TY - JOUR A1 - Rades, Steffi A1 - Kraemer, S. A1 - Seshadri, R. A1 - Albert, B. T1 - Size and crystallinity dependence of magnetism in nanoscale iron boride, alpha-FeB N2 - A nanoscale boride, α-FeB, with grains of variable size and crystallinity was synthesized by precipitation from solution followed by heat treatment (450 °C, 550 °C, 750 °C, 1050 °C). Analysis of transmission electron micrographs, electron diffraction, and magnetic measurements suggests superparamagnetism at room temperature for the smaller, more disordered particles of FeB, while the larger, more crystalline particles of α-FeB, with a particle size of approximately 20 nm, display open magnetic hysteresis loops and blocking. In contrast to the soft ferromagnetism of bulk β-FeB, which was synthesized by conventional solid state reaction at 1500 °C, the sample of α-FeB annealed at 1050 °C is a harder ferromagnet, possibly due to stacking faults that pin the magnetic domains; these stacking faults are apparent in the high resolution transmission electron micrographs. The changes in magnetic behavior are visible from the varying blocking temperatures (63 K, 94 K, 150 K, and >320 K from the smallest to the largest particles) and correlate with the transformations from amorphous to α-FeB and from α-FeB to β-FeB. KW - Iron KW - Boride KW - Nano KW - Magnetism KW - Electron microscopy PY - 2014 DO - https://doi.org/10.1021/cm403167a SN - 0897-4756 SN - 1520-5002 VL - 26 IS - 4 SP - 1549 EP - 1552 PB - American Chemical Society CY - Washington, DC AN - OPUS4-30288 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Dümichen, Erik A1 - Braun, Ulrike A1 - Sturm, Heinz A1 - Kraemer, R. A1 - Deglmann, P. A1 - Gaan, S. A1 - Senz, R. T1 - A new molecular understanding of the thermal degradation of PA 66 doped with metal oxides: Experiment and computation N2 - The thermal molecular degradation of polyamide 66 (PA 66) doped with (partially supported) metal oxide particles (Fe2O3, ZnO, Al2O3) was investigated qualitatively and quantitatively using common analysis techniques like thermogravimetry coupled with IR-spectroscopic evolved gas analysis (TGA-FTIR). Using pyrolysis coupled with gas chromatography mass spectrometry (Py-GC-MS), qualitative conclusions were drawn about the complex hydrocarbon products. However, the combination of TGA with solid-phase extraction, followed by thermal desorption gas chromatography mass spectrometry (TED-GC-MS), allows qualitative and even semi-quantitative conclusions about the decomposition pathway of PA 66 in the presence of various metal oxide particles. The investigations under inert conditions showed that the presence of metal particles increases the rate of decarboxylation and deamination reactions, as well as the formation rate of cyclopentanone and pyridine derivatives. These species are a consequence of various condensation reactions. The condensation reactions release a large amount of water, thus triggering the hydrolysis of PA 66. Molecular thermal degradation mechanisms were developed for the main decomposition as well as for the condensation reactions and supported by quantum chemical calculations. The catalytic effect of the metal oxides in PA 66 increases in the following order: PA 66 = PA 66 – Al2O3 < PA 66 – Fe2O3 < PA 66 – ZnO. KW - PA 66 KW - Metal oxide particles KW - Thermal degradation KW - Solid-phase extraction KW - Molecular modeling PY - 2015 DO - https://doi.org/10.1016/j.polymdegradstab.2015.07.011 SN - 0141-3910 SN - 1873-2321 VL - 120 SP - 340 EP - 356 PB - Elsevier Ltd. CY - London AN - OPUS4-33806 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -