U. Keiderling - Profile on Academia.edu (original) (raw)

Papers by U. Keiderling

IEEE Transactions on Magnetics, 2014

Magnetization reversal process in Nd-Fe-B nanocrystalline magnets was investigated by small-angle... more Magnetization reversal process in Nd-Fe-B nanocrystalline magnets was investigated by small-angle neutron scattering (SANS) using a non-polarized neutron beam. The magnetic-field dependence of the SANS intensities was obtained for as-deformed and Pr-Cu infiltrated Nd-Fe-B magnets. The SANS intensity variation with the magnetic field is suppressed in Pr-Cu infiltrated sample as compared with that in as-deformed sample. The isolation of Nd 2 Fe 14 B grains along the [001]-axis direction was found to be caused by the infiltration of the Pr-Cu eutectic alloy, resulting in coercive force enhancement. The results suggest that magnetic isolation of the grains is the key to developing magnets with high coercive force.

$Research paper thumbnail of X-Ray Diffraction Systems – Technical Advantages and Application Related Benefits$

Ex per i men tal fac tors such as crys tal char ac ter is tics, avail able ex per i ment time and... more Ex per i men tal fac tors such as crys tal char ac ter is tics, avail able ex per i ment time and the prop er ties of the X-ray sources and de tec tors have a strong im pact on data qual ity and can make the dif fer ence be tween suc cess and fail ure in phas ing at tempts or re sult in a more or less ac cu rate atomic model. The talk fo cuses on the XRD equip ment and is in tended as an over view on re cent de vel op ments of X-ray dif frac tion sys tems and the fields where STOE XRD in stru ments are most ben e fi cial. A va ri ety of mea sure ment set ups with re spect to goniometers, dif frac tion ge om e tries, de tec tors, X-ray sources and sam ple en vi ron ments will be pre sented, and both Pow der XRD and Sin gle Crys tal XRD ap pli ca tions will be ex em pli fied. Ad di tion ally, re cent ad vances in de tec tor tech nol ogy, novel in situ cam era and im ple men ta tion of MetalJet X-ray source will be high lighted and the tan gi ble ben e fits for the sci en tists will be...

Comptes Rendus Chimie, 2018

The presence of fluorous tails in room-temperature ionic liquids imparts new properties to their ... more The presence of fluorous tails in room-temperature ionic liquids imparts new properties to their already rich spectrum of appealing features. The interest towards this class of compounds that are of ionic nature with melting point less than 25 C is accordingly growing; in particular, compounds bearing relatively long fluorous tails have begun to be considered. In this invited presentation, we show recent results arising from the systematic study of structural properties of a series of fluorinated room temperature ionic liquids, with growing fluorous chain length. At odd with the current understanding of this class of compounds, we show experimentally that they are characterized by the presence of segregated fluorous domains whose size depends on the fluorous chain length. This experimental finding, based on the synergic use of X-ray and neutron scattering, provides a structural scenario at the mesoscopic spatial scale that is in agreement with the recent state of the art molecular dynamic simulations. We speculate on the potential role of this significant compartmentalization of the bulk liquid phase into different nanoscale domains, as relevant in a series of applications including separation, solubility, catalysis, and so forth.

Oxide Powders for Chemical Mechanical Polishing Produced by Chemical Vapor Synthesis

MRS Proceedings, 2001

ABSTRACTUltrafine silica, alumina and doped alumina/silica powders have been produced by Chemical... more ABSTRACTUltrafine silica, alumina and doped alumina/silica powders have been produced by Chemical Vapor Synthesis (CVS). Primary particle sizes from 3.5 to 12.4 nm have been achieved. Agglomerate sizes ranging from approx. 10 to 150 nm have been achieved in aqueous dispersions.

Journal of Colloid and Interface Science, 2015

Surfactant-based aqueous fluids, such as micellar solutions and microemulsions, are effective, sa... more Surfactant-based aqueous fluids, such as micellar solutions and microemulsions, are effective, safe and selective media for cleaning operations in conservation of cultural heritage. The search for betterperforming systems and eco-friendly cleaning systems is currently a major goal in conservation science. We report here on a ternary o/w microemulsion, composed of diethyl carbonate (DC) as the oil phase and N,N-Dimethyldodecan-1-amine oxide (DDAO) as the surfactant. DDAO is a well known and widely used detergent and solubilizing agent, selected here for its degradability and eco-compatibility. Due to its nonionic/cationic nature, it can be used also when nonionic-based formulations become ineffective because of clouding and phase separation. Moreover, DDAO is insensitive to the presence of divalent metal ions, usually abundant in wall paintings substrates. Small-Angle Neutron Scattering (SANS) provided detailed information about the nanostructure of the surfactant aggregates. Finally, the cleaning effectiveness of the nanofluid was assessed both on fresco mock-ups and on real wall paintings conserved in the archeological site of Tulum, Mexico. Here, conservators successfully used the microemulsion to remove naturally aged films of complex polymer mixtures from the works of art surface.

