Search results for "Chemical engineering"
showing 10 items of 5892 documents
The mechanically activated combustion reaction in the Fe–Si system: in situ time-resolved synchrotron investigations
2002
Mechanical high-energy ball milling of Fe+2Si elemental powder mixtures was used to activate self sustaining combustion reaction in the case of iron disilicide synthesis. The reaction path as well as the influence of the microstructural parameters on phase transformation have been investigated in detail. Time-resolved X-ray diffraction (TRXRD) using the fast recording kinetics offered by the synchrotron radiation was coupled to an infrared camera in order to study the internal structure of the combustion wave. The crystallite size and the amount of mechanically induced phases play an important role during the combustion; the reaction path and the end product composition mainly depend on the…
Thermal evolution and structural study of 2:1 mullite from monophasic gels
2006
Abstract Single phase mullite gels with composition 2Al 2 O 3 ·SiO 2 (2:1) were prepared by the slow hydrolysis method using aluminium nitrate nonahydrate and tetraethylorthosilicate as reagents. The evolution to mullite from gels was studied by infrared (IR) spectroscopy and X-ray diffraction (XRD). Gels thermally treated under fast schedules showed mullite formation below 900 °C. Compositional and microstructural changes in 2:1 mullites through the range of temperature from 900 to 1600 °C were determined by the measurement of lattice parameters and field emission scanning electron microscopy. The alumina-rich mullites formed at low temperatures become almost the nominal 2:1 at 1600 °C. Th…
Investigation of mechanically activated field-activated pressure-assisted synthesis processing parameters for producing dense nanostructured FeAl
2003
The parameters of the mechanically activated field-activated pressure-assisted synthesis (MAFAPAS) process, which were recently developed and patented for producing dense nanostructured materials, were studied in the case of the B2-FeAl intermetallic. Based on x-ray diffraction (XRD) experiments, residual stresses XRD analysis, relative density measurement, and secondary-electron microscopic observations, the optimal synthesis conditions (time, current intensity, and pressure) were studied. Fe + Al powders were comilled in a specially designed planetary mill to obtain a mixture of reactants at the nanoscale without the formation of any product. The milled mixtures were then subjected to a h…
Facile Large Scale Synthesis of WS2 Nanotubes from WO3 Nanorods Prepared by a Hydrothermal Route.
2005
Abstract Hexagonal WO 3 nanorods of 5–50 nm in diameter and 150–250 nm in length have been synthesised in gram quantities by a low temperature hydrothermal route using citric acid as a structural modifier and hexadecylamine as a templating agent. The ratio of [A]/[W] play an important role on WO 3 nanorods formation. These WO 3 nanorods were found highly suitable as a precursor for the synthesis of a good yield of multiwalled WS 2 nanotubes by reducing them with H 2 S at 840 °C for 30 min. The length and the wall thickness of the WS 2 nanotubes could be altered by controlled reduction of the oxide precursor. The morphology, structure and the composition of the WO 3 nanorods and WS 2 nanotub…
Which tool to distinguish transient alumina from alpha alumina in thermally grown alumina scales?
2005
International audience; Alumina scales constitute excellent protective barriers when they form on alumina-forming steels. If they keep tightly adherent to the underlying substrate, they isolate it from the surrounding aggressive atmosphere at high temperature. The protectiveness of the alumina scale is highly dependant upon its growth mechanism. The nucleation and transformation of transient alumina (mainly g-Al2O3 and y-Al2O3) is known to play an important role on alumina scale formation. It is therefore fundamental to characterise these transient alumina especially during the early stages of the oxidation process. The morphology of the transient alumina was observed by scanning electron m…
Synthesis and characterization of ZnO nano and micro structures grown by low temperature spray pyrolysis and vapor transport.
2012
In this work we present a systematic study of ZnO micro and nanostructures grown by spray pyrolysis (SP) and by physical vapour transport (PVT) on glass and c-sapphire substrates at low temperatures. Optimised growth conditions have allowed to obtain homogeneous ZnO nanolayers composed of quasi-spherical nanoparticles in the range 2 to 8 nm by spray pyrolysis, while by PVT the selected growth conditions allow to produce a wide variety of morphologies (tripods, grains, arrows and wires) of nano and microsize dimension. Grazing incidence X-ray diffraction, field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HRTEM), selected area electron dif…
New insight into δ-Pu alloy oxidation kinetics highlighted by using in-situ X-ray diffraction coupled with an original Rietveld refinement method
2018
Abstract The reactivity of a δ-Pu alloy was studied under dry oxygen at different temperatures. Phase analysis has shown the presence of α-and β-Pu2O3, PuO2, as well as the destabilisation of the δ-phase. The oxidation kinetics were studied using in-situ X-ray diffraction coupled with an original method of Rietveld refinement enabling an individual monitoring of the growth of each oxide. The results have evidenced a parabolic stage resulting from the thickening of the α-Pu2O3 layer, in which a compressive stress state develops. This stage is followed by the linear growth of a porous PuO2 scale.
Preparation and Electric Properties of Barium Zirconium Titanate Ceramic
2015
The relaxor behavior of barium zirconium titanate ceramics BaZr0.35Ti0.65O3 prepared by a conventional sintering process was investigated. The synthesized material was determined by an X-ray diffraction and scanning electron microscopy. Based on performed studies, the BaZr0.35Ti0.65O3 ceramic material has been identified as canonical relaxor, related to the Ti-rich polar regions. The freezing temperature Tf and activation energy Ea are calculated from the Vogel-Fulcher relationship.
Controlling the Formation of Sodium/Black Phosphorus IntercalationCompounds Towards High Sodium Content
2021
The solid-state synthesis of pure sodium-black phosphorus intercalation compounds (Na-BPICs) has been optimized in bulk for two stoichiometric ratios. Specifically, in-situ X-Ray diffraction (XRD) allowed the precise identification of the optimal temperature range for the formation of Na-BPICs: 94°C–96°C. Moreover, as the undesired formation of Na3P takes place at this very same range, we succeeded in introducing a new synthetic route based on a fast-thermal ball milling implementation that results in the bulk production of BPIC without Na3P in 9 out of 10 cases. Finally, by combining XRD, Raman spectroscopy, and DFT calculations we developed a new structural model for Na-based BPICs showin…
Apoferritin-encapsulated Ni and Co superparamagnetic nanoparticles
2006
Ni and Co nanoparticles (average diameters 3 and 3.5 nm) have been prepared within the apoferritin cavity. The protein shell prevents bulk aggregation of the metal particles, rendering them water soluble. X-Ray diffraction, transmission electronic microscopy and magnetization measurements have been used for characterizing the nanoparticles. The magnetic study of both nanoparticles confirmed the expected superparamagnetic behavior.