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Paper des Monats
- ja (71)
We report an appropriate preparation of binary isotope calibration mixtures of the three stable isotopes of magnesium to be used in the ab initio calibration of multicollector mass spectrometers (ICPMS and TIMS). For each of the three possible combinations of binary mixtures ("24Mg" + "25Mg", "24Mg" + "26Mg", and "25Mg" + "26Mg"), three individual setups have been prepared under gravimetric control, each of them with an isotope ratio close to unity, and a total magnesium mass fraction close to 20 mg kg-1. The preparation was designed to occur via an intermediate dilution of a parent solution of a highly purified specimen of the isotopically enriched magnesium materials. For the application as calibration mixtures, a complete uncertainty budget was set up, and is presented and discussed in detail, including the aspects that went into the design of the dilution and mixing approach to minimize uncertainty. The principle parameters for the purpose of the later calibration of the mass spectrometers are the absolute masses of isotopically enriched magnesium materials in the primary calibration mixtures. For the first time relative expanded uncertainties U (k = 2) for these masses of ≤0.005% could be achieved for all mixtures.
For the first time, an ab initio calibration for absolute Mg isotope ratios was carried out, without making any a priori assumptions. All quantities influencing the calibration such as the purity of the enriched isotopes or liquid and solid densities were carefully analysed and their associated uncertainties were considered. A second unique aspect was the preparation of three sets of calibration solutions, which were applied to calibrate three multicollector ICPMS instruments by quantifying the correction factors for instrumental mass discrimination. Those fully calibrated mass spectrometers were then used to determine the absolute Mg isotope ratios in three candidate European Reference Materials (ERM)-AE143, -AE144 and -AE145, with ERM-AE143 becoming the new primary isotopic reference material for absolute isotope ratio and delta measurements. The isotope amount ratios of ERM-AE143 are n(25Mg)/n(24Mg) = 0.126590(20) mol/mol and n(26Mg)/n(24Mg) = 0.139362(43) mol/mol, with the resulting isotope amount fractions of x(24Mg) = 0.789920(46) mol/mol, x(25Mg) = 0.099996(14) mol/ mol and x(26Mg) = 0.110085(28) mol/mol and an atomic weight of Ar(Mg) = 24.305017(73); all uncertainties were stated for k = 2. This isotopic composition is identical within uncertainties to those stated on the NIST SRM 980 certificate. The candidate materials ERM-AE144 and -AE145 are isotopically lighter than ERM-AE143 by 1.6 ‰ and 1.3 ‰, respectively, concerning their n(26Mg)/n(24Mg) ratio. The relative combined standard uncertainties are ≤0.1 ‰ for the isotope ratio n(25Mg)/n(24Mg) and ≤0.15 ‰ for the isotope ratio n(26Mg)/ n(24Mg). In addition to characterizing the new isotopic reference materials, it was demonstrated that commonly used fractionation laws are invalid for correcting Mg isotope ratios in multicollector ICPMS as they result in a bias which is not covered by its associated uncertainty. Depending on their type, fractionation laws create a bias up to several per mil, with the exponential law showing the smallest bias between 0.1 ‰ and 0.7 ‰.
High loadings of carbon black (CB) are usually used to achieve the properties demanded of rubber compounds. In recent years, distinct nanoparticles have been investigated to replace CB in whole or in part, in order to reduce the necessary filler content or to improve performance. Multilayer graphene (MLG) is a nanoparticle made of just 10 graphene sheets and has recently become commercially available for mass-product nanocomposites. Three phr (part for hundred rubbers) of MLG are added to chlorine isobutyl isoprene rubber (CIIR)/CB composites in order to replace part of the CB. The incorporation of just 3 phr MLG triples the Young’s modulus of CIIR; the same effect is obtained with 20 phr CB. The simultaneous presence of three MLG and CB also delivers remarkable properties, e.g. adding three MLG and 20 phr CB increased the hardness as much as adding 40 phr CB. A comprehensive study is presented, showing the influence on a variety of mechanical properties. The potential of the MLG/CB combination is illustrated to reduce the filler content or to boost performance, respectively. Apart from the remarkable mechanical properties, the CIIR/CB/MLG nanocomposites showed an increase in weathering resistance.
We use a dynamic scanning electron microscope (DySEM) to map the spatial distribution of the vibration of a cantilever beam. The DySEM measurements are based on variations of the local secondary electron signal within the imaging electron beam diameter during an oscillation period of the cantilever. For this reason, the surface of a cantilever without topography or material variation does not allow any conclusions about the spatial distribution of vibration due to a lack of dynamic contrast. In order to overcome this limitation, artificial structures were added at defined positions on the cantilever surface using focused ion beam lithography patterning. The DySEM signal of such high-contrast structures is strongly improved, hence information about the surface vibration becomes accessible. Simulations of images of the vibrating cantilever have also been performed. The results of the simulation are in good agreement with the experimental images.
Ectoine is an important osmolyte, which allows microorganisms to survive in extreme environmental salinity. The hygroscopic effects of ectoine in pure water can be explained by a strong water binding behavior whereas a study on the effects of ectoine in salty solution is yet missing. We provide Raman spectroscopic evidence that the influence of ectoine and NaCl are opposing and completely independent of each other. The effect can be explained by the formation of strongly hydrogen-bonded water molecules around ectoine which compensate the influence of the salt on the water dynamics. The mechanism is corroborated by first principles calculations and broadens our understanding of zwitterionic osmolytes in aqueous solution. Our findings allow us to provide a possible explanation for the relatively high osmolyte concentrations in halotolerant bacteria.
