Ingenieurwissenschaften und zugeordnete Tätigkeiten
Filtern
Erscheinungsjahr
- 2018 (142) (entfernen)
Dokumenttyp
- Vortrag (88)
- Posterpräsentation (44)
- Beitrag zu einem Tagungsband (5)
- Sonstiges (2)
- Zeitschriftenartikel (1)
- Dissertation (1)
- Forschungsbericht (1)
Referierte Publikation
- nein (142) (entfernen)
Schlagworte
- Corrosion (10)
- Mechanochemistry (10)
- SAXS (8)
- In situ (7)
- Thin polymeric films (7)
- Dielectric spectroscopy (6)
- Boehmite (5)
- MIC (5)
- Nanocomposites (5)
- Thermoresponsive polymer (5)
Organisationseinheit der BAM
- 6 Materialchemie (142) (entfernen)
Eingeladener Vortrag
- nein (88)
Der Mangel an Anwendungsrichtlinien und Validierungsverfahren für struktur-eingebettete faseroptische Dehnungssensoren, insbesondere auf Faser-Bragg-Gitter (FBG)-Basis, führte bislang dazu, dass diese Sensoren trotz ihrer hervorragenden Eigenschaften im Bereich der kommerziellen Material- und Strukturüberwachung nur in geringem Umfange eingesetzt wurden. Fragen zur Degradation der Sensoren unter Beanspruchung, Alterung durch klimatische Einflüsse und Enthaftung infolge Belastung der Struktur konnten bisher nur theoretisch simuliert oder anhand exemplarischer Proben für einzelne einflussnehmende Parameter im Labor untersucht werden. Die Erfassung des Sensorverhaltens im Bauteil unter komplexen Umwelteinflüssen während des Bauteilbetriebes, um damit eine Aussage zur Zuverlässigkeit der Sensormessdaten zu gewinnen, war bisher nicht möglich.
Im Forschungsprojekt FAMOS² wurde deshalb von 2014 bis 2018 die Realisierung eines Autodiagnoseverfahrens für faseroptische Dehnungssensoren erarbeitet, um die Funktionszuverlässigkeit und Langzeitstabilität der Sensoren während des Bauteilbetriebes innerhalb einer Bauteilstruktur bewerten zu können. Im Rahmen des Forschungsprojektes wurde gezeigt, dass ein FBG-Sensor mit einer speziell angepassten magnetostriktiven Schicht magnetisch so angeregt werden kann, dass mit einer zugeschnittenen Messmethodik zu jedem Zeitpunkt eine Bewertung der Sensorzuverlässigkeit unter Betriebsbedingungen möglich ist. Die auf den Sensor aufgebrachte magnetostriktive Schicht erzeugt bei Anregung mit einem passenden Magnetfeld eine gepulste, synthetische Dehnung. Diese Dehnung steht in einem definierten Verhältnis zum anregenden Magnetfeld und wird optisch über die Verschiebung der Bragg-Wellenlänge ausgelesen. Die Konstanz dieses Verhältnisses stellt dann ein Maß für die korrekte Funktionsfähigkeit des Sensors dar. Das Beschichtungs-verfahren, das magnetische Anregungs- und optische Ausleseverfahren, wie auch die Validierung des Sensors unter Berücksichtigung faseroptischer Effekte wurden während des Projekts konzeptionell entwickelt, aufgebaut und charakterisiert. Qualitativ kann mit diesem Verfahren zunächst eine Gut-/Schlecht-Beurteilung des Sensors vorgenommen werden. Perspektivisch bietet das Verfahren jedoch auch die Möglichkeit, verschiedene Versagensmechanismen bestimmen und klassifizieren zu können. Es zeichnete sich schon während des Projektverlaufs ab, dass sich aus den erzielten Ergebnissen über das Autodiagnoseverfahren hinaus weitere Anwendungsmöglichkeiten für den Einsatz des kombinierten magnetostriktiv-faseroptischen Sensorprinzips, beispielsweise als reiner Magnetfeldsensor, ergeben.
Nach Abschluss dieses Forschungsprojekts besteht nun die Möglichkeit, den Funktionszustand faseroptischer Dehnungssensoren jederzeit unabhängig von Alter, Belastung oder Kenntnis eines Referenzzustands zu einem bestimmten Zeitpunkt bestimmen zu können. Aufbauend auf diesen Ergebnissen können weiterführende Forschungen die Messmethodik vertiefend charakterisieren und weitere Anwendungsfälle erschließen.
