Search results for "crystallinity"
showing 10 items of 248 documents
New Generation of Zeolite Materials for Environmental Applications.
2016
International audience; The influence of the morphology (microcrystals, nanocrystals, nanosponges and nanosheets) of MFI and *BEA-type zeolites on their adsorption capacities and adsorption rate of n-hexane at 25 ˚C has been investigated. The capacity of n-hexane adsorption sensitive to micro- and mesopore volume is enhanced by the use of zeolite nanocrystals or hierar-chical nanoporous materials (nanosheets and nanosponges). In the case of hierarchical zeolites MFI and *BEA nano-sponges, the n-hexane adsorption capacities reached values of about 790 and 693 mg/g, respectively, that are much higher than those in the corresponding microcrystals (130 and 103 mg/g, respectively). On the opposi…
Impact of granularity on transport properties of mechanically stressed La0.67Ca0.33MnO3 films
2001
Abstract (La,Ca)MnO 3 is one of so called collosal magnetoresistive materials and it is of interest to correlate its transport properties to film growth in order to optimize its performance. Two-hundred nanometers thick (100)La 0.67 Ca 0.33 MnO 3 films were grown by laser ablation on (100)SrTiO 3 , (100)LaAlO 3 and (100)(LaAlO 3 ) 0.3 +(Sr 2 AlTaO 6 ) 0.7 substrates. The films were granular in structure with low angle boundaries between the grains. The volume of the unit cell was considerably smaller for films grown on a SrTiO 3 substrate than on LaAlO 3 . At temperatures higher than the one where the spins order, the strongest response of resistivity on temperature ρ ( T ) was measured for…
Hygrothermal ageing of reprocessed polylactide
2012
[EN] The influence of an accelerated hygrothermal ageing simulation test on a commercial PLA and its three subsequent mechanically-reprocessed materials was studied. The analysis was focused on the water diffusion kinetics and the physico-chemical changes induced by the hygrothermal degradation. Water diffusion proceeded faster than chain relaxation processes, as defined by a Case II absorption model. It was proved that the water diffusion rate decreased with subsequent reprocessing cycles and increased with higher hygrothermal ageing temperatures. Hydrolytic chain scission provoked significant molar mass decays and consequent general losses of thermal and mechanical performance. The rearra…
Ceramic/metal nanocomposites by lyophilization: Processing and HRTEM study
2012
5 páginas, 8 figuras, 1 tabla.-- El pdf del artículo es el manuscrito de autor.
Dispersions of nanosilica in biocompatible copolymers
2010
Dispersions of nanosilica in matrices of biocompatible copolymers were prepared by melt blending. Copolymers with variable molecular size at fixed hydrophilic/hydrophobic ratio and nanosilicas with different interfacial areas were studied. For comparison, a nanoclay was also investigated. The interfacial area played a relevant role in conferring peculiar properties on the nanohybrids. Amazingly, the macromolecule adsorbed on the nanosilica surface maintains some crystallinity which was quantitatively evaluated. In contrast, all the macromolecule anchored to the nanoclay surface is amorphous. The change of the crystalline state was reflected in the dielectric and the electrical conductivity …
Development of self-assembled bacterial cellulose–starch nanocomposites
2009
Abstract A bioinspired bottom-up process was developed to produce self-assembled nanocomposites of cellulose synthesized by Acetobacter bacteria and native starch. This process takes advantage of the way some bacteria extrude cellulose nanofibres and of the transport process that occurs during the gelatinization of starch. Potato and corn starch were added into the culture medium and partially gelatinized in order to allow the cellulose nanofibrils to grow in the presence of a starch phase. The bacterial cellulose (BC)–starch gels were hot pressed into sheets that had a BC volume fraction higher than 90%. During this step starch was forced to further penetrate the BC network. The self-assem…
Degradation of Diazinon based on photoelectrocatalytic technique using enhanced WO3 nanostructures: Mechanism and pathway
2021
[EN] In this work, a resistant and toxic pesticide called diazinon was degraded through the photoelectrocatalysis (PEC) technique using tungsten oxide (WO3) nanostructures, applying an external bias of 1VAg/AgCl and simulated solar illumination. For this, WO3 nanostructures have been synthesized using electrochemical anodization in 0.05 M hydrogen peroxide and 1.5 M of different acidic electrolytes: H2SO4, CH4O3S or HNO3. Morphology, composition and crystallinity of the samples were evaluated through Field Emission Scanning Electron Microscopy (FE-SEM), Atomic Force Microscopy (AFM) and Raman Spectroscopy. Then, the photoelectrochemical properties of the samples were analyzed by Photo-Elect…
XRD Line Broadening Studies on Mullite
1996
An X-ray diffraction microstructural study on 110, 220, 001 and 111 peaks has been performed on mullite in the temperature range of primary mullite formation in order to monitor nucleation and growth process. Considering the crystallinity of the starting kaolinites, a greater disorder of the kaolinite has been found to enhance the mullite formation. Isothermal growth is related to a decrease in the Al 2 O 3 content of mullite.
Optical, structural, and morphological characterisation of epitaxial ZnO films grown by pulsed-laser deposition
2013
We report on ZnO epitaxial growth by pulsed-laser deposition (PLD) on different substrates, such as quartz, sapphire, and GaN template. Approximately 1 mu m-thick films were grown under different substrate temperatures and background oxygen conditions. X-ray diffraction analysis indicated preferential growth along the c-axis direction with a full-width at half maximum(FWHM) of the rocking curve as narrow as 230 arcs in the case of the GaN template. Low-temperature photoluminescence showed A-excitonic emission near 3.36 eV and a FWHM of (DXA)-X-0 emission as small as 2.89 meV at 9 K. Atomic force microscope measurements showed that roughness as low as 18 nm could be obtained. These results p…
Core-shell PLA/Kef hybrid scaffolds for skin tissue engineering applications prepared by direct kefiran coating on PLA electrospun fibers optimized v…
2021
Abstract Over the recent years, there is a growing interest in electrospun hybrid scaffolds composed of synthetic and natural polymers that can support cell attachment and proliferation. In this work, the physical and biological properties of polylactic acid (PLA) electrospun mats coated with kefiran (Kef) were evaluated. Gravimetric, spectroscopic (FTIR-ATR) and morphological investigations via scanning electron microscopy confirmed the effective formation of a thin kefiran layer wrapped on the PLA fibers with an easy-tunable thickness. Air plasma pre-treatment carried out on PLA (P-PLA) affected both the morphology and the crystallinity of Kef coating as confirmed by differential scanning…