Boehmite nanoparticles show great potential in improving mechanical properties of fiber reinforced polymers. In order to predict the properties of nanocomposites, knowledge about the material parameters of the constituent phases, including the boehmite particles, is crucial. In this study, the mechanical behavior of boehmite is investigated using Atomic Force Microscopy (AFM) experiments and Molecular Dynamic Finite Element Method (MDFEM) simulations. Young’s modulus of the perfect crystalline boehmite nanoparticles is derived from numerical AFM simulations. Results of AFM experiments on boehmite nanoparticles deviate significantly. Possible causes are identified by experiments on complementary types of boehmite, that is, geological and hydrothermally synthesized samples, and further simulations of imperfect crystals and combined boehmite/epoxy models. Under certain circumstances, the mechanical behavior of boehmite was found to be dominated by inelastic effects that are discussed in detail in the present work.The studies are substantiated with accompanying X-ray diffraction and Raman experiments.
Single particle ICP-MS (spICP-MS) has gained great influence in the analysis of engineered nanoparticles (NPs) due to its simplicity, speed and ability to obtain a particle number size distribution. Despite its many advantages, the method is hampered by matrix effects affecting the sensitivity of the instruments.
Consequently, over- or underestimated particle sizes might be obtained. To overcome these challenges, we present in this work the detection of both Ag isotopes with a quadrupole mass spectrometer for the application of isotopic dilution analysis (IDA) in combination with spICP-MS. Here, the isotopes are measured sequentially using the conventional spICP-MS integration time of 10 ms. Citrate stabilized Ag NPs of a spherical shape with the nominal diameters of 30, 40, 50 and 80 nm have been investigated.
The experimental concept of adding ¹⁰⁹Ag+ solutions to the NP suspensions resulted in the NP Spikes being only visible in the ¹⁰⁷Ag trace. Therefore, a maximum of 45% of the particles was detected compared to that by conventional spICP-MS. A modified mass flow equation was applied to determine the particle sizes, particle size distributions and particle number concentrations of various Ag NPs. The addition of different spike concentrations between 0.5 and 4 mg L⁻¹ ¹⁰⁹Ag resulted in similar particle diameters, suggesting that the calculated diameter might be independent of the spike concentration.
This would have the advantage that no size information would be needed before the analysis. By analyzing Ag NP suspensions in a simulated seawater matrix, we demonstrate its significant influence on the particle size determination using conventional spICP-MS. A lower transport efficiency of 6.1% was found in the matrix compared to 7.3% without the matrix. In our approach, the addition of the Matrix influenced the NP intensity stronger than the spike signal, resulting in slightly smaller diameters using IDA–spICP-MS with the matrix compared to the results without the matrix. On the other hand, the IDA–spICP-MS approach with the matrix can result in equivalent results for the particle sizes compared with
conventional spICP-MS using suspensions without the matrix. Due to the lower instrument sensitivity in the matrix, a diameter of 30 nm was found to be close to the detection limit of the instrument.
We present paper-based test strips for chemical sensing with surface enhanced Raman scattering as detection method. The test strips are prepared on glass fibre paper with silver nanoparticles and a spray method with an airbrush spray setup as a low cost fabrication approach. The properties of the test strips are investigated with three classical Raman analytes rhodamine 6G, 4-aminothiophenol and adenine and optimized for a good reproducibility of the intensity measurements. All test analytes can be identified at low concentrations. For adenine, a concentration series from 10⁻⁴ M to 10⁻⁸ M is measured and the calibration data can be fitted and evaluated with a Langmuir isotherm model. The optimized test strips are applied for the identification of two antibiotics enoxacin and enrofloxacin.
The paper describes an experimental investigation of high power laser beam welding with an electromagnetic weld pool support for up to 20 mm thick plates made of duplex steel (AISI 2205) and mild steel (S235JR). The results of the welding tests show a successful application of this technology at ferromagnetic metals. Irregular sagging was suppressed successfully. An ac-power of less than 2 kW at oscillation frequencies between 800 Hz and 1.7 kHz is necessary for a full compasation of the hydrostatic pressure. Thus, it was demonstrated that the electromagnetic weld pool support is not only limited to non-ferromagnetic metals like austenitic steels. For future studies with duplex steel, the use of filler material has to take into account with regard to the balance of the mixed austenitic and ferritic phases.
Amino acid analysis is considered to be the gold standard for quantitative peptide and protein analysis. Here, we would like to propose a simple HPLC/UV method based on a reversed-phase separation of the aromatic amino acids tyrosine (Tyr), phenylalanine (Phe), and optionally tryptophan (Trp) without any derivatization. The hydrolysis of the proteins and peptides was performed by an accelerated microwave technique, which needs only 30 minutes. Two internal standard compounds, homotyrosine (HTyr) and 4-fluorophenylalanine (FPhe) were used for calibration. The limit of detection (LOD) was estimated to be 0.05 µM (~10 µg/L) for tyrosine and phenylalanine at 215 nm. The LOD for a protein determination was calculated to be below 16 mg/L (~300 ng BSA absolute). Aromatic amino acid analysis (AAAA) offers excellent accuracy and a precision of about 5% relative standard deviation, including the hydrolysis step. The method was validated with certified reference materials (CRM) of amino acids and of a pure protein (bovine serum albumin, BSA). AAAA can be used for the quantification of aromatic amino acids, isolated peptides or proteins, complex peptide or protein samples, such as serum or milk powder, and peptides or proteins immobilized on solid supports.
