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Paper des Monats
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Anear-infrared (NIR) light-triggered release method for nitric oxide (NO) was developed utilizing core/shell NaYF4: Tm/Yb/Ca@NaGdF4:Nd/Yb up-conversion nanoparticles (UCNPs) bearing a mesoporous silica (mSiO2) shell loaded with theNOdonor S-nitroso-N-acetyl-DL-penicillamine (SNAP). To avoid overheating in biological samples, Nd3+ was chosen as a sensitizer, Yb3+ ions as the bridging sensitizer, andTm3+ ions as UV-emissive activator while co-doping with Ca2+ was done to enhance the luminescence of the activatorTm3+.NOrelease from SNAP was triggered by an NIR-UV up-conversion process, initiated by 808nmlight absorbed by the Nd3+ ions.NOrelease was confirmed by the Griess method. Under 808nmirradiation, the viability of the liver cancer cell line HepG2 significantly decreased with increasing UCNPs@mSiO2-SNAP concentration. For a UCNPs@mSiO2-SNAP concentration of 200 μgml−1, the cell survival probability was 47%. These results demonstrate that UCNPs@mSiO2-SNAP can induce the release of apoptosis-inducingNOby NIR irradiation.
A new “green” and mild synthesis of highly stable microcrystalline Cs2AgxNa1-xBiyIn1-yCl6 (CANBIC) perovskites under ambient conditions was developed that is scalable to the multi-gram production. Under UV illumination, the CANBIC perovskites emit intense broadband photoluminescence (PL) with a quantum yield (QY) of 92% observed for x = 0.35 and y = 0.01-0.02. The combination of strong UV absorbance and broadband visible emission, high PL QY, and long PL lifetimes of up to 1.4 μs, along with an outstanding stability makes these CANBICs a promising material class for many optical applications.
In the past few years, it has been discussed with increasing frequency, whether cube slip does occur in gamma' hardened nickel-base superalloys. Occurrence of cube slip has consequences for the modeling of orientation dependence of the CRSS. Until now, there are only few experimental investigations.
In principle, cube slip should be possible in primitive cubic lattices (e.g. L12 ordered gamma' phase) but not in face centered cubic ones (e.g. Ni solid solution). The most favourable specimen orientations are near [111], where the Schmid factors for this type of glide exceed those for octahedral systems.
There are two basic methods to detect cube slip: macroscopic slip trace analysis and Transmission electron microscopy (TEM) investigation of the dislocation structure. Few observations of cube slip by macroscopic slip traces are reported in the literature. But it is still uncertain under which test conditions cube slip occurs and what the dislocation mechanisms are. Cube slip was observed during tensile or compression tests of several first generation superalloys, but it seems not to occur during shear creep deformation (e.g. CMSX-4 at 980°C), and it is also lacking under conventional tensile or compression loading, if the gmma' particles are small. No observations were ever reported of dislocations gliding on {001} planes in matrix channels.
This study presents the synthesis and characterization of zwitterionic core–shell hybrid nanoparticles consisting of a core of iron oxide multicore nanoparticles (MCNPs, γ-Fe2O3) and a shell of sultonated poly(2-vinylpyridine-grad-acrylic acid) copolymers. The gradient copolymers are prepared by reversible addition fragmentation chain transfer polymerization of 2-vinylpyridine (2VP), followed by the addition of tert-butyl acrylate and subsequent hydrolysis. Grafting of P(2VP-grad-AA) onto MCNP results in P(2VP-grad-AA)@MCNP, followed by quaternization using 1,3-propanesultone-leading to P(2VPS-grad-AA)@MCNP with a zwitterionic shell. The resulting particles are characterized by transmission electron microscopy, dynamic light scattering, and thermogravimetric analysis measurements, showing particle diameters of ≈70–90 nm and an overall content of the copolymer shell of ≈10%. Turbidity measurements indicate increased stability toward secondary aggregation after coating if compared to the pristine MCNP and additional cytotoxicity tests do not reveal any significant influence on cell viability.
To arrive to sustainable hydrogen-based energy solutions, the understanding of water-splitting catalysts plays the most crucial role. Herein, state-of-the-art hypotheses are combined on electrocatalytic active metal sites toward the oxygen evolution reaction (OER) to develop a highly efficient catalyst based on Earth-abundant cobalt and zinc oxides.
The precursor catalyst Zn0.35Co0.65O is synthesized via a fast microwaveassisted approach at low temperatures. Subsequently, it transforms in situ from the wurtzite structure to the layered γ-Co(O)OH, while most of its zinc leaches out. This material shows outstanding catalytic Performance and stability toward the OER in 1 m KOH (overpotential at 10 mA cm−2 ηinitial = 306 mV, η98 h = 318 mV). By comparing the electrochemical results and ex situ analyses to today’s literature, clear structureactivity correlations are able to be identified. The findings suggest that coordinately unsaturated cobalt octahedra on the surface are indeed the active centers for the OER.
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.
This paper reports the formation of zinc phosphate nanoparticles from the artificial digestion of zinc chloride. Initially, the formation of amorphous primary particles with a mean radius of 1.1 nm is observed, alongside the formation of larger, protein stabilized aggregates. These aggregates, with a radius of gyration of 37 nm, are observed after 5 minutes of exposure to artificial saliva and are shown to be colloidally stable for a minimum time of two weeks. The initially formed primary particles are thought to consist of amorphous zinc phosphate, which is then transformed into crystalline Zn3(PO4)2·4H2O over the course of two weeks. Our results demonstrate that the interaction of inorganic salts with bodily fluids can induce the formation of de novo nanoparticles, which in turn, provides insights into how zinc‐enriched foods may also facilitate the formation of nanoparticles upon contact with saliva. As such, this may be considered as an undesirable (bio)mineralization.
