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Eingeladener Vortrag
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The layer-by-layer Additive Manufacturing (AM) by means of Selective Laser Melting (SLM) offers many prospects regarding the design of a part used in aeroplane components and gas turbines. However, structural deviations from the nominal morphology are unavoidable. The cooling of the finished part leads to shrinkage and a high surface roughness is induced by attached powder particles affecting the part volume too.
The integrity and load-bearing capacity of a SLM produced lattice structure (see Fig.1) has been investigated by means of in-situ X-ray computed tomography during compression. The lattice structure was compressed by 10 % in height with an applied maximum force of 5 kN. Additionally, a single strut has been investigated ex-situ as a component of the lattice structure. With the higher resolution achieved on the single strut, the pore distribution (size and location) as well as the surface roughness were assessed. One of the main results coming from the in-situ analysis was that the nodes were identified as the weakest points in the lattice structure.
Collective Orientational Order and Phase Behavior of a Discotic Liquid Crystal under Confinement
(2018)
Discotic liquid crystals (DLCs) are a promising class of soft matter for electronic applications. This is due to their ability to self-organize into columns in a hexagonal columnar mesophase, driven by the overlapping of the π orbitals of their aromatic cores. This leads to a high charge-carrier mobility along the column axis. Previous studies on DLCs showed that their properties, such as phase transition temperatures and enthalpies, are susceptible to nanoconfinement. In this study, 2,3,6,7,10,11 hexakis[hexyloxy] triphenylene (HAT6) was confined into parallel aligned cylindrical nanopores of anodic aluminum oxide (AAO) membranes by melt infiltration. Furthermore, the pore surfaces of a series of membranes were chemically modified, resulting in a more hydrophobic pore surface than the unmodified ones. Collective orientational order and phase behavior of HAT6 confined into modified and unmodified nanopores of AAO were investigated by broadband dielectric spectroscopy and differential scanning calorimetry respectively.
In recent years, substantial efforts have been devoted to investigating nanoscopic confinement of polymers, and its effect on glassy dynamics. Broadband Dielectric Spectroscopy (BDS) was used to study the dynamics of ultra-thin films of PVME/PS 50/50 wt% blend, employing a novel nano-structured capacitor sample arrangement. The investigated system shows a complex dynamic behavior. First, an α-relaxation, related to a bulk-like layer was found. Second, an α’-relaxation was observed, characteristic for dynamically asymmetric blends, where the out of equilibrium dynamics is attributed to weakly-cooperative PVME segments relaxing within a frozen environment of PS segments. Thirdly, for thinnest films, an Arrhenius-like process was dominant in the dielectric spectra, indicating localized fluctuations of the segments. Relaxation rates of this process resembled that of the degenerated α-relaxation of the adsorbed layer, found for pure PVME, thus it was assigned accordingly. For thinnest films, this process undergoes a further confinement, due to the topological constraints, introduced by PS. Such multiple confinement effect has not been reported for ultra-thin films of polymer blends, before this study.
The polymer matrix region near a filler surface, termed as the interface, witnessed increasing interest, due to its possible influence on the macroscopic properties of the nanocomposite. The interphase is expecting to have different segmental dynamic, as compared to the pure matrix, which can percolate into the entire system. Here, the segmental dynamics of epoxy/Boehmite nanocomposite was studied by Broadband Dielectric Spectroscopy. It was found that an artificial relaxation process is present in the nanocomposite, on the contrary to the pure epoxy system. It was assigned to constrained fluctuations of polymer chains in the interfacial region, due to the nanofiller. However, the overall dynamic Tg of the system decreased with increasing filler concentration, indicating higher segmental mobility. This was in accordance with Temperature Modulated DSC investigations of specific heat capacity of the system, which was found to increase with increasing filler concentration, up to 10 wt%, indicating increasing mobility of the polymer matrix segments. Surprisingly, for the highest filler content, the heat capacity decreases, implying a formation of an immobilized rigid amorphous phase in the interfacial region.
In well-annealed thin polymer films, with non-repulsive polymer/substrate interactions, an irreversibly adsorbed layer is expected to form. These adsorbed layers have shown great potential for technological applications. However, their growth kinetics and molecular dynamics are still not fully understood. This is partially due to the hard accessibility of these layers in thin films. Here, the irreversibly adsorbed layers of homopolymer thin films are revealed by solvent-leaching experiments. First, the growth kinetics of these layers is investigated as a function of annealing times and original film thickness. The thickness, topography and quality of the adsorbed layer is controlled with Atomic Force Microscopy (AFM). Secondly, the molecular mobility of the adsorbed layer is investigated with Broadband Dielectric Spectroscopy (BDS). A recently developed nanostructured capacitor is employed to measure the adsorbed layers with a free surface layer. The results are quantitatively compared and discussed with respect to recently published work.
