Filtern
Erscheinungsjahr
Dokumenttyp
Schlagworte
- Gold (3)
- NEXAFS (2)
- Radiography (2)
- Synchrotron (2)
- Synchrotron radiation (2)
- XPS (2)
- 2D/3D imageanalysis (1)
- Abdominal appendages (1)
- Additive Manufacturing (1)
- Adult insects (1)
Organisationseinheit der BAM
Investigations on primary, secondary and tertiary explosion protection have been performed for micro reactors with slit-like channels which are coated with catalyst. Ethene/oxygen mixtures have been used as model gas mixtures representing explosion group IIB (DIN EN ISO 16852). It could be shown that the explosion regime can be significantly reduced when using micro reactors (primary explosion protection). Furthermore, safe Operation inside the explosion regime is possible with micro reactors (secondary explosion protection), but, at certain conditions thermal runaway and ignition of detonations are possible. An unexpected behaviour has been found, because thermal runaway occurred when Volumetrie flow rate was increased. This behaviour is completely opposite to that of multi tube fixed bed reactors which show an increase of safety when increasing volumetric flow rate. Micro reactors can be constructed pressure-resistant even when detonations occur inside (tertiary explosion protection). For the example of o-xylene oxidation it could be shown that space time yield can be increased significantly when entering explosion regime.
Nanocomposites with a predominantly exfoliated morphology were prepared by melt blending of organically modified doubled layered hydroxide (LDH) and low density polyethylene (PE). The prepared materials were investigated by differential scanning calorimetry (DSC) and in detail by dielectric spectroscopy. The DSC experiments show that the degree of crystallinity decreases linearly with increasing content of the LDH. The extrapolation of this dependence to zero results in a limiting concentration of ca. 50 wt % LDH were the crystallization of PE is completely suppressed by the nanofiller. The dielectric response of pure polyethylene shows different weak relaxation processes. The intensity of dynamic glass transition (β-relaxation) increases with the concentration of LDH. This is attributed to the increasing concentration of the exchanged anion dodecyl benzene sulfonate (SDBS). The SDBS molecules are strongly adsorbed at the exfoliated LDH layers. Therefore, a detailed analysis of the β-relaxation provides information about the structure and the molecular dynamics in the interfacial region between the exfoliated LDH layers and the polyethylene matrix. This analysis shows that the β-relaxation region consists of two processes: both of them obey glassy dynamics. The difference in corresponding Vogel (ideal glass transition) temperatures is about 30 K. The relaxation process at lower frequency is assigned to polyethylene segments with a reduced molecular mobility close to LDH layers. The process at higher frequencies is related to polyethylene segments in a farer distance for the surface of the nanofiller. In the nanocomposite materials an additional process due to Maxwell-Wagner-Sillars (MWS) polarization was observed. The time constant of this MWS process can be correlated with characteristic length scales in nanocomposites and therefore provides additional information on dispersion and delamination/exfoliation of the LDH layers in these materials.
Coarsening of grain-refined semi-solid Al-Ge32 alloy: X-ray microtomography and in situ radiography
(2007)
The photoinduced pseudorotaxane formation between a photoresponsive axle and a tetralactam macrocycle was investigated in solution and on glass surfaces with immobilized multilayers of macrocycles. In the course of this reaction, a novel photoswitchable binding station with azobenzene as the photoswitchable unit and diketopiperazine as the binding station was synthesized and studied by NMR and UV/Vis spectroscopy. Glass surfaces have been functionalized with pyridine-terminated SAMs and subsequently withmultilayers of macrocycles through layer-by-layer self assembly.
A preferred orientation of the macrocycles could be confirmed by NEXAFS spectroscopy. The photocontrolled Deposition of the axle into the surface-bound macrocycle-multilayers was monitored by UV/Vis spectroscopy and led to an increase of the molecular order, as indicated by more substantial linear dichroism effects in angle-resolved NEXAFS spectra.
A novel photoswitchable rotaxane was synthesised and its switching behaviour in solution was analysed with NMR and UV-Vis. A monolayer of rotaxanes was deposited on glass surfaces and the on-surface photoswitching was investigated. Angle-resolved NEXAFS spectra revealed a preferential orientation that reversibly changes upon switching.