Cryoadsorption on the inner surface of porous materials is a promising solution for safe, fast, and reversible hydrogen storage. Within the class of highly porous metal−organic frameworks, zeolitic imidazolate frameworks (ZIFs) show high thermal, chemical, and mechanical stability. In this study, we selected ZIF-8 synthesized mechanochemically by twin-screw extrusion as powder and pellets. The hydrogen storage capacity at 77 K and up to 100 bar has been analyzed in two laboratories applying three different measurement setups showing a high reproducibility. Pelletizing ZIF-8 increases the packing density close to the corresponding value for a single crystal without loss of porosity, resulting in an improved volumetric hydrogen storage capacity close to the upper limit for a single crystal. The high volumetric uptake combined with a low and constant heat of adsorption provides ca. 31 g of usable hydrogen per liter of pellet assuming a temperature−pressure swing adsorption process between 77 K − 100 bar and 117 K − 5 bar. Cycling experiments do not indicate any degradation in storage capacity. The excellent stability during preparation, handling, and operation of ZIF-8 pellets demonstrates its potential as a robust adsorbent material for technical application in pilot- and full-scale adsorption vessel prototypes.
Young's modulus and Poisson's ratio changes due to machining in porous microcracked cordierite
(2016)
Microstructural changes in porous cordierite caused by machining were characterized using microtensile testing, X-ray computed tomography, and scanning electron microscopy. Young's moduli and Poisson's ratios were determined on similar to 215- to 380-mu m-thick machined samples by combining digital image correlation and microtensile loading. The results provide evidence for an increase in microcrack density and decrease of Young's modulus due to machining of the thin samples extracted from diesel particulate filter honeycombs. This result is in contrast to the known effect of machining on the strength distribution of bulk, monolithic ceramics.
High sensitizer and activator concentrations have been increasingly examined to improve the performance of multi-color emissive upconversion (UC) nanocrystals (UCNC) like NaYF4:Yb,Er and first strategies were reported to reduce concentration quenching in highly doped UCNC. UC luminescence (UCL) is, however, controlled not only by dopant concentration, yet by an interplay of different parameters including size, crystal and shell quality, and excitation power density (P). Thus, identifying optimum dopant concentrations requires systematic studies of UCNC designed to minimize additional quenching pathways and quantitative spectroscopy. Here, we quantify the dopant concentration dependence of the UCL quantum yield (ΦUC) of solid
NaYF4:Yb,Er/NaYF4:Lu upconversion core/shell nanocrystals of varying Yb3+ and Er3+ concentrations (Yb3+ series: 20%‒98% Yb3+; 2% Er3+; Er3+ series: 60% Yb3+; 2%‒40% Er3+). To circumvent other luminescence quenching processes, an elaborate synthesis yielding OH-free UCNC with record ΦUC of ~9% and ~25 nm core particles with a thick surface shell were used. High Yb3+ concentrations barely reduce ΦUC from ~9% (20% Yb3+) to ~7% (98% Yb3+) for an Er3+ concentration of 2%, thereby allowing to strongly increase the particle absorption cross section and UCNC brightness. Although an increased Er3+ concentration reduces ΦUC from ~7% (2% Er3+) to 1% (40%) for 60% Yb3+. Nevertheless, at very high P (> 1 MW/cm2) used for microscopic studies, highly Er3+-doped UCNC display a high brightness because of reduced saturation. These findings underline the importance of synthesis control and will pave the road to many fundamental studies of UC materials.
Yb,Nd,Er-doped upconversion nanoparticles (UCNPs) have attracted considerable interest as luminescent reporters for bioimaging, sensing, energy conversion/shaping, and anticounterfeiting due to their capability to convert multiple near-infrared (NIR) photons into shorter wavelength ultraviolet, visible or NIR luminescence by successive absorption of two or more NIR photons. This enables optical measurements in complex media with very little background and high penetration depths for bioimaging. The use of Nd3+ as substitute for the commonly employed sensitizer Yb3+ or in combination with Yb3+ shifts the excitation wavelength from about 980 nm, where the absorption of water can weaken upconversion luminescence, to about 800 nm, and laser-induced local overheating effects in cells, tissue, and live animal studies can be minimized. To systematically investigate the potential of Nd3+ doping, we assessed the performance of a set of similarly sized Yb3+,Nd3+,Er3+-doped core- and core–shell UCNPs of different particle architecture in water at broadly varied excitation power densities (P) with steady state and time-resolved fluorometry for excitation at 980 nm and 808 nm. As a measure for UCNPs performance, the P-dependent upconversion quantum yield (Φ) and its saturation behavior were used as well as particle brightness (B). Based upon spectroscopic measurements at both excitation wavelengths in water and in a lipid phantom and B-based calculations of signal size at different penetration depths, conditions under which excitation at 808 nm is advantageous are derived and parameters for the further optimization of triple-doped UCNPs are given.
X‑ray emission during the ablative processing of biological materials by ultrashort laser pulses
(2023)
The ablative laser processing with ultrashort pulsed laser beams may cause secondary emission of hazardous X-rays. While the effect has recently been proven to be considered in working safety regulations when processing technical materials, such as metals, the X-ray emission rates during the ablative processing of biological tissue materials are widely unexplored yet.
