TY - JOUR A1 - Tran, M.Q. A1 - Ho, K.K.C. A1 - Kalinka, Gerhard A1 - Shaffer, M.S.P. A1 - Bismarck, A. T1 - Carbon fibre reinforced poly(vinylidene fluoride): Impact of matrix modification on fibre/polymer adhesion N2 - The quality of interfacial interaction is dictated by the surface chemistry of the carbon fibres and the composition of the matrix. The composition of poly(vinylidene fluoride) (PVDF) was modified by the addition of maleic anhydride grafted PVDF. The surface properties of the various matrix formulations were characterised by contact angle and electrokinetic measurements. Carbon fibres were modified by industrial electrochemical oxidation and oxidation in nitric acid, or the use of a traditional epoxy-sizing of industrially oxidised fibres. The surface composition, morphology and wetting behaviour of the carbon fibres was characterised. The interaction between modified PVDF and the carbon fibres was studied by direct contact angle measurements between PVDF melt on single carbon fibres and by single fibre pull-out tests. The best wetting and adhesion behaviour was achieved between PVDF containing 5 ppm grafted maleic anhydride (MAH) and epoxy-sized carbon fibres. The addition of MAH-grafted PVDF to the unmodified PVDF caused the apparent interfacial shear strength to increase by 184%. The apparent interfacial shear strength of this fibre–matrix combination allowed for the utilisation of 100% of the yield tensile strength of PVDF. KW - A. Carbon fibres KW - A. Coupling agents KW - B. Interface KW - B. Adhesion KW - Wetting PY - 2008 DO - https://doi.org/10.1016/j.compscitech.2008.02.021 SN - 0266-3538 VL - 68 IS - 7-8 SP - 1766 EP - 1776 PB - Elsevier CY - Barking AN - OPUS4-18259 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Gehlen, C.D. A1 - Wiens, E. A1 - Noll, R. A1 - Wilsch, Gerd A1 - Reichling, K. T1 - Chlorine detection in cement with laser-induced breakdown spectroscopy in the infrared and ultraviolet spectral range N2 - A significant parameter to monitor the status of concrete buildings like bridges or parking garages is the determination of the depth profile of the chlorine concentration below the exposed concrete surface. This information is required to define the needed volume of restoration for a construction. Conventional methods like wet chemical analysis are time- and cost-intensive so an alternative method is developed using laser-induced breakdown spectroscopy (LIBS). The idea is to deploy LIBS to analyze drill cores by scanning the sample surface with laser pulses. Chlorine spectral lines in the infrared (IR) and ultraviolet (UV)-range were studied for chlorine detection in hydrated cement samples. The excitation energies of these spectral lines are above 9.2 eV. Hence high plasma temperatures and pulse energies in the range of some hundred millijoules are needed to induce sufficient line intensity levels at the required working distance. To further increase the line intensity and to lower the detection limit (LOD) of chlorine a measuring chamber is used where different ambient pressures and gases can be chosen for the measurements. The influences on the line intensity for pressures between 5 mbar and 400 mbar using helium as process gas and the influence of different laser burst modi like single and collinear double pulses are investigated. For the first time a LOD according to DIN 32 645 of 0.1 mass% was achieved for chlorine in hydrated cement using the UV line 134.72 nm. KW - Laser-induced breakdown spectroscopy KW - LIBS KW - Hydrated cement KW - Chlorine KW - Limit of detection PY - 2009 DO - https://doi.org/10.1016/j.sab.2009.07.021 SN - 0584-8547 SN - 0038-6987 VL - 64 IS - 10 SP - 1135 EP - 1140 PB - Elsevier CY - Amsterdam AN - OPUS4-20500 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Mero, M. A1 - Clapp, B. A1 - Jasapara, J.C. A1 - Rudolph, W. A1 - Ristau, D. A1 - Starke, K. A1 - Krüger, Jörg A1 - Martin, Sven A1 - Kautek, Wolfgang T1 - On the damage behavior of dielectric films when illuminated with multiple femtosecond laser pulses N2 - The physical effects reducing the damage threshold of dielectric films when exposed to multiple femtosecond pulses are investigated. The measured temperature increase of a Ta2O5 film scales exponentially with the pulse fluence. A polarized luminescence signal is observed that depends quadratically on the pulse fluence and is