Effect of Rare-Earth Oxides on Reaction Sintered Non-Stoichiometric Magnesium Aluminate Spinel

Abstract

Non-stoichiometric spinel compositions with molar ratio of MgO:Al₂O₃ = 1:2 and 2:1, were prepared via single-stage reaction sintering technique at 1550°-1600°C using commercial grade oxide reactants. The effect of different rare-earth oxides, viz. CeO₂, La₂O₃ and Y₂O₃ at 2 wt% level on the properties of different spinel batches was studied. Y₂O₃ was found to favour densification in both the spinel batches while CeO₂ and La₂O₃ were found to favour densification only in the MgO-rich spinel compositions. Phase analysis revealed that Y₂O₃ containing Al₂O₃-rich spinel has a secondary phase with similar crystal structure to spinel (both cubic) and improved densification, while in the MgO-rich condition, Y₂O₃ remained as secondary phase and assisted in densification. CeO₂ and La₂O₃ in Al₂O₃-rich samples formed secondary phases with different crystal structures and resulted in reduced densification. While in MgO-rich condition, CeO₂ (cubic) did not react with Al₂O₃ and La₂O₃ formed a secondary phase with similar crystal structure as that of spinel and therefore assisted in densification. Addition of rare-earth oxides led to improvement in strength of MgO-rich spinels and maximum improvement in strength was observed with the addition of yttria.

GRAPHICAL ABSTRACT

Keywords:

• Non-stoichiometric spinel
• Rare-earth oxide
• Reaction sintering
• Densification
• Strength
• Microstructure