcination at 1273 K gives rise to a second cubic phase richer in cerium and to another tetragonal phase richer in zirconium. Noteworthy a further redox cycle reorganizes the sample to a similar situation as before the calcination treatment and this configuration is maintained for four redox cycles. This alternance is restored after calcination and successive four redox cycles. The total OSC measured after the above treatments is high and increases after the successive cycles.

Abstract: In this paper, we report on a relatively new cerium-doped scintillator—LaCl 3 for γ-ray spectroscopy Crystals of this scintillator have been grown using Bridgman method This material when doped with 10% cerium has high light output (∼50,000 photons/MeV) and fast principal decay time constant (∼20 ns) Furthermore, it shows excellent energy resolution for γ-ray detection For example, energy resolution as low as 32% (FWHM) has been achieved with 662 keV photons ( 137 Cs source) at room temperature Also, high timing resolution (264 ps—FWHM) has been recorded with LaCl 3 -PMT and BaF 2 -PMT detectors operating in coincidence using 511 keV positron annihilation γ-ray pairs Details of crystal growth, scintillation properties, and variation of these properties with cerium concentration are also reported

Abstract: The structural/morphological and oxygen handling properties of two high-surface-area Ce−Tb mixed oxides prepared by a microemulsion method with Ce/Tb atomic ratios of ca. 4 and 1 have been analyzed...

Abstract: A pigment with modified properties because of the powder size being below 100 nanometers. Blue, yellow and brown pigments are illustrated. Nanoscale coated, un-coated, whisker inorganic fillers are included. Stoichiometric and non-stoichiometric composition are disclosed. The pigment nanopowders taught comprise one or more elements from the group actinium, aluminum, antimony, arsenic, barium, beryllium, bismuth, cadmium, calcium, cerium, cesium, cobalt, copper, chalcogenide, dysprosium, erbium, europium, gadolinium, gallium, gold, hafnium, hydrogen, indium, iridium, iron, lanthanum, lithium, magnesium, manganese, mendelevium, mercury, molybdenum, neodymium, neptunium, nickel, niobium, nitrogen, oxygen, osmium, palladium, platinum, potassium, praseodymium, promethium, protactinium, rhenium, rubidium, scandium, silver, sodium, strontium, tantalum, terbium, thallium, thorium, tin, titanium, tungsten, vanadium, ytterbium, yttrium, zinc, and zirconium.

Abstract: Rare earth compositions comprising nanoparticles, methods of making nanoparticles, and methods of using nanoparticles are described. The compositions of the nanomaterials discussed may include scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). The nanoparticles can be used to make organometallics, nitrates, and hydroxides. The nanoparticles can be used in a variety of applications, such as pigments, catalysts, polishing agents, coatings, electroceramics, catalysts, optics, phosphors, and detectors.

Abstract: The interaction of sulfur with ceria under highly reducing conditions was investigated. The phase boundary between CeO 1.83 and Ce 2 O 2 S was determined for temperatures between 873 and 1073 K. This data was used to derive an empirical equation for Δ G f ° of Ce 2 O 2 S in this temperature range. This equation along with thermodynamic data for cerium oxides and sulfides obtained form the literature was used to predict Ce–O–S phase diagrams at 873 and 973 K. These phase diagrams provide insight into the mechanism of the deactivation of ceria-based catalysts by sulfur under reducing conditions.

Abstract: The microstructure and morphology of cerium oxide conversion coatings prepared under different deposition conditions were characterized by transmission electron microscopy (TEM). The coatings were formed by a spontaneous reaction between a water-based solution containing CeCl 3 and aluminum alloy 7075-T6 substrates. Microstructural characterization was performed to determine the crystallinity of the coatings and to obtain a better understanding of the deposition parameters on coating microstructure. The results of TEM imaging and electron diffraction analysis indicated that the as-deposited coating was composed of nanocrystalline particles of a previously unreported cerium compound. The particles of the coatings produced using glycerol as an additive were found to be much finer than those of the coatings prepared in the absence of glycerol. This indicates that glycerol may act as a grain refiner and/or growth inhibitor during coating deposition. After deposition, the coated panels were treated for 5 min in a phosphate sealing solution. The sealing treatment converted the as-deposited coating into hydrated cerium phosphate. Panels coated from solutions containing no glycerol followed by phosphate sealing performed poorly in salt fog tests. With glycerol addition, the corrosion resistance of the coatings that were phosphate sealed improved considerably, achieving an average passing rate of 85%.

Abstract: Polymer nanocomposite implants with nanofillers and additives are described. The nanofillers described can be any composition with the preferred composition being those composing barium, bismuth, cerium, dysprosium, europium, gadolinium, hafnium, indium, lanthanum, neodymium, niobium, praseodymium, strontium, tantalum, tin, tungsten, ytterbium, yttrium, zinc, and zirconium. The additives can be of any composition with the preferred form being inorganic nanopowders comprising aluminum, calcium, gallium, iron, lithium, magnesium, silicon, sodium, strontium, titanium. Such nanocomposites are particularly useful as materials for biological use in applications such as drug delivery, biomed devices, bone or dental implants.

Abstract: The adsorption and decomposition reactions of dimethyl methylphosphonate (DMMP) on cerium and iron oxides supported on aluminum oxide have been examined at 25 °C. The capacities of these solids for the decomposition of DMMP have been measured, and the identities and amounts of the decomposition products determined. The coimpregnated oxide formulations are significantly more reactive than alumina alone, and the current formulations are 2.5× more reactive at room temperature than any other metal oxide studied previously. A series of screening experiments show that the most active formulation is one containing 5 wt % iron and 7.5 wt % cerium. At 25 °C, Al2O3 shows a decomposition capacity of 317 μmol/g, while the alumina-supported iron and cerium oxide combination shows a decomposition capacity of more than 510 μmol/g. Formulations containing similar amounts of iron oxide or cerium oxide individually are more active than the unmodified alumina but less active than the coimpregnated oxide. The results show th...

Abstract: A corrosion-inhibiting pigment comprising a rare earth element and a valence stabilizer combinded to form a rare earth/valence stabilizer complex. The rare earth element is selected from cerium, terbium, praseodymium, or a combination thereof, and at least one rare earth element is in the tetravalent oxidation state. An inorganic or organic material is used to stabilize the tetravalent rare earth ion to form a compound that is sparingly soluble in water. Specific stabilizers are chosen to control the release rate of tetravalent cerium, terbium, or praseodymium during exposure to water and to tailor the compatibility of the powder when used as a pigment in a chosen binder system. Stabilizers may also modify the processing and handling characteristics of the formed powders. Many rare earth-valence stabilizer combinations are presented that can equal the performance of conventional hexavalent chromium systems.

Abstract: The blue-emitting phosphor cerium activated yttrium silicate, (Y1� mCem)2SiO5, was prepared via a novel synthesis technique called combustion synthesis. Combustion synthesis involves a highly exothermic redox reaction between metal nitrates and an organic fuel to produce a solid powder. The combustion synthesis parameter, the fuel-to-oxidizer ratio, has a direct effect on the physical properties of the as-synthesized powders due to the reaction temperature being dependent on the variation of this ratio. Thus, varying the fuel-to-oxidizer ratio produced powders with varying crystallite sizes, carbon contamination and surface areas, which in turn affected the luminescent efficiencies of the as-synthesized powders. The reaction temperature was found to reach a maximum with a 60% fuel rich mixture, with the powders exhibiting the largest crystallite sizes, smallest surface area and carbon contamination, and highest luminescent efficiency in the as-synthesized state. As-synthesized powders exhibit a high degree of porosity due to the large amount of gas to solid formed. To more accurately predict the specific surface areas of porous powders, the standard geometrical model used for gas absorption measurements was modified for porous particles and found to more accurately predict the specific surface area of highly porous powders. # 2002 Elsevier Science B.V. All rights reserved.

Abstract: Conversion coatings comprising a rare earth element and a valence stabilizer combined to form a rare earth/valence stabilizer complex are described for substrate metals. The rare earth element is selected from cerium, praseodymium, terbium, or combinations thereof, and at least one rare earth element is in the tetravalent oxidation state. The coating bath may also contain a preparative or solubility control agent. The oxidized cerium, praseodymium or terbium is present in the coating in a “sparingly soluble” form. The valence stabilizers can be either inorganic or organic in nature. A number of cerium, praseodymium, or terbium/valence stabilizer combinations are presented that can equal the performance of conventional hexavalent chromium systems.