Der Vortrag gibt den aktuellen Stand der Normung im Bereich der Oberflächen-technik insbesondere der Oberflächenanalytik und der Oberflächenmess- und -prüftechnik wider. Vorgestellt wird der Status technischer Berichte, Normenentwürfe und Normen u.a. zur Charakterisierung von funktionellen Glasoberflächen für bioanalytische Anwendungen, zur Messung der Schichtdicke von Nanomaterialien mittels Ellipsometrie, zur Kalibrierung von Interferometern und Interferenzmikroskopen für die Formmessung, zur Rockwelleindringprüfung zur Bewertung der Schicht-haftung, zu den Grundlagen der Ellipsometrie, zur Messung der Schichtdicke mittels Wirbelstromverfahren, zur Schichtpotentialmessung von Mehrfach-Nickelschichten, zu Filtern und Augenschutzgeräten gegen Laserstrahlung sowie zur Bestimmung der Schichthaftung mittels Zugversuch.
The performance of functional coatings and adhesively joined hybrid components relies strongly on the stability of the polymer-metal interface. With the increasing utilization of multi-material structures in the automotive and aerospace industry, it is of great scientific and technical interest to understand the processes leading to interface degradation and to develop novel strategies to increase corrosion and delamination resistance.
The aim of this project is to develop thin epoxy-based films on aluminium alloy AA2024-T3 as a model system and to investigate their interfacial stability under corrosive and coupled corrosive-mechanical load. Electrochemical and spectroscopic methods were used for the characterisation of the film properties and in situ corrosion experiments were performed by means of AFM. The deformation properties of the aluminium alloy and the model coatings were investigated by means of scanning Kelvin probe force microscopy (SKPFM) utilizing the integrated tensile stage.
The presentation will give a brief overview of the capabilities of the new AFM setup to foster future collaborations and summarize our work on the interface stability of model coatings.
UV-curing coatings are nowadays widely used due to their unique advantages. High-quality coatings can be obtained at short curing times and low temperatures so that thermal stress to the substrate is minimised. Photocured Cycloaliphatic-Epoxy Oligosiloxane (CEO) resin was reported to be used as encapsulation material for organic electronics. However, further reinforcement of CEO film properties is desired to achieve requested device lifetime.
In this work we introduced Boehmite nanoparticles (BA) into CEO matrix in order to modify the film properties and study the main changes of the material behaviour with regard to its photocuring kinetics, thermal stability and glass transition. Particular interest was focused on the role of particle surface in nanocomposite properties. Hence, BA particles without (HP14) and with organic surface modifier (OS1) at different loadings (up to 10 wt%) were applied in this study. Morphology investigation with SEM operated in transmission mode showed good BA dispersion forming network-like structure. At the same time, distribution of particles differed for HP14 and OS1 as a result of different interaction in CEO-solvent-particles system. CEO structure obtained via non-hydrolytic sol-gel reaction was verified by 13C and 29Si NMR. In situ monitoring of film curing was performed using RT-IR spectroscopy. No significant modification of final convention degree with particle incorporation was observed in contrast to considerable decrease of curing efficiency reported previously for similar system by Esposito et al.,2008. Further, cured hybrid nanocomposite films were analysed by TGA and DSC, which revealed impact of surface modifier on film thermal properties.
Organic-inorganic nanostructured materials have drawn much attention over the past decade, particularly due to their versatile and outstanding properties. Possessing the properties between those of polymers and those of glasses, siloxane-based resins are non-toxic, easy to synthesize and process hybrid materials, that hold a promising potential in the field of advanced coatings.
Photocurable resins are nowadays widely used as coatings due to their unique advantages. In particular, cationic ring-opening curing is not inhibited by oxygen, leads to low degree of shrinkage and superior adhesion. The most important, it enables production of high-quality coatings within short exposure times without applying temperature, thus, minimizing the presence of the thermal stress in the substrate. Photocured Cycloaliphatic-Epoxy Oligosiloxane (CEO) resin was reported to be used as encapsulation material for organic electronics. However, further reinforcement of CEO properties is desired to achieve requested device lifetime. One of the common approaches to improve material characteristics is by embedding inorganic nanoparticles into polymer matrix. It has been shown that the resulted nanocomposites exhibit enhanced functional properties included but not limited by optical, mechanical, thermal and barrier ones.
