Search results for "hydrothermal synthesis"
showing 10 items of 62 documents
Characteristics of LiFePO4 obtained through a one step continuous hydrothermal synthesis process working in supercritical water
2009
International audience; The olivine-like material LiFePO4 was prepared via a continuous hydrothermal synthesis process working from subcritical to supercritical water conditions. The influence of some processing parameters–temperature and reaction time–was investigated in terms of material purity, grain size and morphology. Supercritical conditions were found to be attractive to synthesize in one step a well-crystallized material without impurities. The primary particles size was in the nanometric range. They showed a natural tendency to form micron size agglomerates, which were supposed to be the cause of the limited capacity, as demonstrated through a cross study using laser particle size…
Particle size and morphology control of the negative thermal expansion material cubic zirconium tungstate
2009
Cubic ZrW2O8 is a negative thermal expansion (NTE) material that is of interest as filler in controlled thermal expansion composites. It is easily accessible from a hydrated precursor, ZrW2O7(OH)2·2H2O, which can be obtained by hydrothermal synthesis. Different reaction conditions were investigated to gain control over the morphology, and to minimize the particle size. Optimized procedures resulted in rod-shaped particles with widths of 10–30 nm and lengths of 200–500 nm, which showed little agglomeration. The particle size and morphology of the precursor are preserved during conversion to the NTE phase at 600–650 °C.
Synthesis of Titanate Nanotubes Directly Coated with USPIO in Hydrothermal Conditions: A New Detectable Nanocarrier
2011
International audience; Abstract: For the first time, titanate nanotubes (TiONts) coated with USPIO (ultrasmall superparamagnetic iron oxide) without polymer functionalization and directly obtained during TiONts formation is reported. The coating of these tubes was performed directly during the TiONts hydrothermal synthesis. After this treatment, in strongly basic conditions, USPIO particles kept their structure and magnetic properties while their size distribution slightly increased. By coupling zeta-potential measurements and TEM observations at different pH it appeared that interactions between nanotubes and USPIO were not electrostatic. This study presents the new design of a titanate n…
Chromium oxide nanoparticles with controlled size prepared from hydrothermal chromium oxyhydroxide precursors
2017
Abstract This work reports the preparation of morphologically well-defined chromium oxide nanoparticles with controlled sizes of 20–30 nm. The synthetic procedure encompass two stages, the first one refers to the preparation of chromium oxyhydroxide nanoparticles by a hydrothermal approach of previously precipitated xerogels, followed by a thermal transformation of CrOOH nanoparticles to Cr2O3. The series of chromium oxyhydroxide particles sized over the range 15–50 nm were prepared through the control of the pH of precipitation of the xerogels and the water/xerogel ratio of the hydrothermal aging. Results showed the formation of non-aggregated oxyhydroxide nanoparticles with two different …
Smart optically active VO2 nanostructured layers applied in roof-type ceramic tiles for energy efficiency
2016
Abstract The capability to control in an smart way the infrared reflectance to environmental temperature variations can be achieved with thermochromic materials like VO2. In this paper, we report the application of VO2 on ceramic tiles aiming to control the reflected infrared radiation on smart roofs and thus improving the energy efficiency, which is associated to the reduction of the carbon dioxide emissions. The VO2 nanoparticles have been produced by hydrothermal synthesis assisted by microwave irradiation, providing a new, quicker and cleaner production route. Afterwards, the VO2 nanoparticles were transferred to the surface of ceramic glassy tiles, which were prepared through dispersin…
Colloidal zeolites and zeolite membranes
2002
The synthesis of zeolite membranes and thin films using the secondary growth process is briefly described. In this process colloidal zeolite particles (sols) are prepared hydrothermally and then subsequently deposited on substrates to produce uniform layers of controlled thickness. In order to optimise this process, an understanding of the nature of the sols and an insight into the structure of the consolidated layer so formed, is required. Such studies are illustrated here with silicalite and zeolite A. The formation and growth of silicalite sols has been investigated in situ by small angle neutron scattering (SANS). SANS measurements on sols at progressively higher concentrations have pro…
Microwave hydrothermal flash synthesis of nanocomposites Fe–Co alloy/cobalt ferrite
2004
Abstract The present article presents, for the first time, the last developments reported for an original microwave hydrothermal flash synthesis of Fe–Co alloys (FeyCo1−y)/cobalt ferrite (Fe3−xCoxO4) nanocomposites. Synthesis was performed in alcoholic solutions of ferrous chloride, cobalt chloride and sodium ethoxide (EtONa) using a microwave autoclave (The RAMO system) specially designed by authors. Compared with conventional synthesis, smaller grains (100 nm compared to 1 μm) can be produced in a short period (e.g. 10 s) using a less basic medium. In all the cases, the microstructure and the amount of metal inside the composite particles are very different from the product obtained via a…
Morphological Control of Hydrothermal Ni(OH)2 in the Presence of Polymers and Surfactants: Nanocrystals, Mesocrystals, and Superstructures
2008
International audience; Polymers with different hydrophilic groups [polyvinylpyrrolidone (PVP), ammonium polyacrylate (APA), and hydroxypropylmethyl cellulose (HPMC)] and surfactants [cetyltrimethylammonium bromide (CTAB) and sodium dodecylbenzensulfonate (SDBS)] were used as additives to modify the crystallization of β-Ni(OH)2 in hydrothermal conditions. Marked morphological changes in the β-Ni(OH)2 particles were observed depending on the additive concentration and on the duration of the hydrothermal treatment. The final morphology is the result of a complex, time-dependent self-assembly and growth process. Well-defined particles with sizes from submicrometer range to a few micrometers co…
One step continuous hydrothermal synthesis of very fine stabilized superparamagnetic nanoparticles of magnetite
2011
International audience; Stable suspensions of citrated SPIO nanoparticles were synthesised in one step using a hydrothermal continuous process. Citrates control the crystallite size and the oxidation degree of metallic ions despite the very short reaction time (4 s). Magnetite particles, Fe2.94O4, with an average size of 4 nm and good monodispersity were obtained.