Therefore, biological materials like water, isotonic saline solution, pig eyes, and human teeth were ablated with ultrashort laser pulses of 1030 nm wavelength, 600 fs pulse duration and 5 kHz pulse repetition rate, aiming to mimic typical surgery situations. Simultaneously, in-situ X-ray dose rate measurements were performed at a short distance from the plasma to display potential X-ray emission. For all four studied biological materials, our measurements prove the secondary emission of laser-induced X-rays.
Direct Laser Writing (DLW) and X-ray computed tomography (XCT) both offer unique possibilities in their respective fields. DLW produces full three-dimensional (3D) polymer structures on the microscale with resolutions below 100 nm. The fabricated structures can be analysed by XCT or X-ray microscopy (XRM), which incorporates additional X-ray lenses, in three dimensions down to a minimal basic spatial resolution of about 500 nm or 50 nm, respectively. In this work, two different DLW structures are analysed via XCT. Internal defects are detected and analysed for the purpose of quality control. Defects and structures with sizes down to 1.5 µm are successfully analysed. A 3D reconstruction and internal, hidden features of the fabricated structures are shown and discussed. In a first-of-its-kind study, we demonstrate the detectability of a single-voxel line inside a fabricated structure that would not be detectable with SEM or light microscopy. Furthermore, the direct fabrication on a PET substrate is shown to overcome the high X-ray absorbance of commonly used glass substrates. Attenuation spectra of SZ2080 and glass substrates are compared to a fabrication route direct on a 170 µm PET foil. The practical aspects of XCT measurements for DLW structures on different substrates will be discussed.
Selective Electron Beam Melting (SEBM) is a promising powder bed Additive Manufacturing technique for near-net-shape manufacture of high-value titanium components. However without post-manufacture HIPing the fatigue life of SEBM parts is currently dominated by the presence of porosity. In this study, the size, volume fraction, and spatial distribution of the pores in model samples have been characterised in 3D, using X-ray Computed Tomography, and correlated to the process variables. The average volume fraction of the pores (b0.2%) was measured to be lower than that usually observed in competing processes, such as selective laser melting, but a strong relationship was found with the differentbeamstrategies used to contour ,and infill by hatching, a part section. The majority of pores were found to be small spherical gas pores, concentrated in the infill hatched region; this was attributed to the lower energy density and less focused beam used in the infill strategy allowing less opportunity for gas bubbles to escape the melt pool. Overall, increasing the energy density or focus of the beam was found to correlate strongly to a reduction in the level of gas porosity. Rarer irregular shaped pores were mostly located in the contour region and have been attributed to a lack of fusion between powder particles.
X-ray tomography characterisation of lattice structures processed by selective electron beam melting
(2017)
Metallic lattice structures intentionally contain open porosity; however, they can also contain unwanted closed porosity within the structural members. The entrained porosity and defects within three different geometries of Ti-6Al-4V lattices, fabricated by Selective Electron Beam Melting (SEBM), is assessed from X-ray computed tomography (CT) scans. The results suggest that horizontal struts that are built upon loose powder show particularly high (~20 x 10⁻³ vol %) levels of pores, as do nodes at which many (in our case 24) struts meet. On the other hand, for struts more closely aligned (0° to 54°) to the build direction, the fraction of porosity appears to be much lower (~0.17 x 10⁻³%) arising mainly from pores contained within the original atomised powder particles.
Ultrashort pulse laser processing of materials allows for precise machining with high accuracy. By increasing the repetition rate to several 100 kHz, laser machining becomes quick and cost-effective. Ultrafast laser processing at high repetition rates and peak intensities above 10^13 W/cm^2 can cause a potential hazard by generation of unwanted x-ray radiation. Therefore, radiation protection must be considered. For 925 fs pulse duration at a center wavelength of 1030 nm, the x-ray emission in air at a repetition rate of 400 kHz was investigated up to a
peak intensity of 2.6 × 10^14 W/cm^2. Based on the presented measurements, the properties of potential shielding materials will be discussed. By extending our previous works, a scaling of the x-ray radiation emission to higher peak intensities up to 10^15 W/cm^2 is described, and emitted x-ray doses are predicted.
X-ray emission hazards from ultrashort pulsed laser material processing in an industrial setting
(2021)
Interactions between ultrashort laser pulses with intensities larger than 10^13 W/cm^2 and solids during material processing can lead to the emission of X-rays with photon energies above 5 keV, causing radiation hazards to operators. A framework for inspecting X-ray emission hazards during laser material processing has yet to be developed. One requirement for conducting radiation protection inspections is using a reference scenario, i.e., laser settings and process parameters that will lead to an almost constant and high level of X-ray emissions. To study the feasibility of setting up a reference scenario in practice, ambient dose rates and photon energies were measured using traceable measurement equipment in an industrial setting at SCHOTT AG. Ultrashort pulsed (USP) lasers with a maximum average power of 220 W provided the opportunity to measure X-ray emissions at laser peak intensities of up to 3.3 × 10^15 W/cm^2 at pulse durations of ~1 ps. The results indicate that increasing the laser peak intensity is insufficient to generate high dose rates. The investigations were affected by various constraints which prevented measuring high ambient dose rates. In this work, a list of issues which may be encountered when performing measurements at USP-laser machines in industrial settings is identified.
In laser machining with ultrashort laser pulses unwanted X-ray radiation in the keV range can be generated when a critical laser intensity is exceeded. Even if the emitted X-ray dose per pulse is low, high laser repetition rates can lead to an accumulation of X-ray doses beyond exposure safety limits. For 925 fs pulse duration at a center wavelength of 1030 nm, the X-ray emission was investigated up to an intensity of 2.6 × 10^14 W/cm2. The experiments were performed in air with a thin disk laser at a repetition rate of 400 kHz. X-ray spectra and doses were measured for various planar target materials covering a wide range of the periodic table from aluminum to tungsten. Without radiation shielding, the measured radiation doses at this high repetition rate clearly exceed the regulatory limits. Estimations for an adequate radiation shielding are provided.
