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A setup for fluorescence upconversion spectroscopy (FLUPS) is described which has 80 fs temporal response (fwhm) for emission in the spectral range 425–750 nm. Broadband phase matching is achieved with tilted gate pulses at 1340 nm. Background from harmonics of the gate pulse is removed and sensitivity increased compared to previous designs. Photometric calibration of the upconversion process is performed with a set of fluorescent dyes. For Coumarin 153 in methanol the peak position, bandwidth, and asymmetry depending on delay time are reported.
The topographic effect of steel counterface, finished by mechanical grinding with Ra ranging from 0.01 to 0.95 µm, on the structure and functionality of the tribofilm of a hybrid nanocomposite, i.e. epoxy matrix filled with monodisperse silica nanoparticles, carbon fibers and graphite, was systematically investigated. The nanostructure of the tribofilm was comprehensively characterized by using combined focused ion beam and transmission electron microscope analyses. It was identified that oxidation of the steel surface, release, compaction and tribosintering of silica nanoparticles and deposition of an epoxy-like degradation product as well as fragmentation of carbon fibers are main mechanisms determining the structure and functionality of the tribofilm. The size of roughness grooves determines the type and size class of wear particles to be trapped at the surface. An optimum groove size leading to a maximum of surface coverage with a nanostructured tribofilm formed mainly from released silica nanoparticles was identified.
Exploring the influence of counterpart materials on tribological behaviors of epoxy composites
(2016)
The dependence of the friction and wear of epoxy (EP) composites materials on counterpart materials, such as standard bearing steel, medium carbon steel and chrome-plating (Cr), was investigated. The conventional composite filled with short carbon fiber (SCF) and graphite shows the highest tribological performance when rubbing against Cr, whereas, the hybrid nanocomposite (EP filled with SCF, graphite and silica nanoparticles) exhibits the lowest friction and wear when sliding against the standard bearing steel. The role of nanoparticles in the tribological performance is distinctly different when sliding against with various counterpart materials. It is demonstrated that counterpart materials exert an important influence on material transfer, tribo-oxidation and mechanical mixing of wear products, resulting in the different formation mechanisms of transfer film.
The tribological performance of short glass fibers (SGF),solid lubricants and silica nanoparticles filled epoxy (EP) composites was investigated under oil lubrication conditions. It is demonstrated that the addition of SGF greatly reduces the friction and wear of EP. However, further addition of solid lubricants and silica nanoparticles does not change obviously the friction and wear. It is identified that the high tribological performance of SGF reinforced EP is related to the high load carrying capacity and abrasion resistance of SGF. The nanostructure of the tribofilm was comprehensively characterized. It is deemed that the tribofilm plays an important role in the tribological performance by avoiding the direct rubbing of the sliding pairs exposed to boundary and mixed lubrication conditions.
Permeability estimation from induced polarization (IP) measurements is based on a fundamental premise that the characteristic relaxation time τ is related to the effective hydraulic radius reff controlling fluid flow. The approach requires a reliable estimate of the diffusion coefficient of the ions in the electrical double layer. Others have assumed a value for the diffusion coefficient, or postulated different values for clay versus clay-free rocks. We have examined the link between a widely used single estimate of τ and reff for an extensive database of sandstone samples, in which mercury porosimetry data confirm that reff is reliably determined from a modification of the Hagen-Poiseuille equation assuming that the electrical tortuosity is equal to the hydraulic tortuosity. Our database does not support the existence of one or two distinct representative diffusion coefficients but instead demonstrates strong evidence for six orders of magnitude of variation in an apparent Diffusion coefficient that is well-correlated with reff and the specific surface area per unit pore volume Spor. Two scenarios can explain our findings:
(1) the length scale defined by τ is not equal to reff and is likely much longer due to the control of pore-surface roughness or
(2) the range of diffusion coefficients is large and likely determined by the relative proportions of the different minerals (e.g., silica and clays) making up the rock. In either case, the estimation of reff (and hence permeability) is inherently uncertain from a single characteristic IP relaxation time as considered in this study.
The composition and nanostructure of a beneficial tribofilm formed during sliding of a hybrid nanocomposite against steel were characterized comprehensively. A similar nanostructure was produced by high energy ball milling of the three identified tribofilm constituents: silica, hematite and graphite. By supplying powders to a pin-on-disc test it has been shown that neither silica, nor hematite, nor a mixture of both provide the low coefficient of friction (COF) observed for the hybrid composite. Only if graphite was blended with the oxides, the low COF was obtained. Thus, a film of finely dispersed stable inorganic wear products containing 15 vol% graphite provides low friction and wear in the considered case.
We applied a combination of Raman spectroscopy (RS) and cross-sectional transmission electron microscopy (X-TEM) to identify silicone oil residues and tribofilms at steel disc surfaces after tribological testing. Neither chemical cleaning nor mechanical removal of a 50 µm thick surface layer produced a surface without any silicone residue. Nevertheless, long-term tribological properties are not affected due to silicone degradation which has been proved by Raman spectroscopy. Excellent anti-wear and anti-friction properties of a nanocomposite at severe stressing conditions correlated with the formation of a silica-based tribofilm containing amorphous and graphite-like carbon nanoparticles. Since reliable carbon quantification by analytical TEM is difficult, RS is a useful complementary method for carbon identification at wear scars.
The effect of steel counterface topography on the formation mechanisms of nanostructured tribofilms of polyetheretherketone (PEEK) hybrid nanocomposites was studied. Three types of surface finishes with mean roughness Ra ranging from nano- to micro-scale were investigated. Tribo-sintering of nanopartides, oxidation of counterface steel and compaction of wear debris are identified to be competing factors dominating the formation and function of the tribofilms. Counterface topography played an important role on the competing factors, and thereby influenced significantly the final structure, the load-carrying capability and the lubrication performance of the tribofilms. It was disclosed that a thin tribofilm, which mainly consists of silica nanoparticles and which forms on the counterface with a submicron roughness, benefits best the tribological performance of the composites
Welding is one of the most common methods in industrial practice for joining components. Its main advantages are high speed in manufacturing combined with low costs and, usually, a high degree of flexibility, integrity and reliability. Nevertheless, welding is a highly complex metallurgical process and, therefore, weldments are susceptible to material discontinuities, flaws and residual stresses which may lead to structural failure and life time reduction. As a consequence weldments are an important field of fracture mechanics methods although its application is more complex than for homogeneous or non-welded structures. The aim of the paper is to provide an overview on the current state of fracture mechanics application to weldments. It starts by discussing the specific features which any fracture mechanics analysis of weldments has to take into account. Then, the experimental determination of fracture toughness, fatigue crack propagation and tensile properties of weldments is addressed. Finally, the analytical determination of the crack driving force in components and structural integrity assessment approaches for weldments are presented.
High-strength steels are favoured materials in the industry for production of safe and sustainable structures. The main technology used for joining the components of such steel is fusion welding.
