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In the framework of a new generation of nuclear reactors, typically sodium fast reactors, supercritical carbon dioxide (CO 2 ) with a Brayton cycle (at 550°C and 250 bars) is identified as a promising energy conversion system to replace the traditional steam generators. Nevertheless, the long-term integrity of the heat exchanger structure in this environment has to be proven over at least 20 years. To this purpose, the corrosion behavior of different metallic materials under static CO 2 at 550°C and 250 bars is studied. The materials under study are one 9 wt% Cr ferrito-martensitic steel (T91) and several austenitic steels. The results about the nature of the corrosion product, morphology, and kinetics of formation were analyzed by glow discharge optical emission spectroscopy, scanning electron microscopy, wavelength-dispersive spectroscopy, and x-ray diffraction. A corrosion mechanism of the different steels is proposed and the most promising materials for heat exchanger applications are discussed.

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Extraction yields and fatty acid profiles from freeze-dried Chlorella vulgaris by microwave pretreatment followed by supercritical carbon dioxide (MW-SCCO2) extraction were compared with those obtained by supercritical carbon dioxide extraction alone (SCCO2). Work performed with pressure range of 20–28 Mpa and temperature interval of 40–70 °C, gave the highest extraction yield (w/w dry weight) at 28 MPa/40 °C. MW-SCCO2 allowed to obtain the highest extraction yield (4.73%) compared to SCCO2 extraction alone (1.81%). Qualitative and quantitative analyses of microalgae oil showed that palmitic, oleic, linoleic and α-linolenic acid were the most abundant identified fatty acids. Oils obtained by MW-SCCO2 extraction had the highest concentrations of fatty acids compared to SCCO2 extraction without pretreatment. Native form, and microwave pretreated and untreated microalgae were observed by scanning electronic microscopy (SEM). SEM micrographs of pretreated microalgae present tearing wall agglomerates. After SCCO2, microwave pretreated microalgae presented several micro cracks; while native form microalgae wall was slightly damaged.