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Paper des Monats
- ja (92)
The mechanism of action of zirconium permanent modifiers on graphite surfaces was investigated in order to understand its influence on the analytical signal in atomic and molecular absorption spectrometry (AAS/MAS). For this, the molecule formation of CaF was studied, which is used for the indirect analytical determination of fluorine in high-resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS-GFMAS). The kinetics of this reaction was established by monitoring its molecular spectrum at different atomisation temperatures. An Arrhenius plot showed a pseudo-first order reaction with respect to fluorine (n = 1). An intermediate state was isolated, and its structure was elucidated by spectroscopic methods: scanning electron microscopy with energy dispersive X-ray spectroscopy (SEMEDX), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XANES and EXAFS), and Raman microspectroscopy. We propose here a mechanism, where ZrO2 acts as a heterogeneous catalyst: after a pyrolytic step, an intermediate state of ZrO(OCaF) is activated, and at higher temperatures, CaF(g) is released from the zirconium-coated graphite surface. No evidence of the formation of zirconium carbide was found. Consequently, as the CaF formation is catalysed by a heterogeneous catalyst, surface modifications with ZrO2 nanoparticles and ZrO xerogels were investigated in order to increase the surface area. Their influence was evaluated in the molecule formation of CaF, CaCl, CaBr, and CaI. Graphite furnace modification with zirconium oxide nanoparticles proves to be the best choice for fluorine analysis with a signal enhancement of more than eleven times with respect a non-coated graphite furnace. However, the influence of zirconium modifications in the analytical signals of Cl, and I is lower than the F signals or even negative in case of the Br. Understanding zirconium modifiers as heterogeneous catalysts offers a new perspective to AAS and MAS, and reveals the potential of surface analytical methods for development of improved permanent modifiers and graphite furnace coatings.
Boron isotope amount ratios n(10B)/n(11B) have been determined by monitoring the absorption spectrum of boron monohydride (BH) in a graphite furnace using high-resolution continuum source molecular absorption spectrometry (HR-CS-MAS). Bands (0→0) and (1→1) for the electronic transition X1Σ+ → A1Π were evaluated around wavelengths 433.1 nm and 437.1 nm respectively. Clean and free of memory effect molecular spectra of BH were recorded. In order to eliminate the memory effect of boron, a combination of 2% (v/v) hydrogen gas in argon and 1% trifluoromethane in argon, an acid solution of calcium chloride and mannitol as chemical modifiers was used. Partial least square regression (PLS) for analysis of samples and reference materials were applied. For this, a spectral library with different isotopes ratios for PLS regression was built. Results obtained around the 433.1 nm and 437.1 nm spectral regions are metrologically compatible with those reported by mass spectrometric methods. Moreover, for the evaluated region of 437 nm, an accuracy of 0.15‰ is obtained as the average deviation from the isotope reference materials. Expanded uncertainties with a coverage factor of k = 2 range between 0.15 and 0.44‰. This accuracy and precision are compatible with those obtained by mass spectrometry for boron isotope ratio measurements.
A fast and simple method for sulfur quantification in crude oils was developed by using high-resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS-GFMAS). For this, heavy crude oil samples were prepared as microemulsion (shake) and injected into a graphite furnace (shut). Finally, the concentration of sulfur was determined by monitoring in situ the transient molecular spectrum of GeS at wavelength 295.205nm after adding a germanium solution as molecular forming agent (and go). Zirconium dioxide in the form of nanoparticles (45–55nm) was employed as a permanent modifier of the graphite furnace. Calibration was done with an aqueous solution standard of ammonium sulfate, and a characteristic mass (m0) of 7.5ng was achieved. The effectiveness of the proposed method was evaluated analizing, ten heavy crude oil samples with Sulfur amounts ranging between 0.3 and 4.5% as well as two NIST standard reference materials, 1620c and 1622e. Results were compared with those obtained by routine ICP-OES analysis, and no statistical relevant differences were found.
High-resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS-GF-MAS) was employed for determining adsorbable organic chlorine (AOCl) in water. Organic chlorine was indirectly quantified by monitoring the molecular absorption of the transient aluminum monochloride molecule (AlCl) around a wavelength of 261.42 nm in a graphite furnace. An aluminum solution was used as the molecularforming modifier. A zirconium coated graphite furnace, as well as Sr and Ag solutions were applied as modifiers for a maximal enhancement of the absorption signal. The pyrolysis and vaporization temperatures were 600 °C and 2300 °C, respectively. Non-spectral interferences were observed with F, Br, and I at concentrations higher than 6 mg L-1, 50 mg L-1, and 100 mg L-1, respectively. Calibration curves with NaCl, 4-chlorophenol, and trichlorophenol present the same slope and dynamic range, which indicates the chlorine atom specificity of the method. This method was evaluated and validated using synthetic water samples, following the current standard DIN EN ISO 9562:2004 for the determination of the sum parameter adsorbable organic halides (AOX) for water quality. These samples contain 4-chlorophenol as the chlorinated organic standard in an inorganic chloride matrix. Prior to analysis, organic chlorine was extracted from the inorganic matrix via solid-phase extraction with a recovery rate >95%. There were no statistically significant differences observed between measured and known values and for a t-test a confidence level of 95% was achieved. The limits of detection and characteristic mass were found to be 48 and 22 pg, respectively. The calibration curve was linear in the range 0.1–2.5 ng with a correlation coefficient R2 = 0.9986.
An energy-based method to determine material constants in nonlinear rheology with applications
(2016)
Many polymer-type materials show a rate-dependent and nonlinear rheological behavior. Such a response may be modeled by using a series of spring-dashpot systems. However, in order to cover different time scales the number of systems may become unreasonably large. A more appropriate treatment based on continuum mechanics will be presented herein. This approach uses representation theorems for deriving material equations and allows for a systematic increase in modeling complexity. Moreover, we propose an approach based on energy to determine thematerial parameters.This method results in a simple linear regression problemeven for highly nonlinearmaterial equations. Therefore, the inverse problem leads to a unique solution. The significance of the proposed method is that the stored and dissipated energies necessary for the procedure are measurable quantities. We apply the proposed method to a 'semi-solid' material and measure its material parameters by using a simple-shear rheometer.
A controlled, reproducible, gram-scale method is reported for the covalent functionalization of graphene Sheets by a one-pot nitrene [2+1] cycloaddition reaction under mild conditions. The reaction between commercially available 2,4,6-trichloro-1,3,5-triazine and sodium azide with thermally reduced graphene oxide (TRGO) results in defined dichlorotriazine-functionalized sheets. The different reactivities of the chlorine substituents on the functionalized graphene allow stepwise post-modification by manipulating the temperature.
This new method provides unique access to defined bifunctional 2D nanomaterials, as exemplified by chiral surfaces and multifunctional hybrid architectures.