In this work we focused on the incorporation of Boehmite nanoparticles (BA) into CEO matrix as a tool to strengthen the film properties and to study the main changes occurred in the material behavior with regard to its photocuring kinetics, thermal stability and glass transition. Particular interest was focused on the role of particle surface in nanocomposite properties. Hence, BA particles without (HP14) and with organic surface modifier (OS1) at different loadings
(up to 10 wt%) were applied in this study. Morphology investigation with SEM operated in transmission mode showed good BA dispersion forming
network-like structure. At the same time, distribution of particles differed for HP14 and OS1 as a result of different interaction in CEO-solvent-particles system. CEO structure obtained via non-hydrolytic sol-gel reaction was verified by 13C and 29Si NMR. In situ monitoring of film curing was performed using
RT-IR spectroscopy. A slight increase of final convention degree with particle incorporation was observed in contrast to the considerable decrease of curing efficiency reported previously for similar system. Further, the cured hybrid nanocomposite films were analyzed by TGA and DSC, which revealed impact of surface modifier on thermal stability and glass transition temperature.
Ferritic high temperature alloys are widely used as boiler tube and heat exchanger materials in coal, biomass and co-fired power plants. All technologies have in common that the applied materials are exposed to different temperatures, process pressures and reactive atmospheres that lead to a change of the material properties and a further degradation of the material. Material changes caused by aging in highly corrosive and toxic gases such as SO2 are mainly studied ex situ after the reaction is finished. The solid material is deposited in the atmosphere for a certain period of time, and material changes are then examined by various microscopic techniques such as optical microscopy (OM), electron microprobe analysis (EMPA), scanning electron microscopy (SEM and TEM) and X-ray diffraction (XRD). Nevertheless, extensive efforts were made to study material changes of high temperature alloys under oxidizing and reducing atmospheres by environmental scanning electron microscopy or in situ TEM techniques However, the possibilities of microscopic in situ techniques are very limited for the use of highly corrosive and toxic gases such as SO2. Since Sulfur induced corrosion at temperatures relevant for coal and biomass fired power plants, which is causing breakaway oxidation and sulfide precipitation at grain boundaries, is still of scientific interest, the current work focuses on the effect of SO2 in an initial stage of corrosion of ferritic alloys. For the analysis of early stages of combined oxidation and sulphidation processes of Fe-Cr model alloys the usage of a light furnace to conduct a rapid reactive annealing experiment is feasible. Previous studies presented distinct results of the influence of chromium on early high temperature corrosion by SO2 by this technique and subsequent classical metallographic analyses. However, it is still not possible to trace the corrosion mechanism in real time by conducting single aging experiments. The current work introduces two different approaches to study the initial stages of high temperature oxidation processes by applying above state of the art X-ray diffraction and spectroscopy methods. One part focuses on the real time observation of the formation of corrosion products such as oxides and sulfides by energy dispersive X-ray diffraction (EDXRD). The potential of this technique to study crystallization and growth processes of thin films in a reactive environment in real time was previously shown for different compound semiconductors. This approach was now applied to follow oxidation and sulphidation processes of ferritic model alloys in SO2 and SO2/H2O environments. The diffraction signals of the X-rays were detected during the corrosion process and the peak area and positions were analyzed as a function of time. This procedure enables monitoring external oxide growth and material loss in real time in an early stage of corrosion.
The other part of the current work presents the possibilities of X-ray absorption near edge structure spectroscopy (XANES) to characterize oxide scales and their growth mechanisms. Precise phase identification and quantification of corrosion products in a multi-phase oxide/sulfide scale is a pre-requisite to understand diffusion paths of metal ions and gas components. It is a challenging task to distinguish structurally similar reaction products such as Fe3O4 and FeCr2O4 especially in thin films with texture effects by diffraction. To illustrate for example Cr-out diffusion of an alloy throughout an inner and external oxide scale the differentiation of Fe3O4 and FeCr2O4 is indispensable. XANES uses the photoionization effect at the metal absorption edge in an aging product and accesses by this structural and chemical information. The current work uses XANES at the Fe-K and Cr-K absorption edge to identify various aging products grown as thin layers on alloys after short time aging experiments. A reaction chamber for combining high temperature oxidation experiments with surface sensitive X-ray absorption near edge structure spectroscopy will be introduced and first results of XANES on scales at high temperatures will be presented.
