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Eingeladener Vortrag
- nein (138)
Two fluorescent dyes were incorporated into sol-gel derived SiO2 matrices. The dye was added to SiO2 precursors of different degrees of pre-condensation and the spectroscopic properties of the immobilized dye were measured at various aging and drying stages of the resulting gels. The significant influence of the processing parameters on the spectroscopic properties is manifested in the relative intensity of a second red shifted emission band (550560 nm), which was observed besides the typical coumarin emission band (495 nm). The appearance of this long wavelength emission might be attributed to dye aggregation or to other reactions with the ambient matrix forced by micro porosity phenomena.
Overlayers of SiO2 (nominally 4, 6 and 8 nm thick) on silicon, prepared by thermal oxidation, were investigated using x-ray photoelectron spectroscopy (XPS). The thickness of these overlayers was obtained from a measurement of the photoelectron intensities originating from the substrate and the oxide overlayer by applying an appropriate quantitative model. The uncertainty budget of that thickness measurement method is given. The relative combined standard uncertainty of the method was found to be 15%. The effective attenuation lengths or the corresponding electron inelastic mean free paths are of considerable importance for both the estimated values of overlayer thickness and combined standard uncertainties. The XPS results were compared with ellipsometry data.
Chemical, morphological and accumulation phenomena in ultrashort-pulse laser ablation of TiN in air
(2000)
Ultrashort-pulse laser ablation (F=130 fs, 5=800 nm, repetition rate 2-20 Hz) of titanium nitride was investigated for laser fluences between 0.3 and 4.5 J/cm2 using the direct focusing technique in air. The influence of the laser pulse number and the peak fluence was investigated by means of several surface analytical techniques (optical microscopy, dynamic friction atomic force microscopy, scanning Auger electron microscopy and small-spot electron spectroscopy for chemical analysis). The correlation of the results about optical, physical and chemical properties of the irradiated areas allows us to propose a simple oxidation model, which explains different observed phenomena associated with surface damage such as mound formation and crater widening and clarifies the incubation behavior reported earlier for this material.
In recent years eure monitoring with ultrasonic methods became more important. An on-line measurement System for industrial applications is presented in this paper. It operates in through-transmission and the measured parameters are the sound velocity and the attenuation of the sound wave. An objective of this paper is to establish the ränge of possible applications for an ultrasonic eure monitoring System.
The stability of microstructure and the microhardness of a NiCoCrAlY alloy was studied after thermal treatment at high temperatures and subsequent quenching into ice water. The alloy revealed mainly two ordered phases, a gamma' phase with L12 lattice structure and a beta phase with B2 structure. The gamma' phase is shown to become unstable in the temperature range between 1073 K and 1373 K where it undergoes an order-disorder phase transformation. The low transformation temperature compared to pure Ni3Al is ascribed to deviations from the Ni3Al stoichiometry and to the additional alloying elements Co and Cr. The gamma'-gamma order-disorder transformation is shown to be attended by a decrease in microhardness of about 30 %.
The acceptor strength of the boron-dipyrromethene chromophore in directly linked donoracceptor compounds can be tuned by substituents in such a way that a fast excited state charge transfer takes place even for the comparatively weak benzo crown electron donor. This leads to strong fluorescence quenching. Upon binding of cations (Na+ and K+) to the benzo crown receptor, the donor properties of the latter are further reduced, partly suppressing charge transfer. Large fluorescence enhancement factors and cation-selective fluorescence decay times result which are the basis for improved analytical application of these dyes as highly sensitive fluorescent probes.
Bioresorbable carriers for subchondral anchoring of tissue-engineered cartilage in articular defects
(2000)
The excitation energy transfer (EET) of a bichromophoric cross-shaped molecule was investigated by stationary polarized fluorescence spectroscopy in the solid state. For this purpose 2,2[prime],7,7[prime]-tetrakis(biphenyl-4-yl)-9,9[prime]-spirobifluorene was embedded in a polymeric bisphenol-A-polycarbonate (PC) matrix. The dependence of the fluorescence on concentration and wavelength was determined. The role of the intermolecular and intramolecular EET is dealt with separately and discussed by means of the degree of polarization. The intermolecular excitation energy transfer is described in terms of a Förster transfer mechanism. The intramolecular transfer is prevented for the zero-point vibrational levels by the molecular cross-shaped structure, but is found for a wide range of wavelength, presumably based on vibrationally excited states.
