Role of different rare earth oxides on the reaction sintering of magnesium aluminate spinel

Role of three rare earth oxides, viz., La2O3, CeO2 and Yb2O3 on reaction sintering of magnesium aluminate spinel having molar ratio of MgO:Al2O3 = 1:2 from its solid oxide precursors was investigated in static and dynamic heating conditions. Effect of these additives (3 wt%) on densification behavior, phase assemblage and microstructure development were studied in the temperatures of 1500–1700 °C. Yb2O3 enhanced the sintering of spinel, while La2O3 and CeO2 negatively impacted the sintering of magnesium aluminate spinel which can be discerned from the shrinkage curve of TMA as well as from static firing regime. This is ascribed to the formation of secondary phases in La2O3 and CeO2 containing samples which have different crystalline structures to that of spinel. This anisotropy due to different crystallinity hindered the pore shrinkage and pore removal and thereby retarded the densification. Whereas, the cubic structure of the secondary phase formed in Yb2O3 containing sample which is isotropic with the crystalline orientation of the parental spinel phase assisted the densification.