Papers by Keyword: Diffraction

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Authors: Ian C. Madsen, Ian E. Grey, Stuart J. Mills
Abstract: A study of the thermal decomposition sequence of a sample of natural arsenian plumbojarosite has been undertaken using in situ X-ray diffraction. The sample was heated to 900°C using an Anton-Paar heating stage fitted to an INEL CPS120 diffractometer. The data were analysed using a whole-pattern, Rietveld based approach for the extraction of quantitative phase abundances. The instrument configuration used required the development and application of algorithms to correct for aberrations in the (i) peak intensities due to differing path lengths of incident and diffracted beams in the sample and (ii) peak positions due to sample displacement. Details of the structural models used were refined at selected steps in the pattern and then fixed for subsequent analysis. The data sequence consists of some 110 individual data sets which were analysed sequentially with the output of each run forming the input for analysis of the next data set. The results of the analysis show a complex breakdown and recrystallisation sequence including the formation of a major amount of amorphous material after initial breakdown of the plumbojarosite.
Authors: Peter Staron, Jie Liu, Stefan Riekehr, Norbert Schell, Norbert Huber, Nikolai Kashaev, Martin Müller, Andreas Schreyer
Abstract: The laser beam welding (LBW) process has many advantages for industrial production; however, it still has to be optimized for two-phase Ti alloys. Phase transformations and residual stresses play a crucial role for welding these alloys. Specific questions about the development of phase content during fast heating with a laser and rapid cooling can only be addressed with time-resolved in-situ experiments, avoiding artefacts from quenching. Also the residual stress development during cooling depends on the occurring phase transformations. Thus, an LBW chamber employing a fibre laser was developed for use with high-energy X-rays from a synchrotron source. Bead-on-plate welding experiments with 2.5 mm thick samples were carried out at the HZG high-energy materials science beamline (HEMS) at DESY, Hamburg. The first experiments focused on the solid-solid phase transformations in a Ti-6Al-4V alloy. Moreover, residual stresses developing during cooling were studied.
Authors: C.A. Koh, J.L. Savidge, C.C. Tang, R.E. Motie, X.P. Wu, R.I. Nooney, R. Westacott
Authors: Ying Tang Zhang, Hua Wa Yu, Qiu Ping Wang, Guang Xi Zhou, Jun Fang Wu
Abstract: The original grating is etched by using the nanometer etching function of Scanning Probe Microscopy (SPM). There are five grooves etched on the surface of polymer material. The grating constant is 796.87 nm, so the fringe density is 1254 lp/mm. Diffraction pattern of the original grating is obtained on Michelson interferometer. A new method of making original grating is found. Since the Nominal Tip Radius of Curvature (NTRC) of Etched Silicon Probe (ESP) of used Veeco SPM is 5-10 nm, the etching grating should have fringe density of 50 000 -100 000 lp/mm.
Authors: Stefano Enzo, G. Mulas, R. Frattini, G. Principi, Rajesh Gupta, R. Cooper, Neil Cowlam
Authors: P.P. Macrí, P. Rose, D.E. Banda, Neil Cowlam, G. Principi, Stefano Enzo
Authors: Pei Liu, Xiao Song Zhang, Chuan Zhen Xin, Meng Zhen Li, Lan Li
Abstract: In this research, a triangular two-dimensional (2D) photonic crystal (PC) was hypothetically introduced into the active layer of a PbS quantum dots (QDs) electroluminescent (EL) device. The attributes of the photonic band gap effect and diffraction effect were considered and evaluated for device performance improvement. We designed and optimized the 2D-PC structure parameters to enhance the emission intensity at wavelength 1124 nm. The optimal structure parameter of PC is determined by normalized radius of r/a=0.49 and lattice constant of a=540 nm when the thickness of PC slab h is 74 nm. The 3D stimulation view of light propagation validates and supports the proposed strategy. The results provide a theoretical prediction for ideal PbS QDs-based EL device.
Authors: Viwanou Hounkpati, Sylvain Fréour, David Gloaguen, Vincent Legrand
Abstract: The historical Eshelby-Kröner self-consistent model is only valid in the case when grains can be assumed similar to ellipsoids aligned preferentially along a same direction into the polycrystal. In this work, distributions of crystallites morphologies and geometrical orientations were accounted for, owing to the so-called generalized self-consistent model, in order to satisfy Hills averages principles. Different nonlinear εφψ-vs.-sin2ψ distributions were predicted in elasticity, even in the absence of crystallographic texture, in the case when several morphologies and geometrical orientations coexist within the same polycrystal.
Authors: Fabrizio Fiori, Emmanuelle Girardin, Alessandra Giuliani, Adrian Manescu, Serena Mazzoni, Franco Rustichelli, Evzen Amler
Abstract: The rapid development of new materials and their application in an extremely wide variety of research and technological fields has lead to the request of increasingly sophisticated characterization methods. In particular residual stress measurements by neutron diffraction, small angle scattering of X-rays and neutrons, as well as 3D imaging techniques with spatial resolution at the micron or even sub-micron scale, like micro-and nano-computerized tomography, have gained a great relevance in recent years.Residual stresses are autobalancing stresses existing in a free body not submitted to any external surface force. Several manufacturing processes, as well as thermal and mechanical treatments, leave residual stresses within the components. Bragg diffraction of X-rays and neutrons can be used to determine residual elastic strains (and then residual stresses by knowing the material elastic constants) in a non-destructive way. Small Angle Scattering of neutrons or X-rays, complementary to Transmission Electron Microscopy, allows the determination of structural features such as volume fraction, specific surface and size distribution of inhomogeneities embedded in a matrix, in a huge variety of materials of industrial interest. X-ray microtomography is similar to conventional Computed Tomography employed in Medicine, allowing 3D imaging of the investigated samples, but with a much higher spatial resolution, down to the sub-micron scale. Some examples of applications of the experimental techniques mentioned above are described and discussed.
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