Drucksondierungen, teufengenaue Probenahme und Präparation MKW-kontaminierter Lockersedimente
(2000)
Using a rail-inspection train, the Deutsche Bahn's system of railroads is continuously checked for traffic-induced defects. Until now, only ultrasonic inspection was used. In addition, eddy-current inspection could successfully and efficiently be used to detect and evaluate certain surface cracks - so-called head checks. There have already been reports about laboratory tests which proved the general suitability of this test method [1,2]. The next step - described here - consisted of practical trials under real-life conditions. A test system which is able to fulfil the strict requirements (test speeds of up to 100 km/h, complex probe guidance, suppression of electrical and mechanical interference, recording of data, filtering and evaluation of data) was developed. As part of the rail-inspection train and as a manual system, this inspection system was successfully tested on the Deutsche Bahn's system of railroads under real-life conditions.
Ermittlung der Messunsicherheit in der organisch-chemischen Analytik - ein Beispiel aus der Praxis
(2000)
Fundamentals of Tribotesting
(2000)
Tribology is an experiment-oriented branch of a complex, interdisciplinary science, in which testing plays a major role in the solution of technical problems, in the field as well as in the development of tribomaterials. Various test methods are used for this purpose, and the results are sensitive to the choice of test method and test conditions.
In this paper, the effects of test parameters on friction and wear results are considered, some selected results of model tests with different types of materials are presented, and guidelines are derived, that help improve the reliability and level of confidence of tribological tests performed in laboratories.
Photo- and thermo-oxidative stability of aromatic spiro-linked bichromophoric cross-shaped molecules
(2000)
An extensive investigation of the photostability and the thermo-oxidative stability is presented for 2,2,7,7-tetrakis(biphenyl-4-yl)-9,9-spirobifluorene and 2,2,4,4,7,7-hexakis(biphenyl-4-yl)-9,9-spirobifluorene. Both compounds are conjugated fully aromatic systems that are being discussed as active functional materials for a variety of advanced applications. The effect of atmosphere, sample thickness and preparation procedure on photo-oxidative degradation are investigated in detail by absorption and fluorescence spectroscopy. Distinct mechanisms are described in terms of relevant parameters such as the quantum yields of the photo-oxidation and the fluorescence. No oxidative degradation could be detected under nitrogen. In ambient air a strong decrease of the fluorescence performance is found due to effective quenching by defective chromophores. Chemiluminescence investigations were performed to characterise the thermo-oxidative behaviour in the temperature region between 300 and 450 K. It becomes clear that even a stable chemical structure such as the investigated aromatic system does not guarantee sufficient photostability with regard to light emitting properties.
About this Journal
A two-dimensional analysis of the Charpy V-notch specimen subjected to impact loading, according to the standard DIN EN 10045-1, is carried out, using a transient explicit dynamic finite element program. An elastic-viscoplastic, temperature dependent, constitutive relation for a porous plastic solid based on the Gurson damage model is developed. Ductile fracture of the matrix material will be described by the nucleation and subsequent growth of voids to coalescence. An updated Lagrange–Jaumann formulation is employed accounting for large strain and rotation. The discretization is based on four-node plane strain solid elements with one Gauss point. The equations of motion are integrated numerically by an explicit integration algorithm utilising a lumped mass matrix. The predictions of the numerical analysis in terms of force deflection response, crack resistance behaviour and deformation energy absorbtion are compared with results from Charpy tests which were carried out according to the low-blow technique.
In situ FTIR spectroscopy of the Zn-Br battery bromine storage complex at glassy carbon electrodes
(2000)
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.
Conventional simultaneous thermal analysis, capillary-coupled TGMS, in situ and ex situ Raman and Mössbauer spectroscopy, as well as chemical analysis have been used for the investigation of the first decomposition step of the mixed valence chloroferrate (dmpipzH2)6[Fe(II)Cl4]2[Fe(III)Cl4]2[Fe(II)Cl5][Fe(III)Cl6]. Under argon at ca. 200°C, an almost complete reduction proceeds in a solid state reaction forming Fe(II). It is accompanied by the release of HCl and, to a minor degree, carbon containing species. A multi-phase product with at least two chloroferrate species, coke, and C,H,N-containing polymers is formed. Binuclear iron complexes, such as (dmpipzH)2[Fe(II)2Cl6], and small amounts of (dmpipzH)[Fe(III)Cl4] have been proposed to be the major and minor component of the product mixture, respectively.
PdSn catalysts prepared by various methods and used for nitrate reduction were investigated by means of in situ 119mSn Mössbauer spectroscopy. Characterization by 119mSn Mössbauer spectroscopy revealed significant differences concerning the modification of the palladium particles supported on alumina. The controlled surface reaction preparation method (CSR) leads to formation of PdSn alloys with different tin contents besides small amounts of Sn(II) species and unalloyed metallic Sn. On the other hand the impregnation method leads to a small amount of PdSn alloys and higher contents of Sn(II) species. Sn(IV) species were found in both kinds of catalysts. The CSR prepared PdSn catalysts showed an improved activity and selectivity compared to the catalysts obtained by the impregnation method.