Optimization of laser treatment parameters of Inconel 686 overlay weld on carbon steel 13Mo4-5
(2017)
The work presents the effects of the change of the laser cladding parameters on microstructure, chemical composition and mechanical properties of Inconel 686 overlays (coatings). To obtain the best quality of these coatings the various parameters of laser cladding such as the power density of the laser beam, the laser beam velocity and overlapping ratio of the weld tracks were applied. The substrates were boilers plate made of the 13Mo4-5 steel. Ni - base alloys characterize by 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 substrate melting 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.
Compact nuclear magnetic resonance (NMR) instruments make NMR spectroscopy and relaxometry accessible in industrial and harsh environments for reaction characterization and process control. Robust field integration of NMR systems have to face explosion protection or integration into process control systems with short set-up times. This paves the way for industrial automation in real process environments.
The design of failsafe, temperature and pressure resistant flow through cells along with their NMR-specific requirements is an essential cornerstone to enter industrial production plants and fulfill explosion safety requirements. Additionally, if fast reactions are monitored, suitable mixing devices need to be placed in close vicinity to the measuring volume to mix the reactants properly.
NMR-specific requirements aim at full quantitative pre-magnetization and acquisition with maximum sensitivity while reducing sample transfer times and dwell-times. All parameters are individually dependent on the applied NMR instrument.
Luckily, an increasing number of applications are reported together with an increasing variety of commercial equipment. However, these contributions have to be reviewed thoroughly.
The performance of sample flow cells commonly used in online analytics and especially for low-field NMR spectroscopy was experimentally and theoretically investigated by 1H-NMR experiments and numerical simulations. Especially, the applicability of 3D printed zirconium dioxide for innovative flow cell designs was of interest. Here, we demonstrate and discuss an automated test method to determine the critical parameters of flow through cells for quantitative online NMR spectroscopy. The setup is based on randomized setpoints of flow rates in order to reduce temperature related effects. Five flow cells and tubing were assessed and compared for high-field as well as low-field NMR spectrometers.
An understanding on crystallization behavior and kinetics in glasses is one of the important topics in the glass science and technology. Tsukada et al.1) found an extremely unique and curious phenomenon in the crystallization of multiferroic (ferroelectric and ferroelastic properties) ’-Gd2(MoO4)3 crystals in Gd2O3-MoO3-B2O3 glasses. That is, crystals formed in the crystallization break into small pieces with a triangle prism or pyramidal shape having a length of 50-150 um spontaneously during the crystallization in the inside of an electric furnace, not during the cooling in air after the crystallization. They proposed to call this phenomenon “self-powdering phenomenon”. To the best of our knowledge, such a self-powdering phenomenon has not been observed in the crystallization of any other glasses. To investigate this phenomenon is very important for the glass science and for the preparation of bulk crystallized glasses with ferroelastic crystals. In this work, the preparation of crystallized glasses keeping the original shape is challenged, and the mechanism of self-powdering phenomenon is proposed. Glasses with the compositions of 21Gd2O3-63MoO3-(16-x)B2O3-xTeO2 (mol%) (x=0, 2, 4, 8) such as 21Gd2O3-63MoO3-16B2O3 (GM16B) and 21Gd2O3-63MoO3-8B2O3-8TeO2 (GM8T8B) were prepared using a conventional melt quenching technique. The quenched glasses were heat-treated at some temperatures, and the crystalline phase present in the crystallized samples was identified by X-ray diffraction (XRD) analyses, and the morphology and birefringence of crystals formed were observed using a polarized optical microscope (POM). The densities of GM16B and GM8T8B glasses are 4.76 g/cm3 and 4.91 g/cam3, respectively, and these values are higher than the density of ’-Gd2(MoO4)3 crystal, 4.555 g/cm3. These differences in the density might induce the large stresses in the inside of crystals during the crystal growth. The crystallized glasses of GM16B with ’-Gd2(MoO4)3 crystals do not keep the original glass shape, showing self-powdering phenomenon (breaking into small pieces). However, the crystallized glasses of GM8T8B keep the original glass shape without indicating any self-powdering. It is proposed that the stress at the interface between the glassy phase and ’-Gd2(MoO4)3 crystalline phase might be reduced in GM8T8B glasses containing TeO2 with weak Te-O bonds.
Additive manufacturing (AM) offers an effective solution to the medical sector. It enables the production, on demand, of customised implants which match the patient’s anatomy, with grafts that promote bone growth, as well as surgical guides that help the surgeons. The objective of this project is to provide a comprehensive basis to enable the safe use of medical AM products with traceable and reliable dimensionalmeasurements. This will guarantee the reliability of medical AM products to notified bodies and facilitate acceptance of AM in the medical sector for a better quality of life.
We present an in situ PXRD investigation of the mechanochemical cocrystal formation of pyrazinamide with pimelic acid in two milling jar materials. DFT calculations of the two synthesized polymorphs suggest that the relative stability is based on a conformation change of pyrazinamide in the cocrystal.
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 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.
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.
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.
Mechanochemistry is increasingly used for synthesizing soft matter materials including metal organic compounds and cocrystals. The ever-increasing interest in this method is contrasted by a limited mechanistic understanding of the mechanochemical reactivity and selectivity. Time-resolved in situ investigations of milling reactions provide direct insights in the underlying mechanisms. We recently introduced a setup enabling in situ investigation of mechanochemical reactions using synchrotron XRD combined with Raman spectroscopy. The specific combination allows to study milling processes comprehensively on the level of the molecular and crystalline structure and thus obtaining reliable data for mechanistic studies. In situ Raman spectroscopy coupled with thermography revealed a low temperature increase during milling reactions due to the mechanical impact and clear temperature increases because of the reaction heat.
Based on the data, temperature rises as postulated in the magma plasma and hot spot theory can be excluded for soft matter milling syntheses. Our results indicate that in situ investigation of milling reactions offer a new approach to tune and optimize mechanochemically synthesized compounds.
In this study, series of coatings with the goal of sensitising gold SPR sensors towards CO, NH4, etc. were prepared. To better understand the mechanism behind the sensitizing effect and to enable the targeted production of optimized layers, the wide range of coatings was studied by multiple methods from spectroscopic ellipsometry for their dielectric function, by XPS for chemical composition and SEM, TEM to determine their microscopic structure. The coatings were deposited at inert Ar gas and reactive Ar/O2 gas mixture by RF magnetron sputtering or DC pulsed magnetron sputtering with settable RF bias on the substrates. The plasma processes were monitors by mass spectrometry.
The metal oxide coatings in SPR sensors have to be prepared reproducible with thickness about 5 nm therefore lower deposition rate conditions were advantages.
Ever since increasing a reaction’s yield while shortening the reaction time is the main objective in synthesis optimization. Microwave reactors meet these demands. In literature however their usage is under discussion due to claims of the existence of non-thermal effects resulting from the microwave radiation. Especially for nano-material syntheses it is of crucial importance to be aware of influences on the reaction pathway. Therefore, we compare ultra-small silver nanoparticles with mean radii of 3 nm, synthesized via conventional and microwave heating. We employed a versatile one-pot polyol synthesis of poly(acrylic acid) (PAA) stabilized silver nanoparticles, which display superior catalytic properties. No microwave specific effects in terms of particle size distribution characteristics, as derived by small-angle X-ray scattering (SAXS) and dynamic light scattering (DLS), are revealed. Due to the microwave reactor’s characteristics of a closed system, syntheses can be carried out at temperatures beyond the solvent’s boiling point. Particle formation was accelerated by a factor of 30 by increasing the reaction temperature from 200 °C to 250 °C. The particle growth process follows a cluster coalescence mechanism. A post-synthetic incubation step at 250 °C induces a further growth of the particles while the size distribution broadens. Thus, utilization of microwave reactors enables an enormous decrease of the reaction time as well as the opportunity of tuning the particles’ size. Possibly, decomposition of the stabilizing ligand at elevated temperatures results in reduced yields. A temperature of 250 °C and a corresponding reaction time of 30 s represent a compromise between short reaction times and high yields.
Silver nanoparticles are one of the most widespread consumer related nanoparticles worldwide. Since the particles show special optical and antibacterial properties they are used for a wide range of applications from biological investigations over medical applications and catalysis. Especially the outstanding question of applicable alternatives for catalysts in diverse reactions can be addressed with the design of versatile system of small silver nanoparticles. In this study we present the synthesis and application of ultra-small silver nanoparticles with a narrow size distribution (R = 3.1 nm, σ = 0.6 nm). The particles are thoroughly characterized by small angle X-ray scattering, dynamic light scattering and UV/Vis spectroscopy. As a representative test reaction the reduction of 4-nitrophenol to 4-aminophenol was chosen. The particles show a catalytic activity of (436 ± 24) L g-1 s-1, which is two orders of magnitude higher than for other silver particles in the literature. The particles surrounding shell, composed of poly(acrylic acid), provides the particles with a good accessibility for the reactants. Since the catalytic activity strongly depends on the surrounding ligand, the particles shell can also be exchanged by other ligands enabling a tuning of the catalytic activity to a desired value. This shows the high flexibility of this system which can also be applied for other catalytic reactions.
