An improved X-ray diffraction method for cellulose crystallinity measurement
Not Available
Ju, Xiaohui↗
SEARCH · Engineering Papers
Results for “DIFFRACTION METHODS”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Diffraction Methods for Qualitative and Quantitative Texture Analysis of Ferroelectric Ceramics
Crystallographic textures are pervasive in ferroelectrics and underpin the functional properties of devices utilizing these materials because many macroscopic properties (e.g., piezoelectricity) require a non-random distribution of dipoles. Inducing a preferred grain texture has become a viable route to improve these functional properties. X-ray and neutron diffraction have become valuable tools to probe crystallographic textures. This paper presents an overview of qualitative and quantitative methods for assessing crystallographic textures in electroceramics (domain and grain textures) and discusses their strengths and weaknesses.
36 MATERIALS SCIENCE↗
Two-dimensional groove density measurement for gratings by diffraction method
A grating groove density measuring system based on diffraction method has been developed to measure the two-dimensional groove density variations of the VLS gratings at NSRL. The measuring system can provide not only the basic data of the two-dimensional groove density variations for evaluating the imaging properties of grating, but also an important tool for improving the grating manufacturing technology. A commercially available concave grating with a curvature radius of 750 mm was measured to test the accuracy of the measuring system. Results show that the system has a measuring accuracy (ΔN/N) of about 5 × 10{sup −5}. Then the groove density variation parameters of the 1200 lines/mm VLS plane grating used in NSRL is measured by the system. The groove curvature of the VLS plane grating has been observed.
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
Observation of coherent optical phonons excited by femtosecond laser radiation in Sb films by ultrafast electron diffraction method
The generation of coherent optical phonons in a polycrystalline antimony film sample has been investigated using femtosecond electron diffraction method. Phonon vibrations have been induced in the Sb sample by the main harmonic of a femtosecond Ti:Sa laser (λ = 800 nm) and probed by a pulsed ultrashort photoelectron beam synchronized with the pump laser. The diffraction patterns recorded at different times relative to the pump laser pulse display oscillations of electron diffraction intensity corresponding to the frequencies of vibrations of optical phonons: totally symmetric (A{sub 1g}) and twofold degenerate (E{sub g}) phonon modes. The frequencies that correspond to combinations of these phonon modes in the Sb sample have also been experimentally observed.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Beyond the Streetlight Effect: A United Future for Relaxation and Diffraction Methods for Residual Stress Measurement
Residual stress measurement techniques can be categorized as either relaxation or diffraction methods. Practitioners often advocate a particular category and sometimes a specific technique (hole drilling, contour, XRD, neutron, etc) based on their experience or capability rather than using the best technique for the particular application. This paper considers some of the implications from applying this “drunkard’s search” or “streetlight” approach by examining examples where the critical stress could be hidden from both relaxation and diffraction measurements. A better approach to planning residual stress measurements would begin with a detailed consideration of why the stresses should be measured and how the results will be used. Only then can the most appropriate measurement plan be developed. Since a single measurement technique cannot reveal the full state of stress, especially in challenging parts, the use of multiple measurement types often provides the most useful information to customers.
36 MATERIALS SCIENCE↗
2010 Diffraction Methods in Structural Biology
Advances in basic methodologies have played a major role in the dramatic progress in macromolecular crystallography over the past decade, both in terms of overall productivity and in the increasing complexity of the systems being successfully tackled. The 2010 Gordon Research Conference on Diffraction Methods in Structural Biology will, as in the past, focus on the most recent developments in methodology, covering all aspects of the process from crystallization to model building and refinement, complemented by examples of structural highlights and complementary methods. Extensive discussion will be encouraged and it is hoped that all attendees will participate by giving oral or poster presentations, the latter using the excellent poster display area available at Bates College. The relatively small size and informal atmosphere of the meeting provides an excellent opportunity for all participants, especially younger scientists, to meet and exchange ideas with leading methods developers.