In this paper we report on the characterization by X-ray computed tomography of calcium phosphate (CaP) and polycaprolactone (PCL) coatings on Ti-6Al-4V alloy scaffolds used as a material for medical implants. The cylindrical scaffold has greater porosity of the inner part than the external part, thus, mimicking trabecular and cortical bone, respectively. The prismatic scaffolds have uniform porosity. Surface of the scaffolds was modified with calcium phosphate (CaP) and polycaprolactone (PCL) by dip-coating to improve biocompatibility and mechanical properties. Computed tomography performed with X-ray and synchrotron radiation revealed the defects of structure and morphology of CaP and PCL coatings showing small platelet-like and spider-web-like structures, respectively.
In this paper we report on the characterization by X-ray computed tomography of calcium phosphate (CaP) and polycaprolactone (PCL) coatings on Ti-6Al-4V alloy scaffolds used as a material for medical implants. The cylindrical scaffold has greater porosity of the inner part than the external part, thus, mimicking trabecular and cortical bone, respectively. The prismatic scaffolds have uniform porosity. Surface of the scaffolds was modified with calcium phosphate (CaP) and polycaprolactone (PCL) by dip-coating to improve biocompatibility and mechanical properties. Computed tomography performed with X-ray and synchrotron radiation revealed the defects of structure and morphology of CaP and PCL coatings showing small platelet-like and spider-web-like structures, respectively.
X-Ray computed tomography and traditional analysis of a capillary absorption test in cement pastes
(2020)
Water absorption testing has the attraction of being simple, relatively quick and use water as a fluid which is the key substance in the possible concrete deterioration. However, in spite of the advantages its application has remained empirical, except for the testing of resistance to frost, through the identification of the critical degree of saturation. Rilem TC-116 studied this test, among others, for the characterization of concrete resistance against transport through the concrete pore network. Results indicated a low discriminating ability of the absorbency for qualifying concrete resistance and then, it seemed necessary to try to move forward by making the link between the absorption testing and the concrete pore microstructure. In the present work, thanks to the X-Ray computed tomography, it is described the evolution of the water front in three paste-specimen with different w/c ratios (different pore radius distributions). The observations allowed us to deduce that all the pores start to fill simultaneously, but the bigger ones fill quicker and rise less. The saturation degree is measured along the height of the sample, showing that each pore size has a different rate which becomes constant after the first hour. Washburn’s equation was applied to the progressive advance of the water front, resulting in a pore radius much smaller than the one expected.
Scientific material analysis of the elemental composition of inks from different strata of a manuscript has the potential to complement scholarly observations using palaeography and philology in reconstructing the history of the manuscript’s production, correction and repair.
There are three typologically different classes of black writing inks: soot inks consist of carbon particles.
Ultrashort pulse laser processing can result in the secondary generation of unwanted X-rays if a critical laser irradiance of about 10^13 W/cm^2 is exceeded. Spectral X-ray emissions were investigated during the processing of tungsten and steel using three complementary spectrometers (based on CdTe and silicon drift detectors) simultaneously for the identification of a worst-case spectral scenario. Therefore, maximum X-ray photon energies were determined, and corresponding dose equivalent rates were calculated. An ultrashort pulse laser workstation with a pulse duration of 274 fs, a center wavelength of 1030 nm, pulse repetition rates between 50 kHz and 200 kHz, and a Gaussian laser beam focused to a spot diameter of 33 µm was employed in a single pulse and burst laser operation mode. Different combinations of laser pulse energy and repetition rate were utilized, keeping the average laser power constant close to the maximum power of 20 W. Peak irradiances ranging from 7.3 × 10^13 W/cm^2 up to 3.0 × 10^14 W/cm^2 were used. The X-ray dose equivalent rate increases for lower repetition rates and higher pulse energy if a constant average power is used. Laser processing with burst mode significantly increases the dose rates and the X-ray photon energies. A maximum X-ray photon energy of about 40 keV was observed for burst mode processing of tungsten with a repetition rate of 50 kHz and a peak irradiance of 3 × 10^14 W/cm^2.
We present a workflow for obtaining fully trained artificial neural networks that can perform automatic particle segmentations of agglomerated, non-spherical nanoparticles from scanning electron microscopy images “from scratch”, without the need for large training data sets of manually annotated images. The whole process only requires about 15 minutes of hands-on time by a user and can typically be finished within less than 12 hours when training on a single graphics card (GPU). After training, SEM image analysis can be carried out by the artificial neural network within seconds. This is achieved by using unsupervised learning for most of the training dataset generation, making heavy use of generative adversarial networks and especially unpaired image-to-image translation via cycle-consistent adversarial networks. We compare the segmentation masks obtained with our suggested workflow qualitatively and quantitatively to state-of-the-art methods using various metrics. Finally, we used the segmentation masks for automatically extracting particle size distributions from the SEM images of TiO2 particles, which were in excellent agreement with particle size distributions obtained manually but could be obtained in a fraction of the time.
