Ingenieurwissenschaften und zugeordnete Tätigkeiten
Filtern
Erscheinungsjahr
Dokumenttyp
- Posterpräsentation (670) (entfernen)
Sprache
- Englisch (670) (entfernen)
Schlagworte
- Additive manufacturing (30)
- Corrosion (30)
- Mechanochemistry (23)
- Nanoparticles (19)
- Additive Manufacturing (18)
- Glass (18)
- Crystallization (16)
- Fluorescence (15)
- In situ (14)
- Computed tomography (13)
Organisationseinheit der BAM
- 6 Materialchemie (198)
- 5 Werkstofftechnik (85)
- 8 Zerstörungsfreie Prüfung (80)
- 6.3 Strukturanalytik (62)
- 6.6 Physik und chemische Analytik der Polymere (54)
- 8.5 Röntgenbildgebung (53)
- 6.1 Oberflächen- und Dünnschichtanalyse (48)
- 9 Komponentensicherheit (46)
- 1 Analytische Chemie; Referenzmaterialien (44)
- 4 Material und Umwelt (34)
- 6.0 Abteilungsleitung und andere (25)
- 7 Bauwerkssicherheit (25)
- 1.2 Biophotonik (24)
- 5.1 Mikrostruktur Design und Degradation (24)
- 5.4 Multimateriale Fertigungsprozesse (21)
- 4.1 Biologische Materialschädigung und Referenzorganismen (19)
- 8.0 Abteilungsleitung und andere (19)
- 6.2 Material- und Oberflächentechnologien (18)
- 9.4 Integrität von Schweißverbindungen (18)
- 5.2 Metallische Hochtemperaturwerkstoffe (17)
- 5.6 Glas (15)
- 9.3 Schweißtechnische Fertigungsverfahren (15)
- 6.5 Synthese und Streuverfahren nanostrukturierter Materialien (14)
- 3 Gefahrgutumschließungen; Energiespeicher (10)
- 4.2 Material-Mikrobiom Wechselwirkungen (9)
- 6.7 Materialsynthese und Design (8)
- 7.1 Baustoffe (8)
- 7.6 Korrosion und Korrosionsschutz (8)
- 9.6 Additive Fertigung metallischer Komponenten (8)
- 1.9 Chemische und optische Sensorik (7)
- 5.3 Polymere Verbundwerkstoffe (7)
- 7.5 Technische Eigenschaften von Polymerwerkstoffen (7)
- 1.4 Prozessanalytik (6)
- 9.0 Abteilungsleitung und andere (6)
- 3.1 Sicherheit von Gefahrgutverpackungen und Batterien (5)
- 1.6 Anorganische Referenzmaterialien (4)
- 2 Prozess- und Anlagensicherheit (4)
- 4.5 Kunst- und Kulturgutanalyse (4)
- 8.1 Sensorik, mess- und prüftechnische Verfahren (4)
- 8.4 Akustische und elektromagnetische Verfahren (4)
- 9.2 Versuchsanlagen und Prüftechnik (4)
- 9.5 Tribologie und Verschleißschutz (4)
- 1.5 Proteinanalytik (3)
- 4.0 Abteilungsleitung und andere (3)
- VP Vizepräsident (3)
- VP.1 eScience (3)
- 1.1 Anorganische Spurenanalytik (2)
- 2.0 Abteilungsleitung und andere (2)
- 3.2 Gefahrguttanks und Unfallmechanik (2)
- 3.4 Sicherheit von Lagerbehältern (2)
- 5.5 Materialmodellierung (2)
- 8.2 Zerstörungsfreie Prüfmethoden für das Bauwesen (2)
- 8.6 Faseroptische Sensorik (2)
- 1.8 Umweltanalytik (1)
- 2.1 Sicherheit von Energieträgern (1)
- 2.2 Prozesssimulation (1)
- 3.3 Sicherheit von Transportbehältern (1)
- 3.6 Elektrochemische Energiematerialien (1)
- 5.0 Abteilungsleitung und andere (1)
- 6.4 Materialinformatik (1)
- 7.2 Ingenieurbau (1)
- 7.4 Baustofftechnologie (1)
- 8.3 Thermografische Verfahren (1)
- MP Mitglied des Präsidiums (1)
- MP.0 Mitglied des Präsidiums und andere (1)
- P Präsident (1)
- PST Präsidiale Stabsstelle (1)
Eingeladener Vortrag
- nein (1)
Large area periodic surface structures were generated on steel surfaces using 30-fs laser pulses at 790 nm wavelength. Two types of steel exhibiting a different corrosion resistance were used, i.e. a plain structural steel (corrodible) and a stainless steel (resistant to corrosion). Homogeneous fields of laser-induced periodic surface structures (LIPSS) were realized utilizing laser fluences close to the ablation threshold while scanning the sample under the focused laser beam in a multi-pulse regime. The nanostructures were characterized with optical and scanning electron microscopy. For each type of steel, more than ten dentical samples were laser-processed.
These samples were subjected to microbial adhesion tests, investigating bacterial adhesion behavior on the laser structures in comparison to polished reference surfaces. Short term experiments (<24h) were carried out to determine initial biofilm development. E. coli as a typical bacterium representing pathogenic bacteria and Shewanella putrefaciens as metal corrosive bacterium were used for biofilm development analyses. Bacterial cell adhesion was determined microscopically after DAPI cell staining (DNA staining). Comparison of the coverage areas between nanostructured and polished surfaces revealed differences in cell adhesion behavior and biofilm structure.
Laser-induced periodic surface structures (LIPSS) were generated on titanium nitride (TiN) hardcoating surfaces (deposited on metallic substrates) upon irradiation with multiple linearly polarized femtosecond laser pulses in air (30 fs duration, 790 nm wavelength, 1 kHz pulse repetition rate). The conditions were optimized in a sample-scanning geometry for the processing of large surface areas (5 mm x 5 mm) covered homogeneously by nanostructures with sub-wavelength periods ranging between ~200 nm and 700 nm. For these nanostructures the coefficient of friction was characterized under reciprocating sliding condition against a ball of hardened steel at 1 Hz using different lubricants (regime of mixed friction). After 1000 cycles, the corresponding wear tracks were characterized by optical and scanning electron microscopy. High-resolution energy dispersive X-ray analyzes (EDX) allowed the visualization of chemical alterations within the wear tracks. For specific conditions, the nanostructures endured the tribological treatment. Our experiments provide a qualification of the tribological performance of the fs-LIPSS on TiN surfaces.
Laser-induced periodic surface structures (LIPSS, ripples) were generated on steel and titanium surfaces upon irradiation with multiple linear polarized femtosecond laser pulses (pulse duration 30 fs, central wavelength 790 nm). The experimental conditions (laser fluence, spatial spot overlap) were optimized in a sample-scanning geometry for the processing of large surface areas covered homogeneously by the nanostructures. The irradiated surface regions were subjected to optical microscopy (OM), white light interference microscopy (WLIM) and scanning electron microscopy (SEM) revealing sub-wavelength spatial periods. The nanostructured surfaces were tribologically tested under reciprocal sliding conditions against a sphere of hardened 100Cr6 steel at 1 Hz using paraffin oil and engine oil as lubricants. After 1000 sliding cycles at a load of 1.0 N, the corresponding wear tracks were characterized by OM and SEM. For specific conditions the laser-generated nanostructures endured the tribological treatment. Simultaneously, a significant reduction of the friction coefficient was observed in the laser-irradiated (LIPSS-covered) areas when compared to the non-irradiated surface, indicating the potential benefit of laser surface structuring for tribological applications.
For the characterization of disperse and porous solids, usually single gas adsorption(GA) is employed. In the case of liquid adsorption (LA), the extraction of information on solids immediately becomes a more sophisticated matter since information on geometric as well energetic parameters of the solids is both superposed by liquid-mixture effects and displayed in excess terms. We have to ask if reliable solid parameters can be also obtained from LA isotherms. The enlarged data bank of gas and liquid adsorption measurements enables us to change systematically solid parameters (e.g., the pore width of MCM-41, the pore entrances of SBA-16, chemical heterogeneity) and to study in this way the influence of solid parameters on LA.
