Geometric imperfections of additive manufactured members. - In: Engineering structures, ISSN 0141-0296, Bd. 252 (2022), 113596
Challenges in civil engineering and construction industries increase, and simultaneously it is necessary to provide a sustainable utilization of resources. Optimising material applications and manufacturing processes is therefore essential for modern constructions. Highly optimised structural components are already in use in lightweight constructions as well as in aircraft and vehicle industries. In the course of digitisation, new possibilities have evolved in recent years for producing individual and optimized solutions with regard to the consumption of materials, especially in construction industries. Methods of generative or additive manufacturing are employed to develop various prototypes of structural components. In this context, Wire-Arc-Additive-Manufacturing (WAAM) is a promising method for steel structures. However, it remains to be investigated to what extent dimensional accuracy, surface finish, weld quality and repeated thermal influences from the build-up process affect the structural behaviour of corresponding members. This paper deals with the geometric imperfections of corresponding additively manufactured profiles and exemplifies their influence on the bearing capacity.
https://doi.org/10.1016/j.engstruct.2021.113596
In-process range-resolved interferometric (RRI) 3d layer height measurements for wire + arc additive manufacturing (WAAM). - In: Measurement science and technology, ISSN 1361-6501, Bd. 33 (2022), 4, 044002, S. 1-12
In this work a range resolved interferometry (RRI) instrument for absolute distance measurements is integrated into a wire + arc additive manufacturing (WAAM) system to provide in-process monitoring of layer height, and prospects for volume and profile monitoring are discussed. Interferometry as a coherent optical technique offers a straightforward in-process measurement even in the harsh welding environment, as compared to non-coherent techniques based either on laser profiling or camera vision systems. RRI can be accomplished at significantly lower cost, and with higher depth of field (up to 10s of cm) than existing optical coherence tomography based weld monitoring. In this experiment titanium feedstock was used to create a 150mm long, 13.5mm high weld-wall comprised of 11 welded layers. The RRI in-process measurements are in very good agreement with both mid-process, on-machine micrometer measurements taken by hand after each weld, and post-process laser scanning measurements of the completed wall. The high depth of field allows direct referencing of the layer height measurements to the build plate making the measurement independent of the motion system and build plate bending, considerably lowering uncertainties. This, together with the capability for cost-effective in-process measurements in harsh environments, should make the proposed approach very interesting for routine use in WAAM systems.
https://doi.org/10.1088/1361-6501/ac440e
Multiple intensity reference interferometry for the correction of sub-fringe displacement non-linearities. - In: Measurement science and technology, ISSN 1361-6501, Bd. 33 (2022), 2, 025201, S. 1-12
Displacement measuring interferometers, commonly employed for traceable measurements at the nanoscale, suffer from non-linearities in the measured displacement that limit the achievable measurement uncertainty for microscopic displacements. Two closely related novel non-linearity correction methodologies are presented here that allow for the correction of non-linearities in cases where the displacement covers much less than a full optical fringe. Both corrections have been shown, under ideal conditions, to be capable of reducing all residual non-linearity harmonics to below the 10 pm level.
https://doi.org/10.1088/1361-6501/ac3aad
An investigation on the heat dissipation in Zn-substituted magnetite nanoparticles, coated with citric acid and pluronic F127 for hyperthermia application. - In: Physica, ISSN 1873-2135, Bd. 625 (2022), 413468
Zinc substituted spinel ferrite nanoparticles are appropriate for magnetic fluid hyperthermia. Stable suspensions of Zn2+ substituted magnetite (ZnxFe3-xO4, 0 ≤ x ≤ 0.20) nanoparticles in aqueous solutions (pH 5.5) were synthesized by means of co-precipitation approach, using citric acid (CA) and pluronic F127 as surfactants for hyperthermia application. The specimens were characterized by different methods. XRD patterns of the precipitates confirmed that all specimens have single phase cubic spinel structures and their lattice parameters increased as Zn2+ content increased. Mean crystallite sizes of the uncoated specimens were determined to be around 28 nm, using Scherrer's formula. By increasing the Zn2+ content, Curie temperature of the uncoated specimens reduced from 545 to 410 ˚C monotonically caused by reduction in super-exchange interactions. Room temperature saturation magnetizations of the uncoated specimens increased to 98.8 emu/g for x = 0.10 initially, and then decreased to 79.6 emu/g for x = 0.20. It is attributed to the replacement of paramagnetic Fe3+ ions by diamagnetic Zn2+ ones and spin canting. FTIR spectra reconfirmed formation of pure magnetite and Zn2+ substituted magnetite nanoparticles and also proved the presence of ligands on the surface of the nanoparticles. TEM investigation showed that mean particle sizes of the coated nanoparticles were in the range of 35-40 nm. The obtained ferrofluids showed a good stability in aqueous medium (pH 5.5) and according to the room temperature magnetic measurements, heating efficiency is scarcely released due to relaxation processes. Maximum obtained specific loss power (SLP) was 539 W/g and that of intrinsic loss power (ILP) was 7.26 nHm2/kg for x = 0.05 (f = 290 kHz, H = 16 kA/m) with a nanoparticle concentration as low as 1.2 mg/ml, which is a promising candidate for magnetic hyperthermia applications potentially.
