| 1. |
- Claesson, Erik, et al.
(författare)
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Carbide Precipitation during Processing of Two Low-Alloyed Martensitic Tool Steels with 0.11 and 0.17 V/Mo Ratios Studied by Neutron Scattering, Electron Microscopy and Atom Probe
- 2022
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Ingår i: Metals. - Basel, Switzerland : MDPI AG. - 2075-4701. ; 12:5
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Tidskriftsartikel (refereegranskat)abstract
- Two industrially processed low-alloyed martensitic tool steel alloys with compositions Fe-0.3C-1.1Si-0.81Mn-1.5Cr-1.4Ni-1.1Mo-0.13V and Fe-0.3C-1.1Si-0.81Mn-1.4Cr-0.7Ni-0.8Mo-0.14V (wt.%) were characterized using small-angle neutron scattering (SANS), scanning electron microscopy (SEM), Scanning transmission electron microscopy (STEM), and atom probe tomography (APT). The combination of methods enables an understanding of the complex precipitation sequences that occur in these materials during the processing. Nb-rich primary carbides form at hot working, while Fe-rich auto-tempering carbides precipitate upon quenching, and cementite carbides grow during tempering when Mo-rich secondary carbides also nucleate and grow. The number density of Mo-rich carbides increases with tempering time, and after 24 h, it is two to three orders of magnitude higher than the Fe-rich carbides. A high number density of Mo-rich carbides is important to strengthen these low-alloyed tool steels through precipitation hardening. The results indicate that the Mo-rich secondary carbide precipitates are initially of MC character, whilst later they start to appear as M2C. This change of the secondary carbides is diffusion driven and is therefore mainly seen for longer tempering times at the higher tempering temperature of 600◦C.
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| 2. |
- Claesson, Erik, et al.
(författare)
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Early precipitation behavior of secondary carbides in medium carbon low alloyed tool steel studied by in-situ polarized small-angle scattering and precipitation modelling
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Tidskriftsartikel (refereegranskat)abstract
- The strength of tempered martensite in low alloyed tool steel depends on the precipitation of secondary carbides. Tempering parameters such as time and temperature together with heating rate to tempering temperature will influence the precipitation sequence and these critical process parameters must be controlled to achieve ultimate precipitation strengthening. In this work precipitation was studied in a low alloyed tool steel using in-situ polarized small angle scattering (SANSPOL) during heating and isothermal holding. It was possible with SANSPOL to study the initial precipitation of secondary Mo- and V-rich carbides. It was found that Mo- and V-rich carbides form above 500 °C, simultaneously to the formation of cementite, which started to form already at lower temperature. It was furthermore found that the cementite particles can be described as having a core-shell structure, the Mo-V-rich carbides small and were approximated as spherical. Precipitation simulations performed using TC-PRSIMA were finally performed to compare with the experimental results, and the simulations were found to describe the experimental results well.
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| 3. |
- Claesson, Erik, et al.
(författare)
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Evolution of iron carbides during tempering of low-alloy tool steel studied with polarized small angle neutron scattering, electron microscopy and atom probe
- 2022
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Ingår i: Materials Characterization. - : Elsevier BV. - 1044-5803 .- 1873-4189. ; 194, s. 112464-112464
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Tidskriftsartikel (refereegranskat)abstract
- The magnetic scattering of iron carbides in low-alloy tool steel was investigated ex-situ by polarized small angle neutron scattering measurements after tempering the steel at 550 °C and 600 °C. Magnetic features could be detected in the as-quenched sample resulting in a negative interference term, believed to be either θ-Fe3C, η-Fe2C, or ε-Fe2-3C. During tempering the evolution of cementite could be studied by the variation of the interference term and in γ-ratio, which is the ratio of the magnetic to nuclear scattering length density contrast. From scanning transmission electron microscopy (STEM) and atom probe tomography, it is evident that cementite (θ-Fe3C) is present directly when reaching the tempering temperature of either 550 °C or 600 °C. At longer tempering times, cementite gets enriched with substitutional elements like chromium and manganese, forming an enriched shell on the cementite particles. STEM and energy dispersive x-ray spectrometry show that the chemical composition of small cementite particles approaches that of Cr-rich M7C3 carbides after 24 h at 600 °C. It is also seen that small non-magnetic particles precipitate during tempering and these correspond well with molybdenum and vanadium-rich carbides.
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| 4. |
- Gentile, Luigi, et al.
