Phase equilibria and crystal chemistry in the calcia-silica-yttria system

摘要

The phase equilibria in the CaO-SiO2-Y2O3 system have been assessed at 1400 degrees C and 1600 degrees C using powders prepared by precipitation from precursors. Four ternary phases were identified: Ca/Y-cyclosilicate (Ca3Y2Si6O26), silico-carnotite (Ca3Y2Si3O12), cuspidine (nominally Ca2Y2S12O9), and apatite (solid solution based on Ca2Y8Si6O26). The melting temperature of each ternary phase was measured and the shape of the liquid field at 1600 degrees C was assessed. The study emphasizes understanding the extent and crystallographic origin of the solid solution homogeneity range for apatite between Ca0.5Y9(SiO4)(6)O-2 and Ca2.5Y7.5(SiO4)(6)O-1.75, deviations from the nominal cuspidine stoichiometry, and solubility of Y2O3 in the high-temperature alpha-Ca2SiO4 polymorph. The results are discussed in the context of molten silicate (CMAS) degradation of thermal and environmental barrier coatings (T/EBCs). (C) 2016 Elsevier Ltd. All rights reserved.