The present study concerns the cleaning of matenats using pulsed laser irradiarton and it summarises the most recent results obtalned by the collaborative research of different European groups, within the kamework of a European program for tralnlng and mobillrv of researchers. A series of pulsed lasers, which emit at various wavelengths (liom UV to IR) wit11 short duration of pulse (few nano-, pico- or fernto-seconds), is used for the removal of metallic, ceramic and organic pollutants kom contaminated solid surfaces of different natures. The scientific results obtained so far are focused on the laser cleaning of silicon wafers from sub-micrometer particles, tile theoretical modelling of particles removal mechanism during dry laser cleaning, the removal of oxide layers from oxidised metals and alloys, as well as on the development of laser imaging as a diagnostrc tool for the estimation of the efficiency of the proposed cleaning technique.
The complexation behaviour of 2,2-bipyridyl-3,3-diol and 2,2-bipyridyl-3-ol, BP(OH)2 and BPOH, with various heavy and transition metal
ions has been investigated in aqueous, alcoholic, and acetonitrile solutions. Whereas the complexes with paramagnetic ions and HgII
are non-fluorescent, ZnII and CdII form highly fluorescent complexes, their coordination geometries depending on the
solvent proticity and hydrogen-bond donating ability. Through a comparative study with the corresponding chelates of 2,2-bipyridyl (bipy),
N,O-coordination in a six-membered ring chelate has been found to be the dominant binding mode in both the ZnII and CdII
complexes in the protic solvents water and ethanol. Only for ZnII and BPOH is exclusive N,N-chelation found in acetonitrile. NMR
measurements on BP(OH)2, BPOH, and bipy in the presence of ZnII and CdII in acetonitrile confirmed these
findings.
The ability and structural requirements of 4-dimethylamino-4-cyano-substituted biphenyls showing photoinduced intramolecular charge transfer (CT) to serve as hydrogen bond- or pH-sensitive fluorescent probes is investigated. The donoracceptor (DA) biphenyls I and II being planar in the CT excited state are most suitable as pH-sensitive fluorescent probes. The two compounds show analytically valuable features such as well-separated absorption and emission bands and signal changes spanning four orders of magnitude and can be employed in ratiometric, self-calibrating, and highly sensitive pH fluorosensing in the range 0<pH<4. Because of an enhanced charge separation in the excited state, the highly twisted DA biphenyl III shows an increased proton sensitivity and can therefore be used to probe solvent proticity ia hydrogen bond formation. The molecular and electronic characteristics of the two types of probes are discussed for the different neutral and acidic alcoholic and/or aqueous solvent mixtures investigated.
Micromachining experiments were performed with Ti:sapphire laser pulses (130 fs - 150 fs, 800 nm, approximately 10 Hz) in air. Employing the direct focusing technique, highly absorbing titanium nitride (TiN) and weakly absorbing polyimide (PI) and polymethylmethacrylate (PMMA) served as target materials. The lateral and vertical precision of the laser ablation and morphological features were characterized by scanning force (SFM), scanning electron (SEM) and optical microscopy. For TiN, incubation can be observed, i.e. the single-pulse surface damage threshold (0.26 J/cm2) is by a factor of two greater than the threshold for 100 pulses. Ablation rates below 10 nm per pulse can be achieved. The evolution of sub-wavelength ripples is presented in dependence on pulse number and laser fluence, respectively. The incubation behavior of the polymers can be described by an accumulation model as for TiN. Experiments on PI with varying focal lengths result in the same modification thresholds. Different polarization states of light (linear, circular) lead to a variation of the ablation rate and to various morphological patterns in the ablation craters (wavelength ripples, cones). Swelling of PMMA occurred at fluences below the ablation threshold.
The influence of hydrogen contained in a sample or otherwise introduced into a glow discharge source (GDS) is here extensively experimentally presented for the case of copper as a sample by means of the addition of small quantities of molecular hydrogen (<1% relative partial pressure) to the argon carrier gas. The progressive addition of molecular hydrogen causes different intensity changes particular to the individual lines of different species such as atomic (Cu I) and ionic (Cu II) copper, and also atomic (Ar I) and ionic (Ar II) argon. Some interesting features of the emission spectrum of hydrogen such as its line, band and even continuum spectrum are observed. It was also found that the depth resolution becomes worse even at very low concentrations of hydrogen.