Steel alloy design concepts combined with advanced processing technologies have been extensively investigated during the development of High-Strength Low-Alloy (HSLA) steels. However, very few studies have addressed the issue of how various alloy designs, even with limited microalloy addition, can influence the properties of high-strength steel welds. In high-strength steel welding practices, the challenges regarding microstructure evolution and the resulting mechanical properties variation, are of great interest. The main focus is the debate regarding the role of microalloy elements on phase transformation and weld performance. Limited Heat Affected Zone (HAZ) softening and limited austenite grain coarsening are significant design essentials, but the primary goal is to ensure excellent toughness and tensile properties in the steel weld. To achieve this purpose, microalloy elements such as Ti, Nb, or V were intentionally added to modern high-strength steels. The focus of this work was to understand the mechanical properties of HSLA steels resulting from differences in alloy design after joining by modern welding processes.
To begin, three microalloyed S690QL steels (Nb, Ti, and Ti+V addition) were investigated. Optical microscopy confirmed that similar mixtures of tempered bainite and martensite predominated the parent microstructure in the three steels, different types of coarse microalloy precipitates were also visible. These precipitates were analysed by using a thermodynamic-based software and then identified by Transmission Electron Microscopy (TEM). Results of mechanical testing revealed that all three steels performed above the standard toughness and tensile strength values, but with varied yielding phenomena. During the welding operation, each of the three steels was joined by using the same filler material. The fused weld metal was influenced by the high dilution of microalloyed elements in the base metal, this was significantly pronounced during the modified spray arc welding technique. As a result, the Nb-containing steel exhibited sufficient amounts of alloy pick-up to transition the microstructure in the weld metal from acicular ferrite to bainite as cooling rate was increased, leading to reduced toughness. This was not observed with the other two steels.
A second focus was made on the microstructure Evolution and toughness properties of the coarse and fine grained HAZ as welding parameters changed. In order to characterise the microstructure and austenite grain growth behaviour, physical simulations were conducted. The microalloy precipitates were found to be a dominant factor restricting the austenite grain coarsening. The extent of Austenite coarsening in the HAZ is closely related to the type and volume fraction of each microalloy precipitate.
Among the three steels, the Ti-containing HAZ exhibited the smallest extent of grain growth due to the sufficient amount of stable Ti-rich precipitates. Microalloy Addition also markedly influenced the subsequent phase transformation in the HAZ. The formation of intragranular acicular ferrite was promoted by Ti-rich precipitate, acting as favourable nucleation sites of ferrite. This structure enhanced the HAZ toughness owing to fine, high-angle boundaries of ferrite plates. The synergistic effect of Nb and Mo elements was beneficial to improve the HAZ toughness at fast cooling rates by promoting fine lower bainite formation. At high heat input, large upper bainite was formed which caused reduced toughness.
The final set of experimental work was concentrated on understanding the HAZ softening mechanisms that influenced variations in the tensile properties of the welded joints. The tensile failure in the softened HAZ or base material depended on the welding parameters and the type of steel being joined. In Ti-containing steel, increased heat Input extended the softened zone width, which caused a significant decrease in hardness and then resulted in failure in this area. Therefore, limited heat Input was used to shift failure position to base material. But this was not observed in the other two steels.
Hence, small differences in microalloy addition exhibited large variation in tensile properties. Among the three steels, Ti-containing welds were found to have the most pronounced softening, followed by Ti+V-containing welds and finally Nb-containing welds. This varied softening phenomenon was related to two significant processes supported by the results of additional dilatometry simulation: phase transformation and tempering behaviour. In the Ti-containing steel, the phase Transformation product ferrite was large-sized, as a consequence of initial large austenite grains. This led to the decreased corresponding hardness of the Ti-containing steel. Furthermore, lower tempering resistance in Ti-containing steel as compared to Nb-containing steel, resulted in additional softening effect in the softened HAZ. Therefore, steel alloy identification and heat Input during welding were critical, proven by the experimentation within the same S690QL steel grade.
This work emphasised the influence of microalloy elements on weld microstructure and mechanical properties in welded joints. Knowledge of this delicate balance between steel alloy design and appropriate welding parameters is critical for the end product. Thus, this work provides specific recommendations and results to ensure proper welding practice and steel design of microalloyed high-strength steels.
Lanthanide-doped upconversion nanoparticles (UCNPs) are of great interest for biomedical applications. Currently, the applicability of UCNP bionanotechnology is hampered by the generally low luminescence intensity of UCNPs and inefficient energy Transfer from UCNPs to surface-bound chromophores used e.g. for photodynamic therapy or analyte sensing. In this work, we address the low-Efficiency issue by developing versatile core-Shell nanostructures, where high-concentration sensitizers and activators are confined in the core and Shell Region of representative hexagonal NaYF2:Yb,Er UCNPs. After Doping concentration optimization, the sensitizer-rich core is able to harvest/accumulate more excitation energy and generate almost one order of Magnitude higher luminescence intesity than conventional homogeneously doped nanostructures. At the same time, the activator Ions located in the Shell enable a ~6 times more efficient resonant energy Transfer from UCNPs to surface-bound acceptor dye molecules due to the short distance between donor-acceptor pairs. Our work provides new insights into the rational design of UCNPs and will greatly encrease the General applicability of upconversion nanotechnologies.
The comparison required the assignment of the mass fraction of folic acid present as the main component in the comparison sample. Performance in the comparison is representative of a laboratory's measurement capability for the purity assignment of organic compounds of medium structural complexity [molecular weight range 300–500] and high polarity (pKOW < −2).
Methods used by the eighteen participating NMIs or DIs were based on a mass balance (summation of impurities) or qNMR approach, or the combination of data obtained using both methods. The qNMR results tended to give slightly lower values for the content of folic acid, albeit with larger associated uncertainties, compared with the results obtained by mass balance procedures. Possible reasons for this divergence are discussed in the report, without reaching a definitive conclusion as to their origin.
The comparison demonstrates that for a structurally complex polar organic compound containing a high water content and presenting a number of additional analytical challenges, the assignment of the mass fraction content property value of the main component can reasonably be achieved with an associated relative standard uncertainty in the assigned value of 0.5%
Bei der Trocknung von Gesteinen vermindert sich der Anteil des Wasservolumens im Porenraum, der als Sättigung bezeichnet wird. Mit abnehmender Sättigung sinkt die elektrische Leitfähigkeit des Gesteins. Die Abhängigkeit der elektrischen Leitfähigkeit von der Sättigung wird durch ein Potenzgesetz entsprechend der 2. Archie-Gleichung beschrieben: log(#CHR:sigma_LOWER#)=n log(S<sub>w</sub>), wobei n der Sättigungsexponent ist. Bei der Trocknung von Gesteinen muss beachtet werden, dass die Wasserleitfähigkeit mit abnehmender Sättigung zunimmt, da die Konzentration der im Wasser gelösten Salze ansteigt. Das hat zur Folge, dass die bei Trocknungsexperimenten bestimmten Sättigungsexponenten deutlich kleiner sind als bei Verdrängungsexperimenten (z.B. Wasser durch Öl) mit gleichbleibender Wasserleitfähigkeit. Bei der Spektral(en) Induzierten Polarisation wird die komplexe elektrische Leitfähigkeit des Gesteins als Funktion der Frequenz betrachtet. Für den Real- und Imaginärteil der elektrischen Leitfähigkeit werden unterschiedliche Sättigungsexponenten bestimmt.
Wir haben an zwei Sandsteinproben (Langenauer und Gravenhorster Sandstein) und einem Baumberger Kalksandstein Trocknungsexperimente durchgeführt. Die Sättigung wurde schrittweise von 100 % bis auf 10 % reduziert. In jeder Sättigungsstufe wurden an den Proben die Spektren der komplexen elektrischen Leitfähigkeit aufgezeichnet. Unsere Experimente zeigen, dass die Sättigungsexponenten für den Imaginärteil der komplexen elektrischen Leitfähigkeit mit 1,23 bis 1,59 deutlich größer sind als die des Realteils mit Werten zwischen 0,41 und 0,90. Dieser Unterschied resultiert aus der Tatsache, dass der Imaginärteil der Leitfähigkeit weniger stark mit zunehmender Wasserleitfähigkeit ansteigt als der Realteil. Für den Realteil der elektrischen Leitfähigkeit wird nach der 1. Archie-Gleichung ein linearer Zusammenhang zwischen Wasserleitfähigkeit und Gesteinsleitfähigkeit erwartet. Der Anstieg des Imaginärteils mit der Wasserleitfähigkeit kann mit einem Potenzgesetz mit einem Exponenten zwischen 0.1 und 0.62 beschrieben werden. Unsere Experimente zeigen, dass der Imaginärteil der elektrischen Leitfähigkeit wesentlich deutlicher auf die Austrocknung von Gesteinen reagiert und damit ein wirksamer Indikator zur Überwachung von Sättigungsänderungen sein kann.
The spectroscopic characterization by surface-enhanced Raman scattering (SERS) has shown great potential in studies of heterogeneous catalysis. We describe a plug-in multifunctional optofluidic platform that can be tailored to serve both as a variable catalyst material and for sensitive optical characterization of the respective reactions using SERS in microfluidic systems. The platform enables the characterization of reactions under a controlled gas atmosphere and does not present with limitations due to nanoparticle adsorption or memory effects. Spectra of the gold-catalyzed reduction of p-nitrothiophenol by sodium borohydride using the plug-in probe provide evidence that the borohydride is the direct source of hydrogen on the gold surface, and that a radical anion is formed as an intermediate. The in situ monitoring of the photoinduced dimerization of p-aminothiophenol indicates that the activation of oxygen is essential for the plasmon-catalyzed oxidation on gold nanoparticles and strongly supports the central role of metal oxide species.
Three high-strength Nb-,.Ti- and Ti+ V-bearing S690QL steels were welded to investigate and compare the effects of microalloy addition on heat-affected zone (HAZ) toughness. Charpy V notch impact tests from three microalloyed welds under different cooling rates have been performed. Fractographic examination shows that several factors, including large-sized grain, upper bainite or hard second phase, interact to determine brittle fracture and impaired toughness in Nb-bearing weld with high heat input. In contrast to this reduced toughness, Ti-bearing welds exhibits satisfied toughness regardless of at fast or slow cooling. This is attributed to its limited austenite grain and refines favorable intragranular acicular ferrite structure. Moreover, in the case of such refined structure as matrix, TiN particles are found to be irrelevant to the facture process. The crystallographic results also confirm that high-angle boundaries between fine ferrites plates provide effective barriers for crack propagation and contribute to improved toughness.
The mixture of ammonium nitrate (AN) prills and fuel oil (FO), usually called ANFO, is extensively used in the mining industry as a bulk industrial explosive. One of the major performance predictors of ANFO mixtures is the fuel oil retention, which is itself governed by the porosity of the AN prills. Standardised tests routinely used to assess oil retention face several important limitations; the first being the difficulty to cover the wide range of porosity contents and morphologies from different types of ammonium nitrate prills; the second being the inability to evaluate the closed porosity, which is an important factor regarding the sensitivity of the explosive to detonation. In this study, we present how X-ray computed tomography (XCT), and the associated advanced data processing workflow, can be used to fully characterise the structure and morphology of AN prills. We show that structural parameters such as volume fraction of the different phases and morphological parameters such as specific surface area and shape factor can be reliably extracted from the XCT data, and that there is a good agreement with the measured oil retention values. XCT can therefore be employed to non-destructively and accurately evaluate and characterise porosity in ammonium nitrate prills.
Temperature variation can be a nuisance that perturbs vibration based structural health monitoring (SHM) approaches for civil engineering structures. In this paper, temperature affected vibration data is evaluated within a stochastic damage detection framework, which relies on a null space based residual. Besides two existing temperature rejection approaches – building a reference state from an averaging method or a piecewise method – a new approach is proposed, using model interpolation. In this approach, a general reference model is obtained from data in the reference state at several known reference temperatures. Then, for a particular tested temperature, a local reference model is derived from the general reference model. Thus, a well fitting reference null space for the formulation of a residual is available when new data is tested for damage detection at an arbitrary temperature. Particular attention is paid to the computation of the residual covariance, taking into account the uncertainty related to the null space matrix estimate. This improves the test performance, contrary to prior methods, for local and global damages, resulting in a higher probability of detection (PoD) for the new interpolation approach compared to previous approaches.
Remote and on-line measurement of chromium on structural steel surface in nuclear power plants is critical for protection against fluid accelerated corrosion. To improve the insufficient sensitivity of fiber-optic laser-induced breakdown spectroscopy toward trace element detection, a dual-pulse spectral enhancement system is set up. In an iron matrix, for the purpose of improving sensitivity of trace chromium analysis and reducing the self-absorption of iron, the effects of key parameters are investigated. The optimal values of the parameters are found to be: 450 ns inter-pulse delay, 700 ns gate delay, 30 mJ/6 mJ pulse energy ratio, and 19.8 mm lens-to-sample distance (corresponding to a 799 μm laser focused spot size). Compared to the single-pulse system, the shot number of dual-pulse ablation is limited for reducing surface damage. After the optimization of the dual-pulse system, the signal-to-noise ratio of the trace chromium emission line has been improved by 3.5 times in comparison with the single-pulse system, and the self-absorption coefficient of matrix iron has been significantly reduced with self-reversal eliminated. The number of detectable lines for trace elements has more than doubled thus increasing the input for spectral calibration without significantly increasing the ablation mass. Three calibration methods including internal standardization, partial least squares regression and random forest regression are employed to determine the chromium and manganese concentrations in standard samples of low alloy steel, and the limit of detection is respectively calculated as 36 and 515 ppm. The leave-one-out cross validation method is utilized to evaluate the accuracy of chromium quantification, and the concentration mapping of chromium is performed on the surface of a steel sample (16MND5) with a relative error of 0.02 wt.%
Light-induced NO release based on exogenous NO donors has attracted substantial attention in clinical applications; the induction light source usually converts near-infrared light to blue or ultraviolet light.
However, the low efficiency of near-infrared light-assisted chemical light energy conversion remains a challenge, especially for NaYF4:Yb3+/Tm3+ photoconverting near-infrared light to ultraviolet (UV) and blue light. In this paper, a luminescence-enhanced strategy is reported by doping Ca2+ into NaYF4:Yb3+/Tm3+ and coating it with NaGdF4 through a two-step solvothermal method. Then, UCNPs modified with methyl-b-cyclodextrin (M-b-CD) are loaded on a ruthenium nitrosyl complex [(3)Ru(NO)(Cl)] as nitric oxide release-molecules (NORMs). X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS) data demonstrated that Ca2+ was successfully doped into NaYF4:Yb3+/Tm3+ nanoparticles as the core, and a pure hexagonal phase, NaYF4, was obtained from the doping of Ca2+. TEM revealed that the crystallinity was significantly improved after Ca2+ doping, and the core–shell structure was successfully synthesized, with NaGdF4 directionally grown on the NaYF4:Ca/Yb/Tm core. Fluorescence tests showed that, especially in the ultraviolet and blue light excitation wavelength regions, the UC emission intensity of the Ca-doped NaYF4:Yb3+/Tm3+@NaGdF4 core–shell UCNPs increased by 302.95 times vs. NaYF4:Yb3+/Tm3+ UCNPs. Finally, the release of NO was tested by the Griess method. Under 980 nm irradiation, the cell viability distinctly decreased with increasing UCNPs@M-b-CD-NORMs concentration. This study Shows that NORM release of NO is triggered by enhanced up-converted UV and blue light, which can be used for the development of UV photo-sensitive drugs.
Grain boundary energy effect on grain boundary segregation in an equiatomic high-entropy alloy
(2020)
Grain boundary (GB) Segregation has a substantial effect on the microstructure evolution and properties of polycrystalline alloys. The mechanism of nanoscale segregation at the various GBs in multicomponent alloys is of great challenge to reveal and remains elusive so far. To address this issue, we studied the GB segregation in a representative equiatomic FeMnNiCoCr high-entropy alloy (HEA) aged at 450 °C. By combining transmission Kikuchi diffraction, atom probe tomography analysis and a density-based thermodynamics modeling, we uncover the nanoscale segregation behavior at a series of well-characterized GBs of different characters. No segregation occurs at coherent twin boundaries; only slight nanoscale segregation of Ni takes place at the low-angle GBs and vicinal \Sigma 29b coincidence site lattice GBs. Ni and Mn show cosegregation of high levels at the general high-angle GBs with a strong depletion in Fe, Cr, and Co. Our density-based thermodynamic model reveals that the highly negative energy of mixing Ni and Mn is the main driving force for nanoscale cosegregation to the GBs. This is further assisted by the opposite segregation of Ni and Cr atoms with a positive enthalpy of mixing. It is also found that GBs of higher interfacial energy, possessing lower atomic densities (higher disorder and free volume), show higher segregation levels. By clarifying the origins of GB segregations in the FeMnNiCoCr HEA, the current work provides fundamental ideas on nanoscale segregation at crystal defects in multicomponent alloys.
The method of movable cellular automata (MCA) was applied to simulate the stress-strain behavior of a nano composite consisting of an epoxy matrix and 6 vol. % silica nano particles. The size of the elements used for modelling was fixed at 10 nm, corresponding approximately to the diameter of the filler particles. Since not only the stress-strain response of the two constituents but also debonding of neighboring particles and granular flow was taken into account, plastic deformation as well as crack initiation and propagation could be simulated with the model. Modelling results were compared with tensile test results of both, pure epoxy as well as the epoxy-6 vol. % SiO2 composite. Since assuming bulk properties of the two constituents did not yield satisfactory results, slight modifications of the nanoparticle response functions and nanostructures were tested numerically. Finally, it was observed that only the assumption of slightly increased strength properties of the epoxy yielded good correlation between experimental and modelling results. This was attributed to an increased cross linking of the epoxy caused by the presence of silica nano particles.
Excellent tribological properties of an advanced polymer matrix composite were obtained by a combination of micro- and nano-sized fillers. Surface features and the nanostructure of tribofilms were characterized by advanced microscopic techniques, and correlated with the macroscopic behavior in terms of wear rate and friction evolution. A model based on movable cellular automata was applied for obtaining a better understanding of the sliding behavior of the nanostructured tribofilms. The failure of the conventional composite without silica nanoparticles could be attributed to severe oxidational wear after degradation of an initially formed polymer transfer film. The hybrid composite preserves its antiwear and antifriction properties because flash temperatures at micron-sized carbon fibers, lead to polymer degradation and subsequent release of nanoparticles. It has been shown that the released particles are mixed with other wear products and form stable films at the disc surface thus preventing further severe oxidational wear. Furthermore, the released wear product also is embedding carbon fibers at the composite surface thus preventing fiber fragmentation and subsequent third body abrasion. With nanoscale modelling we were able to show that low friction and wear can be expected if the nanostructured silica films contain at least 10 vol.% of a soft ingredient.
A model based on movable cellular automata (MCA) is described and applied for simulating the stress–strain and sliding behavior of a nanocomposite consisting of an epoxy matrix and 6 vol.% of homogeneously distributed silica nanoparticles. Tensile tests were used for verification of the model. It was realized that a slight modification of epoxy properties due to the addition of silica nanoparticles had to be taken into account in order to obtain good correlation between experimental and modeling results. On the other hand, sliding simulations revealed no susceptibility of results to slight modifications of matrix properties, but a significant impact of nanoparticles on the interface structure and smoothness of sliding mechanism. Furthermore, assuming both possibilities, bond breaking and rebinding of automata pairs, can explain different friction levels of polymer materials.
Formation and function mechanisms of nanostructured tribofilms of epoxy-based hybrid nanocomposites
(2015)
The nanostructures and properties of the tribofilms of epoxy (EP) composites filled with short carbon fibers (SCF) and different volume fractions of monodisperse silica nanoparticles were investigated. When the conventional composite filled only with SCF was considered under a high pv condition, an iron oxide layer is formed on the steel counterface. The addition of even only 0.05 vol% nano-silica leads to a significant change of the tribofilm's structure and the tribological behavior of the composite. With increasing silica content, the oxidation layer on the steel surface is gradually replaced by a silica-based tribofilm. A close relationship between the tribofilms structure and the tribological behavior of the composites was identified. Mixing, possible reactions and tribo-sintering of silica nanoparticles with other wear products are deemed to be main mechanisms inducing the formation and the lubricity of the silica-based tribofilm.
Dimercaptoazobenzene (DMAB) can be formed from different precursors (e.g., p-Nitrothiophenol and p-Aminothiophenol, see also examples in Figure) by a reaction that can be influenced by localized surface plasmons.[1] Many reaction parameters were shown to influence the pathway of DMAB formation.
The mechanism of DMAB formation is studied by surface enhanced Raman scattering (SERS). It is very interesting to delineate effects due to properties of the reacting molecular species and those related to the plasmonic properties of the nanostructures. Currently, we achieve this e.g., by the comparison of the usage of nanoparticle solutions and immobilized nanoparticles.[2] We perform this work, since we aim at modifying and controlling the reaction conditions precisely in microscopic volumes, exploiting the multifunctional properties of different plasmonic nanoparticles [3]. In our poster, we will show and discuss SERS data obtained in experiments at varying reaction and excitation conditions.