This key comparison aims to assess the capabilities of the participants to determine the amount-of-substance fraction oxygen in nitrogen. The GAWG has classified this as a track B comparison, due to the unexpected 50 μmol/mol argon mole fraction content of the transfer standards, which effects the achievable performance of some measurement techniques such a GC-TCD. The separation of oxygen and argon is challenging, and not all systems in use are equally well designed for it. As this analytical challenge due to a substantial fraction of argon in the transfer standards became a reality, the Gas Analysis Working Group (GAWG) decided to qualify this key comparison as a regular key comparison and not as a core comparison, which may be used to support calibration and measurement capabilities (CMCs) for oxygen in nitrogen, or for oxygen in nitrogen mixtures containing argon only (see also the section on support to CMCs).
The injection of hydrogen into the natural-gas grid is an alternative during the process of a gradual decarbonization of the heat and power supply. When dealing with hydrogen-enriched natural gas mixtures, the performance of the reference equations of state habitually used for natural gas should be validated by using high-precision experimental thermophysical data from multicomponent reference mixtures prepared with the lowest possible uncertainty in composition. In this work, we present experimental density data for an 11-compound high-calorific (hydrogen-free) natural gas mixture and for two derived hydrogen-enriched natural gas mixtures prepared by adding (10 and 20) mol-% of hydrogen to the original standard natural gas mixture. The three mixtures were prepared gravimetrically according to ISO 6142–1 for maximum precision in their composition and thus qualify for reference materials. A single-sinker densimeter was used to determine the density of the mixtures from (250–350) K and up to 20 MPa. The experimental density results of this work have been compared to the densities calculated by three different reference equations of state for natural gas related mixtures: the AGA8-DC92 EoS, the GERG-2008 EoS, and an improved version of the GERG-2008 EoS. While relative deviations of the experimental density data for the hydrogen-free natural gas mixture are always within the claimed uncertainty of the three considered equations of state, larger deviations can be observed for the hydrogen-enriched natural gas mixtures from any of the three equations of state, especially for the lowest temperature and the highest pressures.
Synchrotron radiation-induced X-ray fluorescence (SR-XRF) spectrometry was applied to determine iodine concentrations in alluvial Pt–Pd aggregates with delicate morphological features from Córrego Bom Sucesso, Minas Gerais, Brazil. The millimetre-sized botryoidal and rod-shaped grains of alluvial Pt–Pd–Hg intermetallic compounds have surprisingly high concentrations of iodine, in the range from 10 to ~ 120 μg/g. Because iodine is a strongly biophile element, known to be enriched in peatlands and plant remains in soils by microbial activity, its concentration in the Pt–Pd nuggets suggests biogenic precious-metal fixation in the aqueous alluvial milieu. Biogenic and inorganic processes, such as bioreduction and electrochemical metal accretion, could mutually have contributed to the growth of nanoparticles, formed on organic templates, to millimetric Pt–Pd nuggets.
We present a new high resolution X-ray imager based on a pnCCD detector and a polycapillary optics. The properties of the pnCCD like high quantum efficiency, high energy resolution and radiation hardness are maintained, while color corrected polycapillary lenses are used to direct the fluorescence photons from every spot on a sample to a corresponding pixel on the detector. The camera is sensitive to photons from 3 to 40 keV with still 30% quantum efficiency at 20 keV. The pnCCD is operated in split frame mode allowing a high frame rate of 400 Hz with an energy resolution of 152 eV for Mn Kα (5.9 keV) at 450 kcps. In single-photon counting mode (SPC), the time, energy and position of every fluorescence photon is recorded for every frame. A dedicated software enables the visualization of the elements distribution in real time without the need of post-processing the data. A description of the key components including detector, X-ray optics and camera is given. First experiments show the capability of the camera to perform fast full-field X-Ray Fluorescence (FF-XRF) for element analysis. The imaging performance with a magnifying optics (3×) has also been successfully tested.