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Amphiphilic amino acids represent promising scaffolds for biologically active soft matter. In order to understand the bulk self-assembly of amphiphilic amino acids into thermotropic liquid crystalline phases and their biological properties a series of tyrosine ionic liquid crystals (ILCs) was synthesized, carrying a benzoate unit with 0–3 alkoxy chains at the tyrosine unit and a cationic guanidinium head group. Investigation of the mesomorphic properties by polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction (WAXS, SAXS) revealed smectic A bilayers (SmAd) for ILCs with 4-alkoxy- and 3,4-dialkoxybenzoates, whereas ILCs with 3,4,5-trisalkoxybenzoates showed hexagonal columnar mesophases (Colh ), while different counterions had only a minor influence. Dielectric measurements revealed a slightly higher dipole moment of non-mesomorphic tyrosine-benzoates as compared to their mesomorphic counterparts. The absence of lipophilic side chains on the benzoate unit was important for the biological activity. Thus, non-mesomorphic tyrosine benzoates and crown ether benzoates devoid of additional side chains at the benzoate unit displayed the highest cytotoxicities (against L929 mouse fibroblast cell line) and antimicrobial activity (against Escherichia coli DTolC and Staphylococcus aureus) and promising selectivity ratio in favour of antimicrobial activity.
Novel approaches of tunable devices for millimeter wave applications based on liquid crystal (LC) are presented. In the first part of the paper, a novel concept of a tunable LC phase shifter realized in Low Temperature Cofired Ceramics technology is shown while the second part of the paper deals with a tunable high-gain antenna based on an LC tunable reflectarray. The reflectarray features continuously beam scanning in between ±25°. Also first investigations on radiation hardness of LCs are carried out, indicating that LCs might be suitable for space applications.
This pilot study compares the performance of participants in analyzing gas mixtures of nitrogen dioxide in nitrogen by comparison with in-house gravimetric standards using Fourier transformed infrared spectroscopy (FT-IR). In this study the same gas mixtures were used as in the key comparison CCQM-K74, which was designed to evaluate the level of comparability of National Metrology Institutes' measurement capabilities for nitrogen dioxide (NO2) at a nominal mole fraction of 10 µmol/mol. In the comparison CCQM-K74 most of the participants used chemiluminescence, with a small number using UV absorption or FT-IR spectroscopy, and thus it is of interest to improve understanding of the comparative performance of these techniques because they do not exhibit any cross-sensitivity to nitric acid (HNO3), which was known to be present in the mixtures used for the comparison.
The results of this pilot study indicate good consistency and a level of agreement similar to that reported in the comparison CCQM-K74, demonstrating that FT-IR can be operated as a comparison method when calibrated with appropriate gas standards and can achieve similar measurement uncertainties to chemiluminescence and UV absorption techniques.
An additional pilot study, CCQM-P110-B2, was conducted on the same gas mixtures in parallel with this pilot study. The second study addressed FT-IR spectroscopy when used to measure the gas mixtures with respect to reference spectra. The results of this second study will be reported elsewhere.
Main text. To reach the main text of this paper, click on Final Report.
The final report has been peer-reviewed and approved for publication by the CCQM-GAWG.
DatesIssue 1A (Technical Supplement 2012)
This key comparison was performed to demonstrate the capability of NMIs to analyse the purity of methane for use as a source gas in the preparation of standard gas mixtures. This capability is an essential requirement for the preparation of accurate standards of natural gas and some other fuels.
Since it is difficult to carry out a comparison with individual samples of pure gas, the sample for this comparison was a synthetic mixture of high purity methane with selected added impurities of nitrogen, argon, carbon dioxide and ethane. These mixtures were prepared by a gas company as a batch of 10 cylinders and their homogeneity and stability were evaluated by NMIJ.
The KCRVs for the four different analytes in this key comparison are based on a consensus of values reported by participants. The uncertainties in the degrees of equivalence were calculated by combining the reported uncertainties with the homogeneity of the samples and the uncertainty of the KCRV. The results submitted are generally consistent with the KCRV within the estimated uncertainties.
Finally, this comparison demonstrates that the analysis of nitrogen, argon, carbon dioxide and ethane in methane at amount fractions of 1 µmol/mol to 5 µmol/mol is generally possible with an uncertainty of 5% to 10%.
Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.
The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).
