New analytical developments for powder characterization
Résumé
Powders and divided solids are widely used in industry as intermediate or finished products in many fields foods, cosmetics, construction, pharmaceuticals, transport, electronics and, of course, nuclear energy. Optimizing their use requires control of processing based on an understanding of the phenomena involved (sintering, chemical reactivity, purity, etc.). Modeling and understanding these phenomena require data and characteristics that may be difficult to obtain. The present work cites examples illustrating different physicochemical characterization techniques suitable for analysis of uranium based powder samples (oxide, carbide, fluoride and metallic) in the raw state or after preparation (ion polishing) used in nuclear cycle. The first section discusses dimensional characterization (particle size, morphology, porosity) by means of image analysis and preparation techniques SEM, TEM, FIB, electron and X ray tomography with possible 2D and 3D image analysis. Morphological data in the form of the powder size and shape can be obtained with new developments in 2D analysis of processed SEM images. The second part of this work describes elemental chemical characterization. Low-voltage EDS spectroscopy on polished powder cross sections is used to map the distribution of phases and to detect possible impurities in the solid grains and agglomerates. The contribution of this type characterization to understanding the reaction mechanisms of phase transformations (especially solid-gas reactions) is illustrated for the hydrofluorination of uranium dioxide. Sample preparation by mounting followed by ion polishing, optimization of the EDS analysis parameters, and the contribution to solid-gas reaction models are discussed in this study. Complementary surface analyses as Auger spectrometry allows powder surface oxidation. The third section describes the characterization of the chemical reactivity of powders and property mechanics. Chenical reactivity are performed by high-temperature in situ treatment in an environmental SEM, and allow observation of the powder morphology transformation. Property mechanics are performed by in situ treatment in an SEM FEG with plate of compressive force. The examples discussed concern materials used in nuclear fuel fabrication processes.