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- 5 Werkstofftechnik (16)
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- 6.5 Synthese und Streuverfahren nanostrukturierter Materialien (3)
Eingeladener Vortrag
- nein (2)
Rechnerische Simulation von Versuchen am Beispiel des Wärmeschutzes von Fensterkonstruktionen
(1986)
27Al nuclear magnetic resonance spectra of polycrystalline aluminium borate 9Al2O3 · 2B2O3 have been measured in double rotation at 11.7 and 7.0 T and high-speed magic-angle spinning at 7.0, 9.4, 11.7, 14.1 and 17.6 T. Spinning sidebands from the satellite transitions were observed at 7.0 and 14.1 T. Each of the four structural aluminium sites [Al(IV), Al(V)(1), Al(V)(2) and Al(VI)] are observed, characterised and assigned in the spectra. The obtained parameter set gives a fully consistent interpretation in agreement with the crystal structure of the compound.
The applicability of excimer laser at 308 nm and Nd:YAG laser at 532 nm with fluences below 0.86 J/cm2 for cleaning of cellulose and paper materials was evaluated. The extent of degradation of purified cotton cellulose and Fabriano paper after laser treatment as well as after a period of accelerated humid oven ageing was determined by following the changes in the degree of polymerization. While irradiation of paper with the excimer laser at 308 nm results in depolymerization of cellulose accompanied by a decrease in ISO brightness, no detrimental effects of Nd:YAG laser treatments were observed.
A comparison of different isotope dilution mass spectrometric (IDMS) procedures using inductively coupled plasma mass spectrometry (ICPMS) and thermal ionization mass spectrometry (TIMS) was carried out to examine the degree of equivalence between the used procedures in terms of requirements for reference material certification. The comparison was based on the measurement results and their uncertainties. The sample used in this study is a pure zinc metal to be certified by the Bureau Communie de Référence (BCR) for amount contents of different trace elements. This study focuses on cadmium and thallium. The TIMS values contributed to the certified values. To guarantee identical conditions as far as possible for the procedures under investigation, the samples were split into subsamples after spiking and digestion took place. Thus, every IDMS procedure started with an identical set of samples. In total, four different IDMS procedures and one external calibration procedure using internal standardization as an example of routine analysis were applied. The IDMS procedures divide in a group with and a group without trace/matrix separation. Multicollector TIMS (TI-MC-MS) and multicollector ICPMS (ICP-MC-MS) were used in combination with trace/matrix separation, whereas quadrupole ICPMS (ICP-QMS) and ICP-MC-MS were also applied to nonseparated samples. All IDMS results agree well within their combined uncertainties, while some results from the external calibration procedure do not. IDMS results obtained by ICPMS without separation are comparable to those obtained by TI-MC-MS with separation regarding precision and accuracy. The smallest uncertainties were achieved using ICP-MC-MS in combination with trace/matrix separation.
Das Basisanliegen - Einleitung
Mit der zunehmenden Zahl akkreditierter ZfP-Firmen und zunehmender Anwendung risikobasierender Konzepte ergibt sich die Notwendigkeit, internationale Standards wie die DIN EN ISO 17025 und darüber hinausgehende Richtlinien bei der Verfahrensauswahl in der ZfP zu berücksichtigen. Dieser Aufsatz soll aufzeigen, welche internationalen Aktivitäten gegenwärtig für die Zuverlässigkeitsbetrachtungen von Bedeutung sind (siehe auch [1]). In Übereinstimmung mit den Vereinbarungen und Definitionen der European-American Workshops zur Zuverlässigkeit [2, 3] gilt: Das Basisanliegen der Zuverlässigkeitsuntersuchungen beliebiger diagnostischer Systeme besteht darin, den Grad festzustellen mit dem das Prüfsystem in der Lage ist, seinen vorgesehenen Zweck zu erfüllen. Im Falle der ZfP besteht dieser Zweck zumeist in der Aufgabe, Bauteildefekte aufzufinden und zu beschreiben bzw. die Defektfreiheit von Bauteilen zu bestätigen, sowie Wanddicken zu messen oder Material zu charakterisieren.
Das Basisanliegen der Zuverlässigkeitsuntersuchungen findet seinen Niederschlag bei folgenden international relevanten Aktivitäten:
neue ISO 17025 als Notwendigkeit mit variablen Möglichkeiten der Verfahrensvalidierung
als Kettenglied in RBLM (Risk Based Life Time Management) (r) EPERC-Initiative
CEN/TC138/WG9 "Qualifizierung von ZfP-Verfahren"
Six-Sigma Strategie: als notwendiger Bestandteil
ASNT-Initiative: Standing Committee on NDE Reliability: als Arbeitspaket
Produkthaftung: als notwendige Voraussetzung für die Handhabung
Long-term behaviour of geosynthetic drains - excavations on landfills after up to 12 years service
(2002)
Theory of nucleation in viscoelastic media: application to phase formation in glassforming melts
(2003)
Glassforming melts behave, in the vicinity of the temperature of vitrification Tg, as viscoelastic bodies. A general theory of nucleation in a viscoelastic body developed elsewhere is applicable to the description of phase formation processes in such systems. The present contribution is directed to the demonstration of the relevance of this proposed general theory to describing phase transformation processes in glassforming melts. The application of the theory is shown to explain a number of experimental results on crystallization of glassforming melts, which have not found a satisfactory interpretation so far.
For the first time Metal Matrix Composites (MMC) have been investigated by 3D Computed Tomography combined with enhanced interface contrast due to X-ray refraction. X-ray refraction is a relatively new approach for the characterization of advanced materials. The related techniques of Refraction Topography and Refraction Computed Tomography have been developed and applied at our laboratory during the last decade to meet the actual demand for improved nondestructive characterization of high performance composites, ceramics and other low density materials and components. X-ray refraction occurs, when X-rays crosses interfaces of spherical or cylindrical shape (e.g. pores or fibres) in the same way as visible light is refracted by lenses. These X-ray optical effects can be observed at small scattering angles of few minutes of arc as the refractive index n of X-rays is nearly unity (n = 1 10-6). Due to the short X-ray wavelength of about 0.1 nm the technique determines the amount of inner surfaces and interfaces of nanometer dimensions. The technique is expected to solve many problems in understanding the meaning of micro and sub micro structures in materials science. With the results of the CT investigation, some questions could be clarified for a better understanding of fatigue failure mechanisms under cyclic loading conditions. The specimens for the test programme have been provided by MTU Aero Engines. They consist of a titanium matrix (Ti6242) reinforced by SiC fibres (SCS6). The investigations have been performed at the materials research station of BAM (BAMline) at the Synchrotron Facility BESSY in Berlin, Germany.
The effect of elastic stress and relaxation on crystal nucleation in lithium disilicate glass
(2004)
In the framework of a general theoretical approach recently developed, the effect of elastic stresses on the rate of nucleation of crystallites of critical sizes in the process of crystallization of lithium disilicate glasses is studied. Hereby both the evolution of elastic stresses due to changes in the specific volume of the crystallizing system (i.e., differences in the densities of the melt and the crystal) and their relaxation connected with viscous flow are taken into consideration. If the classical theory of nucleation is employed for the determination of the nucleation rates (modified by taking into account elastic stresses), elastic stresses may lead, for the system under consideration, to a decrease of the nucleation rate by up to two orders of magnitude. As shown, the theory allows an at least qualitatively correct incorporation of the effect of elastic stresses and stress relaxation into the description of nucleation phenomena in glass-forming melts.
Results are reported from a pilot study under the Consultative Committee for Amount of Substance (CCQM) to compare measurements of and resolve any relevant measurement issues in, the amount of thermal SiO2 oxide on (100) and (111) orientation Si wafer substrates in the thickness range 1.5 - 8 nm. As a result of the invitation to participate in this activity, 45 sets of measurements have been made in different laboratories using 10 analytical methods: medium-energy ion scattering spectrometry (MEIS), nuclear reaction analysis (NRA), RBS, elastic backscattering spectrometry (EBS), XPS, SIMS, ellipsometry, grazing-incidence x-ray reflectrometry (GIXRR), neutron reflectometry and transmission electron microscopy (TEM). The measurements are made on separate sets of 10 carefully prepared samples, all of which have been characterised by a combination of ellipsometry and XPS using carefully established reference conditions and reference parameters.