Hot carriers (electrons and holes) generated from the decay of localized surface plasmon resonances can take a major role in catalytic reactions on metal nanoparticles. By obtaining surface enhanced Raman scattering (SERS) spectra of p-aminothiophenol as product of the reduction of p-nitrothiophenol by hot electrons, different catalytic activity is revealed here for nanoparticles of silver, gold, and copper. As a main finding, a series of different ligands, comprising halide and non-halide species, are found to enhance product formation in the reduction reaction on nanoparticles of all three metals. A comparison with the standard electrode potentials of the metals with and without the ligands and SERS data obtained at different electrode potential indicate that the higher catalytic activity can be associated with a higher Fermi level, thereby resulting in an improved efficiency of hot carrier generation. The concept of such a ligand-enhanced hot electron reduction provides a way to make light-to-chemical energy conversion more efficient due to improved electron harvesting.
The container of high-level radioactive waste (HLRW) being in deep geological disposal, the backfill material is needed to serve as the second defense for HLRW and the highly compacted bentonite is generally selected. As the time goes, the underground water will infiltrate the backfill, causing the corrosion of materials for the building of containers in the formed electrolyte. Carbon steel, titanium and its alloy are the potential candidate materials for the fabrication of HLRW containers.
The current investigation aims at assessing the safety of HLRW container in deep geological disposal for hundreds of thousands of years and facilitating the material selection for future Container fabrication by estimating their corrosion behavior in compacted bentonite with a series of moisture content at different temperatures through electrochemical methods including open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curve (PC) measurements. The corrosion rates were estimated for a carbon steel, a pure titanium and a titanium alloy in compacted Gaomiaozi Bentonite infiltrated with simulated underground water in Beishan area of China over an expected disposal period up to 106 years respectively, showing that titanium and its alloy are more reliable materials for building HLRW containers than carbon steel.
The mixture of ammonium nitrate (AN) prills and fuel oil (FO), usually referred to as ANFO, is extensively used in the mining industry as a bulk explosive. One of the major performance predictors of ANFO mixtures is the fuel oil retention, which is itself governed by the complex pore structure of the AN prills. In this study, we present how X-ray computed tomography (XCT), and the associated advanced data processing workflow, can be used to fully characterise the structure and morphology of AN prills. We show that structural parameters such as volume fraction of the different phases and morphological parameters such as specific surface area and shape factor can be reliably extracted from the XCT data, and that there is a good agreement with the measured oil retention values. Importantly, oil retention measurements (qualifying the efficiency of ANFO as explosives) correlate well with the specific surface area determined by XCT. XCT can therefore be employed non-destructively; it can accurately evaluate and characterise porosity in ammonium nitrate prills, and even predict their efficiency.
Ammonium nitrate (AN) prills are commonly used as an ingredient in industrial explosives and in fertilisers. Conventional techniques (such as BET or mercury intrusion porosimetry) can measure the open porosity and specific surface area of AN prill, but the closed porosity is not obtainable. This work was focused on evaluating X-ray computed tomography (XCT) as a non-destructive technique for the assessment of porosity in AN prills. An advanced data processing workflow was developed so that the segmentation and quantification of the CT data could be performed on the entire 3D volume, yet allowing the measurements (e.g.; volume, area, shape factor…) to be extracted for each individual phase (prill, open porosity, closed porosity) of each individual prill, in order to obtain statistically relevant data. Clear morphological and structural differences were seen and quantified between fertiliser and explosive products. Overall, CT can provide a very wide range of parameters that are not accessible to other techniques, destructive or non-destructive, and thus offers new insights and complementary information.
Exceptional ion mobility spectrometry mass spectrometry (IMS-MS) developments by von Helden, Jarrold, and Clemmer provided technology that gives a view of chemical/biological compositions previously not achievable. The ionization method of choice used with IMS-MS has been electrospray ionization (ESI). In this Special issue contribution, we focus on fundamentals of heretofore unprecedented means for transferring volatile and nonvolatile compounds into gas-phase ions singly and multiply charged. These newer ionization processes frequently lead to different selectivity relative to ESI and, together with IMS-MS, may provide a more comprehensive view of chemical compositions directly from their original Environment such as surfaces, e.g., tissue. Similarities of results using solvent- and matrix-assisted ionization are highlighted, as are differences between ESI and the inlet ionization methods, especially with mixtures such as bacterial extracts. Selectivity using different matrices is discussed, as are results which add to our fundamental knowledge of inlet ionization as well as pose additional avenues for inquiry. IMS-MS provides an opportunity for comparison studies relative to ESI and will prove valuable using the new ionization technologies for direct analyses. Our hypothesis is that some ESI-IMS-MS applications will be replaced by the new ionization processes and by understanding mechanistic aspects to aid enhanced source and method developments this will be hastened.
We report the results of a Versailles Project on Advanced Materials and Standards interlaboratory study on the intensity scale calibration of x-ray photoelectron spectrometers using low-density polyethylene (LDPE) as an alternative material to gold, silver, and copper. An improved set of LDPE reference spectra, corrected for different instrument geometries using a quartz-monochromated Al Kα x-ray source, was developed using data provided by participants in this study. Using
these new reference spectra, a transmission function was calculated for each dataset that participants provided. When compared to a similar calibration procedure using the NPL reference spectra for gold, the LDPE intensity calibration method achieves an absolute offset of ∼3.0% and a systematic deviation of ±6.5% on average across all participants. For spectra recorded at high pass energies (≥90 eV), values of absolute offset and systematic deviation are ∼5.8% and ±5.7%, respectively, whereas for spectra collected at lower pass energies (<90 eV), values of absolute offset and systematic deviation are ∼4.9% and ±8.8%, respectively; low pass energy spectra perform worse than the global average, in terms of systematic deviations, due to diminished count rates and signal-to-noise ratio. Differences in absolute offset are attributed to the surface roughness of the LDPE induced by sample preparation. We further assess the usability of LDPE as a secondary reference material and comment on its performance in the presence of issues such as variable dark noise, x-ray warm up times, inaccuracy at low count rates, and underlying spectrometer problems. In response to participant feedback and the results of the study, we provide an updated LDPE intensity calibration protocol to address the issues highlighted in the interlaboratory study. We also comment on the lack of implementation of a consistent and traceable intensity calibration method across the community of x-ray photoelectron spectroscopy (XPS) users and, therefore, propose a route to achieving this with the assistance of instrument manufacturers, metrology laboratories, and experts leading to an international standard for XPS intensity scale calibration.
Mussel-inspired multifunctional coating for bacterial infection prevention and osteogenic induction
(2021)
Bacterial infection and osteogenic integration are the two main problems that cause severe complications after surgeries. In this study, the antibacterial and osteogenic properties were simultaneously introduced in biomaterials, where copper nanoparticles (CuNPs) were generated by in situ reductions of Cu ions into a mussel-inspired hyperbranched polyglycerol (MI-hPG) coating via a simple dip-coating method. This hyperbranched polyglycerol with 10 % catechol groups’ modification presents excellent antifouling property, which could effectively reduce bacteria adhesion on the surface. In this work, polycaprolactone (PCL) electrospun fiber membrane was selected as the substrate, which is commonly used in biomedical implants in bone regeneration and cardiovascular stents because of its good biocompatibility and easy post-modification. The as-fabricated CuNPs-incorporated PCL membrane [PCL-(MI-hPG)-CuNPs] was confirmed with effective antibacterial performance via in vitro antibacterial tests against Staphylococcus aureus (S. aureus), Escherichia coli (E. coli), and multi-resistant E. coli. In addition, the in vitro results demonstrated that osteogenic property of PCL-(MI-hPG)-CuNPs was realized by upregulating the osteoblast-related gene expressions and protein activity. This study shows that antibacterial and osteogenic properties can be balanced in a surface coating by introducing CuNPs.
The discussion of the surface-enhanced Raman scattering (SERS) spectra of p-aminothiophenol (PATP) and of ist photocatalytic reaction product 4,4′-dimercaptoazobenzene (DMAB) is important for understanding plasmon-supported spectroscopy and catalysis. Here, SERS spectra indicate that DMAB forms also in a nonphotocatalytic reaction on silver nanoparticles. Spectra measured at low pH, in the presence of the acids HCl, H2SO4, HNO3, and H3PO4, show that DMAB is reduced to PATP when both protons and chloride ions are present. Moreover, the successful reduction of DMAB in the presence of other, halide and nonhalide, ligands suggests a central role of these species in the reduction. As discussed, the ligands increase the efficiency of hot-electron harvesting. The pH-associated reversibility of the SERS spectrum of PATP is established as an Observation of the DMAB dimer at high pH and of PATP as a product of its hot-electron reduction at low pH, in the presence of the appropriate ligand.
Historians and librarians are interested in watermarks and mould surface patterns in historic papers, because they represent the “fingerprints” of antique papers. However, these features are usually covered or hidden by printing, writing or other media. Different techniques have been developed to extract the watermarks in the paper while avoiding interference from media on the paper. Beta radiography provides good results, but this method cannot be widely used because of radiation safety regulations and the long exposure times required due to weak isotope sources employed. In this work, two promising methods are compared which can be used to extract digital high-resolution images for paper watermarks and these are electron radiography and low energy X-ray radiography. For electron radiography a “sandwich” of a lead sheet, the paper object, and a film in a dark cassette, is formed and it is exposed at higher X-ray potentials (> 300 kV). The photoelectrons escaping from the lead sheet penetrate the paper and expose the film. After development, the film captures the watermark and mould surface pattern Images for the paper being investigated. These images are then digitized using an X-ray film digitizer. The film employed could potentially be replaced by a special type of imaging plate with a very thin protection layer to directly generate digital Images using computed radiography (CR). For the second method, a low energy X-ray source is used with the specimen paper placed on a digital detector array (DDA). This method directly generates a low energy digital radiography (DR) image. Both methods provide high quality images without interference from the printing media, and provide the potential to generate a “fingerprint”
database for historical papers. There were nevertheless found to be differences in the images obtained using the two methods.
The second method, using a low energy X-ray source, has the potential to be integrated in a portable device with a small footprint incorporating user safety requirements. Differences obtained using the two methods are shown and discussed.
Real-time monitoring of newly acidified organelles during autophagy in living cells is highly desirable for a better understanding of intracellular degradative processes. Herein, we describe a reaction-based boron dipyrromethene (BODIPY) dye containing strongly electron-withdrawing diethyl 2-cyanoacrylate groups at the α-positions. The probe exhibits intense red fluorescence in acidic organelles or the acidified cytosol while negligible fluorescence in other regions of the cell. The underlying mechanism is a nucleophilic reaction at the central meso-carbon of the indacene core, resulting in the loss of π-conjugation entailed by dramatic spectroscopic changes of more than 200 nm between its colorless, non-fluorescent leuco-BODIPY form and its red and brightly emitting form. The reversible transformation between red fluorescent BODIPY and leuco-BODIPY along with negligible cytotoxicity qualifies such dyes for rapid and direct intracellular lysosome imaging and cytosolic acidosis detection simultaneously without any washing step, enabling the real-time monitoring of newly acidified organelles during autophagy.
This article is an outcome of a workshop on Fatigue of Additive Manufactured Metallic Components jointly organized by the Federal Institute for Materials Research and Testing (BAM) Berlin, Germany and the National Institute of Standards and Technology (NIST) Boulder, CO, U.S.A. The aim of the workshop was a comprehensive discussion of the specific aspects of additively manufactured (AM) components in regard to failure under cyclic loading. Undoubtedly, a better understanding and the further development of approaches for damage tolerant component design of AM parts are among the most significant challenges currently facing the use of these new technologies.
This article presents a thorough overview of the workshop discussions. It aims to provide a review of the parameters affecting the damage tolerance of AM parts with special emphasis on the process parameters intrinsic to the AM technologies, the resulting defects and residual stresses. Based on these aspects, concepts for damage tolerant component design for AM are reviewed and critically discussed.
The demonstration of competency and equivalence for the assessment of levels of contaminants and nutrients in primary foodstuffs is a priority within the 10-year strategy for the OAWG Track A core comparisons. The measurements are core challenges for reference material producers and providers of calibration Services. This key comparison related to low polarity analytes in a high fat, low protein, low carbohydrate food matrix and Benzo[a]pyrene in edible oil was the model System selected to align with this class within the OAWG strategy. Evidence of successful participation in formal, relevant international comparisons is needed to document measurement capability claims (CMCs) made by national metrology institutes (NMIs) and designated institutes (Dis). 16 National Metrology Institutions participated in the Track A Key Comparison CCQM-K146 Low-Polarity Analyte in high fat food: Benzo[a]pyrene in Olive Oil. Participants were requested to evaluate the mass fractions, expressed in µg/kg, of Benzo[a]pyrene in the olive oil material. The KCRV was determined from the results of all NMIs/DIs participating in the key comparison that used appropriately validated methods with demonstrated metrological traceability. Different methods such as liquid-liquid extraction, GPC and SPE were applied in the sample pretreatment and HPLC-FLD, HPLC-MS/MS, and GC-MS or GC-MS/MS were applied for detection by the participants. The mass fractions for BaP were in the range of (1.78 to 3.09) µg/kg with Standard uncertainties of (0.026 to 0.54) µg/kg, with corresponding relative Standard uncertainties from 0.9% to 21%. Five labs withdrew their result from the Statistical evaluation of the KCRV for technical reasons. One lab was excluded from the KCRV evaluation, as they did not meet the CIPM metrological traceability requirements. A Hierarchical Bayes option was selected for the KCRV value, which was determined as 2.74 µg/kg with a Standard uncertainty of 0.03 µg/kg. The 10 institutes those were included in the calculation of the consensus KCRV all agreed within their Standard uncertainties. Successful participation in CCQM-K146 demonstrates the measurement capabilities in determining mass fraction of organic compounds, with molecular mass of 100 g/mol to 500 g/mol, having low polarity pKow < -2, in mass fraction range from 0.1 µg/kg to 1000 µg/kg in a high fat, low protein, low carbohydrate food matrix.
The lead authors failed to name two collaborators as co-authors. The authors listed should include:
Miss Claudia L. Compean-Gonzalez (ORCID:
0000-0002-2367-8450) and Dr. Giacomo Ceccone (ORCID:
0000-0003-4637-0771).
These co-authors participated in VAMAS project A27, provided data that were analyzed and presented in this publication (and supporting information), and reviewed the manuscript before submission.
We investigate the pore space of rock samples with respect to different petrophysical parameters using various methods, which provide data upon pore size distributions, including micro computed tomography (μ-CT), mercury intrusion porosimetry (MIP), nuclear magnetic resonance (NMR), and spectral induced polarization (SIP). The resulting cumulative distributions of pore volume as a function of pore size are compared. Considering that the methods differ with regard to their limits of resolution, a multiple length scale characterization of the pore space geometry is proposed, that is based on a combination of the results from all of these methods. The findings of this approach are compared and discussed by using Bentheimer sandstone. Additionally, we compare the potential of SIP to provide a pore size distribution with other commonly used methods (MIP, NMR). The limits of resolution of SIP depend on the usable frequency range (between 0.002 and 100 Hz). The methods with similar resolution show a similar behavior of the cumulative pore volume distribution in the overlapping pore size range. The methods μ-CT and NMR provide the pore body size while MIP and SIP characterize the pore throat size. Using this difference, the average pore body to throat ratio is determined to be about three for the Bentheimer sandstone.
Our study shows that a good agreement between the pore radii distributions can only be achieved if the curves are adjusted considering the resolution and pore volume in the relevant range of pore radii. The MIP curve with the widest range in resolution should be used as reference
Role of metal cations in plasmon-catalyzed oxidation: A case study of p-aminothiophenol dimerization
(2017)
The mechanism of the plasmon-catalyzed reaction of p-aminothiophenol (PATP) to 4,4′-dimercaptoazobenzene (DMAB) on the surface of metal nanoparticles has been discussed using data from surface-enhanced Raman scattering of DMAB. Oxides and hydroxides formed in a plasmon-catalyzed process were proposed to play a central role in the reaction. Here, we report DMAB formation on gold nanoparticles occurring in the presence of the metal cations Ag+, Au3+, Pt4+, and Hg2+. The experiments were carried out under conditions where formation of gold oxide or hydroxide from the nanoparticles can be excluded and at high pH where the formation of the corresponding oxidic species from the metal ions is favored. On the basis of our results, we conclude that, under these conditions, the selective oxidation of PATP to DMAB takes place via formation of a metal oxide from the ionic species in a plasmon-catalyzed process. By evidencing the necessity of the presence of the metal cations, the reported results underpin the importance of metal oxides in the reaction.
In der Vergangenheit wurde immer wieder diskutiert, ob die Porenhalsverteilung poröser silikatischer Medien maßgeblich die Relaxationszeit in Messergebnissen der Spektralen Induzierten Polarisation (SIP) bestimmt und dementsprechend auch neuere Ansätze, Porenweitenverteilungen aus diesen Daten abzuleiten, zuverlässig sein können. Systematische Studien an Gesteinen mit sehr unterschiedlichen Porenverteilungen zeigten, dass in Materialien mit engen Porenhälsen (z.B. < 5 μm) vor allem oder zusätzlich zum vermuteten Porenhalspeak niederfrequente Relaxationen zu beobachten sind, deren Ursache noch unklar ist.
Unter Einbeziehung der Methoden Röntgen-Computertomografie (μ-CT), Quecksilberporosimetrie (MIP), Stickstoffabsortion, Nukleare Magnetische Resonanz, SIP und Auflichtmikroskopie untersuchen wir den Porenraum hinsichtlich der Parameter Porosität, Permeabilität und innere Oberfläche und bestimmen die geometrischen Eigenschaften wie Porenweitenverteilungen oder fraktale Dimension durch verschiedene Algorithmen. Dabei ist zu berücksichtigen, dass sich die Methoden hinsichtlich der Grenzen ihres Auflösungsvermögens unterscheiden. Mit einer Zusammenführung der Ergebnisse aller Methoden kann eine mehrere Längenskalen überdeckende Charakterisierung der Porenraumgeometrie erfolgen.
Die Anwendung und Auswertung der verschiedenen Methoden werden am Beispiel von Baumberger Kalksandstein und Bentheimer Sandstein verglichen und diskutiert.
The pore size distribution provides a suitable description of the pore space geometry that can be used to investigate the fractal nature of the pore space or to determine a fractal dimension. Fractal dimension describes the size of geometric objects as a function of resolution. It can be integrated into models of permeability prediction. We investigated the fractal dimension of the pore volume of 11 Eocene sandstone samples from China. This study describes an approach to use spectral induced polarisation spectra to estimate the pore size distribution and to determine the fractal dimension of the pore volume. Additionally, the fractal dimension was derived from data of the capillary pressure curves from mercury intrusion and the transversal relaxation time distribution of nuclear magnetic resonance. For samples with an effective pore radius larger than 1 μm, good agreement exists between the values of fractal dimension derived from the three different methods, which implies the identification of similar pore structures. Spectral induced polarisation can be a non-invasive laboratory technique for the estimation of the pore size distribution, but the application of the methodology for field measurements remains a challenging problem considering the limited frequency range.
Digital radiographic images were analysed to predict the visibility of image quality indicators (IQI), based on normalized noise power spectra (NNPP) and modulation transfer function (MTF) measurements. The fixed pattern noise of some digital detectors result in different noise spectra, which influence the visibility of different IQIs, depending on the hole diameter. Studies, based on measurement of basic spatial resolution and contrast to noise ratio were performed together with presampled MTF measurements and the NNPS in dependence on the spatial frequency. Plate hole IQIs, step hole IQIs, and equivalent penetrameter sensitivity (EPS) IQIs based on ASTM E 746 were measured to verify the influence of the different parameters. Modelling of digital images was used to verify the applied numeric tools. A study has been performed for imaging plates and digital detector arrays to analyse differences. Formulas for the prediction of the visibility functions for hole type IQIs are derived. In consequence the standards for characterization and classification of computed radiography (ASTM E 2446) and radiography with DDAs (ASTM E 2597) need to be revised.