Dynamics of field-induced ordering processes in ferrofluids studied by polarised small-angle neutron scattering

Physica B: Condensed Matter, 2006

Abstract The relaxation of the local ordering of nanoparticles induced by an external magnetic fi... more Abstract The relaxation of the local ordering of nanoparticles induced by an external magnetic field in a concentrated Cobalt ferrofluid was studied by stroboscopic polarised small-angle neutron scattering. Magnetic and nuclear correlations were found to decay exponentially within a characteristic time of few seconds. The local hexagonal particle arrangements with aligned moments transform gradually to uncorrelated segments of dipolar chains. The dynamics is influenced by dipole–dipole interactions.

Nanostructures of the montmorillonite-derived restructured clays K10®, HMO and the Mg2+ exchanged analogue Mg-HMO. A SANS, N2 sorption and XRPD study

Journal of Materials Chemistry, 2003

ABSTRACT Small angle neutron scattering ( SANS) of the montmorillonite ( MO)-derived acid-restruc... more ABSTRACT Small angle neutron scattering ( SANS) of the montmorillonite ( MO)-derived acid-restructured clays K10(R), HMO and the Mg2+ exchanged congener of the latter, Mg-HMO, has been investigated. K10(R) is a strong acid-treated clay, HMO a new, mild-acid treated material with different X-ray powder diffraction (XRPD) characteristics and Mg-HMO a Mg2+ exchanged derivative; the scattering curve of the latter exhibits a peak at Q = 5.46 nm(-1) ascribed to intra-layer Mg2+-Mg2+ distances. Analysis of the mid-Q region (0.2-2.6 nm(-1)) of the curves demonstrates that K10(R) and HMO differ in nanostructure. In particular, the solid matrix of K10(R) exhibits a mass fractal dimension, D-m = 2.53 which is absent from HMO but which is characteristic for sepiolites prepared via prolonged acid treatment. For Mg-HMO, recently found to be an efficient base catalyst for fine chemicals production, both XRPD and SANS point to a more ordered "parallel-plate in primary particle" shape. This is ascribed to both intercalation of Mg2+ between aluminosilicate sheets and enhanced correlation between platelets due to surface Mg2+ cations acting to bind clay platelet packets together face to face in agreement with the high Mg2+ loading level of HMO (10% w/w). The presence of the Mg2+ cations reduces the surface roughness and results in an increase of the length of the platelet packets in line with this enhanced ordering.

Journal of Applied Crystallography, 1999

Silver behenate powder [CH3(CH2)20COOAg] is one of the very few materials featuring cold neutron ... more Silver behenate powder [CH3(CH2)20COOAg] is one of the very few materials featuring cold neutron Bragg reflections in the angular range of 4–26° (2θ) accessible to small-angle neutron scattering (SANS) instruments. These reflections can be analysed with Bragg's law to determine the wavelength of the primary beam produced by the monochromator of the SANS instrument. Compared with the usual time-of-flight (TOF) method for wavelength calibration, this method does not require any additional time-resolving equipment for the instrument. An extensive study has been performed to determine the optimum parameters for the experimental setup and for the data processing procedure. The results of wavelength calibrations using silver behenate and TOF measurements are compared.

Study of structural irregularities of smectite clay systems by small-angle neutron scattering and adsorption

Applied Surface Science, 2007

Small angle neutron scattering (SANS) and its contrast-matching variant are employed in order to ... more Small angle neutron scattering (SANS) and its contrast-matching variant are employed in order to determine structural properties (inter-pillar distances and mass/surface fractal dimensions of the clay layers and pillars) of a series of smectite natural clays (montmorillonite, beidellite, and bentonite) and their pillared and pillared/ion-exchanged analogues. Moreover, a comparative analysis with the adsorption data is carried out on the basis

Physical Review Letters, 2006

The reversal of magnetic moments of nanoparticles in concentrated Co-ferrofluids was monitored in... more The reversal of magnetic moments of nanoparticles in concentrated Co-ferrofluids was monitored in an oscillating magnetic field by new time-resolved stroboscopic small-angle neutron-scattering techniques. Time resolution in the µs range was achieved by using a pulsed beam technique, TISANE, while in continuous mode resolution was limited by the wavelength spread to about 1ms. The frequency dependence of anisotropic scattering patterns has been modeled using Langevin dynamics. The dynamics follows a two step mechanism: Field induced ordering is governed by fast Brownian rotation of nanoparticles with a characteristic time of about 160 µs. Magnetic relaxation of locally ordered domains of about 100 nm in size takes place within a few seconds by Brownian rotation or by Néel type rotation of magnetic moments.

