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Eingeladener Vortrag
- nein (1)
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.
Analytical model for ball-lensed couplers to calculate the insertion loss for each optical mode. The basis for the calculation are commercial perfluorinated polymer optical (PFGI-POFs) and silica based fibres (SOFs). The modal power distribution for given misalignments are presented as well as the reflection-based losses at all optical interfaces. Additionally, the ball-lensed interconnection between PFGI-POF and SOF was theoretically demonstrated.
The duplex stainless steel 1.4062 (X2CrNiN22-2) is used as alternative material to austenitic stainless steels in the construction industry. The corrosion resistance of welded seams is influenced by the base material, the weld filler material, the welding process and also by the final surface treatment. The scale layer next to the weld seam can be removed by grinding, pickling, electro-polishing or blasting depending on the requested corrosion resistance. Blasted surfaces are often used in the industrial practice due to the faster and cheaper manufacturing process compared to pickled or electro-polished surfaces. Furthermore blasting with corundum-grain is more effective than blasting with glass-beads which also lower the process costs. In recent years, stainless steel surfaces showed an unusually high susceptibility to pitting corrosion after grinding with corundum. For this reason, it is now also questioned critically whether the corrosion resistance is influenced by the applied blasting agent. This question was specifically investigated by comparing grinded, pickled, corundum-grain- and glass-bead-blasted welding seams. Results of the SEM analyses of the blasting agents and the blasted surfaces will be presented and correlated with the results of different corrosion tests (KorroPad-testing and pitting potentials).
Sustainable energy and clean engine fuels receive more and more attention. Petrodiesel could be substituted by biofuels such as biodiesel produced from renewable resources. Biodiesel is derived by transesterification of oils with alcohols for example vegetable oils, animal fats or food waste. Its chemical composition of unsaturated fatty methyl acids causes biodiesels susceptibility to oxidation. Especially, the polymer-biodiesel performance under long-term conditions has been considered only in few researches.
Our study addresses a long-term storage scenario of a polymeric fuel tank containing biodiesel or diesel.
High-density polyethylene (PE-HD) is a widely applied plastic for fuel storage tank applications. But such tanks, filled with diesel or biodiesel, provide excellent environmental conditions for growth of a broad spectrum of fungi and various bacteria1. This can result in fuel contamination, engine plugging or possible (bio-) degradation2. Our research focusses on the initial attachment phase of Bacillus sp. and Pseudomonas aeruginosa isolated from a „dieselpest“2 on two distinctly PE-HD materials, typical for fuel storage tank applications, pre-damaged thermally and by UV-irradiation.
UCST-type thermoresponsive polymers that phase separate from solution upon cooling present a tremendous potential not only in aqueous media where they can be used in drug delivery, diagnostic and microfluidic applications, but also in water/alcohol mixtures, where they can be used for instance in sensing systems for alcohol-soluble drugs. However, only a few thermoresponsive polymers have been reported that present an UCST in a relevant temperature range and “green” solvents such as water or ethanol. In this context, acrylamide-based monomers can be very useful building blocks for designing novel UCST-type polymers because of their hydrophilic nature (with the right side chain) and propensity to form hydrogen bonds.
We want to present our latest results on the copolymer poly(acrylamide-co-acrylonitrile) (P(AAm-co-AN)) that present a UCST in water as well as on two homopolymers based on an acrylamide derivative of 2,6-diaminopyridine, namely poly(N-(6-aminopyridin-2-yl)acrylamide) (PNAPAAm) and poly(N-(6-acetamidopyridin-2-yl)acrylamide) (PNAcAPAAm) that show UCST-type thermoresponsiveness in water/alcohol mixtures.
Our focus for P(AAm-co-AN)) is its aggregation behaviour above and below its phase transition temperature as the size of thermoresponsive polymeric systems is of prime importance for biomedical applications (as size dependent processes take place in the body) and is linked to the optical properties of a material that matter in materials science.
In the case of PNAPAAm and PNAcAPAAm, we focused on the co-solvency/co-non solvency effect on the phase transition temperature in water/alcohol mixture. Indeed, polymers with UCST behavior below 60°C in water/alcohol mixtures are extremely promising for the preparation of “smart” materials for sensing.
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.
Influence of corundum grinding processes on the corrosion behaviour of austenitic stainless steels
(2017)
The scientific poster shows by means of corrosion testing in combination with surface analytical methods to which degree corundum grinding influences the corrosion behaviour of stainless steel surfaces. The austenitic stainless steel AISI 304 from a consistent heat was used for all investigations to guarantee the same chemical composition and thus no additional influences caused by the material itself. A wide range of different grinding parameters such as pressure, cooling medium and grain size of the abrasive was varied. Thus, comparison of the corrosion behaviour of different surface states and the evaluation of an optimum grinding process using corundum abrasives were possible. The results will contribute to present discussions and give novel impulses for companies in the metalworking industry.