According to several recent studies, an unexpectedly high number of landmark papers seem to be not reproducible by Independent laboratories. Nontherapeutic antibodies used for research, diagnostic, food analytical, environmental, and other purposes play a significant role in this matter. Although some papers have been published offering suggestions to improve the situation, they do not seem to be comprehensive enough to cover the full complexity of this issue. In addition, no obvious improvements could be noticed in the field as yet. This article tries to consolidate the remarkable variety of conclusions and suggested activities into a more coherent conception. It is concluded that funding agencies and journal publishers need to take first and immediate measures to resolve these problems and lead the way to a more sustainable way of bioanalytical research, on which all can rely with confidence.
Real Time Imaging of Deuterium in a Duplex Stainless Steel Microstructure by Time-of-Flight SIMS
(2016)
For more than one century, hydrogen assisted degradation of metallic microstructures has been identified as origin for severe technical component failures but the mechanisms behind have not yet been completely understood so far. Any in-situ observation of hydrogen transport phenomena in microstructures will provide more details for further elucidation of these degradation mechanisms. A novel experiment is presented which is designed to elucidate the permeation behaviour of deuterium in a microstructure of duplex stainless steel (DSS). A hydrogen permeation cell within a TOF-SIMS instrument enables electrochemical charging with deuterium through the inner surface of the cell made from DSS. The outer surface of the DSS permeation cell exposed to the vacuum has been imaged by TOF-SIMS vs. increasing time of charging with subsequent chemometric treatment of image data. This in-situ experiment showed evidently that deuterium is permeating much faster through the ferrite phase than through the austenite phase. Moreover, a direct proof for deuterium enrichment at the austenite-ferrite interface has been found.
In Near Edge X-Ray Absorption Fine Structure (NEXAFS) spectroscopy X-Ray photons are used to excite tightly bound core electrons to low-lying unoccupied orbitals of the system. This technique offers insight into the electronic structure of the system as well as useful structural information. In this work, we apply NEXAFS to two kinds of imidazolium based ionic liquids ([CnC₁im]⁺[NTf₂]⁻ and [C₄C₁im]⁺[I]⁻). A combination of measurements and quantum chemical calculations of C K and N K NEXAFS resonances is presented. The simulations, based on the transition potential density functional theory method (TP-DFT), reproduce all characteristic features observed by the experiment. Furthermore, a detailed assignment of resonance features to excitation centers (carbon or nitrogen atoms) leads to a consistent interpretation of the spectra.
In this work, fullerene has been functionalized with cyanuric Chloride at room temperature by a nitrene mediated [2 + 1] cycloaddition reaction. The adduct after functionalization is inherently in the form of azafulleroid and shows broad UV absorption in the wavelength range of 200–800 nm, as well as photothermal conversion and fluorescence with a high quantum yield.
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.
Recently developed new transducers for ultrasonic transmission, which can be embedded right into concrete, are now used for non-destructive permanent monitoring of concrete. They can be installed during construction or thereafter. Large volumes of concrete can be monitored for changes of material properties by a limited number of transducers. The transducer design, the main properties as well as installation procedures are presented. It is shown that compressional waves with a central frequency of 62 kHz are mainly generated around the transducer's axis. The transducer can be used as a transmitter or receiver. Application examples demonstrate that the transducers can be used to monitor concrete conditions parameters (stress, temperature,
) as well as damages in an early state or the detection of acoustic events (e.g., crack opening). Besides application in civil engineering our setups can also be used for model studies in geosciences.
Various plant compartments of a single bell pepper plant were studied to verify the variability of boron isotope composition in plants and to identify possible intra-plant isotope fractionation. Boron mass fractions varied from 9.8 mg/kg in the fruits to 70.0 mg/kg in the leaves. Boron (B) isotope ratios reported as δ11B ranged from -11.0 to +16.0 (U ≤ 1.9, k=2) and showed a distinct trend to heavier δ11B values the higher the plant compartments were located in the plant. A fractionation of Δ11Bleaf-roots = 27 existed in the studied bell pepper plant, which represents about about 1/3 of the overall natural boron isotope variation (ca. 80). Two simultaneous operating processes are a possible explanation for the observed systematic intra-plant δ11B variation: 1) B is fixed in cell walls in its tetrahedral form (borate), which preferentially incorporates the light B isotope and the remaining xylem sap gets enriched in the heavy B isotope and 2) certain transporter preferentially transport the trigonal 11B-enriched boric acid molecule and thereby the heavy 11B towards young plant compartments which were situated distal of the roots and typically high in the plant. Consequently, an enrichment of the heavy 11B isotope in the upper young plant parts located at the top of the plant could explain the observed isotope systematic. The identification and understanding of the processes generating systematic intra-plant δ11B variations will potentially enable the use of B isotope for plant metabolism studies.