Mass spectrometry-based methods play a crucial role in the quantification of the main iron metabolism regulator hepcidin by singling out the bioactive 25-residue peptide from the other naturally occurring N-truncated isoforms (hepcidin-20, -22, -24), which seem to be inactive in iron homeostasis. However, several difficulties arise in the MS analysis of hepcidin due to the sticky character of the peptide and the lack of suitable standards. Here, we propose the use of amino- and fluoro-silanized autosampler vials to reduce hepcidin interaction to laboratory glassware surfaces after testing several types of vials for the preparation of stock solutions and serum samples for isotope dilution liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS). Furthermore, we have investigated two sample preparation strategies and two chromatographic separation conditions with the aim of developing an LC-MS/MS method for the sensitive and reliable quantification of hepcidin-25 in serum samples. A chromatographic separation based on usual acidic mobile phases was compared with a novel approach involving the separation of hepcidin-25 with solvents at high pH containing 0.1% of ammonia. Both methods were applied to clinical samples in an intra-laboratory comparison of two LC-MS/MS methods using the same hepcidin-25 calibrators with good correlation of the results. Finally, we recommend an LC-MS/MS-based quantification method with a dynamic range of 0.5–40 μg/L for the assessment of hepcidin-25 in human serum that uses TFA-based mobile phases and silanized glass vials.
Predictable Peptide Conjugation Ratios by Activation of Proteins with Succinimidyl Iodoacetate (SIA)
(2017)
The small heterobifunctional linker succinimidyl iodoacetate (SIA) was examined for the preparation of peptide–protein bioconjugates with predicable conjugation ratios. For many conjugation protocols, the protein is either treated with a reductant to cleave disulfide bonds or is reacted with thiolation chemicals, such as Traut’s reagent. Both approaches are difficult to control, need individual optimization and often lead to unsatisfactory results. In another popular approach, a heterobifunctional linker with a N-hydroxysuccinimide (NHS) and a maleimide functionality is applied to the protein. After the activation of some lysine ε-amino groups with the NHS ester functionality, a cysteine-containing peptide is attached to the activated carrier protein via maleimide. Particularly, the maleimide reaction leads to some unwanted byproducts or even cleavage of the linker. Many protocols end up with conjugates with unpredictable and irreproducible conjugation ratios. In addition, the maleimide-thiol addition product should be assumed immunogenic in vivo. To avoid these and other disadvantages of the maleimide approach, we examined the known linker succinimidyl iodoacetate (SIA) in more detail and developed two protocols, which lead to peptide–protein conjugates with predefined average conjugation ratios. This holds potential to eliminate tedious and expensive optimization steps for the synthesis of a bioconjugate of optimal composition.
Hepcidin-25 was identified as the main iron regulator in the human body, and it by binds to the sole iron-exporter ferroportin. Studies showed that the N-terminus of hepcidin is responsible for this interaction, the same N-terminus that encompasses a small copper(II)-binding site known as the ATCUN (amino-terminal Cu(II)- and Ni(II)-binding) motif. Interestingly, this copper-binding property is largely ignored in most papers dealing with hepcidin-25. In this context, detailed investigations of the complex formed between hepcidin-25 and copper could reveal insight into its biological role. The present work focuses on metal-bound hepcidin-25 that can be considered the biologically active form. The first part is devoted to the reversed-phase chromatographic separation of copper-bound and copper-free hepcidin-25 achieved by applying basic mobile phases containing 0.1% ammonia. Further, mass spectrometry (tandem mass spectrometry (MS/MS), high-resolution mass spectrometry HRMS)) and nuclear magnetic resonance (NMR) spectroscopy were employed to characterize the copper-peptide. Lastly, a three-dimensional (3D)model of hepcidin-25with bound copper(II) is presented. The identification of metal complexes and potential isoforms and isomers, from which the latter usually are left undetected by mass spectrometry, led to the conclusion that complementary analytical methods are needed to characterize a peptide calibrant or reference material comprehensively. Quantitative nuclear magnetic resonance (qNMR), inductively-coupled plasma mass spectrometry (ICP-MS), ion-mobility spectrometry (IMS) and chiral amino acid analysis (AAA) should be considered among others.
Quasi-static dispersion of dusts for the determination of lower explosion limits of hybrid mixtures
(2022)
Knowledge of explosion limiting concentration of explosible materials is necessary forthe design of explosion protection measures. Currently employed methods of testing MEC of a dust cloud or LEL of a hybrid mixture are based on arbitrary assumptionsand possess technical limitations that often lead to values of MEC/LEL, which are unrealistically low or poorly reproducible. This contribution presents an improved method for experimental determination of MEC of a combustible dust cloud or LEL of a flammable gas or hybrid mixture. The new setup operates under laminar conditions and allows a uniform suspension of dust particles in an open top acrylic glass tube. Dust concentration is measured with the help of infrared sensors installed a few centimeters above and below the ignition source. In order to evaluate the dependence of MEC on flow front velocity, MEC of lycopodium was determined at four flow velocities. The results show that the flow field intensity does not significantly influence the MEC of lycopodium for the flow ranges tested in this work. Moreover, LEL of hybrid mixtures of lycopodium and methane was also tested at flow velocities of 4.7 cm/s, 5.8 cm/s, 7 cm/s and 11 cm/s and compared with the values obtained from other sources. The results suggest that the requirement of high energy pyrotechnical igniter may be relinquished, provided that a truly homogeneous suspension of dust particles could be achieved. Moreover, the effect of relative amount of dust and gas, on the course of ignition and flame propagation in hybrid mixtures at their LEL, was studied by the help of high speed videos. For hybrid mixtures of carbonaceous dusts (like lycopodium) at their LEL, ignition occurs in the gas phase, however, flame propagation is only possible through a two-way interaction of dust and gas during the course of combustion.
Starch is one of the most common and easily obtained natural polymers, making it attractive as a potential bio-based alternative to synthetic polymers. This study shows that a simple quaternary ammonium salt combined with urea or glycols forms effective modifiers that produce flexible plastics with good mechanical properties that are comparable to some polyolefin plastics. The processing conditions are shown to significantly affect the structure of the polymer which has a concomitant effect upon the mechanical and physical properties of the resulting plastic. Using a glycerol based modifier results in a totally sustainable and biodegradable material which can be injection moulded.
We report on the mechanical properties of Cu–Nb alloys produced by combinatorial magnetron sputtering.
Depending on the composition, the microstructure is either fully amorphous (~30–65 at.% Cu), a dispersion of Cu crystallites in an amorphous matrix (~70 at.%), or a dominant crystalline phase with separated nanoscale amorphous zones (~80 at.% Cu). Nanomechanical probing of the different microstructures reveals that the hardness of the fully amorphous alloy is much higher than a rule of mixture would predict. We further demonstrate a remarkable tunability of the resistance to plastic flow, ranging from ca. 9 GPa in the amorphous regime to ca. 2 GPa in the fully crystalline regime. We rationalize these findings based on fundamental structural considerations, thereby highlighting the vast structure-property design space that this otherwise immiscible binary alloy provides.