DatesIssue 1A (Technical Supplement 2012)
The surface properties of original high strength and preoxidized high modulus carbon fibers were altered by electrocopolymerizing acryl amide and carbazole and therefore depositing a copolymer coating onto the fibers. Scanning electron microscopy and zeta-potential measurements confirmed the presence of a rough but dense and continuous electrocoating with a basic surface character. Therefore, lsquogoodrsquo adhesion behavior between the electrocoated carbon fibers and an epoxy resin matrix should be expected. The interfacial adhesion was measured using the single fiber pull-out and single fiber indentation test. It was shown that only lsquointermediatersquo adhesion was present between the carbon fibers and the electrocoating, but superior adhesion between the coating and epoxy resin exists. The single fiber model composites always failed at the fiber/electrocoating interface. However, as shown by using the indentation test, the interfacial adhesion between fibers and electrocoating can be significantly improved if preoxidized fibers are used as substrate for electropolymerization. A very high tensile strength for the electrocoating can be expected as derived from the single fiber pull-out tests.
The requirement for a metrological infrastructure to ensure the interchangability of 'nonconventional’ energy gases within existing European infrastructure1 was the driving force behind the work undertaken in the three-year EMRP Characterisation of energy gases project EMRP ENG01 (June 2010 - May 2013).
As part of work package one of the project, Standards and methods were used to perform composition and impurity measurements on samples of real energy gases collected from around Europe. The aim of this study was to compare the results obtained from different labs, and thereby provide an evaluation of the labs’ capabilities and provide insight into the feasibility of different analytical methodologies for use with future measurements.
Most studies about the interaction of nanoparticles (NPs) with cells have focused on how the physicochemical properties of NPs will influence their uptake by cells. However, much less is known about their potential excretion from cells. However, to control and manipulate the number of NPs in a cell, both cellular uptake and excretion must be studied quantitatively. Monitoring the intracellular and extracellular amount of NPs over time (after residual noninternalized NPs have been removed) enables one to disentangle the influences of cell proliferation and exocytosis, the major pathways for the reduction of NPs per cell. Proliferation depends on the type of cells, while exocytosis depends in addition on properties of the NPs, such as their size. Examples are given herein on the role of these two different processes for different cells and NPs.
A novel coordination oligo/polymer is synthesized by metal-directed self-assembly from equimolar amounts of the (dppp)M(OTf)2 precursor complexes (dppp = bis-(diphenylphosphino)-propane, OTf = triflate; M = PdII or M = PtII) and banana-shaped bidentate dipyridyl ligands. The assemblies were characterized by ESI mass spectrometry and NMR spectroscopy. The analysis of the cloudy suspension prepared by dissolving the coordination polymer in aqueous methanol solutions indicates nanosized spherical objects to form. Evidence for vesicle formation from these metallo-supramolecular oligomers comes from (cryogenic) transmission electron microscopy (TEM, cryo-TEM). Atomic force microscopy revealed stable nanospheres on hydrophilic mica and monolayer formation on hydrophobic highly oriented pyrolitic graphite (HOPG) substrates. On mica, also torus-shaped object were observed, which are rationalized by vesicles that opened during the drying procedure and released the internal solvent. Elemental analysis of the nanoassemblies by X-ray photoelectron spectroscopy (XPS) indicates uncoordinated and coordinated pyridines in the coordination polymers that form the nanospheres. Various control experiments using different metal centers and modified ligands support the conclusions.
XUV- and X-ray free-electron-lasers (FEL) combine short wavelength, ultrashort pulse duration, spatial coherence and high intensity. This unique combination of properties opens up new possibilities to study the dynamics of non-reversible phenomena with ultrafast temporal and nano- to atomic-scale spatial resolution. In this contribution we wish to present results of time-resolved experiments performed at the XUV-FEL FLASH (HASYLAB/Hamburg) aimed to investigate the nano-scale structural dynamics of laser-irradiated materials. Thin films and fabricated nano-structures, deposited on Si3N4-membranes, have been excited with ultrashort optical laser pulses. The dynamics of the non-reversible structural evolution of the irradiated samples during laser-induced melting and ablation has been studied in an optical pump - XUV-probe configuration by means of single-shot coherent scattering techniques (i.e. diffraction imaging [1]). In a first set of experiments we investigated the formation of laser induced periodic surface structures (LIPSS) on the surface of thin Si-films (thickness 100 nm). In a simplified view LIPPS are generated as a result of interference between the incident laser pulse and surface scattered waves which leads to a periodically modulated energy deposition. Time-resolved scattering using femtosecond XUV-pulses (with a wavelength of 13.5 nm and 7 nm) allowed us to directly follow LIPSS evolution on an ultrafast time-scale and with better than 40 nm spatial resolution. The observed scattering patterns show almost quantitative agreement with theoretical predictions [2] and reveal that the LIPSS start to form already during the 12 ps pump pulse. In the second set of measurements we studied picosecond and femtosecond laser induced ablation and disintegration of fabricated nano-structures. Correlations of coherent diffraction patterns measured at various time delays to the pattern of the undisturbed object show that order in the structure is progressively lost starting from short length scales. This structural rearrangement progresses at close to the speed of sound in the material. Under certain circumstances (e.g. adequate sampling) it became also possible to reconstruct real-space images of the object as it evolves over time [3]. The possibility of femtosecond single-shot imaging of ultrafast dynamic processes with nanoscale resolution provides yet more details of the physical processes involved. [1] H. N. Chapman et al. Nature Phys. 2, 839 (2006). [2] J. F. Young et al., Phys. Rev. B 27, 1155 (1983). [3] A. Barty et al. Nature Phot. 2, 415 (2008).
