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  • 1.
    Bergqvist, Hans
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Chen, J.
    Jädernäs, D.
    Bengtsson, B.
    CHaracterization of PWR CRUD phases and their variation under plant operation by transmission electron microscopy2009In: 14th International Conference on Environmental Degradation of Materials in Nuclear Power Systems Water Reactors 2009, 2009, p. 1136-1147Conference paper (Refereed)
    Abstract [en]

    The solid particles suspended and circulated in PWR primary water may consist of fuel CRUD, solid corrosion products of water-contacting materials, additives and various impurities of reactor water. This paper demonstrates a new methodology by using transmission electron microscopy to characterize the phase compositions of CRUD particles and their variation under reactor operation. Several new CRUD phases have been imaged and confirmed by energy dispersive X-ray spectroscopy and selected area electron diffraction studies. The differences in CRUD phase composition between scraped fuel CRUD, CRUD from primary water in an event of elevated Co-58 activity or shutdown or H 2O 2 injection are reported and discussed with respect to the thermodynamic stability of some phases and possible chemical reactions involved.

  • 2. Chen, J.
    et al.
    Bergqvist, Hans
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Jädernäs, D.
    Granath, G.
    High resolution electron microscopy study on the thin oxide films formed on type 316L stainless steel exposed under simulated BWR water chemistry conditions2009In: 14th International Conference on Environmental Degradation of Materials in Nuclear Power Systems Water Reactors 2009, 2009, p. 604-613Conference paper (Refereed)
    Abstract [en]

    This paper describes the microstructures of the oxide films formed on a type 316L stainless steel material exposed under simulated BWR water chemistry conditions. High resolution electron microscopy (both FE-SEM and FE-TEM) was used. A TEM specimen was prepared by using focused ion beam technique. It is revealed that the inner thin oxide layer, unlike commonly believed, contains a large fraction of voids in some locations. There are concentration gradients of Fe, Ni and Cr elements in this layer. Furthermore, the TEM investigation revealed that the relatively large grains as commonly seen on the corroded surface sometimes consist of several small crystals of either different crystallographic orientations or different chemical compositions. The implication of the observed microstructures of the oxide films to the radioactivity build-up on BWR plant system piping surfaces is elaborated.

  • 3. Gault, B.
    et al.
    Felfer, P. J.
    Ivermark, M.
    Bergqvist, Hans
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Cairney, J. M.
    Ringer, S. P.
    Atom probe microscopy characterization of as quenched Zr-0.8 wt% Fe and Zr-0.15 wt% Cr binary alloys2013In: Materials letters (General ed.), ISSN 0167-577X, E-ISSN 1873-4979, Vol. 91, p. 63-66Article in journal (Refereed)
    Abstract [en]

    Two binary Zr-alloys with a β-quenched structure were analysed by atom probe tomography to provide a better understanding of how Fe and Cr perform in industrial Zr alloys. In a Zr-0.8 Fe (wt%) alloy, we observed a dispersion of precipitates with a composition close to Zr3Fe, and Fe segregated to a grain boundary. In a Zr-0.15 Cr (wt%) alloy, Cr was observed in solid solution in the Zr-matrix and segregated to grain boundary where it formed small spherical particles or elongated atmospheres.

  • 4.
    Hedberg, Yolanda
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Norell, Mats
    Materials and Manufacturing Technology, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden.
    Linhardt, Paul
    Institute for Chemical Technologies and Analytics (CTA), Vienna University of Technology, Getreidemarkt 9/164, A-1060 Vienna, Austria.
    Bergqvist, Hans
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Odnevall Wallinder, Inger
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Influence of Surface Oxide Characteristics and Speciation on Corrosion, Electrochemical Properties and Metal Release of Atomized 316L Stainless Steel Powders2012In: International Journal of Electrochemical Science, ISSN 1452-3981, E-ISSN 1452-3981, Vol. 7, no 12, p. 11655-11677Article in journal (Refereed)
    Abstract [en]

    Surface oxide characteristics of powder particles are important to consider for any toxicological risk assessment based on in-vitro or in-vivo tests. This study focuses on a multi-analytical approach (X-ray photoelectron spectroscopy, Auger electron spectroscopy, scanning- and transmission electron microscopy, and different electrochemical techniques) for in-depth characterization of surface oxides of inert-gas-atomized (GA) AISI 316L stainless steel powder, compared with massive sheet and a water-atomized (WA) 316L powder. Implications of differences in surface oxide phases and their surface distribution on corrosion, electrochemical properties and metal release are systematically discussed. Cr was enriched in an inner surface layer for both GA powders, with Mn and S enriched in the outermost surface oxide. The surface oxide was 2-5 nm thick for both GA powder size fractions, amorphous for the GA powder sized <4 μm and partially crystalline for the powder sized <45 μm. A strong ennoblement, i.e. positive shift in open circuit potential, of up to 800 mV, depending on solution, was observed for the GA powders. This ennoblement was induced by catalytic oxygen reduction properties of tri- or tetravalent Mn-oxides, not present on the massive sheet or WA powder. In contrast to the predominant presence of a trivalent Cr-oxide in the surface oxide of the GA powder particles, the WA<45μm powder revealed oxidized Cr, most probably present in its hexavalent state (not chromate), within a silicate-rich surface oxide. This study clearly shows that the surface oxide composition and speciation of differently sized GA and WA powders are unique (strongly connected to the atomization process) and of large importance for their pitting corrosion and metal release properties. For the GA<45μm powder, Mn-rich oxide nanoparticles were proposed to account for its higher pitting corrosion susceptibility, a more stable surface ennoblement, and a shift of the MnO2 oxidation/reduction peaks in the cyclic voltammogram, compared with the GA particles sized <4μm. The thermodynamically unstable ferritic structure of the small sized particle fraction (GA <4μm), despite an austenitic composition, revealed a higher pitting corrosion susceptibility and higher nickel release compared with the austenitic particle fraction of the GA <45 μm powder.