Explosion regions of propane, isopropanol, acetone, and methyl acetate/inert gas/air mixtures
(2016)
The explosion regions for propane, isopropanol, acetone, and methyl acetate with air in the presence of nitrogen, argon, helium, and carbon dioxide were determined experimentally according to EN 14756/EN1839, method T. Except for propane, all the measurements were executed at 323 K and 1 bar. Propane experiments were carried out at 293 K and 1 bar. The results show that for the same type of inert gas, propane, isopropanol, and acetone have great closeness concerning the concentration of the inert gas at the apex of the explosion envelope in a ternary diagram with air as oxidizer. This leads to consistency in the limiting oxygen concentration (LOC) and minimum required amount of inert gas (MAI) values. Concerning methyl acetate, the apex was always reached at higher percentages of inert gases compared with the other fuels. This can be attributed to the presence of two oxygen atoms inside the chemical structure. Calculation of the explosion regions was carried out based on calculated adiabatic flame temperature (CAFT) method. The flame temperatures for the experimentally determined fuel/air/N2 mixtures were calculated. Then, these temperatures were used to predict the explosion limits of similar mixtures with other inert gases than nitrogen. The modeling results show reasonable agreement with the experimental results.
The explosion regions of 1-propanol, 2-propanol, acetone and 1-butanol in air were measured in the presence of CO2, He, N2 and Ar in accordance with EN1839 method T at high temperatures and at atmospheric pressure. The experimental results show that 1-propanol, 2-propanol and acetone have very similar lower explosion limits (LELs). 1-Butanol shows a slightly wider explosion area near the LEL line. In addition, the explosion regions of all combustible/inert gas/air mixtures were calculated with the method of constant adiabatic flame temperature profiles (CAFTP), using the flame temperature profile along the explosion region boundary curve of each combustible/N2/air mixture as a reference to determine the explosion regions of combustible/inert gas/air mixtures with inert gases other than N2 at different initial temperatures. To calculate the explosion regions for systems containing He, the calculation method was modified to include the very different physical transport properties of He. Moreover, the procedure for calculating the apexes in the ternary explosion diagrams was modified. The calculation results show good agreement with the experimental results.
In this study, experimental determination and modelling investigations for the explosion regions of 1,3-dioxolane/inert gas/N2O and 1,3-dioxolane/inert gas/air mixtures were carried out and compared. The experimental measurements were carried out at 338 K and atmospheric pressure according to EN1839 method T using the inert gases N2, CO2, He and Ar. The results showed that the ratio of the lower explosion limit in N2O (LELN2O) to the lower explosion limit in air (LELair) is 0.52 and the ratio of the maximum oxygen content in air (MOCair) to the limiting oxidizer fraction in nitrous oxide (LOFN2O) is 0.36 ± 0.02 independent of the inert gas. When comparing the inert gas amount at the apex based on the pure oxidizing component, which is O2 in case of air, N2O-containing mixtures need less inert gas to reach the limiting oxidizer quantity whereas the efficiency of inert gases is in the same order. The coefficients of nitrogen equivalency however were found to differ to some extent. The explosion regions of 1,3-dioxolane/inert gas/oxidizer mixtures were modelled using the calculated adiabatic flame temperature profile (CAFTP) method as well as corrected adiabatic flame temperatures. The results indicate good agreement with experimental data for CO2, N2 and Ar- containing mixtures. The noticeable deviations that occur when He is the inert gas are due to the lacking transport data of that mixture.
Microfluidic electrochemical immunosensor for the trace analysis of cocaine in water and body fluids
(2018)
Quick but accurate testing and on‐the‐spot monitoring of cocaine in oral fluids and urine continues to be an important toxicological issue. In terms of drug testing, a number of devices have been introduced into the market in recent decades, notably for workplace inspection or roadside testing. However, these systems do not always fulfill the requirements in terms of reliability, especially when low cut‐off levels are required. With respect to surface water, the presence of anthropogenic small organic molecules such as prescription and over‐the‐counter pharmaceuticals as well as illicit drugs like cannabinoids, heroin, or cocaine, has become a challenge for scientists to develop new analytical tools for screening and on‐site analysis because many of them serve as markers for anthropogenic input and consumer behavior. Here, a modular approach for the detection of cocaine is presented, integrating an electrochemical enzyme‐linked immunosorbent assay (ELISA) performed on antibody‐grafted magnetic beads in a hybrid microfluidic sensor utilizing flexible tubing, static chip and screen‐printed electrode (SPE) elements for incubation, recognition, and cyclic voltammetry measurements. A linear response of the sensor vs. the logarithm of cocaine concentration was obtained with a limit of detection of 0.15 ng/L. Within an overall assay time of 25 minutes, concentrations down to 1 ng/L could be reliably determined in water, oral fluids, and urine, the system possessing a dynamic working range up to 1 mg/L.
This study focused on quantitative detection of cocaine on Euro banknotes in Germany. A sensitive direct competitive immunoassay was developed and optimized with a limit of detection (LOD) of 5.6 ng/L. Exhaustive cocaine extraction by solvent was tested using different methanol concentrations and buffered solutions. Crossreactivity studies were performed to determine the degree of interference of cocaine metabolites with the immunoassay. Sixty-five Euro banknotes obtained from different districts in Berlin were evaluated. A 100% contamination frequency with cocaine was detected. A comparison between the amount of cocaine extracted by cotton swabbing of one square centimeter of the banknote showed a good correlation for lower contamination levels. This assay showed high sensitivity of detecting pg of cocaine per 1 cm2 of one banknote by swabbing 1 cm2: 0, 14, and 21 pg/cm2. Moreover, three notes of different denominations revealed high cocaine concentration; 1.1 mg/note, and twice 55 μg/note.
One of the major challenges in chemical synthesis is to trigger and control a specific reaction route leading to a specific final product, while side products are avoided. Methodologies based on resonant processes at the molecular level, for example, photochemistry, offer the possibility of inducing selective reactions. Electrons at energies below the molecular ionization potential (<10 eV) are known to dissociate molecules via resonant processes with higher cross sections and specificity than photons. Here we show that even subexcitation electrons with energies as low as 1 eV produce ethylene and acetylene from dimethyl sulfide in competing reactions. However, the production of ethylene can specifically be targeted by controlling the energy of electrons (∼3 to 4 eV). Finally, pure ethylene is selectively desorbed by heating the substrate from 90 to 105 K. Beyond the synthesis of these versatile hydrocarbons for various industrial applications from a biogenic sulfur compound, our findings demonstrate the feasibility of electron-induced selective chemistry applicable on the nanoscale.
Ultrafast laser processing can be used to realize various morphological surface transformations, ranging from direct contour shaping to large-area-surface functionalization via the generation of “self-ordered” micro- and nanostructures as well as their hierarchical hybrids. Irradiation with high-intensity laser pulses excites materials into extreme conditions, which then return to equilibrium through these unique surface transformations. In combination with suitable top-down or bottom-up manufacturing strategies, such laser-tailored surface morphologies open up new avenues toward the control of optical, chemical, and mechanical surface properties, featuring various technical applications especially in the fields of photovoltaics, tribology, and medicine. This article reviews recent efforts in the fundamental understanding of the formation of laser-induced surface micro- and nanostructures and discusses some of their emerging capabilities.
