Subsolidus phase equilibria in the CeO2-x-SiO2-ZrO2 system:: An experimental study

The phase equilibria in the CeO2-xSiO2-ZrO2 system were studied in the subsolidus region in argon atmosphere, under isothermal heating and hot pressing, at 1400 degrees C, different ceria, silica, and zirconia mixtures. X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) were performed to identify phases and to establish phase equilibria. Based on the results of many preliminarily investigated ternary compositions, possible tie lines are predicted. Compositions from the proposed tie lines were successively fired and ground until the changes of the phase compositions were not detected or were low enough to be neglected. Phases identified in these compositions confirmed the existence of five tie lines: Ce2Si2O7-ZrSiO4, Ce2Si2O7-ZrO2, Ce-4.67(SiO4)(3)O-ZrO2, Ce-4.67(SiO4)(3)O-Ce2Zr2O7 and Ce2SiO5-Ce2Zr2O7, which divide the CeO2-x-SiO2ZrO2 composition triangle into six compatibility triangles. The formation of ternary compounds or ternary solid solutions in the CeO2-x-SiO2-ZrO2 system was not observed. The monoclinic high temperature polymorph of Ce2Si2O7 was detected. The cubic pyrochlore phases had different lattice parameters, caused by incomplete reduction of the tetravalent cerium ions also observed in the non-stoichiometric cerium oxide.