In the context of a research project carried out by BAM, nine different steel alloys were exposed to maritime environmental conditions at the German Island of Helgoland over a period of five years and their corrosion behavior was compared and evaluated. In order to evaluate the influence of a possible concentration of corrosion specific crucial air constituents on the investigated steel grades, a series of sample surfaces were freely exposed to the we ather while other samples were protected from direct rain in a covered area. The parallel investigation of four different surface finishes (cold rolled, dry grinded, electro-polished, blasted) of the respective alloys also made it possible to take account of the specific influences and features of the surface finish during the material comparison. On the basis of the results of the natural exposure tests, conclusions were drawn about the influence of the alloy composition, the surface finish and the exposure time under maritime conditions. The samples of the three investigated duplex alloys exhibited the best corrosion resistance under the given maritime environmental conditions over the five-year period, both with and without crevice geometry. Likewise, the molybdenum alloy ferrite 1.4521 could achieve comparable corrosion resistance as the austenitic standard materials 1.4301 and 1.4404. The results on the freely exposed surfaces showed, that due to the washing effect the influence of the exposure time on the corrosion of the samples is low while the particular surface finish has a great influence on the overall corrosion behavior of the stainless steels. Thus, the electro-polished surfaces showed few signs of corrosion while the blasted surfaces exhibited very poor corrosion behavior. In the case of the covered specimens, the respective material-specific corrosion resistance as well as the exposure time have a significant influence on the corrosion behavior while the surface finishes were of marginal importance.
Conventional methods of crack detection only provide a snapshot of the fatigue evolution at a specific location and in the moment of examination. The crack luminescence method realizes a clear visibility of the occurring cracks in loaded components during ongoing operation. Several different experiments show that due to the sensitive coating even the early stage of the crack formation can be detected what makes the crack luminescence helpful to determine the incipient crack opening behavior depending on load alternation. Due to the emitting of light under UV-radiation the crack gets clearly visible what makes continuous monitoring and automated crack detection possible. This can reduce costs and time needed for maintenance and inspection.
Electroplated magnetostrictive actuator layer enabling the external diagnosis of strain sensors
(2017)
Embedded fibre-opticaloptical strain sensors are suitable for structural health monitoring. In order to validate long-term performance (e.g.sensors integrated in airplane wings or wind power turbine blades) an external diagnostics is required.
A strain-detecting region of the optical fibre, the fibre Bragg grating (FBG, is encased by a magnetostrictive layer system serving as actuator. For the validation of the correct sensor function, an external magnetic field introduces mechanical strain resulting in a defined shift of the Bragg wavelength. The layer system is realized by acombined PVD /ECD process optimized regarding magnetostrictive and mechanical properties. The long -term stability of layer adhesion and actuator function has been verified.
Pharmaceutical cocrystals are homogenous crystalline structures made up of two or more components in a definite stoichiometric ratio, where at least one of the components in the crystal lattice is an active pharmaceutical ingredient (API).1 Pharmaceutical cocrystals have opened the opportunity for engineering solid-state forms designed to have tailored properties to enhance drug product bioavailability and stability, as well a enhance processability of the solid material inputs in drug product manufacture. In this work the cocrystallization of bexarotene, an approved API by the U.S. Food and Drug Administration that belongs to Biopharmaceutics Classification System Class II (low solubility–high permeability), with pyridine carboxamide isomers (picolinamide, nicotinamide and isonicotinamide) was successfully undertaken. The synthesis was achieved by liquid assisted grinding (LAG) and the solids obtained were characterized by differential scanning calorimetry (DSC), infrared spectroscopy (FTIR-ATR), powder X-ray diffraction (XRPD), single crystal X-ray diffraction (SXD), and polarized light thermomicroscopy (PLTM). For bexarotene: picolinamide and bexarotene:isonicotinamide, 1:1 cocrystals were obtained directly from milling. SXD data of bexarotene:isonicotinamide cocrystal reveal acid∙∙∙aromatic nitrogen supramolecular heterosynthon and that the homosynthon amide∙∙∙amide in isonicotinamide is preserved. The bexarotene:nicotinamide mixtures prepared by ball milling give rise to simple binary solid–liquid phase diagram with an eutectic point, well described by the Schröder-van Laar equation. Melt crystallization of the 1:1 mixture gives rise to a cocrystal for which a complex phase behaviour is observed.
1. Introduction
Alumina coatings are one possibility to increase the corrosion resistance, lifetime and application range of thermally loaded steel components, e.g. in modern power plants where the use of the Oxy-fuel technology corrosive fuel gas (H2O-CO2-O2-SO2 at 650 °C) affects the steel parts. In previous investigations the efficacy of protective alumina coatings on steel P 92 under those conditions was demonstrated. A shutdown and re-start of power plants or parts of them causes thermal stresses of the components which can cause detrimental effects like microstructural changes in the steel itself, changes in its oxidation behavior, delamination or microstructural changes in the coating. All those effects can lead to failure of the components, resulting in lifetime reduction.
2. Objectives
As a first step, we concentrate on the influence of thermal cycling tests and observe the impact on the microstructure of the coating and the interface in laboratory air. These investigations will help understanding the processes which occur, show directions of potentially necessary changes of the coating due to improved thermal stress behaviour.
3. Materials & methods
P 92 is a ferritic-martensitic steel, containing 9% Cr which forms protective Cr-oxide-rich scales in dry environments and non-protective ones in water-containing environments. Coupons of P 92, having ground surfaces, were dip-coated via a sol-gel process and subjected to thermal cycling for 500 h (1000 cycles) in laboratory air in a temperature range between room temperature and 660° C. The resulting mass loss was determined by weighing.
