Cerium Dioxide Powders Research Articles

Antioxidant Activity of Ablated Cerium Dioxide Nanoparticles in an Oxidative Photocatalytic Reaction

Purpose of the study. Study and comparison of the antioxidant properties of ablated cerium dioxide nanoparticles in the oxidative photocatalytic degradation of methylene blue ablated from imported and laboratory targets.Methods. By pressing cerium dioxide powder and annealing the pressed target, laboratory targets were obtained, which were subjected to the laser ablation process. Atomic force microscopy was used to characterize cerium dioxide nanoparticles. The spectrophotometric method was used to study the antioxidant properties of cerium dioxide nanoparticles. The antioxidant activity of ablated nanoparticles obtained from two targets in an oxidative photocatalytic reaction has been studied and compared. Cerium dioxide nanoparticles with high antioxidant activity were obtained by laser ablation.Results. Using atomic force microscopy, the average limiting sizes of non-centrifuged and centrifuged samples at a speed of 1000 rpm of ablated cerium dioxide nanoparticles were established. It was found that the elemental composition of the cerium dioxide powder, from which the laboratory target was pressed, and the elemental composition of the imported target are the same, and the percentage of impurities in them is within the limits acceptable for the laser ablation process. The antioxidant activity of cerium dioxide nanoparticles ablated from laboratory and imported targets was compared. The data obtained in the course of the study indicate that cerium dioxide nanoparticles obtained from a laboratory target exhibit the highest antioxidant activity.Conclusion. Cerium dioxide nanoparticles subjected to laser ablation from a laboratory target are nanomaterials that are antioxidants that inactivate reactive oxygen species in a photocatalytic reaction. The antioxidant activity of cerium dioxide nanoparticles obtained from a laboratory target is not lower, but higher than that of nanoparticles obtained from an imported target. These properties of cerium dioxide nanoparticles are due to the presence of crystalline defects such as oxygen vacancies on their surface.

Three-dimensional numerical simulation of heating and melting behaviors of cerium oxide powders in radio frequency thermal plasma

The present study aims at the numerical simulations of the melting process of cerium oxide particles in RF thermal plasma. The physical model and the calculating method were described firstly; the interaction between cerium oxide particles and plasma was analyzed; specific attention was given to the effects of particle initial size, injection velocity on the particle melting and trajectory in plasma. The influence of the temperature field and velocity field distribution of the plasma around the particle trajectory on the melting effect is analyzed, and the relationship between the heat absorption efficiency of the particles and the particle size reduction process is further determined. It is also found that there exists an optimal particle initial injection velocity which led to a more concentrated final particle size distribution and a more significant reduction of particle size. The results could provide effective guidance for understanding the plasma spheroidization process of uranium dioxide and cerium dioxide powder particles.

High Pressure Brillouin Spectroscopy and X-ray Diffraction of Cerium Dioxide

Simultaneous high-pressure Brillouin spectroscopy and powder X-ray diffraction of cerium dioxide powders are presented at room temperature to a pressure of 45 GPa. Micro- and nanocrystalline powders are studied and the density, acoustic velocities and elastic moduli determined. In contrast to recent reports of anomalous compressibility and strength in nanocrystalline cerium dioxide, the acoustic velocities are found to be insensitive to grain size and enhanced strength is not observed in nanocrystalline CeO. Discrepancies in the bulk moduli derived from Brillouin and powder X-ray diffraction studies suggest that the properties of CeO are sensitive to the hydrostaticity of its environment. Our Brillouin data give the shear modulus, = 63 (3) GPa, and adiabatic bulk modulus, = 142 (9) GPa, which is considerably lower than the isothermal bulk modulus, 230 GPa, determined by high-pressure X-ray diffraction experiments.

Spectroscopic and structural properties of CeO2 nanocrystals doped with La3+, Nd3+ and modified on their surface with Ag nanoparticles

The purpose of this work is to present our efforts focused on applications of chemical synthesis of nanocrystalline cerium dioxide (CeO2) powders doped with La3+ ions and CeO2:Nd3+ modified, on their surface, with Ag nanoparticles (NPs). The synthesized powders were examined by X-ray powder diffraction (XRD), absorption, emission spectroscopy, scanning electron (SEM) and atomic force microscopy (AFM). The relations between crystallographic properties and stability of CeO2 compounds doped by La ions and surface-modified by Ag were studied. XRD patterns revealed that all studied samples are single-phase and crystallized in the cubic fluorite-type structure, in space group Fm-3m. The average crystallite sizes estimated by Rietveld method of series: La-doped CeO2 were in the range of 7–14 nm, and CeO2:1%Nd3+/n-Ag (n: 1- 5wt.%) were found to be in the range of 29–34 nm, respectively. The lattice parameter a for La-doped CeO2 powders varying from 5.416 to 5.482 Å with increasing content of La3+ ions from 0 to 20wt.%, respectively. For series of CeO2:Nd3+/n-Ag materials lattice parameter a was at the same level and in accordance with the standard value a0 = 5.411 Å (ICDD - 43-1002). The SEM and AFM observations depicted the grainy structure of all obtained CeO2-powder samples. The estimated grain size ranged from 50 to 500 nm. The diverse grain shapes and packing was remarked in the samples. According to our knowledge, the relationship between the structural, spectroscopic and morphological characteristics of CeO2 samples was presented in this work for the first time.

"Green" Synthesis of Cerium Oxide Particles in Water Extracts Petroselinum crispum

Background:Synthesis of metal oxides nanoparticles with specific morphology and size has become the subject of many experimental protocols. Biosynthesis of the nanoparticles using plants is more preferable than physical and chemical methods because of its environmental friendliness.Objective:The purpose of this study was to report the potential for green synthesis of cerium oxide nanoparticles using plant extracts with a high content of phenolic metabolites.Methods:We have synthesized the CeO2 nano- and microparticles using Petroselinum crispum aqueous extract. The particles were characterized by UV-visible spectroscopy, IR spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM) and dynamic light scattering analysis. For detection the reduction capacity of the extract the evaluation of total phenolic and flavonoid content as well as high-performance liquid chromatography-mass spectrometry (HPLC-MS) were performed. Biological activity of the particles was identified by bioluminescent tests and bio tests with Triticum vulgare.Results:Testing on T. vulgare showed that biogenic cerium dioxide powders stimulated the growth of up to 5-11,4% relative to intact samples, significantly increased the length of the leaves of seedlings and the root length. When seedings were exposed to the biosynthesized CeO2 particles, the level of chlorophylls was more stable and even slightly higher than control. Noticeable protective properties of the biosynthesized CeO2 powder under oxidation conditions were observed on the plant T. vulgare after a brief exposure (from 4 to 24 h).Conclusion:Thus, biogenic CeO2 can be potentially utilized in oxidative damage protection of agricultural plants.

A simple synthesis of the refractory ceramic sulfide CeS by electron beam irradiation

AbstractA new, relatively fast and simple synthesis of the refractory sulfide CeS using electron beam irradiation has been developed. Differently from the most common procedures involving highly reactive and/or toxic precursors such as cerium hydride and carbon disulfide, the approach here presented is based on the electron beam irradiation of pellets composed of a mixture of cerium sesquisulfide, cerium dioxide and graphite powders, i.e., nontoxic and nonreactive materials in ambient conditions that do not need any special caution during their use. CeS with a purity ≥98 wt% has been obtained, being Ce2O2S the impurity and whose amount can be lowered by annealing on a graphite surface.