A simple method of creating defined PMMA and poly (MMA-co-Cz) electrocoatings on carbon fibres is described. The electrodeposition of poly methylmethacrylate (PMMA) onto unsized, unmodified carbon fibres was performed by simple constant current electrolyses of methylmethacrylate (MMA) monomer in dimethylformamide (DMF) solutions and the pure liquid monomer using sodium nitrate and lithium perchlorate as supporting electrolytes. The presence of polymeric coatings successfully attached to the carbon fibres was verified by scanning electron microscopy and photoelectron spectroscopy (XPS).
Performing the electrolysis in dilute MMA in DMF solutions ([MMA] < 5 M) results in the deposition of powder-like polymer on the carbon fibre electrodes. Increasing the MMA concentration in the DMF solution results in a homogeneous PMMA coating of the carbon fibres. The degree of grafting or coating increases with increasing MMA concentration, except when pure MMA is used without solvent.
The adhesive strength between the electrocoated carbon fibres and a PMMA matrix was determined using the single fibre pull-out test. It was found that the interfacial fracture behaviour of all carbon fibre/PMMA model composites is rather brittle. The adhesion strength between the unmodified carbon fibres and the PMMA matrix was equal to the cohesive strength of the polymer matrix itself. Nevertheless, the electrodeposition of thin and homogeneous PMMA coatings resulted in much improved adhesion strengths.
The sintering behavior and the thermoelectric performance of Ca3Co4O9 multilayer laminates were studied, and a multilayer thermoelectric generator was fabricated. Compacts and multilayer samples with anisotropic microstructure and residual porosity were obtained after conventional sintering at 920 °C, whereas dense and isotropic multilayer samples were prepared by firing at 1200 °C and reoxidation at 900 °C. A hot-pressed sample has a dense and anisotropic microstructure. Samples sintered at 920 °C exhibit low electrical conductivity due to the low density, whereas the Seebeck coefficient is not sensitive to preparation conditions. However, thermal conductivity of multilayers is very low, and, hence acceptable ZT values are obtained. A ransversal multilayer thermoelectric generator (TMLTEG) was fabricated by stacking layers of Ca3Co4O9 green tapes, AgPd conductor printing, and co-firing at 920 °C. The TMLTEG has a power output of 3 mW at ΔT =200 K in the temperature interval of 25 °C to 300 °C.
Coordination chemistry was applied to deposit pyridine-functionalized gold nanoparticles on silicon substrates. The particles were synthesized through the Brust/Schiffrin route with a subsequent ligand exchange reaction yielding well-defined particles of two different sizes. Multilayer deposition was carried out on a pyridine-terminated SAM, anchored on a hydroxyl-terminated silicon surface. Analogously, Hunter/Vögtle-type tetralactam macrocycle multilayers were deposited as well as mixed layers containing both either in an alternating sequence or as a macrocycle multilayer with a terminating nanoparticle layer. These composite layers were examined with respect to their ability to bind squaraine axles in the macrocycle cavities. The amount of guest bound is higher for the composite layer with alternating macrocycles and nanoparticles.
Reliability study of a tunable ka-band SIW-phase shifter based on liquid crystal in LTCC-technology
(2014)
A tunable substrate-integrated waveguide phase shifter using low-temperature co-fired ceramic (LTCC)-technology is presented in this paper. By changing the effective permittivity in the liquid crystal (LC)-filled waveguide, the differential phase can be tuned continuously. This is achieved by means of an analog signal applied to the electrodes, surrounding the LC. The design allows for precise tuning of the differential phase, which is proven with a Monte Carlo measurement resulting in phase errors of less than 3° at 28 GHz. Besides that, the ambient temperature dependency of the module is shown. The phase shifter has a high integration level and can be included into a complete and lightweight single-phased array antenna module. The phase shifter is realized with a high level of integration which is available through the multilayer process of the LTCC. It has a length of 50 and provides a differential phase shift of more than 360° at 28 GHz. The figure of merit for tunable phase shifters is >40°/dB.