Characterization of silver nanoparticles in cell culture medium containing fetal bovine serum
(2015)
Nanoparticles are being increasingly used in consumer products worldwide, and their toxicological effects are currently being intensely debated. In vitro tests play a significant role in nanoparticle risk assessment, but reliable particle characterization in the cell culture medium with added fetal bovine serum (CCM) used in these tests is not available. As a step toward filling this gap, we report on silver ion release by silver nanoparticles and on changes in the particle radii and in their protein corona when incubated in CCM. Particles of a certified reference material, p1, and particles of a commercial silver nanoparticle material, p2, were investigated. The colloidal stability of p1 is provided by the surfactants polyethylene glycol-25 glyceryl trioleate and polyethylene glycol-20 sorbitan monolaurate, whereas p2 is stabilized by polyvinylpyrrolidone. Dialyses of p1 and p2 reveal that their silver ion release rates in CCM are much larger than in water. Particle characterization was performed with asymmetrical flow field-flow fractionation, small-angle X-ray scattering, dynamic light scattering, and electron microscopy. p1 and p2 have similar hydrodynamic radii of 15 and 16 nm, respectively. The silver core radii are 9.2 and 10.2 nm. Gel electrophoresis and subsequent peptide identification reveal that albumin is the main corona component of p1 and p2 after incubation in CCM that consists of Dulbecco's modified Eagle medium with 10% fetal bovine serum added.
SASfit: a tool for small-angle scattering data analysis using a library of analytical expressions
(2015)
SASfit is one of the mature programs for small-angle scattering data analysis and has been available for many years. This article describes the basic data processing and analysis workflow along with recent developments in the SASfit program package (version 0.94.6). They include (i) advanced algorithms for reduction of oversampled data sets, (ii) improved confidence assessment in the optimized model parameters and (iii) a flexible plug-in system for custom user-provided models. A scattering function of a mass fractal model of branched polymers in solution is provided as an example for implementing a plug-in. The new SASfit release is available for major platforms such as Windows, Linux and MacOS. To facilitate usage, it includes comprehensive indexed documentation as well as a web-based wiki for peer collaboration and online videos demonstrating basic usage. The use of SASfit is illustrated by interpretation of the small-angle X-ray scattering curves of monomodal gold nanoparticles (NIST reference material 8011) and bimodal silica nanoparticles (EU reference material ERM-FD-102).
The adsorption of porphyrin derivatives on a Au(111) surface was studied by scanning tunneling microscopy and spectroscopy at low temperatures in combination with density functional theory calculations. Different molecular appearances were found and could be assigned to the presence of single gold adatoms bonded by a coordination bond underneath the molecular monolayer, causing a characteristic change of the electronic structure of the molecules. Moreover, this interpretation could be confirmed by manipulation experiments of individual molecules on and off a single gold atom. This study provides a detailed understanding of the role of metal adatoms in surface–molecule bonding and anchoring and of the appearance of single molecules, and it should prove relevant for the imaging of related molecule–metal systems.
Micro structured reactors are attractive candidates for further process intensification in heterogeneous catalysis. However, they require catalytic coatings with significantly improved space-time yields compared to traditional supported catalysts. We report the facile synthesis of homogeneous nanocrystalline Pt coatings with hierarchical pore structure by electrochemical dealloying of amorphous sputter-deposited platinum silicide layers. Thickness, porosity and surface composition of the catalysts can be controlled by the dealloying procedure. XPS analysis indicates that the catalyst surface is primarily composed of metallic Pt. Catalytic tests in gas-phase hydrogenation of butadiene reveal the typical activity, selectivity and activation energy of nanocrystalline platinum. However, space time yields are about 13 to 200 times higher than values reported for Pt-based catalysts in literature. The highly open metallic pore structure prevents heat and mass transport limitations allowing for very fast reactions and reasonable stability at elevated temperatures.
Lewis and Brønsted sites were quantified in a series of weak acidic hydroxylated magnesium fluorides by Fourier transform infrared spectroscopy (FTIR) and solid state nuclear magnetic resonance spectroscopy (NMR) with pyridine as probe molecule. Molar extinction coefficients, which are necessary for quantitative FTIR measurements, were calculated by an easy approach. It utilizes the fact that both signals, used for the quantification by FTIR, are caused by the same deformation vibration mode of pyridine. Comparison of quantitative FTIR experiments and quantification by NMR shows that concentrations of acidic sites determined by FTIR spectroscopy have to be interpreted with caution. Furthermore, it is shown that the transfer of molar extinction coefficients from one catalyst to another may lead to wrong results. Molar extinction coefficients and concentrations of acidic sites determined by FTIR spectroscopy are affected by grinding and probably the particle size of the sample. High temperature during FTIR experiments has further impact on the quantification results.
While polymorphism is a common phenomenon in the crystallization processes of organic compounds, polyamorphism has gained importance only recently. Using sophisticated sample environments and applying in situ scattering methods and vibrational spectroscopy, the complete crystallization process of organic compounds from solution can be traced and characterized. Diffuse scattering from amorphous intermediates can be investigated by analyzing the atomic pair distribution function (PDF) to gain further insights into molecular pre-orientation. The crystallization behavior of paracetamol was studied exemplarily under defined, surface-free conditions. Based on the choice of the solvent, the formation of different polymorphs is promoted. The thermodynamically stable form I and the metastable orthorhombic form II could be isolated in pure form directly from solution. For both polymorphs, the crystallization from solution proceeds via a distinct amorphous precursor phase. PDF analyses of these different amorphous states indicate a specific pre-orientation of the analyte molecules introduced by the solvent. The resulting crystalline polymorph is already imprinted in these proto-crystalline precursors. Direct experimental evidence for the polyamorphism of paracetamol is provided.
The need for technological progress in bio-diagnostic assays of high complexity requires both fundamental research and constructing efforts on nano-scaled assay recognition elements that can provide unique selectivity and design-enhanced sensitivity features. Nanoparticle induced sensitivity enhancement and its application related to multiplexed capability Surface-Enhanced InfraRed Absorption (SEIRA) assay formats are well suitable for these purposes. The potential of diverse fluorophore–antibody conjugates, being chemisorbed onto low-cost gold nanoparticulate SEIRA substrates, has been explored with respect to their spectral discriminability. These novel biolabels deliver molecular SEIRA fingerprints that have been successfully analyzed by both uni- and multivariate analyzing tools, to discriminate their multiplexing capabilities. We show that this robust spectral encoding via SEIRA fingerprints opens up new opportunities for a fast, reliable and multiplexed high-end screening in biodiagnostics.
The demands for the assessment of water quality are increasing steadily, making it necessary to routinely monitor multiple contaminants in water samples. For this application a hapten microarray was developed. In order to reach the required low detection limits a design of experiments (DoE) approach was used to optimize the assay performance. Here we show that a Box-Behnken design plan is an adequate choice for the straightforward exploration of hapten microarray assay parameters. For both read-out systems studied (fluorophore-labelled detection antibodies or enzymatic signal development followed by reflectometric scan, respectively), it was possible to significantly extend the measurement ranges. Furthermore, it could be shown that multivariate data analysis, here partial least squares regression (PLS), can improve the prediction accuracy of 'unknown' samples when used as calibration model, compared to classical, univariate data evaluation methods.
A novel synthetic strategy toward highly fluorinated BODIPY dyes with exceptional photostabilities relying on sustainable gold catalysis has been developed. A key to the tailored pyrrole precursors is the gold catalysis performed in ionic liquids as the reaction medium, allowing a facile recycling of the catalysts. The dyes prepared are well-matching with the spectral windows of popular rhodamine dyes and possess high brightness while showing a distinctly higher photostability than the rhodamines especially in aprotic solvents.
CONRAD-2 is an imaging instrument using low-energy (cold) neutrons. The instrument is installed at the end of a curved neutron guide which avoids the direct line of sight towards the reactor core. This ensures a very low background of high-energy neutrons and. photons at the sample position. The cold neutron beam provides a wavelength range which is suitable for phase-and diffraction-contrast imaging such as grating interferometry and Bragg edge mapping. The instrument is well suited for high resolution imaging due to the high efficiency of the very thin scintillators that can be used for the detection of cold neutrons. An instrument upgrade was performed recently as a part of an upgrade program for the cold neutron instrumentation at HZB. The parameters of the instrument as well as some research highlights will be presented.
Several ultrasonic approaches for material determination are formulated in terms of an (nonlinear) inverse problem, e.g. immersion technique (Castaings et al. (2000)) or plate-waveguide techniques (Marzani et al. (2012)). In this contribution we focus on cylindrical waveguides for ultrasonic material determination and especially on the sensitivity of recorded transmission signals to the material properties. We utilize composite scaled sensitivities to determine the information content that can be achieved by the setup to certain parameters and discuss the limitations of the approach.
Die Zahl der industriellen Anwendungen mit Einsatz von Faserverbundwerkstoffen wächst kontinuierlich vor allem wegen der exzellenten Materialeigenschaften und des geringen Gewichtes dieses Werkstoffes. Entsprechend steigen die Anforderungen an zerstörungsfreie Prüfsysteme zur Gewährleistung des sicheren Betriebes von Komponenten und Strukturen bestehend aus Verbundwerkstoffen.
Im Rahmen des EU-Projekes VITCEA (Validated Inspection Techniques for Composites in Energy Applications) wird das Ziel verfolgt, neue Prüfverfahren für moderne Verbundwerkstoffe zu entwickeln und zu validieren. Im Vordergrund steht hierbei als Applikation im Industriesektor Energieversorgung die Prüfung von sicherheitsrelevanten Komponenten von onshore und offshore Windkraftanlagen, wie z.B. deren Rotorblätter und tragende Strukturen.
Eine Teilaufgabe innerhalb des Projektes stellen der Vergleich und die Validierung verschiedener Ultraschallprüfmethoden bezüglich ihrer Fähigkeit zum Nachweis der typischen Herstellungs- und betriebsbedingten Materialschädigungen von CFK und GFK dar.
Neben verschiedenen konventionellen Ultraschall-Prüftechniken, werden die Phased-Array-Prüfung, insbesondere die Prüfung mit Matrixarrays, sowie die Untersuchung mit berührüngsloser Luftultraschalltechnik bezüglich ihrer Nachweisgrenzen und der Möglichkeiten zur Fehlercharakterisierung an Faserverbundwerkstoffen untersucht. Die Ergebnisse werden mit Untersuchungen mit thermographischen Methoden und Mikrowellentechnik verglichen.
The objects of this investigation were sculptures taken from a ca. three hundred years old baroque epitaph of a church in Tonning, a town in Northern Germany. Around 1900 it was found in a disastrous state heavily damaged by wood-worm. At that time, the whole artwork was treated with the tar extract carbolineum as a remedy. Nowadays, this substance has been identified as carcinogenic, and its presence can be perceived by its stench and visually at certain spots on the surface where it has penetrated the covering paint.
A gold-painted sculpture of a massive wooden skull was interrogated with X-rays and fast neutrons to investigate the internal distribution of the carbolineum. The X-ray tomography, with its excellent spatial resolution revealed galleries left over from the worm infestation in the outer areas and cracks in the central region. The golden color coating appeared as a thick and dense layer. In comparison the tomography with fast neutrons, though being of lower resolution and yet unresolved artefacts revealed sections of slightly different densities in the bulk of the wood. These differences we attribute to the differences in the distribution of the impregnant in the wood, visible due to its higher hydrogen content making it less transparent for neutrons.