In 2018, the production of Municipal SolidWaste (MSW) in EU-28 reached 250.6 Mt, with the adoption of different management strategies, involving recycling (48 wt %), incineration and thermal valorization (29 wt %) and landfilling (23 wt %). This work was based on the analysis of the baseline situation of MSW management in EU-28 in 2018, considering its progress in 2008–2018, and discussed the possible improvement perspectives based on a framework involving incineration and recycling as the only possible alternatives, specifically evaluating the capability of already-existing incineration plants to fulfill the EU needs in the proposed framework. The results of the assessment showed two main crucial issues that could play a pivotal role in the achievement of Circular Economy action plan targets: the need to increase the recycling quotas for specific MSW fractions through the separate collection, and therefore the improvement of definite treatment process chains; the optimization of the recovery of secondary raw materials from incineration bottom ash, involving the Recycling of ferrous and nonferrous metals and the mineral fraction. Both issues need to find an extensive application across all member states to decrease the actual differences in the adoption of sustainable MSW management options.
The main obstacle to bottom ash (BA) being used as a recycling aggregate is the content of salts and potential toxic elements (PTEs), concentrated in a layer that coats BA particles. This work presents a dry treatment for the removal of salts and PTEs from BA particles. Two pilotscale abrasion units (with/without the removal of the fine particles) were fed with different BA samples. The performance of the abrasion tests was assessed through the analyses of particle size and moisture, and that of the column leaching tests at solid-to-liquid ratios between 0.3 and 4.
The results were: the particle-size distribution of the treated materials was homogeneous (25 wt % had dimensions <6.3 mm) and their moisture halved, as well as the electrical conductivity of the leachates. A significant decrease was observed in the leachates of the treated BA for sulphates (44%), chlorides (26%), and PTEs (53% Cr, 60% Cu and 8% Mo). The statistical analysis revealed good correlations between chloride and sulphate concentrations in the leachates with Ba, Cu, Mo, and Sr, illustrating the consistent behavior of the major and minor components of the layer surrounding BA particles. In conclusion, the tested process could be considered as promising for the improvement of BA valorization.
The present work shows results on elemental distribution analyses in Cu(In,Ga)Se2 thin films for solar cells performed by use of wavelength-dispersive and energy-dispersive X-ray spectrometry (EDX) in a scanning electron microscope, EDX in a transmission electron microscope, X-ray photoelectron, angle-dependent soft X-ray emission, secondary ion-mass (SIMS), time-of-flight SIMS, sputtered neutral mass, glow-discharge optical emission and glow-discharge mass, Auger electron, and Rutherford backscattering spectrometry, by use of scanning Auger electron microscopy, Raman depth profiling, and Raman mapping, as well as by use of elastic recoil detection analysis, grazing-incidence X-ray and electron backscatter diffraction, and grazing-incidence X-ray fluorescence analysis. The Cu(In,Ga)Se2 thin films used for the present comparison were produced during the same identical deposition run and exhibit thicknesses of about 2 µm. The analysis techniques were compared with respect to their spatial and depth resolutions, measuring speeds, availabilities, and detection limits.
Iron Oxide Nanocubes as a New Certified Reference Material for Nanoparticle Size Measurements
(2023)
The rational design and increasing industrial use of nanomaterials require a reliable characterization of their physicochemical key properties like size, size distribution, shape, and surface chemistry. This calls for nanoscale reference materials (nanoRMs) for the validation and standardization of commonly used characterization methods closely matching real-world nonspherical nano-objects. This encouraged us to develop a nonspherical nanoRM of very small size consisting of 8 nm iron oxide nanocubes (BAM-N012) to complement spherical gold, silica, and polymer nanoRMs. In the following, the development and production of this nanoRM are highlighted including the characterization by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) as complementary methods for size and shape parameters, homogeneity and stability studies, and calculation of a complete uncertainty budget of the size features. The determination of the nanocubes’ edge length by TEM and SAXS allows a method comparison. In addition, SAXS measurements can also provide the mean particle number density and the mass concentration. The certified size parameters, area equivalent circular diameter and square edge length, determined by TEM with a relative expanded uncertainty below 9%, are metrologically traceable to a natural constant for length, the very precisely known (111) lattice spacing of silicon. Cubic BAM-N012 qualifies as a certified nanoRM for estimating the precision and trueness, validation, and quality assurance of particle size and shape measurements with electron microscopy and SAXS as well as other sizing methods suitable for nanomaterials. The production of this new iron oxide nanocube RM presents an important achievement for the nanomaterial community, nanomaterial manufacturers, and regulators.
Phosphotyrosine residues are essential functional switches in health and disease. Thus, phosphotyrosine biomimetics are crucial for the development of chemical tools and drug molecules. We report here the discovery and investigation of pentafluorophosphato amino acids as novel phosphotyrosine biomimetics. A mild acidic pentafluorination protocol was developed and two PF5-amino acids were prepared and employed in peptide synthesis. Their structures, reactivities, and fluorine-specific interactions were studied by NMR and IR spectroscopy, X-ray diffraction, and in bioactivity assays. The mono-anionic PF5 motif displayed an amphiphilic character binding to hydrophobic surfaces, to water molecules, and to protein-binding sites, exploiting charge and H−F-bonding interactions. The novel motifs bind 25- to 30-fold stronger to the phosphotyrosine binding site of the protein tyrosine phosphatase PTP1B than the best current biomimetics, as rationalized by computational methods, including molecular dynamics simulations.
Modeling of silicon surface topographies induced by single nanosecond laser pulse induced melt-flows
(2019)
Irradiation with a single nanosecond laser pulse in the melting regime can result in a characteristic change in the surface morphology of crystalline silicon. This has been verified experimentally in a variety of situations, where dimple-shaped surface topographies are produced. In this work, the dimple height, depth, and width are modeled following and extending in a more rigorous manner the approach of Wood and Giles [Phys. Rev. B 23, 2923–2942 (1981)] and that of Schwarz-Selinger and coworkers [Phys. Rev. B 64, 155323 (2001)], upon varying the laser irradiation parameters such as peak energy density, pulse duration, and wavelength. This is achieved with numerical simulations of one-dimensional heat flow as input to the analytical fluid-flow equations.
Irradiation with a single spatially Gaussian-shaped nanosecond laser pulse in the melting regime can result in a characteristic annular change in the surface morphology of crystalline silicon. This has been verified experimentally in a variety of situations, where dimple-shaped surface topographies are produced. In a recent work we have investigated the induced changes in the surface topography upon exposure to wavelengths in the visible and near infrared spectral region. Irradiation in the UV requires a more detailed analysis due to the enhanced absorption of the material. In the present analysis, we determine under which conditions our previous model can be used and the corresponding results are presented.