Ferritic-martensitic alloys with 12-16 % Cr in weight are subject to devices for various energy systems, such as coal power plants and waste incineration plants. These materials are exposed to a highly corrosive environment which lead to a degradation of the material. Especially the simultaneous oxidation and sulfidation is thereby of special interest. Proper spatially resolved measurements that determine not only chemical compositions but phases are rare. However, precise phase identification and quantification of corrosion products within the multi-phase corrosion scales is a key aspect to understand diffusion paths of metal ions and gas ions/molecules. This study investigated Fe-Cr model alloys with Cr contents from 0 to 13 % in weight in 0.5 % SO2 and 99.5 % Ar atmosphere to aim in a fundamental and systematic analysis. Samples were aged at 650 °C for time scales from 12 h to 250 h. The results presented here correspond to depth dependent phase identification of oxide and sulphide phases in the corrosion scales by using X-ray absorption near edge spectroscopy (XANES). Per sample a series of ca. 20 spots (1-5 µm spot size) from scale-gas to scale-metal interface were measured. XANES spectroscopy was performed at the Fe-K edge (7.11 keV) on polished cross sections. The collected spectra were fitted to a combination of reference materials to quantify the present phases at different positions within the scale.The phase distribution differs with Cr content and the Cr diffusion through pure Fe-oxide and mixed Fe-Cr-oxide phases is discussed.
The presence of polycarboxylate ether (PCE) based superplasticizers (SPs) has an enormous influence on the early hydration of cement. The hydration is retarded and the timing of formation and the morphology of hydrates is affected. This short paper presents experimental results about the influence of delayed addition time of PCE SPs on hydration of cement and alite pastes, investigated by isothermal heat flow calorimetry. For cement as well as for alite pastes the hydration is retarded with SP, whereby the high charge PCE has a stronger retarding effect than the low charge PCE. The retardation caused by PCE is much more pronounced for alite than for cement mixes. If PCE is added later to the mix, the induction period is shortened and the hydration is accelerated compared to simultaneous addition. This applies for cement and alite pastes. With delayed PCE addition the alite shows a clearly less retarded setting and main hydration than after simultaneous addition. It is obvious that for alite pastes there is less retardation the later the addition of SP.
Clustering of magnetic nanoparticles can drastically change their collective magnetic properties, which in turn may influence their performance in technological or biomedical applications. Here, we investigate a commercial colloidal dispersion (FeraSpinTMR), which contains dense clusters of iron oxide cores (mean size around 9 nm according to neutron diffraction) with varying cluster size (about 18–56 nm according to small angle x-ray diffraction), and its individual size fractions (FeraSpinTMXS, S, M, L, XL, XXL). The magnetic properties of the colloids were characterized by isothermal magnetization, as well as frequency-dependent optomagnetic and AC susceptibility measurements. From these measurements we derive the underlying moment and Relaxation frequency distributions, respectively. Analysis of the distributions shows that the clustering of the initially superparamagnetic cores leads to remanent magnetic moments within the large clusters. At frequencies below 105 rad s−1, the relaxation of the clusters is dominated by Brownian (rotation) relaxation. At higher frequencies, where Brownian relaxation is inhibited due to viscous friction, the clusters still show an appreciable magnetic relaxation due to internal moment relaxation within the clusters. As a result of the internal moment relaxation, the colloids with the large clusters (FSL, XL, XXL) excel in magnetic hyperthermia experiments.
Microbially influenced corrosion (MIC) of iron is usually attributed to sulfate-reducing microorganisms (SRM) which act upon the metal by the reactiveness of hydrogen sulfide, and by withdrawal of the available electrons in electrical contact with the metal. Methanogenic archaea can also cause MIC by directly withdrawing electrons from the iron surface for methanogenesis. However, the mechanistic details and kinetics of the overall process are poorly understood. Precipitation of siderite, a by-product of methanogenesis, (4Fe + 5HCO3 + 5H+ 4FeCO3 + CH4 + 3H2O) can lead to an insulating layer on the metal surface and lower the corrosion rate. Still, the extent of FeCO3 precipitation may be significantly influenced by environmental conditions such as pH and advective processes.