Ionic Liquids (ILs) are employed in various fields, for example, reaction engineering (reactions with gases, such as hydroformylation (CO, H2), hydrogenation (H2), oxidation (O2)) or separation technology (separations of gases, reactants, and high-volatility reaction products). For the basic engineering of such processes, knowledge of phase equilibria, particularly of mixtures, over a broad (p,T) range is mandatory. This contribution reports on recent experimental results from our laboratory: – for the simultaneous solubility of a binary gas mixture in a pure ionic liquid – for the solubility of a single gas in a binary liquid solvent mixture.
The term „Alternative Solvents“ often refers to ionic liquids (ILs), mainly to distinguish these substances from traditional (i.e., molecular) solvents.
In applications, any „alternative“ is required to perform better than something that is proven and tested.
To bring ILs into practical use, availability and costs are the fundamental points to be addressed.
There are two ways to proceed:
▬ tailoring a molecule, implanting the expected characteristics
advantage: optimization of the targeted performance possible
risks: outcome not always foreseeable, costly and time-intensive (“trial and error“)
▬ to target on mixtures of well-characterized ILs with molecular solvents
advantage: substance characteristics are known, less costly, less time-consuming,
mixture composition another tunable parameter
risks: the same but with less impact
For the basic engineering of technical processes, knowledge of phase equilibria, particularly of
mixtures, over a broad (p,T) range is mandatory.
This contribution reports on recent experimental results from our laboratory:
▬ the solubility of CO2 in a mixture of water and [bmim][CH3SO4]
▬ the solubility of CO2 in a mixture of methanol and [bmim][PF6]
While polymorphism is a common phenomenon in the crystallization processes of organic compounds, polyamorphism has gained importance only recently. Using sophisticated sample environments and applying in situ scattering methods and vibrational spectroscopy, the complete crystallization process of organic compounds from solution can be traced and characterized. Diffuse scattering from amorphous intermediates can be investigated by analyzing the atomic pair Distribution function (PDF) to gain further insights into molecular pre-orientation. The crystallization behavior of Paracetamol was studied exemplarily under defined, surface-free conditions. Based on the choice of the solvent, the formation of different polymorphs is promoted. The thermodynamically stable form I and the metastable orthorhombic form II could be isolated in pure form directly from solution. For both polymorphs, the crystallization from solution proceeds via a distinct amorphous precursor phase. PDF analyses of these different amorphous states indicate a specific pre-orientation of the analyte molecules introduced by the solvent. The resulting crystalline polymorph is already imprinted in these proto-crystalline precursors. Direct experimental evidence for the polyamorphism of paracetamol is provided.
One-part-geopolymers, produced by addition of water to a mixture of solid silica and sodium alumi-nate, are a less exhaustively studied approach to form geopolymeric binders. Depending on the silica source, the reaction products show significant amounts of zeolite Na-A besides amorphous compounds. Previously, 29Si MAS NMR has been used to analyze the chemical structure of such one-part geopolymers, having crystalline structures and amorphous phases (Q2, Q3, Q4).
In this work, pure zeolites and three different one-part-geopolymers cured for 1 day were investigated by 29Si-27Al TRAPDOR NMR. It was used to identify aluminum phases in overlapping silicon sites. Zeolites Na-X (Si/Al=1.4) and Na-Y (Si/Al=2.7) served as model systems to measure the TRAPDOR effect of the structural units Q4(mAl). Both materials show several Q4(mAl) signals, which are all separated by their chemical shifts. The more aluminum surrounds the silicon tetrahedron the higher are the normalized TRAPDOR difference signals (S0/∆S). The intensity ratios between Q4(mAl) to Q4({m-1}Al) of these signals is fixed but vary slightly between both zeolites. These results are transferred to the complex geopolymer structure.
Mechanochemistry is increasingly used for synthesizing various materials including cocrystals and metal organic compounds. Although this synthesis approach offers a fast and pure synthesis in high yields there is a lack in understanding the mechanisms of milling reactions. The driving forces triggering the formation of cocrystals under milling conditions were investigated using a set of multi-component competitive milling reactions. In these reactions, different active pharmaceutical ingredients were ground together with a further compound acting as coformer. The study was based on new cocrystals including the coformer anthranilic acid. The results of the competitive milling reactions indicate that the formation of cocrystals driven by intermolecular recognition are influenced and inhibited by kinetic aspects including the formation of intermediates and the stability of the reactants.