There is a high international priority attached to activities which reduce NOx in the atmosphere. The current level of permitted emissions is typically between 50 µmol/mol and 100 µmol/mol, but lower values are expected in the future. Currently, ambient air quality monitoring regulations also require the measurement of NOx mole fractions as low as 0.2 µmol/mol. The production of accurate standards at these levels of mole fractions requires either dilution of a stable higher concentration gas standard or production by a dynamic technique, for example one based on permeation tubes.
The CCQM-K74 key comparison was designed to evaluate the level of comparability of National Metrology Institutes' measurement capabilities and standards for nitrogen dioxide (NO2) at a nominal mole fraction of 10 µmol/mol.
The measurements of this key comparison took place from June 2009 to May 2010.
Seventeen laboratories took part in this comparison coordinated by the BIPM and VSL. The key comparison reference value was based on BIPM measurement results, and the standard measurement uncertainty of the reference value was 0.042 µmol/mol.
This key comparison demonstrated that the results of the majority of the participants agreed within limits of ±3% relative to the reference value. The results of only one laboratory lay significantly outside these limits. Likewise this comparison made clear that a full interpretation of the results of the comparison needed to take into account the presence of nitric acid (in the range 100 nmol/mol to 350 nmol/mol) in the cylinders circulated as part of the comparison, as well as the possible presence of nitric acid in the primary standards used by participating laboratories.
Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.
The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).
DatesIssue 1A (Technical Supplement 2012)
Natural zeolite clinoptilolite CLIN with a framework ratio of Si/Al ≥ 4 containing mainly potassium and calcium ions in its internal channel system was used as a starting material. The acidic HCLIN catalysts were prepared under soft conditions avoiding the use of environmental less benign mineral acids. The starting material was ion exchanged using a 0.2 M aqueous ammonium nitrate solution at a temperature 80 ◦C for 2 h. The obtained NH4CLIN was converted into the acid HCLIN catalyst by calcination at 300–600 ◦C. The obtained samples were characterized by XRD, FTIR, SEM/TEM, AAS, and EDX element mapping. The state of aluminium and silicon was studied by 27Al- and 29SiMAS NMR spectroscopy. The textural properties of the catalysts were investigated by nitrogen adsorption and desorption measurements. The Brønsted acidity of the HCLIN catalysts was studied by temperature-programmed decomposition of the exchanged ammonium ions releasing ammonia as well as 1H MAS NMR, {1H–27Al} Trapdor, and {1H–27Al}
Redor experiments. The strongly agglomerated samples were crystalline and thermally stable up to >500 ◦C. Although a part of the clinoptilolite framework is maintained up to 600 ◦C, a loss of crystallinity is already observed starting from 450 ◦C. The specific surface areas of the starting CLIN and ammonium exchanged NH4CLIN are low with ca. 26 m2/g. The pores are nearly blocked by the exchangeable cations located in the zeolite pores. The thermal decomposition of the ammonium ions by calcination at 400 ◦C causes an opening of the pore entrances and a markable increase in the specific micropore area and micropore volume to ca. 163 m2/g and 0.07 cm3/g, respectively. It decreases with further rising calcination temperature indicating some structural loss. The catalysts show a broad distribution of Brønsted acid sites (BS) ranging from weak to strong sites as indicated the
thermal decomposition of exchanged ammonium ions (TPDA). The ammonium ion decomposition leaving BS, i.e., H+ located at Al–O–Si framework bridges, starts at ≥250 ◦C. A part of the Brønsted sites is lost after calcination specifically at 500 ◦C. It is related to the formation of penta-coordinated aluminium at the expense of tetrahedral framework aluminium. The Brønsted sites are partially recreated after repeated ammonium ion exchange. The catalytic performance of the acidic HCLIN
catalysts was tested in the etherification of glycerol as a green renewable resource with different C1 -C4 alcohols. The catalysts are highly active in the etherification of glycerol, especially with alcohols containing the branched, tertiary alkyl groups. Highest activity is observed with the soft activated catalyst HCLIN300 (300 ◦C, temperature holding time: 1 min). A total of 78% conversion of glycerol to mono and di ether were achieved with tert-butanol at 140 ◦C after 4 h of reaction.
The mono- and di-ether selectivity were 75% and 25%, respectively. The catalyst can be reused.
Improved large mesoporous ordered molecular sieves - Stabilization and acid/base functionalization
(2010)
The preparation of nanoporous materials with enhanced stability using an improved synthesis route using reactive inorganic silica and alumina species is reported. This way improved mesoporous molecular sieves were obtained. The synthesized aluminum substituted mesoporous molecular materials (Al-MMS) contain very large pores of 50200 Å size combined with an improved pore wall thickness. Increased wall thickness and Al substitution lead to an improved chemical stability against alkaline solution. The textural, structural and acid properties are investigated by physico-chemical methods. The catalytic performance acidic materials was tested in the benzoylation reaction; amino functionalized materials were studied in the base catalyzed Michael addition.
Continuously tuneable liquid crystal based stripline phase shifter realised in LTCC technology
(2015)
This work presents the design, fabrication and measurements of a low temperature cofired ceramic (LTCC) integrated liquid crystal (LC) phase shifter. The effective permittivity of the phase shifter and therefore its differential phase shift can be tuned continuously by orienting the LC directors with electric fields. The phase-shift demonstrator is designed for Ka-band frequencies around 30 GHz and represents a stripline filled with LC, embedded inside an LTCC multilayer structure, which provides a space-qualified and hermetically-sealed LC cavity within an RF-capable material system. The total length of the device is 37 mm while the phase shifting LC section has a length of 14.6 mm. At 30 GHz it exhibits a differential phase shift of 60° with an insertion loss around 6 dB, resulting in a figure of merit around 10°/dB. An advantage is that the insertion loss is nearly independent of the tuning state of the LC. The response time of the phase shifter, depending on the desired LC orientation, is between 62 ms and 37 s.
To examine the action of acid atmospheric precipitation on the light stabilisers in automotive coatings two common clearcoat types (TSA and 2K-PU) blended with commercially available HALS and UVA were subjected to artificial weathering (Acid Dew and Fog test and Acid-free weathering test) and natural weathering outdoors in Jacksonville, FL. Tracing gloss and haze during weathering the test results showed that the influence of acid stress on the long-term performance of the clearcoats depended on the kind of the stabilisation system.
Untertitel:
Zur Funktionsweise der Systeme
Unterscheidung in Fahrzeug-Stabilisierung und Anhänger-Wank-Stabilisierungsfunktion
Stand von Wissenschaft und Technik
allgemein anerkannte Regeln der Technik
Warum ist die Wirkvorschrift so wichtig? Gibt es Alternativen?
Ist eine Einführung von elektronischen Fahrstabilisierungseinrichtungen auch ohne gesetzliche Vorgabe denkbar?
Einbindung in den Markt (u. a. Bustouristik)
Welche weiteren Vorstöße werden unternommen, um die vorhandenen Systeme in Regelwerke und damit in die Flotten einzuführen?
Vorgehen in Dänemark
It is highly desirable to improve attractive interactions between carbon fibers and unreactive thermoplastic matrices to the possible maximum. This could be achieved by a simple grafting process to create a covalently bonded interface or interlayer, which should result in cohesive interactions between the polymer-grafted fibers and the same matrix material, leading to a better adhesion strength in the obtained composite material. Here, we are describing the grafting of styrene onto unmodified and unsized carbon fibers via free-radical bulk polymerization in the presence of fibers. After grafting, the surface properties of the carbon fiber approach those of pure polystyrene which was proven by contact angle and zeta ({zeta}) potential measurements. As indicated by the water contact angle, the carbon fiber surface becomes more hydrophobic. Scanning electron microscopy (SEM) provides evidence of grafted polymer. This simple procedure results in a continuous polystyrene coating. The fiber diameter increases significantly after polymer grafting. The adhesion and fracture behavior between the original and polystyrene-grafted carbon fibers to a polystyrene (VESTYRON®) matrix was characterized using the single-fiber pull-out test. There is a considerable increase in the measurable adhesion, i.e., the interfacial shear strength IFSS, by almost 300% between the grafted fibers and polystyrene as compared to untreated original fibers. Two planes of interfacial failure could be distinguished; first in the fiber coating interface leading to lower interfacial shear strength and second in the PS-matrix-PS-coating interphase resulting in a higher interfacial shear strength. In addition to the improved adhesion, there are also clear differences in the pull-out behavior between the nongrafted and grafted fibers. After the initial debonding process corresponding to the maximal pull-out force is completed, the pull-out force is increasing again.
