TY - JOUR A1 - Stößer, R. A1 - Feist, M. A1 - Menzel, Michael A1 - Nofz, Marianne T1 - Fe3+ ions acting as probes and agents in aggregation processes and solid-state reactions in AlO(OH)/Al2O3 matrices N2 - The fate of doped iron species during various mechanically and thermally initiated redox reactions and aggregation processes in crystalline and amorphous AlO(OH) or Al2O3 matrices was investigated. The amorphization of the matrix was performed by chemical (i.e., via sol-gel processes) or mechanochemical treatment (high-energy ball milling). Thermal analysis, coupled with mass spectrometry (TA-MS), Mössbauer spectroscopy, and electron spin resonance (ESR), was used. The TA under various gas atmospheres allowed preparing samples under a controlled temperature regime, together with a controlled gas influence. Both the effect of mechanical activation and the influence of the iron doping could be followed macroscopically via the down-shift of the peak temperature of the corundum formation. The ESR data characterize the Fe3+ ions and their interaction with the magnetic surrounding based on the fine structure parameters. The Mössbauer data allowed the characterization of the Fe(0), Fe2+, and Fe3+ species, together with providing information about their coordinative surrounding. Both methods provided general complementary spectroscopical information. Unexpectedly, (FeOx)n and (FexAl1-x)2O3 aggregates could also be detected in the range of low Fe concentrations. It was demonstrated that even in the low-level doped systems [(FexAl1-x)2O3 with x ≥ 0.01], all the essential spectroscopic phenomena occur. At higher Fe concentrations, they were discovered to be caused by magnetic and spin exchange interactions as well as by solid-state reactions during and after the mechanical activation. PY - 2010 DO - https://doi.org/10.1111/j.1551-2916.2009.03596.x SN - 0002-7820 SN - 1551-2916 VL - 93 IS - 5 SP - 1447 EP - 1456 PB - Blackwell Publishing CY - Malden AN - OPUS4-21235 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Stößer, R. A1 - Menzel, Michael A1 - Feist, M. T1 - The fate of Fe3+ ions in the system {AlO(OH)-xerogel/Fe-compounds} after mechanical activation and different thermal treatments studied by Mössbauer, ESR spectroscopy and thermal analysis KW - Mössbauer KW - ESR KW - Thermal analysis KW - High energy ball milling KW - Activation/deactivation processes KW - Local mechano-chemical reactions KW - Heterogeneous redox reactions PY - 2009 DO - https://doi.org/10.1007/s10751-009-9920-0 SN - 0304-3843 SN - 1572-9540 VL - 190 IS - 1-3 SP - 43 EP - 49 PB - Kluwer CY - Dordrecht AN - OPUS4-19478 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Stößer, R. A1 - Menzel, Michael A1 - Feist, M. A1 - Nofz, Marianne A1 - Renz, F. T1 - Competing redox reactions in Fe-containing AlO(OH) and Al2O3 matrices: A combined investigation by Mössbauer, ESR spectroscopy and thermal analysis N2 - The investigation of iron-doped AlO(OH)/Al2O3 systems revealed that the combined employment of Mössbauer and ESR spectroscopies together with thermal analysis yields meaningful data with complementary information. This mutual complementarity is based on the coexistence of Fe point defects with the corresponding aggregated FeOx species which has been observed even for very low Fe concentrations. Competing redox processes between the dopant, the AlOx matrix, and the gas atmosphere during the thermal treatment enable the generation of solid phases exhibiting specific chemical properties. The entire reaction process is influenced by a specific mechanical and thermal pre-treatment that affects predominantly oxydative processes in the matrix. A protecting influence of the matrix preventing further reductive attack of the Fe3+ Fe2+ ions by hydrogen has