attributed to twophoton excitation of self-trapped excitons that form after band-to-band excitation. The damage fluence decreases with increasing pulse number, but is independent of the repetition rate from 1 Hz to 1 kHz at a constant pulse number. The repetition rate dependence of the breakdown threshold is also measured for TiO2 , HfO2, Al2O3, and SiO2 films. A theoretical model is presented that explains these findings. KW - Laser-induced damage KW - Laser materials KW - Ultrafast phenomena KW - Coatings PY - 2005 DO - https://doi.org/10.1117/1.1905343 SN - 0892-354X VL - 44 IS - 5 SP - 051107-1-051107-7 PB - Dekker CY - New York, NY AN - OPUS4-7406 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Ho, K.K.C. A1 - Kalinka, Gerhard A1 - Tran, M.Q. A1 - Polyakova, N.V. A1 - Bismarck, A. T1 - Fluorinated carbon fibres and their suitability as reinforcement for fluoropolymers N2 - The interaction between direct fluorinated carbon fibres and various fluoropolymers (ethylene-chlorotrifluoroethylene, poly vinylidene fluoride, fluorinated ethylene propylene copolymer and tetrafluoroethylene-perfluoro alkoxy vinyl ether copolymer) was studied by means of direct wetting measurements between fibres and the polymer melts and single fibre pull-out tests. The results of both techniques allow the adhesion behaviour between the fibres and the matrices to be predicted. The results obtained show that a low degree of surface fluorination of carbon fibres leads to an improved wettability between the fibres and fluoropolymer melts and this is an indicator for an improved thermodynamic work of adhesion. The apparent interfacial shear strength as measure of practical adhesion, determined by the single fibre pull-out test, increases with increasing degree of surface fluorine content up to a maximum, which depends on the degree of fluorination of the matrix used. The improved interaction between the fibre and the matrix is due to an enhanced compatibility at the fibre/matrix interface. KW - Adhesion KW - A. Carbon fibres KW - B. Debonding KW - B. Interfacial strength PY - 2007 DO - https://doi.org/10.1016/j.compscitech.2007.02.012 SN - 0266-3538 VL - 67 IS - 13 SP - 2699 EP - 2706 PB - Elsevier CY - Barking AN - OPUS4-15814 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Ho, K.K.C. A1 - Lamoriniere, S. A1 - Kalinka, Gerhard A1 - Schulz, Eckhard A1 - Bismarck, A. T1 - Interfacial behavior between atmospheric-plasma-fluorinated carbon fibers and poly(vinylidene fluoride) N2 - Atmospheric-plasma fluorination was used to introduce fluorine functionalities onto the surface of carbon fibers without affecting their bulk properties. The interfacial adhesion between atmospheric-plasma-fluorinated carbon fibers and poly(vinylidene fluoride) (PVDF) was studied by means of direct wetting measurements and single fiber pullout tests. Measured contact angles of PVDF melt droplets on modified carbon fibers show that short exposure times of carbon fibers to atmospheric-plasma fluorination (corresponding to a degree of surface fluorination of F/C = 0.01 (1.1%)) leads to improved wettability of the fibers by PVDF melts. The apparent interfacial shear strength as a measure of practical adhesion, determined by the single-fiber pullout test, increases by 65% under optimal treatment conditions. The improved practical adhesion is not due to the formation of transcrystalline regions around the fibers or a change of the bulk matrix crystallinity or to an increased surface roughness; it seems to be due to the compatibilization of the interface caused of the atmospheric-plasma fluorination of the carbon fibers. KW - Carbon fibers KW - Fluorination KW - Contact angle KW - Interface KW - Adhesion KW - Surface area KW - Fiber properties PY - 2007 DO - https://doi.org/10.1016/j.jcis.2007.04.076 SN - 0021-9797 SN - 1095-7103 VL - 313 IS - 2 SP - 476 EP - 484 PB - Elsevier CY - Orlando, Fla. AN - OPUS4-16026 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Hansen, H.