Wire arc additive manufacturing enables the production of near-net shape large-volume metallic components leveraging an established industrial base of welding and cladding technology and adapting it for layer-wise material deposition. However, the complex relationship between the process parameters and resulting mechanical properties of the components still remains challenging. In case of high-strength Al-Mg-Si aluminum alloys, no commercial filler wires are yet available due the high susceptibility of solidification cracking as well as the necessary efforts to obtain acceptable mechanical properties. To address this need, we evaluated a novel filler wire based on AlMg0.7Si doped with a Ti5B1 master alloy to foster fine equiaxed grains within the deposited metal. The correlation between the process parameters and component quality was examined by analyzing the size and distribution of pores as well as the grain morphology. Furthermore, we evaluated the influence of different post-weld heat treatment strategies to achieve mechanical properties corresponding to the reference wrought material. We demonstrated that fine equiaxed grains in the weld metal reduced the susceptibility of solidification cracking significantly. The novel AlMg0.7Si-TiB (S Al 6063-TiB) filler wire facilitated wire arc additive manufacturing of high-strength aluminum components with mechanical properties that were almost as superior as the corresponding wrought base material.
Shape memory alloy structures for actuator and vibration damper applications may be manufactured using wire arc additive manufacturing (W AAM), which is one of the additive manufacturing technologies. Multilayer deposition causes heat accumulation during W AAM, which rises the preheat temperature of the previously created layer. This leads to process instabilities, which result in deviations from the desired dimensions and mechanical properties changes. During W AAM deposition of the wall structure, a systematic research is carried out by adjusting the interlayer delay from 10 to 30 s. When the delay period is increased from 10 to 30 s, the breadth decreases by 45% and the height increases by 33%. Grain refinement occurs when the interlayer delay duration is increased, resulting in better hardness, phase transformation temperature, compressive strength, and shape recovery behavior. This study shows how the interlayer delay affects the behavior of W AAM-built nickel-titanium alloy (NiTi) structures in a variety of applications.
Compared with most common construction materials, fiber reinforced cementitious materials are well known to exhibit better physical, working and mechanical properties. In this study, three fibers were selected: polypropylene fiber (PPF) and polyvinyl alcohol fiber (PVAF), which represented synthetic fibers, and sisal fiber (SF), which represented natural fibers. Effects of these fibers on the flowability, rheological properties, and adsorption behavior of the cement paste with polycarboxylate superplasticizer (PCE) were investigated. Furthermore, the above experimental results were verified by measuring the contact angle of the fiber with water and PCE solution and the apparent morphology of the fiber. Results revealed that the addition of fibers significantly reduces the fluidity of the cement paste, while the yield stress and plastic viscosity of the cement paste increase with the addition of fibers. From the contact angle and scanning electron microscope, the surface of SF was relatively rough, and the contact angle of SF with water or PCE solution was the smallest. It can be concluded that the plant fiber has a significant influence on the fluidity and rheology of cement paste.
An artificial digestion of silver nitrate is reported. It is shown that AgSCN nanoparticles emerge from ionic silver in saliva and remain present during the entire digestion process. The particles were characterized by infrared spectroscopy and small- and wide-angle X-ray scattering (SAXS/WAXS) regarding their composition and size distribution.
The definition of the term “conversion” is discussed for a variety of polymer syntheses. It is demonstrated that in contrast to organic and inorganic chemistry several different definitions are needed in polymer science. The influence of increasing conversion on structure and topology of homo- and Copolymers is illustrated. Chain-growth polymerizations, such as radical polymerization or living anionic polymerizations of vinyl monomers, condensative chain polymerization, two and three-dimensional step-growth polymerizations, ring–ring or chain–chain equilibration and chemical modification of polymers are considered.
The wireless high-frequency technology requires a robust, cost-effective, and highly integrated substrate technology offering the capability for areas of tailored permittivity. The wet-chemical porosification of low temperature co-fired ceramics (LTCC) substrates offers such an approach by locally embedding air. Porosification of LTCC in both extremely acidic and alkaline media has been investigated in previous works. However, for improving the available knowledge on the porosification of LTCC with H3PO4 as a standard and a widely used etching solution, the impact of solution concentration was systematically investigated and a substantial improvement in the etching performance was achieved. Moreover, in the present study, for the first time, the intermediate pH values, and the impact of pH as a key parameter on the etching process have been investigated. For this purpose, the applicability of phosphate buffer solution (PBS) as a prospective novel etchant mixture for the porosification of a commercially available LTCC tape (Ceramtape GC) was explored. Valuable information about surface morphology, crystalline composition, and the pore structure of the etched LTCCs was gathered employing scanning electron microscopy, transmission electron microscopy, X-ray diffraction analysis, and mercury porosimetry measurements. Based on these findings, the performance of PBS-based etchant systems towards the generation of porous LTCCs combining high depths of porosification with acceptable surface characteristics for subsequent metallization is demonstrated. Based on the obtained results, by application of a 0.2 mol L−1 solution of PBS, the effective relative permittivity of test samples with a thickness of approximately 600 µm and a porosification depth of 186 µm from each side, could be reduced up to 10% of its initial “as fired” value. Also, based on the measurement results and by measuring the depth of porosification, the permittivity of the etched layer was estimated to show a reduction of up to 22% compared to the initial “as fired” value.
High-strength steels are increasingly applied in modern steel constructions to meet today’s lightweight requirements. Welding of these steels demands a profound knowledge of the interactions between the welding process, cooling conditions, heat input, and the resulting metallurgical occurrences in the weld and its vicinity. Additionally, welding stresses may be detrimental for the safety and performance of high-strength steel component welds during fabrication and service, especially due to the high yield ratio. For a development of strategies to adjust welding heat control, all these effects should be considered, to reach a complete exploitation of the high-strength steel potential. In recent researches at BAM, multilayer GMAW experiments were performed with high-strength steels, in which cooling conditions and resulting microstructure were analyzed for varied heat control parameters. The application of a unique 3d-operating testing facility and X-ray diffraction measurements allowed the analysis of local stresses in the weld while welding and cooling under component relevant shrinkage restraints. As a result, correlations between material behavior, welding, and cooling condition and the arising multi-axial stresses and forces were found. Based on this study, statements for the development of adapted heat control concepts were derived, which are presented by means of specific analysis examples.
