Analysis of Nuclei in a Heavy-Section Nodular Iron Casting

The microstructure of heavy section nodular graphite cast irons often presents a bimodal distribution of nodule size associated with so-called primary and secondary graphite nucleation. It has been found that the nuclei in both types of nodules consist mainly in magnesium sulphide. However, nuclei in primary nodules contain some traces of calcium and are thus related with the inoculation treatment. On the contrary, nuclei in secondary nodules do not contain any element that could be associated to inoculation. It is suggested they form in the late stage of the eutectic reaction as a result of microsegregation build-up in magnesium and sulphur

Ordering phenomena in the diphosphate tungsten bronzes with hexagonal tunnels : Ba (P2O4)2 (WO3)2m

Superstructure phenomena in the barium diphosphate tungsten bronzes with hexagonal tunnels, Ba (P2O4)2 (WO3 )2m , are characterized by electron diffraction and high resolution electron microscopy. A model of superstructure is deduced from the observations and used to perform image calculations. The comparison of experimental and calculated images allows to associate the superstructure phenomena to orderings of the barium cations in the hexagonal tunnels.Les phénomènes de surstructure dans les bronzes diphosphates de tungstène à tunnels hexagonaux au baryum, Ba (P2O4)2 (WO3)2m , sont caractérisés par diffraction électronique et microscopie électronique haute résolution. Un modèle de surstructure est déduit des observations et utilisé dans les calculs de simulation d'images. La comparaison des images expérimentales et calculées permet d'associer aux phénomènes de surstructure, des mises en ordre des cations baryum dans les tunnels de section hexagonale

Analysis of Nuclei in a Heavy-Section Nodular Iron Casting

International audienceThe microstructure of heavy section nodular graphite cast irons often presents a bimodal distribution of nodule size associated with so-called primary and secondary graphite nucleation. It has been found that the nuclei in both types of nodules consist mainly in magnesium sulphide. However, nuclei in primary nodules contain some traces of calcium and are thus related with the inoculation treatment. On the contrary, nuclei in secondary nodules do not contain any element that could be associated to inoculation. It is suggested they form in the late stage of the eutectic reaction as a result of microsegregation build-up in magnesium and sulphur

Overview on Zener diode pulsed EOS characterization

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Investigation of the internal structure of flax fibre cell walls by transmission electron microscopy

International audienceThe development of the use of flax fibre as reinforcement of eco-friendly composite materials requires a good knowledge of its hydrothermal and mechanical behaviours. To this end the fibre internal structure must be finely investigated. Transmission electron microscopy was used to analyse the morphology of the fibre cell walls in terms of the arrangement of the layers and their thickness. Thus, an alternative eco-friendly staining method, based on oolong tea extract was successfully implemented. The results reveal an arrangement at the nanoscale slightly different from the classical four layer model encountered in the literature the inner layer includes three to four sub-layers. The cell walls comprises two outer layers of relative thickness of about 10 %, a middle layer of about 70 % and a group of thinner layers (called sub-layers) that are contiguous to the lumen with relative thickness of about 20 %. © 2015, Springer Science+Business Media Dordrecht

High-resolution FIB-TEM-STEM structural characterization of grain boundaries in the high dielectric constant perovskite CaCu3Ti4O12

International audienceIn this work, the grain boundaries composition of the polycrystalline CaCu3Ti4O12 (CCTO) was investigated. A Focused Ion Beam (FIB)/lift-out technique was used to prepare site-specific thin samples of the grain boundaries interface of CCTO ceramics. Scanning transmission electron microscopy (STEM) coupled with energy dispersive X-ray spectrometry (EDXS) and Electron Energy Loss Spectroscopy (EELS) systems were used to characterize the composition and nanostructure of the grain and grain boundaries region. It is known that during conventional sintering, discontinuous grain growth occurs and a Cu-rich phase appears at grain boundaries. This Cu-rich phase may affect the final dielectric properties of CCTO but its structure and chemical composition remained unknown. For the first time, this high-resolution FIB-TEM-STEM study of CCTO interfacial region highlights the composition of the phases segregated at grain boundaries namely CuO, Cu2O and the metastable phase Cu3TiO4

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High-resolution FIB-TEM-STEM structural characterization of grain boundaries in the high dielectric constant perovskite CaCu3Ti4O12

International audienceIn this work, the grain boundaries composition of the polycrystalline CaCu3Ti4O12 (CCTO) was investigated. A Focused Ion Beam (FIB)/lift-out technique was used to prepare site-specific thin samples of the grain boundaries interface of CCTO ceramics. Scanning transmission electron microscopy (STEM) coupled with energy dispersive X-ray spectrometry (EDXS) and Electron Energy Loss Spectroscopy (EELS) systems were used to characterize the composition and nanostructure of the grain and grain boundaries region. It is known that during conventional sintering, discontinuous grain growth occurs and a Cu-rich phase appears at grain boundaries. This Cu-rich phase may affect the final dielectric properties of CCTO but its structure and chemical composition remained unknown. For the first time, this high-resolution FIB-TEM-STEM study of CCTO interfacial region highlights the composition of the phases segregated at grain boundaries namely CuO, Cu2O and the metastable phase Cu3TiO4

On the role of impurities on spheroidal graphite degeneracy in cast irons

International audienceThough manufacturing spheroidal graphite cast irons is a well-established industrial process, good nodularity which is essential for mechanical properties may be hampered by several factors. Amongst them is the presence of impurities at trace level which lead to the growth of protrusions and the question is how they can destroy the spheroidizing effect of magnesium. For the first time, it is shown that such impurities are present together with magnesium at the interface between spheroid and protrusion. For getting this result, site-specific electron transparent lamellae were prepared using Focused Ion Beam and characterized at nanometric scale using atomic resolution scanning-transmission electron microscope. It is also shown by automatic crystal orientation mapping that there is no definite crystallographic relationship between protrusions and underlying spheroids