Fire and explosion hazards associated with storage and transportation of flammable materials have been a matter of great interest in the recent times. BLEVE is a scenario that occurs when a closed fuel container is subjected to heat for a longer duration. Such events are disastrous to human beings and assets both. In the past there have been numerous studies on BLEVEs and fireballs of hydrocarbon fuels, e.g. kerosene, gasoline, LPG, LNG and others. Though, the fireballs of peroxy-fuels are not looked into detail as such. This article tries to overcome this lack of knowledge. Both, experimental investigation and CFD simulations are performed to measure and predict the fireball characteristics of a peroxy-fuel. Due to thermal decomposition in the liquid phase and active oxygen content a peroxy-fuel fireball burns at a very fast rate and emit higher thermal radiation whereas exhibits smaller diameter and elevation compared to hydrocarbons. That eventually leads to consideration of larger safety distances from them which are also verified by CFD results.
Neutron tomography has been applied to investigate the mechanism of hydrogen assisted cracking in technical iron and supermartensitic steel. Rectangular technical iron block samples showed blistering due to intense hydrogen charging and the tomographic method revealed in situ the spatial distribution of hydrogen and cracks. Hydrogen accumulated in a small region around cracks and the cracks are filled with hydrogen gas. Cracks close to the surface contained no hydrogen. Hydrogenous tensile test samples of supermartensitic steel were pulled until rupture and showed hydrogen accumulations at the notch base and in the plastically deformed region around the fracture surface.
A multifunctional fluorescence platform has been constructed based on gold nanoparticle (AuNP)-catalyzed uranine reduction. The catalytic reduction of uranine was conducted in aqueous solution using AuNPs as nanocatalyst and sodium borohydride as reducing reagent, which was monitored by fluorescence and UV-vis spectroscopy. The reaction rate was highly dependent on the concentration, size and dispersion state of AuNPs. When AuNPs aggregated, their catalytic ability decreased, and thereby a label-free fluorescent assay was developed for the detection of melamine, which can be used for melamine determination in milk. In addition, a fluorescent immunoassay for aflatoxin B1 (AFB1) was established using the catalytic reaction for signal amplification based on target-induced concentration change of AuNPs, where AFB1-BSA-coated magnetic beads and anti-AFB1 antibody-conjugated AuNPs were employed as capture and signal probe, respectively. The detection can be accomplished in 1 h and acceptable recoveries in spiked maize samples were achieved. The developed fluorescence system is simple, sensitive and specific, which could be used for the detection of a wide range of analytes.
This paper gives a brief overview on3D imaging of magnetic domains with shearing grating neutron tomography. We investigated the three-dimensional distribution of magnetic domain walls in the bulk of a wedge-shaped FeSi single crystal. The width of the magnetic domains wasanalyzed at different locations within the crystal. Magnetic domains close to the tip of the wedge are much smaller than in the bulk. Furthermore, the three-dimensional shape of individual domains wasinvestigated. We discuss prospects and limitations of the applied measurement technique.
Geosynthetics are planar polymeric products, which are used in connection with soil, rock or other soil-like materials to fulfill various functions in geoenvironmental engineering. Geosynthetics are of ever-growing importance in the construction industry. Sealing of waste storage facilities to safely prevent the emission of wastewater, landfill gas and contaminated dust as well as the diffusion of pollutants into the environment and coastal protection against storms and floods and reconstruction after natural disaster are important fields of application. We will give an overview of the various geosynthetic products. Two examples of the material problems related to geosynthetics are discussed in detail: the effect of creep on the long-term performance of geocomposite drains and the numerical simulation of the interaction of soil with geogrids. Both issues are of importance for the use of these products in landfill capping systems. The various functions, which geosynthetics may fulfill in the protection of coastal lines, are illustrated by case studies. The geosynthetic market is evaluated and economical and environmental benefits, as well as environmental side effects related to the use of geosynthetics, are discussed.
Synthesis, structure determination, and formation of a theobromine: oxalic acid 2:1 cocrystal
(2015)
The structure and the formation pathway of a new theobromine : oxalic acid (2 : 1) cocrystal are presented. The cocrystal was synthesised mechanochemically and its structure was solved based on the powder X-ray data. The mechanochemical synthesis of this model compound was studied in situ using synchrotron XRD. Based on the XRD data details of the formation mechanism were obtained. The formation can be described as a self-accelerated ('liquid like') process from a highly activated species.
In carrier gas hot extraction the calibration of low amounts of non-metals with masses of a few micrograms with small uncertainty remains a challenge. To achieve high flexibility a high precision gas mixture pump was combined with an automated syringe drive. The gas mixing pump allows filling the syringe with different gas compositions; the automated syringe drive allows matching to modulate the signal profiles to those of real samples. The system was designed and its experimental potential explored. The resulting calibration curves were comparable to those obtained by calibration using solid materials of sufficient purity and stoichiometry. However smaller uncertainties and lower limits of quantification (i.e. 0.5 µg and 0.6 µg for O and N, respectively) were found using the gas calibration device.