During Rutherford cable production the wires are plastically deformed and their initially round shape is distorted. Using X-ray absorption tomography we have determined the 3D shape of an unreacted Nb3Sn 11 T dipole Rutherford cable, and of a reacted and impregnated Nb3Sn cable double stack. State-of-theart image processing was applied to correct for tomographic artefacts caused by the large cable aspect ratio, for the segmentation of the individual wires and subelement bundles inside the wires, and for the calculation of the wire cross sectional
area and shape variations. The 11 T dipole cable cross section oscillates by 2% with a frequency of 1.24 mm (1/80 of the transposition pitch length of the 40 wire cable). A comparatively stronger cross sectional area variation is observed in the individual wires at the thin edge of the keystoned cable where the wire aspect ratio is largest.
Influence of deposition hatch length on residual stress in selective laser melted Inconel 718
(2017)
Additive Manufacturing (AM) by Selective Laser Melting (SLM) offers ample scope for producing geometrically complex parts in comparison to the traditional subtractive manufacturing strategies. Developing during the manufacturing process, residual stresses may limit the application of SLM parts by reducing the load bearing capacity as well as induce unwanted distortion depending on the boundary conditions specified in manufacturing.
The present study aims to evaluate the bulk residual stresses in SLM parts by using neutron diffraction measurements performed at E3 line -BER II neutron reactor- of Helmholtz-Zentrum für Materialien und Energie (HZB) Berlin. Together with microstructure characterization and distortion measurements, it is possible to describe the stress state throughout the whole sample. The sample was measured in as-build condition (on a build plate) and after releasing from the build plate. The used material is the nickel based superalloy 718. This alloy is widely used in aerospace and chemical industries due to its superior corrosion and heat resistant properties.
Obtained results indicated different residual stress states for each of the transversal, longitudinal and normal component. The normal and transversal component exhibits a rather compressive behavior while the longitudinal was tensile in the center part of the sample and became compressive towards the tip. As expected, the absolute values of all stress components decreased after releasing the sample from the building plate. A surface scan utilizing a coordinate-measuring machine (CMM) allowed us to present top surface distortion before and after releasing. The top surface showed a distortion around ±80µm after releasing. Microstructure evolution in the scanning-building cross-section is largely dominated by columnar grains. In addition, many small random orientated grains are prominent in the regions of a laser overlap during SLM.
In summary, for the sample of superalloy 718 manufactured by SLM, a small distortion occurred when removing the sample from the build plate whereby the residual stress state decreases. Moreover, the observed columnar grains in the building direction could give a reason for the lowest stress values in that normal direction. However, the most important parameter controlling the residual stresses is the temperature gradient. Hence, future investigations are planned for a different scan strategy to distribute the laser impact in a more homogenous manner.
Damage Analysis in Metal Matrix Composites by means of Synchrotron Radiation Computed Tomography
(2017)
The damage evolution after compression tests of two types of MMC, consisting of eutectic AlSi12CuMgNi alloy and reinforced with 15vol% of Al2O3 fibers and with 7vol% of Al2O3 fibers+15vol% of SiC particles was studied by synchrotron CT. Internal damage at different pre-strain conditions in eutectic Si, intermetallic phases and Al2O3 fibers was observed, as well as debonding of SiC particles.
Multielectrodes are arrays of single electrodes arranged in a particular geometry. In our work, all the single electrodes are identical stainless steel X5CrNi18-10 (1.4301) wire electrodes. Using a multielectrode analyser all single electrodes are connected via zero resistance ammeters, simulating a galvanically coupled single electrode surface. The advantage of the multielectrode analyser (MMA) is that the currents flowing between single electrodes can be measured. Thus, real-time maps can be generated indicating where anodic and cathodic areas lie on the surface of the multielectrode and how they behave.
The combination of the multielectrode analyser with the scanning electrochemical microscopy (SECM) enables the identification of corrosion sites and the detailed electrochemical analysis.
Geothermal brine is considered to be an aggressive environment as it contains various dissolved salts. Even though carbon steel is commonly used as a construction material due to its machinability and economical reason, it is susceptible to uniform and localized corrosion in a high temperature and high pressure system. Therefore, a coating system is introduced to protect the carbon steel against corrosion in such environment.
-It is necessary to find the optimum composition of SiO2 addition in the organic coatings to enhance the material performance, i.e. coatings adhesion, thickness optimization, thermal resistance.
Current project aims at the addition of Polyaniline (PANi) as the active agent to improve the corrosion resistance of materials against a high saline medium at elevated temperatures.
Nuclear magnetic resonance (NMR) is a well established laboratory / borehole method to characterize the storage and transport properties of rocks due to its direct sensitivity to the corresponding pore fluid saturation (water or oil) and pore sizes.
