In situ synchrotron XRD measurements during solidification of a melt in the CaO-SiO 2 system using an aerodynamic levitation system.

Phase formation and evolution was investigated in the CaO-SiO ₂ system in the range of 70-80 mol% CaO. The samples were container-less processed in an aerodynamic levitation system and crystallization was followed in situ by synchrotron x-ray diffraction at the beamline P21.1 at the German electron synchrotron (DESY). Modification changes of di- and tricalcium silicate were observed and occurred at lower temperatures than under equilibrium conditions. Despite deep sample undercooling, no metastable phase formation was observed within the measurement timescale of 1 s. For the given cooling rates ranging from 300 K s ^-1 to about 1 K s ^-1 , no decomposition of tricalcium silicate was observed. No differences in phase evolution were observed between reducing and oxidizing conditions imposed by the levitation gas (Ar and Ar + O ₂ ). We demonstrate that this setup has great potential to follow crystallization in refractory oxide liquids in situ . For sub-second primary phase formation faster detection and for polymorph detection adjustments in resolution have to be implemented.
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