The results have been assessed against the National Physical Laboratory (NPL) data and all show excellent linearity. The remaining data sets correlate with the NPL data with average root-mean-square scatters of 0.15 nm, half being better than 0.1 nm and a few at or better than 0.05 nm. Each set of data allows a relative scaling constant and a zero thickness offset to be determined. Each method has an inherent zero thickness offset between 0 nm and 1 nm and it is these offsets, measured here for the first time, that have caused many problems in the past. There are three basic classes of offset: water and carbonadeous contamination equivalent to ~1 nm as seen by ellipsometry; adsorbed oxygen mainly from water at an equivalent thickness of 0.5 nm as seen by MEIS, NRA, RBS and possibly GIXRR; and no offset as seen by XPS using the Si 2p peaks. Each technique has a different uncertainty for the scaling constant and consistent results have been achieved. X-Ray photoelectron spectroscopy has large uncertainties for the scaling constant but a high precision and, critically, if used correctly, has zero offset. Thus, a combination of XPS and the other methods allows the XPS scaling constant to be determined with low uncertainty, traceable via the other methods. XPS laboratories returning results early were invited to test a new reference procedure. All showed very significant improvements. The reference attenuation lengths thus need scaling by 0.986 ± 0.009 (at an expansion factor of 2) deduced from the data for the other methods. Several other methods have small offsets and, to the extent that these can be shown to be constant or measurable, then these methods will also show low uncertainty. Recommendations are provided for parameters for XPS, MEIS, RBS and NRA to improve their accuracy.
Erstmals wurden MMCs mit Hilfe der Interface-Kontrast verstärkenden Röntgen-Refraktions-Technik in Kombination mit der 3D-CT-Technik untersucht. Die Methode der Röntgen-Refraktions-Topography sowie der Röntgen-Refraktions-Tomography wurden in den letzten Jahren speziell für die zerstörungsfreie Charakterisierung von Leichtbau-Hochleistungs-Werkstoffen wie Verbund-Werkstoffen und Keramiken entwickelt. Die Technik basiert auf der Refraktion von Röntgenlicht an Grenzflächen zwischen Bereichen unterschiedlicher Elektronendichte wie z.B. Faser- und Matrix-Werkstoff. Auf Grund der kurzen Röntgen-Wellenlänge hat der Brechungsindex einen Wert dicht bei eins, sodass der Streuwinkel nur wenige Bogenminuten beträgt. Der Vorteil der kurzen Wellenlänge besteht jedoch darin, dass Poren und Risse detektiert werden können, deren Größe im Nanometerbereich liegen. Damit kann die Refraktions-Technik zum besseren Verständnis von Mikro- und Submikro-Strukturen in der Materialwissenschaft eingesetzt werden. Mit der hier vorgestellten Refraktions-CT wurden Ermüdungsmechanismen an MMCs, bestehend aus SiC-Faser verstärktem Titan (Ti6242) untersucht. Die Messungen wurden am Röntgen-Messplatz der BAM (BAMline) am Synchrotron-Speicherring-BESSY in Berlin Adlershof durchgeführt.
The sintering of Low Temperature Co-fired Ceramics prepared from alumoborosilicate
glass- and Al2O3 powders of similar small particle size was studied by dilatometry, heating microscopy,
microstructure analysis, glass- and effective viscosity measurements. The steric effect of
Al3O3 inclusions was studied using a gnon-reactiveh model composite. With increasing Al3O3 volume
fraction (Φ ≤ 0.45), sintering decelerates and its final stage shifts to higher temperature. The
attainable shrinkage is reduced as Al2O3 particle clusters bearing residual pores become more frequent.