Samples for TEM investigations were produced as cross sections normal to the sample surface by FIB preparation (Quanta 3D, (FEI)). The TEM/STEM investigations were performed using a JEM2200FS (JEOL) operated at 200 kV. The microstructure of the coating and the interface after cycling tests was characterized via TEM, HREM, and STEM images, electron diffraction as well as EDX and EFTEM methods.
4. Results
At steep edges in the surface profile the coating was imperfect and cracks have formed during the thermal cycling. Flat surface regions are well-covered. The whole interface region between the steel and the coating shows a dense Cr-oxide-rich zone, which can form protective regions in case of local failure. The Cr-oxide zone is followed by a region of mixed oxides, containing Cr, Mn, Fe, and Al in variable composition, to which a porous δ-Al2O3 zone is joined.
5. Conclusions
• Alumina coatings promote the formation of dense, Cr-rich zones at the interface, which makes the system self-healing.
• These zones are stable during thermal stresses, even in regions with cracked coatings.
• They cause reduction of outward diffusion and mass loss during thermal cycling.
Typical transport packages used in Germany are equipped with wooden impact limiting devices. In this paper we give an overview of the latest status regarding the development of a finite element material model for the crush of spruce wood. Although the crush of wood – mainly in longitudinal direction – is a phenomenon governed by macroscopic fracture and failure of wood fibres we smear fracture and failure mechanisms over the continuous voume. In first step we altered an existing LS-DYNA material model for foams, which considers an ellipse shaped yield surface written in terms of the first two stress invariants. The evolution of the yield surface in the existing model depends on the volumetric strain only. For the use with spruce wood, we modified the existing material model to consider the deviatoric strain for the evolution of the yield surface as well. This is in accordance with the results of crush tests with spruce wood specimens, where the crushing deformation was rather deviatoric for uniaxial stress states and rather volumetric for multiaxial stress states We rate the basic idea of this approach to be reasonable, though other problems exist regarding the shape of the yield surface and the assumption of isotropic material properties. Therefore we developed a new transversal isotropic material model with two main directions, which considers different yield curves according to the multiaxiality of the stress state via a multi-surface yield criterion and a non-associated flow rule. The results show the ability to reproduce the basic strength characteristics of spruce wood. Nevertheless, problems with regularization etc. show that additional investigations are necessary.
Acoustics is an important aspect for large rooms especially in schools, kindergartens and offices. Foam tiles made from melamine resins are often used for acoustic insulation because they show good fire resistance and good thermal insulation properties. But they can emit formaldehyde. In Germany there are cases with a resulting indoor air concentration of higher than 100 µg/m³. In this study samples from two schools and one office were investigated. Additionally, new tiles were purchased and tested to evaluate the general potential as formaldehyde source.
Partially crystalline glasses are predominantly used as solid oxide fuel cell (SOFC) sealants due to their superior long term durability. However, cracks caused by thermal cycling still remain a substantial bottleneck in developing durable SOFC sealants inasmuch as, in contrast to crystal free glasses, large crystal volume fractions can retard healing. Hence, the basic understanding of crack healing in glassy crystalline materials and the effects of micro structure are important for finding optimum micro structures for both, durability and crack healing.
For studying these effects, several model glass matrix composites (GMC), for which simultaneous crystal growth and crack healing can be excluded, have been synthesized. Sodium calcium silicate glass – zirconia GMC turned out to provide sufficiently homogeneous, dense and durable model GMC for our studies. The microstructure of this GMC shows large crystal free glassy regions embedded in network of finely dispersed ZrO2 nanoscale crystals. Whereas the glassy regions allow easy local crack healing, the network of dispersed crystals increases the effective viscosity on a global scale. This effect substantially retards crack broadening during later healing stages, which often ends up in large pores. Therefore, this type of microstructure seems to be an interesting candidate for crack healing optimized sealants.
Crack healing in glasses
(2017)
Fundamental understanding of crack healing in glassy crystalline materials is very important for many applications, especially for solid oxide fuel cells (SOFC) sealants since cracks caused by mechanical stress or thermal cycling still remain a substantial bottleneck in developing durable SOFC. Previous studies on soda lime silicate glass published by Singh showed that crack healing is driven by viscous flow. There he postulated that the healing progress is proportional to time, t, and the inverse viscosity. This finding would allow to present for a given glass data of crack healing measured at different temperatures in a master curve, if the healing progress is plotted versus t/η. Such master curves would be a helpful tool in understanding crack healing kinetics. To verify the applicability of such master curves, crack healing in non-crystallizing soda-lime-silicate (NCS) and sodium-borosilicate glasses (NBS) was studied. Cracks were generated by Vickers indention and healed isothermally at different temperatures. Crack healing progress was monitored by optical and electron microscopy. The results show that the above mentioned proportionalities applies to the two glasses. In both cases the afore developed master curve could be obtained.
Mit der Verfügbarkeit der Mehr-Proben-Prüfung von bis zu 8 Klebverbunden mittels CAT-Technologie (CAT: centrifugal adhesion testing) wurde im Forschungsvorhaben OKTETT ein durchgehendes Mehr-Proben-Konzept zur Validierung der Klebfestigkeit angewendet. Dazu gehört ein universeller Probenteller (Abb.1) zur Mehr-Proben-Handhabung bei Vorbehandlung, Lagerung, Transport und Klebung. Für das Mehr-Proben-Kleben wurde die MSB-Technologie (MSB: multiple sample bonding) unter Verwendung einer instrumentierten hydraulischen Mehr-Proben-Kleb-vorrichtung entwickelt. Damit kann der Klebandruck für bis zu 8 Prüfkörper über einen Drucksensor definiert eingestellt und die gesamte Vorrichtung beim Kleben Temperaturen von bis zu 180°C ausgesetzt werden.
