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Thermodynamic assessment of the Al2O3-TiO2-SiO2 system for modeling interactions at the ceramic filter-melt interfaceWednesday (07.10.2020) 15:00 - 15:20
The Al2O3-TiO2-SiO2 system is important for a metal melt filtration process. In recent years, a concept of the installation of Al2O3-based filter systems, through which steel or Al melt passes, is being developed [1,2,3,4]. It should be noted that the main system to model Al melt filtration is the Al-Mg-Ti-Si-O system. For instance, TiO2 coating deposited on corundum is supposed to filter actively MgAl2O4 spinel phase from Al-based molten alloy. Besides this, the Al-based melt can then react with TiO2 reducing it to sub-oxides and metallic titanium. An excess of Ti, not dissolved in Al, can form intermetallic compounds TiAl3, TiAl2, or TiAl. In the Al melt containing Mg, the MgAl2O4 or MgTiO3 phases can form. In Si-containing Al alloy, Ti5(Si,Al)3, Ti(Al,Si)3 and ternary phases can form. Therefore, to model chemical reactions at the interface between ceramic filter and Al melt, a thermodynamic database of the Al-Mg-Ti-Si-O system is necessary. The Al2O3-TiO2-SiO2 system is a sub-system of the mentioned complex system. To ensure a reliable thermodynamic description of the ternary system, phase relations in the Al2O3-TiO2-SiO2 system were studied experimentally. The samples prepared by a co-hydrolysis method followed by annealing experiments were investigated using XRD, SEM/EDX, and DTA. The isothermal sections at 1213, 1449, 1474, and 1517°C were constructed based on obtained results which are mainly in an agreement with the literature data [5,6,7]. However, the solid-state invariant reaction of a transitional type, TiO2 + Al6Si2O13 ↔ SiO2 + Al2TiO5, was indicated at 1470°C for the first time. On the liquidus surface, a eutectic invariant reaction between TiO2 rutile, SiO2 crystoballite, and Al2TiO5 tialite was detected at 1477°C. An invariant transitional-type reaction L+Al6Si2O13↔SiO2+Al2TiO5 was found at 1506°C in the SiO2-rich area. Other invariant reaction L+Al2O3↔Al6Si2O13+Al2TiO5 was observed at 1733°C in the alumina-rich area of the ternary system. The experimental data obtained as well as previously reported databases for the binary Al2O3-TiO2, TiO2-SiO2, and Al2O3-SiO2 systems were used to derive the thermodynamic description of the Al2O3-TiO2-SiO2 system.
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