been established. KW - Mössbauer KW - ESR spectroscopy KW - Thermal analysis KW - Al2O3 KW - Magnetite KW - Fe(0) KW - Fe(2+) KW - Fe(3+) PY - 2010 UR - http://iopscience.iop.org/1742-6596/217/1/012028/pdf/1742-6596_217_1_012028.pdf DO - https://doi.org/10.1088/1742-6596/217/1/012028 SN - 1742-6588 SN - 1742-6596 VL - 217 IS - 1 SP - 012028-1 - 012028-5 PB - IOP Publ. CY - Bristol, UK AN - OPUS4-21876 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Stößer, R. A1 - Feist, M. A1 - Patzwaldt, K. A1 - Menzel, Michael A1 - Emmerling, Franziska ED - Brooks, H. T1 - Redox reactions of K3[Fe(CN)6] during mechanochemically stimulated phase transitions of AlOOH N2 - Thermally induced redox reactions of K3[Fe(CN)6] (1) were investigated for a broad temperature range by thermal methods and structure analytical methods (ESR and Mößbauer spectroscopy, X-ray Powder diffraction and XANES). Based on the influence of the mechanically activated and transforming matrices 2 and 3, redox processes can be tuned to form doped Al2O3 systems which contain either isolated Fe3+ centres or redox active phases and precursors like (Al1-xFex)2O3 (4), (Al3-xFex)O4 (5), Fe3O4, Fe2O3 and Fe0. The phase Fe3C and the chemically reactive C-species were detected during the reaction of 1. The final composition of the doped products of α-Al2O3 is mainly influenced by the chemical nature of the Fe doping component, the applied temperature and time regime, and the composition of the gas phase (N2, N2/O2 or N2/H2). From the solid state chemistry point of view it is interesting that the transforming matrix (2 and 3) possesses both oxidative and protective properties and that the incorporation of the Fe species can be performed systematically. KW - A. Inorganic compounds KW - C. Mössbauer spectroscopy KW - C. Thermogravimetric analysis KW - D. Electron paramagnetic resonance KW - ESR-Spektroskopie KW - Kaliumhexacyanoferrat(III) KW - Mechanische Aktivierung KW - Mößbauer-Spektroskopie KW - Redoxreaktionen KW - TA-MS-Messungen PY - 2011 DO - https://doi.org/10.1016/j.jpcs.2011.03.016 SN - 0022-3697 VL - 72 IS - 6 SP - 794 EP - 799 PB - Pergamon Press CY - New York, NY AN - OPUS4-23685 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Stößer, R. A1 - Feist, M. A1 - Willgeroth, Carola A1 - Emmerling, Franziska A1 - Menzel, Michael A1 - Reuther, H. T1 - The 'quiet Goldschmidt' - a mechanochemical, thermoanalytical, and spectroscopic study of selected steps of the aluminothermic reaction N2 - The Goldschmidt reaction (2Al+α-Fe2O3) was investigated both under mechanical and thermal activation by employing a combination of analytical methods such as ESR and Mössbauer spectroscopy, magnetic susceptibility, X-ray powder diffraction, and thermal analysis (TA). Both the mechanical treatment and the TA runs under air caused the reaction conditions of 'quiet redox reactions' due to a retarding effect and enabled a reaction study in a 'slow motion mode'. This allowed to establish distinct partial steps of the integral reaction process depending on the intensity of the mechanical impact, the educt composition, the gas phase composition, and, finally, the thermal excitation in the TA runs. Particular attention was payed to the role of the gas phase and to the reaction of aluminum with differently activated oxygen species. The phlegmatizing effect was traced back to the formation of Al2O3 coverages of the Al particles. KW - Thermite reaction KW - Iron ESR and Mössbauer spectroscopy KW - Mechanochemical activation KW - Magnetic moments KW - DTA-TG KW - XRD PY - 2013 DO - https://doi.org/10.1016/j.jssc.2013.02.032 SN - 0022-4596 SN - 1095-726X VL - 202 SP - 173 EP - 190 PB - Elsevier CY - San Diego, Calif. AN - OPUS4-29528 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -