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Eingeladener Vortrag
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Bone development and bone structure depend on surface roughness and structure of metalic implants
(2000)
Bioresorbable carriers for subchondral anchoring of tissue-engineered cartilage in articular defects
(2000)
Zur Alterung von Smalten - Materialuntersuchungen bei der Restaurierung eines Gründerzeit-Mosaiks
(2001)
Das Mosaik "Muse der Kunst" war in Berlin-Mitte mehrere Jahrzehnte hinter einer Vermauerung verborgen, bevor es nun wiederentdeckt und restauriert wurde. Die Smalten zeigten zum Teil Risse, Verkrustungen und Farbveränderungen in Folge von Alterungsprozessen der historischen Materialien. Einzelne Deckgläser von Goldsmalten waren abgesprengt.
Zur genaueren Kenntnis des Einflusses der Ermüdungsbelastung auf das Versagen von Beton wurde das Ermüdungsverhalten von gekerbten Betonbalken in kraft- und verformungsgeregelten Dreipunktbiegezugversuchen untersucht. Für die verformungsgeregelten Versuche wurde eine neuentwickelte Versuchstechnik angewendet, mit der auch unter hochzyklischer Beanspruchung mit Lastspielzahlen von bis zu einer Million Zyklen sowohl der ansteigende als auch der abfallende Ast in einem Kraft-Verformungsdiagramm aufgezeichnet werden kann.
Glass-ceramics containing Ca2KNa(PO4)2 as the main crystalline phase have a solubility which is 8 times higher than that of alpha-tricalcium phosphate ceramics. When using these compositions in drug delivery systems, especially in bone, it is necessary to create a material with a high open porosity. A Ca2KNa(PO4)2-based glass-ceramic was prepared from a borosilicate glass melt. The processed material includes minor amounts of boron which are low enough for medical application. Tissue response was studied using an animal model. Particles were implanted in rabbit femurs. Bone and soft tissue development occurred at the particle interfaces. In general, most particles were enclosed in the network of trabecular bone. The advantages of using a biomaterial with high porosity (pore size of 1-3 micron), together with rapid biodegradation, bioactivity and biocompatibility, despite traces of boron, were shown. 4 refs.
In vivo test of a high porous rapidly resorbable dicalcium potassium sodium phosphate glass-ceramics
(2002)
Fabrication of carbon/silica hybrid materials using cationic polymerization and the sol-gel process
(2002)
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.
The Micro Structure of Traditional Brazilian Lime Plasters - The Custom House of Florianopolis
(2005)
Ein effektives Wassermanagement ist ein wichtiger Aspekt in der Entwicklung von Brennstoffzellen hinsichtlich Langzeitstabilität und Optimierung der Leistungsfähigkeit. Eine zentrale Rolle spielt dabei die Gasdiffusionslage, die für die gleichmäßige Verteilung der Reaktionsgase auf die elektrochemisch aktive Schicht (Katalysator) sorgen soll. In diesem Beitrag werden gemeinsame Forschungsaktivitäten des Helmholtz-Zentrums Berlin für Materialien und Energie (Entwicklung bildgebender Verfahren) sowie des Zentrums für Sonnenenergie- und Wasserstoff-Forschung (ZSW, Entwicklung von Brennstoffzellen) vorgestellt. Im Rahmen dieser Kooperation werden die Entstehung, die Verteilung und der Transport von flüssigem Wasser, kurz das Wassermanagement, unter Betriebsbedingungen untersucht. Mittels Synchrotronradiografie und -tomografie werden kleinste Wassercluster in der Gasdiffusionslage detektiert. Die gewonnenen Erkenntnisse dienen der Modifikation und einer gezielten Auswahl der eingesetzten Materialien.
The German Federal Institute for Materials Research and Testing (BAM) has established a testing guideline to assess the suitability of geosynthetic or geocomposite drain (GCD) elements for final landfill cover systems. In an earlier paper the uniform procedure according to the BAM guideline for determining long-term water flow capacity was described, and the structural stability of drain cores under creep was investigated. The extrapolation of creep curves is permissible only when it can be shown, over the extrapolated period (at least 100 years), that oxidative aging does not invoke any relevant changes in the polyolefin material. This can be shown by measuring antioxidant depletion and mechanical degradation of the drain cores and filter/protection geotextiles in oven aging and water immersion tests. In this paper the results of such aging studies on three different GCD products are reported. Degradation of the tensile strength of HALS-stabilized polypropylene needle-punched nonwoven geotextiles (PP NWGTs) starts right from the beginning of the oven aging. This has to be taken into account for lifetime predictions based on residual tensile strength. The rate of oxidative degradation of NWGTs decreases significantly with increasing mass per area. Therefore the expected service life sets a limit on acceptable geotextile grammage. Antioxidant depletion in the drain cores, which are made of relatively thick PP strands or HDPE ribs, is about an order of magnitude slower than in filter and protection NWGTs, which are made of thin fibers. Service life values in excess of 100 years may be obtained for the products when the geotextiles and drain cores are properly stabilized and designed.