The X-ray crystallographic study of the macrocyclic tetrakis-N[N-2-hydroxyethyl-piperazino]calix[4]resorcinarene·3CH3CH2OH·H2O (3) reveals a self-assembled dimeric capsule-like complex held together by an array of intermolecular hydrogen bonds. Pairs of concave molecules associate directly in bowl-to-bowl fashion and enclose an accessible supramolecular cavity of Å3 hosting one water and three ethanol molecules. The supramolecular arrangement displays alternating layers of facing bowls and interlocking lower rim aliphatic moieties. The helical conformation of the 2-hydroxyethyl piperazinomethyl moieties displays chirality of a bimolecular capsule frozen in the solid state. 3 crystallises in the triclinic space group P-1 with two symmetry independent molecules in the asymmetric unit. Two enantiomeric capsules form a racemic pair in the unit cell.
Composites of carbon fiber and cyanate ester matrix have been investigated. The research has been focused on the interfacial behaviour. The influence of carbon fiber surface treatments, sizing and oxidation, and also modification of thermoset matrix by the addition of a thermoplastic, has been analysed. In order to relate the interfacial behaviour with the characteristics of the components, a physico-chemical characterisation of the carbon fibers and of the cyanate ester resins has been carried out. Thereafter, the apparent interfacial shear strength, the interlaminar shear strength and the Mode II delamination fracture toughness, GIIC, have been measured by pull-out test, short beam-shear test, and end-notched flexure test, respectively. For fractographic analysis the surfaces of laminates fractured under Mode II deformation have also been examined by scanning electron microscopy.
The paper gives a survey of the Soviet (Russian) -German activities which started in 1988 with the objective of creating a long-term scientific-technical cooperation in the field of transport and storage casks for spent nuclear fuel. The first step, i.e., the step of informing each other about the state of development is done. The more complicated second phase with concerted common activities of both the Russian and German competent authorities and industrial enterprises is intended to start in the near future.
The molecular mobility of a MOF-5 metal–organic framework was investigated by broadband dielectric spectroscopy. Three relaxation processes were revealed. The temperature dependence of their relaxation rates follows an Arrhenius law. The process observed at lower temperatures is attributed to bending fluctuations of the edges of the cages involving the Zn–O clusters. The processes ('region II') at higher temperatures were assigned to fluctuations of phenyl rings in agreement with the NMR data found by Gould et al. (J. Am. Chem. Soc. 2008, 130, 3246). The carboxylate groups might also be involved. The rotational fluctuations of the phenyl rings leading to the low frequency part of relaxation region II might be hindered either by some solvent molecules entrapped in the cages or by an interpenetrated structure and have a broad distribution of activation energies. The high frequency part of region II corresponds nearly to a Debye-like process: This is explained by a well-defined structure of empty pores.
Viscoelastic properties of the interphase in fibre reinforced polymers - measurement and simulation
(1999)
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.
In this paper we present results of our recent efforts to understand the mechanical interface behaviour of single-walled carbon nanotubes (CNTs) embedded in metal matrices. We conducted experimental pull-out tests of CNTs embedded in Pd or Au and found Maximum forces in the range 10 - 102 nN. These values are in good agreement with forces obtained from molecular Dynamics simulations taking into account surface functional Groups (SFGs) covalently linked to the CNT material. The dominant failure mode in experiment is a CNT rupture, which can be explained with the presence of SFGs. To qualify the existence of SFGs on our used CNT material, we pursue investigations by means of fluorescence labeling of surface species in combination with Raman imaging. We also report of a tensile test system to perform pull-out tests inside a transmission electron microscope to obtain in situ images of CNT-metal interfaces under mechanical loads at the atomic scale.
To increase efficiency, modern steam plants are pushing their operational regime from super-critical (600 °C/300 bar) to ultra-super-critical (740/760 °C/350 bar) stretching existing turbine materials to their limits. The focus is on new generation functional materials and technologies which complement the inherent properties of existing materials.
Current work proposes a novel High Power Impulse Magnetron Sputtering (HIPIMS) Deposition technology, for the first time, for deposition of a ceramic based CrN/NbN coating with a nanoscale multilayer structure (bi-layer thickness Δ = 1.9 nm) with superior adhesion (LC2 = 80 N) to protect low Chromium P92 steel widely used in steam power plants. Thermodynamic calculations predict the equilibrium phases and aggressive gaseous compounds generated by the interaction of steam with the coating. CrN/NbN coated P92 steel samples oxidised at 600 °C in a high pressure (50 bar) 100% steam atmosphere for up to 1000 h reveal the coating's superior oxidation resistance and protective mechanisms, especially against the detrimental effect of Hydrogen. High temperature (650 °C) Tensile Strength, Low Cycle Fatigue and Creep tests confirm that, unlike other state-of-the-art PVD technologies, HIPIMS is not detrimental to the mechanical properties of the substrate material. Water droplet erosion tests confirm no measurable weight loss after 2.4 X 10⁶ impacts.
