Mullite phase formation in oxide mixtures in the presence of Y2O3, La2O3 and CeO2

The effect of oxides (Y2O3, La2O3, and CeO2), on phase formation of mullite, reaction sequence and microstructure evolution, in the mixtures of Al2O3 and SiO2, has been investigated. All three dopants showed a positive effect on the mullitization behavior, lowering the mullite formation temperature by about 100degreesC. The improved mullitization behavior was attributed to the formation of the low-viscosity liquid phase due to the addition of dopants. The reaction sequence was different in the three doping cases. Two types of yttrium silicate were found in the samples doped with Y2O3, with one being favored at low temperature and another at high temperature. No reaction was observed between CeO2 and Al2O3 or SiO2, while La2O3 was not detected by the X-ray diffraction (XRD) measurement for all doping levels. The samples with La2O3 had the best densification behavior among the three doping cases, while the effect of CeO2 on densification was slightly better than that of Y2O3. The difference in the effects of the three oxides on the mullitization and densification behavior of the doped samples implied the difference in the characteristics of the low-viscosity glass phases formed at high temperatures. (C) 2003 Elsevier B.V. All rights reserved.