Ultrasonic echo testing has become a common method in civil engineering for the investigation of concrete structures. The detection of inhomogeneities, reinforcing elements and the geometry of the object is required for quality assurance and Inspection. This assessment depends on the quality of ultrasonic images which can be improved by using Reverse Time Migration (RTM) rather than the standard method, Synthetic Aperture Focusing Technique (SAFT). Although RTM provides a better mapping of circular objects and (dipping) reflectors, the image is corrupted by migration noise. To suppress the image noise, we have tested various filter methods in the spatial domain, frequency domain as well as in the curvelet domain on ultrasonic RTM images. We found that either a spatial edge detection filter in combination with a lowpass filter (Laplacian of Gaussian filter) or two lowpass filter with different filter parameters (Difference of Gaussian filter) removed artefacts. An additional smoothing was obtained by applying the first generation curvelet transform after downsampling the image matrix and adding Gaussian noise. The proposed filter scheme is able to suppress RTM noise and enhance the image quality such that the objective interpretation of ultrasonic images for Quality assessment of concrete specimen is simplified.
One of the alternative renewable fuels is biomass but it is a difficult fuel because of its diversity and complexity. It can contain high percentages of K and Cl responsible for corrosion together with sand that have additionally an abrasive effect during combustion. Because of permanently extending the surface reaction due to abrasion the corrosion of the materials increases. In particular in power plants, the superheater tubes are exposed to a corrosive abrasive attack that is one of the main sources of concern. The development of new alloys for multilayer surface, which combines corrosive and abrasive resistance is therefore of high importance. Those new technical approaches must be at the same time cost-effective to be an alternative to conventional materials. The aim of the presented investigation methods is to test and develop suitable alloys for coatings for the super heater tubes of biomass power plants. First results of abrasion investigations show improved abrasion resistance compared to the multi-component reference material Alloy 625.
The integration of finite element method (FEM) into the least-squares adjustment presented in is further extended for a joint evaluation of an elastostatic model and displacement field measurement. For linear solids which obey the Hooke's law, the material parameters determination from measurements is being examined.
Hard materials consist of a hard phase embedded in a metallic binder. In order to achieve high toughness and strength, it is necessary to have a perfect mixing of hard phase and binder, which is mainly achieved by ball milling. Niobium carbide (NbC) has a high potential to substitute tungsten carbide as hard material.
The publication presents the development of stable homogeneous and de-agglomerated NbC-dispersions. To prevent agglomeration of the powder, stable suspensions were achieved by surface treatments with the dispersants (PD and HD), which resulted in a charge reversal from a negative to a positive zeta potential. This surface-modified powder guaranteed a stable re-dispersion in the binder suspension. Nickel powder was added as metallic binder. This suspension was suited for 3D-printing. The green samples could be sintered in vacuum or Argon atmosphere.
Microbial induced corrosion (MIC) is a crucial problem in many technical plants as well as fuel tanks, leading to considerable damage and huge financial losses. Successful prevention of MIC requires the localization of first signs of corrosion as well as the identification of factors influencing the corrosion process. In this respect, also the determination of corrosion rates can be of interest for the possible prevention of MIC. Hence, there is a growing need for sensitive and preferably inexpensive tools that enable the early detection of MIC. Of special interest are methods, which provide spatially and time-resolved information and allow the study of changes on metal surfaces as prerequisites for a more detailed analysis of ongoing corrosion processes at a MIC-affected site.
Biofilm formation can lead to changes in pH, oxygen and chloride concentration as well as to the release of certain metal ions like Fe(II) and Mn(II) depending on the type of metal surface involved. Hence, optical methods enabling the detection of these analytes at very low concentration and monitoring of their changes can be used for MIC detection. Here, we propose to utilize polymeric nanosensors for MIC detection via the determination of the local pH value changes in different biofilms. Such nanosensors are known to have several advantages in imaging applications such as intracellular pH measurements including the ease of doping or labeling with a multitude of analyte-responsive and inert dye molecules for the realization of a high analyte sensitivity and ratiometric sensing. Moreover, they can be surface functionalized with target-specific ligands e.g., lectins, for the specific binding to the outer surface of certain types of bacteria. In this respect, different polymer architectures will be studied to identify an optimal candidate in terms of imaging performance in conjunction with several classes of pH-responsive fluorescent dyes like cyanines, aza-BODIPYs, and xanthenes, utilizing different mechanism of signal generation such as photo-induced electron transfer or protonation-induced changes in the spectral position of absorption and emission spectra.