High-strength steels with yield strengths ≥ 690 MPa are becoming increasingly significant for modern steel constructions. Both quenched and tempered (QT) high-strength steels and steels produced by the thermo-mechanically controlled process (TMCP) are currently available. TMCP-steels are usually provided with a typical mill scale. Apart from the manufacturing process these steels differ also in their chemical composition. The influence of these differences are investigated here with focus on the residual stresses formed during TIG welding. Bead on plate welds have shown characteristic residual stress distributions depending on the type of steel as well as on the heat input and preheat temperature. The following work demonstrates that the fluid flow, induced by the elements present in the mill scale, leads to a deeper penetration of the material. This can also lead to increased residual stresses in the surface of the weld and the HAZ. Furthermore, higher heat input and preheat temperature can induce higher tensile residual stresses − which are evident in the present study.
Welding residual stresses have an impact on the performance of welded structures, on their fracture resistance, their resistance against fatigue crack propagation and, most important, their fatigue strength and fatigue lifetime. The present paper provides an overview on the issue mainly from the point of view of the application of fracture mechanics to the determination of the fatigue strength as the topic of this Special issue. Besides own experimental and theoretical data a comprehensive discussion is provided in that context which includes the definition and interaction of short- and long-range (or reaction) residual stresses, the effect of cyclic mechanical loading and its treatment in fracture and fatigue analyses.
High-entropy alloys (HEAs) and compositionally complex alloys (CCAs) represent new classes of materials containing five or more alloying elements (concentration of each element ranging from 5 to 35 at. %). In the present study, HEAs are defined as single-phase solid solutions; CCAs contain at least two phases. The alloy concept of HEAs/CCAs is fundamentally different from most conventional alloys and promises interesting properties for industrial applications (e.g., to overcome the strength-ductility trade-off). To date, little attention has been paid to the weldability of HEAs/CCAs encompassing effects on the welding metallurgy. It remains open whether welding of HEAs/CCAs may lead to the formation of brittle intermetallics and promote elemental segregation at crystalline defects. The effect on the weld joint properties (strength, corrosion resistance) must be investigated. The weld metal and heat-affected zone in conventional alloys are characterized by non-equilibrium microstructural evolutions that most probably occur in HEAs/CCAs. The corresponding weldability has not yet been studied in detail in the literature, and the existing information is not documented in a comprehensive way. Therefore, this study summarizes the most important results on the welding of HEAs/CCAs and their weld joint properties, classified by HEA/CCA type (focused on CoCrFeMnNi and AlxCoCrCuyFeNi system) and welding process.
The geometry of the melt pool in laser beam welding plays a major role to understand the dynamics of the melt and its solidification behavior. In this study, a butt configuration of 15 mm thick structural steel and transparent quartz glass was used to observe the weld pool geometry by means of high-speed camera and an infrared camera recording. The observations show that the dimensions of the weld pool vary depending on the depth. The areas close to the weld pool surface take a teardrop-shape. A bulge-region and its temporal evolution were observed approximately in the middle of the depth of the weld pool. Additionally, a 3D transient thermal-fluid numerical simulation was performed to obtain the weld pool shape and to understand the formation mechanism of the observed bulging effect. The model takes into account the local temperature field, the effects of phase transition, thermo-capillary convection, natural convection and temperature-dependent material properties up to evaporation temperature. The numerical results showed good accordance and were furthermore used to improve the understanding of the experimentally observed bulging effect.
Self-mated magnesia stabilized zirconia (Mg-PSZ) ceramic sliding couples have been investigated at 100 N load (P0max= 1324 MPa) in oscillating sliding conditions in different humidity conditions in air and in hot steam. Temperatures have been varied up to 400 °C and pressures up to 6 bars. The results show that the wear behavior of MgO-ZrO2 under high Hertzian contact pressures is strongly dependent on temperature and is similar for both dry oscillating and oscillating in hot steam. However, although the evolution in wear rates on temperature is similar and the wear rates of MgO-ZrO2 plunged above 300 °C in hot steam and air by nearly three orders of magnitude, SEM micrographs revealed in hot steam at 400 °C smooth wear tracks. In contrast, hot steam enhanced the tribochemistry of self-mated alumina couples and reduced wear rates. Hot steam decreased the coefficients of friction of MgO-ZrO2 with increasing temperature, but not the wear rates.
Wear behavior of innovative niobium carbide cutting tools in ultrasonic-assisted finishing milling
(2023)
The resources of niobium exceed the ones of tungsten by an order of magnitude. With 92%, Brazil is today the main global producer of niobium. Hence, niobium carbides (NbC) are a sustainable and economic alternative to conventionally used cutting materials, especially tungsten carbides (WC). Moreover, NbC can be used in Ni alloy matrix and thus offer significant advantages by substituting WC in Co matrix as cutting materials in terms of health risks and raw material price and supply risk. Based on recent studies which found an increased performance of NbC compared to WC cutting tools in machining higher strength steels, the composition NbC12Ni4Mo4VC was chosen for finish machining of a high-strength steel S960QL in this study. The experiments were carried out on an ultrasonic-assisted 5-axis milling machine using NbC tools specially made to benchmark them with commercially available coated WC cutting inserts. In addition, the influence of a coating system for the NbC inserts is tested and evaluated for its performance in the cutting process. Tool wear and cutting force analyses are implied to identify optimal parameter combinations as well as tool properties for the novel NbC tool. Together with the oscillation of ultrasonic-assisted milling, the loads on the component surface and the tool can be reduced and the wear behavior of the novel NbC tool can be refined. These milling tests are accompanied by standardized wear tests, i.e., pin-on-disc, between the aforementioned material combinations, and the results are correlated with each other. Finally, the behavior when using hard-to-cut materials such as Ni alloys, or innovative materials such as iron aluminide is also being tested, as these are constantly in the focus of machining optimization. With this strategy, comprehensive knowledge is achievable for future efficient application of NbC for milling tools, which have already been researched for decades using WC.
