Up-Date of a Thermodynamic Database of the ZrO2-Gd2O3-Y2O3-Al2O3 System for TBC Applications

Abstract

The thermodynamic database of the ZrO 2 -Gd 2 O 3 -Y 2 O 3 -Al 2 O 3 system is up-dated taking into account new data on lattice stabilities of ZrO 2 , Gd 2 O 3 and Y 2 O 3 and heat capacity measurements for the monoclinic phase Gd 4 Al 2 O 9 and phase with garnet structure Gd 3 Al 5 O 12 . New data for the heat capacities of Gd 2 Zr 2 O 7 (pyrochlore) and GdAlO 3 (perovskite) as well as on the enthalpy of formation of fluorite solid solutions (Zr 12x Gd x )O 22x/2 were found to be in good agreement with calculated results. In comparison with the previous assessment, taking into account new experimental data resulted in a change of the melting character of the Gd 4 Al 2 O 9 phase from a peritectic one to a congruent one in the Gd 2 O 3 -Al 2 O 3 system. Correspondently, in the ternary system ZrO 2 -Gd 2 O 3 -Al 2 O 3 , the melting character of the three-phase assemblage Gd 2 O 3 (B), Gd 4 Al 2 O 9 and GdAlO 3 changed from eutectic to transition type U. The T 0 -lines for T/M and F/T diffusionless transformations and driving force of partitioning to equilibrium assemblage T + F were calculated in the ZrO 2 -Gd 2 O 3 -Y 2 O 3 system.

Durable aluminate toughened zirconate composite thermal barrier coating (TBC) materials for high temperature operation

“…The monolithic GAP and GZO pellets exhibited the expected orthorhombic and pyrochlore phases, respectively. No reaction was observed in any of the composite pellets over the duration of the heat treatment, consistent with the phase equilibria predicted by several authors and provided in Figure …”

“…GAP is a member of the RE aluminate family, a group of materials which can exhibit high melting temperatures of up to 2500°C, and improved toughness with respect to the RE zirconates . Most importantly, the RE aluminates have thermochemical stability with the pyrochlore zirconates, as shown in the Gd 2 O 3 ‐ZrO 2 ‐Al 2 O 3 system (Figure ). In addition to thermodynamic compatibility with GZO, GAP possesses phase stability up to its melting temperature of ~2045°C, as well as a reportedly high fracture toughness .…”

Effects of crystal structure and cation size on molten silicate reactivity with environmental barrier coating materials

“…Such is the case of zirconium oxide (ZrO 2 ), which exhibits phase transformations from monoclinic (7 coordination) to tetragonal (8 coordination, ~1100°C‐2300°C) and cubic (8 coordination, ~2300°C‐melting). Doping of ZrO 2 with yttrium oxide (Y 2 O 3 ), a material with a larger cation, aids in stabilizing the tetragonal and cubic structures below the transition temperatures of ZrO 2 itself . In the case of DyDS, below the formation temperature of Dy 9.33 (SiO 4 ) 6 O 2 , the apatite structure formed when enough CaO was present to aid in stabilizing the structure (CMAS‐1, CMAS‐2, and CMAS‐2.5).…”

Phase relations in the ZrO2–La2O3–Gd2O3 system: Experimental studies and phase modeling

“…The thermodynamic description of the ZrO 2 –La 2 O 3 –Gd 2 O 3 system was based on the binary descriptions ZrO 2 –La 2 O 3 , ZrO 2 –Gd 2 O 3 , and La 2 O 3 –Gd 2 O 3 from the assessment of Zinkevich . Since experimental data on phase equilibria in the ZrO 2 –La 2 O 3 –Gd 2 O 3 system were not available, the La–Gd binary interactions in the fluorite phase and ternary interactions parameters for other solid phases were not considered by Shin et al…”