  • 5.
    Tilliander, Ulrika
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Bergqvist, Hans
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Morphology studies of a W/Cu alloy synthesized by hydrogen reduction2006In: Journal of Materials Research, ISSN 0884-2914, E-ISSN 2044-5326, Vol. 21, no 6, p. 1467-1475Article in journal (Refereed)
    Abstract [en]

    Because of the applications for W/Cu composite materials in high technology, the advantages of synthesizing this alloy by the hydrogen reduction route were investigated, with special attention to the properties of the product that was formed. Kinetic studies of reduction indicated that the mechanism changes significantly at 923 K, and the product had unusual properties. In the present work, morphological studies of the W/Cu alloy with 20 wt% Cu, produced at 923 K, were carried out by x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analyses. The structural studies performed by XRD indicated that, at 923 K, Cu dissolved in W, forming a metastable solid solution in the nanocrystalline state. The samples produced at higher as well as lower temperatures, on the other hand, showed the presence of two phases, pure W and pure Cu. The SEM results were in agreement with the XRD analysis and confirmed the formation of W/Cu alloy. TEM analysis results confirmed the above observations and showed that the particle sizes were about 20 nm. The structure of the W/Cu alloy produced in the present work was compared with those for pure Cu, produced from Cu2O produced by hydrogen reduction under similar conditions. This indicated that the presence of W hinders the coalescence of Cu particles, and the alloy retains its nano-grain structure. The present results open up an interesting process route toward the production of intermetallic phases and composite materials under optimized conditions.

  • 6.
    Yar, Mazher Ahmed
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Wahlberg, Sverker
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Bergqvis, Hans
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Salem, Hanadi G.
    Johnsson, Mats
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Chemically produced nanostructured ODS-lanthanum oxide-tungsten composites sintered by spark plasma2011In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 408, no 2, p. 129-135Article in journal (Refereed)
    Abstract [en]

    High purity W and W-0.9La(2)O(3) (wt.%) nanopowders were produced by a wet chemical route. The precursor was prepared by the reaction of ammonium paratungstate (APT) with lanthanum salt in aqueous solutions. High resolution electron microscopy investigations revealed that the tungstate particles were coated with oxide precipitates. The precursor powder was reduced to tungsten metal with dispersed lanthanum oxide. Powders were consolidated by spark plasma sintering (SPS) at 1300 and 1400 degrees C to suppress grain growth during sintering. The final grain size relates to the SPS conditions, i.e. temperature and heating rate, regardless of the starting powder particle size. Scanning electron microscopy revealed that oxide phases were mainly accumulated at grain boundaries while the tungsten matrix constituted of nanosized sub-grains. The transmission electron microscopy revealed that the tungsten grains consist of micron-scale grains and finer sub-grains. EDX analysis confirmed the presence of W in dispersed oxide phases with varying chemical composition, which evidenced the presence of complex oxide phases (WO-La) in the sintered metals.

  • 7.
    Yar, Mazher Ahmed
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Wahlberg, Sverker
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Bergqvist, Hans
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Salem, H. G.
    Johnsson, Mats
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Spark plasma sintering of tungsten-yttrium oxide composites from chemically synthesized nanopowders and microstructural characterization2011In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 412, no 2, p. 227-232Article in journal (Refereed)
    Abstract [en]

    Nano-crystalline W-1%Y2O3 (wt.%) powder was produced by a modified solution chemical reaction of ammonium paratungstate (APT) and yttrium nitrate. The precursor powder was found to consist of particles of bimodal morphology i.e. large APT-like particles up to 20 pm and rectangular yttrium containing ultrafine plates. After thermal processing tungsten crystals were evolved from W-O-Y plate like particles. spark plasma sintering (SPS) was used to consolidate the powder at 1100 and 1200 degrees C for different holding times in order to optimize the sintering conditions to yield high density but with reduced grain growth. Dispersion of yttrium oxide enhanced the sinterability of W powder with respect to lanthanum oxide. W-1%Y2O3 composites with sub-micron grain size showed improved density and mechanical properties as compared to W-La2O3 composites. Sample sintered in two steps showed improved density, due to longer holding time at lower temperature (900 degrees C) and less grain growth due to shorter holding time at higher temperature i.e. 1 min at 1100 degrees C.

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