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Inorganic and organic functional nanomaterials (NM) of different size, shape, chemical composition, and surface chemistry are relevant for many key technologies of the 21st century. Decisive for most applications of NM are their specific surface properties, which are largely controlled by the chemical nature and number of ligands and functional groups (FG on the NM surface. The surface chemistry can strongly affect the physicochemical properties of NM, their charge, hydrophilicity/hydrophobicity, reactivity, stability, and processability and thereby their impact on the environment and biological species as well as their possible risk for human health. Thus, reliable, validated, and eventually standardized analytical methods for the characterization of NM surface chemistry, i.e., the chemical identification, quantification, and accessibility of FG and surface ligands 1,2] flanked by interlaboratory comparisons, control samples, and reference materials, 2 ,3 are of considerable importance for process and quality control of NM production and function. This is also important for the safe use of NM the design of novel NM, and sustainable concepts for NM fabrication. Here, we provide an overview of analytical methods for FG analysis and quantification and highlight method and material related challenges for selected NM. Analytical techniques address ed include electrochemical titration methods, optical assays, nuclear magnetic resonance (NMR) and vibrational (IR) spectroscopy, and X ray based and thermal analysis methods. Criteria for method classification and evaluation include the need for a signal generating label, provision of either the total or derivatizable number of FG, and suitability for process and production control.
The use of proton-transfer-reaction mass spectrometry (PTR-MS) for the determination of formaldehyde, ammonia and volatile sulfur organic compounds is described and suggestions are made for the application of stationary PTR-MS in a test laboratory. One advantage of PTR-MS compared to TD-GC-MS (thermal desorption gas chromatography mass spectrome-try) is the faster online measurement. Another advantage is the simultaneous determination of formaldehyde, ammonia, very volatile organic compounds (VVOC) and volatile organic com-pounds (VOC) which normally needs four different kinds of sampling. Coupling the PTR-MS with (multiple) air sample canisters or (multiple) emission test chambers would enable a quick analysis of indoor air and material emissions.
Structural health monitoring (SHM) using ultrasonic-guided waves (UGWs) enables continuous monitoring of components with complex geometries and provides extensive information about their structural integrity and their overall condition. Composite overwrapped pressure vessels (COPVs) used for storing hydrogen gases at very high pressures are an example of a critical infrastructure that could benefit significantly from SHM. This can be used to increase the periodic inspection intervals, ensure safe operating conditions by early detection of anomalies, and ultimately estimate the remaining lifetime of COPVs. Therefore, in the digital quality infrastructure initiative (QI-Digital) in Germany, an SHM system is being developed for COPVs used in a hydrogen refueling station. In this study, the results of a lifetime fatigue test on a Type IV COPV subjected to many thousands of load cycles under different temperatures and pressures are presented to demonstrate the strengths and challenges associated with such an SHM system. During the cyclic testing up to the final material failure of the COPV, a sensor network of fifteen surface-mounted piezoelectric (PZT) wafers was used to collect the UGW data. However, the pressure variations, the aging process of the COPV, the environmental parameters, and possible damages simultaneously have an impact on the recorded signals. This issue and the lack of labeled data make signal processing and analysis even more demanding. Thus, in this study, semi-supervised, and unsupervised deep learning approaches are utilized to separate the influence of different variables on the UGW data with the final aim of detecting and localizing the damage before critical failure.
Low-Temperature High Stress (LTHS) creep plays a crucial role in Ni-base Superalloys, particularly affecting components like blades near the root. Below 850°C, the precipitate microstructure remains stable, characterized by periodically arranged ’ cubic precipitates surrounded by the -matrix. In these conditions, macroscopic traces of cubic slip have been observed in <111> oriented tensile specimens, whereas their microscopic origin has been a topic of debate. Furthermore, in LTHS conditions, Superlattice Intrinsic, Extrinsic Stacking Faults (SISF/SESF), or micro-twins are also frequently reported in crept specimens. Usually, these mechanisms are investigated separately, so that a unified picture and a detailed understanding of these mechanisms and their activation conditions have only recently emerged in the literature, despite the intensive investigations of the last decades.