Municipal sewage sludge is a carrier of nutrients most important phosphorus (P) but also contains organic pollutants and heavy metals. A two steps thermal treatment is suggested based on 1. mono-incineration of sewage sludge under destruction of organic pollutants and 2. thermochemical treatment of the resulting ashes to remove heavy metals and increase P-bioavailability. The targeted products are marketable P-fertilisers. The thermochemical treatment was investigated in a gas tight lab-scale rotary furnace. Seven sewage sludge ashes of different origin and composition and one residue from gasification of sewage sludge were mixed with a chlorine donor (e.g. MgCl2) and thermochemically treated under systematic variation of operational parameters. The distributions of the heavy metals between solid and gas phase were determined. The heavy metals concentrations of the treated ashes met the legislative limits in most cases. The products from thermochemical treatment are suited raw materials for P-fertiliser production. Relevant process parameters such as temperature, type and concentration of Cl-donor and retention time were optimised for the thermochemical treatment step.
Phosphorus (P) is an essential element for all living organisms and cannot be replaced. Municipal sewage sludge is a carrier of phosphorus, but also contains organic pollutants and heavy metals. A two-step thermal treatment is suggested, including mono-incineration of sewage sludge and subsequent thermochemical treatment of the ashes. Organic pollutants are completely destroyed by mono-incineration. The resulting sewage sludge ashes contain P, but also heavy metals. P in the ashes exhibits low bioavailability, a disadvantage in farming. Therefore, in a second thermochemical step, P is transferred into mineral phases available for plants, and heavy metals are removed as well. The thermochemical treatment was investigated in a laboratory-scale rotary furnace by treating seven different sewage sludge ashes under systematic variation of operational parameters. Heavy metal removal and the increase of the P-bioavailability were the focus of the investigation. The present experimental study shows that these objectives have been achieved with the proposed process. The P-bioavailability was significantly increased due to the formation of new mineral phases such as chlorapatite, farringtonite and stanfieldite during thermochemical treatment.
Slags from the production of high-alloyed steel contain both chemically bound chromium (mainly as Cr2O3) in the mineral fraction and elemental chromium in the metallic remainders. Thermochemical post treatment of the slag in an electric arc furnace under reducing conditions enables the nearly complete recovery of the total amount of chromium in form of a metallic alloy. The best results were achieved by resistance melting (submerged electrodes) with addition of a reducing agent into the melt. The efficiencies of the reducing agents carbon, aluminium, silicon (as ferrosilicon) and silicon carbide were investigated and compared. As aluminium is the strongest reducing agent, it is less selective and reduces much more SiO2 than Cr2O3. While SiC shows only low reactivity because of its high thermal resistance, carbon and silicon had the highest reducing potentials: More than 97% of the chemically bound chromium can be recovered by application of these reducing agents. Due to the high temperature required for the reduction of the chromium compounds, the reduction of SiO2 as an undesired side reaction cannot be avoided. However, compared with mechanical procedures that are limited to the recovery of the metallic remainders, the total chromium recovery can be significantly increased by the described reductive melting procedure.
Based on recently published research on leaching control mechanisms in electric arc furnace (EAF) slags, it is assumed that a FeO/SiO2 ratio of around one leads to low leached V and Cr concentrations. This ratio influences the mineral phase composition of the slag toward higher amounts of spinel and a lower solubility of calcium silicate phases by suppressing the formation of magnesiowuestite and highly soluble calcium silicate phases. To evaluate this hypothesis, laboratory and scaled up tests in an EAF pilot plant were performed on slag samples characterized by elevated V and Cr leaching and a high FeO/SiO2 ratio. Prior to the melting experiments, the optimum FeO/SiO2 ratio was calculated via FactSageTM. In the melting experiments, the ratio was adjusted by adding quartz sand, which also decreased the basicity (CaO/SiO2) of the slag. As a reference, remelting experiments without quartz sand addition were conducted and additionally, the influence of the cooling rate of the slag was examined. The remelted (without quartz sand) and the remelted modified slags (with quartz sand) were analyzed chemically and mineralogically and the leaching behavior was investigated. The modification of the slags yielded a minimized release of V and Cr, supporting the hypothesis that the FeO/SiO2 ratio influences the mineralogy and the leaching behavior.
Background. Currently, there is no reliable nonsurgical treatment for abdominal aortic aneurysm (AAA). This study, therefore, investigates if doxycycline reduces AAA growth and the number of rupture-related deaths in a murine ApoE−/− model of AAA and whether gadofosveset trisodium-based MRI differs between animals with and without doxycycline treatment. Methods. Nine ApoE−/− mice were implanted with osmotic minipumps continuously releasing angiotensin II and treated with doxycycline (30 mg/kg/d) in parallel. After four weeks, MRI was performed at 3T with a clinical dose of the albumin-binding probe gadofosveset (0.03 mmol/kg). Results were compared with previously published wild-type control animals and with previously studied ApoE−/− animals without doxycycline treatment. Differences in mortality were also investigated between these groups. Results. In a previous study, we found that approximately 25% of angiotensin II-infused ApoE−/− mice died, whereas in the present study, only one out of 9 angiotensin II-infused and doxycycline-treated ApoE−/− mice (11.1%) died within 4 weeks. Furthermore, doxycycline-treated ApoE−/− mice showed significantly lower contrast-to-noise (CNR) values in MRI compared to ApoE−/− mice without doxycycline treatment. In vivo measurements of relative signal enhancement (CNR) correlated significantly with ex vivo measurements of albumin staining (R2 = 0.58). In addition, a strong visual colocalization of albumin-positive areas in the fluorescence albumin staining with gadolinium distribution in LA-ICP-MS was shown. However, no significant difference in aneurysm size was observed after doxycycline treatment. Conclusion. The present experimental in vivo study suggests that doxycycline treatment may reduce rupture-related deaths in AAA by slowing endothelial damage without reversing aneurysm growth.
Abdominal aortic aneurysm (AAA) is a life-threatening vascular disease with an up to 80% mortality in case of rupture. Current biomarkers fail to account for size-independent risk of rupture. By combining the information of different molecular probes, multi-target molecular MRI holds the potential to enable individual characterization of AAA. In this experimental study, we aimed to examine the feasibility of simultaneous imaging of extracellular collagen and inflammation for size-independent prediction of risk of rupture in murine AAA. The study design consisted of: (1) A outcome-based longitudinal study with imaging performed once after one week with follow-up and death as the end-point for assessment of rupture risk. (2) A week-by-week study for the characterization of AAA development with imaging after 1, 2, 3 and 4 weeks. For both studies, the animals were administered a type 1 collagen-targeted gadolinium-based probe (surrogate marker for extracellular matrix (ECM) remodeling) and an iron oxide-based probe (surrogate marker for inflammatory activity), in one imaging session. In vivo measurements of collagen and iron oxide probes showed a significant correlation with ex vivo histology (p < 0.001) and also corresponded well to inductively-coupled plasma-mass spectrometry and laser-ablation inductively-coupled plasma mass spectrometry. Combined evaluation of collagen-related ECM remodeling and inflammatory activity was the most accurate predictor for AAA rupture (sensitivity 80%, specificity 100%, area under the curve 0.85), being superior to information from the individual probes alone. Our study supports the feasibility of a simultaneous assessment of collagen-related extracellular matrix remodeling and inflammatory activity in a murine model of AAA.
