1,721,201 research outputs found
Experimental investigation of high He/dpa microstructural effects in neutron irradiated B-alloyed Eurofer97 steel by means of small angle neutron scattering (SANS) and electron microscopy
No full textHigh He/dpa microstructural effects have been investigated, by means of small-angle neutron scattering (SANS) and transmission electron microscopy (TEM), in B-alloyed ferritic/martensitic steel Eurofer97-1 (0.12 C, 9 Cr, 0.2 V, 1.08 W wt%, B contents variable between 10 and 1000 ppm), neutron irradiated at the High Flux Reactor of the JRC-Petten at temperatures between 250 °C and 450 °C, up do a dose level of 16 dpa. Under these irradiation parameters, B activation is expected to produce corresponding helium contents variable between 80 and 5600 appm, with helium bubble distributions relevant for the technological applications. The SANS measurements were carried out under magnetic field to separate nuclear and magnetic SANS components; a reference, un-irradiated sample was also measured to evaluate as accurately as possible the genuine effect of the irradiation on the microstructure. Increasing the estimated helium content from 400 to 5600 appm, the analysis of the SANS cross-sections yields an increase in the volume fraction, attributed to helium bubbles, of almost one order of magnitude (from 0.007 to 0.038); furthermore, the difference between nuclear and magnetic SANS components is strongly reduced. These results are discussed in correlation with TEM observations of the same samples and are tentatively attributed to the effect of drastic microstructural changes in Eurofer97-1 for high He/dpa ratio values, possibly relating to the dissolution of large B-carbides due to transmutation reactions. © 2016 The Author
Polarised SANS study of microstructural evolution under neutron irradiation in a martensitic steel for fusion reactors
No full textThis work presents the results of polarised small-angle neutron scattering (SANS) measurements of modified martensitic steel DIN1.4914, originally developed for application in future fusion reactors (MANET steel). SANS measurements were made using the D22 instrument at the ILL Grenoble using an ad hoc polarised beam set-up. The investigated MANET samples were neutron irradiated and subsequently post-irradiation tempered to reproduce as much as possible the expected service conditions. The results, based on the analysis of the nuclear-magnetic interference, are discussed taking into account both the occurrence of Cr redistribution phenomena with correlated changes in the composition of the precipitate phases, and the growth of non-magnetic defects (He-bubbles or microvoids)
SANS and TEM investigation of laser-synthesized photoluminescent Si nanoparticles
No full textLaser-synthesized photoluminescent Si nanopowders, of interest for application in optoelectronics, have been studied by small-angle neutron scattering (SANS) and transmission electron microscopy (TEM) to characterize their size-distribution function, which correlates with emission spectra and optical performances. The SANS measurements were carried out over a wide Q-range by using the D22 instrument at ILL. The analysis of the size distributions obtained from the SANS data reveals that the microstructure of such powders includes particles as large as those observed by TEM (30-200 Å in diameter) and a distribution of tiny inhomogeneities (5-10 Å in diameter), possibly micropores, which can have relevant consequences on material performance
Microstructural investigation of low-dose neutron irradiation effects in martensitic steels for nuclear application by means of small-angle neutron scattering
No full textThe microstructural effect of low-dose neutron irradiation and subsequent high-temperature tempering in the reduced activation ferritic/martensitic steel F82H-mod. (7.73 Cr, 0.09 C, 0.08 Mn, 0.19 V, 2.06 W, 0.02 Ta, wt%, bal. Fe) has been studied using small-angle neutron scattering (SANS). The investigated samples were irradiated with thermal neutrons at 523 K, to dose levels of 2.4 displacements per atom then tempered for 2 h at 1043 K. The SANS measurements were carried out at the D22 instrument of the High Flux Reactor at the Institut Max von Laue-Paul Langevin, Grenoble, France. The differences observed in nuclear and magnetic small-angle neutron scattering cross-sections after subtraction of the reference sample from the irradiated one suggest that the irradiation and the subsequent post-irradiation tempering produce the growth of non-magnetic precipitates; the results are also compared with those obtained on other ferritic/martensitic steels, with different chemical composition, irradiated under the same conditions
Photoluminescence properties and size distribution in laser synthesized Si nanopowders for optoelectronic devices
No full textSmall-angle neutron scattering (SANS) and transmission electron microscopy (TEM) have been used to investigate the correlation between photoluminescence properties and particle size distributions in laser synthesized Si nanopowders, of interest for application in optoelectronics. The Si nanoparticle volume distributions obtained from the SANS data are in good agreement with the TEM histogram for particle diameters ranging between 30 and 200, Å approximately. Furthermore the SANS data confirm that, as it is known from photoemission spectra, in the case of highly luminescent powders a secondary distribution of particles ranging between 10 and 20 Å approximately (hardly visible by TEM) is present. Finally the SANS data analysis suggests that tiny inhomogeneities (5-10 Å in diameter), possibly micropores which may have relevant consequences on material performance, are also present in all the investigated samples