Temperature-memory polymers are able to generate a substantial mechanical response when heated above the temperature, at which a preceding deformation was carried out. Here we show how to design the temperature-memory effect (TME) by thermomechanical treatment. As a model polymer, phase segregated poly(ester urethane) (PEU) containing crystallizable segments of poly(1,4-butylene adipate) (PBA) was used. For programming, strain elongation was applied at temperatures within the PBA melting transition area, before temperature holding, unloading and cooling were carried out. Upon heating under stress-free or constant strain recovery conditions, precisely set temperature-memory onsets could be witnessed. Most importantly, strain fixities and recoverabilities the same as maximum recovery stresses turned out to be controllable by strain rate and temperature holding time after deformation, while transition temperatures remained largely unaffected. The tailoring of thermoresponsiveness was structurally enabled by different PBA crystallinities in the programmed state as verified by wide-angle X-ray scattering (WAXS). The reported studies intend to design TMEs in semicrystalline polyurethanes according to user-defined needs to make this technology broadly applicable.
We present a systematic study on the effect of surface ligands on the luminescence properties and colloidal stability of β-NaYF4:Yb3+,Er3+ upconversion nanoparticles (UCNPs), comparing nine different surface coatings to render these UCNPs water-dispersible and bioconjugatable. A prerequisite for this study was a large-scale synthetic method that yields ~2 g per batch of monodisperse oleate-capped UCNPs providing identical core particles. These ~23 nm sized UCNPs display an upconversion quantum yield of ~0.35% when dispersed in cyclohexane and excited with a power density of 150 W cm-2, underlining their high quality. A comparison of the colloidal stability and luminescence properties of these UCNPs, subsequently surface modified with ligand exchange or encapsulation protocols, revealed that the ratio of the green (545 nm) and red (658 nm) emission bands determined at a constant excitation power density clearly depends on the surface chemistry. Modifications relying on the deposition of additional (amphiphilic) layer coatings, where the initial oleate coating is retained, show reduced non-radiative quenching by water as compared to UCNPs that are rendered water-dispersible via ligand exchange. Moreover, we could demonstrate that the brightness of the upconversion luminescence of the UCNPs is strongly affected by the type of surface modification, i.e., ligand exchange or encapsulation, yet hardly by the chemical nature of the ligand.
Polyglycerol (PG) coated polypropylene (PP) films were synthesized in a two-step approach that involved plasma bromination and subsequently grafting hyperbranched polyglycerols with very few amino functionalities. The influence of different molecular weights and density of reactive linkers were investigated for the grafted PGs. Longer bromination times and higher amounts of linkers on the surface afforded long-term stability. The protein adsorption and bacteria attachment of the PP-PG films were studied. Their extremely low amine content proved to be beneficial for preventing bacteria attachment.
This paper reflects recent progress in the field of fluorescent polymer optical fiber sensors (F-POF) for partial discharge (PD) detection in high voltage (HV) cable accessories using optical-only PD detection by coincidence single photon counting. In experiments with artificial PD sources these sensors show the ability to detect optical emissions from picocoulomb-level PDs in a real-scale model of a translucent high voltage cable accessory. False positives (caused by detector noise) are efficiently suppressedwhile maintaining sufficient sensitivity,even when the sensor is located in an unfavorable position.
Selective Electron Beam Melting (SEBM) is a promising powder bed Additive Manufacturing technique for near-net-shape manufacture of high-value titanium components. However without post-manufacture HIPing the fatigue life of SEBM parts is currently dominated by the presence of porosity. In this study, the size, volume fraction, and spatial distribution of the pores in model samples have been characterised in 3D, using X-ray Computed Tomography, and correlated to the process variables. The average volume fraction of the pores (b0.2%) was measured to be lower than that usually observed in competing processes, such as selective laser melting, but a strong relationship was found with the differentbeamstrategies used to contour ,and infill by hatching, a part section. The majority of pores were found to be small spherical gas pores, concentrated in the infill hatched region; this was attributed to the lower energy density and less focused beam used in the infill strategy allowing less opportunity for gas bubbles to escape the melt pool. Overall, increasing the energy density or focus of the beam was found to correlate strongly to a reduction in the level of gas porosity. Rarer irregular shaped pores were mostly located in the contour region and have been attributed to a lack of fusion between powder particles.
The reaction of iron chlorides with an alkaline reagent is one of the most prominent methods for the synthesis of iron oxide nanoparticles. We studied the particle formation mechanism using triethanolamine as reactant and stabilizing agent. In situ fast-X-ray absorption near edge spectroscopy and small-angle X-ray scattering provide information on the oxidation state and the structural information at the same time. In situ data were complemented by ex situ transmission electron microscopy, wide-angle X-ray scattering and Raman analysis of the formed nanoparticles. The formation of maghemite nanoparticles (γ-Fe2O3) from ferric and ferrous chloride was investigated. Prior to the formation of these nanoparticles, the formation and conversion of intermediate phases (akaganeite, iron(II, III) hydroxides) was observed which undergoes a morphological and structural collapse. The thus formed small magnetite nanoparticles (Fe3O4) grow further and convert to maghemite with increasing reaction time.
The color X-ray camera SLcam® is a full-field, single photon detector providing scanning-free, energy and spatially resolved X-ray imaging. Spatial resolution is achieved with the use of polycapillary optics guiding X-ray photons from small regions on a sample to distinct energy dispersive pixels on a charged-coupled device detector. Applying sub-pixel resolution, signals from individual capillary channels can be distinguished. Therefore, the SLcam® spatial resolution, which is normally limited to the pixel size of the charge-coupled device, can be improved to the size of individual polycapillary channels. In this work a new approach to a sub-pixel resolution algorithm comprising photon events also from the pixel centers is proposed. The details of the employed numerical method and several sub-pixel resolution examples are presented and discussed.
