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Eingeladener Vortrag
- nein (138)
Bruchmechanische Analyse des Grenzflächenversagens bei Einzelfaser Pull-out und Fragmentation Tests
(2000)
Entwicklung, Herstellung und Einsatz von Referenzmaterialien für die organische Umweltanalytik
(2000)
Vergleich von IR- und GC-Verfahren zur Bestimmung von Mineralölkohlenwasserstoffen (MKW) in Waseer
(2000)
Chemische Reaktionen
(2000)
Bewertung kritischer Befunde bei der Ultraschallprüfung an Schweißnähten mit Modellrechnungen
(2000)
Environmental Risk Assessment of Treated Timber in Service - the Environment Focus Group Approach
(2000)
In the context of the Biocidal Products Directive (98/8/EC), and of the OECD work on wood preservatives, the Environment Focus Group (EFG), comprising 8 institutes and the European Wood Preservative Manufacturers Group, has been working on the environmental risk assessment of treated timber in service. A literature review of emissions from treated timber has revealed that very little existing data is usable for environmental risk assessment; the most relevant data are kinetic curves of emissions over time, which show clearly the non-linear emissions behaviour of treated wood over time. The EFG has suggested real exposure conditions for treated timber in the environment, and listed typical exposure scenarios. Five representative scenarios are characterised in detail, for use in the calculation of Predicted Environmental Concentrations (PECs). The existing methods to determine emissions from treated wood have been reviewed. Most existing experimental models cannot be used to predict environmental emissions. Monitoring of commodities in service has its specific constraints. Chemical analysis and ecotoxicity testing have also been reviewed and their relationship has been discussed. Principles for the design of experimental models, for the determination of emission fluxes from treated wood to the environment, have been established.
Acoustic emission characteristics of micro-failure processes in polymer blends and composites
(2000)
Acoustic emission (AE) characteristics of micro-failure processes in HDPE/PP blends with and without compatibilizer, single-fibre composites (glass/epoxy, carbon/epoxy, glass/polycarbonate) and unidirectionally reinforced multi-fibre composites (glass/polypropylene) were studied. For blends, the number and the elastic fracture energy release of micro-failure processes are theoretically approximated and correlated with the number of AE signals and the AE energy. A qualitative correlation of the mechanical energy released from fibre/matrix debonding and fibre-fracture processes in single-fibre pull-out experiments with the measured AE energy is demonstrated. For the single-fibre fragmentation of glass fibres and carbon fibres, a quantitative approximation of the AE amplitudes at locations of the fragmentation sources is achieved. A new method for the selection of single transient acoustic emissions and the classification of failure mechanisms in composites is introduced. Selected emissions are classified into matrix cracking, fibre breakage and interface processes (fibre/matrix debonding or fibre pull-out) from their total power in defined frequency intervals of the spectral power density. A fracture-mechanics investigation of the delamination behaviour of unidirectional composites accompanied by AE examinations is discussed. The extension of the damage zone around the crack tip is quantified by the location of AE events and compared with the theoretically approximated dimensions. The size of the damage zone is used for theoretical calculations of the mechanical energy release from micro-failure processes. A correlation of the AE energy-release rates with the mechanical energy-release rates from participated failure mechanisms like matrix cacking, fibre/matrix debonding and fibre breakage is presented.
Mode I fracture toughness tests on Double Cantilever Beam specimens from carbon-fibre and glassfibre reinforced polymer-matrix composites were monitored with Acoustic Emission (AE) and loaddisplacement traces and delamination lengths were recorded. AE characterized the kinetics of delamination propagation. The progress of AE activity and AE intensity with load and AE source location plots are used to determine the delamination onset on the microscopic and macroscopic scale.
Energy dissipating processes initiated in the damage zone near the delamination tip. Low Interface adhesion results in lower debonding stresses and larger damage zones compared with composites with good adhesion. Time-dependent linear location of AE sources yields the average length of the damage zone and the average speed of delamination propagation. Parameter analysis has been used empirically for identifying AE source mechanisms. A new Classification Software for transient AE waveforms permits identification of the source mechanism of individual AE signals. A micro-mechanical fracture model based on the AE results describes the contributions of microscopic matrix and Interface mechanisms to the interlaminar fracture energy.