-C. A1 - Lagrèze, W. A1 - Krüger, Oswald A1 - Helmke, K. T1 - Dependence of the optic nerve sheath diameter on acutely applied subarachnoidal pressure - an experimental ultrasound study N2 - Purpose: To determine the distensibility and elastic characteristics of the optic nerve sheath for development of a basic understanding of ultrasound studies aimed to measure optic nerve sheath diameter (ONSD) for detection of acutely elevated intracranial pressure (ICP). Methods: Isolated human optic nerves preparations obtained from autopsies were submitted to predefined pressure alterations, and consecutive changes in ONSD were measured by B-scan ultrasound under defined conditions. Results: Following submission to pressure, the diameter of the nerve sheath increased up to 140% of its baseline value. The increase (mean 1.97 mm, SD 0.52 mm) corresponded to the magnitude of pressure steps measured in the perineural subarachnoidal space (SAS). Similarly, the ONSD declined in each of the preparations within a few minutes after the optic nerve was decompressed. However, it did not reach its baseline value again when pressure loads of 45–55 mmHg or more had been applied. Conclusions: The elasticity of the anterior sheath of the optic nerve is sufficient for the detection of pressure changes in the SAS especially for upward pressure steps. This is basically important for the application of clinical monitoring of the sheath diameter to facilitate the identification of patients with elevated ICP non-invasively (screening). However, further implementation of this procedure in neurointensive care and emergency medicine has to consider that the sheath diameter reversibility may be impaired after episodes of prolonged intracranial hypertension and a model for hysteresis is proposed. KW - Intensive care KW - Intracranial pressure KW - Neuromonitoring KW - Optic nerve sheath KW - Ultrasound PY - 2011 DO - https://doi.org/10.1111/j.1755-3768.2011.02159.x SN - 1755-375X SN - 1755-3768 VL - 89 IS - 6 SP - e528 EP - e532 PB - Blackwell CY - Oxford AN - OPUS4-24017 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kuka, K. A1 - Illerhaus, Bernhard A1 - Fox, C.A. A1 - Joschko, M. T1 - X-ray computed microtomography for the study of the soil-root relationship in grassland soils N2 - We present results from the analysis of three-dimensional X-ray computed tomography images of undisturbed soil samples in grassland sites. A strong positive correlation between root parameters and the solid surface/solid volume ratio was found. Preliminary analyses suggest that the relationship between soil structure and root patterns is related to the intensity of land management at the grassland sites, with reduced root volumes at sites with increased land use intensity. The exploration of soil structure and its consequences for ecological functions is of prime importance for understanding of the 'critical zone.' In soils, the relationship between soil structure and plant roots—which influences water dynamics in soil—deserves special interest. With X-ray computed microtomography (micro-CT), soil structure and roots may be visualized and quantified simultaneously. We analyzed undisturbed soil samples from three grassland sites. After scanning the soil cores with an X-ray micro-CT scanner (resolution 40 µm), roots were delineated from the soil material and soil pore space by means of their X-ray grey value characteristics followed by the use of space transformation during image analyses. To determine efficacy of the X-ray micro-CT to identify roots, root volumes and surfaces were quantified with a standard root washing method showing good correspondence. A strong positive correlation between root volume and surfaces and the solid surface/solid volume ratio was found, with greater root growth in a more aggregated and porous soil. Preliminary analyses suggest that the relationship between soil structure and root patterns is related to the intensity of land management at the grassland sites, with reduced root volumes and surfaces at sites with increased land use intensity. This methodology has substantial potential for further research on management influences on soil structure and root growth across landscapes. KW - X-ray micro-CT KW - CT KW - Computed tomography KW - Micro-CT KW - Computed microtomography KW - Soil structure KW - Grassland sites KW - Plant roots KW - 3D PY - 2013 DO - https://doi.org/10.2136/vzj2013.01.0014 SN - 1539-1663 VL - 12 IS - 4 SP - 1 EP - 10 CY - Madison, Wis. AN - OPUS4-29643 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kipphardt, Heinrich A1 - Russe, K. A1 - Broekaert, J.A.C. T1 - Determination of main and minor components of silicon based materials by a combustion with elemental fluorine. Separation of gaseous fluorination products by