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Eingeladener Vortrag
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Non-isothermal heating rate kinetics was applied to two epoxy resin systems. In situ near-infrared (NIR) measurements were taken with a heatable NIR cell which allowed the cure to be monitored by characteristic absorption bands. An autocatalyzed reaction of the nth order was shown to describe the epoxy conversion curves. Differential Scanning Calorimetry (DSC) was used as a complementary method. The kinetic models developed by both NIR and DSC are in good accordance with experimental epoxy conversion in the in situ NIR setup for single and multiple cure temperature ramps.
A linear calibration curve of the characteristic absorption bands of epoxy normalized to aromatic vibrations was introduced. The curing degree of structural epoxies that were cured according to an industrial temperature cure profile was determined by NIR using the calibration curve. The epoxy conversions of the structural components showed good agreement with the experimental in situ NIR. Several degrees of cure for structural specimens were evaluated by NIR and residual reaction enthalpy by DSC. We present the non-destructive NIR spectroscopy as an alternative to determine fast and non-destructive epoxy conversion, particularly suitable for high degrees of cure on structural components.
Photoluminescence techniques are amongst the most widely used tools in the life sciences, with new and exciting applications in medical diagnostics and molecular imaging continuously emerging. Advantages include their comparative ease of use, unique sensitivity, non-invasive character, and potential for multiplexing, remote sensing, and miniaturization. General drawbacks are, however, signals, that contain unwanted wavelength- and polarization contributions from instrument-dependent effects, which are also time-dependent due to aging of instrument-components, and difficulties to measure absolute fluorescence intensities. Moreover, scattering systems require special measurement geometries and the interest in new optical reporters with emission > 1000 nm strategies for reliable measurements in the second diagnostic for the comparison of material performance and the rational design of new fluorophores with improved properties.
Here, we present strategies to versatile method-adaptable liquid and solid fluorescence standards for different fluorescence parameters including traceable instrument calibration procedures and the design of integrating sphere setups for the absolute measurement of emission spectra and quantum yields in the wavelength region of 350 to 1600 nm. Examples are multi-emitter glasses, spectral fluorescence standards, and quantum yield standards for the UV/vis/NIR
Lanthanide-doped up-converting nanoparticles (UCNPs) are promising reporters for medical diagnostics and bioimaging, which are excited in the near infrared (NIR) by multiphoton absorption processes, and show multiple narrow emission bands in the visible (vis) and NIR, long luminescence lifetimes in the μs range, and excellent photostability. Current limitations present their relative low absorption cross sections and low fluorescence efficiencies, with the latter being affected by particle size, surface chemistry, and microenvironment, particularly water.
Here, we present results from systematic studies of the excitation power density dependent upconversion luminescence spectra, intensities/intensity ratios of the individual emission bands, slope factors, and quantum yields of UCNPs of varying size, dopant concentration, and surface chemistry in different microenvironments as well as the up- and downconversion luminescence decay kinetics of the different emission bands. Moreover, first studies of the energy transfer from UCNPs to surface-bound organic dyes acting as fluorescence acceptors are shown. Based upon these measurements, fluorescence deactivation channels are identified and spectroscopic parameters for the screening of material performance are derived.
Lanthanide-doped up-converting nanoparticles (UCNPs) are promising reporters for medical diagnostics and bioimaging. Current limitations present their relative low absorption cross sections and low fluorescence efficiencies, with the latter being affected by particle size, surface chemistry, and microenvironment, particularly water.
Here, we present results from systematic studies of the excitation power density dependent upconversion luminescence spectra, intensities/intensity ratios of the individual emission bands, slope factors, and quantum yields of UCNPs of varying size, dopant concentration, and surface chemistry in different microenvironments as well as the up- and downconversion luminescence decay kinetics of the different emission bands. Moreover, first studies of the energy transfer from UCNPs to surface-bound organic dyes acting as fluorescence acceptors are shown. Based upon these measurements, fluorescence deactivation channels are identified and spectroscopic parameters for the screening of material performance are derived.
In order to study the temporally distributed energy deposition in the formation of laser-induced periodic surface structures (LIPSS) on single-crystalline zinc oxide (ZnO), two-colour double-fs-pulse experiments were performed. Parallel or cross-polarised double-pulse sequences at 400 and 800 nm wavelength were generated by a Mach–Zehnder interferometer, exhibiting inter-pulse delays up to a few picoseconds between the sub-ablation 50-fs-pulses. Twenty two-colour double-pulse sequences were collinearly focused by a spherical mirror to the sample surface. The resulting LIPSS periods and areas were analysed by scanning electron microscopy. The delay-dependence of these LIPSS characteristics shows a dissimilar behaviour when compared to the semiconductor silicon, the dielectric fused silica, or the metal titanium. A wavelength-dependent plasmonic mechanism is proposed to explain the delay-dependence of the LIPSS on ZnO when considering multi-photon excitation processes. Our results support the involvement of nonlinear processes for temporally overlapping pulses. These experiments extend previous two-colour studies on the indirect semiconductor silicon towards the direct wide band-gap semiconductor ZnO and further manifest the relevance of the ultrafast energy deposition for LIPSS formation.
Der Vortrag widmet sich der Validierung der Verbundfestigkeit von optischen Schicht-/Substrat-systemen mittels Zentrifugentechnologie und diskutiert Versagensbilder und gemessene Werte der Verbundfestigkeit ausgewählter feinoptischer bzw. ophtalmischer Schichten in Abhängigkeit von den plasto-elastischen Eigenschaften und der Dicke der Substrate.
Kikuchi diffraction patterns can provide fundamental information about the lattice metric of a crystalline phase. In order to improve the possible precision and accuracy of lattice parameter determination from the features observed in Kikuchi patterns, some useful fundamental relationships of geometric crystal-lography are reviewed, which hold true independently of the actual crystal symmetry. The Kikuchi band positions and intersections and the Kikuchi band widths are highly interrelated, which is illustrated by the fact that all lattice plane trace positions of the crystal are predetermined by the definition of only four traces. If, additionally, the projection centre of the gnomonic projection is known, the lattice parameter ratios and the angles between the basis vectors are fixed. A further definition of one specific Kikuchi band width is sufficient to set the absolute sizes of all lattice parameters and to predict the widths of all Kikuchi bands. The mathematical properties of the gnomonic projection turn out to be central to an improved interpretation of Kikuchi pattern data, emphasizing the importance of the exact knowledge of the projection centre.