The objective of this work is to develop a dislocation-based constitutive law that includes these recent developments. In particular, the pseudo-cubic slip mechanism is considered as resulting from the lack of hardening in <111> oriented tensile specimens and is represented by a novel estimate of the back-stresses based on the spectral decomposition of a tensorial representation of the back-stress. An additional novelty is that SISF- and SESF-related slip systems are accounted for as distinct slip systems with corresponding dislocation densities. The model has been implemented as a user-defined constitutive law for commercial Finite Element codes and identified as well as validated with data from the literature obtained with <001>, <011> and <111> oriented crystals tested in tension and compression creep.
Grain boundary embrittlement in medium-Mn steels and liquid metal embrittlement (LME) in Zn-coated high strength steels are among key challenges on the way of safe application of sustainable steels for automotive industry. Using a novel density-based model for grain boundaries, we reveal that the affinity of a grain boundary to attract Mn and Zn atoms result in a segregation transition accompanied by interfacial structural changes. In case of the Zn, the simulations show that the amount of segregation abruptly increases with decreasing temperature, while the Zn content in the alloy, required for triggering the segregation transition, decreases. The results are discussed in the context of CALPHAD-integrated density-based grain boundary phase diagrams.
Die Fourier-Transformations-Infrarotspektroskopie (FTIR-Spektroskopie) bietet eine herausragende Charakterisierungsmöglichkeit für Bitumen und bitumenhaltige Bindemittel. In Kombination mit multivariaten Analysemethoden und somit einem chemometrischen Ansatz erlaubt die FTIR-Charakterisierung Aussagen über verschiedene übergeordnete Eigenschaften, wie die Raffinerie, den Alterungszustand oder die Alterungsempfindlichkeit, eine Abschätzung verschiedener chemischer und physikalischer Kennwerte, wie z.B. den Asphaltengehalt, den Erweichungspunkt Ring und Kugel, die Nadelpenetration sowie den komplexen Schermodul und den Phasenwinkel sowie die Identifizierung verschiedener Additive wie Polymere oder Wachse.
The main advantage of air-coupled ultrasonic testing is the absence of a liquid couplant, which can damage some materials. However, most air-coupled testing scenarios have the challenge of low signals and a signal-to-noise ratio (SNR) several orders of magnitude lower than with couplant-assisted techniques. Since this challenge of small SNR also exists in radar technology, the pulse compression used there was adapted and applied to the physical conditions of air-coupled ultrasonic testing. This paper presents ultrasonic transmission measurements on a carbon-fibre-reinforced polymer plate using two experimental setups: 1) a thermoacoustic transmitter and an optical microphone and 2) a pair of ferroelectret transducers as transmitter and receiver. Thermoacoustic transmitters convert electrical energy to heat, which causes the air to expand thus producing acoustic waves. The optical microphone is based on a Fabry-Perot interferometer. Ferroelectrets are charged cellular polymers, having piezoelectric properties and excellent acoustic matching to air. Both thermoacoustic transmitters and ferroelectrets are non-linear regarding the relationship between the excited sound pressure and the excitation voltage. Due to these physical boundary conditions, unipolar coding was used to modulate the excitation signals. Various codes were tested, and parameters of the excitation pulses were varied to find the optimal combination for each experimental setup. The application of pulse compression to the combination of thermoacoustic transmitter and optical microphone increased the signal-to-noise ratio by up to 16 dB and for the ferroelectret transducers by up to 23 dB.
A journey in science from a graduate student in physical chemistry to head of division biophotonics
(2024)
I will provide a personal overview of the most important steps of my career in science, a journey from a graduate student in physical chemistry in an environment dominated by male-scientists over a postdoc with a female professor in the US to the leader of a research group, head of division Biophotonics at BAM. This will include my choices of research topics, how I learnt to write well cited publications, even on topics such as reference materials and quality assurance,1-4 and eventually started to give lectures at Free University Berlin granting me the right to act as first supervisor of undergraduate and graduate students.