Es wurden Gläser im System Li2O-B2O3-V2O5 und ZnO-B2O3-V2O5 wie auch kristalline Referenzmaterialien mit Hilfe der Röntgenabsorptions- (V-K-EXAFS, -XANES) und der RAMAN-Spektroskopie untersucht. Zur Diskussion der Ergebnisse wird angenommen, dass in den Gläsern in Abhängigkeit von der chemischen Zusammensetzung diskrete Sauerstoffkoordinationspolyeder der Kationen in unterschiedlicher Verknüpfung vorliegen.
1. Die Gläser enthalten vor allem BO3- bzw. BO4- sowie VO4-Polyeder.
2. Die VO4-Tetraeder besitzen abhängig von der Glaszusammensetzung eine unterschiedliche Verzerrung. Sie verknüpfen sich zu Struktureinheiten ähnlich denen der kristallinen Vanadate oder sie werden in Boratstrukturen eingebaut.
3. In Gläsern mit einem hohen Netzwerkwandler-Gehalt und geringer Vanadiumoxid-Konzentration treten reguläre Tetraeder von isolierten Ortho- oder Pyrovanadat-Gruppen in Gegenwart von Pyroborat-, Orthoborat- und BO4-Gruppen auf. Mit steigendem V2O5-Gehalt werden zunehmend verzerrte Tetraeder gebildet, die sich z. B. zu Metavanadat-Gruppen verknüpfen oder in Metaborat-Baugruppen eingebaut werden.
Glasses in the systems Li2OB2O3V2O5 and ZnOB2O3V2O5 as well as crystalline reference substances were investigated by V-K-EXAFS. The glasses have a high modifier content ([Li2O, ZnO]/[B2O3] ratio>1) and contain 1050 mol% V2O5. The VO interatomic distance, coordination number and DebyeWaller factor were determined from the analysis of the measured absorption spectra. In the glasses investigated (and in binary lithium or zinc vanadate glasses too) VO4 tetrahedra are the predominant coordination polyhedra for the vanadium ions. The symmetry of the tetrahedra is more or less distorted in comparison to crystalline substances. The VO4 tetrahedra can be either directly connected to each other or incorporated into borate BO3/BO4 groupings. Structural elements which are comparable to those in crystalline substances can be discussed. In glasses of the metaborate composition, vanadium can be incorporated in chain or ring [BØ2O-]n metaborate groupings. With increasing V2O5 content the vanadium ions can extensively replace boron ions and form distorted tetrahedra in VØ2O2- metavanadate groups. In glasses of high modifier content and low vanadium amount the vanadium ions create nearly regular tetrahedra of isolated VO43- ortho- or V2ØO64- pyrovanadate groups in the presence of B2ØO44- pyroborate, BO33- orthoborate and BØ4- groups.
CdSe films grown on Ti-coated polished steel by constant-current deposition from an aqueous solution containing selenosulfite and cadmium nitrilotriacetate have been studied by spectroscopic ellipsometry under in-situ conditions. Ellipsometric parameters, tan? and cos?, were measured both as a function of deposition time at ? = 825 nm and of wavelength (? = 500-900 nm) for constant film thickness from 0.02 µm to 2.3 µm. The model used for data analysis, Ti-substrate | TiO2 | CdSe-film | solution, with optically homogenous phases was valid for film thickness larger than 0.3 µm. Refractive indices and extinction coefficients of the 2.3-µm film were derived for ? = 500900 nm. A direct band-gap of 1.72 eV was determined. The faradaic efficiency of electrodeposition was 0.93 for a current density of 50 µA cm-2.
Characterization of silicon polymers by coupling of chromatographic methods with MALDI-TOF-MS
(2000)
Characterization of silicon polymers by coupling of liquid chromatographic methods with MALDI-TOF-MS
(2000)
Bioresorbable carriers for subchondral anchoring of tissue-engineered cartilage in articular defects
(2000)
Bewertung kritischer Befunde bei der Ultraschallprüfung an Schweißnähten mit Modellrechnungen
(2000)
Aktuelle HPLC/MS-Kopplungen
(2000)
Amorphous carbon (a-C) multilayered films consisting of sequential layers rich in sp2 (A) and sp3 (B) content have been developed by magnetron sputtering. We study here the effect of thickness d of the A layer in developing stable thick films with controllable stress and elastic properties. In situ spectroscopic ellipsometry is used to calculate the thickness and the composition of the individual layers. The latter were compared with those obtained by depth profiling X-ray photoelectron spectroscopy, which also provides the different chemical bonding of the multilayers in depth. The stress and hardness of the deposited a-C films were found to be related to the thickness of the Aj layers and the relative ratio dAj/dB of thicknesses. The possible mechanisms for the stress control, stability and enhancement of elastic properties of multilayered a-C films are discussed.