In dem Projekt soll die vollständige Wiederverwertbarkeit der Schlacke und ihrer Bestandteile demonstriert werden. Dazu gehören die vollständige Rückgewinnung der metallischen Phase, die in die Edelstahlherstellung zurückgeführt werden kann, sowie die Aufwertung der mineralischen Fraktion, die ihre uneingeschränkte Verwendung als Zementzumahlstoff oder mineralischer Baustoff erlaubt. Bei geeigneter Prozessführung des elektrischen Lichtbogenofens können durch „reduzierendes Schmelzen“ die chromhaltigen Wertstoffe zusammen mit anderen Schwermetallen zu 97% in einer Metalllegierung angereichert und separiert werden. Diese kann als Rohstoff in der Metallurgie eingesetzt werden. Der Chromgehalt der mineralischen Komponte der Schlacke konnte von ca. 3% auf unter 0,1% verringert werden. Die mineralische Fraktion lässt sich durch entsprechende Zuschläge während des Schmelzbetriebes und eine anschließende Granulation der schmelzflüssigen Phase zu einem Material aufwerten, das in seiner Zusammensetzung und seinen Eigenschaften typischen Zementkomponenten entspricht und als Rohstoff in der Zementproduktion eingesetzt werden kann. Dafür müssen allerdings noch die rechtlichen Voraussetzungen geschaffen werden, da der Rohstoffeinsatz gerade im Zement strengen Auflagen unterliegt und die Zemente bestimmte Normen erfüllen müssen.
Durch die in RECARC aufgezeigte Möglichkeit der Wiederverwertung können somit Stoffkreisläufe geschlossen werden, die ansonsten zu einem Verlust wertvoller Rohstoffe führen. Vor allem die steigenden Rohstoffkosten, aber auch die immer stärker limitierten CO2-Emissionen zeigen die hohe Relevanz im Umgang mit metallurgischen Reststoffen. Eine Überführung des in RECARC demonstrierten Verfahrens in die Industrie könnte einen wichtigen Beitrag zur nachhaltigen Schonung der natürlichen Ressourcen und der Umwelt leisten.
In dem Projekt sollten die Aufbereitung der Betonbrechsandfraktion aus Bauschutt mittels eines Nassverfahrens zu einer geeigneten Gesteinskörnung für die Betonherstellung sowie die vollständige Verwertung der bei diesem Verfahren anfallenden Reststoffe demonstriert werden.
Der im Rahmen der geordneten Vorsortierung mit zahlreichen Schritten zur Qualitätssicherung hergestellte Betonbrechsand war qualitativ hochwertig und wies nur geringe Schadstoffgehalte auf. Für die Nassaufbereitung des Betonbrechsands wurde vom Projektpartner Allmineral der Prototyp einer Sandsetzmaschine zur Dichtetrennung designt und konstruiert. Diese Sandsetzmaschine wurde für die umfangreichen Betonbrechsandversuche in die Aufbereitungsanlage der BAM integriert. Begleitend zur Aufbereitung wurden die eingesetzten Materialien, Bauschutt und Prozesswasser, sowie die Austragsprodukte chemisch-physikalisch und mineralogisch untersucht.
Die anschließenden Baustoffuntersuchungen zeigten, dass durch das im Demonstrationsprojekt angewandte Nassaufbereitungsverfahren eine deutliche Verbesserung der Materialeigenschaften des Betonbrechsandes erzielt werden konnte. Die Qualität von Natursteinkörnungen wurde (z.B. aufgrund von Kornschädigungen durch den Bruch des Altbetons und noch verbleibende Zementanhaftungen) gleichwohl nicht erreicht. Gerade die Betonprüfungen (mit Anteilen von bis zu 50% Betonbrechsand an der gesamten Gesteinskörnung) haben jedoch gezeigt, dass es dennoch sehr wohl möglich wäre, größere Mengen von aufbereitetem Betonbrechsand in der Betonherstellung zu verwerten und so im Sinne der Nachhaltigkeit den Verbrauch von natürlichen Sandvorkommen zu reduzieren.
Die bei der Nassaufbereitung des Betonbrechsands anfallenden Restsstoffe, nämlich die Fraktionen Leichtgut und Feinstfraktion wurden separat erfasst und bilanziert. Diese Materialien wurden auf die Eignung als Kompostzugabe in Hinblick auf Schadstoffanreicherungen und Pflanzenverträglichkeit untersucht (Projektpartner Deisl). Nach der Kompostierung in Rotteboxen wurden Wachstumsversuche mit dem Referenzgewächs Kresse (Kressetest nach ÖNORM) mit zufriedenstellenden Ergebnissen durchgeführt. Die Reststoffe Feinstgut und Leichtgut aus dem Nassaufbereitungsprozess könnten – sofern die Schadstoffgehalte nachweislich unter den vorgegebenen Grenzwerten liegen – als Zugabe zur Vererdung in der Kompostierung eingesetzt werden.
The use of renewable energy technologies, such as photovoltaics (PV) should be sustainable and environmentally compatible and therefore protect the environment from risks and damaging impacts. Regarding the growing number of installed photovoltaic systems, the end-of-life management of the pv-modules will become increasingly important. Thin film panels contain hazardous substances that may harm the environment if they are not recycled or disposed properly after reaching the end of their service life. Heavy metals, for example, can be toxic as well as carcinogenic or teratogenic. Processing methods for the recycling of PV thin film modules have to take these facts into account. Currently the available recycling techniques usually utilise chemicals such as acids for a wet-chemical treatment of end-of-life modules. The aim of RESOLVED was to identify and test alternative methods for a wet-mechanical treatment in order to reduce the consumption of chemicals in the recycling of thin film modules. Furthermore, the recovered Cadmium-Telluride (CdTe) and Copper-Indium-Diselenide/Disulfide (CIS) should be helping to save scare resources especially for limited elements such as tellurium and indium. The project RESOLVED investigated the recovery of semiconductors material as secondary raw material and the decontamination of the residues of the PV thin film modules. These goals were achieved by testing and optimising existing technologies for the recycling process as well as for the enrichment of the semiconductor materials. The target is to re-use the enriched recovered material in the production of new PV modules. Special efforts were made to look into life cycle analysis, process sustainability, economical aspects, and resource availability.
