Search results for "Diffraction"
showing 10 items of 1584 documents
A new calcium sulfate hemi-hydrate
2010
Calcium sulfate hydrates receive significant attention due to numerous large scale industrial applications. There has been a long debate on the possible existence of two gypsum hemi-hydrate polymorphs, denoted alpha- and beta-CaSO(4).0.5H(2)O. In this work, a new crystal structure of calcium sulfate hemi-hydrates is presented, denoted beta-CaSO(4).0.5H(2)O. The structure was solved using powder neutron diffraction data, the space group is P3(1) and the unit cell in a hexagonal setting a = 6.9268(1), c = 12.7565(3) A. The structure has two calcium-oxygen coordination polyhedra: Ca1 is eight coordinated and has Ca-O bond lengths in the range 2.31(3) to 2.89(2) A and Ca2 is nine coordinated an…
Contribution of exclusive diffractive processes to the measured azimuthal asymmetries in SIDIS
2019
Hadron leptoproduction in Semi-Inclusive measurements of Deep-Inelastic Scattering (SIDIS) on unpolarised nucleons allows one to get information on the intrinsic transverse momentum of quarks in a nucleon and on the Boer-Mulders function through the measurement of azimuthal modulations in the cross section. These modulations were recently measured by the HERMES experiment at DESY on proton and deuteron targets, and by the COMPASS experiment using the CERN SPS muon beam and a $^6$LiD target. In both cases, the amplitudes of the $\cos\phi_h$ and $\cos 2\phi_h$ modulations show strong kinematic dependences for both positive and negative hadrons. It has been known since some time that the measu…
Synthesis and characterization of ZnS nanoparticles in water/AOT/n-heptane microemulsions
1999
ZnS nanoparticles were synthetized using water-containing AOT reversed micelles as nanoreactors and characterized by UV-Vis spectrophotometry, HRTEM (high-resolution transmission electron microscopy), SAED (selected-area electron diffraction), and digital image processing. The experimental data evidence a slow growing process of fractal-like ZnS nanoparticles’ coupled with a change of their photophysical properties. Both these processes are well described by power laws. The nanoparticles size is mainly controlled by the micellar size. After evaporation of the organic solvent, it has been found that the deposit is constituted by smaller and more stable ZnS nanoparticles bathed in a surfactan…
Heptane Adsorption in Silicalite-1: Neutron Scattering Investigation
2007
International audience; Structural properties of confined deuterated n-heptane in silicalite-1 have been investigated by neutron scattering experiments during the adsorption process. At 300 K, the adsorption isotherm shows a sharp inflection at a loading near Nads ) 4 molecules per silicalite-1 unit cell. In addition, the diffusivities obtained from recent QENS data exhibit a loading dependence. Our motivation is to find structural signatures of the peculiar behavior of n-heptane in silicalite-1 and to check the numerous computer simulation findings of this behavior. Our detailed neutron diffraction investigation agrees with the MONO-ORTHO phase transition of the silicalite-1 above a Nads v…
Single-crystal I h ice surfaces unveil connection between macroscopic and molecular structure
2017
Physics and chemistry of ice surfaces are not only of fundamental interest but also have important impacts on biological and environmental processes. As ice surfaces—particularly the two prism faces—come under greater scrutiny, it is increasingly important to connect the macroscopic faces with the molecular-level structure. The microscopic structure of the ubiquitous ice Ih crystal is well-known. It consists of stacked layers of chair-form hexagonal rings referred to as molecular hexagons. Crystallographic unit cells can be assembled into a regular right hexagonal prism. The bases are labeled crystallographic hexagons. The two hexagons are rotated 30° with respect to each other. The linkage…
Synthesis and High-Pressure Study of Corundum-Type In2O3
2015
This work reports the high-pressure and high-temperature (HP-HT) synthesis of pure rhombohedral (corundum-type) phase of indium oxide (In2O3) from its most stable polymorph, cubic bixbyite-type In2O3, using a multianvil press. Structural and vibrational properties of corundum-type In2O3 (rh-In2O3) have been characterized by means of angle-dispersive powder X-ray diffraction and Raman scattering measurements at high pressures which have been compared to structural and lattice dynamics ab initio calculations. The equation of state and the pressure dependence of the Raman-active modes of the corundum-type phase are reported and compared to those of corundum (α-Al2O3). It can be concluded that …
Nanocrystallization of amorphous alloys using microwaves:In situtime-resolved synchrotron radiation studies
2009
Important energy and time savings can be achieved with the thermal treatment of materials by replacing conventional heating methods with microwave heating. The nano- crystallization of Co-Fe-W-B amorphous alloy powders under microwave irradiation was followed for the first time by in situ time-resolved synchrotron radiation powder diffraction. It is shown that even a very short exposure to the electromagnetic field (single pulse microwave application) typically of the order of a few seconds is sufficient to obtain the bulk nano- crystalline state. A metastable high-temperature Co-W-B orthorhombic phase forms during the microwave heating, which gradually transforms to the tetragonal Co2B sta…
Holographic recording in amorphous As2S3 films at 633nm
2006
Abstract Holographic grating recording with focused (light intensity I = 14–124 W/cm 2 ) and unfocused ( I = 0.50–0.78 W/cm 2 ) 633 nm He–Ne laser sub-bandgap light in non-annealed and annealed a-As 2 S 3 films has been experimentally studied. The focused light recording is found to be much more efficient (diffraction efficiency up to 14.9%, specific recording energy down to 216 J/(cm 2 %)) than the unfocused light recording (0.11%, 72 400 J/(cm 2 %)). Some other properties are also different. The hologram lifetime of more than two years and positive refractive index changes take place in the case of focused recording versus two days and negative refractive index changes for unfocused r…
Influence of complexation between amylose and a flavored model sponge cake on the degree of aroma compound release
2008
International audience; Flavoring is used in the food industry to reinforce the aroma profile of baked cereal goods. During the processing of such products, interactions between starch and aroma compounds can occur, and this may have an impact on aroma release and perception. In the present study, 20 aroma compounds were tested to establish whether they formed complexes with amylose. The structure of the complexes was determined by wide-angle X-ray scattering (WAXS). A cocomplexation study proved that several complexing compounds could be present in the same crystalline aggregate. WAXS and differential scanning calorimetry (DSC) experiments were performed in a flavored model sponge cake at …
Impulsive solvent heating probed by picosecond x-ray diffraction
2006
The time-resolved diffraction signal from a laser-excited solution has three principal components: the solute-only term, the solute-solvent cross term, and the solvent-only term. The last term is very sensitive to the thermodynamic state of the bulk solvent, which may change during a chemical reaction due to energy transfer from light-absorbing solute molecules to the surrounding solvent molecules and the following relaxation to equilibrium with the environment around the scattering volume. The volume expansion coefficient alpha for a liquid is typically approximately 1 x 10(-3) K(-1), which is about 1000 times greater than for a solid. Hence solvent scattering is a very sensitive on-line t…