Simvastatin is a prominent member of the statin family, a class of antilipidemic drugs widely used in the treatment of high plasma cholesterol levels, and thus in the prevention of atherosclerosis and cardiovascular diseases. Simvastatin is typically employed as a solid and it is well known that, in this case, the detection and characterization of polymorphism is of considerable importance. Polymorphs differ by their packing arrangements and also, occasionally, by the conformations of the molecules in the crystal lattice. These structural variations are normally reflected by differences in physical properties, such as solubility and dissolution rate in a given media, which may significantly affect the bioavailability of a drug. The lack of control of polymorphism can, therefore, play havoc with the safe use of a drug.
"The optical properties of semiconductor nanocrystals (SCNC) are controlled by constituent material, particle size, and surface chemistry, specifically the number of dangling bonds favoring nonradiative deactivation. This can lead to a distribution of photoluminescence Quantum yields (PL QY) amongst the SCNC particles, i.e., mixtures of “bright” and “grey” or “dark” SCNCs.
Particularly the number of absorbing, yet not emitting particles can have a significant effect on the PL quantum yield obtained in ensemble measurements, leading to ist underestimation. The “dark fraction” is not assessable in common ensemble measurements; it can be probed only on a single particle level using a confocal laser scanning microscope coupled with an AFM. Such a setup was used to study core‐shell CdSe SCNCs with different shells and surface chemistries. Special emphasis was dedicated to correlate brightness, blinking, dark fraction, and decay kinetics of the single SCNCs with the ensemble PL QY and the PL decay kinetics. The results of this study can help to identify new synthetic routes and surface modifications to colloidally and photochemically stable SCNCs with a PL QY of close to unity."
Discotic liquid crystals (DLC) filled into cylindrical nanopores exhibit a liquid crystalline phase with their molecules arranged in hexagonal columns. The columns orient perpendicular (radially) or parallel (axially) with respect to the pore axis depending on surface anchoring conditions and pore size. Axially oriented columns enable the fabrication of organic nanowires utilizing the high conductivity in the stacking direction due to overlapping π-electrons. This leads to interesting applications in e.g. organic semiconductorbased devices. The molecular ordering of the liquid crystalline columns can be probed by temperature dependent optical retardation measurements supplemented by X-ray diffraction sensitive to the translational order.
We investigated the DLC 2, 3, 6, 7, 10, 11 - hexakis [hexyloxy] triphenylene (HAT6) embedded in nanoporous alumina and silica membranes as function of the pore diameter (12 nm - 180 nm). Due to their hydrophilic nature porous membranes enforce face-on anchoring leading to a radial orientation. To obtain edge-on anchoring conditions, and thus favoring axial orientation, the silica membrane surface is chemically modified. The optical retardation measurements show that the columns orient radially in these membranes independent of the anchoring conditions. Interestingly, a quantized phase transition of each molecular layer is found indicated by a distinct increase of the optical orientation. Additionally, an axial orientation of HAT6 filled into alumina membranes with a pore diameter of 25 nm is achieved. A Landau-de Gennes ansatz semi-quantitatively describes the phase transition behavior observed. X-ray diffraction experiments performed at the 3rd generation synchrotron radiation source PETRA III at DESY giving detailed information about the translational order support these findings. Summarizing, this study shows the existence of a phase transition in the molecular range as well as the suitability of the membrane with 25 nm pores as a template for preparing organic nanowires.
Ternary semiconductors Quantum Dots (t-QDs) like AgInS (AIS) QDs are interesting alternatives to Cd-based QDs for applications as optical active materials in light-emitting diodes (LEDs), solar concentrators and solar cells as well as as biodiagnostic tools, respectively.
AIS QDs exhibit broad photoluminescence (PL) spectra in the visible and near infrared, which are tunable by size and chemical composition (ratio of components or doping).
In order to enhance the PL quantum yield (PL QY or Fpl) and prevent material deterioration and oxidation, these QDs are covered by ZnS shell. Here we show a spectroscopic study of differently colored AIS QDs synthesized in water, evaluating their PL properties, their PL QY and their PL decay.
The simple aqueous synthesis that avoids further ligand exchange steps for bioanalytical applications, the tunable emission color, the high PL QY, the high absorption coefficients and the long lifetime make these t-QDs promising Cd-free materials as biodiagnostic tools or optical active materials.
Lanthanide doped photon upconverting nanophosphors (UCNPs) have the unique capability to produce narrow band, multi-color emission in the UV/vis/NIR upon multiphotonic absorption of infrared light, which makes them promising reporters for diagnostic, bioanalytical, and biological applications. This minimizes background signals, which normally occur due to autofluorescence from auxochromes, in biological matrices and enables deep penetration depths in biological applications. Moreover, UCNPs show long luminescence lifetimes in the μs range favorable for time gated emission in conjunction with a high photostability and chemical inertness and they do not blink. One of the most efficient upconversion (UC) phosphors for conversion of 976 nm to 655 nm and 545 nm light presents the hexagonal NaYF4-host crystal doped with 20 % Yb3+ used as sensitizer to absorb infrared light and 2 % Er3+ acting as activator mainly responsible for light emission. The high transparency in the relevant spectral windows of this host together with its low phonon frequencies ensure relatively high luminescence efficiencies.