https://doi.org/10.1016/j.physb.2021.413468
A highly robust self-supporting nickel nanoarray based on anodic alumina oxide template for determination of dopamine. - In: Sensors and actuators, ISSN 0925-4005, Bd. 350 (2022), 130835
Ratiometric electrochemical sensors can effectively reduce system errors and environmental interference during the detection of a target, affording good sensitivity, reproducibility, and a linear response range. However, traditional proportional electrochemical sensors are limited by the need for complex modifications and the lack of internal reference probes. In this study, we developed a ratiometric electrochemical sensing platform based on nickel nanoarrays as a self-supporting electrode (NiNASSE) by using an anodic alumina oxide template method. An internal reference probe was developed based on nickel nanoparticles (NiNPs) as nickel nanoarrays, presenting a facile modification process and stable redox signal. Furthermore, the highly ordered nanoarray structure expands the specific surface area of NiNASSE and accelerates the electron transfer rate. This new self-supporting proportional electrochemical sensor was successfully applied for the detection of dopamine and displayed good electrocatalytic ability, stability, and feasibility.
https://doi.org/10.1016/j.snb.2021.130835
Yttrium and rare-earth modified lithium orthoborates: glass formation and vibrational activity. - In: Journal of non-crystalline solids, ISSN 0022-3093, Bd. 575 (2022), 121152
Glass formation and structure-property relations were explored in highly modified borate glasses containing high loads of rare-earth elements, whose crystalline analogues display a trigonal to tetrahedral borate phase transition (BO33- -> BØ2O23-, where Ø and O- indicate bridging and non-bridging oxygen atoms). The resulting borate networks are completely depolymerized, where borate anions are crosslinked to rare-earth and modifier cations via ionic bonds. The borate structure was found to be based on a single structural unit, BO33- triangles, whose fundamental vibrations are all active in both the Raman and infrared. The local environment of the rare-earth ions in orthoborate glasses was studied with far infrared spectroscopy and, in some cases, by using terbium as a probe ion. A linear correlation was obtained between the effective force constant in the far infrared and the field strength of the rare-earth cation.
https://doi.org/10.1016/j.jnoncrysol.2021.121152
Luminescence-site symmetry correlations in Dy3+ doped alkali-alkaline earth orthoborates of the type XZBO3 with X = Li, Na, K and Z = Mg, Ca, Ba. - In: Journal of luminescence, ISSN 0022-2313, Bd. 241 (2022), 118429, S. 1-12
A systematic investigation of the luminescence properties of Dy3+ doped alkali-alkaline earth orthoborates of the stoichiometric composition XZBO3 with X = Li, Na, K and Z = Mg, Ca, Ba was conducted. XRD diffractograms show that the compounds LiMgBO3, LiCaBO3, LiBaBO3, NaMgBO3, NaCaBO3, NaBaBO3, and KMgBO3 could be produced in high purity. Relatively intense luminescence was observed only for the phases LiCaBO3, NaMgBO3, NaCaBO3 and NaBaBO3. Micro Raman investigations show that the Dy3+ luminesence mainly originates from the orthoborate phase in these samples. Photo-luminescence spectroscopy of LiCaBO3, NaCaBO3 and NaBaBO3 shows the typical Dy3+ emission with the prominent emission peak in the yellow spectral range around 575 nm. A second, but much less intense peak is observed at around 485 nm (cyan). The luminescence emission spectrum of Dy3+:NaMgBO3 is much different: here, the highest emission intensity is observed at about 485 nm. It is proposed that the Dy3+ ions occupy the Na positions in this crystal phase which has a much higher symmetry than the alkaline earth positions in the other examined crystal phases. This is supported by broadened and more split up peaks in the excitation and emission spectra of Dy3+:NaMgBO3 suggesting a much stronger local crystal field at the rare earth position in this compound. The results are additionally compared to spectroscopic data of different well known Dy3+ doped crystalline compounds and Dy3+ and Eu3+ doped alkali-alkaline earth orthoborates from other publications, which offer further insight into the relation between the crystallographic sites of the doped rare earth ions and their luminescence.
https://doi.org/10.1016/j.jlumin.2021.118429
Construction of Co0.85Se@nickel nanopores array hybrid electrode for high-performance asymmetric supercapacitors. - In: Chemical engineering science, Bd. 247 (2022), 117081, insges. 9 S.
