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Friederich J.,Goethe University Frankfurt | Gebhard R.,Archaologische Staatssammlung Munich | Krause R.,Goethe University Frankfurt | Riederer J.,Rathgen Forschungslabor | And 2 more authors.
Journal of Physics: Conference Series | Year: 2010

In the course of a study of pottery from Celtic Central Europe, we report on an investigation of pottery found in the context of a Celtic ditched square enclosure near the modern town of Bopfingen in Baden-Wurttemberg, Germany. The studied pottery may be visually subdivided into wheel-turned ware, graphite ware, and coarse ware. The Mössbauer spectra are surprisingly uniform, indicating that all types of pottery were fired in a similar manner. Firing in a reducing environment at 800 °C was usually followed by re-oxidation during cooling, which leads to unique features in the low temperature Mössbauer patterns. © 2010 IOP Publishing Ltd.

Wagner F.E.,TU Munich | Gebhard R.,Archaologische Staatssammlung Munich | Hausler W.,TU Munich | Wagner U.,TU Munich | And 5 more authors.
Hyperfine Interactions | Year: 2016

Archaeological iron objects often corrode rapidly after their excavation, even though they have survived long times of burial in the ground. Chlorine that accumulates during burial is thought to play a major role in this destructive post-excavation corrosion. It is therefore important for the conservation of such objects to determine the chlorine content in a non-destructive manner and, if necessary, to remove the chlorine from the artefacts by appropriate methods. Such methods are leaching in alkaline solutions or heating in a reducing atmosphere at temperatures up to 800 ∘C. We have studied the efficiency of the heating method using prompt gamma activation analysis (PGAA) for monitoring the Cl content and Mössbauer spectroscopy at room temperature (RT) and 4.2 K as well as X-ray diffraction to study the mineralogical transformations of the rust layers. The heat treatments were performed a N2/H2 (90/10) mixture at temperatures up to 750 ∘C. As test specimens sections of iron rods from the Celtic oppidum of Manching (Bavaria) were used. The initial Cl contents of the pieces varied in the range of several hundred ppm, referring to the iron mass. Annealing for 24 h at 350, 550 and 750 ∘C was found to reduce the Cl contents of the specimens, to about 70, 30 and 15 % of the original values, respectively. The rust consists mainly of goethite with admixtures of magnetite, lepidocrocite and akaganeite, which is thought to be a major carrier of chlorine, probably together with iron chlorides. Much of the goethite is so fine-grained that it does not split magnetically at RT. Annealing converts the rust mainly to maghemite at 350 ∘C, to magnetite at 550 ∘C and to wüstite plus magnetite and metallic iron at 750 ∘C. Pure akaganeite behaves in nearly the same manner. © 2016, Springer International Publishing Switzerland.

Wagner U.,TU Munich | Demoulin T.,Archaologische Staatssammlung Munich | Gebhard R.,Archaologische Staatssammlung Munich | Hausler W.,TU Munich | And 3 more authors.
Hyperfine Interactions | Year: 2012

Archaeological iron objects that were buried in the ground for long times often corrode rapidly once they have been excavated. We have used Mössbauer spectroscopy and X-ray diffraction to elucidate some specific problems of the corrosion of such objects and gain insights that may help to improve the methods of conservation. © 2011 Springer Science+Business Media B.V.

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