A laser induced breakdown spectroscopy (LIBS) system was combined with the Gas Tungsten Arc (TIG) Welding process for the in situ monitoring of chemical compositions in austenitic stainless steels during welding. The purpose of this project is to develop a prototype of an online chemical composition control system for welding applications. One of the use cases of this new LIBS-based measurement system can be the controlling of potentially dangerous emissions during the welding process in order to improve the working safety conditions.
Synchrotron Radiation with its high intensity and the opportunity to tune the wavelength offers unique possibilities to investigate real catalysts, even under industry-like conditions.
A good example is a XAFS study performed at supported Ni catalysts used for the dimerization of butene at elevated temperature and pressure. Another example are investigations at titania supported Pd based catalyst elucidating the role of co-components (e.g. Sb, Co, Mn and Au) which are necessary to get the desired promising performance in the gas phase acetoxylation of toluene to benzyl acetate, an environmentally benign alternative for the conventional process using chlorine.
Furthermore, investigations about the redox properties of different Cu catalysts will be presented. It could be shown that the redox properties of Cu have a great impact on the performance of such catalysts, not only in some gas phase reactions, but also in photocatalytic applications, e.g. water splitting.
Additive Manufacturing by Selective Laser Melting (SLM) offers ample scope for producing geometrically complex parts as compared to the traditional subtractive manufacturing strategies. However, the residual stresses (RS) developed during the processing can reduce the load bearing capacity as well as induce unwanted distortion, limiting the application of SLM parts. In the present work, residual stresses in additivly manufactured IN718 part were analised by means of neutron diffraction and synchrotron X-ray diffraction.
The work aims at addressing the modelling and implementation of criteria for multiple crack propagation, including interaction and coalescence, for a more reliable fracture mechanics-based prediction of stress-life curves for weldments.
A large experimental work is presented in which micro-cracks have been made visible by heat-tinting at successive stages of fatigue life of the welded specimens. Here the correlation between the number of initiation sites and the applied stress level has been also investigated.
The criteria have been implemented in in-house software, which allows multiple fatigue crack propagation, and validated against selected experimental tests. The results have shown that the modelling of multiple crack propagation and interaction is crucial for the prediction of the fatigue strength of weldments, both in finite and infinite life regime.
The work aims at addressing the modelling and implementation of criteria for multiple crack propagation, including interaction and coalescence, for a more reliable fracture mechanics-based prediction of stress-life curves for weldments.
A large experimental work is presented in which micro-cracks have been made visible by heat-tinting at successive stages of fatigue life of the welded specimens. Here the correlation between the number of initiation sites and the applied stress level has been also investigated.
The criteria have been implemented in in-house software, which allows multiple fatigue crack propagation, and validated against selected experimental tests. The results have shown that the modelling of multiple crack propagation and interaction is crucial for the prediction of the fatigue strength of weldments, both in finite and infinite life regime.
Faser-Kunststoff-Verbunde werden zunehmend in der Luft- und Raumfahrt, der Automobil- und Windenergieindustrie eingesetzt. Die hier entwickelten Bauteile sind oft nicht nur multiaxialen mechanischen Belastungen, sondern auch hohen klimatischen Beanspruchungen ausgesetzt. Einsatztemperaturen zwischen -60°C und 100°C bei 10-90% relativer Feuchte sind keine Seltenheit, in der Raumfahrt sind die thermischen Belastungen sogar noch extremer. Die Auswirkungen einer Wechselwirkung extremer klimatischer Beanspruchungen mit multiaxialen mechanischen Belastungen wurden bisher kaum betrachtet. Das Ziel des Projektes ist die Untersuchung des Ermüdungsverhaltens der Faser-Kunststoff-Verbunde in Abhängigkeit von multiaxialer mechanischer Belastung, Temperatur und Feuchte. Dazu werden umfangreiche experimentelle Untersuchungen an Flach- und Rohrproben sowie numerische und analytische Berechnungen durchgeführt.
Für die Durchführung der Experimente werden zunächst Glasfaser-Preforms in einem an der BAM entwickelten Haspelverfahren ohne nominelle Ondulation hergestellt. Aus diesen Preforms werden anschließend in einem vakuumunterstützten Resin Transfer Molding (RTM)-Prozess die GFK-Probekörper gefertigt.
Bisher wurden die thermoelastischen Eigenschaften und die Festigkeiten des Faser-Kunststoff-Verbundes und der Matrix mit Zug- und Druckversuchen unter paralleler Temperaturlast im Bereich von -60°C bis +80°C ermittelt. Auf der Basis eines Konzeptes zur Berechnung der Matrixbeanspruchung wurde ein Modell zur Bestimmung des Schädigungsbeginns von Laminaten unter quasistatischer thermomechanischer Belastung weiterentwickelt und experimentell validiert.
Im weiteren Verlauf des Projekts wird das Verhalten von Glasfaser-Kunststoff-Verbunden unter schwingender Belastung und paralleler Temperaturlast untersucht. Hier wurden bereits Experimente bei Raumtemperatur durchgeführt. Mit dem Verfahren der Grauwertanalyse ist es dabei möglich, in-situ die Schädigung des Werkstoffs zu messen. Des Weiteren wird das Verhalten von Faser-Kunststoff-Verbunden unter zyklischer Temperaturlast ohne mechanische Belastung untersucht. Auch hier zeigen sich bereits nach wenigen Lastwechseln erste Zwischenfaserbrüche.
Up to now, there exists a lack of methods for the additive manufacturing of voluminous ceramic parts with properties comparable to those of conventionally manufactured ones. A high density after sintering is needed to reach the superior properties of ceramic materials. We have developed a new additive manufacturing method, Laser-Induced Slip casting (LIS), to generate ceramic green bodies with high particle packing density and with virtually no restriction in the particle size of the feedstock, especially in terms of small particles. This is achieved by laser-induced local drying of slurries, with the process resembling many features of the well-established stereolithography, but without the excessive use of polymeric material. Thus, unlike the stereolithography process, the resulting green bodies can be processed like traditionally produced ceramic parts. This method allows large and dense additive-manufactured parts to be obtained from conventional water-based ceramic slurries. As an example, we will demonstrate the application of this novel technique with Si3N4.
