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Organisationseinheit der BAM
In contrast to classical low temperature polymer electrolyte fuel cells (LT-PEFCs), the membrane conductivity in high temperature polymer electrolyte fuel cells (HT-PEFCs) (operating temperature ~ 160 °C) is based on proton transport within phosphorus-oxygen acids at different levels of hydration, orthophosphoric acid (H3PO4) being the simplest example. We present for the first time in-situ synchrotron X-ray radiography measurements applied to a HT-PEFC to gain insight into the local composition of the membrane electrode assembly (MEA) under dynamic operating conditions. Transmission changes during the radiographic measurements exhibit a clear influence of the formation of product water on the membrane composition.
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.
Fe-ZSM-5 Catalysts for the Selective Reduction of NO by Isobutane - The Problem of the Active Sites
(2002)
Relations between the structure of FeZSM-5 catalysts prepared by interaction of FeCl3 with HZSM-5 and their catalytic behavior in the SCR of NO by isobutane were investigated by combining results of catalytic studies (1000 ppm NO, 1000 ppm isobutane, and 2% O2 in He, 30,000 h-1) and of physicochemical characterization (XRD, EXAFS, Mössbauer spectroscopy, TPR, IR, XPS). By variation of the preparation conditions (method of FeCl3 introductionchemical vapor deposition or solid-state ion exchange, washing intensity, calcination regime) and of the matrix (HZSM-5 with normal and high defect density), FeZSM-5 materials with strongly varying properties (aggregation degree of the Fe phase, acidity) were obtained. Significant discrepancies between conclusions derived from EXAFS, TPR, and Mössbauer spectroscopy were ascribed to a preference of Mössbauer spectroscopy for the detection of aggregated phases and a high defectivity of Fe oxide clusters formed upon calcination. The critical step for the preparation of a highly disperse Fe phase is extensive washing after Fe introduction. The catalytic behavior of overexchanged FeZSM-5 materials prepared by interaction of FeCl3 with HZSM-5 of normal defect density was not influenced by aggregation of a significant part of the Fe phase. The comparison of their catalytic properties with those of a Fe2O3/HZSM-5 mechanical mixture and of catalysts prepared by aqueous ion exchange or by CVD of FeCl3 into HZSM-5 of high defect density implies that the particular activity of overexchanged FeZSM-5 arises from minority sites. In these, the Fe ions are probably isolated. Other Fe sites of low nuclearity appear to add to the activity. The poor SCR performance (at a given ability for isobutane activation) of FeZSM-5 prepared with a defective ZSM-5 matrix may indicate that the Fe sites which provi de the particular activity of overexchanged FeZSM-5 require the cooperation of acidic sites.
The first hard X-ray beamline at BESSY II will be installed by BAM and PTB at a superconducting 7 T wavelength shifter. The main optical elements of the beamline are a Double-Multilayer-Monochromator and a Double-Crystal-Monochromator. The two devices can be used separately or in-line. Main applications of monochromatic radiation with photon energies up to 50 keV are X-ray fluorescence analysis, micro-computed tomography, X-ray topography, detector calibration and reflectometry. Calculable undispersed radiation up to 200 keV will be available for radiometric applications.
The impact of very high cycle fatigue (VHCF) load conditions on the microstructure of specimens consisting of nodular cast iron is analyzed by means of micro-computed tomography (µCT) utilizing both monochromatic synchrotron radiation and polychromatic X-ray tube radiation. Using 3D µCT, the microstructure in the region of the smallest cross-sections of shouldered round specimens is imaged in different stages of the VHCF loading. By digital image correlation (DIC) of these tomograms strain fields are analyzed three-dimensionally. Strain levels in the range of a few percent were detected. It is proven that a localization of strain allows to predict the site of the crack which precedes and induces the macroscopic failure of the specimens.