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Eingeladener Vortrag
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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)