Volume fraction determination of discretely oriented disc-shaped precipitates in transmission mode
(2017)
In der vorliegenden Arbeit wurde eine Formel zur Berechnung des Volumenantei ls dis kret orientierter scheibenförmiger Phasen für die Untersuchung im Transmissionsmodus hergeleitet, validiert und mit bereits veröffent lichen Formeln verglichen. Bei diesem Ver gleich konnte gezeigt werden,dass die in zahl reichen Veröffentlichungen benutzte Formel von E. E. Underwood für die Volumenanteils bestimmungbeidiskret orientierten Ausschei dungsphasen nicht benutzt werden sollte, da sie den Volumenanteil deutlich unterschätzt.
Die Ursache liegt in der von E.E. Underwood getroffenen Annahme, dass die kreisförmigen Scheiben regellos angeordnet und nicht aus gerichtet sind, was in Al-Legierungen in der Regel nicht der Fall ist.
Die transiente nichtlineare 3D-Wärmeleitungsgleichung wurde zur numerischen Lösung mittels der Finite-Elemente-Methode im Ort und mittels explizitem Eulerschema in der Zeit diskretisiert. Der resultierende Algorithmus wurde in ein Computerprogramm überführt wobei besonderer Wert auf paralleles Rechnen gelegt wurde. Das Programm wurde auf die numerische Berechnung eines schweißtypischen transienten Temperaturfelds angewandt. Die Rechenzeit und Skalierbarkeit des Computerprogramms bezüglich der Anzahl verwendeter CPU Kerne wurde untersucht und mit dem kommerziellen FEM Programm Abaqus 6.14 verglichen. Die Anwendung der expliziten Zeitintegration resultiert in verbesserter Skalierbarkeit bezüglich der Anzahl verwendeter CPU Kerne und Rechenzeitersparnis gegenüber der in Abaqus implementierten impliziten Zeitintegrationsmethode.
An approach to develop an arc sensor for gap-width estimation during automated NG-GMAW with a weaving electrode motion is introduced by combining arc sensor readings with optical measurement of the groove shape to allow precise analyses of the process. The two test specimen welded for this study were designed to feature a variable groove geometry in order to maximize efficiency of the conducted experimental efforts, resulting in 1696 individual weaving cycle records with associated arc sensor measurements, process parameters and groove shape information. Gap width was varied from 18 to 25 mm and wire feed rates in the range of 9 to 13 m/min were used in the course of this study. Artificial neural networks were used as a modelling tool to derive an arc sensor for estimation of gap width suitable for online process control that can adapt to changes in process parameters as well as changes in the weaving motion of the electrode. Wire feed rate, weaving current, sidewall dwell currents and angles were used as inputs to calculate the gap width. Evaluation the proposed arc sensor model show very good estimation capabilities for parameters sufficiently covered during experiments.
The aim of the present work was to investigate the possibilities of hybrid laser arc welding regarding reliable production of longitudinal welds of high strength pipe steels X80 and X120 and to evaluate achievable mechanical properties of laser hybrid welds. The study focused on weld toughness examination in low temperature range up to -60 °C. SЮТЭКЛХО ПТХХОЫ ЦКЭОЫТКХЬ were identified in the context of this task. It could be shown that metal cored electrodes guaranteed sufficient Charpy impact toughness at low temperature for both investigated materials. Modern arc welding technologies such as modified pulsed spray arc were used to promote deeper Penetration of the filler material into the narrow laser welding gap. Edge preparation with a 14 mm deep root face was considered as optimum, because no penetration of the filler material could be detected beyond this depth limit and therefore any metallurgical influences on the weld metal properties through the welding wire could be excluded.
The process of laser metal deposition can be applied in many ways. Mostly, it is relevant to coating, for repair welding and for additive manufacturing. To increase the effectiveness and the productiveness, a good process understanding is necessary. Statistical test planning is effectual and often used for this purpose. For financial and temporal reasons, a restriction of the test space is reasonable. In this case, it is recommended to use a D-optimal experimental design which is practically applied to extend existing test plans or if process Limits are known. This paper investigates the applicability of a D-optimum experimental design for the laser metal deposition. The results are compared to the current results of a full factorial test plan.
Known restrictions are used for the limitation of the test space. Ti6Al4 is utilized as Substrate material and powder. Comparable results of the D-optimal experimental design and of the full factorial test plan can be demonstrated. However, 80 % of time can be saved by the experimental procedure. For this reason, the application of D-optimal experimental design for laser metal deposition is recommend.
Borosilicate glass has a wide range of technical applications due to its high chemical durability and thermal-shock resistivity. Here the effect of H2O on 16 Na2O, 10 B2O3,74 SiO2 glass is studied over a wide range of water contents from 0 to 8 wt.%. MIR spectra give evidence for the coexistence of strongly and weakly H-bonded hydrous species. Evaluation of NIR bands at 5200 cm-1 (molecular H2O), 4700 cm-1 (B-OH), and 4500 cm-1 (Si-OH) reveal that OH groups dominate up to ~6 wt.% H2O, with B-OH/Si-OH of ≈ 0.8. The incorporation of low amounts of H2O has strong impact on structure. NMR spectra of nominally dry glasses indicate a significant fraction (12 %) of 3-coordinated boron, but almost all boron is 4-coordinated after addition of 3 wt.% H2O. Raman spectra show that hydration results preferentially in transformation of Q4 to Q2 while Q3 remain unchanged, probably stabilized by bonding to BO4 tetrahedra. Viscosity measurements and differential thermal analysis give consistent results, confirming strong decrease of the glass transition temperature with addition of water from 849 K (dry) to 540 K (5 wt% H2O). An additional relaxation mechanism in hydrous glasses is inferred from dynamic mechanical analysis and is assigned to cooperative processes involving hydrous species. It is postulated that this relaxation mechanism plays an important role in crack growth kinetics.
