Nano CeO2 Research Articles

Hydrothermal Synthesis of Single Crystalline Nano CeO2 and Its Structural, Optical, and Electronic Characterization

Single crystalline CeO2 powder was prepared by precipitation-hydrothermal technique. The hydrothermal treatment temperature and time were the two parameters chosen to observe their effect on nature of ceria. The synthesized samples were characterized for structural, optical, and electrical properties using X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscope (SEM), transmission electron microscope (TEM), ultraviolet-visual (UV-Vis), and photoluminescence (PL) spectroscopy. Single crystalline CeO2 nanoparticles of about 5 to 9 nm were formed when the precipitated precursor was heated at 200°C for 3 h. The mean crystalline diameter (MCD) obtained from XRD using Scherrer's formula matched with the particle size as observed from TEM confirming the single crystalline nature of ceria. The crystallinity of sample increased with increase in reaction temperature and time while the lattice parameters decreased, as observed from XRD data. Observation from the micrographs obtained from SEM indicated the decrease in particle size as well agglomeration with increase in reaction temperature which was also confirmed by blue shift in absorption spectra of the sample obtained at 200°C. Room temperature PL spectra of CeO2 nano crystals, excited at wavelength 300 nm, showed emission at 400 and 360 nm corresponding to CeO2 synthesized at temperatures 160°C, and 200°C with corresponding E g values of 2.94 eV and 3.60 eV, respectively.

Three dimensional finite element modeling of laser solid freeform fabrication of cobalt alloy stellite 21 with 1.5% nano[formula omitted] on the low carbon steel 1015

Our purpose is to model the multilayer laser solid freeform fabrication (LSFF) process for the material properties of low carbon steel 1015 for workpiece and cobalt alloy stellite 21 with 1.5 wt.% nano CeO2 as the powder particles. In this paper, transient heat transfer and mass transfer equations in laser solid freeform fabrication process are solved by Finite Element Method (FEM). In this approach, the geometry of the deposited material, temperature and thermal stress fields across the process area are predicted. For each layer the clad height is computed and computations are done by the use of MATLAB and COMSOL software.

Assessing exposure, uptake and toxicity of silver and cerium dioxide nanoparticles from contaminated environments

The aim of this project was to compare cerium oxide and silver particles of different sizes for their potential for uptake by aquatic species, human exposure via ingestion of contaminated food sources and to assess their resultant toxicity. The results demonstrate the potential for uptake of nano and larger particles by fish via the gastrointestinal tract, and by human intestinal epithelial cells, therefore suggesting that ingestion is a viable route of uptake into different organism types. A consistency was also shown in the sensitivity of aquatic, fish cell and human cell models to Ag and CeO2 particles of different sizes; with the observed sensitivity sequence from highest to lowest as: nano-Ag > micro Ag > nano CeO2 = micro CeO2. Such consistency suggests that further studies might allow extrapolation of results between different models and species.

Preparation of CeO<sub>2</sub> Nanophotocatalyst Using Precipitation Method

Ceria (CeO2) nano particles were synthesized by new technique named a two-stage precipitation The cerium(III) nitrate hexahydrate, hydrogen peroxide and ammonia were used as the raw materials. The Ce 3+ ions were oxidized to Ce 4+ ions by hydrogen peroxide, the Ce 4+ were then precipitated by ammonium hydroxide to form the precursor in the chemical reaction process. The CeO 2 nano particles were obtained by the heat treatment of the precursor for 2 hrs. at 400∼800°C after drying treatment. The phase composition and the crystal structure of the CeO2 nano particles were studied by XRD (X-ray diffraction) patterns measured at room temperature. The crystal structure of CeO 2 is cubic system. It's space group is O 5 h Fm3m. The morphogenesis of CeO2 particles is ball-like particle observed by scanning electron microscopy (SEM). The average grain size of CeO2 nano crystal was identified by transmission electron microscopy (TEM) to be about 10 nm by heating treatment for 2 hrs at 400°C. The result of ultraviolet radiation-visible light photometer measurement shows that the ultraviolet absorption capability of CeO 2 particles depends on the grain size. The CeO 2 nanoparticle prepared by the process has better ultraviolet absorption property than that of commercial ceria microparticles. The CeO 2 nano particles exhibited photocatalytic activity for the decomposition of methyl orange under UV light irradiation.

Novel wet-chemical synthesis and characterization of nanocrystalline CeO2 and Ce0.8Gd0.2O1.9 as solid electrolyte for intermediate temperature solid oxide fuel cell (IT-SOFC) applications

Novel wet-chemical methods of synthesis have been adopted to synthesize nano-crystalline CeO2 and Gd-substituted compositions aiming to explore an efficient oxide ion conducting solid electrolyte for intermediate temperature solid oxide fuel cell (IT-SOFC) applications. Nano-crystalline CeO2 powders were synthesized by combustion method using redox mixture of cerric ammonium nitrate or cerium nitrate and maleic acid or 1,3-dimethylurea and compared with high surface area CeO2 powders prepared by hydrothermal technique with microwave precipitated precursor from aqueous solutions of (NH4)2Ce(NO3)6 and urea. The grain size achieved by the hydrothermal technique is ∼7 nm which is smaller than that of commercial nano CeO2 powders. Conventional or microwave sintering was used to prepare dense Ce0.8Gd0.2O1.9 pellets from the ceria powders made of redox mixture of cerium nitrate, 1,3-dimethylurea (DMU) and Gd2O3 as the starting ingredients. The samples were characterized by X-ray diffractometry (XRD), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), and ac impedance spectroscopy. The ionic conductivity measured for the pellet sintered at 1400 °C is 1 × 10−2 and 2.4 × 10−2 S/cm at 700 °C and 800 °C respectively.

Cyclic Oxidation Behavior of Electrodeposited Ni3Al–CeO2Base Coatings at 850°C

The cyclic-oxidation behavior of electrodeposited pure, nano CeO2 (9–15 nm)- and micron CeO2 (5 μm)-modified Ni3Al coatings on Fe–Ni–Cr substrates have been investigated at 850°C for periods up to 1000 hr. All the coatings showed good oxidation resistance in the early stage, but decreased oxidation protection during the intermediate stage of exposure. The formation of slow-growing γ-Al2O3 scales provided the coatings with good oxidation resistance in the early stage. However, a high volume fraction of pores in the coatings decreased oxidation resistance in the intermediate stage by forming oxidized channels between the pores. After long-term exposure, however, the pores in the coatings were healed by coating–substrate interdiffusion, and an improvement in cyclic-oxidation resistance was observed. The CeO2 particles in the coating affected the stability of the protective oxide scale and the pore-healing behavior. The most significant effect was from nano size CeO2 particles, which improved the stability of the protective oxide scale but retarded the rate of pore healing.