A 30GHz liquid-crystal-based amplitude tuner is proposed for the first time. The amplitude of a signal can be controlled by using the interference principle. An input signal is divided into a tunable liquid crystal phase shifter and a fixed transmission line. Later, the divided signals are combined together at the output port. The output amplitude depends on the phase difference between the tunable and the fixed line. The low temperature co-fired ceramic technology is utilized to fabricate the device. The measurement shows an attenuation range of 11 dB to 30 dB with a maximum biasing voltage of 100V.
Tunable microwave devices will play an important role in future wireless systems, in which high-frequency bands, e.g. millimeter waves, will become promising, due to its huge spectrum availability. At such frequency bands, liquid crystals (LCs) exhibit low microwave loss, which is excellent compared with the other tuning elements. In this paper, LC-based microwave components are fabricated by using low temperature co-fired ceramic technology, allowing the integration of the LC into microwave structures. The first component, the Amplitude tuner, controls the signal’s amplitude by using the interference concept, which exhibits a tunable attenuation range from 11 dB to 30 dB at 30 GHz. The second component is a 3-pole tunable bandpass filter, which is realized by using a substrate integrated waveguide topology, enabling a device with comparatively high-quality factors (Q-factors). The measurement results show Q-factors in the range of 68 to 100 for a frequency tuning of 29.4–30.1 GHz, i.e. a tuning range of 700 MHz, accompanied by an insertion loss 2 dB to 4 dB.
The material properties of recycled concrete aggregates (RCA) are
correlated to the sorting accuracy of the former demolition waste. Impurities like
wood, clay bricks or gypsum can lead to inferior building material properties. Harmful
substances like heavy metals or organic pollutants should be minimised as well.
Hence the non-concrete materials have to be separated from the concrete material
stream. This can be done during the demolition process by using selective
dismantling techniques. Alternatively a variety sorting and classifying techniques to
purify the crushed concrete can be utilized.
A research project, funded by the Federal Ministry for the Environment, Nature
Conservation and Nuclear Safety, investigated the possibilities of gaining recycled
concrete aggregates of a high quality for the reuse in the production of concrete. The
work focuses especially on how gypsum respectively sulphates in the crushed
concrete can be reduced. Sulphates can impair the setting behaviour of concrete
and also damage set concrete by causing expansion. Therefore the content of
sulphates in RCA is restricted by guidelines and standards in Germany.
Generally, gypsum in construction waste originates from interior fittings like gypsum
walls, floor screeds, plaster boards and also plaster. Most of these materials can be
reconstructed using selective dismantling techniques. This can be achieved either by
manual labour or by using mechanical equipment e.g. to remove floor screeds by
milling. Depending on the specific deconstruction site it can be more effective and/or
more environmentally compatible to remove sulphates by treating the crushed
concrete. Applicable treatments for sulphate reduction include dry processes like
manual sorting of gypsum wall blocks as well as wet treatments e.g. jigging.
In addition this research project an environmental performance evaluation was
undertaken to assess different techniques for reducing sulphates in recycled
concrete aggregates.