Im Gegensatz zur Impuls-Echo-Technik, die im Wesentlichen auf der
Anton Erhard, Berlin Reflexion am Fehler basiert, wird bei der Time-Of-Flight Diffraction Technique (TOFD-Technik) die Beugung der Schallwellen am Fehler zum Nachweis genutzt. Zwei Winkelprüfköpfe für Longitudinalwellen sind in V-Durchschallung angeordnet. Die Prüfköpfe befinden sich jeweils auf einer Seite der Schweißnaht und werden bei der Messung parallel zur Schweißnaht verschoben. Das ausgesandte Schallbündel trifft auf Fehlerränder, an denen gebeugte Wellenanteile entstehen, die je nach Entstehungsort mit unterschiedlichen Schalllaufzeiten empfangen, in hochfrequenten A-Bildern abgespeichert und für die Auswertung in B-Bildern dargestellt werden.
Die Untersuchungen zeigen, dass die TOFD-Technik Beiträge zur Fehlergrößenabschätzung liefert, aber keinesfalls die Impuls-Echo-
Technik mit nachgeschalteter Röntgenprüfung ersetzen kann.
Clear evidence of the effects caused by hydrogen, introduced in different forms in an analytical glow discharge source (GDS) operated with argon, is presented for the different matrix elements copper, stainless steel, titanium, aluminium and silicon. When hydrogen is present even in small quantities in argon, not only are there significant changes in the emission line intensities of most elements (analyte and plasma species), but also new spectral features, such as emission bands of new compounds (hydrides of sputtered sample constituents) and a continuous background in the range ~220440 nm. Moreover, the discharge current (the dependent parameter in our experiments) decreases with increasing hydrogen concentration. Different modes of hydrogen introduction, externally in gaseous form or sputtered as a sample constituent, cause very similar effects in terms of discharge current, line intensity (of analyte and plasma gas) and emission continua, which implies similar changes in the discharge processes in the two cases. The excitation of the hydrogen continuum appears to quench the population of the argon metastables (11.55 and 11.72 eV) and, consequently, other elementary processes in the plasma in which the argon metastables take part, but to a different extent for each analyte.
Summary form only given. Machining investigations of crystalline silicon have been performed with laser pulses at a wavelength of 780 nm in the range between 5 fs and 400 fs. Applying 100 pulses per spot, surface damage thresholds were determined by the measurement of the damage diameter. In this pulse duration regime, the threshold fluences were nearly constant. Single-pulse investigations with 5 fs pulses yielded a value of about 0.15 J cm-2 identical to the multi-pulse experiment. This is in contradiction to the behaviour of dielectrics where incubation effects alter the optical properties down to the 5 fs pulse regime. Employing laser pulses with a duration of 130 fs at a wavelength of 800 nm, single-pulse ablation thresholds of 0.23 J cm-2 and 0.16 J cm-2 were determined for Si and InP in air, respectively. The threshold fluence was calculated from the linear relation between the square of the diameters versus the logarithm of the laser fluences.
Aufbereitungsuntersuchungen an schwermetallbelastetem Baggergut aus dem ältesten Kanal Deutschlands
(2000)
Neu entwickelte Gasturbinen werden im Prüffeld mit wechselnden Belastungen beaufschlagt. Dazu wird die Gasturbine mit einer Wasserreibbremse gekoppelt, mit der eine definierte Last erzeugt werden kann.
Ursprünglich war die Wasserreibbremse für eine bestimmte Leistung, die den früheren Leistungen der Gasturbine entsprach, ausgelegt worden. Die erste Prüfung fand im Jahr 1975 statt. Da neuere Gasturbinen wesentlich höhere Leistungen erbringen und die vorhandene Wasserreibbremse weiterhin eingesetzt werden sollte, musste eine Nachqualifizierung vorgenommen werden. Das Ziel war die Absicherung auf eine mögliche Sprödbruchgefahr.
Zunächst wurde eine Studie zur Prüfbarkeit erstellt. An speziellen Testkörpern wurden im Ultraschallabor der BAM Vorversuche zur Machbarkeit, zur Empfindlichkeitsein-stellung und zur Vorbereitung der Prüfung durchgeführt. Dazu wurden spezielle Gruppenstrahlerprüfköpfe gefertigt und ein an die komplizierte Geometrie der Bremsscheiben angepasster Manipulator gebaut. Ferner wurde, um die Prüfzeiten zu reduzieren, die Software zur Datenerfassung und zur Auswertung angepasst.
Im Werk Berlin der Siemens AG wurde in Zusammenarbeit mit der Siemens AG Erlangen eine Ultraschallprüfung mit der Gruppenstahlertechnik der Wasserreibbremse durchgeführt. Überprüft wurde das gesamte Volumen auf axial, radial und tangential beanspruchte Fehler in den Bereichen der Welle und der Bremsscheibe.Die Überprüfung ergab keine relevanten Fehler, so dass die Wasserreibbremse weiterhin eingesetzt werden kann.