Abstract
Phase formation and evolution was investigated in the CaO–SiO2 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 + O2). 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.
Highlights
At the time when the first equilibrium phase diagrams were generated for the system CaO–SiO2, the existence, the stability and the formation of tricalcium silicate were controversially discussed (Day and Shepherd 1906, Rankin 1915, Kühl 1951).Some years later, the melting point of tricalcium silicate was determined by Nurse (1960) to be 2070 ◦C.Tricalcium silicate is a nesosilicate consisting of isolated SiO4 tetrahedrons and oxygen ions octahedrally coordinated by Ca2+ ions (Ludwig and Zhang 2015)
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)
Seven modifications of tricalcium silicate were identified between room temperature and the melting point by differential thermal analysis (DTA), high temperature x-ray diffraction (XRD) and hightemperature optical microscopy (Stephan 1999)
Summary
At the time when the first equilibrium phase diagrams were generated for the system CaO–SiO2, the existence, the stability and the formation of tricalcium silicate were controversially discussed (Day and Shepherd 1906, Rankin 1915, Kühl 1951).Some years later, the melting point of tricalcium silicate was determined by Nurse (1960) to be 2070 ◦C.Tricalcium silicate is a nesosilicate consisting of isolated SiO4 tetrahedrons and oxygen ions octahedrally coordinated by Ca2+ ions (Ludwig and Zhang 2015). Seven modifications of tricalcium silicate were identified between room temperature and the melting point by differential thermal analysis (DTA), high temperature x-ray diffraction (XRD) and hightemperature optical microscopy (Stephan 1999). Between 980–1070 ◦C three monoclinic modifications (space group C1m1) occur: 1060–1070 ◦C M3; 990–1060 ◦C M2, 980–990 ◦C M1, and between room temperature and 980 ◦C three triclinic modifications (T1 and T3 space group P1, T2 space group disputed) occur: 920–980 ◦C T3, 620–920 ◦C T2,
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