Surface water-induced broadening of crack initiation probability of zinc aluminosilicate glasses
(2017)
The crack generation probability by Vickers indentation of glass surfaces is known to be influenced by the atmospheric conditions under which the Vickers experiment is performed [1]. However, the effect of surface water due to preparation and storage of the glass surfaces prior to the indentation is less understood. Therefore, zinc aluminosilicate glasses of perzinc, peraluminous as well as nominally NBO-free meta-aluminous composition were prepared by melt quenching. Surfaces of cut and polished specimens of these glasses were either stored for seven days under constant atmosphere (50 °C; 55% RH) or etched (HF: 20vol%; 20 min) shortly before indentation. The obtained results show a strong variation of crack initiation behavior depending on chemical composition of the glasses as well as sample preparation. All experiments were performed in dry nitrogen gas to minimize the influence of atmospheric humidity during indentation. While the regular glass surfaces exposed to humid air prior to Vickers indentation show a broad distribution of crack initiation probability, this distribution narrows down if etched glass surfaces are tested. SNMS depth profiling shows a water enriched layer at the surface (150 μm) for the non-etched and stored specimens leading to the conclusion that surface water causes broadening of the crack initiation probability of glass surfaces.
Borosilicate glass has a wide range of technical applications due to its high chemical durability and thermal-shock resistivity. Here the effect of H2O on 16 Na2O, 10 B2O3,74 SiO2 glass is studied over a wide range of water contents from 0 to 8 wt.%. MIR spectra give evidence for the coexistence of strongly and weakly H-bonded hydrous species. Evaluation of NIR bands at 5200 cm-1 (molecular H2O), 4700 cm-1 (B-OH), and 4500 cm-1 (Si-OH) reveal that OH groups dominate up to ~6 wt.% H2O, with B-OH/Si-OH of ≈ 0.8. The incorporation of low amounts of H2O has strong impact on structure. NMR spectra of nominally dry glasses indicate a significant fraction (12 %) of 3-coordinated boron, but almost all boron is 4-coordinated after addition of 3 wt.% H2O. Raman spectra show that hydration results preferentially in transformation of Q4 to Q2 while Q3 remain unchanged, probably stabilized by bonding to BO4 tetrahedra. Viscosity measurements and differential thermal analysis give consistent results, confirming strong decrease of the glass transition temperature with addition of water from 849 K (dry) to 540 K (5 wt% H2O). An additional relaxation mechanism in hydrous glasses is inferred from dynamic mechanical analysis and is assigned to cooperative processes involving hydrous species. It is postulated that this relaxation mechanism plays an important role in crack growth kinetics.
Diverse animal species consume toxins, minerals or secondary compounds as an adaptive response to pathogen infection – a process termed self-medication. Recent studies have also shown that macronutrients can play an important role in an individual’s infection response. For instance African army worm caterpillars select a diet rich in protein and low in carbohydrate upon baculovirus infection. Here we investigate whether dietary choice of macronutrients also plays a role in immunity in the omnivorous cockroach: Blatta orientalis. After challenging individual cockroaches with a common entomopathogenic soil bacterium, Pseudomonas entomophila, we conducted food-choice experiments using two artificial diets differing in their relative protein to carbohydrate ratio. We show for the first time that cockroaches are able to self-select a protein-enriched diet as a response to bacterial infection. This is driven by a sharp decline in carbohydrate intake rather than an increase in protein intake. Additionally, infected cockroaches reduced their overall nutrient intake, which is consistent with an illness-induced anorexia-like response. The feeding pattern of bacteria-challenged individuals returned to normality approx 4 days after challenge. We also investigate whether cockroach survival and hemolymph immunity are enhanced in individuals when restricted to a protein-rich vs. carbohydrate-rich diet. Overall, our findings demonstrate that macronutrient preferences follow a general pattern independent of pathogen type. Furthermore, we show that interactions between nutrition and immunity are highly conserved in evolution, highlighted by the fact that caterpillars and cockroaches diverged some 386 million years ago.
Quantum dot (QD) based nanomaterials are very promising materials for the fabrication of optoelectronic devices like solar cells, light emitting diodes (LEDs), and photodetectors as well as as reporters for chemo- and biosensing and bioimaging. Many of These applications involve the monitoring of changes in photoluminescence intensity and energy transfer processes which can strongly depend on excitation wavelength or energy. In this work, we analyzed the excitation energy dependence (EED) of the photoluminescence quantum yields (PL QYs) and decay kinetics and the circular dichroism (CD) spectra of CdSe/CdS core/shell QDs with different thicknesses of the surface passivation shell. Our results demonstrate a strong correlation between the spectral position of local maxima observed in the EED of PL QY and the zero-crossing points of the CD profiles. Theoretical analysis of the energy band structure of the QDs with effective mass approximation suggests that these structures could correspond to exciton energy levels. This underlines the potential of CD spectroscopy for the study of electronic energy structure of chiroptically active nanocrystals which reveal quantum confinement effects.
Several Additive Manufacturing (AM) processes are based on the deposition of a powder to form a powder bed layer-by-layer, which typically has a low packing density (35-50%) and consequently hinders the ability of sintering ceramic parts to full density.
The layerwise slurry deposition (LSD) is an innovative process for the deposition of layers in AM. In the LSD, a slurry with no or small organic content is repetitively spread as thin layers on each other by means of a doctor blade. During the deposition, the ceramic particles settle to form thin layers with a high packing density (55-60%). When coupled with a printing head or with a laser, the LSD enables novel AM technologies inspired to the 3D printing or selective laser sintering, but taking advantage of having a highly dense powder-bed.
The LSD combined with inkjet binder printing (LSD-print) was applied to a submicron Al2O3 powder to produce samples which had a comparable density to uniaxially pressed samples, both in the green and in the sintered state.
The work presents the microstructure, chemical composition and mechanical properties of Inconel 686 coatings after high - temperature corrosion in environment of aggressive gases. To produce the Ni - base weld overlays the QS Nd:YAG laser beam was used. The substrates were 13Mo4-5 boilers plate steel. Ni - base alloys characterize the excellent high temperature corrosion resistance, good strength and good ability to work in aggressive environments. Applied overlays had a proper combination of the metal substrate in particular small amount of Fe. This could be achieved by the reduction of the melting of the substrate and its dissolution into the overlays. The microstructure, chemical composition of the obtained overlays were investigated by means of a light microscope, a scanning electron microscope (SEM) equipped with the EDS detector. The overlays had cellular-dendritic structure. The variations of the chemical composition (especially Mo, Ni and W ) in the interdendritic and dendritic regions were observed. The interdendritic regions were enriched during solidifications in Mo and W and had lower content of Ni.
