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Eingeladener Vortrag (wissenschaftliche Konferenzen)
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A set of 59 ancient magical artefacts, mainly made of lead, was selected from the collections of the Staatliche Museen zu Berlin in order to unravel their origins. All the selected artefacts have been studied for their Pb isotope compositions, which covered the whole range of the Mediterranean ore deposits. However, the majority (≈86%) were made of lead matching the small compositional range of the Laurion ore deposits. Only eight out of the 59 artefacts were made of recycled lead or lead from other ore deposits.
Additionally, all but two were approximately dated based on their inscriptions. The lead isotopic composition together with information obtained from the inscriptions, the resulting dating, the context of the find and the known history of each item allowed us to gain more detailed information about the origins of these magical artefacts. The Attic provenance of 36 curse tablets was confirmed, whereas for 11 curse tablets previously classified as non-Attic, the provenance was either confirmed and specified (six artefacts) or changed to Attic (five artefacts). Surprisingly, the majority (six out of eight) of the analysed curse tablets from the Egyptian collection showed a lead isotopic composition closely matching that of Laurion.
A Laurion-like lead isotopic composition was also observed for three of the four analysed oracular tablets from Dodona. Together with the dating information, this points to Laurion as the major and dominant lead source in the Aegean, at least during the fourth–third century B.C. The few curse tablets from earlier than the fourth–third century B.C. point to the use of multiple and thus isotopically more variable lead sources compared with the Roman times.
Mikrostrukturelle und mineralogische Eigenschaften leichter Gesteinskörnungen aus Mauerwerkbruch
(2015)
Poröse RC-Leichtgranulate mit Rohdichten zwischen 600 kg/m³ und 1400 kg/m³ können nach einem mehrstufigen mechanischen Prozess durch thermische Erhärtung bei 1180 °C aus ziegelhaitigern Mauerwerkbruch hergestellt werden. Diese Granulate erfüllen die Anforderungen an leichte Gesteinskörnungen nach DIN EN 13055 und es lassen sich damit Leichtbetone nach DIN EN 206-1/DIN 1045-2 herstellen. Ihre Festigkeits- und Dauerhaftigkeitseigenschatten sind mit denen herkömmlicher Leichtbetone mit Blähtonkörnungen sehr gut vergleichbar. Das ist das Fazit aus dem in den letzten Jahren durchgeführten Verbundforschungsvorhaben "Aufbaukörnungen". Um jedoch die Granulatentstehung bzw. den Vorgang der Porosierung besser verstehen, den Herstellungsprozess optimieren und die Eigenschaften der Granulate maßschneidern zu können, wurden zusätzlich zu den makroskopischen Charakteristika, wie beispielsweise Porosität und Wasseraufnahme, die chemisch-mineralogischen und mikrostrukturellen Eigenschaften der Leichtgranulate untersucht. Dazu dienten Analysen mittels ICP-Emissionsspektrometrie, Röntgenpulverdiffraktometrie, Quecksilberporosimetrie und mikroskopischen Verfahren. Im Beitrag wird über die Ergebnisse der Gefüge- und Porenstrukturuntersuchungen an Leichtgranulaten im Vergleich zu herkömmlichem Blähton berichtet.
A model system was used to simulate the properties of tribofilms which form during automotive braking. The model system was prepared by ball milling of a blend of 70 vol.% iron oxides, 15 vol.% molybdenum disulfide and 15 vol.% graphite. The resulting mixture was characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and various transmission electron microscopic (TEM) methods, including energy dispersive X-ray spectroscopy (EDXS), high resolution investigations (HRTEM) with corresponding simulation of the HRTEM images, diffraction methods such as scanning nano-beam electron diffraction (SNBED) and selected area electron diffraction (SAED). It could be shown that the ball milling caused a reduction of the grain size of the initial components to the nanometer range. Sometimes even amorphization or partial break-down of the crystal structure was observed for MoS2 and graphite. Moreover, chemical reactions lead to a formation of surface coverings of the nanoparticles by amorphous material, molybdenum oxides, and iron sulfates as derived from XPS.
The present work shows that U can be effectively removed from groundwater using permeable reactive barriers with hydroxyapatite (HAP) as reactive material. The main factor influencing the removal processes is the composition of the groundwater, namely the concentration of Ca and carbonate. Sorption of U onto the HAP surface seems to be the dominant removal process with the possibility of remobilisation. Newly formed U-phosphate minerals were detected by ESEM/EDX and XRD in samples with high U content indicating either a dissolution-precipitation mechanism or sorption onto the apatite surface followed by alteration of the structure. The formed U-phosphate minerals are stable under common groundwater conditions and can be remobilised only at high pH-values and high carbonate concentrations.
Diffraction of hard synchrotron radiation as well as constant-wavelength and time-of-flight neutron diffraction were used for the structural characterization of a silicon carbide powder having extremely low levels of chemical impurities, high perfection of the crystalline lattice and a grain size of up to 150 µm. The presence of three polytypes was ascertained and the ratios of their mass fractions were determined to be w15R : w6H = 0.002,3(8) and w4H : w6H = 0.000,6(2).