Although UCNPs are ideal candidates for many chemical and biological sensing and imaging applications, compared to other well-known chromophores like organic dyes or QDs, they suffer from a comparatively low brightness due to the low absorption cross sections of the parity forbidden f-f-transitions and low photoluminescence quantum yields (QYUC) particularly in the case of small nanoparticles with sizes of < 50 nm. The rational design of more efficient UCNPs requires an improved understanding of the nonradiative decay pathways in these materials that are influenced by particle architecture including dopant ion concentration and homogeneity of dopant distribution within UCNPs, size/surface-to-volume ratio, surface chemistry, and microenvironment. A promising approach to overcome the low efficiency of UCNPs is to use plasmonic interactions between a noble metal (Ag or Au) structure in the proximity of UCNPs and the incident light. This interaction leads to a modification of the spectroscopic properties due
to local field enhancements and can involve an increase of the photoluminescence. In this respect, we study the interactions of UCNPs with metal structures (clusters and shells) by varying shape and size. Here, first results derived from integrating sphere spectroscopy and time-resolved fluorescence measurements are presented.
Theoretical and experimental studies indicate that crystal nucleation can take more complex pathways than expected on the ground of the classical nucleation theory. A direct in situ observation of the different pathways of nucleation from solution is challenging since the paths can be influenced by heterogeneous nucleation sites, such as container walls.
The custom-made acoustic levitator using in these experiments regulates the influence that solid surfaces, temperature, and humidity have on the crystallization process. The investigations of the crystallization process of paracetamol were performed with in situ analytical techniques and theoretical simulations to gain a comprehensive insight into processes, occurring intermediates, and required reaction conditions. The targeted choice of the solvent and the concentration enabled the guidance of the pathways, therefore, resulting in the isolation of one desired crystalline structure.
X-ray refraction techniques represent a very promising, yet not so wide-spread, set of X-ray techniques
based on refraction effects. They allow determining internal specific surface (surface per unit volume) in a non-destructive fashion, position and orientation sensitive, and with nanometric detectability. While they are limited by the X-ray absorption of the material under investigation, we demonstrate showcases of ceramics and composite materials, where understanding of microstructural features could be achieved in a way unrivalled even by high-resolution techniques such as electron microscopy or computed tomography.
Alkaline earth metal fluoride nanoparticles have been investigated for application in wood protection. Sols of MgF2 and CaF2 were synthesized and their efficacy was tested against fungi and termites (Rehmer 2016, Krahl et al. 2016). The sols were characterized by XRD and SEM. The wood specimens were vacuum impregnated with nanoparticles and then exposed to fungi and termites according to EU certified test conditions. Our results show that wood impregnated with metal fluoride nanoparticles significantly reduce cellulose hydrolysis by fungi and termites. The wood samples were exposed to brown-rot fungi; Coniophora puteana and Poria placenta. Between the two fungi, the overall mass lost due to fungal degradation was lower for treated (MgF2 and CaF2) wood samples exposed to Coniophora puteana. Thus, the metal fluoride nanoparticles impregnated in the wood samples were more efficient in reducing cellulose degradation from Coniophora puteana than from Poria placenta. However the mass loss in samples treated with MgF2 was similar to those treated with CaF2, irrespective of type of fungi. Therefore, it is likely that fungal degradation in treated samples was dependent on the biocidal action of fluorides rather than on the differences in chemical and physical properties of MgF2 and CaF2, respectively. Conversely, for termite exposure, wood samples treated with MgF2 had lower cellulose degradation compared to those treated with CaF2. A possible explanation for this difference in results could be fungi and termites use separate mechanisms for cellulose hydrolysis which will be further investigated. Future experiments include testing the leaching potential of MgF2 and CaF2 nanoparticles from wood. The results from the leaching experiment will test if metal fluoride nanoparticles can provide long-term and environmentally safe protection to wood.
For concrete production aggregates, cement and water are mixed together and after 28 days of hydration a porous and multiphase material is formed. To consider the heterogeneity of concrete a 2D scanning system is used. The coarse aggregates (limit > 2 X d ) can be excluded. laser spot The remaining content is a mixture of flour grains and cement particles (micro heterogeneity). Harmful species like chlorides may penetrate together with water through the capillary pore space. A quantification of Cl regarding to the cement content only (European standard EN 206) is necessary for the damage assessment. A LIBS system operating with a NdCr:YAG laser (pulse energy of 3 mJ, a wavelength of 1064 nm, a pulse width of 1.5 ns, a repetition rate of 100 Hz) and two Czerny-Turner spectrometer (UV and NIR range) have been used.
The practical strength of glasses under ambient conditions is substantially lower compared to its intrinsic strength because of sub-critical crack growth (SCCG) from microscopic flaws. While SCCG is related to the humidity of the ambient atmosphere, leading to stress corrosion phenomena, the detailed kinetics are still not fully understood. To get better insight to the contribution of water on the crack-tip, highly water bearing glasses will be investigated by a new device for inert SCCG-measurements using double cantilever beam (DCB) geometry specimens. This device was designed to investigate the stress intensity factor in modus I and crack velocity in vacuum, but different atmospheres can also be introduced.
