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Synthesis of hercynite and related spinel structures using SPSWednesday (07.10.2020) 17:40 - 18:00
Synthesis of hercynite and related spinel structures using SPS
Anton Salomon* and David Rafaja
Institute of Materials Science, TU Bergakademie Freiberg, Gustav-Zeuner-Straße 5, 09599 Freiberg, Germany
* Corresponding author:
Conference topic: Special Session CRC 920
In this study, hercynite (FeAl2O4) and related spinel-like phases with the general composition (MgxFe1-x)Al2O4 were synthesised. These phases are intended for use as active coatings on ceramic filter structures for the filtration of non-metallic inclusions from metal melts. For this reason, the newly developed spinel coatings were exposed to molten aluminium alloy AlSi7Mg0.6, and the reactions at the interfaces between the metal melt and the filter surfaces were investigated. The syntheses of the phases and the generation of the alloy melt-spinel interfaces were performed in a Spark Plasma Sintering device, which offers high heating rates of up to 1000 K∙min-1, fast cooling and specifically adjustable sintering and heat treatment conditions.
Single-phase samples of (MgxFe1-x)Al2O4 spinels were synthesized at 1600 °C within 15 min using either α- or γ-Al2O3, Fe2O3, MgO and graphite as starting materials. The obtained pellets with almost zero porosity were polished and subjected to the reaction with the Al alloy melt for 1 to 60 min at 750 °C. The chemical reactions between the spinel and the molten alloy were analysed. The exchange of divalent cations between the (MgxFe1-x)Al2O4 spinel and molten AlSi7Mg0.6 alloy should facilitate the removal of Fe as the main contaminant from the melt. A proof of the cation exchange was the Vegard-like change of the lattice parameter of (MgxFe1-x)Al2O4, which increased with increasing amount of Fe. Finally, the results obtained for SPS samples are compared with the results obtained on conventionally sintered and heat-treated samples.
The methods utilised for the analyses of the phase formation and the phase distribution at the metal/ceramic interface included scanning electron microscopy with energy-dispersive X-ray spectroscopy and electron backscatter diffraction, electron probe microanalysis with wavelength-dispersive X-ray spectroscopy, and X-ray diffraction.
Funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation), CRC 920 – Project-ID 169148856.