Water-Soluble Aza-BODIPYs: Biocompatible Organic Dyes for High Contrast In Vivo NIR-II Imaging
(2020)
A simple NIR-II emitting water-soluble system has been developed and
applied in vitro and in vivo. In vitro, the fluorophore quickly accumulated in 2D and 3D cell cultures and rapidly reached the tumor in rodents, showing high NIR-II contrast for up to 1 week. This very efficient probe possesses all the qualities necessary for translation to the clinic as well as for the development of NIR-II emitting materials.
Water is generally considered to be an undesirable substance in fuel system, which may lead to microbial contamination. The antibacterial strategies that can turn water into things of value with high disinfection efficacy have been urgently needed for fuel system. Here, we reveal a water-fueled autocatalytic bactericidal pathway comprised by bi-metal micro-electrode system, which can spontaneously produce reactive oxygen species (mainly H2O2 and O2•–) by the electron Fenton-like reaction in water medium without external energy., The respiratory chain component of bacteria and the galvanic corrosion on the coated metals were two electron sources in the system. The specific model of Ag-Ru water-fueled autocatalytic (WFA) microelectrode particles presents extremely high disinfection efficiency (>99.9999%) in less than one hour for three aerobic bacteria (Escherichia coli, Pseudomonas aeruginosa and Bacillus subtilis) in LB media and high disinfection efficiency for the anaerobic bacteria (Desulfovibrio alaskensis) in Postgate E media without natural light irradiation. Overall, the novel WFA Ag-Ru antibacterial material explored in this study has a high potential for sterilizing applications in fuel system and this work provides the potential for the development of non-chemical and water-based antibacterial materials, such as WFA Ag-Ru antibacterial coating on stainless steel.
In the present study we have investigated whether the effect of water on properties of borate glasses resembles that of alkali oxide. Soda-lime-borate glasses with nominal compositions of x Na2O, 10 CaO, (90-x) B2O3 (x = 5, 15 and 25 mol%) were doped with up to 8 wt.% H2O by processing glass powder + distilled water in platinum capsules in an internally heated gas pressure vessel at 1523 K and 500 MPa. The water content of hydrous glasses was determined by Karl-Fischer titration and near-infrared spectroscopy. The glass transition temperature T-g. was derived from DTA and micropenetration experiments for which the effect of water loss at the surface of the hydrous glasses was studied. Heating glass samples at 10 K min(-1) in the DTA resulted in T-g values which are close to T-12 isokom temperatures confirming the equivalence of enthalpy relaxation and viscous relaxation for borate glasses. For all three glass series it is shown that T-g strongly decreases whereas the liquid fragility strongly increases upon the addition of water. These findings reveal that H2O primarily causes breaking of B-O-B bonds rather than supporting 4-fold coordinated boron as it is well-known for alkali oxides in this concentration range. (C) 2015 Elsevier B.V. All rights reserved.
Water migration in one-side heated concrete: 4D in-situ CT monitoring of the moisture-clog-effect
(2019)
Explosive spalling due to fire exposure in concrete structures can lead severe damage and, in the worst case, to premature component failure. For this reason, an in situ investigation of water Migration in concrete due to surface heating was undertaken.
During these experiments, a miniaturized concrete specimen within a confining and insulating double-hull was subjected to surface heating during simultaneous X-ray computed tomography (CT) scanning. Through the use of subtraction-based Image analysis techniques, it was possible to observe and quantify not only drying within areas of the concrete matrix close to the heated surface, but also the migration of moisture to both pore and matrix regions deeper within the specimen. It was also discovered that the correction of CT images for specimen deformation using DVC and variable detector performance using calibrated image filters significantly improved the quality of the results. This clearly demonstrates the potential of X-ray CT for evaluation of other rapid-density-change phenomena in concrete and other building materials.
To understand the influence of water and alkalis on aluminosilicate glasses, three polymerized glasses with varying ratios of Na/K were synthesized [(22. 5-x)Na2O-xK2O-22.5 Al2O3-55 SiO2 with x = 0, 7.5, and 11.25]. Subsequently, these glasses were hydrated (up to 8 wt% H2O) in an internally heated gas pressure vessel. The density of hydrous glasses linearly decreased with water content above 1 wt%, consistent with the partial molar volume of H2O of 12 cm3/mol. Near-infrared spectroscopy revealed that hydroxyl groups are the dominant species at water content of <4 wt%, and molecular water becomes dominating at water content of >5 wt%. The fraction of OH is particularly high in the pure Na-bearing glass compared to the mixed alkali glasses. 27Al magic angle spinning-NMR spectroscopy shows that aluminum is exclusively fourfold coordinated with some variations in the local geometry. It appears that the local structure around Al becomes more ordered with increasing K/Na ratio. The incorporation of H2O reinforces this effect. The differential thermal analysis of hydrous glasses shows a significant mass loss in the range of glass transition already during the first upscan, implying the high mobility of water in the glasses. This observation can be explained by the open structure of the aluminosilicate network and by the low dissociation enthalpy of H2O in the glasses (≈ 8 kJ/mol). The effect of the dissolved H2O on the glass transition temperature is less pronounced than for other aluminosilicate glasses, probably because of the large fraction of Al in the glasses.