Recent studies have shown that host-microbiota interactions can lead to dramatic changes in host phenotype. We investigate the causal drivers of microbe-associated shifts in host phenotype by examining how feeding behaviour is modulated by microbiota interactions in two omnivorous cockroaches: Blatta orientalis and Blatella germanica. We conducted food-choice experiments after challenging hosts with a common entomopathogenic soil bacterium to understand the impact of pathogens on host macronutrient preference. We find that immune challenge by a pathogenic microbe drives a sharp decline in carbohydrate intake and results in a relative increase in the ratio of protein to carbohydrate (P:C) consumed. Additionally, infected cockroaches reduce their overall nutrient intake, which is consistent with an illness-induced anorexia-like response. We show for the first time that cockroach feeding behaviour is dynamically modulated by a pathogen, and examine the influence of modified feeding behaviour on host immunity. We also investigate whether in addition to pathogens, gut commensals are causally responsible for shifts in host behavioural phenotype. Here, we conduct food-choice and immune-challenge experiments in germ-free cockroaches, which have been refaunated with gut microbiota that are experimentally adapted to variable macronutrient (P:C) diets.
Recent studies have shown that host-microbiota interactions can lead to dramatic changes in host phenotype. We investigate the causal drivers of microbe-associated shifts in host phenotype by examining how feeding behaviour is modulated by microbiota interactions in two omnivorous cockroaches: Blatta orientalis and Blatella germanica. We conducted food-choice experiments after challenging hosts with a common entomopathogenic soil bacterium to understand the impact of pathogens on host macronutrient preference. We find that immune challenge by a pathogenic microbe drives a sharp decline in carbohydrate intake and results in a relative increase in the ratio of protein to carbohydrate (P:C) consumed. Additionally, infected cockroaches reduce their Overall nutrient intake, which is consistent with an illness-induced anorexia-like response. We show for the first time that cockroach feeding behaviour is dynamically modulated by a pathogen, and examine the influence of modified feeding behaviour on host immunity. We also investigate whether in Addition to pathogens, gut commensals are causally responsible for shifts in host behavioural phenotype. Here, we conduct food-choice and immune-challenge experiments in germ-free cockroaches, which have been refaunated with gut microbiota that are experimentally adapted to variable macronutrient (P:C) diets.
The microstructure of weld overlay Ni - base alloy deposited on carbon steel by laser QS-Nd:YAG
(2017)
Ni- base alloys are used as a one of the most important coating material and can be applied in a different environments and elements of devices having various applications. To protect the surface of the material from aggressive gases at high temperature, there are use different kinds of the Ni- base alloys. One of such alloy is Ni-Cr-Mo-W called commercial Inconel 686. This alloy based on NiCr22Mo9Nb (Inconel 625), in which content of molybdenum increased and niobium was replaced with the addition of tungsten, in order to counteract the strong segregation in the microstructure, which results in homogeneity of the chemical composition of the structure. Inconel 686 is also characterized by greater resistance to high temperature corrosion and heat resistance than Inconel 625. The Inconel 686 alloy was deposited on 13CrMo4-5 steel by laser QS - Nd:YAG. In the poster the microstructure (SEM) and chemical composition (EDS) of obtained weld overlays were investigated.
185 cracks were initiated in a soda-lime-silica glass by Vickers indentation and grown under controlled dry nitrogen atmosphere. Direct observation of subcritical crack growth (SCCG) upon indentation was performed using a video camera with an image acquisition rate of 3 ms. The results show that the validity of K(c) relations used to determine the indentation fracture toughness from a single imprint is questionable. It seems that correlation of crack length to stress intensity necessitate the use of statistical significant data of multiple crack events.
Hydrous silicate and borate glasses of up to 8 wt% water were prepared using wet condition of melting under external pressure. Rheological experiments were conducted to determine the effect of the total water content on viscous flow and kinetic fragility. The findings indicate that dissolved water acts as a strong fluxing agent in both glass types. Water decreases particularly viscosity at the glass transition range, makes the viscosity-temperature curve "longer" and thus decreases kinetic fragility. Recent IR and NMR data are presented to link the dynamics of hydrous silicate and borate glasses with their structure particularly with regard to changes in the water-, silicon- and boron-speciation.
Um das Risswachstum in Gläsern zu untersuchen, sind in einer Glovebox 185 Risse ausgehen von Vickers-Eindrücken in Kalk-Natron-Glas initiiert und gewachsen. Die direkte Beobachtung des unterkritischen Risswachstums erfolgte mit einer Hochgeschwindigkeitskamera. Die Ergebnisse zeigen, dass die statistische Auswertung vieler radialer Risse von multiplen Rissevents notwendig ist, um eine Korrelation zum Spannungsintensitätsfaktor ziehen zu können.
Glasig-kristalline Werkstoffe für Schlüsseltechnologien - Prozessbegleitende Prüfung und Simulation
(2017)
Eigenschaftsprofile und Kennwertstreuungen keramischer und glaskeramischer Komponenten und Bauteile werden durch ihren Herstellungsprozess wesentlich mitbestimmt. Prozessbegleitende Prüf- und Simulationsmethoden gewinnen so wachsenden Einfluss auf die Erschließung neuer Applikationsfelder dieser Werkstoffe. Eine wichtige Rol¬le spielen hierbei oft thermokinetische Prozesse, die u. a. Wärmetransport- und Diffusionsvorgänge, Phasengrenzflächenreaktionen, das rheologische Verhalten heterogener Systeme sowie deren Gefügeevolution beim Sintern umfassen. Ziel des Vortrages ist es, diesen Trend anhand ausgewählter Bei-spiele aus der Arbeit des Fachbereichs Glas der BAM zu illustrieren.