carrier gas distillation and gas mass spectrometry N2 - For the determination of main and minor components in silicon-based ceramic powders, a decomposition by a combustion with elemental fluorine and separation of the volatile fluorination products by a carrier-gas distillation with a subsequent detection by quadrupole mass spectrometry is described. The necessity and success of the separation step is demonstrated for the determination of boron as a minor constituent in SiC, where the spectral interferences of silicon on the boron signals are decreased considerably. The method developed is shown to be directly applicable to determination of silicon in Si3N4, SiC, and SiO2. The determination of nitrogen in Si3N4 requires additional effort, to separate nitrogen from the excess of fluorine. For the determination of boron, a complete mobilization of BF3 is assured by the presence of an adequate amount of GeF4. Analysis results obtained with different types of calibration show a precision of 30 g for boron at the milligram-per-gram level and a precision between 0.5 and 2% (m/m) for the main components, silicon and nitrogen. Within these standard deviations, the results agree well with the values expected from the stoichiometry, with the results for silicon and boron obtained by wet chemical decomposition and slurry techniques in combination with ICP-OES and with the results for nitrogen obtained by carrier gas heat extraction. PY - 2000 DO - https://doi.org/10.1021/ac991238c SN - 0003-2700 SN - 1520-6882 VL - 72 IS - 16 SP - 3875 EP - 3880 PB - American Chemical Society CY - Washington, DC AN - OPUS4-989 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Babu, N. K. A1 - Brauser, S. A1 - Rethmeier, Michael A1 - Cross, C.E. T1 - Characterization of microstructure and deformation behaviour of resistance spot welded AZ31 magnesium alloy N2 - Resistance spot welds were prepared on 3 mm thick sheets of continuous cast and rolled AZ31 magnesium alloy. The microstructure and composition analysis of weld nugget, heat affected zone (HAZ) and base metal were examined using optical and scanning electron microscopy (HR-SEM and EDS/X). The resistance spot welded magnesium alloy joints consist mainly of weld nugget and HAZ. The nugget contains two different structures, i.e. the cellular-dendritic structure at the edge of the nugget and the equiaxed dendritic structure in the centre of the nugget. The structure transition is attributed to the changes of solidification conditions. In the HAZ, grain boundary melting occurred and grain boundaries became coarse. It has been shown that hardness reduction in the weld nugget and HAZ compared with base metal is evident due to dendritic microstructure and grain growth, respectively. The results showed that spot welded joints have failed in interfacial mode under torsion and tensile–shear loading conditions. Digital image correlation during tensile–shear testing showed that low surface strains occur in the interfacial failure mode, because fracture and deformation happened primarily in the nugget area. KW - Resistance spot welding KW - AZ31 magnesium alloy KW - Microstructure KW - Hardness KW - Torsion KW - Tensile–shear PY - 2012 DO - https://doi.org/10.1016/j.msea.2012.04.021 SN - 0921-5093 SN - 1873-4936 VL - 549 SP - 149 EP - 156 PB - Elsevier B.V. CY - Amsterdam AN - OPUS4-25924 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Agudo Jácome, Leonardo A1 - Pöthkow, K. A1 - Paetsch, O. A1 - Hege, H.-C. T1 - Three-dimensional reconstruction and quantification of dislocation substructures from transmission electron microscopy stereo pairs N2 - A great amount of material properties is strongly influenced by dislocations, the carriers of plastic deformation. It is therefore paramount to have appropriate tools to quantify dislocation substructures with regard to their features, e.g., dislocation density, Burgers vectors or line direction. While the transmission electron microscope (TEM) has been the most widely-used equipment implemented to investigate dislocations, it usually is limited to the two-dimensional (2D) observation of three-dimensional (3D) structures. We reconstruct, visualize and quantify 3D dislocation substructure models from only two TEM images (stereo pairs) and assess the results. The reconstruction is based on the manual interactive tracing of filiform objects on both images