Die Voraussetzungen für die Vorhersage der Sichtbarkeit von Bildgüteprüfkörpern (BPK) wurden seit Beginn der kommerziellen Anwendung der technischen Radiographie diskutiert und in diversen nationalen und internationalen Standards festgeschrieben. Diese Fragen werden nach Einführung der digitalen Radiographie und der CT wieder neu diskutiert. Draht BPKs wurden in Deutschland seit 1935 (DIN 1915: 1935) und später in den meisten europäischen Ländern benutzt. In den USA und Frankreich wurden vorzugsweise BPKs mit Löchern verwendet (ASTM E 1025 seit 1984 oder E 1742 seit 1992 bzw. die Vorgängernorm MIL STD-543 seit 1962). Jetzt werden auch die Umrechnungsnormen zur Erkennbarkeit von Draht zu Loch-BPKs in Frage gestellt. ISO 19232-3, der französische RCCM-Kode einerseits und ASTM E 747 und ASME BPVC Section V Tab. T-276 andererseits unterscheiden sich erheblich bei den Anforderungen im Bereich hoher Wandstärken (Hochenergieradiographie). Untersuchungen dazu werden vorgestellt. Mit Einführung der digitalen Detektoren ändern sich auch die Rauschspektren. Durch die Herstellung werden insbesondere bei Speicherfolien "Rauschmuster" eingeprägt, die bei hohen Belichtungsdosen sichtbar werden. Diese veränderten Rauschspektren ergeben auch veränderte Erkennungsparameter für menschliche Bildauswerter. Hierzu wurden an ausgewählten Detektoren MTFs (presampled) und normierte Rauschspektren gemessen. Erweiterte Erkennbarkeits-Formeln zur Vorhersage der Sichtbarkeit von BPKs für Bildauswerter und erste Ergebnisse werden vorgestellt.
Efficient water oxidation catalysts are required for the development of water splitting technologies. Herein, the synthesis of layered hybrid NiFephenylphosphonate compounds from metal acetylacetonate precursors and phenylphosphonic acid in benzyl alcohol, and their Oxygen evolution reaction performance in alkaline medium, are reported. The hybrid particles are formed by inorganic layers of NiO6 and FeO6 distorted octahedra separated by bilayers of the organic group, and template the Formation in situ of NiFe hydroxide nanosheets of sizes between 5 and 25 nm and thicknesses between 3 and 10 nm. X-ray absorption spectroscopy measurements suggest that the hybrid also acts as a template for the local structure of the metal sites in the active catalyst, which remain distorted after the transformation. Optimum electrocatalytic activity is achieved with the hybrid compound with a Fe content of 16%. The combination of the synergistic effect between Ni and Fe with the structural properties of the hybrid results in an efficient catalyst that generates a current density of 10 mA cm−2 at an overpotential of 240 mV, and also in a stable catalyst that operates continuously at low overpotentials for 160 h.
Carbon nanotube-grafted carbon fiber polymer composites: Damage characterization on the micro scale
(2017)
Multiwall carbon nanotubes (CNTs) e carbon fibers (CFs)hybrid materials were produced by directly growing CNTs on CFs by means of chemical vapor deposition. For the latter, the oxidative dehydrogenation reaction of C2H2 and CO2 was applied, which allows growing CNTs without damaging the CF surface. Uni-directional nano-engineered carbon fiber reinforced composites (nFRCs) were fabricated by impregnating these hybrid materials with epoxy. The nFRCs subjected to single fiber push-out tests revealed a decrease of the interfacial shear strength (IFSS) of about 36% compared to the carbon fiber composites without CNTs. By means of transverse three-point bending tests performed on pre-notched composite beams inside a scanning electron microscope, the fracturing behavior parallel to the fibers was studied in-situ. The nFRCs showed significantly reduced fiber/matrix debonding while CNTs pull-out, CNTs bridging as well as matrix failure occurred. These results demonstrate that the presence of CNTs in nFRCs affects the stress distribution and consequently the damage Initiation as well as the damage propagation. The presence of CNTs suppresses the stress concentration at the fiber/Matrix interface and reduces the debonding of CFs from the matrix. However, our results indicate that the stress concentration shifts towards the CNTs' ends/matrix interface and causes promoted matrix failure leading to lower IFSS.
We investigate the pore space of rock samples with respect to different petrophysical parameters using various methods, which provide data on pore size distributions, including micro computed tomography (µ-CT), mercury Intrusion porosimetry (MIP), nuclear magnetic resonance (NMR), and spectral-induced polarization (SIP). The resulting cumulative distributions of pore volume as a function of pore size are compared. Considering that the methods differ with
regard to their limits of resolution, a multiple-length-scale characterization of the pore space is proposed, that is based on a combination of the results from all of these methods.
The approach is demonstrated using samples of Bentheimer and Röttbacher sandstone. Additionally, we compare the potential of SIP to provide a pore size distribution with other commonly used methods (MIP, NMR). The limits of Resolution of SIP depend on the usable frequency range (between 0.002 and 100 Hz). The methods with similar Resolution show a similar behavior of the cumulative pore volume distribution in the verlapping pore size range. We assume that µ-CT and NMR provide the pore body size while MIP and SIP characterize the pore throat size. Our study Shows that a good agreement between the pore radius distributions can only be achieved if the curves are adjusted considering the resolution and pore volume in the relevant range of pore radii. The MIP curve with the widest range in Resolution should be used as reference.
Cancer is the second leading cause of death globally according to the WHO 2018. Lung, prostate, colorectal, stomach and liver cancer are the most common types of cancer in men, while breast, colorectal, lung, cervix and thyroid cancer are the most common among women. Sialic acid (SA) plays an important role in a variety of biological processes in cells. Tumor cells express high levels of SA, which is often associated with poor prognosis due to increased invasive potential. In this study, we have performed a screening of SA-MIPs binding to different cancer cell lines. The overall aim is to use the SA-MIPs for detection of tumor cells, analyzed by flow cytometry and fluorescence microscopy. To confirm the levels of SA expression on the investigated cell lines, we started out by analyzing the binding of the lectins MAL I and SNA. The staining pattern of the two lectins binding to either α-2,3 or α-2,6 linkage SA, respectively, was compared with the staining pattern of the SA-MIPs. We show that the different cell types analyzed have a varying pattern of SA-MIP binding. The comparison with lectin binding will be further evaluated.
The characterization of a catalyst often occurs by averaging over large areas of the catalyst material. On the other hand, optical probing is easily achieved at a resolution at the micrometer scale, specifically in microspectroscopy. Here, using surface-enhanced Raman scattering (SERS) mapping of larger areas with micrometer-sized spots that contain tens to hundreds of supported gold nanoparticles each, the photoinduced dimerization of p-aminothiophenol (PATP) to 4,4′-dimercaptoazobenzene (DMAB) was monitored. The mapping data reveal an inhomogeneous distribution of catalytic activity in the plasmon-catalyzed reaction in spite of a very homogeneous plasmonic enhancement of the optical signals in SERS. The results lead to the conclusion that only a fraction of the nanostructures may be responsible for a high catalytic activity. The high spot-to-spot variation in catalytic activity is also demonstrated for DMAB formation by the plasmon-catalyzed reduction from p-nitrothiophenol (PNTP) and confirms that an improvement of the accuracy and reproducibility in the characterization of catalytic reactions can be achieved by microspectroscopic probing of many positions. Using SERS micromapping during the incubation of PATP, we demonstrate that the reaction occurs during the incubation process and is influenced by different parameters, leading to the conclusion of dimerization in a gold-catalyzed, nonphotochemical reaction as an alternative to the plasmon-catalyzed process. The results have implications for the future characterization of new catalyst materials as well as for optical sensing using plasmonic materials.