The results presented in this paper have clarified experimentally, that titania-based Magnéli-phases (Ti4O7/Ti5O9 and Ti6O11) with (121)-shear planes exhibit more anti-wear properties than lubricious (low-frictional) properties. The results for dry sliding indicate that the coefficients of friction lie in the range of 0.10.6 depending on sliding speed and ambient temperature. The COF decreased with increasing temperature (T= 22800°C) and increasing sliding speed (?= 1-6 m/s). The dry sliding wear rate was lowest for the Al2O3 at 1 m/s at 800°C with values of 1.7 × 10-8 and 6.4 × 10-8 mm3/N m, comparable to boundary/mixed lubrication, associated with a high dry frictional power loss of 30 W/mm2. The running-in wear length and, more important, the wear rate decreased under oscillating sliding tests with increasing relative humidity. The contact pressure for high-/low-wear transition increased under oscillating sliding tests with increasing relative humidity. At room temperature and a relative humidity of 100% the steady-state wear rate under dry oscillating sliding for the couple Al2O3/Ti4O7Ti5O9 was lower than 2 × 10-7 mm3/N m and therefore inferior to the resolution of the continuous wear measurement sensor. TEM of wear tracks from oscillating sliding revealed at room temperature a work-hardening as mechanism to explain the running-in behavior and the high wear resistance. The hydroxylation of titania surfaces favours the high-/low-wear transition.
Multi-layer ohmic contact systems such as Au/Pt/Ti/Pt on III-V double layers such as n-InGaP/p+-GaAs are of considerable technological relevance, e.g. for heterojunction bipolar transistors. The paper shows that such contacts can be effectively reacted through the InGaP layer and exhibit very good contact resistances (0.1 O mm) to the base layer if the thickness of the first Pt layer is properly matched to the thickness of the contacted InGaP layer. Interdiffusion and phase formation associated with the annealing processes are studied by cross-sectional analytical transmission electron microscopy, thin-film x-ray diffraction and Auger electron spectroscopy depth profiling. Thermal ageing experiments up to 400 °C show good electrical stability. Device related reliability tests do not show any degradation effect related to this novel base contact.
Entwicklung und Herstellung von Boden-Referenzmaterialien für die anorganische Umweltanalytik
(2000)
Separation of hydrophobic pulmonary surfactant proteins using preparative HPLC with UV detection
(2000)
Characterization of silicon polymers by coupling of liquid chromatographic methods with MALDI-TOF-MS
(2000)
Liquid adsorption chromatography at critical conditions (LACCC) in normal and in reversed-phase modes provides independent information on the molar mass distributions of both blocks of poly(methyl methacrylate)-block-poly(tert-butyl methacrylate), even if no information about the precursor is available. In addition, the amount of unreacted precursor can be determined, even if its molar mass is comparable to that of the total block copolymer. The reversal of elution order by changing of stationary and mobile phases makes it possible to independently characterize each block in the SEC mode of the LACCC system. Thus, complete structural information is obtained even without using two-dimensional chromatographic techniques.