of the stereo pair. The reconstruction and quantification method are demonstrated on dark field (DF) scanning (S)TEM micrographs of dislocation substructures imaged under diffraction contrast conditions. For this purpose, thick regions (> 300 nm) of TEM foils are analyzed, which are extracted from a Ni-base superalloy single crystal after high temperature creep deformation. It is shown how the method allows 3D quantification from stereo pairs in a wide range of tilt conditions, achieving line length and orientation uncertainties of 3% and 7°, respectively. Parameters that affect the quality of such reconstructions are discussed. KW - Dislocation KW - Diffraction contrast KW - Scanning transmission electron microscopy (STEM) KW - Stereoscopy KW - Visualization PY - 2018 DO - https://doi.org/10.1016/j.ultramic.2018.08.015 SN - 0304-3991 VL - 195 SP - 157 EP - 170 PB - Elsevier B.V. CY - Amsterdam AN - OPUS4-46355 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Lukowiak, M.C. A1 - Wettmarshausen, Sascha A1 - Hidde, Gundula A1 - Landsberger, Petra A1 - Boenke, Viola A1 - Rodenacker, K. A1 - Braun, Ulrike A1 - Friedrich, Jörg Florian A1 - Gorbushina, Anna A1 - Haag, R. T1 - Polyglycerol coated polypropylene surfaces for protein and bacteria resistance N2 - Polyglycerol (PG) coated polypropylene (PP) films were synthesized in a two-step approach that involved plasma bromination and subsequently grafting hyperbranched polyglycerols with very few amino functionalities. The influence of different molecular weights and density of reactive linkers were investigated for the grafted PGs. Longer bromination times and higher amounts of linkers on the surface afforded long-term stability. The protein adsorption and bacteria attachment of the PP-PG films were studied. Their extremely low amine content proved to be beneficial for preventing bacteria attachment. PY - 2015 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-325406 DO - https://doi.org/10.1039/c4py01375a SN - 1759-9954 SN - 1759-9962 VL - 6 IS - 8 SP - 1350 EP - 1359 AN - OPUS4-32540 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Maul, Ronald A1 - Greer, B. A1 - Campbell, K. A1 - Elliott, C.T. T1 - Detection of freshwater cyanotoxins and measurement of masked microcystins in tilapia from Southeast Asian aquaculture farms N2 - Recently, there has been a rise in freshwater harmful algal blooms (HABs) globally, as well as increasing aquaculture practices. HABs can produce cyanotoxins, many of which are hepatotoxins. An ultra-performance liquid chromatography tandem mass spectrometry method was developed and validated for nine cyanotoxins across three classes including six microcystins, nodularin, cylindrospermopsin and anatoxin-a. The method was used to analyse free cyanotoxin(s) in muscle (n = 34), liver (n = 17) and egg (n = 9) tissue samples of 34 fish sourced from aquaculture farms in Southeast Asia. Conjugated microcystin was analysed by Lemieux oxidation to ascertain the total amount of microcystin present in muscle. Some tilapia accumulated free microcystin-LR in the muscle tissue at a mean of 15.45 μg/kg dry weight (dw), with total microcystin levels detected at a mean level of 110.1 μg/kg dw, indicating that the amount of conjugated or masked microcystin present in the fish muscle accounted for 85% of the total. Higher levels of cyanotoxin were detected in the livers, with approximately 60% of those tested being positive for microcystin-LR and microcystin-LF, along with cylindrospermopsin. Two fish from one of the aquaculture farms contained cylindrospermopsin in the eggs; the first time this has been reported. The estimated daily intake for free and total microcystins in fish muscle tissue was 2 and 14 times higher, respectively, than the tolerable daily intake value. This survey presents the requirement for further monitoring of cyanotoxins, including masked microcystins, in aquaculture farming in these regions and beyond, along with the implementation of guidelines to safeguard human health. KW - Harmful algal bloom KW - UPLC-MS/MS KW - Bioaccumulation KW - Human health PY - 2017 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-404669 DO - https://doi.org/10.1007/s00216-017-0352-4 SN - 1618-2642 SN - 1618-2650 VL - 409 IS - 16 SP - 4057 EP - 4069 PB - Springer CY - Heidelberg AN - OPUS4-40466 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -