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- Chemieingenieurwesen (CIW) (331) (entfernen)
Ab initio calculation of the attempt frequency of oxygen diffusion in pure and samarium doped ceria
(2017)
The Effect of Ionic Defect Interactions on the Hydration of Yttrium-Doped Barium Zirconate, Phys
(2021)
Kinetic Monte Carlo Simulations for Solid State Ionics: Case Studies with the MOCASSIN Program, Diff
(2021)
This study investigated the ability of electrically conductive carbon rovings to detect cracks in textile-reinforced concrete (TRC) structures. The key innovation lies in the integration of carbon rovings into the reinforcing textile, which not only contributes to the mechanical properties of the concrete structure but also eliminates the need for an additional sensory system, such as strain gauges, to monitor the structural health. Carbon rovings are integrated into a grid-like textile reinforcement that differs in binding type and dispersion concentration of the styrene butadiene rubber (SBR) coating. Ninety final samples were subjected to a four-point bending test in which the electrical changes of the carbon rovings were measured simultaneously to capture the strain. The mechanical results show that the SBR50-coated TRC samples with circular and elliptical cross-sectional shape achieved, with 1.55 kN, the highest bending tensile strength, which is also captured with a value of 0.65 Ω by the electrical impedance monitoring. The elongation and fracture of the rovings have a significant effect on the impedance mainly due to electrical resistance change. A correlation was found between the impedance change, binding type and coating. This suggests that the elongation and fracture mechanisms are affected by the number of outer and inner filaments, as well as the coating.
Crystallographic and Photoluminescence Studies on the Solid Solution Li3Ba2La3–xPrx(WO4)8 (x = 0-3
(2022)
Spectroscopic Studies on Pr3+ Doped LuPO4 and YPO4 upon VUV and Synchrotron Radiation Excitation
(2022)
UV emitting nanoparticles enhance the effect of ionizing radiation in 3D lung cancer spheroids
(2022)
Bridging the scales in high-throughput dielectrophoretic (bio-)particle separation in porous media
(2018)
Contact Forces between Single Metal Oxide Nanoparticles in Gas-Phase Applications and Processes
(2017)
Advances in scalable gas-phase manufacturing and processing of nanostructured solids: A review
(2017)
Transfer of highly porous nanoparticle layers to various substrates through mechanical compression
(2013)
A new approach to determine the elements carbon, hydrogen, nitrogen and oxygen (CHNO) in polymers by wavelength-dispersive X-ray fluorescence analysis (WDXRF) in combination with partial least squares (PLS) regression was explored. The quantification of CHNO was achieved by using the Rayleigh and Compton scattering spectra of an Rh X-ray tube from 84 different polymers. Concealed differences of the corresponding scattering spectra could be utilized to quantify CHNO in a multivariate manner. It was shown that the developed model was capable of determining these commonly non-measurable matrix elements in polymers using WDXRF. Furthermore, the influence of spectral resolution, which is given by the collimator and the crystal, on the prediction of CHNO was explored in this study. It was found that minimal spectral resolution led to the most accurate CHNO predictions. Information about matrix composition could be used to improve so-called semi-quantitative XRF methods based on fundamental parameters (FP) for the analysis of plastics, soil or other samples with high organic content.
The design of anion-sensitive probes with sufficient sensitivity and selectivity is a demanding task in analytical sciences and chemical sensor technology. The reversible binding of anions to lanthanide centers is a possible approach for the development of molecular anion sensors, as reversibility is a prerequisite for continuous sensing and monitoring of enzymatic reactions. Some anion species lead to a strong increase of luminescence intensities and lifetimes by the replacement of luminescence quenching water molecules, though the selectivity of the luminescence response is still a major problem. We synthesized a series of positively charged pyridyl-based multidentate europium complexes (five-, four- and three dentate) including sensitizing chromophores and studied their luminescence intensity and lifetime responses to different polyphosphates, pyrophosphate, phosphate anions, and carboxyanions. The results revealed that the number and symmetry of the binding sites have a significant impact on the response. The five-dentate complex was used for the real-time monitoring of the activity of the ATP hydrolyzing enzyme apyrase.
In this communication a novel concept for pH sensing is introduced which is specifically adapted to monitor carbonation induced corrosion in concrete structures. The method is based on a ratiometric measurement principle, exploiting the pH sensitive colour switching of thymol blue in the basic pH regime and the emissive properties of two different (Zn)CdSe/ZnS core shell quantum dots. The transition point of thymol blue in a Hydrogel D4 matrix was determined to be at around pH 11.6, which fits ideally to the intended application. Next to the fundamental spectroscopic characterization of the ratiometric response, a new design for a sensor head, suitable for the incorporation into concrete matrices is presented. Toward this, a manufacturing process was developed which includes the preparation of a double layer of polymers containing either thymol blue or a quantum dot mixture inside a porous ceramic tube. Results of a proof-of-priciple performance test of the sensor head in solutions of different pH and in cement specimens are presented, with encouraging results paving the way for future field tests in concrete.
Lanthanide-doped NaYF4 upconversion nano- and microcrystals were synthesized via a facile solvothermal approach. Thereby, the influence of volume ratios of ethylene glycol (EG)/H2O, molar ratios of NH4F/RE3+ (RE3+ represents the total amount of Y3+ and rare-earth dopant ions), Gd3+ ion contents, types of activator dopant ions, and different organic co-solvents on the crystal phase, size, and morphology of the resulting particles were studied systematically. A possible formation mechanism for the growth of crystals of different morphology is discussed. Our results show that the transition from the α- to the β-phase mainly depends on the volume ratio of EG/H2O and the molar ratio of NH4F/RE3+, while the morphology and size could be controlled by the type of organic co-solvent and Gd3+ dopant ions. Furthermore, the reaction time has to be long enough to convert α-NaYF4 into β-NaYF4 during the growth process to optimize the upconversion luminescence. The formation of larger β-NaYF4 crystals, which possess a higher upconversion luminescence than smaller particles, proceeds via intermediates of smaller crystals of cubic structure. In summary, our synthetic approach presents a facile route to tailor the size, crystal phase, morphology, and luminescence features of upconversion materials.
Phenanthroline chromophore as efficient antenna for Tb3+ green luminescence: A theoretical study
(2021)
The quaternary tungstates Li3Ba2RE3(WO4)8 (RE = La-Nd, Sm-Ho) were obtained by a ceramic synthesis route and were characterized by powder and single crystal X-ray diffraction. The structures of Li3Ba2Pr3(WO4)8 and Li3Ba2Tb3(WO4)8 were refined from single crystal diffractometer data: RbLiBi2(MoO4)4 type, space group C2/c, a = 528.57(2), b = 1292.39(6), c = 1934.80(10) pm, b = 91.522(4)°, 2151 F2 values, 108 parameters for Li3Ba2Pr3(WO4)8 and a = 520.54(2), b = 1272.03(6), c = 1918.85(10) pm, b = 91.948(4)°, 2020 F2 values, 108 variables for Li3Ba2Tb3(WO4)8. Striking polyhedral building units in these tungstates are WO4 tetrahedra and LiO6 octahedra, while the mixed occupied site and the barium atoms have higher coordination numbers, i.e. RE/Li@O8 and Ba@O10. In addition to the powder quality assessment by means of reflection spectroscopy, the synthesized samples were studied for their suitability as a scintillator material. Therefore, X-ray excited luminescence measurements where performed. Apart from Li3Ba2Ce3(WO4)8 and Li3Ba2Nd3(WO4)8, all compounds show strong emission under X-ray irradiation. Li3Ba2La3(WO4)8 and Li3Ba2Gd3(WO4)8 show blue CT luminescence caused by tungstate units, while the other samples show typical and multiple lines due to well known [Xe]4fn → [Xe]4fn transitions.
We report on a watt-level highly efficient europium laser operating at the 5D0→7F4 transition. It is based on the stoichiometric KEu(WO4)2 crystal. Under pumping by a green laser at 532.1 nm, the KEu(WO4)2 laser generated a maximum peak output power of 1.11 W at ∼703nm with a slope efficiency of 43.2% and a linear polarization (????‖????????). A laser threshold as low as 64 mW was achieved. True continuous-wave operation was demonstrated. The polarized emission properties of monoclinic KEu(WO4)2 were determined.