Solid-state phase relationships in the calcia-titania-zirconia system at 1200 C

Phase relationships were investigated in the CaO-TiO2-ZrO2 system at 1200 C for compositions containing <50 mol% CaO using X-ray diffraction and electron probe microanalysis. The existence of two previously reported ternary phases, zirconolite (CaZrTi2O7) and calzirtite (Ca2Zr5Ti2O16), was confirmed. Each of these phases exhibited a significant range of homogeneity between TiO2 and ZrO2, while maintaining a nearly constant concentration of CaO. The ternary solubilities of the constituent binary phases were found to be small (typically <1 mol%), with the exceptions of the perovskites (CaTiO3 and CaZrO3). These latter phases displayed mutual solubilities of at least 22 mol% but exhibited significant variations in composition from grain to grain. Thermodynamic equilibrium was clearly not established in several samples, although most of the phase relationship information obtained was self-consistent