For validation of the new device, first experiments were performed on microscope slides as well as on a soda-lime silicate and a borosilicate crown glass. The results achieved will be presented in comparison to the published results of Wiederhorn.
A comparison between the results obtained from a Computational Fluid Dynamic (CFD) simulation and from the application of an empirical formula for determining the temperature distribution inside a tunnel in case of fire is presented. The temperature is measured and calculated at different distances from the location of the fire and at different time intervals. The fire considered varies with time following a time-heat release rate curve which has a parabolic growing phase, a constant period and a linear decay. The comparison reveals differences in the results. The temperatures calculated with the empirical formula resulted higher than the temperatures obtained by means of the CFD simulation. A list of possible reasons for this limited correspondence is also presented and commented. A proposal for further studies to better define the limitations of both the procedures and to define the influence of each parameter involved is finally presented.
We have shown that for C-ODTR based DAS two UV-inscribed scattering segments within an optical fiber have a significant influence on the local sensitivity Fading characteristics. This method was experimental proven to be suitable for distributed dynamic strain measurement in a thermally unstable environment. Signal-to-noise ratio analyses for detecting a signal peak within the time-dependent spectra were performed. Results show an increase in SNR and additionally that the occurrence of total loss of sensitivity (SNR <1) could be decreased by a factor of six when compared to an untreated standard fiber.
Microstructure and wear behavior of improved NbC cermets for (BS-1452) grey cast iron machining
(2017)
Tungsten carbide (WC) and cobalt (Co) based cermets are the most successful commercial cermets beacuse of the good combination of physical, mechanical and behavioral properties. Niobium carbide (NbC) has good mechanical and physical properties, such as high hardness, very high melting point and low density. SPS refined the NbC grains and increased the hardness, while substitution of Co with Ni improved the fracture toughness.
The widespread use of antibiotics in livestock farming leads to trace residues in food products and wastewater, potentially entailing antimicrobial resistance in food-borne pathogens. The determination of antibiotics in aqueous environments and foodstuff is thus of major concern.
We have been developing optical sensors based on molecularly imprinted polymers (MIPs) due to the low production costs, stability, format adaptability and the possibility to imprint and thus their ability to recognize a wide variety of target analytes. As a fluorescently responding moiety in the polymer matrix a tailor-made fluorescent indicator cross-linker for direct transfer of the binding event into an optical signal was used. If such a cross-linker is integrated into a thin MIP-shell on microspheres such core/shell particles can be readily used in advanced multiplexing sensory fiber-optic microarrays.
Here, we propose such a fiber-optic microarray based on fluorescent MIP microspheres for antibiotics. The binding behavior and the selectivity of a microarray using these silica core/MIP shell beads were examined and compared with a non-imprinted polymer (NIP) control, employing the target molecules and other structurally closely related antibiotics.
Mediaeval stained glass has been treated with Polymethylmetacrylate coatings by Kwiatkowski in Poland during the 1950th. Such treated panels were found in the Johannis Church of Toruń (without protective glazing), in the Cathedral of Włocławek (behind a protective glazing), and on glass kept in exhibition cases in the museum of Toruń. Surface coatings have been detected and analyzed. There was no extensive contamination by fungi or bacteria if the glass was either coated or not.
The manufacturing of NbC with Ni binder with addition of titanium carbide by using a colloidal process for blending the different powders without a milling step were investigated. The the sintering process and formation of the resulting microstructures, the phase relations and the hardness of the produced cermet materials are characterized.
The Federal Institute for Materials Research and Testing (BAM) and the Institute for Machine Tools and Factory Management (IWF) of the Technical University Berlin analyzed the suitability of various NbC types in comparison to tungsten carbide (WC) for use as a tool in cutting processes. The focus was placed on the optimization of the functional profile of NbC-based cutting materials with reproducible industrial production.
An efficient energy provision using fuel cells is linked to effecitve hydrogen storage capabilities. Because of its low intrinsic hydrogen permeability, glass has a huge potential in modern concepts of hydrogen storage. Previous studies on oxidic glasses showed an empirical connection between glass composition and gas permeation, which was mainly derived from the behavior of silica glass. In this study we focus on the relationship between topologic (free volume; network polymerization) and thermodynamic (configurational entropy) parameters. The comparison of three glasses within the meta (earth-) alkaline alumino silicate system to silica glass shows that an increase of the atomic packing factor (APF) does not necessarily decrease the permeability. Furthermore, the results suggest a connection between ΔCp at Tg and hydrogen permeability of the glass. All experiments were performed assuming that chemical hydrogen solubiltity in glass is negligible at temperatures well below the glass transition temperature.
Most crucial for components of complex shape or heterogeneous micro structure, precise control of sintering has decisive influence on dimensional accuracy, mechanical integrity and reliability of sintered components. In these cases, only in situ 3D high-temperature shape screening during shrinkage would allow revealing temporary sinter warpage and hereby caused potential defects. Against this background, nokra Optische Prüftechnik und Automation GmbH, HTM Reetz GmbH and BAM developed a testing device for in situ 3D shape screening for ceramic and glass-ceramic tapes up to 1000°C by means of high-temperature laser profilometry. The local repeatability of the sample-sensor distance (sample height profile) is 10 µm at 1000°C. Current work is focused on dropping these restrictions in sample shape and temperature. In a second testing device, currently being in development, samples up to 5 cm x 5 cm x 5 cm can be measured at temperatures up to 1500°C.The presentation illustrates the current state of this work and possible applications of the method.