Up to now, the mechanisms of surface nucleation and surface-induced texture formation are far from being understood. Corresponding phenomena are discussed hypothetically or even controversial, and related studies are restricted to very few glasses. As a main drawback, the vast majority of previous work on oriented growth of surface crystals do not consider the possible effects of glass surface treatments (like polishing defects, adhered particles and cracks, …) or ambient annealing conditions (vacuum or atmospheric pressure) which both can influence crystal nucleation and growth. Moreover, very few observations of crystal orientation related to surface crystallization were focused on separately growing crystals. In conclusion, up to now, no systematic studies on initially oriented crystal growth or nucleation from defined active nucleation sites have been pursued.
Therefore, the main objective of the proposed project is to gain a basic understanding of the mechanisms of surface-induced microstructure formation in glass ceramics. We shall answer the question whether preferred orientation of surface crystals is the result of oriented nucleation or caused by other orientation selection mechanisms acting during early crystal growth. In both cases, crystal orientation may be caused by the orientation of the glass surface itself or the anisotropy and orientation of active surface nucleation defects.
New techniques of experimental characterization of surface-crystallized glasses shall be applied to find answers to the questions posed above. Based on a controlled preparation and annealing of the glass sample surfaces, that includes the defined creation of active nucleation defects, and followed by the microstructural characterization especially during the very early growth stages of separated surface crystals, the orientation relations between defect and initiated surface crystal will be analyzed. In order to gain new insights, a couple of entirely new microstructure diagnostics techniques, including chemically contrasted XRM, laser-based sample preparation for XRM, and 3D electron backscatter diffraction shall be developed or applied.
This way, using X-ray microscopy as a pivotal technique for the non-destructive 3D characterization of relatively large samples at superior spatial resolution (but also complemented by other microstructure diagnostics techniques, e.g. TEM elemental mappings at cross-sectioned samples) unprecedented insights into the microstructure evolution upon surface crystallization of model glasses will be gained.
The manufacture of sintered glasses and glass-ceramics, glass Matrix composites and glass-bounded ceramics or pastes is often affected by gas bubble formation. Against this background, we studied sintering and foaming of barium silicate glass powders used as SOFC sealants using different powder milling scenarios. Sintering was measured by means of heating microscopy backed up by XPD, DTA, Vacuum Hot Extraction (VHE) and optical and electron microscopy. Foaming increased significantly as milling progressed. For moderately milled glass powders, subsequent storage in air could also promote foaming. Although the powder compacts were uniaxially pressed and sintered in air, the milling environment significantly affected foaming. The strength of this effect increased in the order Ar >> N2 < air < CO2. Conformingly, VHE studies revealed that the pores of aerated samples predominantly encapsulated CO2, even for powders milled in Ar and N2. Results of this study thus indicate that foaming is caused by carbonaceous species trapped on the glass powder surface. Foaming could be substantially reduced by milling in water and 10 wt% HCl.
Up to now, the mechanisms of surface nucleation and surface-induced texture formation are far from being understood. Corresponding phenomena are discussed hypothetically or even controversial, and related studies are restricted to very few glasses. As a main drawback, the vast majority of previous work on oriented growth of surface crystals do not consider the possible effects of glass surface treatments (like polishing defects, adhered particles and cracks, …) or ambient annealing conditions (vacuum or atmospheric pressure) which both can influence crystal nucleation and growth. Moreover, very few observations of crystal orientation related to surface crystallization were focused on separately growing crystals. In conclusion, up to now, no systematic studies on initially oriented crystal growth or nucleation from defined active nucleation sites have been pursued.
Therefore, the main objective of the proposed project is to gain a basic understanding of the mechanisms of surface-induced microstructure formation in glass ceramics. We shall answer the question whether preferred orientation of surface crystals is the result of oriented nucleation or caused by other orientation selection mechanisms acting during early crystal growth. In both cases, crystal orientation may be caused by the orientation of the glass surface itself or the anisotropy and orientation of active surface nucleation defects.
New techniques of experimental characterization of surface-crystallized glasses shall be applied to find answers to the questions posed above. Based on a controlled preparation and annealing of the glass sample surfaces, that includes the defined creation of active nucleation defects, and followed by the microstructural characterization especially during the very early growth stages of separated surface crystals, the orientation relations between defect and initiated surface crystal will be analyzed. In order to gain new insights, a couple of entirely new microstructure diagnostics techniques, including chemically contrasted XRM, laser-based sample preparation for XRM, and 3D electron backscatter diffraction shall be developed or applied.
This way, using X-ray microscopy as a pivotal technique for the non-destructive 3D characterization of relatively large samples at superior spatial resolution (but also complemented by other microstructure diagnostics techniques, e.g. TEM elemental mappings at cross-sectioned samples) unprecedented insights into the microstructure evolution upon surface crystallization of model glasses will be gained.
The layer-wise slurry deposition (LSD) is an innovative process for the deposition of powder layers with a high packing density for Additive Manufacturing (AM). A slurry with small organic content is repetitively spread as thin layers on top of each other by means of a doctor blade. During the deposition, the ceramic particles settle to form thin layers with a high packing density (55-60%). Each layer is then dried, resulting in the stacking of a dry powder bed with high powder packing. When coupled with a printing head or with a laser source, the LSD enables novel AM technologies inspired to the 3D printing or selective laser sintering, but taking advantage of having a highly dense powder bed.
The LSD -3D printing, in particular, offers the potential of producing large (> 100 mm) and high quality ceramic parts, with microstructure and properties similar to traditional processing.
This presentation will give an overview of the milestones in the development of this technology, with focus on the latest results applied both to silicate and to technical ceramics.
Lanthanide-doped upconversion nanoparticles (UCNPs) are of great interest for biomedical applications. Currently, the applicability of UCNP bionanotechnology is hampered by the generally low luminescence intensity of UCNPs and inefficient energy Transfer from UCNPs to surface-bound chromophores used e.g. for photodynamic therapy or analyte sensing. In this work, we address the low-Efficiency issue by developing versatile core-Shell nanostructures, where high-concentration sensitizers and activators are confined in the core and Shell Region of representative hexagonal NaYF2:Yb,Er UCNPs. After Doping concentration optimization, the sensitizer-rich core is able to harvest/accumulate more excitation energy and generate almost one order of Magnitude higher luminescence intesity than conventional homogeneously doped nanostructures. At the same time, the activator Ions located in the Shell enable a ~6 times more efficient resonant energy Transfer from UCNPs to surface-bound acceptor dye molecules due to the short distance between donor-acceptor pairs. Our work provides new insights into the rational design of UCNPs and will greatly encrease the General applicability of upconversion nanotechnologies.