SANS and TEM study of y2O3 particle distributions in oxide-dispersion strengthened EUROFER martensitic steel for fusion reactors
No full textTransmission electron microscopy (TEM) and small-angle neutron scattering (SANS) were used to characterize the microstructure of two variants of oxide-dispersion strengthened (ODS) Eurofer-97 steel (9% CrWVTa), that is being developed for future fusion reactors. More specifically the Y2O 3 particle size distributions obtained with different Y 2O3 contents have been characterized, since the mechanical properties are strongly correlated with such features. The SANS measurements have been carried out by the D22 instrument at the High Flux Reactor of the Institut Laue-Langevin, Grenoble. There is a good agreement between TEM histograms and SANS distributions of the Y2O3 particles. Furthermore, relevant and unique information is provided by the SANS measurements that reveals particles of size smaller than 1 nm approximately
Helium bubble evolution in F82H-mod - Correlation between SANS and TEM
No full textThe growth of He-bubbles after low temperature He-implantation and subsequent high temperature tempering in F82H-mod steel has been studied by using transmission electron microscopy (TEM) and small-angle neutron scattering (SANS). The results obtained by both techniques show that after implantation the bubbles are homogeneously distributed around an average size of 11 Å, while after subsequent tempering He-bubbles one order of magnitude larger grow in size and volume fraction. Additionally, the SANS data show a consistent population of bubbles smaller than 10 Å, which is discussed with reference to the possible migration and coalescence mechanisms during high temperature tempering
Small angle neutron scattering investigation of microporosity in marbles
No full textSmall angle neutron scattering (SANS) measurements have been carried out on different marble and limestone samples, of relevance to cultural heritage safeguard, to investigate the micropore size distribution. Different varieties of marble have been studied using a CaCO3 single crystal as a pore-free reference. A series of red scaglia limestone samples has also been studied, obtaining in this case identical SANS cross sections for specimens issued from a modern quarry and for samples issued from an historical building. The micropore volume distribution functions, obtained from the SANS data, are compared with porosimetry results
Micro-structural effects of irradiation temperature and helium content in neutron irradiated B-alloyed Eurofer97-1 steel
No full textThe micro-structural effects of different neutron irradiation temperatures and helium contents, for 16 dpa dose, have been investigated by means of small-angle neutron scattering (SANS) in B-alloyed ferritic/martensitic steel Eurofer97-1 (0.12 C, 9 Cr, 0.2 V, 1.08 W wt%, B concentrations up to 1000 ppm); due to B transmutations, fusion relevant He/dpa values are expected to be produced under neutron irradiation. SANS measurements have been carried out on a sample irradiated at 350 °C, with estimated helium content of 5600 appm, and compared to previous SANS results, obtained on two other irradiated samples of this same B-alloyed steel. These new measurements confirm that for such high helium contents the SANS cross-section increases in order of magnitude and the magnetic SANS component is strongly reduced, compared to lower helium content (400 appm). Such effects are attributed to increase in helium bubbles density and to the presence of micro-cavities, produced after dissolution of large B-carbides. The SANS data analysis procedure has been improved, also thanks to the additional information provided by the new measurements, and more accurate helium bubble size distributions have been obtained for all the investigated samples. For 5600 appm helium content, bubble volume fractions are found of 0.025 for the sample irradiated at 350 °C and of 0.041 for the previously investigated sample irradiated at 400 °C, significantly increasing with the irradiation temperature. These values are approximately one order of magnitude larger than the value of 0.003 previously found for the sample with 400 appm helium. The size distributions are compared with electron microscopy observations of these same samples. It appears that the occurrence of complex micro-structural changes in irradiated Eurofer97-1 steel should be taken in due account when considering its application under high He/dpa ratio values. © 201
Polarised Small Angle Neutron Scattering study of microstructural radiation damage in steels for nuclear applications
No full textPolarised SANS has been used to investigate two martensitic steels for fusion reactor technology (MANET and OPTIFER, differing in their initial Cr content), before and after neutron irradiation. The measurements were carried out at the instrument D22 of the ILL, Grenoble, using an ad hoc polarised beam set-up. The results show both the occurrence of Cr redistribution phenomena with correlated changes in the composition of the precipitate phases, and the growth of non-magnetic defects (possibly microvoids), depending on the irradiation conditions and on the original steel composition
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