59 BASIC BIOLOGICAL SCIENCES↗
Metrological characterization of X-ray diffraction methods at different acquisition geometries for determination of crystallite size in nano-scale materials
Crystallite size values were determined by X-ray diffraction methods for 183 powder samples. The tested size range was from a few to about several hundred nanometers. Crystallite size was calculated with direct use of the Scherrer equation, the Williamson–Hall method and the Rietveld procedure via the application of a series of commercial and free software. The results were statistically treated to estimate the significance of the difference in size resulting from these methods. We also estimated effect of acquisition conditions (Bragg–Brentano, parallel-beam geometry, step size, counting time) and data processing on the calculated crystallite size values. On the basis of the obtained results it is possible to conclude that direct use of the Scherrer equation, Williamson–Hall method and the Rietveld refinement employed by a series of software (EVA, PCW and TOPAS respectively) yield very close results for crystallite sizes less than 60 nm for parallel beam geometry and less than 100 nm for Bragg–Brentano geometry. However, we found that despite the fact that the differences between the crystallite sizes, which were calculated by various methods, are small by absolute values, they are statistically significant in some cases. The values of crystallite size determined from XRD were compared with those obtained by imaging in a transmission (TEM) and scanning electron microscopes (SEM). It was found that there was a good correlation in size only for crystallites smaller than 50 – 60 nm. Highlights: • The crystallite sizes for 183 nanopowders were calculated using different XRD methods • Obtained results were subject to statistical treatment • Results obtained with Bragg-Brentano and parallel beam geometries were compared • Influence of conditions of XRD pattern acquisition on results was estimated • Calculated by XRD crystallite sizes were compared with same obtained by TEM and SEM.
36 MATERIALS SCIENCE↗
Bending Behavior of a Wrought Magnesium Alloy Investigated by the In Situ Pinhole Neutron Diffraction Method
The tensile twinning and detwinning behaviors of a wrought magnesium alloy have been investigated during in situ four-point bending using the state-of-the-art high spatial resolution pinhole neutron diffraction (PIND) method. The PIND method allowed us to resolve the tensile twinning/detwinning and lattice strain distributions across the bending sample during a loading-unloading sequence with a 0.5 mm step size. It was found that the extensive tensile twinning and detwinning occurred near the compression surface, while no tensile twinning behavior was observed in the middle layer and tension side of the bending sample. During the bending, the neutral plane shifted from the compression side to the tension side. Compared with the traditional neutron diffraction mapping method, the PIND method provides more detailed information inside the bending sample due to a higher spatial resolution.
36 MATERIALS SCIENCE↗
Application of Anomalous Diffraction Methods to the Study of DNA and DNA-Complexes
Anomalous scattering is commonly used to solve X-ray structures. As discussed here, anomalous scattering is also useful for characterizing complex systems with mixed and partial occupancies, where true electron density is represented by unresolvable ensemble averages. The solvent environment surrounding nucleic acids is an example of such a system, as are some DNA-ligand systems. The atomic number and wavelength dependencies of anomalous scattering allow one to filter out the electron densities of C, N, and O, and to cleanly visualize the electron densities of heavier atoms. Therefore, anomalous scattering can make beacons of selected atoms. In addition, anomalous scattering provides a model-independent method for determining atomic identities. Here, we describe applications of anomalous scattering to the structure determination of DNA-platinum complexes and in cation associations of free DNA, of DNA-anthracycline complexes, of chemically modified DNA, and of DNA-protein complexes. The utility of Rb{sup +} and Tl{sup +} as K{sup +} substitutes is supported by similarities in Rb{sup +} and Tl{sup +} association with DNA.
59 BASIC BIOLOGICAL SCIENCES↗
Investigation of residual stress distribution in wire-arc directed energy deposited refractory molybdenum alloy utilizing numerical thermo-mechanical analysis and neutron diffraction method
Directed energy deposition (DED), a metal additive manufacturing (AM) technique, offers higher deposition rates and energy efficiency, making it suitable for fabricating components from refractory molybdenum alloys, such as molybdenum-titanium-zirconium (TZM). However, large thermal gradients and non-equilibrium thermal cycles in DED could generate high residual stress in the component, potentially deteriorating quality and performance. Thus, this study aims to investigate residual stress generation and its distribution in wire-arc DED of TZM thin-wall, utilizing thermo-mechanical analysis and high-fidelity neutron diffraction (ND) method. Two interpass temperatures (50°C and 200°C) have been considered to investigate their impact on residual stress formation. During experiments, in-situ thermal data has been recorded using thermocouples, which have been utilized for calibrating the thermal model. Thermocouple data shows a good agreement with the simulation results, having a difference of less than 10 %. Post-deposition part deformation has been observed, which is measured using a coordinate measuring machine, showing maximum values of 0.93 mm and 0.78 mm for interpass temperatures of 50°C and 200°C, respectively. Numerical predictions of distortion deviated by less than 15% from the experimental results. ND measurement and simulation results indicate that residual stress magnitude and evolution vary across the TZM deposits, revealing microstructural anisotropy in both conditions. Notably, lower interpass temperatures resulted in higher residual stresses, confirmed by experimental and simulation data. Further, this study demonstrated that an integrated experimental and thermo-mechanical analysis can potentially reveal the temperature history, part deformation, and residual stress formation in wire-arc DED TZM alloy.