Micelles are of increasing importance as versatile carriers for hydrophobic substances and nanoprobes for a wide range of pharmaceutical, diagnostic, medical, and therapeutic applications. A key Parameter indicating the Formation and stability of micelles is the critical micelle concentration (CMC). In this respect, we determined the CMC of common anionic, cationic, and non-ionic surfactants fluorometrically using different fluorescent probes and fluorescence Parameters for Signal detection and ompared the results with conductometric and surface Tension measurements. Based upon These results, requirements, Advantages, and pitfalls of each methods are discussed. Our study underlines the versatility of fluorometric methods that do not impose specific requirements on surfactants and are especially suited for the quantification of very low CMC values. Conductivity and surface Tension measurements yield smaller uncertainties particularly for high CMC values, yet are more time- and substance consuming and not suitable for every surfactant.
Corrosion fatigue (CF) of duplex stainless steel (DSS) X2CrNiMoN22-5-3 was investigated in in-situ geothermal conditions of the Northern German Basin (NGB). The influence of the load type on CF behavior of the alloy was examined by applying push/pull and rotating bending cyclic load to failure. The hour-glass shaped specimens with both polished and precisely turned surface finish were tested in corrosion chambers allowing for the permanent circulation of Northern German Basin electrolyte heated to 369 K. Additionally, the influence of a protective cathodic potential on the CF life expectancy was investigated by employing a potentiostat. The rotating bending cyclic load led to a higher CF life expectancy, which decreased with increasing duration of the experiment due to a higher deterioration rate of the material. The application of a cathodic potential caused a significant increase of the CF lifespan from 4.7 x 105 (open-circuit potential (OCP)) to 107 cycles (preset threshold cycle number) for the potential range from USHE = – 450 to – 900 mV. Microstructural analysis of the CF damage revealed horizontal grain attack within corrosion pit cavities, multiple fatigue cracks and preferable deterioration of the austenitic phase.
The paper provides an overview on the results of a German cluster project on the use of fracture mechanics to the determination of the fatigue strength of weldments with fatigue cracks originating at the weld toes. The approach includes (a) a concept for short crack propagation for which the common ΔK concept is not applicable and the crack closure effects are still being gradually build-up, (b) a method for determining fatigue life relevant initial crack sizes as they are needed in any fracture mechanics analysis and (c) multiple cracking and crack coalescence at load levels higher than the endurance limit. The analyses are stochastically performed. Both, the endurance limit and the finite life branch of the S-N curve are determined.
Besides a brief introduction into the approach, validation examples are presented. These comprise different weldment types (butt welds, cross joints and longitudinal stiffened plates), two steels (S355NL and S960QL) of quite different strengths, different weld geometries due to different welding techniques (WIG, MAG), as-welded and stress relieved welds and different stress ratios varying from R = -1 to R = 0.5.
The additive manufacturing technology of Selective Laser Melting (SLM) experiences a rapid development within an increasing marked of quite different application fields. The properties of SLM materials and structures are influenced by a number of tech-nological parameters such as the metal powder (particle size, homogeneity, cleanliness), the laser tool (power, beam diameter, pulse lengths), the scanning operation (speed, sequence and orientation of melting paths), parameters of the over-all equipment (design and preheating of the base plate, currents and turbulence in the protective gas atmosphere) and, last not least, the hatching strategy including the build-up direction of the structure with respect to the loading direction of the component.
For the perspective use of SLM structures as load carrying, safety-relevant components the knowledge of their mechanical properties is necessary. It is essential to understand these in the context of the manufacturing-related features and at the back-ground of the basic characteristics of metallic materials: crystal lattice, microstructure and material defects. The paper provides an overview on factors which affect the mechanical parameters stiffness, strength, ductility, toughness, fatigue crack propagation and fatigue strength in the context of selective laser melting.
Damage development and damage tolerance of structures manufactured by selective laser melting
(2017)
The additive manufacturing technology of Selective Laser Melting (SLM) experiences a rapid development within an increasing marked of quite different application fields. The properties of SLM materials and structures are influenced by a number of tech-nological parameters such as the metal powder (particle size, homogeneity, cleanliness), the laser tool (power, beam diameter, pulse lengths), the scanning operation (speed, sequence and orientation of melting paths), parameters of the over-all equipment (design and preheating of the base plate, currents and turbulence in the protective gas atmosphere) and, last not least, the hatching strategy including the build-up direction of the structure with respect to the loading direction of the component.
For the perspective use of SLM structures as load carrying, safety-relevant components the knowledge of their mechanical properties is necessary. It is essential to understand these in the context of the manufacturing-related features and at the back-ground of the basic characteristics of metallic materials: crystal lattice, microstructure and material defects. The paper provides an overview on factors which affect the mechanical parameters stiffness, strength, ductility, toughness, fatigue crack propagation and fatigue strength in the context of selective laser melting.
Absorption edge tomography is a method which exploits the sudden change of the attenuation coefficient, when the photon energy crosses the absorption edge of an element. The beamline BAMline at BESSY II, which is operated by the Federal Institute for Materials Research and Testing, can provide a monochromatized beam in a photon energy range from 5 keV up to 80 keV with a bandwidth of 2%. Together with the microtomography setup, this enables differential tomography sensitive to any element with N >= 24 (Cr) by using an appropriate K- or L-edge in this range. Here, absorption edge tomography at the Yttrium edge is employed to perform a non-destructive 3D characterization of the microstructure of a high strength Mg-Y-Zn alloy. The long period stacking ordered (LPSO) phase which forms fibres in this material was extracted based on the Yttrium content and the fibre length distribution was analysed.
A 30GHz liquid-crystal-based amplitude tuner is proposed for the first time. The amplitude of a signal can be controlled by using the interference principle. An input signal is divided into a tunable liquid crystal phase shifter and a fixed transmission line. Later, the divided signals are combined together at the output port. The output amplitude depends on the phase difference between the tunable and the fixed line. The low temperature co-fired ceramic technology is utilized to fabricate the device. The measurement shows an attenuation range of 11 dB to 30 dB with a maximum biasing voltage of 100V.