Evaluation of T2G band intensity distribution across a surface of an UO2 ceramic

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Determination of the longitudinal thermal conductivity of low‐ordered carbon fibers by using an optothermal Raman technique

International audienceThe usage of carbon fibers (CFs) for high‐temperature applications has been increasing in recent years. However, the determination of thermal properties at high temperatures is a challenging task. In this study, the thermal conductivity of two different types of CF having a diameter in the range from 5–7 m, as a function of temperature, was examined by using the optothermal Raman method. Raman spectroscopy was first used to obtain the structural organization and structural homogeneity of the fibers. Then, owing to the fact that Raman spectra are sensitive to laser excitation power and external temperature, Raman spectroscopy was used as a contactless thermometer to determine the local temperature rise of the fibers. A formula was derived by solving the heat diffusion equation for cylindrical fibers and a set of boundary conditions, similar to the experimental conditions, which allows accurate estimation of longitudinal thermal conductivity. The results are discussed in relation with the phonon scattering theory and can be attributed to the combined effect of scattering from defects. The radiative and convective heat losses were estimated, and their influence on thermal conductivity was also determined

RAMAN STUDY OF SECONDARY MINERALS IN A RECENT LAVA TUBE

International audienceIn this paper, we present first the technical adaptations made for a field use of the laboratory in situ spectrometer, its capabilities and limits as well.Secondly, we present identification of secondary mineral phases growing in the lava tube with a particular emphasis on the study of white speleothems and dendrites by mean of XRD, SEM-EDX and Raman spectroscopy

Annealing of the defects observed by Raman spectroscopy in UO2 irradiated by 25 MeV He2+ ions

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Raman imaging and principal component analysis-based data processing on uranium oxide ceramics

A ceramic sample of uranium dioxide is probed by Raman imaging followed by a combined Lorentzian fitting – Principal Component Analysis process. This allows to evidence structural or chemical inhomogeneities of the material, which affect Raman line intensities but also line positions, evidencing local symmetry lowering. The inhomogeneities were observed not only between grain cores and boundaries, but also inside grain cores themselves. Only a part of these intensity inhomogeneities is as expected due to different orientations of the ceramic grains. Besides, a zone noticeably differing from others has been distinguished, presumably due to local strains or to chemical nature (oxygen stoichiometry), showing the sensitivity of the analysis. This underlines the importance to perform Raman analysis in such ceramic materials at least on several points and better, in imaging mode

Raman spectroscopy as suitable tool for the field study of recent volcanic environments

International audienceIn 2013, a portable Raman setup was implemented for on-site and rear-base characterization of volcanic products. Silica and rutile rock coatings, sulfate incrustations and speleothems, plagioclase, clinopyroxene, and (Fe, Ti, Cr) oxides lava minerals were identified on the young lava flows of Piton de la Fournaise volcano. These analytical abilities opens the way of in situ study of the first aging and weathering steps of recent lava flows. This paper relates the preliminary results of the field campaign. Three months after the investigation, all the speleothems have naturally disappeared. Copyright © 2016 John Wiley & Sons, Ltd

Characterization of an UO2 ceramic via Raman imaging and electron back-scattering diffraction

A surface state analysis of an UO2 ceramic is performed by combining Raman imaging and electron back-scattering diffraction. Special attention is paid to the behavior of the T2g band intensity versus the crystalline orientation. In order to clarify the origin of the T2g intensity variation in the appropriate Raman image, electron back-scattering diffraction (EBSD) measurements are carried out. EBSD data allow a theoretical estimation of the Raman T2g band intensities. Both maps have been compared in order to correlate them, and to distinguish regions where they are analogous, from those where some physical or chemical effects (stoichiometry, or strains) induce different behavior. More generally, this highlights the interest and the complementarity of combining Raman spectroscopy and EBSD for a better microstructure knowledge