For petrophysical applications there are several different NMR laboratory devices commercially available varying over a wide range of e.g. magnetic field strength / frequency (2 MHz to 30 MHz), applicable measurement protocols (T1, T2, T1-T2, T2-D, etc.) and sample sizes (2.5 cm to 10 cm in diameter). In this work we present NMR measurements, layed out in a round robin like manner, on a set of 20 sandstone samples. We use three different NMR devices containing two standard setups with homogenous magnetic fields (LIAG and RWTH) and one single-sided setup with gradient field (BGR) to measure T1 and T2 relaxation data. In our evaluation we especially focus on the comparison of the individually inverted relaxation time distributions to quantify the differences arising from different laboratory setups. Diverging results can be deduced on the one hand to the inherit differences between homogeneous and gradient fields but on the other hand also due to quality differences between the two homogeneous setups. Additionally, we also examine the influence of the individually chosen inversion parameters (signal processing, distribution sampling points, error weighting, regularization, etc.) to establish a general standardized best practice recommendation for future petrophysical NMR laboratory measurements.
A research project of reconstructing historical gold mosaics deals with reconstructing weatherproof gold and silver mosaics according to historical models.
The gold mosaics examinded originate mainly from germany from 1880 to 1920 and are composed of three parts. They consist of a matching support glass, the gold or silver layer and a cover glass. By examining the morphology and layer thicknesses with the ESEM, and using chemical analysis with the EDX, the relationship of glass composition and damage patterns was established. The glass analysis provided quantitative composition data and made it possible to determine its chemical stability. It supplied the basis for calculating glass characteristics and was referred to when casting suitable historical mosaic glass. The analysis of the qualitative composition of the gold and silver layers also served as a model for reconstruction. After testing selected reconstructed gold mosaics in the climate chamber, the ESEM was used for capturing leaching and other process data and the glass composition was optimized accordingly. Over 100 predominantly historical gold mosaics were analyzed and the results entered into a database which can now be consulted for comparative investigations to determine both origin and date.
A number of environmental monitoring projects were performed on historic stained-glass windows in Germany. The quality of the protective glazing was assessed by recording environmental parameters in the interspace between the original and the protective glazing and on the inside of the original window. For this purpose, temperature, humidity and air velocity were measured. Particles were sampled with different methods and analysed by scanning electron microscopy combined with energy dispersive X-ray spectroscopy to determine their chemical composition. The effect of particles on model glass samples was investigated in climate chambers under accelerated weathering conditions.
Methanogenic Archaea
(2017)
Different environmental samples reveal that methanogenic Archaea are part of a multi-species biofilm on corroding metallic structures. Studies on microbial influenced corrosion (MIC) focus mainly on sulphate reducing Bacteria (SRB), leading to the assumption that they are exclusively responsible for metal corrosion. In fact, methanogenic Archaea are known to be involved in metal corrosion as well (e.g. Methanococcus maripaludis DSM 2067). In some cases SRB and methanogenic Archaea have comparable high corrosion rates. However, the underlying mechanisms causing corrosion are still unknown.
The goal of this study is to develop suitable methods for analyzing two environmental isolates (M. maripaludis DSM 2067, M. maripaludis KA1) and two human-related isolates (Methanobrevibacter oralis and Methanobrevibacter smithii) for their ability to deteriorate/transform metals, which are relevant for technical and clinical applications. Moreover, the studies will provide essential information on the interaction mechanisms of human-related Archaea, which are frequently found in peri-implantitis, with dental material such as implants, crowns and bridges leading to their degradation and transformation.
The project has developed a variety of new multifunctional and flexible building components for a healthier indoor environment. [H] house solutions are durable, energy efficient, safe and affordable. They are suitable for use in new buildings and for renovation. [H] house solutions cover aspects of long service life, reduced maintenance and long-term improvement of energy efficiency.
We investigated, the damped Received Signal Strength Indicator (RSSI) of a Bluetooth Low Energy (BLE) signal, transmitted from the BLE-module embedded in building materials with changing moisture content, Fig. 1. The BLE-module communicates with a mobile Smart Device as tablet via 2.45 GHz-ISM-frequency band where water dipoles start to oscillate, Fig. 2. The damping model demonstrates this damping effect on RSSI by the abstraction of the reality observed in a real system. Through the reproduction of the active relationships, the system behavior is decomposed in such a way that a separate consideration of the required system parameters is possible.
Mechanochemistry has become a valuable method for the synthesis of new materials, especially for pharmaceutical cocrystals. The Advantages of fast reactions in high purity and yield face a lack of understanding the underlying mechanism. Therefore, in situ setups to study mechanochemical reactions have been established. Herein, we present an in situ investigation of the mechanochemical cocrystal formation of pyrazinamide (PZA) with pimelic acid (PM) using synchrotron XRD. Two new polymorphs of PZA:PM (1:1) were synthesized by milling the starting materials in milling jars of different materials. While Form I is only obtained using a steel jar, Form II can be obtained purely in jars made of Perspex. In situ XRD experiments reveal a direct formation of Form II in Perspex and an intermediate formation of Form II in steel jars converting to Form I upon further grinding. Heating experiments and DFT calculations predict that Form II is the thermodynamically more stable polymorph. Therefore, the reaction progress in the steel jar contradicts Ostwald’s rules of stages as the more stable Form II converts into the metastable Form I. Hence, mechanochemistry offers the possibility to synthesize new materials that cannot be obtained using conventional methods.