Merging High Doxorubicin Loading with Pronounced Magnetic Response and Bio-repellent Properties in Hybrid Drug Nanocarriers

Small, 2012

Hybrid magnetic drug nanocarriers are prepared via a self-assembly process of poly(methacrylic ac... more Hybrid magnetic drug nanocarriers are prepared via a self-assembly process of poly(methacrylic acid)-graft-poly(ethyleneglycol methacrylate) (p(MAA-g-EGMA)) on growing iron oxide nanocrystallites. The nanocarriers successfully merge together bio-repellent properties, pronounced magnetic response, and high loading capacity for the potent anticancer drug doxorubicin (adriamicin), in a manner not observed before in such hybrid colloids. High magnetic responses are accomplished by engineering the size of the magnetic nanocrystallites (∼13.5 nm) following an aqueous single-ferrous precursor route, and through adjustment of the number of cores in each colloidal assembly. Complementing conventional magnetometry, the magnetic response of the nanocarriers is evaluated by magnetophoretic experiments providing insight into their internal organization and on their response to magnetic manipulation. The structural organization of the graft-copolymer, locked on the surface of the nanocrystallites, is further probed by small-angle neutron scattering on single-core colloids. Analysis showed that the MAA segments selectively populate the area around the magnetic nanocrystallites, while the poly(ethylene glycol)-grafted chains are arranged as protrusions, pointing towards the aqueous environment. These nanocarriers are screened at various pHs and in highly salted media by light scattering and electrokinetic measurements. According to the results, their stability is dramatically enhanced, as compared to uncoated nanocrystallites, owing to the presence of the external protective PEG canopy. The nanocarriers are also endowed with bio-repellent properties, as evidenced by stability assays using human blood plasma as the medium.

Journal of Applied Crystallography, 2011

Exposure of a superalloy to an external load results in anisotropic coarsening of the γ′ precipit... more Exposure of a superalloy to an external load results in anisotropic coarsening of the γ′ precipitates, so-called rafting. It was reported in the past that γ′ rafting can also occur as a result of purely thermal treatment, without the simultaneous presence of an external load, if the specimen has been pre-deformed at relatively low temperature. The evolution of γ′ morphology in pre-deformed specimens of SCA425 Ni-base superalloy was examined in the present study. Unlike in the previous experiments, the compressive stress was used for pre-straining.In situsmall-angle neutron scattering (SANS) was employed, which enabled the determination of the morphology directly at high temperature. Both for strong and for weak pre-straining, rounding of the originally cuboidal precipitates towards an ellipsoidal shape on heating was observed. Weak pre-straining (0.1, 0.5%) does not cause rafting on subsequent heating. On the other hand, the detailed evaluation of SANS data provides some indication ...

General formula of determination of cross-section from measured SANS intensities

Scientific reports, Jan 20, 2016

We have investigated the influence of multiple scattering on the magnetic small-angle neutron sca... more We have investigated the influence of multiple scattering on the magnetic small-angle neutron scattering (SANS) from a Nd-Fe-B nanocrystalline magnet. We performed sample-thickness- and neutron-wavelength-dependent SANS measurements, and observed the scattering vector dependence of the multiple magnetic scattering. It is revealed that significant multiple scattering exists in the magnetic scattering rather than the nuclear scattering of Nd-Fe-B nanocrystalline magnet. It is considered that the mean free path of the neutrons for magnetic scattering is rather short in Nd-Fe-B magnets. We analysed the SANS data by the phenomenological magnetic correlation model considering the magnetic microstructures and obtained the microstructural parameters.

Nanostructured Fluid Based on Nonionic Surfactants for the Removal of Polymer Films from Works of Arts

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2000

A polarized neutron beam has been installed at the small-angle neutron-scattering instrument V4 a... more A polarized neutron beam has been installed at the small-angle neutron-scattering instrument V4 at BENSC Berlin. The main component of this new option is a 1.8 m long cavity transmission polarizer. The advantages of this device compared to the conventional bender polarizers are: (i) high transmission (35% of unpolarized beam at "6 A s); (ii) the polarization is better than 93% in the wavelength band 4 A s ((10 A s and drops slightly to 80% at "18 A s ; (iii) the neutron beam is not de#ected. Thus, the polarized beam can be switched on and o! by rotating the polarizer or a conventional neutron guide into the beam without any readjustment of the beam path downstream the polarizer. An adiabatic radio frequency gradient spin #ipper in front of the sample provides high #ipping e$ciency over the whole wavelength band. First results on a sample with weak magnetic scattering (nanosized Fe O particles embedded in a glass matrix) are presented and compared to a measurement with unpolarized neutrons.

Journal of Membrane Science, 1997

The pore structure of an alumina membrane was studied by adsorption in conjunction with small-ang... more The pore structure of an alumina membrane was studied by adsorption in conjunction with small-angle neutron scattering (SANS). The effect of an incomplete contrast matching was investigated and simple formulae allowing the calculation of the amount of water adsorbed and the film areas, at various relative pressures, were derived for the ternary system. In the vicinity of the contrast matching point, however, incomplete contrast matching does not introduce a substantial complication to data analysis. The adsorption isotherm was reconstructed from the SANS data and agrees well with the experimental adsorption isotherm. For the alumina membrane, a coordination number of ~10 was estimated from the SANS determined areas.

Nanocrystalline Al O and ZrO powders as aerogels and in aqueous solutions measured with SANS and photon correlation spectroscopy

Silver Behenate as a Standard for Instrumental Resolution and Wavelength Calibration for Small Angel Neutron Scattering

Materials Science Forum, 2000