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Nanometric Size (nanometric + size)
Selected AbstractsPreparation of Lanthanide Hydrides of Nanometric Size by the Catalytic MethodCHINESE JOURNAL OF CHEMISTRY, Issue 11 2002Yin-Heng Fan Abstract Rare-earth metals were hydrogenated in the presence of TICI4 catalyst in tetrahydrofuran (THF) at 45 °C under normal pressure. Transmission electron micrographs showed that the resulting lanthanide hydrides were in the form of nanoparticles. The rate of hydrogenation decreased with increasing atomic number of the rare-earth elements. [source] Evaluation of RuxWySez Catalyst as a Cathode Electrode in a Polymer Electrolyte Membrane Fuel CellFUEL CELLS, Issue 1 2010K. Suárez-Alcántara Abstract The oxygen reduction reaction (ORR) on RuxWySez is of great importance in the development of a novel cathode electrode in a polymer electrolyte membrane fuel cell (PEMFC) technology. The RuxWySez electrocatalyst was synthesised in an organic solvent for 3,h. The powder was characterised by transmission electron microscopy (TEM), and powder X-ray diffraction (XRD). The electrocatalyst consisted of agglomerates of nanometric size (,50,150,nm) particles. In the electrochemical studies, rotating disc electrode (RDE) and rotating ring-disc electrode (RRDE) techniques were used to determine the oxygen reduction kinetics in 0.5,M H2SO4. The kinetic studies include the determination of Tafel slope (112,mV,dec,1), exchange current density at 25,°C (1.48,×,10,4,mA,cm,2) and the apparent activation energy of the oxygen reaction (52.1,,,0.4,kJ,mol,1). Analysis of the data shows a multi-electron charge transfer process to water formation, with 2% H2O2 production. A single PEMFC with the RuxWySez cathode catalysts generated a power density of 180,mW,cm,2. Performance achieved with a loading of 1.4,mg,cm,2 of a 40,wt% RuxWySez and 60,wt% carbon Vulcan (i.e. 0.56,mg,cm,2 of pure RuxWySez). Single PEMFC working was obtained with hydrogen and oxygen at 80,°C with 30,psi. [source] Synthesis and Characterization of Nanostructured Cerium Dioxide Thin Films Deposited by Ultrasonic Spray PyrolysisJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2010Mario F. García-Sánchez Nanostructured thin films of cerium dioxide have been prepared on single-crystalline silicon substrates by ultrasonic spray pyrolysis using cerium acetylacetonate as a metal,organic precursor dissolved in anhydrous methanol and acetic acid as an additive. The morphology, structure, optical index, and electrical properties were studied by X-ray diffraction, scanning electron microscopy, atomic force microscopy, ellipsometry, and impedance spectroscopy. The use of additives is very important to obtain crack-free films. The substrate temperature and flow rate was optimized for obtaining smooth (Ra<0.4 nm), dense (n>2), and homogeneous nanocrystalline films with grain sizes as small as 10 nm. The influence of thermal annealing on the structural properties of films was studied. The low activation energy calculated for total conductivity (0.133 eV) is attributed to the nanometric size of the grains. [source] Aggregated structure of flocculated asphaltenesAICHE JOURNAL, Issue 1 2001Theophylaktos G. Savvidis Many petroleum processing problems are related to asphaltene flocculation. A detailed understanding of the colloidal structure of asphaltenes in oild can play a decisive role in improving processing facilities and/or operating conditions. The structure of the flocculated part of the asphaltenes of a crude oil far above the flocculation threshold was studied to understand its links with macroscopic phase separation. Asphaltene filtrations were performed using filter pore sizes from 0.025 to 10 ,m. According to small angle X-ray scattering (SAXS) spectra and density measurements, these extracted asphaltenes in toluene solutions did not have any physical differences. Measurements of nanometric sizes for the dispersed particles after dissolution in toluene show that micron-size flocculated asphaltenes are strongly aggregated structures. Therefore, filtration experiments separate asphaltenes corresponding powders show spherically shaped aggregates of micron size. SAXS and USAXS techniques were used to investigate the internal structure of the asphaltene powder. The aggregates are clearly a compact organization of asphaltenic material. This dense structure explains why flocculated asphaltenes are subject to sedimentation, which induces the visible macroscopic phase separation. [source] | ||||||||||