(författare)
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Rheochaos and flow instability phenomena in a nonionic lamellar phase
- 2013
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 9:4, s. 1133-1140
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Tidskriftsartikel (refereegranskat)abstract
- In this study we report on instability phenomena in a solution where shear induces multilamellar vesicles (MLVs) from a lamellar phase. A shear-thickening regime has been observed for hexadecyl tetraethylene glycol ether (C16E4) dissolved in D2O at 40 degrees C. In this regime, unstable temporal viscosity behavior, i.e. periodic oscillations, has been observed at 2, 5 and 10 s(-1). Moreover at a shear rate of 10 s(-1) shear banding manifests itself as the occurrence of transparent and turbid bands stacked along the vorticity direction. We perform time-resolved-rheo-small angle neutron scattering (rheo-SANS) experiments to understand the nature of the viscosity oscillations and spatial-resolved experiments to obtain a structural characterization of vorticity bands.
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| 5. |
- Isabettini, Stéphane, et al.
(författare)
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Mastering the magnetic susceptibility of magnetically responsive bicelles with 3β-amino-5-cholestene and complexed lanthanide ions
- 2017
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 19:17, s. 10820-10824
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Tidskriftsartikel (refereegranskat)abstract
- The magnetic susceptibility of lanthanide-chelating bicelles was selectively enhanced by introducing 3β-amino-5-cholestene (aminocholesterol, Chol-NH2) in the bilayer. Unprecedented magnetic alignment of the bicelles was achieved without altering their size. An aminocholesterol conjugate (Chol-C2OC2-NH2), in combination with different lanthanide ions, offers the possibility of fine-tuning the bicelle's magnetic susceptibility.
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| 6. |
- Junker, Katja, et al.
(författare)
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Mechanistic aspects of the horseradish peroxidase-catalysed polymerisation of aniline in the presence of AOT vesicles as templates
- 2012
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Ingår i: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 2:16, s. 6478-6495
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Tidskriftsartikel (refereegranskat)abstract
- The mechanism of the horseradish peroxidase (HRP)-H2O 2-catalysed polymerisation of aniline in the presence of AOT vesicles was investigated. AOT (= bis-(2-ethylhexyl)sulfosuccinate) served as vesicle-forming surfactant and dopant for obtaining at pH = 4.3 and room temperature within 24 h under optimal reaction conditions the green emeraldine salt form of polyaniline in 90-95% yield. Based on UV/VIS/NIR and EPR measurements carried out during the polymerisation reaction, and based on changes in aniline and H2O2 concentrations and HRP activity, a mechanism is proposed. According to this "radical cation mechanism" chain growth occurs on the vesicle surface through addition of aniline radical cations to the growing polymer chain. H2O2 plays two essential roles, to oxidise the heme group of HRP, and to oxidise the growing polymer chain for allowing the stepwise addition of new aniline radical cations. The entire reaction can be divided into three kinetically distinct phases. In the first rapid phase (5-10 min), the actual polymer formation takes place to yield the emeraldine salt form of polyaniline in its bipolaron state. In the second and third slower phases (1-2 days) the bipolarons transform into polarons with unpaired electrons. During the reaction, the HRP activity is decreasing until the enzyme becomes inactive after polymer formation. Reactions carried out with partially deuterated anilines were analysed by 2H magic-angle spinning (MAS) NMR spectroscopy to demonstrate the regioselectivity of the chain growth: para-coupling of the aniline units clearly dominates. Association of the formed polyaniline with the vesicle membrane is evident from cryo-TEM and SANS measurements.
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| 7. |
- Kumar, Sugam, et al.
(författare)
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Evolution of Interactions in the Protein Solution As Induced by Mono and Multivalent Ions
- 2019
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 20:5, s. 2123-2134
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Tidskriftsartikel (refereegranskat)abstract
- The evolution of interactions in the bovine serum albumin (BSA) protein solution on addition of mono and multivalent (di, tri and tetra) counterions has been studied using small-angle neutron scattering (SANS), dynamic light scattering (DLS) and zeta-potential measurements. It is found that in the presence of mono and divalent counterions, protein behavior can be well explained by DLVO theory, combining the contributions of screened Coulomb repulsion with the van der Waals attraction. The addition of mono or divalent salts in protein solution reduces the repulsive barrier and hence the overall interaction becomes attractive, but the system remains in one-phase for the entire concentration range of the salts, added in the system. However, contrary to DLVO theory, the protein solution undergoes a reentrant phase transition from one-phase to a two-phase system and then back to the one-phase system in the presence of tri and tetravalent counterions. The results show that tri and tetravalent (unlike mono and divalent) counterions induce short-range attraction between the protein molecules, leading to the transformation from one-phase to two-phase system. The two-phase is characterized by the fractal structure of protein aggregates. The excess condensation of these higher-valent counterions in the double layer around the BSA causes the reversal of charge of the protein molecules resulting into reentrant of the one-phase, at higher salt concentrations. The complete phase behavior with mono and multivalent ions has been explained in terms of the interplay of electrostatic repulsion and ion induced short-range attraction between the protein molecules.
