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Der Frequenzbereich der Terahertzwellen liegt im elektromagnetischen Spektrum zwischen den Mikrowellen und dem infraroten Licht – also etwa im Bereich von 0,1 bis 10 Terahertz (THz). Der VDI-Statusreport „Terahertzsysteme und Anwendungen“ stellt die unterschiedlichen Konzepte für Terahertzsysteme vor und zeigt Anwendungsbeispiele, bei denen die Terahertztechnik erfolgreich eingesetzt wird. Umfangreiche Literaturangaben ermöglichen eine intensivere Beschäftigung mit allen Themen des VDI-Statusreports.
he mutual influence of F and OH groups in neighboring sites in topaz (Al2SiO4(F,OH)2) was investigated using magic angle spinning nuclear magnetic resonance (MAS NMR) and Raman spectroscopy. The splitting of 19F and 1H NMR signals, as well as the OH Raman band, provides evidence for hydrogen bond formation within the crystal structure. Depending on whether a given OH group has another OH group or fluoride as its neighbor, two different hydrogen bond constellations may form: either OH···O···HO or F···H···O. The proton accepting oxygen was determined to be part of the SiO4 tetrahedron using 29Si MAS NMR. Comparison of the MAS NMR data between an OH-bearing and an OH-free topaz sample confirms that the 19F signal at −130 ppm stems from F− ions that take part in H···F bonds with a distance of ∼ 2.4 Å, whereas the main signal at −135 ppm belongs to fluoride ions with no immediate OH group neighbors. The Raman OH sub-band at 3644 cm−1 stems from OH groups neighboring other OH groups, whereas the sub-band at 3650 cm−1 stems from OH groups with fluoride neighbors, which are affected by H···F bridging. The integrated intensities of these two sub-bands do not conform to the expected ratios based on probabilistic calculations from the total OH concentration. This can be explained by a difference in the polarizability of the OH bond between the different hydrogen bond constellations or partial order or unmixing of F and OH, or a combination of both. This has implications for the quantitative interpretation of Raman data on OH bonds in general and their potential use as a probe for structural (dis-)order. No indication of tetrahedrally coordinated Al was found with 27Al MAS NMR, suggesting that the investigated samples likely have nearly ideal Al/Si ratios, making them potentially useful as high-density electron microprobe reference materials for Al and Si, as well as for F.
A flexible, sustainable, one-step thermal decomposition route for the synthesis of hierarchical, heteroatom doped carbon foams is presented. Task-specific semi-organic crystals combine functions for three different purposes: the carbon and heteroatom source, a foaming agent (CO2) and an in situ generable template (NaCl). Insights to the decomposition pathway were gained through FTIR/MS coupled TGA and an ultrafast out-of-furnace heating procedure and the products were analysed with (HR)SEM/TEM, EELS, FTIR, and N2 sorption. The resulting macroporous carbon foams are excellent supports for metallic nanoparticles due to their hierarchical structure, high surface area and tuneable heteroatom contents. This was demonstrated for catalytically active copper or the magnetic CoNi alloy for water purification.
The rhodium(I) and iridium(I) complexes [M(Cl){ArN=C(H)C(H)=NAr}(CNtBu)] (1: M = Rh, Ar = 2,6-iPr2C6H3; 2: M = Rh, Ar = Mes; 3: M = Ir, Ar = Mes; Mes = 2,4,6-Me3C6H2) have been prepared by the reaction of [M(µ-Cl)(coe)2]2 (M = Rh, Ir; coe = cyclooctene) with the α-dialdimines ArN=C(H)C(H)=NAr (Ar = 2,6-iPr2C6H3, Mes) in thf, followed by the addition of CNtBu. XANES spectra and DFT calculations on 2 and 3 suggest an oxidation state +I at the metal centers. Treatment of the complexes 2 and 3 with O2 or 18O2 gave the peroxido complexes [M(Cl)(O2){MesN=C(H)C(H)=NMes}(CNtBu)] (4a: M = Rh; 5a: M = Ir) and [M(Cl)(18O2){MesN=C(H)C(H)=NMes}(CNtBu)] (4b: M = Rh; 5b: M = Ir). The reaction of 3 with dihydrogen resulted in the formation of the iridium dihydrido complex [Ir(Cl)(H)2{MesN=C(H)C(H)=NMes}(CNtBu)] (6a). Two isomeric α-imine-amine complexes [Ir(Cl)(H)2{MesN(H)CH2C(H)=NMe}(CNtBu)] (7/7') were obtained after prolonged reaction under H2. All of the complexes were characterized by NMR and IR spectroscopy. In addition, complexes 2, 3,and 7 were characterized by X-ray crystallography.
Chemical derivatization XPS is used for the quantitative determination of amines at conventional organic surfaces, and it is also applied to plasma-processed aminated surfaces. When using TFBA and PFB as derivatization reagents for tagging primary amino groups, unexpected fluorine species were observed in the second case. The existence of reaction pathways other than those expected for amine derivatization with PFB or TFBA has to be assumed. This phenomenon is tentatively interpreted as the result of C—F bond cleavage during derivatization reactions of TFBA and PFB at plasma-polymerized allylamine and other plasma-processed aminated surfaces. As a consequence, quantification procedures based on derivatization by PFB or TFBA will underestimate amine surface concentrations.
In this study, carried out within the Joint Danube Survey 4, a comprehensive microplastic screening in the water column within a large European river basin from its source to estuary, including major tributaries, was realized. The objective was to develop principles of a systematic and practicable microplastic monitoring strategy using sedimentation boxes for collection of suspended particulate matter followed by its subsequent analysis using thermal extraction desorption-gas chromatography/mass spectrometry. In total, 18 sampling sites in the Danube River Basin were investigated. The obtained suspended particulate matter samples were subdivided into the fractions of >100 μm and <100 μm and subsequently analyzed for microplastic mass contents. The results showed that microplastics were detected in all samples, with polyethylene being the predominant polymer with maximum contents of 22.24 μg/mg, 3.23 μg/mg for polystyrene, 1.03 μg/mg for styrene-butadiene-rubber, and 0.45 μg/mg for polypropylene. Further, polymers such as different sorts of polyester, polyacrylates, polylactide, and natural rubber were not detected or below the detection limit. Additional investigations on possible interference of polyethylene signals by algae-derived fatty acids were assessed. In the context of targeted monitoring, repeated measurements provide more certainty in the interpretation of the results for the individual sites. Nevertheless, it can be stated that the chosen approach using an integrative sampling and determination of total plastic content proved to be successful.
In line with the industrial trend of additive manufacturing, cold spray as a non-laser-based process is becoming increasingly important for many fields of application. For the evaluation of additive manufacturing of winding components made of copper for large electrical high-voltage machines, material and component properties such as electrical conductivity, mechanical load capacity and the component size that can be produced are of particular importance. In this context, the cold spray process offers advantages over laser-based additive manufacturing processes such as laser powder bed fusion (LPBF) or laser cladding by using the kinetic energy of the copper powder particles to generate particle cohesion. To investigate the electrical conductivity as well as the mechanical load capacity of cold spray parts, specimens were machined out of cold sprayed bulk copper deposits. The characteristic values were obtained with regard to the direction of deposition, which is defined by the direction of the robot’s movement. Thus, for the investigation of the component properties, specimens were provided that had been produced both longitudinally and transversely as well as orthogonally to the direction of deposition. The results of the investigations show that both the electrical conductivity and the mechanical load capacity of the specimen have a strong preferential direction of the specimen orientation with respect to the direction of deposition. Furthermore, it could be shown that by increasing the deposition height, there is an increasing oxygen content in the sample material, combined with increasingly significant defect networks. These effects have a negative impact on the electrical conductivity as well as on the mechanical load capacity. As a conclusion, further need for investigation is identified in the optimization of the process parameters as well as in the deposition strategy for the additive manufacturing of large-volume components with cold spray.
In line with the industrial trend of additive manufacturing, cold spray as a non-laser-based process is becoming increasingly important for many fields of application. For the evaluation of additive manufacturing of winding components made of copper for large electrical high-voltage machines, material and component properties such as electrical conductivity, mechanical load capacity and the component size that can be produced are of particular importance. In this context, the cold spray process offers advantages over laser-based additive manufacturing processes such as laser powder bed fusion (LPBF) or laser cladding by using the kinetic energy of the copper powder particles to generate particle cohesion. To investigate the electrical conductivity as well as the mechanical load capacity of cold spray parts, specimens were machined out of cold sprayed bulk copper deposits. The characteristic values were obtained with regard to the direction of deposition, which is defined by the direction of the robot’s movement. Thus, for the investigation of the component properties, specimens were provided that had been produced both longitudinally and transversely as well as orthogonally to the direction of deposition. The results of the investigations show that both the electrical conductivity and the mechanical load capacity of the specimen have a strong preferential direction of the specimen orientation with respect to the direction of deposition. Furthermore, it could be shown that by increasing the deposition height, there is an increasing oxygen content in the sample material, combined with increasingly significant defect networks. These effects have a negative impact on the electrical conductivity as well as on the mechanical load capacity. As a conclusion, further need for investigation is identified in the optimization of the process parameters as well as in the deposition strategy for the additive manufacturing of large-volume components with cold spray.
Tire and road wear particles (TRWPs) are heteroagglomerates of tire rubber and other particles deposited on the road surface and one of the main contributors to non-exhaust emissions of automobile traffic. In this study, samples from road environments were analyzed for their TRWP contents and concentra- tions of eight organic tire constituents. TRWP concentrations were determined by quantifying Zn in the density fraction < 1.9 g/cm ³and by thermal extraction desorption-gas chromatography-mass spectrometry (TED-GC/MS) and the concentrations ranged from 3.7 to 480 mg TRWP/g. Strong and statistically signif- icant correlations with TRWPs were found for 2-hydroxybenzothiazole and 2-aminobenzothiazole, indi- cating that these substances may be suitable markers of TRWPs. The mass distribution of TRWPs in road dust suggests that the main mass fraction formed on roads consists of coarse particles ( > 100 μm). Data for a sedimentation basin indicate that the fine fraction ( < 50 μm) is preferentially transported by road runoffinto receiving waters. The size distribution and density data of TRWP gathered by three different quantitation approaches also suggest that aging of TRWPs leads to changes in their particle density. An improved understanding of the dynamics of TRWP properties is essential to assess the distribution and dissipation of this contaminant of emerging concern in the environment.