The development of glassy hydrogen barriers requires the determination of low H2 permeabilities. Previous studies and numerical simulations have shown that the VHE powder method (vacuum hot extraction with mass spectrometric gas detection) is suitable for this purpose. The measured isothermal gas emission is fitted to a classical diffusion model for spherical particles from which the diffusion coefficient of the glass is calculated. The H2 permeability is determined by means of the solubility determined from the same measurement data. This presentation is referring to the optimization of the method regarding sample preparation and measurement data evaluation using suitable experimentally determined particle size distributions is reported. For quartz glass, it is shown that the accuracy of classical measuring methods is achieved with the VHE powder method. Furthermore, other examples of substantially gas-tighter glasses are given.
The chemical industry has expressed great interest in using polyethylene terephthalate (PET) as material for packagings for the transport of dangerous goods. Due to the high strength and stiffness of PET, the wall thickness and weight of packagings can be reduced.
The aim of this work was to find a laboratory test method for the determination of the stress cracking resistance of PET. One test method is the Full Notch Creep Test (FNCT), which was developed for polyethylene (PE) and is described in the standards EN ISO 13274 and EN 15507. It was investigated whether testing specimens made of PET with a full coplanar notch around the middle of the specimens show weakening after the impact of a tensile force in a wetting solution at 50°C. Unfortunately, this method couldn’t be used for PET because the specimens broke during notching due to the high brittleness of PET. The molding of the sheets and the following temper process for twelve hours are very time-consuming, Another possibility is laid down in BAM’s Dangerous Goods Rule BAM-GGR 015. This test was carried out with 1l PET bottles, which were filled with a 5% wetting solution and mounted with a clamping tool for 28 days at 40°C. Tensile test specimens were cut out afterwards from the middle of the bottles in the deformed areas. The tensile properties of the PET specimens couldn’t be determined due to the hardness of the material.
In conclusion, the only way to provide information about the stress cracking resistance of PET was to perform stacking tests with PET design types of packagings. 1l bottles made of PET were filled with a 5% wetting solution and stored with a stacking load for 28 days at 40°C according to EN ISO 16495. The test bottles of PET passed the stacking tests.
Several restoration projects of stained-glass windows have been performed in Poland since 2010.Chemical analysis of glass samples was performed with SEM/EDX on a FEI ESEM-XL 30, (EDX-EDAX) and with Micro-XRF (M4 Tornado, Bruker).The chemical composition of medieval glass samples and of glass samples of the 19th Century have been determined.
Leichtbaustrukturen aus Verbundwerkstoffen stellen einen immer größeren Anteil im Flugzeug- und Automobilbau dar. Hiermit steigt die Nachfrage nach zuverlässigen, zerstörungsfreien Prüfmethoden, welche an solche Strukturen angepasst sind. Besonders Luftultraschall (LUS) eignet sich für diese Aufgabe, da hier kein Koppelmedium benötigt wird. Derzeit wird für diese Methode jedoch oft ein beidseitiger Bauteilzugang für eine Prüfung in Durchschallung vorausgesetzt. Handelsübliche Prüfköpfe für Luftultraschallanwendungen nutzen zudem meist Anpassschichten um den Impedanzunterschied zwischen Schwinger und Luft zu reduzieren. Sowohl Signal-Rausch-Abstand als auch die Bandbreite der resultieren-den Prüfköpfe ist für viele Anwendungen jedoch nicht ausreichend. Durch den Einsatz von Ferroelektreten wie zellulärem Polypropylen (zPP) kann hingegen vollständig auf Anpassschichten verzichtet werden. Hierbei handelt es sich um polarisierte, zelluläre Polymerschichten mit sehr geringer Dichte, Steifigkeit und Schallgeschwindigkeit.
In diesem Beitrag stellen wir drei verschiedene Sende-Empfangs-Prüfköpfe vor, welche auf zellulärem Polypropylen basieren. Anhand von Schallfeld, Signal-Rausch-Abstand und Sendepegel werden diese Prüfköpfe charakterisiert. Die Ergebnisse werden mit den Ergebnissen von Referenzprüfköpfen ohne Sende-Empfangs-Charakteristik verglichen. Bei den Referenzprüfköpfen werden sowohl handelsübliche LUS-Prüfköpfe, sowie bisher entwickelte Prüfköpfe aus zellulärem Polypropylen berücksichtigt.
Ferritic steels with chromium contents up to 13 wt% are used as materials for power plant components as boiler materials (< 2 wt% Cr) and super heater tubes (> 9 wt% Cr). These materials are subject to aggressive corrosion caused by hot gases such as CO2, H2O, O2 and SO2. Especially SO2 causes fatal corrosion even as a minor component. To examine sulfurous corrosion mechanisms, experiments with pure SO2 were conducted. A proper analysis of the material changes requires phase identification and quantification with a high lateral resolution within the corrosion scale.
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.