To investigate early stage corrosion processes of stainless steel 1.4301 taking place during the biofilm formation of the organism Shewanella putrefaciens electrochemical impedance spectroscopy (EIS) in a multielectrode approach has been used. The multielectrode array consisted of up to 25 electrically isolated electrodes made of stainless steel wires of diameters ranging from 100 µm to 500 µm. They were connected to a multichannel microelectrode analyzer (MMA) electrically coupled through zero resistance ammeters. Current flow between electrodes in the array as well as changes in impedance of individual electrodes over time were recorded and analyzed with respect to the onset of localized corrosion and biofilm formation. The results were complemented by optical microscopy, SEM and AFM images which were taken immediately after the respective experiment. To verify that the multielectrode arrays correctly indicated the initial stages of the corrosion process and of biofilm formation they were introduced in a flow cell reaction vessel containing test specimens made from stainless steel 1.4301, which were checked regularly for signs of localized corrosion and biofilms. Preceding results with the multielectrode array in solutions containing high amounts of chloride ions and hydrogen peroxide at low pH also showed that it is possible with the MMA to monitor individual electrodes becoming local anodes as local corrosion set in, while the remaining electrodes predominantly acted as cathodes.
Different strategies for the synthesis of polylactides were presented with special focus on Ring-opening Polymerization (ROP) and simultaneous ROP and Polycondensation (ROPPOC) mechanism. The mechanism of the formation of cyclic Polyesters is discussed in detail and established theories about the formation of cycles in polycondensation reactions are critically reviewed.
We present the synthesis of four mesoporous templated iron oxides: Ferrihydrite, Hematite, Maghemite, Magnetite/Maghemite and the influence of water on the crystallization mechanism and the kinetics. The absence of water stabilize the ferrihydrite structure. By monitoring the dissolution in situ by using a QCMB and ex situ microscopy we got details in the dissolution mechanism of ferrihydrite.
Polynuclear aluminium species (Al13 keggin cluster) find application in different areas like water purification [1], contaminant transport [2], and as pilling clays with high specific surface areas[3], due to their strong binding ability to aggregates and high positive charge.
In the present contribution, we report on the in situ investigation of the Al13 sulfate synthesis by synchrotron wide-angle X-ray scattering (WAXS). Al13 cluster were crystallized by precipitating hydrolyzed aluminum solutions by the addition of sodium sulfate. The measurements were performed using a custom-made acoustic levitator as sample holder. The study provides information about the intermediates during the crystallization process. From the data, a mechanism was derived indicating the influence of the crystallization process.
The state of fresh concrete is predominantly determined by the rheological properties of the cement paste. In order to control performance spectra and requirements of novel concretes and to better understand macroscopic phenomena, comprehensive knowledge of the material behavior of fresh cement suspensions as well as of the complex relationships of mechanisms at the nano and micro scale are necessary. This work focuses on micro and nano rheology of suspensions of cementitious model systems and the influence of polycarboxylate-based admixtures on the rheology. The phenomena are driven by multiple parameters such as adsorption and particle interactions. Hence, the first part examines the interaction between polycarboxylate ether (PCE) and synthesized clinker phases and hydration products as model systems with regard to early hydration products.
Mechanochemistry is a fast and efficient method applicable for the synthesis of new organic[1], metal-organic[2], and inorganic[3] compounds. The direct monitoring of milling reactions is still challenging. The underlying reaction mechanisms remain often unclear. In the last years, have established a tandem in situ approach for investigating mechanochemical reactions using time-resolved in situ XRD coupled with Raman spectroscopy.[4] Here, we present an in situ coupling of synchrotron XRD, Raman spectroscopy, and thermography allowing the observation of mechanochemical reactions in real time.[5] Information on the crystalline, molecular, and temperature state of the materials during grinding could be collected. The chemical composition of the reaction mixture was found to be directly correlated with changes in the temperature profile of the reaction. Furthermore, the presented setup allows the detection of crystalline, amorphous, eutectic as well as liquid intermediates. The resulting deeper kinetic and thermodynamic understanding of milling processes is the key for future optimization of mechanochemical syntheses.
Mechanochemistry is increasingly used for synthesizing various materials including metal organic compounds and cocrystals. 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 necessary data can only be obtained in in situ experiments, which were only recently established for milling reactions. Herein, we present a novel setup enabling a combined in situ investigation of mechanochemical reactions using synchrotron XRD and Raman spectroscopy.