Aufgrund der großen Massenströme ist das Recycling von Baurestmassen von besonderer Bedeutung
für die Schonung von natürlichen Ressourcen. Eine wichtige Voraussetzung für ein hochwertiges
Recycling, wie z.B. eine Wiederverwertung von aufbereitetem Bauschutt/Altbeton als rezyklierte
Gesteinskörnung im Hochbau, ist die Einhaltung von Grenzwerten für Stör- und Schadstoffe. Dabei
steht der Sulfatgehalt im Eluat von Bauschutt besonders im Fokus. In der vorliegenden Studie wird
untersucht, wie durch die Optimierung von Abbrucharbeiten und Bauschuttaufbereitung hochwertige
Gesteinskörnungen aus Altbeton gewonnen werden können. Anhand von Literatur- und
Datenrecherchen werden zunächst Sulfatquellen in Gebäuden sowie verfügbare Abbruch- und
Aufbereitungstechniken zusammengestellt. Am Beispiel von unterschiedlichen Gebäudetypen werden
Szenarien für selektiven und nicht selektiven Abbruch (Schwerpunkt: Sulfatentfachtung) in Hinblick auf
ihre Umweltwirkungen ökobilanziell bewertet. Ergänzt werden diese Bewertungen durch
Untersuchungen an realen Bauschuttmaterialien und Abbruchprojekten. Auf dieser Basis werden
Handlungsempfehlungen für die Gewinnung von hochwertigen RC-Gesteinskörnungen erarbeitet und
diskutiert.-----------------------------------------------------------------------------------------
Due to the large-scale mass flow of construction and demolition wastes, the recycling of those
residues is of particular importance for the conservation of natural resources. An important
requirement for recycling on a high level, like the reuse of crushed concrete as recycled concrete
aggregate, is the observation of limits for hazardous substances and impurities. This study is focusing
on the reduction of sulphates in the eluate of crushed concrete. An investigation of possibilities to
optimize demolition and dismantling as well as treatment of crushed concrete with the objective of
gaining recycled concrete aggregates of high quality. Based on a literature research and a data review
the origins of sulfates in buildings and also the availability of techniques for demolition and treatment
of crushed concrete are listed and evaluated. Using the examples of different building types scenarios
for selective dismantling and non-selective demolition (focused on reducing suphates) are evaluated in
terms of affecting the environment. In addition samples from real demolition construction sites and
plants for treatment of construction rubble were investigated. Based on these results
recommendations for the production of high quality recycled concrete aggregates are worked out.
With CO2 being one reason for climate change carbon capture and storage (CCS) is discussed to mitigate climate change. When emission gases are compressed into deep geological layers CO2-corrosion can easily cause failure of injection pipes. Different steels 42CrMo4, X46Cr13 and X20Cr13 were tested as well as X35CrMo17 and X5CrNiCuNb16-4 in a laboratory Environment similar to the conditions of the CCS engineering site at the Northern German Bassin. Samples were exposed to synthetic aquifer water saturated with technical CO2 at a flow rate of 3 NL/h.
Corrosion rates obtained via mass loss vary in a wide range (0,005 to 2.5 mm/year). The precipitations within the corrosion scale revealed a complicated multiphase layer containing siderite FeCO3, goethite α-FeOOH, lepidocrocite γ-FeOOH, mackinawite FeS and akaganeite Fe8O8(OH)8Cl1,34 and spinelphases of various compositions.
This paper presents, the investigation of tunable components based on LTCC technology, implementing ferroelectric tunable thick-film dielectric. The tunable loaded line phase shifters are fabricated with metal-insulator-metal (MIM) varactors to demonstrate the capabilities of this method for packaging of the tunable components. The MIM varactors consist of one tunable dielectric paste layer that is printed between two silver layers. The tunable ferroelectric paste is optimized for LTCC sintering temperature around 850°C. The phase shifters are fabricated in two different process. They were achieved a figure of merit of 24°/dB (phase shift 192°) at 3 GHz and 18°/dB (phase shift 98°) at 4.4 GHz by using seven unit cells that each unit cell consisting of two MIM varactors.
In order to understand the role of dipolar interactions vs. H-bonding, a series of hydrazones were synthesised from 4-alkoxy-, 3,4-dialkoxy- or 3,4,5-trialkoxybenzaldehydes and phenyl, bromo- or nitrophenylhydrazine, respectively. Their mesomorphic properties were investigated by differential scanning calorimetry (DSC), polarising optical microscopy (POM), X-ray diffraction (WAXS, SAXS) and compared with known members. Only those hydrazones derived from 3,4,5-trisalkoxybenzaldehyde and either meta, meta-dinitro- or ortho, para-dinitrophenylhydrazine displayed hexagonal columnar mesophases. All other derivatives were non-mesomorphic, even when H-bonds were present. Dipole moments of the various nitro-substituted hydrazones were experimentally determined by dielectric measurements and supported by theoretical DFT calculations, which indicated that the mesophase formation is mostly governed by strong dipole moment and further enforced by intramolecular H-bonding.
30GHz liquid-crystal-based amplitude tuner is proposed for the first time. The amplitude of a signal can be controlled by using the interference principle. An input Signal is divided into a tunable liquid crystal phase shifter and a fixed transmission line. Later, the divided signals are combined together at the output port. The output amplitude depends on the phase difference between the tunable and the fixed line. The low temperature co-fired ceramic technology is utilized to fabricate the device. The measurement shows an attenuation range of 11 dB to 30 dB with a maximum biasing voltage of 100V.