We prepared 2,2-dibutyl-2-stanna-1,3-dithiacycloalkanes from dibutyltin oxide and ,-dimercaptoalkanes. Heterocycles with five-, six-, seven-, or nine-ring members were used as bifunctional monomers for polycondensations with aliphatic dicarboxylic acid chlorides. These polycondensations conducted in bulk were highly exothermic and yielded poly(thio ester)s with number average molecular weights (Mn's) in the range of 5000-30,000 Da. These poly(thio ester)s proved to be rapidly crystallizing materials with melting temperatures in the range of 90-150 °C. In addition to the success of the new synthetic approach, two interesting and unpredictable results were obtained. All volatile species detectable by matrix assisted laser desorption induced-time of flight (MALDI-TOF) mass spectrometry were cyclic oligo- and poly(thio ester)s. Second, several polyesters showed a reversible first-order change of the crystal modification as identified by differential scanning calorimetry measurements and X-ray scattering with variation of the temperature. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3656-3664, 2000
2,2-Dibutyl-2-stanna-1,3-dioxepane (DSDOP) was polycondensed with bis(4-chlorothiophenyl) suberat under various reaction conditions, but only moderate molecular weights (Mn 10000) were obtained. The MALDI-TOF mass spectrosmetry revealed the formation of cyclic oligo- and polyesters in addition to linear species having OH, CO2H, and unreacted 4-chlorothiophenyl ester endgroups.
Furthermore, -Caprolactone (-CL) was polymerized with DSDOP as the initiator at monomer/initiator (M/I) ratios of 20 and 50. The resulting tin-containing macrocyclic polylactones were reacted with sebacic acid bis(4-thiocresyl)ester at three different temperatures and with different reaction times. Analogous polycondensations were conducted with suberic acid bis(4-chlorothiophenyl) ester. The presence of thioarylester endgroups in the isolated polyesters was checked by 1H NMR spectroscopy. The highest conversions were found at long reaction times (24 or 72 hours), or after the addition of pyridine and N,N-dimethylaminopyridine as catalysts. Despite high conversions, the number average molecular weights (Mn's) did not exceed values around 20000. Even in the samples having the highest molecular weights, unreacted 4-chlorothiophenylester endgroups were detected by GPC measurements evaluated with a UV-detector. It is concluded that both factors, cyclization and incomplete conversion, contribute to the limitation of the chain growth.
Chemical heterogeneities and molecular weight distributions of poly(ethylene oxide) (PEO)-co-polymethylene (PM) model oligomers, which are relevant to the synthesis of commonly used tensides, were investigated. For analytical characterization, the well-known principle of liquid adsorption chromatography at 'critical conditions' (LACCC) was modified. Near the critical conditions of adsorption of the PEO unit, e.g., at slight adsorption conditions of PM, the copolymers could be separated according to their PM chain length. The eluates were separated and single fractions of each peak were continuously transferred onto the MALDI target by means of a commercially available device. Simultaneously, the MALDI matrix solution was continuously added with a second pump. This procedure offers the possibility of the formation of homogeneous matrix-polymer textures. By MALDI-MS a complete characterization of the chemical composition (PEO and PM chain length) of each peak could be achieved. The obtained MALDI mass spectra of the eluates at different retention times could be used for the molecular weight calibration of the LAC system. In this way, an additional application of SEC, as in conventional 2D-chromatography, was avoided by using the MALDI method as quasi chromatographic separation
The curing conditions play an important role in the quality assurance of composite products.
Especially as composite materials are widely used in high tech areas so that they are required to fulfil high quality Standards. Some problems which occur during curing, for instance undercuring, can hardly be detected using Standard NDT investigations, mainly because they are manifested only at high temperatures, particularly close to glass-rubber-transition. On-line eure monitoring has the outstanding advantage that it can monitor the material parameters even at the highest temperatures possible.
In recent years eure monitoring with ultrasonic methods has become more populär. In comparison to dielectric methods mechanical parameters are measured directly. The quantities to be measured are the velocity and the attenuation of the sound wave. On this basis the storage and loss modulus can be calculated. Depending on the form of excitation with longitudinal or transversal waves these moduli are referred to as long wave or shear modulus.
Well developed Computer based technology and sensor materials are available in the non-destructive testing (NDT) market. The measuring equipment employed a commercial NDT System, which worked computer-aided. With a special Software the demands of automatic Operation under industrial conditions was accomplished. This measurement equipment was tested on composites. Its structure, performance and some practical results will be presented in the following paper.
Indolizines, known as a useful class of fluorophores, were bridged yielding biindolizines. We intended to obtain long wavelength absorbing and emitting fluorescent systems suitable for fluorescence labeling of biomolecules. The influence of the different kinds of coupling on the absorption and fluorescence behaviour of the resulting biidolizines was studied. The new fluorophore systems were characterized spectroscopically by their absorption and emission maxima and their quantum yields.