An original precipitation route toward the preparation and the sintering of highly reactive uranium cerium dioxide powders

The preparation of dense U1−xCexO2 mixed dioxides pellets was achieved from the initial precipitation of highly reactive precursors. In a first step, a wet chemistry route, based on the mixture of U4+ and Ce4+ in acidic solution with large excess of NH4OH, was set up to reach the precipitation of the cations. The solid phase was then dried under vacuum to avoid aggregation phenomena. Further characterization of the powders by XRD, EDS and TEM revealed the formation of hydrated U1−xCexO2⋅nH2O that probably resulted from the aging of hydroxide compounds. Also, microscopy investigations evidenced the nanosized character of the powder which was associated to high values of specific surface area, typically in the 100–150m2g−1 range.The behavior of U1−xCexO2⋅nH2O versus temperature was investigated in a second part. If the increase of the heat temperature allowed one to observe an improvement of the crystallization state linked with the growth of crystallites, it was also accompanied by a strong decrease of the powders reactivity. On this basis, sintering tests were conducted in reducing atmosphere on the compounds as prepared. Dilatometry experiments indicated a low densification temperature compared to other ways of preparation reported in the literature. Also, the pellets prepared after firing at different temperatures (1350–1550°C) showed that a wide range of microstructures was achievable. Particularly, bulk materials with densities of 90–95% of the calculated value could be prepared with average grain size ranging from around 100nm to more than 5μm. This simple process of elaboration of dense materials from highly reactive hydrated oxide precursor thus appears as a very interesting way to prepare actinide oxides materials.

Growth and optical properties of cerium dioxide nanocrystallites prepared by coprecipitation routes

Nanosized cerium dioxide (CeO2) powders have been synthesized using coprecipitation methods and cerium nitrate hexahydrate (Ce(NO3)3·6H2O) as the starting material. The growth and optical properties of nanosized CeO2 powders were investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), nano-beam electron diffraction (NBED), high resolution TEM (HRTEM), and ultraviolet–visible (UV–vis) absorption spectrophotometry. The XRD result shows that the dried CeO2 precursor powders (both before and after calcination at various temperatures and times) contained a single crystalline phase of CeO2. In the dried precursor powders, the crystallites of CeO2 measured 10.4nm and 66.8nm before and after calcination at 1273K for 240min, respectively. The indirect band gap energy (Ei) of CeO2 decreased from 3.03eV to 2.68eV as the crystallite size increased from 10.4nm to 66.8nm, whereas the direct band gap energy (Ed) of CeO2 also decreased from 3.79eV to 3.38eV.

Preparation, characterisation and dissolution of a CeO2 analogue for UO2 nuclear fuel

The behaviour of spent nuclear fuel under geological conditions is a major issue underpinning the safety case for final disposal. This work describes the preparation and characterisation of a non-radioactive UO2 fuel analogue, CeO2, to be used to investigate nuclear fuel dissolution under realistic repository conditions as part of a developing EU research programme. The densification behaviour of several cerium dioxide powders, derived from cerium oxalate, were investigated to aid the selection of a suitable powder for fabrication of fuel analogues for powder dissolution tests. CeO2 powders prepared by calcination of cerium oxalate at 800°C and sintering at 1700°C gave samples with similar microstructure to UO2 fuel and SIMFUEL. The suitability of the optimised synthesis route for dissolution was tested in a dissolution experiment conducted at 90°C in 0.01M HNO3.

ChemInform Abstract: Characterization of a Cerium Dioxide Powder from Its Equilibrium with Water Vapour.

Abstract The equilibrium between water and a cerium dioxide powder was studied by means of thermogravimetry between 373 and 573 K. The isotherms can be interpreted by the additive contribution of water adsorbed on two distinct sites which differ in their standard enthalpy of fixation and their relative population. The results agree with the model water is fixed on the ceria surface through direct bonds to cerium atoms and by hydrogen bonding to hydroxyl groups located in the micropores. The latter sites disappear following calcination at high temperature. This is confirmed by transmission electron microscopy photographs and nitrogen adsorption measurements.

From cerium oxycarbonate to nanostructured ceria: Relations between synthesis, thermal process and morphologies

Nanostructured cerium dioxide rods and powders were synthesized via two sol–gel routes, respectively at 200 °C, and in room conditions without any thermal treatment. The initial solution involved nitrates, urea and polyvinyl-pyrrolidine in aqueous medium. In a first step, we synthesized cerium oxycarbonate by heating the solution at 80 °C: crystalline grains of (Ce 3+) 2O(CO 3) 2, H 2O phase were obtained in the form of elongated crystalline spindles (5–10 μm long). Thermal decomposition of these spindle-like crystals gave rise to smaller elongated rods of nanostructured ceria. A second sol–gel route allowed obtaining nanosized ceria, after NH 4OH addition and without any heating process. X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses allowed characterizing the oxycarbonate polycrystalline samples and the two types of nanocrystalline ceria phases.