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| 8. |
- Kumar, Sugam, et al.
(författare)
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Reentrant phase behavior of nanoparticle solutions probed by small-angle scattering
- 2019
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Ingår i: Current Opinion in Colloid & Interface Science. - : Elsevier BV. - 1359-0294 .- 1879-0399. ; 42, s. 17-32
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Forskningsöversikt (refereegranskat)abstract
- The nanoparticles in solution represent a model system, where the well-established colloidal theories such as the Debye-Huckel theory and/or Derjaguin- Landau-Verwey-Overbeek theory can be implemented to predict the nanoparticle phase behavior. Recently, reentrant phase transitions in a wide range of colloids (e.g., inorganic and organic nanoparticles, polymers, and biomolecules) have been observed, which are not consistent with these theories. The colloids in the reentrant phase behavior undergo a phase change and return back to the original phase with respect to a specific physiochemical parameter (e.g., ionic strength, concentration of different additives, temperature, and so on). The nanoparticle-polymer/multivalent ion systems, demonstrating such phase transition and the corresponding phase behavior in terms of interparticle interactions, have been probed by small-angle scattering. It has been shown how the tuning in interparticle interactions using external parameters can lead to reentrant phase behavior and use the nanoparticle aggregation for building nanohybrids. The deviations of the present observations from those of the standard colloidal theories and the anticipated challenges are also discussed.
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| 9. |
- Lehofer, Bernhard, et al.
(författare)
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High Hydrostatic Pressure Induces a Lipid Phase Transition and Molecular Rearrangements in Low-Density Lipoprotein Nanoparticles
- 2018
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Ingår i: Particle and Particle Systems Characterization. - : Wiley. - 0934-0866. ; 35:9
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Tidskriftsartikel (refereegranskat)abstract
- Low-density lipoproteins (LDL) are natural lipid transporter in human plasma whose chemically modified forms contribute to the progression of atherosclerosis and cardiovascular diseases accounting for a vast majority of deaths in westernized civilizations. For the development of new treatment strategies, it is important to have a detailed picture of LDL nanoparticles on a molecular basis. Through the combination of X-ray and neutron small-angle scattering (SAS) techniques with high hydrostatic pressure (HHP) this study describes structural features of normolipidemic, triglyceride-rich and oxidized forms of LDL. Due to the different scattering contrasts for X-rays and neutrons, information on the effects of HHP on the internal structure determined by lipid rearrangements and changes in particle shape becomes accessible. Independent pressure and temperature variations provoke a phase transition in the lipid core domain. With increasing pressure an interrelated anisotropic deformation and flattening of the particle are induced. All LDL nanoparticles maintain their structural integrity even at 3000 bar and show a reversible response toward pressure variations. The present work depicts the complementarity of pressure and temperature as independent thermodynamic parameters and introduces HHP as a tool to study molecular assembling and interaction processes in distinct lipoprotein particles in a nondestructive manner.
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| 10. |
- Liebi, Marianne, 1984, et al.
(författare)
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Small-angle X-ray scattering tensor tomography: Model of the three-dimensional reciprocal-space map, reconstruction algorithm and angular sampling requirements
- 2018
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Ingår i: Acta Crystallographica Section A: Foundations and Advances. - 2053-2733. ; 74:1, s. 12-24
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Tidskriftsartikel (refereegranskat)abstract
- Small-angle X-ray scattering tensor tomography, which allows reconstruction of the local three-dimensional reciprocal-space map within a three-dimensional sample as introduced by Liebi et al. [Nature (2015), 527, 349-352], is described in more detail with regard to the mathematical framework and the optimization algorithm. For the case of trabecular bone samples from vertebrae it is shown that the model of the three-dimensional reciprocal-space map using spherical harmonics can adequately describe the measured data. The method enables the determination of nanostructure orientation and degree of orientation as demonstrated previously in a single momentum transfer q range. This article presents a reconstruction of the complete reciprocal-space map for the case of bone over extended ranges of q. In addition, it is shown that uniform angular sampling and advanced regularization strategies help to reduce the amount of data required.The mathematical framework and reconstruction algorithm for small-angle scattering tensor tomography are introduced in detail, as well as strategies which help to reduce the amount of data and therewith the measurement time required. Experimental validation is provided for the application to trabecular bone.
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