Obtaining high quality upconverting nanocrystals with only little crystal defects and hence, a high luminescence, affords a reliable synthesis route. Only this guarantees the reproducibility of the material and its spectroscopic properties required for future application. The fluorolytic sol-gel synthesis appears to be a convenient attempt, as this is a method with only few steps influencing the material properties, which can be well controlled.
Also creating bright upconverting nanocrystals requires a profound understanding of the interplay of photophysical processes like multiphoton absorption, radiative and non-radiative pathways, and energy transfer in the material.
Based on steady-state and time resolved luminescence measurements at different excitation power densities, the influence of the lanthanide doping ratio and synthesis parameters such as the annealing process on SrF2-nanocrystals obtained via the fluorolytic sol-gel synthesis was systematically studied.
In this paper, titanium-di-boride is dispersed on a cold-working tool steel by use of a pulsed fiber laser with high beam quality to produce separated and elevated surface features. The potential to adjust the geometry as well as the mechanical properties of the produced structures in dependence on the process parameters (pulse power, pulse duration) is described by means of metallographic and topographical investigations. It can be ascertained that very hard (hardness > 1000 HV1) surface features of different shape (spots and short lines) can be produced. They are characterized by a fine-grained microstructure resulting from a rapid solidification and finely dispersed TiB2 particles. Finally, the paper proposes different applications for this structuring technique.
Solar glass in arid and semi-arid regions is exposed to sand storms which can affect the durability of PV modules. Related erosion processes have been extensively studied but the results given are difficult to compare due to being obtained by different variables like particle speed and sand mass. This study correlates the damage of solar panels to the cumulative impact energy as a global parameter.
Polycrystalline Ni materials with grain sizes less than 100 nm (nano crystalline NC) and with grain sizes in the micrometer range (micro crystalline MC) in form of thin films have become important in many technologies due to their improved physical, chemical and mechanical properties. Usual the mechanical properties of such coatings are described by a Hardness value and a Young´s modulus measured by Instrumented Indentation Testing (IIT).The behavior of such coatings during indentation test is influenced by different size effects having their representative length scale – grain size, coating thickness, length that characterizes the depth dependence of the hardness (Indentation Size Effect ISE). To estimate realistic values for the intrinsic coating Hardness and Young´s modulus all size effects have to be considered.
For this work thin nano crystalline Ni – coatings (average grain size 30 nm) with thickness from 1 μm to 5 μm were electrodeposited on brass substrates. Indentation tests in the continuous stiffness measurement (CSM) mode were provided on as prepared Ni – coatings using a G200 Nanoindentation system (Fa. Keysight). For estimation of the intrinsic hardness of the coatings from composite hardness values calculated from the measured force –displacement curve using the Oliver & Pharr method, the model described by Z.S. Ma [1] was used.
It was found that the experimental data can be well described by the model. The fitted values for the intrinsic hardness and the fitting parameters will be given. The different values of intrinsic hardness and of length characterizing depth dependence of the hardness for different coating thickness are discussed as results of changes in the coating structure because of changes in deposition parameters.
[1] Z.S. Ma, Y.C. Zhou, S.G. Long, C. Lu: On the intrinsic hardness of a metallic film/substrate system: Indentation size and substrate effects. International Journal of Plasticity 34 (2012) 1-11.
This work is supported by European Metrology Program for Innovation and Research (EMPIR)
(JRP 14IND03 Strength – ABLE)
To avoid a catastrophic failure of insulation in high-voltage (HV) applications, a monitoring of partial discharges (PD) is necessary. Fluorescently labelled polymer optical fibres (F-POF) offer an electrically passive method for PD detection in HV facilities. F-POF could be embedded into HV cable insulation material, which are usually made of silicone rubber. Due to the difficult accessibility of HV cable accessories, a self-healing silicone rubber, based on incorporated capsules, with prolonged service life after PD detection represents an attractive material design for HV electrical insulation.
Different environmental samples reveal that methanogenic Archaea are part of a
multi-species biofilm on corroding metallic structures (Fig. 1). Studies on microbial
influenced corrosion (MIC) focus mainly on sulphate reducing Bacteria (SRB),
leading to the assumption that they are exclusively responsible for metal corrosion.
