1,089 research outputs found
Nanosecond molecular relaxations in lipid bilayers studied by high energy resolution neutron scattering and in-situ diffraction
We report a high energy-resolution neutron backscattering study to
investigate slow motions on nanosecond time scales in highly oriented solid
supported phospholipid bilayers of the model system DMPC -d54 (deuterated
1,2-dimyristoyl-sn-glycero-3-phoshatidylcholine), hydrated with heavy water.
Wave vector resolved quasi-elastic neutron scattering (QENS) is used to
determine relaxation times , which can be associated with different
molecular components, i.e., the lipid acyl chains and the interstitial water
molecules in the different phases of the model membrane system. The inelastic
data are complemented both by energy resolved and energy integrated in-situ
diffraction. From a combined analysis of the inelastic data in the energy and
time domain, the respective character of the relaxation, i.e., the exponent of
the exponential decay is also determined. From this analysis we quantify two
relaxation processes. We associate the fast relaxation with translational
diffusion of lipid and water molecules while the slow process likely stems from
collective dynamics
Advances in martensitic transformations in Cu-based shape memory alloys achieved by in situ neutron and synchrotron X-ray diffraction methods
This article deals with the application of several X-ray and neutron diffraction methods to investigate the mechanics of a stress induced martensitic transformation in Cu-based shape memory alloy polycrystals. It puts experimental results obtained by two different research groups on different length scales into context with the mechanics of stress induced martensitic transformation in polycrystalline environment
Rietveld Quantitative Phase Analysis of Oil Well Cement: in Situ Hydration Study at 150 Bars and 150 °C
Oil and gas well cements are multimineral materials that hydrate under high pressure
and temperature. Their overall reactivity at early ages is studied by a number of techniques
including through the use of the consistometer. However, for a proper understanding of the
performance of these cements in the field, the reactivity of every component, in real‐world
conditions, must be analysed. To date, in situ high energy synchrotron powder diffraction studies
of hydrating oil well cement pastes have been carried out, but the quality of the data was not
appropriated for Rietveld quantitative phase analyses. Therefore, the phase reactivities were
followed by the inspection of the evolution of non‐overlapped diffraction peaks. Very recently, we
have developed a new cell specially designed to rotate under high pressure and temperature. Here,
this spinning capillary cell is used for in situ studies of the hydration of a commercial oil well
cement paste at 150 bars and 150 °C. The powder diffraction data were analysed by the Rietveld
method to quantitatively determine the reactivities of each component phase. The reaction degree
of alite was 90% after 7 hours, and that of belite was 42% at 14 hours. These analyses are accurate,
as the in situ measured crystalline portlandite content at the end of the experiment, 12.9 wt%,
compares relatively well with the value determined ex situ by thermal analysis, i.e., 14.0 wt%. The
crystalline calcium silicates forming at 150 bars and 150 °C are also discussed.This research was funded by Spanish MINECO, grant number BIA2017‐82391‐R which is co‐funded
by FEDER.
We thank Marc Malfois for his help during the experiment performed at NCD‐SWEET
beamline at ALBA synchrotron. We also thank Marcus Paul (Dyckerhoff GmbH) for providing the OWC
sample with its characterization and helpful discussions
Revisiting the hydrogen storage behavior of the Na-O-H system
Solid-state reactions between sodium hydride and sodium hydroxide are unusual among hydride-hydroxide systems since hydrogen can be stored reversibly. In order to understand the relationship between hydrogen uptake/release properties and phase/structure evolution, the dehydrogenation and hydrogenation behavior of the Na-O-H system has been investigated in detail both ex- and in-situ. Simultaneous thermogravimetric-differential thermal analysis coupled to mass spectrometry (TG-DTA-MS) experiments of NaH-NaOH composites reveal two principal features: Firstly, an H2 desorption event occurring between 240 and 380 °C and secondly an additional endothermic process at around 170 °C with no associated weight change. In-situ high-resolution synchrotron powder X-ray diffraction showed that NaOH appears to form a solid solution with NaH yielding a new cubic complex hydride phase below 200 °C. The Na-H-OH phase persists up to the maximum temperature of the in-situ diffraction experiment shortly before dehydrogenation occurs. The present work suggests that not only is the inter-phase synergic interaction of protic hydrogen (in NaOH) and hydridic hydrogen (in NaH) important in the dehydrogenation mechanism, but that also an intra-phase Hδ+… Hδ– interaction may be a crucial step in the desorption process
Understanding the deformation mechanism of individual phases of a ZrTi-based bulk metallic glass matrix composite using in situ diffraction and imaging methods
The plasticity of a ZrTi-based bulk metallic glass composite consisting of glassy matrix and crystalline dendritic phase was studied in-situ under identical tensile loading conditions using scanning electron microscopy and synchrotron X-ray diffraction. A generic procedure was developed to separate the diffraction information of the crystalline phases away from that of the matrix and to precisely calculate the microscopic strains of the two phases at different macroscopic load steps. In this way, the time-evolved quantitative links between shear bands nucleation/propagation and the corresponding microscopic stress fields around them are established, providing more quantitative understanding on (1) how the shear bands are driven by the local stress field, and (2) the critical stresses required for the shear bands to nucleate in the crystalline phase, propagate through the crystalline/matrix interface, and finally into the matrix
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