36 MATERIALS SCIENCE↗
Modern X-ray Diffraction Methods in Mineralogy and Geosciences
This section is not intended to be comprehensive or detailed, because diffraction is such a vast subject. The principles of diffraction theory, however, are summarized under the assumption that the reader is familiar with basic concepts of the crystalline state. We will briefly review the basics of diffraction techniques, using laboratory and synchrotron X-ray sources and highlight some of their applications in geoscience.
58 GEOSCIENCES↗
Measurement of piezoelectric constants of lanthanum-gallium tantalate crystal by X-ray diffraction methods
A method for measuring piezoelectric constants of crystals of intermediate systems by X-ray quasi-multiple-wave diffraction is proposed and implemented. This technique makes it possible to determine the piezoelectric coefficient by measuring variations in the lattice parameter under an external electric field. This method has been approved, its potential is evaluated, and a comparison with high-resolution X-ray diffraction data is performed.
36 MATERIALS SCIENCE↗
Characterizing single isolated radiation-damage events from molecular dynamics via virtual diffraction methods
In this study, the evolution and characterization of single-isolated-ion-strikes are investigated by combining atomistic simulations with selected-area electron diffraction (SAED) patterns generated from these simulations. Five molecular dynamics simulations are performed for a single 20 keV primary knock-on atom in bulk crystalline Si. The resulting cascade damage is characterized in two complementary ways. First, the individual cascade events are conventionally quantified through the evolution of the number of defects and the atomic (volumetric) strain associated with these defect structures. These results show that (i) the radiation damage produced is consistent with the Norgett, Robinson, and Torrens model of damage production and (ii) there is a net positive volumetric strain associated with the cascade structures. Second, virtual SAED patterns are generated for the resulting cascade-damaged structures along several zone axes. The analysis of the corresponding diffraction patterns shows the SAED spots approximately doubling in size, on average, due to broadening induced by the defect structures. Furthermore, the SAED spots are observed to exhibit an average radial outward shift between 0.33% and 0.87% depending on the zone axis. Finally, this characterization approach, as utilized here, is a preliminary investigation in developing methodologies and opportunities to link experimental observations with atomistic simulations to elucidate microstructural damage states.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Structural analysis of Gd 6 FeBi 2 from single-crystal X-ray diffraction methods and electronic structure calculations
The crystal structure of the gadolinium iron bismuthide Gd 6 FeBi 2 has been characterized by single-crystal X-ray diffraction data and analyzed in detail using first-principles calculations. The structure is isotypic with the Zr 6 CoAl 2 structure, which is a variant of the ZrNiAl structure and its binary prototype Fe 2 P (Pearson code hP 9, Wyckoff sequence g f d a ). As such, the structure is best viewed as an array of tricapped trigonal prisms of Gd atoms centered alternately by Fe and Bi. The magnetic-ordering temperature of this compound ( ca 350 K) is much higher than that of other rare-earth metal-rich phases with the same or related structures. It is also higher than the ordering temperature of many other Gd-rich ternary phases, where the magnetic exchange is typically governed by Ruderman–Kittel–Kasuya–Yosida (RKKY) interactions. First-principles calculations reveal a larger than expected Gd magnetic moment, with the additional contribution arising from the Gd 5 d electrons. The electronic structure analysis suggests strong Gd 5 d –Fe 3 d hybridization to be the cause of this effect, rather than weak interactions between Gd and Bi. These details are of importance for understanding the magnetic response and explaining the high ordering temperature in this material.
Chemistry↗
Grating-based holographic diffraction methods for X-rays and neutrons: phase object approximation and dynamical theory
A method dubbed grating-based holography was recently used to determine the structure of colloidal fluids in the rectangular grooves of a diffraction grating from X-ray scattering measurements. Similar grating-based measurements have also been recently made with neutrons using a technique called spin-echo small-angle neutron scattering. The analysis of the X-ray diffraction data was done using an approximation that treats the X-ray phase change caused by the colloidal structure as a small perturbation to the overall phase pattern generated by the grating. In this paper, the adequacy of this weak phase approximation is explored for both X-ray and neutron grating holography. Additionally, it is found that there are several approximations hidden within the weak phase approximation that can lead to incorrect conclusions from experiments. In particular, the phase contrast for the empty grating is a critical parameter. Finally, while the approximation is found to be perfectly adequate for X-ray grating holography experiments performed to date, it cannot be applied to similar neutron experiments because the latter technique requires much deeper grating channels.
36 MATERIALS SCIENCE↗
Effective residual stress prediction validated with neutron diffraction method for metal large-scale additive manufacturing
Not Available
36 MATERIALS SCIENCE↗