In fact, methanogenic Archaea are known to be involved in metal corrosion as well
(e.g.Methanococcus maripaludis DSM 2067). In some cases SRB and methanogenic
Archaea have comparable high corrosion rates. However, the underlying
mechanisms causing corrosion are still unknown. The goal of this study is to
analyse two environmental isolates (M. maripaludis DSM 2067, M. maripaludis
KA1) and two human-related isolates (Methanobrevibacter oralis and
Methanobrevibacter smithii) for their ability to deteriorate/transform metals,
which are relevant for technical and clinical applications. Moreover, the studies will
provide essential information on the interaction mechanisms of human-related
Archaea, which are frequently found in peri-implantitis, with dental material such
as implants, crowns and bridges leading to their degradation/transformation.
The tribological behavior of PAEK composites were investigated in air and vacuum environment. Results indicate that the tribological performance of these compounds depends on material compositions, fiber orientation as well as test conditions. In vacuum, very low friction and wear coefficient were obtained at low sliding speed while severe wear occurred at high speed.
Laser-induced Nanostructures as Biomimetic Model of Fluid Transport in the Integument of Animals”, aims on laser-fabrication of biomimetic surfaces with unique wetting properties, which are inspired by the hierarchical micro- and/or nano- structures of animal body surfaces. LiNaBioFluid is a Research and Innovation Action funded by the European Commissions’ Horizon 2020 - FET Open Programme, which supports early-stage research on any idea for a new technology (Grant Agreement no: 665337). It brings together 7 partners from 4 different countries and is strongly interdisciplinary combining renowned experts from the fields of zoology, physics, mechatronics, life sciences, materials sciences, laser-matter interaction, production technology, tribology, and biomimetics. www.laserbiofluid.eu/
Laser-induced periodic surface structures (LIPSS) can be generated by irradiation of almost any material with linearly polarized laser beams, particularly when using ultrashort laser pulses.
Within this work, different types of steel were irradiated at optimized conditions for the processing of large surface areas. For these nanostructured surfaces, the coefficient of friction (COF) using different lubricants was determined and the corresponding wear tracks were characterized by scanning electron microscopy (SEM). Our experiments provide a qualification of the tribologicalperformance of the fs-LIPSS on different steel surfaces, which are relevant for technical applications.
Possibility of post-fabrication doping of commercial PMMA fibers using well-known solution doping technique is presented. The cladding of 1 mm PMMA fiber is doped with Rhodamine B with the help of methanol-mediated diffusion of the dye molecules into the fiber material. Doping of the fiber core was not possible even at extended doping times. The proposed method represents rather simple and cheap way for preparing custom cladding-doped POFs with high flexibility of dopant choice and fiber length. Produced cladding-doped fibers have potential for various sensing or lighting applications.
In the course of the energy transformation from fossil fuels to renewable energy sources, the use of hydrogen as fuel and energy storage can play a key role. This presents new challenges to industry and scientific community alike.
The storage and transport of hydrogen, which is nowadays mainly realised by austenitic stainless steels, remains problematic. That is due to the degradation of mechanical properties and the possibility of phase transformation by hydrogen diffusion and accumulation. Development of materials and technologies requires a fundamental understanding of these degradation processes. Therefore, studying the behaviour of hydrogen in austenitic steel contributes to an understanding of the damage processes which is crucial for both life assessment and safe use of components in industry and transportation.
As one of the few tools that is capable of depicting the distribution of hydrogen in steels, time-of-flight secondary ion mass spectrometry (ToF-SIMS) was conducted after electrochemical charging. To obtain furthermore information about the structural composition and cracking behaviour, electron-backscattered diffraction (EBSD) and scanning electron microscopy (SEM) were performed. Gathered data of chemical composition and topography was treated employing data fusion, thus creating a comprehensive portrait of hydrogen-induced effects in the austenite grade AISI 304L.
Specimens were electrochemically charged with deuterium instead of hydrogen. This arises from the difficulties to distinguish between artificially charged hydrogen and traces existing in the material or the rest gas in the analysis chamber. Similar diffusion and permeation behaviour, as well as solubility, allow nonetheless to draw conclusions from the experiments.
While the increase in use of renewable energy sources is a necessity in times of climate change the use of gas turbines as back-up requires them to be run in a much more flexible manner in order to compensate for side effects like sudden fluctuations of energy generation. The significant changes of stress and temperature levels in turbine blades due to start-up and shut down can cause crack initiation and growth in the blades‘ alloy. The aim of this research project is to identify a model for lifetime prediction for gas turbine components made of a Nickel base superalloy under high temperature with a Focus on stress concentration points such as cooling holes.
The electrospun fibers with micrometer diameter show ribbon-like morphology, the physical features are further studied by Scanning Electron Microscopy (SEM), Fourier Transformed Infrared Spectroscopy (FTIR) and Raman and XPS Spectroscopy is used to study the changes after irradiation. Partial electron beam treatment of the electrospun mats lead to localized fluorescence with a broad band emission. The change in the optical response of the fluorescent area in the mats is measured under different chemical environments to evaluate their suitability as an optical chemical sensor in polar and non polar environments.