Effect of fluorescent staining on size measurements of polymeric nanoparticles using DLS and SAXS
(2015)
The influence of fluorescence on nanoparticle size measurements using dynamic light scattering (DLS) and small angle X-ray scattering (SAXS) was investigated. For this purpose, two series of 100 nm-sized polymer nanoparticles stained with different concentrations of the fluorescent dyes DY555 and DY680 were prepared, absorbing/emitting at around 560 nm/590 nm and 695 nm/715 nm, respectively. SAXS measurements of these particle series and a corresponding blank control (without dye) revealed similar sizes of all particles within an uncertainty of 1 nm. DLS measurements carried out at three different laboratories using four different DLS instruments and two different laser wavelengths, i.e., 532 nm and 633 nm, revealed also no significant changes in size (intensity-weighted harmonic mean diameter, ZAverage) and size distribution (polydispersity index, PI) within and between the two dye-stained particle series and the blank sample. Nevertheless, a significant decrease of the detected correlation coefficients was observed with increasing dye concentration, due to the increased absorption of the incident light and thus, less coherent light scattering. This effect was wavelength dependent, i.e. only measurable for the dye-stained particles that absorb at the laser wavelength used for the DLS measurements.
This paper describes the production and characteristics of the nanoparticle test materials prepared for common use in the collaborative research project NanoChOp (Chemical and optical characterization of nanomaterials in biological systems), in casu suspensions of silica nanoparticles and CdSe/CdS/ZnS quantum dots (QDs). This paper is the first to illustrate how to assess whether nanoparticle test materials meet the requirements of a "reference material" (ISO Guide 30, 2015) or rather those of the recently defined category of "representative test material (RTM)" (ISO/TS 16195, 2013). The NanoChOp test materials were investigated with small-angle X-ray scattering (SAXS), dynamic light scattering (DLS), and centrifugal liquid sedimentation (CLS) to establish whether they complied with the required monomodal particle size distribution. The presence of impurities, aggregates, agglomerates, and viable microorganisms in the suspensions was investigated with DLS, CLS, optical and electron microscopy and via plating on nutrient agar. Suitability of surface functionalization was investigated with attenuated total reflection Fourier transform infrared spectrometry (ATR-FTIR) and via the capacity of the nanoparticles to be fluorescently labeled or to bind antibodies. Between-unit homogeneity and stability were investigated in terms of particle size and zeta potential. This paper shows that only based on the outcome of a detailed characterization process one can raise the status of a test material to RTM or reference material, and how this status depends on its intended use.
In order to assess the anisotropy-related uncertainties of relatively determined photoluminescence quantum yields (ΦPL) of molecular emitters and luminescent nanomaterials, we compared ΦPL values measured without and with polarizers using magic angle conditions and studied systematically the dependence of the detected emission intensity on the polarizer settings for samples of varying anisotropy. This includes a dispersion of a spherical quantum dot (QD) with an ideally isotropic emission, a solution of a common small organic dye in a fluid solvent as well as dispersions of elongated quantum dot rods (QDR) with an anisotropic luminescence and a small organic dye in a rigid polymeric matrix, as ideally anisotropic emitter. Our results show that for instruments lacking polarizers, anisotropy-related measurement uncertainties of relative photoluminescence quantum yields can amount to more than 40%, with the size of these systematic errors depending on the difference in emission anisotropy between the sample and the standard.
Melt flow and dripping of the pyrolysing polymer melt can be both a benefit and a detriment during a fire. In several small-scale fire tests addressing the ignition of a defined specimen with a small ignition source, well-adjusted melt flow and dripping are usually beneficial to pass the test. The presence of flame retardants often changes the melt viscosity crucially. The influence of certain flame retardants on the dripping behaviour of four commercial polymers, poly(butylene terephthalate) (PBT), polypropylene (PP), polypropylene modified with ethylene-propylene rubber (PP-EP) and polyamide 6 (PA 6), is analysed based on an experimental monitoring of the mass loss due to melt dripping, drop size and drop temperature as a function of the furnace temperature applied to a rod-shaped specimen. Investigating the thermal transition (DSC), thermal and thermo-oxidative decomposition, as well as the viscosity of the polymer and collected drops completes the investigation. Different mechanisms of the flame retardants are associated with their influence on the dripping behaviour in the UL 94 test. Reduction in decomposition temperature and changed viscosity play a major role. A flow limit in flame-retarded PBT, enhanced decomposition of flame-retarded PP and PP-EP and the promotion of dripping in PA 6 are the salient features discussed.
In this work, sample losses of silver nanoparticles (Ag NPs) in asymmetrical flow field-flow fractionation (AF4) have been systematically investigated with the main focus on instrumental conditions like focusing and cross-flow parameters as well as sample concentration and buffer composition. Special attention was drawn to the AF4 membrane. For monitoring possible silver depositions on the membrane, imaging laser ablation coupled to inductively coupled plasma mass spectrometry (LA-ICP-MS) was used. Our results show that the sample residue on the membrane was below 0.6% of the total injected amount and therefore could be almost completely avoided at low sample concentrations and optimized conditions. By investigation of the AF4 flows using inductively coupled plasma mass spectrometry (ICP-MS), we found the recovery rate in the detector flow under optimized conditions to be nearly 90%, while the cross-flow, slot-outlet flow and purge flow showed negligible amounts of under 0.5%. The analysis of an aqueous ionic Ag standard solution resulted in recovery rates of over 6% and the ionic Ag content in the sample was found to be nearly 8%. Therefore, we were able to indicate the ionic Ag content as the most important source of sample loss in this study.