We present a first direct measurement of the temperature during milling combined with in situ Raman spectroscopy monitoring. The data reveal a low temperature increase due to the mechanical impact and clear temperature increases as a consequence of the reaction heat. Based on the data, temperature rises as postulated in the magma plasma and hot spot theory can be excluded for soft matter milling syntheses.
Offshore wind turbines (OWT) are a major goal of the energy strategy of Germany encompassing the increase of the installed wind power. OWT components are manufactured from welded steel plates with thicknesses up to 200 mm. The underlying standards and technical recommendations for construction of OWTs encompass specifications of so-called minimum waiting time (MWT) before non-destructive testing of the weld joints is allowed. Reason is the increased risk of time-delayed hydrogen assisted cold cracking as hydrogen diffusion is very slow due to the very thick plates. The strict consideration of those long MWT up to 48 h during the construction of OWTs leads to significant financial burden (like disproportionately high costs for installer ships as well as storage problems (onshore)). In this study, weld joints made of S355 ML were examined in comparison with the offshore steel grade S460 G2+M. The aim was to optimize, i.e., reduce, the MWT before NDT considering varied heat input, hydrogen concentration and using self-restraint weld tests. This would significantly reduce the manufacturing time and costs of OWT construction. To quantify the necessary delay time until hydrogen-assisted cold cracks appear, acoustic emission analysis was applied directly after welding for at least 48 h.
Despite considerable advances in synthesizing high-quality core/shell upconversion (UC) nanocrystals (NC; UCNC) and UCNC photophysics, the application of near-infrared (NIR)-excitable lanthanide-doped UCNC in the life and material sciences is still hampered by the relatively low upconversion luminescence (UCL) of UCNC of small size or thin protecting shell. To obtain deeper insights into energy transfer and surface quenching processes involving Yb3+ and Er3+ ions, we examined energy loss processes in differently sized solid core NaYF4 nanocrystals doped with either Yb3+ (YbNC; 20% Yb3+) or Er3+ (ErNC; 2% Er3+) and co-doped with Yb3+ and Er3+ (YbErNC; 20% Yb3+ and 2% Er3+) without a surface protection shell and coated with a thin and a thick NaYF4 shell in comparison to single and co-doped bulk materials. Luminescence studies at 375 nm excitation demonstrate backenergy transfer (BET) from the 4G11/2 state of Er3+ to the 2F5/2 state of Yb3+, through which the red Er3+ 4F9/2 state is efficiently populated. Excitation power density (P)-dependent steady state and time-resolved photoluminescence measurements at different excitation and emission wavelengths enable to separate surface-related and volume-related effects for two-photonic and threephotonic processes involved in UCL and indicate a different influence of surface passivation on the green and red Er3+ emission.
The intensity and lifetime of the latter respond particularly to an increase in volume of the active UCNC core. We provide a threedimensional random walk model to describe these effects that can be used in the future to predict the UCL behavior of UCNC.
Emission testing of volatile organic compounds (VOC) from materials and products is commonly based on emission test chamber measurements. To ensure the comparability of results from different testing laboratories, their measurement performance must be verified. For this purpose, Bundesanstalt für Materialforschung und -prüfung (BAM) organizes an international proficiency test (round robin test, RRT) every two years using well-characterized test materials (one sealant, one furniture board, and four times a lacquer) with defined VOC emissions. The materials fulfilled the requirements of homogeneity, reproducibility, and stability. Altogether, 36 VOCs were included of which 33 gave test chamber air concentrations between 13 and 83 µg/m3. This is the typical concentration range to be expected and to be quantified when performing chamber tests. Three compounds had higher concentrations between 326 and 1105 µg/m3. In this paper, the relative standard deviations (RSD) of BAM round robin tests since 2008 are compared and the improvement of the comparability of the emission chamber testing is shown by the decrease of the mean RSD down to 28 % in 2018. In contrast, the first large European interlaboratory comparison in 1999 showed a mean RSD of 51 %.
Visualization of surface modifications may be very challenging for coating/substrate systems of either almost identical optical constants, e.g. transparent films on substrates of the same material, or minor film thickness, substance quantity and affected area, e.g. ultra-thin or island films. Methods for visualization are optical microscopy (OM), imaging ellipsometry (IE), and referenced spectroscopic ellipsometry (RSE). Imaging ellipsometry operates at oblique incidence near Brewster angle of the bare, clean or unmodified substrate. In this configuration, reflected intensities are rather weak. However, the contrast to add-on and sub-off features may be superior. Referenced spectroscopic ellipsometry operates in a two-sample configuration but with much higher intensities. In many cases, both ellipsometric techniques reveal and visualize thin films, printed-pattern, laser-induced changes, and impurities better than optical microscopy. In particular for stratified homogeneous modifications, ellipsometric techniques give access to modelling and hence thickness determination. Modifications under investigation are polymer foil residue on silicon, laser-induced changes of ta-C:H coatings on 100Cr6 steel, imperfections of ta-C:H on thermal silicon oxide, degradation of glass, thin film tin oxide pattern on silicon, printed and dried pattern of liquids such as deionized water, cleaning agents, and dissolved silicone. © 2016 Elsevier B.V. All rights reserved.