Phase equilibria in the CaO-TaO2.5-YO1.5 system and its implication for YTaO4 reactivity with CMAS

Phase equilibria in the CaO-TaO2.5-YO1.5 system were experimentally investigated and the isothermal section at 1400 degrees C was constructed. Ten three-phase equilibrium fields were determined, and the solid solution regions of the binary compounds were analyzed. The Ca4Ta2O9 in the ternary system is marked as (YO3/2)(x)(Ca(2/3)(1/3)(Ta)O3/ 2)(1x). Its maximum solubility is the formula of Ca2YTaO6. The solubilities of CaO in the M '-YTaO4 and fluorite phases reach up to about 2.0 mol% and 8.9 mol%, respectively. A ternary pyrochlore-type phase was found, which was expressed as the chemical formula of Ca-0.5-0.5x(Y)0.75x(Ta)0.5-0.25x(O)1.75. The morphology of pyrochlore was polygonal, and it was the only reaction product when the YTaO4 oxides were corroded by the molten silicate (CMAS). Since the CaO is the main reactant, the CaO-TaO2.5-YO1.5 phase diagram was used to successfully explain the corrosion behavior of YTaO4. The current experimental phase diagram is important to understand the CMAS degradation of the thermal barrier coatings.

Automated summary

Phase equilibria in the CaO-TaO2.5-YO1.5 system were experimentally investigated, with the construction of an isothermal section at 1400 degrees C. The study identified ten three-phase equilibrium fields and analyzed the solid solution regions of binary compounds. The phase diagram provided insights into the corrosion behavior of YTaO4, particularly in the presence of CaO.