The kinetics of sintering could be described formally superposing the weighed contributions
of differentially sized and randomly composed glass-crystal particle clusters and assuming a sintering
rate controlled by the effective matrix viscosity, which increases with Φ and with progressive
wetting of Al2O3 particles during densification. The "reactive" model composite shows significant
dissolution of Al2O3 into the glass, which has two opposed effects on sintering: reducing Φ and increasing
glass viscosity. For the present case (Φ = 0.25), the latter effect dominates and sintering is
retarded by Al2O3 dissolution. Crystallization of wollastonite starts after full densification. Dissolution
of Al2O3 was found to promote the subsequent growth of anorthite.
In this study 50 construction products were tested in emission test chambers according to the requirements of the AgBB-scheme: 7 acrylic and 6 silicone sealants, 6 paste-like synthetic resin plasters, 13 wood based products, 4 adhesives, 5 lacquers, 6 wall paints and 3 further construction products. VOC and odour emissions were tested on the 1st, 3rd, 10th, and 28th day. In addition to the VOC-measurements, a test procedure was developed to evaluate odour emission of construction products.This test is planned to be implemented into the AgBB-Scheme. A direct evaluation by a sensory panel in the emission test chamber was not possible. So the odour samples were collected in 300- litre tedlar bags which were evaluated later. Odour intensity of the samples was compared with different acetone concentrations. Within this study an interlaboratory comparison was conducted using the newly developed odour test method. Additionally, VVOC emissions, detection of carcinogenic compounds, repeatability of emission test chamber tests, and other issues are presented. This project has shown that construction products can be evaluated in accordance with the AgBB scheme. A sensory evaluation is intended to be introduced in the AgBB scheme. A method for this evaluation is described in this study. The test procedure should be enhanced and validated for practical utilisation.
We studied sintering of LTCC-type glass matrix composites (GMCs) consisting of small glass and alumina particles of equal size. Primarily, crystals act as rigid inclusions, decelerating the densification rate. In later stages, they also dissolve, partially increasing the viscosity. Release of alumina finally induces crystallization of alumosilicates, which enables post-firing stability. To study both effects, two model GMCs were prepared: an α-Al2O3 + barium alumoborosilicate glass (BABS)GMC, which shows neither significant dissolution nor crystallization, and an α-Al2O3 + calcium alumoborosilicate glass (CABS)GMC, which dissolves readily and promotes crystallization. The kinetics of shrinkage for both GMC were modeled by utilizing Frenkel theory for the early stage and MackenzieShuttleworth theory for the late stage, assuming that sintering is superimposed by the weighted contributions of triparticle glasscrystal clusters, their random occurrence (ideal mixing), and a shrinkage rate controlled by the GMC effective viscosity. In agreement with modeling, the experimental results showed that the shrinkage rate of BABSGMC decreases progressively for crystal volume fractions Φ > 0.15. The attainable shrinkage is reduced by up to 8% for Φ = 0.45. For the CABSGMC with Φ = 0.25, a reduction of Φ to 0.20 was evident due to partial α-Al2O3 dissolution. This effect was found able to increase the sintering temperature by ~5060 K.
The viscosity of silica glasses with different water contents was measured by penetration of sapphire microspheres in the range from 1012-1014·7 Pas at ambient pressure. Commercial silica glasses were used together with hydrous silica glasses, which were prepared by melting glass powder plus water in an internally heated pressure vessel at 2-3 kbar and 1350-1450°C. The temperature dependence of the viscosity of silica glasses with total water contents Cw of 5·4×10-4, 7·0×10-4, 1·00×10-2, and 1·55×10-2(Cw in mass fractions) can be described by Arrhenius equations. From the results, the linear dependence of the T12 isokom (K) with the logarithm of the water content was determined as T12=192-409 logCw. The analysis of the compositional dependence of the T12 isokom in the H2O-Na2O-SiO2 system reveals a temperature depression of up to 200 K for mixed water- and sodium-bearing glasses compared to H2O-SiO2 and Na2O-SiO2 glasses with same molar silica content. From these findings we conclude that protons may contribute significantly to the mixed alkali effect in glasses.