Die Mikrostruktur ferromagnetischer Materialien hat einen maßgeblichen Einfluss auf deren magnetischen Eigenschaften. Gerade bei niedrigen Feldstärken zeigen sich Parameter wie Koerzitivität, Permeabilität und Verlustleistung hoch sensitiv.
Wir zeigen am Beispiel des unlegierten Baustahls S235JR, dass die magnetische Mikrostruktur an der Probenoberfläche in hohem Maße mit inhomogenen Dehnungen übereinstimmt. Zur Detektion der Kleinststreufelder verwenden wir speziell designte GMR Sensorik, die Sensitivität (3mV/V/kA/m) mit hoher Ortsauflösung (180 µm) vereint. Infolgedessen können wir auf eine aktive magnetische Anregung verzichten. Wir nutzen allein die sich durch magneto-mechanische Prozesse ausbildende „spontane“ magnetische Mikrostruktur des Materials.
Das hervorragende Signal-Rausch-Verhältnis unserer GMR-Sensorik für inhomogene Streufelder erlaubt, schon geringe und lokal abgegrenzte plastische Deformationen in Form und Position reproduzierbar zu visualisieren. Die zugehörigen Signale zeigen die typische Sequenz von erhöhten positiven und negativen Normalkomponenten wie sie bei einer Rissanzeige der aktiven Streuflussprüfung (MFL - Magnetic Flux Leakage) beobachtet wird. Magnetisch kann eine plastische Zone daher als Vorstufe eines Risses betrachtet werden, deren relative Permeabilität für den Riss als Grenzfall zu μr = 1 tendiert.
Die mechanische Spannung ist ein maßgeblicher Parameter ferromagnetischer Materialien. Wird ein solches Material unter die Curie Temperatur abgekühlt, zerfällt es spontan in nahezu selbstgesättigte magnetische Domänen. Diese Magnetisierung führt gleichzeitig zu einer Verformung der mit ihr gekoppelten Kristallgitter. Ein Effekt der auch reziprok gilt: wird die Gitterverformung durch eine Spannung behindert ändert sich zwangsweise der magnetische Zustand.
Man kann annehmen, dass zwischen unterschiedlichen, für sich aber homogen verspannten Werkstoffbereichen, lokale magnetische Streufelder auftreten, weil magneto-mechanische Effekte eine Inkompatibilität der Domänenstruktur induzieren. Bekanntlich bilden sich Spannungsgradienten nach Schweißprozessen durch ungleichmäßigen Wärmeeintrag, thermischer Dehnung, und unterschiedlichen Abkühlraten aus.
Unter dieser Prämisse untersuchen wir Wolfram-Inertgas geschweißte Blindnahtproben (250x100x4,8 mm^3) aus einem hypereutektoiden Baustahl.
Der Spannungszustand der Proben wurde anhand von Neutronendiffraktometrie (ND) am Instrument E3 am Reaktor BERII (Helmholzzentrum Berlin, HZB) charakterisiert. ND ist ein Referenzverfahren für die quantitative Bestimmung von elastischen Dehnungen in kristallinen Materialien, deren Gitter selbst der Messmaßstab ist. Die Auswertung zeigt hohe Längsspannungen mit lokalen Maxima in Größenordnung von 600 MPa, die von umgebenen Druckspannungszonen kompensiert werden.
Zur Detektion der magnetischen Kleinststreufelder verwenden wir speziell designte GMR-Sensorik (GMR - Giant Magneto Resistance), die aufgrund der geringen Größe ihrer aktiven Sensorelemente hohe Ortsauflösung mit Sensitivität vereint. Die Visualisierung der Messergebnisse lässt eine klare magnetische Mikrostruktur der Schweißnähte erkennen, in der die Streufelder lateral in Größenordnung des Erdmagnetfeldes variieren (~50 µT).
Wir zeigen durch einen Vergleich beider Messverfahren, dass lokale magnetische Streufeldmaxima in hohem Maße mit den Spannungsgradienten übereinstimmen.
Regelwerke zur zerstörungsfreien Bestimmung des Reinheitsgrades wie das SEP 1927 und die ASTM E588 erreichen ihre Vergleichbarkeit unter Anwendung von - vergleichsweise einfachen - Referenzfehlern. Hinsichtlich Realisierbarkeit wird somit der Kompromiss zwischen Herstellung des Referenzfehlers und der erreichbaren Nachweisgrenze gefunden.
Zur Weiterentwicklung über die Grenzen der SEP1927 hinaus, wurde der Versuch unternommen Fehler kleiner 500 μm herzustellen - welche aufgrund der geringen geometrischen Ausdehnung fertigungsbedingt schwierig zu realisieren sind. Bei den vergleichenden Untersuchungen kristallisierten sich zwei Fertigungsverfahren, Funkenerosion (EDM: electrical discharge maching) und die Fertigung der Bohrungen unter Verwendung eines Hochleistungslasers, als vielversprechend heraus. Zunächst wurden die Fehler mit beiden Verfahren in unterschiedlichen Größen (100, 250 und 100 μm) und Tiefen (1, 1,5 und 2 mm) unter Anwendung von computertomographischen Verfahren der Röntgenprüfung, die Geometrie der eingebrachten Fehlstellen und anschließend durch hochauflösende Tauchtechnikmessungen das Reflektionsverhalten charakterisiert.