Oxidation of a Fe-13Cr alloy under water vapor at 600 °C produced a zone of nano-sized precipitation underneath the outside scale formed by iron oxides and Fe‒Cr spinel. The majority of the spinel layer shows a mixed orientation relationship to the ferritic matrix {100}α || {100}sp & <011>α || <001>sp. However, also the discovered precipitated particles are characterized by the same crystallographic orientation relationship to the respective ferritic parent grain. The habit of the precipitates is best described by a lath morphology with their main axis parallel to <100> of ferrite.
Energy dispersive X-ray spectroscopy (EDX) and electron backscatter diffraction (EBSD) in an scanning electron microscope (SEM) have been applied to characterize the oxide layer in the micrometer scale. The clearly smaller precipitates were subsequently investigated by transmission electron microscopy (TEM). Specimens have been prepared by focused ion-beam (FIB) milling at an area previously characterized by EBSD. They cover the ferritic base material, but mainly the precipitation zone and the Fe‒Cr spinel layer. Energy filtered selected area diffraction (SAD) in the conventional (C)TEM and high-angle annular darkfield (HAADF) imaging in the scanning (S)TEM mode were employed in the characterization of the specimens.
Evaluation of nano-sized internal oxidation in a Fe-13Cr alloy exposed to water vapor atmosphere
(2016)
The topotactic formation of nano-sized precipitates immediately under the internal oxide layer in a Fe-13Cr alloy exposed to oxidizing water vapor atmosphere was recently reported. The precipitates were identified as lath-shaped Fe-Cr spinel exhibiting a crystallographic orientation relationship with the ferritic matrix. The authors proposed that these precipitates could act as a precursor to the formation of the spinel layer observed in the adjacent part of the oxide scale.The occurrence of internal oxidation in Fe–Cr alloys subjected to similar conditions had been previously identified and directly correlated to the presence of water vapor. In the present work, we attempt to rationalize the processes occurring during the oxidation of this alloy through thermodynamic and kinetic analyses based on the CALPHAD approach, using the geometrical representation of phase equilibria and concepts developed to describe internal oxidation. The influence of water vapor on the mechanism and kinetics of formation of the nano-sized precipitates and its role in the overall oxidation process is also considered.
The investigation of creep behavior of the single crystal superalloy CMSX-4 at 1288°C is important for the understanding of deformations mechanisms under hot isostatic pressing (HIP). This treatment is used to increase the lifetime of single crystal superalloys by reducing the number of cavities. The understanding of the internal processes during this treatment is still limited due to the material being not single-phase at room temperature, the extreme conditions of HIP and the complexity of the material.
The result of predicting the pore shrinkage rate using classical crystal plasticity was not satisfying. A more complex model has been implemented, now taking the heterogeneity of dislocation sources into account. By introducing a dislocation density, one can describe the transport, nucleation and interaction of dislocations.
Commercial grade-1 titanium samples (Ti, 99.5% purity) were treated using three alternative methods, i.e., fs-laser processing in air, thermal heat treatment in an oven, or anodization in an electrochemical bath, all resulting in the formation of differently conditioned superficial oxide layers. The laser processing was carried out by a Ti:sapphire laser (pulse duration 30 fs, central wavelength 790 nm, pulse repetition rate 1 kHz) in a regime of generating laser-induced periodic surface structures (LIPSS). The experimental conditions (laser fluence, spatial spot overlap) were optimized in a sample-scanning geometry for the processing of several square-millimetres large surface areas covered homogeneously by these nanostructures. The thermal processing in the oven was done at two different temperatures, while the electrochemical anodization was performed at room temperature, aiming to generate different polymorphs of titanium oxide at similar oxide layer thickness. The irradiated surface regions were characterized by optical and scanning electron microscopy, and micro Raman spectroscopy. The tribological performance of the differently treated titanium surfaces was characterized in the regime of mixed friction by reciprocating sliding tests against a sphere of hardened steel in un-additivated paraffin oil and fully formulated engine oil as lubricants. The specific tribological performance of the differently treated surfaces is discussed on the basis of possible physical and chemical mechanisms.
Compared to its intrinsic strength, the practical strength of glasses is substantially
lowered by microscopic flaws. Their sub critical growth from the surface is strongly
affected by ambient humidity.
A new device was designed to enable the observation of sub critical crack growth
(SCCG) in vacuum and controlled atmosphere. It allows measurements in transparent and
semi-transparent materials in double cantilever beam (DCB) geometry. The aim of the
present work is to study the effect of crystals on crack growth.