Search results for "Thermal"
showing 10 items of 3576 documents
Morphology and structure of electrospun CoFe2O4/multi-wall carbon nanotubes composite nanofibers
2010
CoFe2O4/multiwall carbon nanotubes (MWCNTs) composite nanofibers were produced by electrospinning a dispersion of MWCNTs in a solution of polyvinylpyrrolidone, iron(III) nitrate nonahydrate, cobalt (II) acetate tetrahydrate, absolute ethanol and H2O. Microstructure was examined by scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HR-TEM). Thermal behaviour was studied by thermogravimetry and differential thermal analysis (TG-DTA) and phase analysis of calcined fibers was performed by X-ray diffraction (XRD). Upon thermal treatment at 450 °C defect-free, randomly oriented composite fibers having a mean diameter of 60 ± 10 nm were obtained. The results s…
Structural and Electric Properties of Sodium Lithium Niobate Ceramic Solid Solution Li0.08Na0.92NbO3
2011
A lead-free solid solution Li0.08Na0.92NbO3 was prepared by a two-stage hot-pressing technology. The structure and morphology of Li0.08Na0.92NbO3 were characterised by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The studies of electric conductivity were performed depending on temperature and frequency of electric measuring field on heating and cooling processes. These measurements revealed that the a.c. conductivity changed with the frequency according to the formula: σ(ω)=σ dc +Aω n where n < 1. These results were discussed considering the conduction mechanism as a type of polaron hopping.
Synthesis of bulk FeAl nanostructured materials by HVOF spray forming and Spark Plasma Sintering
2006
Abstract This paper examines the efficiency of two consolidation processing techniques: High Velocity Oxy-Fuel (HVOF) spray forming and Spark Plasma Sintering (SPS) to obtain bulk nanostructured materials from an Y 2 O 3 reinforced Fe–40Al (at.%) milled powder. The microstructures of the sintered end-products were characterized by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) in order to gain new insights in their microstructure formation mechanisms. HVOF spray forming is more effective to retain fine nanograins, in particular within retained unmelted powder particles. The drawbacks of this technique are that it inevitably leads to a high fraction of porosity…
Tritium distribution and chemical forms in the irradiated beryllium pebbles before and after thermoannealing
2011
Abstract Beryllium pebbles are foreseen as a neutron multiplier in the tritium breeding blanket of the future fusion devices. Tritium inventory in the beryllium as a result of neutron-induced transmutations is a significant safety and technological issue for the operation of the breeding blanket. In this study, beryllium pebbles from 3 different irradiation experiments: BERYLLIUM, EXOTIC 8/3-13 and PBA, performed at High Flux Reactor HFR have been investigated. The distribution of tritium in the bulk of the pebbles and the abundance ratios of chemical forms of tritium T 0 , T + and T 2 have been analysed before and after the different thermo-annealing experiments. In order to determine the …
Rare earth doped glass–ceramics containing NaLaF4 nanocrystals
2016
Abstract Oxyfluoride glasses 16Na 2 O–9NaF–5LaF 3 –7Al 2 O 3 –63SiO 2 (mol%) activated with 3% terbium, dysprosium, praseodymium and neodymium fluorides have been prepared and studied by differential thermal analysis, cathodoluminescence, X-ray induced luminescence, X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. We found out that the presence of crystalline phase enhances the X-ray induced luminescence intensity. X-ray induced luminescence is the most intense for the sample activated with terbium and treated at 700 °C, whereas the praseodymium and neodymium activated samples have the fastest decay times.
Magnetic and optical properties in degenerated transition metal and Ga co-substituted ZnO nanocrystals
2019
Abstract In order to study the influence of itinerant electrons on magnetic properties of transition metal substituted ZnO nanocrystals, nanopowders containing different amounts of Ga and fixed amounts of Fe, Ni and Mn ions were synthesized. The ions of different transition metals and Ga were successfully introduced into the ZnO structure using solvothermal synthesis method. X-ray diffraction, scanning electron microscopy, hard X-ray photoelectron spectroscopy and Rietveld refinement were used to characterize the synthesized nanocrystals. Optical measurements revealed that Ga substitution can change the light transmittance/absorption in the infrared part of the electromagnetic light spectru…
Pd2Mo3N: a new molybdenum bimetallic interstitial nitride
2001
The molybdenum bimetallic nitride Pd2Mo3N has been synthesized by ammonolysis of the stoichiometric mixture of low sized pure oxide crystallites (2PdO/3MoO3) as resulting from low temperature thermal decomposition of precursor powders obtained by freeze-drying of aqueous solutions of the appropriate metal salts. This compound has been characterized by elemental analysis, energy dispersive analysis of X-rays, X-ray diffraction, scanning electron microscopy (field emision) and thermogravimetry under oxygen atmosphere. Pd2Mo3N crystallizes in the cubic space group P4132 (no. 213) (Pd2Mo3N, a = 6.81770(3) A, Z = 4), and presents the unusual filled β-manganese structure. It is stable under oxyge…
Synthesis and thermoelectric characterisation of bismuth nanoparticles
2009
An effective method of preparation of bismuth nanopowders by thermal decomposition of bismuth dodecyl-mercaptide Bi(SC12H25)3 and preliminary results on their thermoelectric properties are reported. The thermolysis process leads to Bi nanoparticles due to the efficient capping agent effect of the dodecyl-disulfide by-product, which strongly bonds the surface of the Bi clusters, preventing their aggregation and significantly reducing their growth rate. The structure and morphology of the thermolysis products were investigated by differential scanning calorimetry, thermogravimetry, X-ray diffractometry, 1H nuclear magnetic resonance spectroscopy, scanning electron microscopy, and energy dispe…
Properties of atomic layer deposited nanolaminates of zirconium and cobalt oxides
2018
Producción Científica
Stress-induced dislocation generation in large FZ- and CZ-silicon single crystals—numerical model and qualitative considerations
2001
When growing silicon crystals with higher diameter (presently up to 300 mm) the thermal stresses and possible dislocation generation in single crystals become a serious problem for both FZ- and CZ-methods. A two-dimensional problem oriented code for the FEM-package ANSYS has been developed to calculate the temperature field in the growing crystal considering radiation exchange with reflectors and environment and thermal stresses. Comparing calculated stresses with critical stresses, the dislocated zone is determined. A qualitative concept for the occurrence of dislocations using the metastable state is developed. In a parametric study for different thermal boundary conditions and crystal ge…