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THERMODYNAMIC ASSESSMENTS OF THE LIQUID IMMISCIBILITIES IN THE BAO-SIO2 AND TIO2-SIO2 SYTEMS USING THE IONIC TWO SUBLATTICE MODEL

par Boulay, Emilie ;Nakano, Jinichiro;Godet, Stéphane
Référence CALPHAD (2012: Berkeley, USA)
Publication Non publié, 2012

Communication à un colloque

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Résumé :

Glass-ceramics in the BaO-SiO2-TiO2 system exhibit strong photoluminescence properties due to the fresnoite phase formation. This effect can be enhanced by controlling a prior amorphous phase separation, which promotes the formation of finer crystals. The thermodynamic stability and metastability of the liquid phase in this system are critical information in order to design optimal compositions and processes of the glass exhibiting the maximum photoluminescence effect. However, the liquid phase in the BaO-SiO2-TiO2 system has never been assessed in the past and there is a lack of experimental data. Corresponding sub-binary systems were evaluated in literature but using different thermodynamic models: the BaO-SiO2 system was performed on the basis of the structural model for silicate melts and glasses [1] and the TiO2-SiO2 binary system using a Margule type excess polynomial model [2]. The BaO-TiO2 system was already assessed by using the Ionic Two Sublattice model [3]. To construct a ternary description of the BaO-SiO2-TiO2 system, the Ionic Two Sublattice model was used in this work to first describe liquid phases in both BaO-SiO2 and TiO2-SiO2 systems. Available experimental data from literature were evaluated to assess the thermodynamic parameters of these liquid phases by the CALPHAD method. The assessments were conducted using a PARROT module of the Thermo-Calc software. A set of optimized parameters was obtained and calculated phase diagrams related to the stable and metastable liquid miscibility gaps in the BaO-SiO2 and TiO2-SiO2 are consistent with experimental data as shown in Figure 1 and Figure 2. The validity of liquidus projection interpolations into the ternary system by Muggianu’s model is investigated. Discussion is further expanded to experiments and the parameter assessment required for the prediction of the resulting BaO-SiO2-TiO2 equilibrium diagrams.[1] A. Romero-Serrano et al., Thermodynamic modeling of the BaO-SiO2 binary melts. Glass Phys. and Chem., 2010, Vol.36 n°2, pp.171-178.[2] M. Kirschen, C. DeCapitani, Immiscible silicate liquids in the system SiO2-TiO2-Al2O3. Eur.J.Mineral, 1999, Vol.11, pp.427-440.[3] X. Lu, Z. Jin, Thermodynamic assessment of the BaO-TiO2 quasibinary system. Calphad. Pergamon, 2000, Vol.24, 3, pp.319-338.