New experimental investigations of phase relations in the Yb2O3–Al2O3andZrO2–Yb2O3–Al2O3systems

∗
Corresponding author. Tel.: +49 3731 3931il address: fabrich@ww.tu-freiberg.de (O. Fabrichnaya).
it should be mentioned that Yb3 Al5 O12 phase with garnet structure has good optical properties and presents interest for laser application [6,7]. The Yb2 O3 –Al2 O3 system is also of interest because of possible application of directionally solidified eutectics [8]. The Yb3 Al5 O12 (YbAG) phase was also suggested as new thermal barrier coating material [9]. The investigation performed in the present paper is aimed to investigate phase relations in the ZrO2 –Yb2 O3 –Al2 O3 system and assess thermodynamic parameters of this system. The Al2 O3 is the main component of thermally grown oxide (TGO) forming during thermal cycling of TBC. The derived thermodynamic database can be used for modelling interface reactions between top coat of TBC and (TGO). Interaction of multiple co-doped YSZ with Al2 O3 is important to estimate stability of TBC during thermal cycling. The ZrO2 –Yb2 O3 –Al2 O3 system is one of the constituent system of the ZrO2 –RE2 O3 –Yb2 O3 –Y2 O3 –Al2 O3 system (RE = La, Nd, Sm, Gd) which is important for developments of new TBC materials. Phase relations in the ZrO2 –Yb2 O3 –Al2 O3 system were experimentally studied and different phase diagram such as
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Journal of the European Ceramic Society 35 (2015) 2855–2871
New experimental investigations of phase relations in the Yb2O3–Al2O3 and ZrO2–Yb2O3–Al2O3 systems and assessment of thermodynamic parameters
O. Fabrichnaya a,∗ , S.M. Lakiza b , M.J. Kriegel a , J. Seidel c , G. Savinykh a , G. Schreiber a
a
Institute of Materials Science, Technical University Bergakademie Freiberg, Gustav-Zeuner Str. 5, D-09599 Freiberg, Germany b Frantsevich Institute for Problems of Materials Science, NASU, Krzhizhanovsky Str. 3, 03142 Kiev, Ukraine c Institute Physical Chemistry, Technical University Bergakademie Freiberg, Leipziger Str. 29, D-09599 Freiberg, Germany Received 12 March 2015; received in revised form 26 March 2015; accepted 29 March 2015 Available online 18 April 2015
Keywords: Phase diagrams; Electron microscopy; X-ray methods; Thermal analysis; Thermodynamic modelling
1. Introduction The co-doping of Y2 O3 stabilised zirconia (YSZ) by Yb increases oxygen conductivity [1,2] and stability of YSZ against transformation to monoclinic phase [3]. Additionally, Yb co-doping improves mechanical properties of YSZ [4] and decreases its thermal conductivity [3]. Therefore Yb co-doped YSZ is of interest for such applications as oxygen sensors, solid state electrolytes and thermal barrier coating (TBC). The effects of reduction of thermal conductivity and increase of phase stability important for TBC application can be enhanced by multiple co-doping of YSZ with two cations one larger (i.e. Sm, Nd, La) and other smaller (i.e. Yb, Sc) than Y. Such co-doping leads to nano-scale clustering of the smaller and larger cations with uniformly distributed Y cations contributes to phonon scattering and therefore to thermal conductivity reduction [5]. Additionally
/10.1016/j.jeurceramsoc.2015.03.037 0955-2219/© 2015 Elsevier Ltd. All rights reserved.
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O. Fabrichnaya et al. / Journal of the European Ceramic Society 35 (2015) 2855–2871
Abstract Phase relations were experimentally studied in the Yb2 O3 –Al2 O3 and ZrO2 –Yb2 O3 –Al2 O3 systems. Samples were prepared from oxide mixture and by co-precipitation. Phase equilibria were studied in the range 1523–2023 K and investigated by XRD and SEM/EDX. Heat capacity of the Yb3 Al5 O12 (YbAG) phase was measured between 293 and 1473 K by DSC. Phase transformations and melting relations were investigated by DTA up to 2373 K. The stability range of Yb4 Al2 O9 (YbAM) phase was determined to be between 1923 and 2186 K. The character of its melting was determined from crystallisation microstructure and DTA as peritectic. The thermodynamic parameters of the Yb2 O3 –Al2 O3 system were derived based on obtained results. Melting relations in the ternary system were studied experimentally. Based on the data obtained a thermodynamic description for the ternary system was derived. The new experimental study of the ZrO2 –Yb2 O3 system is recommended to get better fit of experimental data in ternary system. © 2015 Elsevier Ltd. All rights reserved.