Current pollen screening information networks are based on time-consuming, microscopic determination of the genus-specific pollen morphology. Additionally, the given information relies on prediction of plant growth, wind direction and seasonal information.
Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) was introduced for rapid analysis of complex biological samples. MALDI-TOF provides the possibility to measure species-specific mass peak patterns of pollen and offers a powerful tool for investigation of taxonomic relations.
Our objective is to develop a fast, reliable, routine method for detecting single pollen grains in pollen mixtures. The obtained spectra are analyzed by multivariate statistics.
The controlled production of supramolecular aggregates formed by the self-assembly of dendritic amphiphiles is of great interest owing to their potential application in the fields of nanotechnology and nanomedicine. Dendritic amphiphiles as building blocks offer the advantage that their structure and size can be precisely tuned through organic synthesis. This synthetic flexibility enables the fine-tuning of the hydrophobic to hydrophilic ratio of the dendritic segments, which mainly controls the morphology of the self-assembled structures.
A promising method for the controlled preparation of supramolecular assemblies is based on the use of micromixers.[5,6] Due to their mixing times in the range of milliseconds at the microscale level, the application of such microfluidic systems benefits from a high mixing efficiency, a low mixing time and a reproducible synthesis compared to conventional batch-based techniques such as the solvent injection method or the film hydration method.
Herein, we report on the microfluidic-assisted self-assembly of several dendritic amphiphiles and the impact of the mixing parameters on the self-assembly process.
The use of high-performance concretes holds great promise for many structural applications. This paper investigates the performance of these materials when used in combination with traditional reinforcing bars. An improved understanding of failure during reinforcing bar pull-out from high-performance concretes is needed in order to better predict the embedment length required to develop full reinforcing bar pull-out strength and the required thickness of reinforcing bar cover for adequate corrosion protection. The cracking structures surrounding the reinforcing bars were analyzed using x-ray computed tomography (CT) in order to determine the stress states causing failure. This was accomplished by conducting in-situ reinforcing bar pull-out experiments during CT scanning. A conventional concrete, a high-strength concrete, and a high-strength fiber reinforced concrete were all tested during the experiments. The results of these experiments showed that the levels of brittleness of the different concrete materials had a major impact on the failure mechanisms that they experienced during reinforcing bar pull-out. It was also clear that the specimen geometry and the casting method had a major impact on fiber orientation. The inclusion of fibers within concrete was also found to significantly improve strength and corrosion protection during reinforcing bar pull-out.
High resolution in situ monitoring of the initial cement hydration influenced by organic admixtures
(2015)
Numerous admixtures are used in the building practice to customize the properties of the cement paste during application. The influences of admixtures on the course of cement hydration and formation of hydrate phases have to be considered. Polycarboxylate ether (PCE) based polymeric superplasticizers (SPs) are known to retard the setting of the cement paste. The extent of the retardation differs depending on the molecular structure of the SP. Additionally, the presence of a stabilizing agent (SA) in the cement paste has a retarding side effect on the setting. The initial cement hydration processes and the detailed mechanisms of the retardation influenced by PCEs, as well as their interactions with particular SAs, are insufficiently understood. Up to now, only the results of phenomenological studies were taken into account to describe this retardation process. A detailed structure analysis monitoring the change of the phase composition during the hydration was never applied. Both SP and SA affect the adsorption of the sulphate ions on the clinker particles, causing changes in the formation of ettringite during the initial hydration, and are therefore a crucial part of the setting process itself. Here, the initial hydration of cement influenced by the interaction of SP and SA was monitored in situ by synchrotron X-ray diffraction. The high time resolution of the measurements allowed a continuous detection of the hydrates formed. The hydration was followed from the starting point of water addition and for couple of hours afterwards. The hydration of the levitated cement pellets containing starch as SA was initialized by adding aqueous solutions of different commercial SPs. Changes in the ettringite formation were detected in comparison to the reference hydration of pure cement.