Abdominal aortic aneurysm (AAA) remains a fatal disease. Its development encompasses a complex interplay between hemodynamic stimuli on and changes in the arterial wall. Currently available biomarkers fail to predict the risk of AAA rupture independent of aneurysm size. Therefore, novel biomarkers for AAA characterization are needed. In this study, we used a mouse model of AAA to investigate the potential of magnetic resonance imaging (MRI) with an albumin-binding probe to assess changes in vascular permeability at different stages of aneurysm growth. Two imaging studies were performed: a longitudinal study with follow-up and death as endpoint to predict rupture risk and a week-by-week study to characterize AAA development. AAAs, which eventually ruptured, demonstrated a significantly higher in vivo MR signal enhancement from the albumin-binding probe (p = 0.047) and a smaller non-enhancing thrombus area compared to intact AAAs (p = 0.001). The ratio of albumin-binding-probe enhancement of the aneurysm wall to size of non-enhancing-thrombus-area predicted AAA rupture with high sensitivity/specificity (100%/86%). More advanced aneurysms with higher vascular permeability demonstrated an increased uptake of the albumin-binding-probe. These results indicate that MRI with an albumin-binding probe may enable noninvasive assessment of vascular permeability in murine AAAs and prediction of rupture risk.
Background: Prevention of metastatic invasion is one of the main challenges in the treatment of alveolar rhabdomyosarcoma. Still the therapeutic options are limited. Therefore, an anti-tumor screening was initiated focusing on the anti-metastatic and anti-invasion properties of selected medicinal plant extracts and phytoestrogens, already known to be effective in the prevention and treatment of different cancer entities.
Methods: Treatment effects were first evaluated by cell viability, migration, invasion, and colony forming assays on the alveolar rhabdomyosarcoma cell line RH-30 in comparison with healthy primary cells.
Results: Initial anti-tumor screenings of all substances analyzed in this study, identified the plant extract of Vincetoxicum arnottianum (VSM) as the most promising candidate, harboring the highest anti-metastatic potential. Those significant anti-motility properties were proven by a reduced ability for migration (60%), invasion (99%) and colony formation (61%) under 48 h exposure to 25 μg/ml VSM. The restricted motility features were due to an induction of the stabilization of the cytoskeleton – actin fibers were 2.5-fold longer and were spanning the entire cell. Decreased proliferation (PCNA, AMT, GCSH) and altered metastasis (e. g. SGPL1, CXCR4, stathmin) marker expression on transcript and protein level confirmed the significant lowered tumorigenicity under VSM treatment. Finally, significant alterations in the cell metabolism were detected for
25 metabolites, with levels of uracil, N-acetyl serine and propanoyl phosphate harboring the greatest alterations. Compared to the conventional therapy with cisplatin, VSM treated cells demonstrated a similar metabolic shutdown of the primary cell metabolism. Primary control cells were not affected by the VSM treatment.
Conclusions: This study revealed the VSM root extract as a potential, new migrastatic drug candidate for the putative treatment of pediatric alveolar rhabdomyosarcoma with actin filament stabilizing properties and accompanied by a marginal effect on the vitality of primary cells.
Ethnopharmacological relevance: Berberis orthobotrys (BORM) is a medical plant with a long history in traditional usage for the treatment of wounds, cancer, gastrointestinal malady and several other diseases. Our previous studies identified the endemic Pakistani plant Berberis orthobotrys Bien. ex Aitch. as promising source for the treatment of breast cancer and osteosarcoma.
Aim of the study: The present study was aimed to evaluate the anti-cancer properties of 26 plant derived extracts and compounds including the methanolic root extract of Berberis orthobotrys (BORM) on pediatric alveolar rhabdomyosarcoma (RMA), which is known to develop drug resistance, metastatic invasion and potential Tumor progression.
Materials and methods: The main anti-tumor activity of BORM was verified by focusing on morphological, cell structural and metabolic alterations via metabolic profiling, cell viability measurements, flow cytometry, western blotting and diverse microscopy-based methods using the human RMA cell line Rh30.
Results: Exposure of 25 μg/ml BORM exerts an influence on the cell stability, the degradation of oncosomes as well as the shutdown of the metabolic activity of RMA cells, primarily by downregulation of the energy metabolism.
Therefore glycyl-aspartic acid and N-acetyl serine decreased moderately, and uracil increased intracellularly. On healthy, non-transformed muscle cells BORM revealed very low metabolic alterations and nearly no cytotoxic impact. Furthermore, BORM is also capable to reduce Rh30 cell migration (~50%) and proliferation (induced G2/M cycle arrest) as well as to initiate apoptosis confirmed by reduced Bcl-2, Bax and PCNA expression and induced PARP-1 cleavage.
Conclusions: The study provides the first evidence, that BORM treatment is effective against RMA cells with low side effects on healthy cells.
Over the last decade there have been increasing efforts to develop three-dimensional (3D) scaffolds for bone tissue Engineering from bioactive ceramics with 3D printing emerging as a promising technology. The overall objective of the present study was to generate a tissue engineered synthetic bone graft with homogenously distributed osteoblasts and mineralizing bone Matrix in vitro, thereby mimicking the advantageous properties of autogenous bone grafts and facilitating usage for reconstructing segmental discontinuity defects in vivo . To this end, 3D scaffolds were developed from a silica-containing calcium alkali orthophosphate, using, fi rst, a replica technique – the Schwartzwalder – Somers method – and, second, 3D printing, (i.e. rapid prototyping). The mechanical and physical scaffold properties and their potential to facilitate homogenous colonization by osteogenic cells and extracellular bone matrix formation throughout the porous scaffold architecture were examined.
Osteoblastic cells were dynamically cultured for 7 days on both scaffold types with two different concentrations of 1.5 and 3 × 10⁹ cells/l. The amount of cells and bone matrix formed and osteogenic marker expression were evaluated using hard tissue histology, immunohistochemical and histomorphometric analysis. 3D-printed scaffolds (RPS) exhibited more micropores, greater compressive strength and silica release. RPS seeded with 3 × 10⁹ cells/l displayed greatest cell and extracellular Matrix formation, mineralization and osteocalcin expression. In conclusion, RPS displayed superior mechanical and biological properties and facilitated generating a tissue engineered synthetic bone graft in vitro, which mimics the advantageous properties of autogenous bone grafts, by containing homogenously distributed terminally differentiated osteoblasts and mineralizing bone matrix and therefore is suitable for subsequent in vivo implantation for regenerating segmental discontinuity bone defects.