Experimental Study on Cryogenic Polishing Single Silicon Wafer with Nano-Sized Cerium Dioxide Powders

Cryogenic polishing single silicon wafer with nano-sized CeO2 abrasives can be known as cryogenic fixed abrasives CMP (CFA-CMP). The abrasive slurry was made of nano-sized CeO2 particles dispersed in de-ionized water with a surfactant and the polishing slurry froze to form cryogenic polishing pad. Then the polishing tests of the blanket silicon wafers in the presence of the cryogenic polishing pad containing the nano-particulates were carried out. The morphologies and surfaces roughness of the polished silicon wafers were observed and examined on an atomic force microscope (AFM). The results show that a super smooth surface with roughness of 0. 293 nm is obtained within 5000 nm× 5000 nm and the removal of material is dominated by plastic flowage.

Optimal Conditions for Preparing Ultra-Fine CeO 2 Powders in A Submerged Circulative Impinging Stream Reactor

Abstract Cerium carbonate powders were produced in a submerged circulation impinging stream reactor (SCISR) from Ce(NO 3) 3 · 6H 2O. NH 4HCO 3 was used as a precipitant in the reaction. Cerium carbonate powders were roasted to produce ultra-fine cerium dioxide (CeO 2) powders. The optimal conditions of such production process were obtained by orthogonal and one-factor experiments. The results showed that ultra-fine and narrowly distributed cerium carbonate powders were produced under the optimal flowing conditions. The concentrations of Ce(NO 3) 3 and NH 4HCO 3 solutions were 0.25 and 0.3 mol · L -1, respectively. The concentration of PEG4000 added in these two solutions was 4 g · L -1. The stirring ratio, reaction temperature, feeding time, solution pH, reaction time and digestion time were 900 r · min -1, 80 °C, 20 min, 5∼6, 5 min and 1 h, respectively. The final product, CeO 2 powders, was obtained by roasting the produced cerium carbonate in air for 3 h at 500 °C. The finally produced CeO 2 powders were torispherical particles with a narrow size distribution of 0.8∼2.5 μm. The crystal structure of CeO 2 powders belonged to cubic crystal system and its space point group was O 5 H-F M3M. Under optimal conditions, powders produced by SCISR were finer and more narrowly distributed than that by Stirred Tank Reactor (STR).

Effects of the synthesis methods on the physicochemical properties of cerium dioxide powder

The CeO 2 powders were synthesized using several different methods and characterized by X-ray diffraction (XRD), laser diffraction particle size analyzers, BET surface area analysis and transmission electron microscopy (TEM). The results show that CeO 2 crystals prepared by different methods possess all the same fluorite structure. On the other hand, the physicochemical properties including particle size, cubic specific surface area, fluidity and density of cerium dioxide powder depend on the different synthesis procedures. This means that the properties requested for industrial applications can be tuned by generative methods. The calcined temperature is another very important parameter for the preparation of monodisperse superfine powder.

CeO<sub>2</sub> 微粒子の緻密化における焼結曲線の屈曲

The sintering behavior of fine cerium dioxide (CeO2) powders from direct homogeneous precipitation using hexamethylenetetramine was examined by monitoring the continuous shrinkage of powder compacts during heating from 30 to 1700°C. Depending on the pre-heat-treatment condition of powders, the sintering curves of two starting powder compacts showed different shrinkage behavior. A powder heated at 650°C showed a normal sintering curve (S-type) with the highest shrinkage rate at around 1000°C. However, a powder heated at 350°C showed an extremely high shrinkage rate with inflection points in the sintering curve at 1300-1500°C. We analyzed the microstructure, pore structure and the secondary particle size of sintered bodies after sintering curve inflection. Grains 0.08 μm in size were roughly packed one another in the microstructure at 900°C after local sintering in the interior part of aggregated particles. The rapid shrinkage after rearrangement started at higher temperatures of 1300-1500°C, inducing large grain growth. The combination of rapid rearrangement and grain growth, which resulted in a sintering curve inflection, was assumed at temperatures as high as 900-1500°C.

Structural and thermal investigations on cerium oxalate and derived oxide powders for the preparation of (Th,Ce)O 2 pellets

Ce 2(C 2O 4) 3· nH 2O powder was prepared by adding oxalic acid to a cerium nitrate solution. Cerium oxalate was identified by chemical and thermal analysis (DTA/TGA). Cerium oxalate powder was calcined to oxides at different temperatures and the powder properties (specific surface area, particle size distribution, mean particle size, bulk and tap densities) of these oxides were determined. X-ray diffraction (XRD) patterns of cerium dioxide powders obtained at different calcination temperatures were evaluated. The crystallite size was calculated both from XRD data using Sherrer's equation and from specific surface area data for each temperature. (Th 0.95Ce 0.05)O 2 powder was prepared by mixing the binary oxides. The compacted pellets were calcined in air at 1050 °C. The XRD patterns of these pellets were evaluated to characterise the formed solid solution.

Synthesis of Ultrafine Ceria Powders by Mechanochemical Processing

The synthesis of ultrafine cerium dioxide (CeO2) powders via mechanochemical reaction and subsequent calcination was studied. Anhydrous CeCl3 and NaOH powders, along with NaCl diluent, were mechanically milled. A solid‐state displacement reaction—CeCl3+ 3NaOH → Ce(OH)3+ 3NaCl—was induced during milling in a steady‐state manner. Calcination of the as‐milled powder in air at 500°C resulted in the formation of CeO2 nanoparticles in the NaCl matrix. A simple washing process to remove the NaCl yielded CeO2 particles ∼10 nm in size. The particle size was controlled in the range of ∼10–500 nm by changing the calcination temperature.

The study of process production of polishing powder based on cerium dioxide

Finely divided cerium dioxide powder is an excellent polishing agent for optical glass under intensive processing conditions. Cerium dioxide powder was produced from a mixture of rare earth carbonates by conversion to oxides, reacting with acid to separate a sediment of CeO(OH) 2 from solution containing the trivalent rare earth ions, washing the sediment, and drying and annealing it to produce finely divided CeO 2. Physical and chemical investigations of each stage of the processing were performed. A relation was established between the properties of CeO(OH) 2 (such as degree of fineness and crystal structure) and the properties of the REE oxides that were used. It was shown that very fine REE oxides generate fine CeO(OH) 2. It was also shown that to obtain CeO 2 powder with high specific surface area and perfect crystal structure, the CeO(OH) 2 must be annealed in two steps: (1) dehydration of intermediate CeO 1.5(OH) to produce very fine powder, and (2) dehydration at 800–1050°C.

Kinetics of CeO2 Surface Area Reduction in a Mixture of HCI, H2O, and O2

Surface area reduction of a cerium dioxide powder is studied at 900 K in a HCI, H2O, and O2 atmosphere. The rate of surface area decrease is determined as a function of the surface chloride content and of the partial pressure of hydrogen chloride. It is shown that particle growth occurs due to the surface diffusion of cerium and hydroxyl ions, which results from hydrogen chloride adsorption. Adsorbed chloride ions react to give gaseous chlorine. The rate‐determining step of the process of initial coarsening is hydrogen chloride fixation at the surface of cerium dioxide particles.

Characterization of a cerium dioxide powder from its equilibrium with water vapour

The equilibrium between water and a cerium dioxide powder was studied by means of thermogravimetry between 373 and 573 K. The isotherms can be interpreted by the additive contribution of water adsorbed on two distinct sites which differ in their standard enthalpy of fixation and their relative population. The results agree with the model water is fixed on the ceria surface through direct bonds to cerium atoms and by hydrogen bonding to hydroxyl groups located in the micropores. The latter sites disappear following calcination at high temperature. This is confirmed by transmission electron microscopy photographs and nitrogen adsorption measurements.