Nanostructured current collectors have larger specific surface area and short ion/electron transport path, which are highly desirable for supercapacitors applications. Herein, Co0.85SeNiNPs (Co0.85Se@NiNP) hybrid electrodes are proposed and fabricated, in which NiNP is served as nanostructured current collectors. NiNP has a vertical pore structure and a large specific surface area, which could effectively promote the ion/electron transport efficiency and reduce internal electrical resistance. Compared with Ni foam and Ni foil as current collectors, NiNP enables Co0.85Se@NiNP electrodes show significantly improved specific capacity, rate performance and cycle stability. Finally, an asymmetric supercapacitor device was assembled with Co0.85Se@NiNP hybrid electrode as the binder-free positive electrode and activated carbon (AC) coated on nickel foam as negative electrode. The Co0.85Se@NiNP//AC asymmetric supercapacitors can work in a wide potential window of 0 - 1.6 V with an ultrahigh specific capacity of 182.3 F g^-1 at 1 A g^-1. Most importantly, Co0.85Se@NiNP//AC has a high energy density of 64.81 Wh kg^-1 at 800 W kg^-1 and an outstanding cycle stability of up to 12000 cycles, indicating that Co0.85Se@NiNP electrode has great application potential in supercapacitors.
https://doi.org/10.1016/j.ces.2021.117081
Hybrid nanomaterials of biomolecule corona coated magnetic nanoparticles and their interaction with biological systems. - In: Physical sciences reviews, ISSN 2365-659X, Bd. 7 (2022), 11, S. 1311-1344
Magnetic nanoparticles (MNPs) are interesting for various applications in medicine. If administered to a biological system like the human body, a so-called biomolecule corona is formed on the surface of the particles, which highly determines the biological fate of the particles. To elucidate whether a preconditioning of the MNPs by incubation with biomolecules influences biocompatibility and bioavailability, the formation of such a corona was investigated in more detail. For this, the influence of particle characteristics, e.g., surface charge, as well as various incubation parameters on the resulting corona was investigated. It was found that the biomolecule corona is formed immediately after bringing together the particles with the biomolecule source. By variation of the biomolecule content of the incubation medium, the size of the corona can be modulated. Regarding the interaction of the nanoparticles with cells, it was shown that the presence of a biomolecule corona reduces the interaction and that a more pronounced biomolecule corona leads to a reduced uptake of the magnetic nanohybrids into the cells. Cell viability tests confirmed biocompatibility of the biomolecule-coated particles. A more pronounced corona promotes a higher cell viability. By using a shell-less hen's egg model, no or reduced adverse effects of all biomolecule-coated MNP for this in vivo test were found. Resulting from these investigations, we were able to demonstrate that our newly developed nanohybrids significantly reduce in vivo toxicity compared to uncoated MNPs.
https://doi.org/10.1515/psr-2019-0110
Magnetic hybrid materials interact with biological matrices. - In: Physical sciences reviews, ISSN 2365-659X, Bd. 7 (2022), 12, S. 1443-1500
Magnetic hybrid materials are a promising group of substances. Their interaction with matrices is challenging with regard to the underlying physical and chemical mechanisms. But thinking matrices as biological membranes or even structured cell layers they become interesting with regard to potential biomedical applications. Therefore, we established in vitro blood-organ barrier models to study the interaction and processing of superparamagnetic iron oxide nanoparticles (SPIONs) with these cellular structures in the presence of a magnetic field gradient. A one-cell-type-based blood-brain barrier model was used to investigate the attachment and uptake mechanisms of differentially charged magnetic hybrid materials. Inhibition of clathrin-dependent endocytosis and F-actin depolymerization led to a dramatic reduction of cellular uptake. Furthermore, the subsequent transportation of SPIONs through the barrier and the ability to detect these particles was of interest. Negatively charged SPIONs could be detected behind the barrier as well as in a reporter cell line. These observations could be confirmed with a two-cell-type-based blood-placenta barrier model. While positively charged SPIONs heavily interact with the apical cell layer, neutrally charged SPIONs showed a retarded interaction behavior. Behind the blood-placenta barrier, negatively charged SPIONs could be clearly detected. Finally, the transfer of the in vitro blood-placenta model in a microfluidic biochip allows the integration of shear stress into the system. Even without particle accumulation in a magnetic field gradient, the negatively charged SPIONs were detectable behind the barrier. In conclusion, in vitro blood-organ barrier models allow the broad investigation of magnetic hybrid materials with regard to biocompatibility, cell interaction, and transfer through cell layers on their way to biomedical application.
https://doi.org/10.1515/psr-2019-0114