Methyl 4-O-methyl-?-Image-ribo-hex-3-ulopyranoside (2), a model compound for partially oxidized anhydroglucose units in cellulose, was crystallized from CHCl3/n-hexane by vapor diffusion to give colorless plates. Crystal structure determination revealed the monoclinic space group P21 with Z=2C8H14O6 and unit cell parameters of a=8.404(2), b=4.5716(10), c=13.916(3) Å, and ?=107.467(4)°. The structure was solved by direct methods and refined to R=0.0476 for 1655 reflections and 135 parameters. The hexulopyranoside occurs in a distorted chair conformation. Both hydroxyls are involved in hydrogen bonding and form zigzag bond chains along the b-axis. One of the two hydrogen bonds is bifurcated. The solid-state 13C NMR spectrum of 2 exhibits eight carbon resonances, with well-separated signals for the two methoxyls (1-OMe: 55.72 ppm, 4-OMe: 61.25 ppm) and a keto resonance with relatively large downfield shift (206.90 ppm). Differences in the C-4 and the methoxyls chemical shifts in the solid and liquid states were found
Oxidative aging induces significant stiffening of asphalt binders that leads to a pronounced reduction in the overall durability of asphalt pavements. The strategic implementation of antioxidant additives provides a potential solution to alleviate this issue. This work presents results from the second phase of the global consortium for antioxidants research aimed at investigating the effectiveness of potential antioxidants in increasing the durability of asphalt binders. Sixteen laboratories around the world participated in this effort and a total of 28 binders from diverse geographical regions were tested. Two promising antioxidants, namely zinc diethyldithiocarbamate (ZDC) and kraft lignin were evaluated in this phase and blended with the binders at specific proportions. Subsequently, a comprehensive investigation was conducted to assess rheological characteristics and chemical properties of the various blends, utilising Dynamic Shear Rheometer (DSR) measurements and Fourier Transform Infrared (FTIR) Spectroscopy. The findings indicate that additives such as ZDC hold considerable promise as an effective antioxidant, particularly when considering a wide diversity of binders. In general, its incorporation does not compromise the rutting performance of the binders and significantly improves fatigue performance. Therefore, research efforts should be focused on exploring additional facets to assess its practical applicability in field.
With the publication of EN ISO 6892-1:2009, the harmonisation of tensile testing at room temperature in Europe was achieved by combining EN 10002-1:2001 with ISO 6892:1998. Essential changes are the introduction of the strain rate and the strain rate control as the significant testing rate or control mode, respectively, referred to as “Method A”. By using this method in the correct way it is guaranteed that in the moment of determination of properties comparable resulting strain rates at the test piece in smaller ranges of specified strain rates are adopted — also if different stiffnesses of the testing equipment are present. This leads especially for strain rate sensitive materials to better comparable results. In this paper it is documented the need for the implementation of method A, methods for the realisation — also by the use of older testing systems — and an example of the comparability of results of the methods for a strain-rate-sensitive-steel.
Nanotechnology has enabled the discovery of a multitude of novel materials exhibiting unique physicochemical (PChem) properties compared to their bulk analogues. These properties have led to a rapidly increasing range of commercial applications; this, however, may come at a cost, if an association to long-term health and environmental risks is discovered or even just perceived. Many nanomaterials (NMs) have not yet had their potential adverse biological effects fully assessed, due to costs and time constraints associated with the experimental assessment, frequently involving animals. Here, the available NM libraries are analyzed for their suitability for integration with novel nanoinformatics approaches and for the development of NM specific Integrated Approaches to Testing and Assessment (IATA) for human and environmental risk assessment, all within the NanoSolveIT cloud-platform. These established and well-characterized NM libraries (e.g. NanoMILE, NanoSolutions, NANoREG, NanoFASE, caLIBRAte, NanoTEST and the Nanomaterial Registry (>2000 NMs)) contain physicochemical characterization data as well as data for several relevant biological endpoints, assessed in part using harmonized Organisation for Economic Co-operation and Development (OECD) methods and test guidelines.
Integration of such extensive NM information sources with the latest nanoinformatics methods will allow NanoSolveIT to model the relationships between NM structure (morphology), properties and their adverse effects and to predict the effects of other NMs for which less data is available. The project specifically addresses the needs of regulatory agencies and industry to effectively and rapidly evaluate the exposure, NM hazard and risk from nanomaterials and nano-enabled products, enabling implementation of computational ‘safe-by-design’ approaches to facilitate NM commercialization.
Sand erosion of solar glass: Specific energy uptake, total transmittance, and module efficiency
(2018)
Surface roughness, R Z , normal transmittance, Τ N , total transmittance, Τ T , and photovoltaic (PV) module efficiency, η S , were measured for commercial solar glass plates and PV test modules identically sandblasted with different loads of quartz sand (200 – 400 μ m), impact inclination angles, and sand particle speed. Measured data are presented versus the specific energy uptake during sand blasting, E (J/m2). Cracks, adhering particles, and scratch ‐ like textures probably caused by plastic flow phenomena could be observed after sand blasting. Their characteristic size was much smaller than that of sand particles.
After blasting and subsequent cleaning, the glass surface was still covered with adhering glass particles. These particles, cracks, and scratch ‐ like textures could not be removed by cleaning. For sand blasting with α = 30° inclination angle and E = 30 000 J/m2, normal transmittance, total transmittance, and relative module efficiency decreased by 29%, 2% and ∽ 2%, respectively. This finding indicates that diffusive transmission of light substantially contributes to PV module efficiency and that the module efficiency decrease caused by sand erosion can be better estimated from total than by normal transmittance measurements.
The current furfural production yield is low due to the use of non-selective homogeneous catalysts and expensive separation. In this work, partially hydroxylated MgF2 catalysts, synthesized using different water contents, were screened during xylose dehydration in watertoluene at 160 °C. The different Lewis/Brønsted ratios on the MgF2 catalysts showed that under-coordinated Mg can isomerize xylose to xylulose, whilst the surface OH-groups were responsible for the dehydration reactions. The presence of glucose as a co-carbohydrate reduced the furfural selectivity from 86 to 81%, whilst it also led to high 5-hydroxymethylfurfural selectivity. The tests catalyzed by MgF2 in combination with simultaneous N2-stripping showed that a furfural selectivity of 87% could be achieved using low xylose loadings. Moreover, the catalysts regenerated by H2O2 showed high activity during the dehydration tests in watertoluene at 160 °C.
Spectroscopy in Catalysis
(2020)
Knowledge-based catalyst development is always an interaction between preparation, analysis and catalytic testing. Only if these three factors fit together can success be expected. For the analytic side of this triangle, spectroscopic methods play a crucial role. Whereas with diffraction, scattering and microscopy, decisive insights into the structure and morphology of the catalysts can be obtained, spectroscopy produces new knowledge about the chemical nature of the catalyst, e.g., its bonding and valence states.
The properties of the encapsulant are critical to the long-term performance of photovoltaic (PV) modules under the influence of sunlight including UV, elevated temperature, humidity and diffusion of oxygen. Encapsulation process represents a bout 40% of the whole PV module cost. The introduction of new non-EVA encapsulant material type "Low-Cost, High-Performance" should provide a solution to outdoor yellowing degradation problems. The emerging encapsulant materials exhibit a good compatibility with emerging PV solar cells for long term durability. This new generation of encapsulant materials has the advantage to improve e the PV module performances and long term durability for specific climate like desert regions. This scientific contribution presents an overview of the different encapsulant materials currently on the market, the general requirements of the emerging encapsulant materials and characterizations techniques for degradation, diagnostic and reliability lifetime estimation in the framework of Algerian renewable energy strategy.
The present work describes the shear creep behavior of the superalloy LEK 94 at temperatures between 980 and 1050 °C and shear stresses between 50 and 140 MPa for loading on the macroscopic crystallographic shear system (MCSS) (011)[01-1]. The strain rate versus strain curves show short primary and extended secondary creep regimes. We find an apparent activation energy for creep of Qapp = 466 kJ/mol and a Norton-law stress exponent of n = 6. With scanning transmission electron microscopy, we characterize three material states that differ in temperature, applied stress, and accumulated strain/time. Rafting develops perpendicular to the maximum principal stress direction, gamma channels fill with dislocations, superdislocations cut gamma' particles, and dislocation networks form at gamma/gamma' interfaces. Our findings are in agreement with previous results for high-temperature and low-stress [001] and [110] tensile creep testing, and for shear creep testing of the superalloys CMSX-4 and CMSX-6 on the MCSSs (111)[01-1] and (001)[100]. The parameters that characterize the evolving gamma/gamma' microstructure and the evolving dislocation substructures depend on creep temperature, stress, strain, and time.
Oxidation of a Fe –13Cr alloy under water vapor at 600°C produced a zone of nano-sized precipitation underneath the outside scale formed by iron oxides and Fe–Cr spinel. The majority of the spinel layer shows a fixed orientation relationship to the ferritic matrix: {1 0 0}α || {1 0 0}sp & <0 1 1>α || <0 0 1>sp . However, also the discovered precipitated particles are characterized by the same crystallographic orientation relationship to the respective ferritic parent grain. The habit of the precipitates is best described by a lath morphology with their main axis parallel to <1 0 0> of ferrite. Energy dispersive X-ray spectroscopy (EDX) and electron backscatter diffraction (EBSD) in scanning electron microscope (SEM) have been applied to characterize the oxide layer in micrometer scale. The clearly smaller precipitates were subsequently investigated by transmission electron microscopy (TEM). Specimens have been prepared by focused ion-beam (FIB) milling at an area previously characterized by EBSD. They cover the ferritic base material, but mainly the precipitation zone and the Fe–Cr spinel layer. Energy filtered selected area diffraction (SAD) in the conventional (C)TEM and high-angle annular dark field (HAADF) imaging in the scanning (S)TEM mode were employed in the characterization of the specimens.
The creep anisotropy of the single crystal superalloy LEK 94 deformed in tension along [0 0 1] and [1 1 0] directions at 1293 K and 160 MPa was investigated. Elementary microstructural processes which are responsible for a higher increase in creep rates with strain during [1 1 0] as compared to [0 0 1] tensile loading were identified. [1 1 0] tensile creep is associated with a higher number of γ' phase cutting events, where two dislocations with equal Burgers vectors of type <1 1 0> jointly shear the γ' phase. The resulting <2 2 0>-type superdislocation can move by glide. In contrast, during [0 0 1] tensile loading, two dislocations with different <1 1 0>-type Burgers vectors must combine for γ' phase cutting. The resulting <2 0 0>-type superdislocations can only move by a combination of glide and climb. The evolution of dislocation networks during creep determines the nature of the γ' phase cutting events. The higher [1 1 0] creep rates at strains exceeding 2% result from a combination of a higher number of cutting events (density of mobile dislocations in γ') and a higher superdislocation mobility (<2 2 0> glide) in the γ' phase.
A great amount of material properties is strongly influenced by dislocations, the carriers of plastic deformation. It is therefore paramount to have appropriate tools to quantify dislocation substructures with regard to their features, e.g., dislocation density, Burgers vectors or line direction. While the transmission electron microscope (TEM) has been the most widely-used equipment implemented to investigate dislocations, it usually is limited to the two-dimensional (2D) observation of three-dimensional (3D) structures. We reconstruct, visualize and quantify 3D dislocation substructure models from only two TEM images (stereo pairs) and assess the results. The reconstruction is based on the manual interactive tracing of filiform objects on both images of the stereo pair. The reconstruction and quantification method are demonstrated on dark field (DF) scanning (S)TEM micrographs of dislocation substructures imaged under diffraction contrast conditions. For this purpose, thick regions (> 300 nm) of TEM foils are analyzed, which are extracted from a Ni-base superalloy single crystal after high temperature creep deformation. It is shown how the method allows 3D quantification from stereo pairs in a wide range of tilt conditions, achieving line length and orientation uncertainties of 3% and 7°, respectively. Parameters that affect the quality of such reconstructions are discussed.
The results of a structural study combining NMR and Raman spectroscopy of several melt-derived glasses in the system Na2OMgOCaOP2O5SiO2 are presented. The Raman spectra show clear changes in the SiOSi vibrational modes (related to the bridging oxygen atoms, BO) and also verify the presence of non-bridging oxygen atoms (NBO), also named terminal oxygens. The intensity of the SiONBO stretching mode depends on the cation concentration. It can be concluded from the NMR studies that the MgO-containing samples have orthophosphate units charge-compensated by Ca2+ and Mg2+. The silicate matrix also contains both types of two-valent cations and consists of Q2 and Q1 units. Similarly, the Na2O-containing samples contain isolated orthophosphate units in a silicate matrix (Q2 and Q3 units), both charge-compensated by mixed cations Ca2+ and Na+. These experimental data were compared with theoretical parameters given by the Stevels model, which is a suitable tool for understanding bioactive behavior of these glasses. Furthermore, results of the in vitro tests carried out in simulated body fluids are presented and compared with both Raman and NMR structural data.
Photon upconversion upon 1550 nm excitation is of high relevance for applications in the third biological excitation window, for photovoltaics beyond current limitations, and enables appealing options in the field of glass Fiber telecommunications. Trivalent doped erbium ions (Er3+) are the material of choice for 1550 nm excited upconversion, however, they suffer from a low absorption cross-section and a low brightness. Therefore, the ability of Silicon metasurfaces to provide greatly enhanced electrical near-fields is employed to enable efficient photon upconversion even at low external Illumination conditions. Hexagonally shaped β-NaYF4:Er3+ nanoparticles are placed on large-area silicon metasurfaces designed to convert near-infrared (1550 nm) to visible light. More than 2400-fold enhanced photon upconversion luminescence is achieved by using this metasurface instead of a planar substrate.
With the aid of optical simulations based on the finite-element method, this result is attributed to the coupling of the excitation source with metasurface resonances at appropriate incident angles. Analysis of the excitation power density dependence of upconversion luminescence and red-to-green-emission ratios enables the estimation of nanoscale near-field enhancement on the metasurface. The findings permit the significant reduction of required external excitation intensities for photon upconversion of 1550 nm light, opening perspectives in biophotonics, telecommunication, and photovoltaics.